IRLF
SB 3E 3MS
AN INTRODUCTION TO CHEMICAL
ENGINEERING
FROM THE SAME PUBLISHERS
VOLUMETRIC ANALYSIS
By JOHN B. COPPOCK, B.Sc.(LoND.), F.C.S.
Second edition, revised and enlarged.
This book contains an exhaustive collection
of all the commoner determinations usually
made by potassium permanganate solution
and standard solutions of acids and alkalis.
Standard solutions of iodine and sodium
theosulphate are also included. In crown
8vo., cloth, 100 pp., 3s. 6d. net.
ACIDS, ALKALIS, AND SALTS
By G. H. J. ADLAM, M.A., B.Sc., F.C.S.
Describes in simple language the properties
of the various acids, etc., and their uses.
In crown 8vo. , cloth, 112 pp., 2s. 6d. net.
SIR ISAAC PITMAN AND SONS, LTD.
i AMEN CORNER, LONDON, E.C. 4
AN INTRODUCTION TO v
CHEMICAL ENGINEERING
AN ELEMENTARY TEXTBOOK FOR THE
USE OF STUDENTS AND USERS OF
CHEMICAL MACHINERY
BY
A. F. ALLEN
B.SC.HONS., F.C.S., LL.B., LATE CAPT. R.A.F.
WITH 177 ILLUSTRATIONS
LONDON
SIR ISAAC PITMAN & SONS, LTD., i AMEN CORNER, E.C. 4
(INCORPORATING WHITTAKER & co.)
BATH, MELBOURNE, AND NEW YORK
1920
PREFACE
THIS book has been prepared for the student of chemistry
who has received a fair grounding in that science together
with the correlated subjects of physics and mathematics.
Chemistry is one of the most interesting and educative
of the sciences, and probably stands alone in that it is
practical in the true sense of the word, for many of the
operations carried out in the school laboratory are iden-
tical in method with, and on the same scale as, similar
operations in industry.
Previous to the war, except in the case of our great
colleges, chemistry had been almost completely banned
from the curriculum, owing mainly to the travesty of the
subject that was taught for the purposes of passing stupid
examinations set by charlatan educationists. Although
the evil they did still lives, there are not wanting signs of
a new and healthy growth of interest in this universally
operating science.
The author has to thank the several manufacturers for
their ready assistance in the preparation of much that is in
the book, and F. E. Palmer, Esq., for the execution and
revision of various diagrams.
By pointing out errors and suggesting improvements^
those who know will be rendering a service to those who
are willing to learn.
A. F ALLEN.
1 , ELM COURT,
THE TEMPLE,
LONDON, E.C. 4.
April, 1920.
466610
INTRODUCTION
THE student of chemistry realizes very early in his
career that he cannot make good progress in his subject
without spending a considerable amount of time in the
laboratory, doing practical work. A retentive memory
may serve to carry a student through a so-called
theoretical examination, but without practical experience
in laboratory work his value as a chemist is nil, and there
is no use for him in the industrial world when his student
days have ended.
In the years before the war the outlook for a trained
chemist was not a rosy one, and responsible positions
were few and far between, but now it may be said that
the demand exceeds the supply. The value of the
chemist has at last been recognized, and he is being
called upon to fill most of the positions which in the less
scientific pre-war days were taken by the engineer.
The type of chemist demanded is one having a certain
amount of engineering training, and it is a sign of the
times that the various colleges and institutions through-
out the country are taking in hand the question of
providing suitable courses in chemical engineering.
It will take some time before courses are standardized,
and the student on the threshold of the industrial world
will naturally look around for such guidance and in-
formation as is available at the moment.
The object of this book is to serve as an introduction
to chemical engineering by familiarizing the student
with those types of machines which are in general use in
the chemical industry. It must not be assumed that
the machines put forward represent the acme of perfection
vii
viii INTRODUCTION
from the chemist's point of view; in many cases they
are the product of the engineering mind pure and simple,
with but scanty knowledge of the laws of chemistry and
physics.
The methods of chemical industry may be described
roughly as the methods of the laboratory modified
so as to permit of operations on a large scale.
The plan of this book has been to take the various
pieces of apparatus in common use in a chemical labora-
tory and to describe their industrial counterparts.
The series of operations involved in the quantitative
analysis of a mineral afford a very convenient means of
calling to mind the different types of apparatus in
daily use by the chemist. These include the mortar
and pestle for grinding, the beaker and stirring rod for
dissolving and mixing, the filtering apparatus for separat-
ing solids and liquids, the evaporating basin for the
recovery of soluble solids, the drying oven with its method
of temperature regulation for drying solids, the crucible
and muffle for high-temperature work, the distillation
apparatus for the recovery of valuable solvents, the
supply of heat, and the provision of water and steam.
Each of these groups has been treated separately in
the following pages, and to them has been added a section
on Transport — a point of no account in a laboratory,
but one of considerable magnitude in the chemical
industry.
CONTENTS
PAGES
PREFACE v
INTRODUCTION - vii-viii
LIST OF ILLUSTRATIONS - xiii-xvi
CHAPTER I
CRUSHING AND GRINDING MACHINERY
Jaw Crusher or Nipper — Crushing Rolls — High-speed Crushing
Rolls — Sugar-cane Crusher — Rotary Fine Crusher or Cracker —
Edge Runner Mill or Chaser — Iron Edge Runner Mill — Granite
Edge Runner Mill — Overhead Driven Mill with Revolving
Pan — Disintegrators — Use of Screens — Buhrstone Mills —
Vertical Runner Mill— Roller Mills— Ball Mills— Pebble Mills-
Tube Mills— Combination Tube Mill —Stamps - 1-39
CHAPTER, II
SEPARATING AND MIXING MACHINERY
The Grizzly — Sieves — The Trommel — Telescopic Screen — Sifting
Reels — Centrifugal Dressing Machines — Powder Dresser —
Vibration Machines — Newaygo Screen — Shaking Sifter —
Gravity Leg Separator — Air Separators — Electro-magnetic
Machines — Magnetic Pulley — Water Separation — Settling
Tanks — Cane Juice Subsider — Levigating Mill — Mixing
Machines — Putty Mill — Pug Mill — Horizontal Mixer — Cone
Mill— Batch Mixer— Crutching Machines •- 40-69
CHAPTER III
FILTERING APPARATUS
Bag Filter — The Filter Press — Frame Press — Chamber Press —
Filter Plates— Filter Cloths— Methods of Closing— Methods of
Feeding — Centrifugal Machines — Weston Centrifugals — Types
of Lining — Friction Pulley — Water -driven Centrifugals —
Interlocking Gear ... 70-97
ix
x INTRODUCTION TO CHEMICAL ENGINEERING
CHAPTER IV
DRYERS AND EVAPORATORS
PASES
Flue Heater — Steam Heater — Firman Dryer — Rotary Dryer —
Warm-Air Drying — Sturtevant System — Timber Drying —
Triple Drying System — Vacuum Drying — Shelf Dryer —
Vacuum Rotary Dryer — Vacuum Drum Dryer — Passburg
System — Johnstone Dryer— Combined Vacuum Dryer, Mixer
and Ball Mill— Continuous Dryer — Evaporators — Spontaneous
Evaporation — Kettles — Open Pans — The Grainer — Steam-
jacketed Pans — Steam- jacketed Kettles — Tilting Kettles —
Steam Evaporating Pans — Wetzel Evaporating Pan — Vacuum
Pans — Jet Condenser — Surface Condenser — Wet and Dry
Vacuum Pumps — Calandria Vacuum Pan — Multiple-effect
Vacuum Pans— Kestner System — Climbing and Falling Film
Evaporators — Salting Type Evaporators— Multiplex Evapor-
ators - 98-144
CHAPTER V
DISTILLING APPARATUS
Column Still— Rectifying Still — Continuous Still— Coffey Still —
Extraction Plant — Mineral Oil Plant — Lubricating Oil Plant —
Tar Stills— Retorts — Nitric Acid Retorts — Pot Stills — By-pro-
duct Coke Ovens — Gas Retorts — Dowson Process — Pressure
Plant — Suction Plant — Bituminous Plant — Hydrogen Plant —
Kilns — Chamber Kilns — Rotary Calciner — Cement Kilns —
Muffle Furnace — Reverberatory Furnace — Regenerative Fur-
nace— Roasting Furnaces — Air and Water Cooled Shafts 145-178
CHAPTER VI
WATER TREATMENT PLANT
Hardness of Water — Common Impurities — Scale — Corrosion- —
Frothing — Water Softening — Lime-Soda Process — Intermittent
Plant — Continuous Plant — Automatic Apparatus — Permutit
Processes - - - 179-193
CHAPTER VII
THE CONTROL OF TEMPERATURE
Steam Control— Baldwin System — Isothermal Valve— Applications
to Still — Jacketed Pan — Dye Vessel — Vulcanizing Press — Gas
Producers — Gas Heating — Reducing Valve — Refrigerating
Machinery — Lightfoot System — Ammonia System — Carbon
Dioxide System — Ice-making— Can Ice — Cell Ice— Plate Ice —
Cold Storage— Brine Pipe System — Direct Expansion Pipe
System— Air Circulation System— Absorption System - 194-210
CONTENTS xi
CHAPTER VIII
TRANSPORT
PAGES
Conveying Solids — Wheelbarrow — Tipping Waggons — Runways —
Aerial Wire Ropeways — Single Wire System — Double Wire
System — Bucket Elevators — Conveyors — Worm Conveyor —
Scraper Conveyor — Mechanical Raker — Belt Conveyors —
Throw-off Carriage — Apron Conveyor — Bucket Conveyor —
Shaking Conveyor — Grasshopper Conveyor — |ConVeying Liquids
— Pipes — Anti-corrosion Material — Tantiron — Ironac — Vitreon
— Vitreosil — Ceratherm — \Vitreosate — Elevating Liquids — The
Acid Egg — The Air Lift or Pohle System — Plunger Pumps —
Centrifugal Pumps — Ceratherm Pumps — Conveying Gases —
Pipes — Chimneys — Fans — Radial Flow Fans — Mixed Flow
Fans — Rateau Fan — Rotary Blower — Compressors — Hori-
zontal and Vertical Types — Multi-stage Compressors — Vacuum
Pumps — Roughing Pumps — Siemens Oil Pump — Mercury
Diffusion Pump - 211-255
CHAPTER IX
APPENDIX
Distillation of Liquid Mixtures — Air Compression — Belt Conveyors
— Belting — Shafting — Refrigerating Machines — Low Boiling-
Point Liquids — Freezing-Point of Brines — Freezing-Point of
Calcium Chloride Solutions — Freezing Mixtures — Comparison
of Thermometer Scales — Percentage of Lime in Milk of Lime —
Specific Gravities of Soda Solutions — Useful Data of Common
Substances — Temperature, Pressure, and Total Heat of
Steam - - - - V - - 256-267
INDEX ^ ..... 268-272
LIST OF ILLUSTRATIONS
FIG. PAGE
1. "STAG" ORE-CRUSHER . 3
2. " STAG " ORE-CRUSHER: SECTION - - 4
3. G.A. HIGH-SPEED CRUSHING ROLLS - -7
4. FINE CRUSHING ROLLS, TYPE 5, CLASS 2 8
5. FINE CRUSHING ROLLS, TYPE 5, CLASS 1 9
6. SUGAR-CANE MILL - - - 10
7. ROTARY CRUSHER: SECTION - 11
8. IRON EDGE RUNNER MILL - - 12
9. GRANITE EDGE RUNNER MILL - 13
10. MILLS WITH REVOLVING PAN - 15
11. DISINTEGRATOR - 17
12. DISINTEGRATOR: SECTION - 19
13. DISINTEGRATOR: SECTION - - 19
14. G.A. DISINTEGRATOR PLANT: ELEVATION - 21
15. G.A. DISINTEGRATOR PLANT: PLAN - 23
16. MILLSTONE MILL - - 25
17. VERTICAL RUNNER MILL - - 26
18. ENCLOSED END RUNNER MILL - 27
19. TRIPLE GRANITE ROLLER MILL - 28
20. BALL GRINDING MILL - 30
21. " ATLAS " PEBBLE GRINDING MILL - - 32
22. " STAG " BALL MILL: SECTION - 33
23. " STAG " TUBE MILL: SECTION - 36
24. STAMPS FOR CRUSHING - 38
25. PORTABLE SCREEN - - 41
26. TELESCOPIC REVOLVING SCREEN - 42
27. REELS - 43
28. SIFTING REELS - 43
29. POWDER DRESSER - -44
30. CENTRIFUGAL DRESSING MACHINE V - 45
31. SHAKING SIFTER * - 47
32. SHAKING SIFTER AND CONVEYOR - - 48
33. GRAVITY OR LEG SEPARATOR - 49
34. " STAG " AIR SEPARATOR - 51
35. ARRANGEMENT OF ELECTRO -MAGNETS IN SPOUT - 53
36. ELECTRO-MAGNETIC SEPARATOR - 54
37. MAGNETIC PULLEY - - 55
38. LEVIGATING MILL - 56
39. CANE-JUICE SUBSIDER - 58
xiii
xiv INTRODUCTION TO CHEMICAL ENGINEERING
FIG. PAGE
40. DESIGN OF LEVIGATING PLANT: PLAN - 59
41. DESIGN OF LEVIGATING PLANT: ELEVATION - - 60
42. FLOW SHEET OF MILLING PROCESS - 61
43. POSITIVE DRIVEN PUTTY MILL - 62
44. VERTICAL PUG MILL - 63
45. " POWERFUL " HORIZONTAL MIXER - - 64
46. CONE PAINT MILL: SECTION - - 65
47. DOUBLE MIXER FOR SEMI-HQULDS - 66
48. " OPEN-DRUM " MIXER - 67
49. UNDER-GEARED MIXER - 68
50. CRUTCHING MACHINE: SECTION - 69
51. BAG FILTER - - 71
52. FILTER PRESS PLATES AND FRAMES - 74
53. FILTER PRESS: SECTIONS - - 76
54. FILTER PRESS: PLATE AND FRAME TYPE - 77
55. FILTER PRESS PLATE: RECESSED TYPE - 78
56. FILTER CLOTH CLIPS: BAYONET TYPE - 78
57. FILTER CLOTH CLIPS: SCREW TYPE - - 79
58. FILTER CLOTH: FIXING IN RECESSED TYPE - - 79
59. FILTER PRESS: RECESSED TYPE - 80
60. FILTER PRESS: CENTRAL SCREW CLOSING - - 80
61. FILTER PRESS: RACK AND PINION CLOSING - - 81
62. FILTER PRESS: COMPRESSED AIR CLOSING - - 82
63. FILTER PRESS: HYDRAULIC RAM CLOSING - - 83
64. " WESTON " CENTRIFUGAL BASKET: SECTION - 85
65. TYPES OF LININGS FOR BASKETS - - 86
66. BEARING FOR CENTRIFUGAL SPINDLE - 87
67. BEARING FOR CENTRIFUGAL SPINDLE - 88
68. CENTRIFUGAL FRICTION PULLEY - - 89
69. " WESTON " CENTRIFUGAL MACHINE - 91
70. " WESTON " CENTRIFUGAL MACHINE : WATER-DRIVEN - 93
71. INTERLOCKING GEAR FOR WATER-DRIVEN CENTRIFUGAL:
SECTION - - 96
72. "FIRMAN" DRYER: LONGITUDINAL SECTION - 99
73. "FIRMAN" DRYER: CROSS SECTION - 100
74. " HERSEY " ROTARY DRYER: CROSS SECTION - 101
75. COMBINATION ROTARY DRYER: CROSS SECTION - 101
76. G.A. DRYING PLANT: PARALLEL DRIVE - 102
77. G.A. DRYING PLANT: RIGHT-ANGLE DRIVE - - 102
78. RECORDING HYGROMETER - - 104
79. TYPICAL GUIDE CHART - - 104
80. HYGROMETRIC CHART - - 106
81. STURTEVANT TRIPLE DUCT DJRYER: SECTION - 108
82. VACUUM SHELF DRYER - - - 110
83. VACUUM DRUM DRYER - - - 113
84. VACUUM " JOHNSTONE " DRYER: SECTION - - 114
85. VACUUM DRYER: MIXER AND BALL MILL - - - 116
86. CONTINUOUS CONE V,ACU/UM DRYER - - 117
87. EVAPORATING PAN: OPEN TYPE - ... 120
LIST OF ILLUSTRATIONS xv
FIG. PAGE
88. CRYSTALLIZING PAN: STEAM HEATED - 122
89. TILTING KETTLE - 123
90. ASPINALL STEAM EVAPORATING PAN - 124
91. WETZEL EVAPORATING PAN - 126
92. COPPER VACUUM PAN - 128
93. CAST IRON CALANDRIA VACUUM PAN - 129
94. G.A. VACUUM PAN: JET CONDENSER - 130
95. G.A. VACUUM PAN: TORRICELLIAN CONDENSER - 131
96. INJECTION CONDENSER: SECTION - - 132
97. SURFACE CONDENSER: SECTION - 132
98. KESTNER CLIMBING FILM SINGLE -EFFECT EVAPORATOR - 136
99. KESTNER FALLING FILM SINGLE-EFFECT EVAPORATOR - 136
100. KESTNER QUADRUPLE -EFFECT, ETC.: DIAGRAM - 138
101. KESTNER SALTING TYPE EVAPORATOR: SECTION - - 139
102. " MULTD?LEX " FILM TRIPLE-EFFECT EVAPORATOR - - 142
103. "MULTIPLEX" TRIPLE-EFFECT EVAPORATOR: SECTION - 143
104. DIAGRAM OF STILL COLUMN - - 146
105. RECTIFYING STILL - - 148
106. CONTINUOUS DISTILLATION APPARATUS: DIAGRAM - - 149
107. CONTINUOUS STILL: DIAGRAM - 150
108. DIAGRAM OF COFFEY STILL - - 151
109. EXTRACTION APPARATUS - 153
110. SCOTT OIL EXTRACTION APPARATUS: DIAGRAM - 155
111. LUBRICATING OIL DISTILLING PLANT: ELEVATION - - 156
112. LUBRICATING OIL DISTILLING PLANT: PLAN - 157
113. " DOWSON " STEAM JET PRESSURE GAS PLANT - 161
114. " DOWSON " SUCTION GAS PLANT - 162
115. 30 H.-P. SUCTION GAS PLANT - - 164
116. DOWSON BITUMINOUS PLANT - - 165
117. ROTARY CALCINER - - 168
118. SIEMENS REGENERATIVE FURNACE: DIAGRAM - 170
119. HARRIS MECHANICAL ROASTING FURNACE - - 172
120. " A " TYPE SHAFT FOR ROASTING FURNACE - 173
121. " B " TYPE SHAFT FOR ROASTING FURNACE - 175
122. H.H. TYPE MECHANICAL ROASTING FURNACE - - 177
123. RECTANGULAR WATER SOFTENING APPARATUS - 186
124. AUTOMATIC WEIGHING AND MEASURING APPARATUS FOR
WATER-SOFTENING APPARATUS - - 187
125. POSITIVE DISCHARGE VALVE FOR WATER-SOFTENING APPA-
RATUS - - 189
126. CYLINDRICAL WATER-SOFTENING APPARATUS - 191
127. PERMUTIT WATER-SOFTENING APPARATUS: DIAGRAM - 192
128. " ISOTHERMAL " STEAM VALVE - 195
129. " ISOTHERMAL " THERMOMETER - 196
130. G.A. " ISOTHERMAL " TEMPERATURE CONTROL APPARATUS - 197
131. "ISOTHERMAL" CONTROL OF STILL - - 198
132. " ISOTHERMAL " CONTROL OF STEAM- JACKETED PAN - 199
133. " ISOTHERMAL " CONTROL OF DYE VESSEL - - 200
134. " ISOTHERMAL " CONTROL OF EXHAUST STEAM - - 200
xvi INTRODUCTION TO CHEMCIAL ENGINEERING
FIG. PAGE
135. " ISOTHERMAL " CONTROL OF VULCANIZING PAN - - 201
136. " ISOTHERMAL " CONTROL OF BLAST FOR GAS PRODUCER - 201
137. " ISOTHERMAL " CONTROL OF COTTON-SPINNING ROOMS - 202
138. *' ISOTHERMAL " SUPERHEATED STEAM VALVE - 202
139. " ISOTHERMAL " GAS VALVE - - 203
140. " ISOTHERMAL " GAS VALVE - - 203
141. DIAGRAM OF LIGHTFOOT REFRIGERATION SYSTEM - - 204
142. OPEN CONDENSER - - 205
143. HORIZONTAL AMMONIA COMPRESSOR - - 207
144. VERTICAL CARBON DIOXIDE COMPRESSOR - - 207
145. SIDE-TIPPING WAGGON - 212
146. END-TIPPING WAGGON - 212
147. RUNWAY FOR MINE - - 213
148. INTERWORKS TRAFFIC: PORTABLE ROPEWAY - 214
149. STANDARD FOR SINGLE-ROPE SYSTEM - 215
150. STANDARD FOR DOUBLE -ROPE SYSTEM - 216
151. ELEVATOR CHAIN - - 218
152. GRAVITY BUCKET CHAIN - 219
153. DUST PROOF ELEVATOR - 220
154. BOOT FOR ELEVATOR - 221
155. HOOD FOR ELEVATOR - 222
156. SPIRAL FOR WORM CONVEYOR - 223
157. SPIRAL CONVEYOR - - 224
158. SCRAPER CONVEYOR - 225
159. THREE-PULLEY BELT CARRIER - 227
160. THROW-OFF CARRIAGE - - 228
161. ELEVATOR AND CONVEYOR - 229
162. SLAT CONVEYOR - 230
163. GRASSHOPPER CONVEYOR - - 232
164. TANTIRON ACID EGG - 237
165. TANTIRON HORIZONTAL PUMP - 239
166. TANTIRON VERTICAL PUMP - ... 240
167. CERATHERM BODY IN IRON CASTING - 241
168. CERATHERM IMPELLER - 242
169. CERATHERM PUMP: INTERIOR - 242
170. CERATHERM PUMPt SMALL SIZE - - 243
171. CERATHERM PUMP! SUCTION SIDE INTERIOR - 244
172. CERATHERM PUMP: PRESSURE SIDE INTERIOR - 244
173. VITREOSATE THREE-WAY TAP .... 247
174. ROBEY COMPRESSOR - - ... 251
175. VERTICAL OPEN-TYPE AIR COMPRESSOR - 252
176. BELT-DRIVEN THREE-STAGE COMPRESSOR - - 253
177. FOUR-STAGE OXYGEN COMPRESSOR - 254
INTRODUCTION TO CHEMICAL
ENGINEERING
CHAPTER I
CRUSHING AND GRINDING MACHINERY
GRINDING is one of the most important operations in
the industrial preparation of chemical products, because
it facilitates the handling of the raw material and shortens
the time required for any subsequent reaction, and for
the selfsame reason many chemical products have to be
put on the market in the form of a powder or paste.
In the selection of any particular machine the nature
of the initial material and the result desired are the
determining factors, but it is useful to remember that
reduction by easy stages is, in the long-run, the most
economical of time and money. This fact has long been
recognized by makers of grinding machinery, with the
result that there are on the market many types of
machines designed to deal with all kinds and conditions of
material, from the crushing of the hardest rocks to the
production of the finest powders.
Jaw-Crusher. — This machine is often known as a
" nipper," and is one of the simplest and cheapest crush-
ing machines available. Many forms of jaw-crushers
exist, but generally it may be said they are so designed
that one part of the machine is stationary, with a cor-
rugated face of chilled iron against which works a similar
but movable face or jaw, with a V-shaped opening be-
tween. The movable plate is moved alternately forward
1
2 INTRODUCTION TO CHEMICAL ENGINEERING
and back by an eccentric on the shaft. These nippers,
or jaw-crushers, are made in different sizes, the rock
opening varying from 12 by 6 inches to 36 by 48 inches ;
they weigh anything up to 30 tons, and require from
1 to 100 horse -power. These machines require a very
solid foundation on account of the very great strain
during working. As a rule a method of adjusting the
working parts, such as a screw or similar device, is pro-
vided, so that the machine can be set for the production
of a rough or fine product.
The jaw-crusher will crush the hardest materials, and
is very largely employed for ore -crushing and in the
gypsum industry; the rock is broken to somewhat less
than the size of a man's fist, or capable of passing a 2j-inch
ring. The capacity of a jaw-crusher, in tons per hour, and
the power required vary with the condition of the rock,
and as a rule dry rock, especially gypsum, is more easily
crushed than wet.
Fig. 1 shows a popular size of the " Stag " ore -crusher,
manufactured by Edgar Allen and Co., Ltd., Sheffield,
to which the following details refer: Massive cast-iron
body with easily renewable bearings. The Pitman is of
cast iron of substantial design, with renewable cast-iron
adjustable bush for eccentric shaft, and is also fitted
with renewable cast-steel toggles to receive the nose
toggle plates. The swing jaw is of cast iron, accurately
bored and fitted to shaft, and fitted with renewable cast-
steel toggle seatings. The jawT faces are of manganese
steel, cored out at the back to reduce weight, and spelter
is run in to ensure a soft cushion for bedding on the swing
jaw. The jaw faces are readily accessible, and can be
reversed or renewed by an unskilled labourer. The side
plates are of hard cast iron, made in one piece, and assist
to hold the fixed jaw face securely in position. The toggle
plates are of hard cast iron, held in position by the tension
rod, which is fitted with india-rubber buffers. The shafts
are made from best hammered mild steel forgings,
CRUSHING AND GRINDING MACHINERY 3
accurately turned to gauge and polished all over. The
flywheels are of cast iron, bored to gauge, fitted and
keyed to the eccentric shaft, and turned to receive a
flanged pulley. The fast pulleys are of cast iron, flanged
FIG. 1. — " STAG " ORE-CRUSHER.
and bolted to either flywheel, turned and crowned on the
face; the loose pulleys of wrought iron have a suitable
bush of brass, and must revolve at a rate of not less than
250 to 280 revolutions per minute. Each machine can
4 INTRODUCTION TO CHEMICAL ENGINEERING
be regulated while running to break the material to any
special size, by means of cast-iron wedge blocks, the
output of all machines being calculated for crushing
limestone to pass a 2j-inch ring.
CRUSHING AND GRINDING MACHINERY 5
Fig. 2 is a sectional illustration of the breakers with
cast-iron bodies, sizes 20 by 8 inches and 20 by 10 inches.
Crushing Rolls. — This type of machine is of heavy
construction, and is designed for reducing the produce
of the jaw-crusher to sand. The essential part of these
machines consists of two cylinders capable of being given
an inward turning motion whereby material as it is fed
to them is carried along and crushed between them. As
a rule the bearings of one roller are rigidly fixed, whereas
the bearings of the other roller are held in position
by powerful springs, which not only allow the rollers to
be set at a definite distance apart — usually J inch or the
size of the finished product — but also allow the rollers
to give when any material is fed to the machine which
it cannot crush without causing damage to the machine
itself. Each roller is generally made up of an outer
shell of cast steel, chilled cast iron, manganese steel,
or a steel forging, which is fixed to a centre of cast iron
in such a way that it can be easily removed and replaced
when worn out. Owing to the hard wear on the rollers,
they require to be constantly trued-up, an operation
which can be effected in the ordinary way or by the use
of an emery wheel on the rollers when in position. To
diminish the amount of dust or smalls formed, the sur-
faces of the rollers are often fluted, the pitch of the
serrations being varied according to the product required.
In some cases the rollers are provided with teeth, when
designed for cubing granite, limestone, macadam, etc.,
and will take pieces up to 6 inches cube and reduce them
to 2 J inches cube.
To obtain a true crushing action the rollers should be
driven at the same peripheral speed, but in practice it
is found that a small difference in speed reduces the
amount of wear very considerably without causing
excessive grinding. The speed of the rolls varies from
100 to 1,000 feet per minute, according to the degree of
fineness required; the higher the speed, the coarser the
6 INTRODUCTION TO CHEMICAL ENGINEERING
product will be. The size of the feed to a large extent
decides the diameter of the rolls, but in any case to get
the best results from a machine the material to be treated
should not be more than four or five times as large as
the product required. High speeds can be best obtained
when each roll is separately belt-driven, which method
also allows a certain amount of slip to occur, thus avoiding
excessive grinding of the roll face. Where the rolls are
geared together both a lower speed and lower efficiency
are the result. The diameter of the rolls varies from 8 to
36 inches, but a very common size in practice is 18 inches,
and, it is worth remarking again, it is better to reduce
by steps than in one operation, for not only is the first
cost often less, but also the running costs are most
decidedly so.
The capacity of the rolls depends to a great extent
upon the nature of the material to be crushed, and to a
lesser amount upon the width of the rolls, which are made
10 to 42 inches, according to the diameter chosen; but
the narrow roll has the advantage in that it can be run at
much higher speeds, and for this and other reasons the
12-inch roll is in common use.
An important factor in the efficiency and economy of
upkeep of this machine is the provision of a method of
even feeding, so that even wear on the faces of the rollers
results. Crushing rolls are usually of heavy construction
and made in all sizes, having a capacity from 5 to 65 tons
per hour and requiring from 5 to 100 horse-power.
Fig. 3 shows the general arrangement of high-speed
crushing rolls as made by Edgar Allen and Co.. Ltd.,
Sheffield.
The frame is in one piece, on which are cast two
pedestals for receiving the bearings of the fixed roll.
The bearings for the other roll have machined soles which
slide in dove -tailed grooves and are held in position by
powerful springs attached to forged steel tension rods
which pass through the bearings and frame. The roll
8 INTRODUCTION TO CHEMICAL ENGINEERING
shells are made of cast steel or manganese steel, and are
fitted to cast-iron centres in such a way that the shell can
be renewed easily when required. Each roll is fitted with
a heavy cast-iron belt pulley which also acts as a flywheel.
The following particulars of one size are given as a
guide : Diameter of rolls, 1 8 inches ; width of rolls, 12 inches ;
r.p.m. of rolls and driving pulleys, 100 to 200; diameter
of driving pulleys, 36 inches; width of driving pulleys,
6 inches; approximate h.p. required, 5 to 10; approxi-
FIG. 4. — FINE CRUSHING ROLLS, TYPE 5, CLASS 2.
mate product per hour when rolls are set J inch apart,
4 to 8 tons.
Fig. 4 shows a type of low-priced machine made by
J. Harrison Carter, Ltd., Duns table, to meet a growing
demand.
These machines are constructed in a cast-iron sectional
frame which is protected from undue strains by relief
springs behind the movable roller. The renewable roll
shells are rigidly secured to the shafts by the improved
sliding internal cone arrangement; the bearings are of
CRUSHING AND GRINDING MACHINERY
9
swivel type, instantly renewed or replaced, self -lubricat-
ing, and are protected from dust or grit; the rolls are
direct driven, each roller by a separate belt. The hopper
illustrated contains an automatic feeding device.
Pig. 5 shows a similar type of machine made by the
same firm, but having only one roller driven, the other
roller following, an arrangement which is supplied when
only a single drive is available.
FIG. 5. — FINE CRUSHING ROLLS, TYPE 5, CLASS 1.
Fig. 6 shows a type of machine built by Blair, Campbell
and McLean, Glasgow, for sugar-cane work.
This arrangement is suitable where sufficient motive
power already exists and can be transmitted to the mill
conveniently by belt. The rollers are of special cast
metal, having gudgeons of mild steel running in gun-
metal bushes, compound spur gearing of special cast
iron, with mild steel shafts, and the driving pulleys are of
wrought iron for lightness.
10 INTRODUCTION TO CHEMICAL ENGINEERING
Rotary Fine Crusher. — This machine, known also as a
"cracker," is almost universally used for reducing rocks
of moderate hardness, such as gypsum, limestone,
graphite, etc. In its common form it resembles a coffee
mill, being in shape like an hourglass and often provided
with double doors, so that it can be opened up quite
easily and the. parts inspected. In its simplest form a
shaft with a corrugated-iron shoe revolves within a
conical shell having a corrugated inner surface, and by
means of an adjusting wheel can beset while the machine
FIG. 6. — SUGAR-CANE MILL.
is running, to give a fine or coarse product as desired.
The ordinary reduction is to fragments which will pass
a 1 1 -inch ring. These rotary crushers weigh from 1 to 7
tons, requiring from 1 to 35 horse -power, and having a
capacity of from 2 to 30 tons, the largest sizes taking
pieces up to 14 inches in diameter.
Fig. 7 gives a sectional view of a rotary crusher.
Edge Runner Mill. — This mill, also known as a
" chaser." is particularly useful for dealing with sub-
stances such as clay, putty, drugs, chalk seeds, etc.,
where a very fine reduction is not required. It is also
CRUSHING AND GRINDING MACHINERY 11
largely used for mixing mortar, for mixing loams for
use in the foundry, and for grinding materials which are
not of a very hard nature.
FIG. 7. — ROTARY CRUSHER: SECTION.
The mill is constructed with a steel or stone bed on
which roll two or more heavy rollers of cast iron or stone,
known as edge runners or travellers, the whole being
contained in a pan provided with a suitable discharging
arrangement. In some cases the pan is driven and the
12 INTRODUCTION TO CHEMICAL ENGINEERING
rolls rotate of themselves, and in other cases the drive
is to the rolls themselves, but in all cases an arm is pro-
vided carrying a scraper which travels just in front of the
rolls, and which brings the material into the track of the
rollers.
As a general rule this machine is used for dealing with
batches of material necessitating frequent charging and
discharging; but if required for continuous service, grates
FIG. 8. — IRON EDGE RUNNER MILL.
are provided under the rolls having a definite mesh,
according to the nature of the material dealt with, and
the ground material is gradually forced through the open-
ings into the stationary pan beneath. In some classes
of work the rolls are supported at a definite distance
above the surface of the pan, so that a certain depth of
material is necessary before crushing takes place.
Fig. 8 shows a " Standard " iron edge runner mill made
CRUSHING AND GRINDING MACHINERY 13
by Follows and Bates, Ltd., Manchester, which is suitable
for pulverizing a great variety of materials, wet or dry,
or in oil or water, etc. It is strong, durable, and designed
to deal with small requirements. In order to ensure
good work, the pan and runners are turned dead true
on the faces, and the guides and scrapers are specially
designed so as to bring the whole of the materials whilst
being crushed directly under the track of the runners.
FIG. 9. — GRANITE EDGE RUNNER
When the grinding operation has been completed, the
contents of the pan are quickly and automatically dis-
charged by simply turning the handwheel shown in front.
Fig. 9 shows a granite edge runner mill suitable for
grinding and mixing crystals, powders, pastes, drugs, etc.,
either wet or dry, and is made by the same firm. The
object sought has been to produce a mill that will operate
upon materials in the most effective manner without their
14 INTRODUCTION TO CHEMICAL ENGINEERING
coming in contact with iron. To this end the solid bed
and runners are made of hard, close-grained grey granite,
having surfaces perfectly dressed and dead true. The
hopper in which the runners rotate is built up of hard
sycamore sections, neatly tongued, grooved, and riveted
together in such a manner as to prevent shrinkage or
leakage and to be as absolutely clean as the granite itself.
The scrapers that clear the runners and the scrapers
which are plough -shaped and revolve with the cross-head
are of lignum vitse and keep the bed clear, causing all the
materials being ground to pass into and under the track
of the runners, which possess a rolling as well as a grinding
action, thereby, in a short time, reducing the contents
of the hopper to one uniform and smooth consistency.
Fig. 10 shows a type of overhead driven mill with re-
volving pan, having a perforated bottom with a stationary
pan underneath. These mills are specially suitable for
pulverizing all kinds of dry materials, such as ashes,
lime, gypsum, plaster of Paris, silica, sandstone, bricks
for making cement, fireclay, coke, etc., and are provided
with a set of grates having a mesh down to y\ inch.
These mills weigh from 3 to 11 tons, requiring from
3 to 20 horse-power, and have a capacity of from 8 to 100
cwt. of ordinary burnt limestone per hour.
Disintegrators. — These machines, also known as pul-
verizing mills, are especially adapted for dealing with
substances of a lumpy nature which are neither hard nor
gritty, such as gypsum, dry colours, sulphur, borax,
starch, bones, etc. The essential features of these
machines are as follows: Two circular plates, mounted on
a horizontal axis, revolve concentrically in opposite
directions; each plate is fitted with one or more circles
of short iron bars, rigidly fixed at right angles, and so
arranged that they interlock with those of the other
plate, thus forming a circular cage made up of two or
more concentric circles of short rods.
The material is fed into the centre of the cage, and
CRUSHING AND GRINDING MACHINERY 15
drops down upon the first set of bars, which, travelling
at high speed, beat the material to pieces, and at the same
time impart a centrifugal motion to it, forcing it through
the bars on to the second set, which are travelling at a
high rate of speed in the opposite direction. By the
16 INTRODUCTION TO CHEMICAL ENGINEERING
time the material reaches the outer bars it has been
reduced to a fine powder.
The speed of the machine largely determines the fine-
ness of the product, which is also to a lesser extent
affected by the distance apart at which the bars are set.
The peripheral speed of these machines often reaches
20,000 feet per minute; they are made in sizes up to 55
inches in diameter, from 3,000 to 15,000 pounds in weight,
requiring from 6 to 45 horse -power and having a capacity,
which depends upon the degree of fineness sought and the
nature of the material, of from 8 to 75 tons in ten hours.
In addition to the usual disadvantages belonging to all
high-speed machinery, it is obvious that these machines
in running tend to generate a certain amount of heat,
which in some cases may become excessive, although the
action of the beaters creates a strong air current, which
exercises ' both a cooling and a drying action on the
material being pulverized.
These machines must be carefully fitted to a perfectly
dust-tight receiving chamber provided with a proper
means of discharge, and at the same time the strong
current of dust-laden air must be filtered through gauze
screens in a dust chamber or allowed to pass to dust
balloons, which, being made of porous material, allow
the air to escape and the dust to accumulate at the
bottom, from which it can be discharged by means of a
valve .
It may be again noted that a better result is obtained
by allowing the machine to do its own screening and
returning the coarser material to the centre of the
machine .
Fig. 11 shows a type of disintegrator made by
J. Harrison Carter, Ltd., Dunstable, to which the following
details refer: The body of the machine is of cast iron,
the inside of the circular grinding chamber being lined
with renewable chilled-iron sides to reduce the wear.
The bottom half of the circumference of this chamber is
CRUSHING AND GRINDING MACHINERY 17
formed by screens held in position by adjustable screws.
A strong spindle carried in self -lubricating bearings runs
through the centre of the grinding chamber and carries a
cast iron and steel combined disc, which in turn holds a
series of from four to six beaters, the tips of which run
close to the inner circumference of the grinding chamber,
and, when running, cover the whole width of this
chamber.
The beaters are mainly responsible for the grinding,
being assisted, however, to some considerable extent by
M94-/2
FIG. 11. — DISINTEGRATOR.
the ratcheted sides and top of the machine. The beaters
are easily changed and are hardened to resist wear ; they
can also be cheaply repaired when worn.
The use of screens of various meshes enables the
finished material^to be ground to any desired size, fine
or coarse, and also allows the finished material to escape
at once. The mesh of screens, varying as they may
from ^V inch and rising in gradations of ^ inch, up to
2
18 INTRODUCTION TO CHEMICAL ENGINEERING
a 3 -inch mesh, enables the disintegrator to treat almost
every article likely to be ground, with the following
exceptions: Substances of a very gritty and cutting
nature, such as hard quartz, hard limestone, cement
clinker, flint, and similar materials, or those containing
a large percentage of moisture, such as plastic clay. The
screens and, to an extent, the speed regulate the degree of
fineness to which any material is reduced; and these
screens, being made in very varied meshes — viz., with from
rV-inch to 3 -inch spaces — enable a great variety of
materials to be ground and a large number of grades
produced. The grinding and discharging action is con-
tinuous, and to obtain the full output from the machine
the feed should also be continuous and even. The speed,
to obtain the best results, must be kept regular and
maintained at the full value given for the machine.
Many manufacturers object to the use of sifters to
follow the grinding machine; this is generally false
economy, both as regards output and power. For
example a No. Ij machine fitted with -g^-inch screens
would grind about 4 cwt. per hour of sugar or similar
material. The same machine fitted with a T\-inch
screen would pass about 10 cwt. per hour, 60 per cent,
of which would be as fine as that passing the JT-*nch
mesh screens. This 60 per cent, or 6 cwt. per hour would
be taken out by the sifter, leaving the 40 per cent, of
overtails to go again to the disintegrator to be further
reduced, thus showing a gain of 2 cwt. per hour. The
sifter and grinder should always be so connected that
they work automatically, in order that there should be
no additional cost for labour. Further, the material,
to pass a disintegrator fitted with a JT-inch screen,
must be quite dry, whereas a material containing a fair
percentage of moisture would readily pass a TVinch
screen.
Figs. 12 and 13 show sectional views of this type of
machine.
CRUSHING AND GRINDING MACHINERY 19
A-Spindte
B— Disc
C— Beaters
D— Screw for adjusting Screens
E— W.I. Cross Bar -
F— Top Side Ratchets
G— Bottom ditto
H— Screens
J— Bottom Screen Block
J— Top Screen Block
K— Top Door Ratchet Linings
L— Top Doors
M- Special End Door
N — Ordinary End Door
P— Top Cross Block for 3? and
4| machines only
FIG. 12. — DISINTEGRATOR: SECTION
FIG. 13. — DISINTEGRATOR: SECTION.
20 INTRODUCTION TO CHEMICAL ENGINEERING
It is requisite for the efficient working of these machines
that a continuous current of air pass through them.
This current of air, when the machine is properly fed,
enters with the feed and also around the spindle at
the centre of the machine, and continues to do so as long
as the screens are clear. The air passes, in the ordinary
working, with the ground material through the screens
into the box or stand, and becomes charged with dust,
and as the action of the beaters is somewhat fan-like a
considerable air pressure is caused inside the box. This
pressure, if not relieved, causes back pressure against the
incoming material, and in consequence greatly lessens
the grinding capacity, and also causes a greater con-
sumption of power in driving. If air blows out of the
centre, it is generally an indication of back pressure or
overfeeding. In all cases when the receiving box is
made air-tight a trunk is led away from the top of it to a
dust chamber or dust balloon. The trunk should be as
large as possible, fixed as nearly vertical as it can be,
and with as few bends as possible. The dust room
should be made as large as possible, so as to allow the air
to expand and come to rest, and thus drop the suspended
dust.
Figs. 14 and 15 show a standard fixing as supplied by
J. Harrison Carter. The disintegrator is fixed upon a
dust-tight wooden grinding box or stand placed upon the
ground. The machine is driven by a counter -shaft either
suspended from the roof or bolted to wooden sleepers in the
ground. The counter -shaft is driven off the flywheel or
pulley on an engine or motor. In this arrangement the
stand shown is made of a top and bottom framework
of timber, the timbers of each frame being morticed and
securely pinned together. The top and bottom frames
are then joined together at the proper distance apart by
four vertical legs morticed and bolted to both frames.
Two other cross-timbers are also required in the top frame
to receive the holding-down bolts of the machine; these
CRUSHING AND GRINDING MACHINERY 21
timbers should be placed parallel with the grinding chamber
and not across it, so as not to block up the discharge from
the machine. The top of the stand should be covered over
22 INTRODUCTION TO CHEMICAL ENGINEERING
with planking, laid down perfectly even and flat, the
joints being placed parallel to the cross -timbers, tongued
and made dust-tight. The planking should be securely
fixed to the top of the frame and an opening cut between
the cross -timbers for the escape of the ground material.
The stand should be completely enclosed by match-
boarding, made dust- tight, and a sliding door, having a
dust-tight seating, provided in one of the sides to allow
of periodical cleaning. It is of the greatest importance
for the proper working of the machines that plenty of room
is left underneath them. The stands or hoppers should
be made as deep as convenient, so as to leave room for
the air blown into them by the revolving of the beaters.
In no case must a machine be fixed so that there is not a
free escape for this air, and in order to get rid of this air
and dust a spout should be taken from the top of the
stand and led to a dust room or balloon.
Great care must be taken that the material is fed into
the machine as evenly as possible . The feed should enter
continuously and not intermittently, and should be
examined for any foreign substance such as iron. Before
starting to feed, the machine should be allowed to attain
its full speed judged by the hum of the beaters, and the
rate of feeding regulated by this hum. In very fine
grinding, when it is of importance that no pieces of grit
should appear in the product, the screens must be packed
by a layer of putty or string along that part of the screen
which rests on the inner lining of the machine.
The bearings are self -lubricating, and should be
inspected two or three times a day and new oil put in
every other day.
When the beaters are repaired or replaced, care must
be taken that they (the disc and the spindle) are perfectly
balanced, so that on turning they show no tendency to
come to rest in any particular position.
The disintegrator has been somewhat fully treated
owing to the great range of usefulness which it possesses,
CRUSHING AND GRINDING MACHINERY 23
as will be seen from the following list of materials which
it is claimed are reduced by this means: Alkali, alum,
ammonia, anthracene, antimony, asbestos, asphalte, bark,
24 INTRODUCTION TO CHEMICAL ENGINEERING
barley, barytes, beans, biscuits, blacklead, blood manure,
blue, bones, borax, breeze, bricks, cattle foods, chalk,
charcoal, coal, clay, cocoanut husks, copper ore, cork,
feathers, felt, fuller's earth, gas carbon, glue, guano, gum,
gypsum, hops, iron oxide, lead ore, lime, linseed, magnesite,
mica, nuts, oyster shells, paper, phosphates, pitch, rags,
resin, salt, shavings, soap powder, sugar, tan, wheat,
wood fibre, etc.
Buhrstone Mill. — This machine is in very common use
for dry or wet fine grinding of materials such as flour,
steatite, graphite, pigments, dry colours, etc.
A buhrstone mill consists of two rough, siliceous discs,
one of which is stationary and the other revolving against
it. The stones are usually of French buhr or Derbyshire
Peak, set either horizontally or vertically. Radiating
grooves, about | an inch deep and 2 inches wide, inclined
to the radii, are cut into the grinding surface of each
stone . These grooves must be recut every time the stones
wear smooth, which in practice is about once a fortnight,
extra stones being provided so that no time is lost during
redressing. As the stones naturally wear more towards
the outer edges they are usually dressed slightly concave .
A much more satisfactory stone is one built up upon a
centre of buhrstone with concentric rings of grooved
emery blocks, the whole being surrounded with an iron
band and having the loose blocks cast in metal.
This type of stone was devised to remedy the wearing
away of the outer part of the buhrstone more rapidly than
the centre, and in practice not only requires less frequent
dressing, but also can be safely driven at 5,000 feet
per minute peripheral speed. Usually the material is fed
through a hole about 10 inches in diameter in the upper
stone, being driven by centrifugal force to the outer edge
and cut by the sharp edges of the grooves. To secure an
efficient and sweet running mill the rotating stone must
be carefully balanced, and if this is done a speed of 4,000
feet per minute instead of 1,000 may be attained^with
CRUSHING AND GRINDING MACHINERY 25
safety. The limit of speed and therefore of output, apart
from the mechanical strength of the stones, is determined
by the amount of heat evolved which may be deleterious
to the material ground, and to prevent any excessive
amount of which a water -cooling arrangement is often
provided.
FIG. 16. — MILLSTOXE MILL.
The degree of fineness of the product is regulated by
means of set screws at the side, and for paste or paint
grinding a scraper is provided on the rotating stone to
remove the product as it passes the grinding face.
The vertical mills grind faster but not as uniformly
fine as the horizontal mills. In some cases the rotating
stone is of smaller diameter than the stationary stone,
26 INTRODUCTION TO CHEMICAL ENGINEERING
and is driven eccentrically to it, thereby redressing one
another at the same time . Such mills are particularly use -
ful for wet grinding and for paints, graphite, chalk, etc.
Fig. 16 shows a millstone mill made by J. Harrison
Carter, Dunstable, in which the stones are made of French
buhrstone or Derbyshire Peak, according to the material
to be ground. If used for grinding cement, phosphates,
etc., the mill is specially constructed and the stones
thickened.
A very useful modification of the eccentric mill is the
Vertical^ Runner Mill, which is mainly used for small
FIG. 17. — VERTICAL RUNNER MILL.
outputs. Fig. 17 shows such a mill as made by W. M.
Fuller, junr., Birmingham. The stones are replaced by a
mortar and pestle or runner, the latter having about half
the diameter of the former. They are made in cast iron,
stone, or wedgwood ware, and scrapers are provided for
both runner and mortar. In the smaller sizes the runner
may be swung clear and the mortar removed for emptying.
CRUSHING AND GRINDING MACHINERY 27
Their efficiency is not high, but they are extremely useful
for small operations.
Fig. 18 shows a larger size of runner mill made by
the same firm. This machine has been specially designed
for mixing and grinding chemicals, drugs, fine colours,
dyes, inks, explosives, etc. The mortar and runner are
entirely enclosed by a cover, which is easily removable,
and an automatic discharge is provided which can be used
without stopping the machine.
Roller Mills. — This machine combines a very high
efficiency with the production of the finest output. It
consists essentially of a roll of granite or steel which
revolves in a cavity formed by a piece of the same
FIG. 18. — ENCLOSED END RUNNER MILL.
material as the roll, and which is capable of a lateral
movement for the purpose of equalizing wear.
The type of roller mill most commonly found in use
consists of three rolls driven at speeds varying in a fixed
ratio. The fastest-running roll, which is the delivery
roll, is fitted with a scraper, commonly referred to as the
" doctor," upon the setting and adjustment of which
much of the successful working of the machine depends.
Much that has been said previously in connection with
the working of high-speed fine crushing rolls applies with
equal force to roll mills. To obtain the best grinding
action the surface of the rolls must not be allowed to
become polished, but must be roughened, either by sand
blasting in the case of steel rolls, or by the use of the
28 INTRODUCTION TO CHEMICAL ENGINEERING
diamond turning tool in the case of granite rolls. It need
be hardly mentioned that it is of extreme importance that
the rolls and spindles must be ground and turned dead
true, and any wear due to working immediately remedied.
As a necessary consequence the frame and bearings
must be of substantial design, and the pressure on the
rolls must be capable of being evenly distributed and
adjusted to suit the class of material dealt with. The
FIG. 19. — TRIPLE GRANITE ROLLER MILL.
usual practice to secure even wear in the case of triple
roller mills is for the central roller to be given a uniform
lateral to-and-fro movement of about J inch.
Owing to the fine work required, the type of gearing
employed is of the greatest importance to secure smooth
and efficient running. In a good-class machine the gearing
is either plain machine-cut in cast iron or cast steel, or,
better, machine-cut noiseless train gear running in oil,
CRUSHING AND GRINDING MACHINERY 29
with the pinions so arranged as to be capable of adjust-
ment to compensate for any reduction in the diameter of
the rolls.
Fig. 19 shows a triple roller mill made by Follows and
Bate, Manchester, for amalgamating and finishing white
lead, zinc white, oxides, paints, etc. Other forms are
made by the same firm for treating ochres, blues, ink,
fine colours, enamel paste, etc. The rollers are of Scotch
grey granite, fine-grain hard granite, porphyry, cast iron,
or chilled iron, according to the class of work to be
undertaken, and range in size from 24 inches by 12 inches
to 30 inches by 15 inches, requiring from 3 to 5 horse-
power, with an output ranging up to 8 tons per day. These
machines have a heavy framework, to ensure absolute
steadiness, and accurately machined bearing-ways per-
fectly aligned, with steel plates secured by studs and
lock nuts. The rolls are of grey granite mounted securely
on steel shafts and protected from accident by means
of spiral springs, even wear being obtained by securing
an even distribution of strains throughout and a uniform
lateral movement of the central roller. The scraper is
of steel, and has a fine adjustment device ; the gears are
powerful and almost noiseless, and the counter-shaft is
in adjustable plummer blocks supported by a pedestal
bracket. Patent parallel roller adjustments are provided
to front and back rolls, which prevent " sugar -loafing "
and ensure fine work.
Ball Mills. — During the last few years these machines
have increased in favour, owing to their simplicity of
construction, ease of working, low running costs, and
freedom from breakdown. They consist of one or more
jars of iron or stoneware arranged horizontally in a
frame and rotated about a common axis. The grinding
action is produced by means of a number of balls or
pebbles of porcelain or flint, the jar being driven at a
speed of about 80 r.p.m. By using multiple jar machines
small quantities of different materials may be treated
30 INTRODUCTION TO CHEMICAL ENGINEERING
at the. same time, and owing to the small cost of jars the
losses due to cleaning may be avoided by keeping separate
jars for different materials.
~
Fig. 20tshows one of the many types of ball mills made
by Hind and Lund, Ltd., Preston. These machines
create no dust during working, resulting in no loss of
material, and pulverize all the material to a uniform
product. The capacity of such mills is given in pounds
CRUSHING AND GRINDING MACHINERY 31
of sand from which the capacity for other materials
may be estimated, taking as a basis that 1 cubic foot of
sand weighs 90 pounds.
The machine in question is fitted with two porcelain
jars 13 J inches diameter by 12 inches inside, mounted in
sheet-iron receptacles, and have an inlet or neck of
8J inches diameter. The approximate power required is
1 b.h.p. when driven at a speed of 40 to 50 r.p.m. The
charge of porcelain balls or flint pebbles for each jar
amounts to 45 pounds, giving a grinding capacity of 26
pounds of sand per day for dry grinding and 3 gallons
per jar for wet grinding.
For heavy work pebble mills are used having a lining
of porcelain, silex blocks, chilled iron or steel plates,
the grinding medium being hard flints or porcelain balls
according to the class of material to be treated. For
special work, steel, brass, hardwood, or vulcanite balls
are made.
Fig, 21 shows the " Atlas " pebble grinding mill made
by the same firm. The body of the mill is built up on
steel gudgeons of substantial design on which the cast-
iron side plates are keyed, the outer shell being built up
of mild steel plates. Spur wheels are fitted, also barring
gear to the end of the counter -shaft, thus allowing the
manhole to be brought into position when it is necessary
to change the covers for charging or discharging the mill.
The gudgeons of these machines are sometimes fitted
with stuffing glands and pipe connections for steam or
air inlet on one gudgeon and an outlet with cock on the
other, to enable grinding to be done under pressure.
The operation of cleaning out the mill is performed
by placing in the bottom of the mill a charge of dry sand
equal to the given capacity of the mill, and then filling
in carefully by hand the charge of balls or flint pebbles.
The charge of sand is sufficient to fill in the crevices
between the balls or pebbles, and the total volume is
equal to half the volume of the mill. The manhole is
32 INTRODUCTION TO CHEMICAL ENGINEERING
then closed by the solid cover, and the mill rotated at the
specified speed for several hours. The solid cover is
then replaced by a perforated cover, and the mill again
run until all the sand is sifted out, only the balls or
pebbles being retained.
It is of the greatest importance that pebbles should
be of the best quality, as soft pebbles not only wear out
rapidly, but also deteriorate the quality of the material
FIG. 21. — "ATLAS" PEBBLE GRINDING MILL.
being pulverized. Pebbles of uniform shape, round or
oval, are preferable to those of irregular shape, and
greatly increase the grinding capacity. On no account
should chips or fragments of pebbles be allowed to remain
in the mill, as they lower the efficiency considerably.
As the main action of these machines is that of grinding
CRUSHING AND GRINDING MACHINERY 33
and not crushing, all material must be crushed to a suitable
degree of fineness before being fed to the machine.
Fig. 22 shows a form of ball mill made by Edgar Allen
and Co., Ltd., Sheffield, and designed for continuous
working. The periphery of the mill is made of hard steel
EDGAR ALLEN & CO. LD,
SHEFFIELD.
" STAG "
BALL MILL.
FIG. 22. — "STAG" BALL MILL: SECTION.
grinding plates, stepped as shown; the plates, being
perforated, allow the material to leave the inner chamber
of the mill as it is reduced to powder; that portion
passing from the inner chamber falls on to a second per-
forated plate or check sieve, which allows only the finer
3
34 INTRODUCTION TO CHEMICAL ENGINEERING
portion to enter the outer chamber, on which is fixed
a final series of sieves, so arranged as to produce the
necessary fineness. In each case the rejected portions are
returned automatically to the inner chamber for further
reduction; consequently, the process of grinding becomes
continuous and automatic. The ground material is
delivered from the bottom or hopper portion of the
chamber into bags by operating a slide, or the bottom
may be left open for the finished material to be carried
away by a conveyer. The usual type of machine can
be fed with material up to 2 inches cube, but machines
are made capable of taking material up to 7 inches cube.
The side plates, which are of rolled steel in the larger
sizes and of cast iron in the smaller sizes, are mounted
on cast-iron centres keyed on to the main shaft. The
feed hopper, which is bolted to the inner edge of the main
sole plate, is of heavy construction, so as to remain
steady under all conditions of working.
The dust casing, constructed of steel plates in sections,
with angle iron joints, consists of two parts, of which
the top one is fitted with a nozzle from which the dust
generated by the rotary action of the mill may be carried
away to a balloon or dust settler. Where only limited
power is available, a friction clutch is substituted for
the fast and loose pulleys, so that starting up may be
accomplished more easily and with less shock to the
gearing.
These mills require from 3 to 60 b.h.p., and are
charged with from 3 to 60 cwt. of steel balls according to
their capacity. The main purpose of these mills is to
reduce material to a suitable degree of fineness in order
to feed a finishing mill.
Tube Mills. — The tube mill is essentially a machine
for fine grinding, and since its introduction a few years
ago it has replaced practically all other machines for
this purpose. It is essentially a special form of ball mill,
as the grinding is effected by the rubbing of the material
CRUSHING AND GRINDING MACHINERY 35
between the flint pebbles or steel balls and the sides of
the mill, but a certain amount of crushing is performed
by the rolling of the balls and also by their impact in
falling after they have been raised a certain distance by
the revolution of the mill. The difference in action is
that the material to be ground is fed in at one end and is
delivered as a finished product at the other, the degree
of reduction being controlled by the speed of the feed,
since the longer the pebbles are allowed to operate, or,
in other words, the slower the feed, the finer will be the
condition of the ultimate product. Some machines are
provided with a spiral worm feed whereby a certain amount
of material is allowed to travel to the grinding chamber,
and from whence, after passing a perforated plate, it is
carried by another worm and discharged.
These machines are capable of being used for either
dry or wet grinding, and in the former case the material to
be ground must be quite dry, as 1 per cent, of moisture
will seriously reduce the output, and in the latter case,
for wet grinding, sufficient moisture must be present
so as to form a sludge or slurry.
Edgar Allen and Co., Ltd., Sheffield, divide tube mill
grinding into four classes and provide machines ac-
cordingly :
1. For grinding either wet or dry material which has
been previously roughly ground or pulverized in a pre-
paratory mill such as a ball mill (Fig. 23).
2. For the preliminary treatment of either wet or
dry material which has been reduced to a size equal to
about 2 inches cube.
3. For the preliminary and final treatment of either
wet or dry material which has been reduced to a size
equal to about 2 inches cube.
4. For the treatment of dry material, in conjunction
with air separation, the material having be en reduce
to a size equal to about 2 inches cube.
The first type of mill, made in several sizes according
CRUSHING AND GRINDING MACHINERY 37
to the quantity and fineness of the finished product
required, is designed to carry a charge of flint pebbles
in some cases and small steel balls in others.
In the case of flint pebbles being used, the mill is lined
with either quartzite or chilled cast-iron plates, the end
lining plates being of manganese steel. The quartzite
lining is preferable to cast iron, both on account of its
longer life and the fact that the efficiency of the mill is
increased, due to the quartzite bricks having a rough
face, which prevents slip of the pebbles down the sides
of the mill.
The mill carrying a charge of small steel balls is suitable
for dealing with refractory material, and is lined with
steel plates designed to prevent slip. The fineness of
the feed supplied to this machine should be such as to
pass a 16-mesh sieve — viz., one which has 256 holes per
square inch.
The second type of mill is intended for preliminary
reduction only and the product passed to a finishing
mill as described above. This mill is lined throughout
in hard cast steel or manganese steel, and the diameter is
larger in relation to the length as compared with a
finishing mill. It takes a feed up to a size equal to a
2-inch cube, and is charged with steel balls from 3 inches
to 5 inches diameter.
The third type of mill is a combination tube mill,
being divided internally by a special diaphragm into two
chambers, one of which contains steel balls, the other,
which is the finishing chamber, containing flint pebbles.
Hard cast steel is used for lining the first chamber and
quartzite for the remainder, so that this machine is well
suited for grinding cement, clinker, coal, and various
kinds of ore.
The fourth type is practically the same as the second
type, but it is used for " bulk-grinding," by which is
meant that a large quantity of feed is given to the mill,
but only a portion is reduced to the required fineness
38 INTRODUCTION TO CHEMICAL ENGINEERING
during its first passage . The whole of the product, coarse
and fine, is passed through an air separator, which extracts
the fine portion and returns the oversize to the mill for
regrinding. The advantage of this system is that there
is a saving of power required, and that by means of
adjustments made at the air separator the fineness is
controlled through a wide range.
FIG. 24. — STAMPS FOR CRUSHING.
These mills are made up to 30 feet in length and 6 feet
diameter, carrying a charge of 350 cwt. of pebbles and
requiring about 180 h.p.
Stamps. — This type of reduction machine performs its
work by the simple method of repeated blows on the
material by means of a falling weight under the action of
gravity or power. Although of very poor mechanical
CRUSHING AND GRINDING MACHINERY 39
efficiency, the low running costs make them very suitable
in the larger sizes for the mining industry, and in the
chemical industry the small sizes are found decidedly
useful for reducing material of a sticky or oily nature,
and for nuts, mustard, etc.
Fig. 24 shows this latter type of machine, made by
J. Harrison Carter, Ltd., Dunstable, consisting of two
iron pots having heavy stamps lifted by cams and dropped
by their own weight into the pots.
Although there are many points of interest in stamps
as used by the mining engineer, it is felt that they are
not strictly within the scope of this volume, and for
further information the student is referred to books
dealing with mining machinery.
CHAPTER II
SEPARATING AND MIXING MACHINERY
IN the chemical industry it may be necessary either to
separate different sized particles of the same material
or particles of different nature from one another, and for
each class of work distinctive machinery is used.
The simplest form of sifting machine is known as the
" Grizzly," and is used, for the sake of economizing power,
for separating the smaller pieces of material from the
larger, so that the former can go to the fine crusher direct
and not with the latter through the jaw-crusher.
A grizzly is an incline built up of parallel bars set
transversely, an inch or more apart, according to require-
ments.
For finer work the ordinary sieve or screen, in which
the screening surface is formed by a plate having slots
punched through it or by a woven wire, is in common
use.
The obvious development of the common sieve is the
cylindrical or conical form, which can be rotated about
its axis.
The Trommel. — This machine needs very little descrip-
tion, as it consists of a cylindrical perforated plate
mounted so that, in the smallest sizes, it can be rotated
on an axle, or, in the larger sizes, on friction rollers.
The cylinder is set at a slight inclination so as to pass
the material through rapidly, and very often several
cylinders having different degrees of perforation are
arranged concentrically, thus grading the material into
several sizes at one operation.
40
SEPARATING AND MIXING MACHINERY 41
42 INTRODUCTION TO CHEMICAL ENGINEERING
Fig. 25 shows a portable hand-driven screen made by
Edgar Allen and Co., Sheffield, and Fig. 26 gives a view
of a telescopic screen made by the same firm.
SEPARATING AND MIXING MACHINERY 43
Sifting Reels. — In cases where it is required to grade
any ground material into one or more different sizes after
it leaves the disintegrator or other grinding machine, or
when it is imperative that the finished material be abso-
FIG. 27. — REELS.
lutely all of one mesh, or very finely dressed, this machine
is the most satisfactory.
For coarse material a cover of coarse mesh is gripped
by means of steel straps arranged on a number of cast-iron
spiders keyed on a strong spindle, as shown in Fig. 27.
FIG. 28. — SIFTING REELS.
To save wear on the cover a wrought-iron ring is fitted at
the feed end. These reels are mounted in an inclined
position, in casings, which are usually built round them
at the factory where installed.
When fine work is desired, the sifting medium is made
from fine metal or silk gauze, which requires supporting
44 INTRODUCTION TO CHEMICAL ENGINEERING
on either a hexagonal or circular reel. The hexagonal
type is suitable in the great majority of cases, but if a
very fine product is required and the material is of a
sticky nature, the circular reel provided with an exterior
brush to keep the cover clean is the best arrangement.
Fig. 28 shows a hexagonal type of sifting reel made
by J. Harrison Carter, Ltd., Dunstable.
Fig. 29 shows the " quick-change " powder dresser or
sifter for colour manufacturers made by Follows and Bate,
Ltd., Manchester. This machine is used for ground
colours, ochres, oxides, sugar, flour, blacklead, etc., and
FIG. 29. — POWDER DRESSER.
is so arranged that various grades of powder may be
produced at the same time. The provision of a removable
barrel allows many powders to be dressed on the same
machine, as all parts are designed for quick cleaning.
In the cases of the machines just mentioned a little
consideration will show that a large percentage of the
sifting medium is inactive, owing to the machine being
gravity controlled.
A more highly efficient machine is obtained by the
addition of internal beaters or paddles which can be
driven at a high speed. By this means the whole of the
sifting surface is rendered active, owing to the centrifugal
SEPARATING AND MIXING MACHINERY 45
action set up, and the generation of a strong air blast
also adds considerably to the output.
Fig. 30 shows a centrifugal dressing machine made by
J. Harrison Carter, Ltd., which is manufactured with
reels up to 10 feet in length by 2 feet in diameter, driven
at 180 to 260 r.p.m. The type illustrated by Fig. 29
attains a size having a reel 20 feet in length by 3J feet
in diameter, but driven only at 40 to 20 r.p.m.
Vibration Machines. — When a charge of material is
placed upon a screen it is obvious that the amount of
material which passes through depends upon the ratio
FIG. 30. — CENTRIFUGAL DRESSING MACHINE.
between the sum of the areas of the openings to the
total area of the screen. This ratio is known as the
opening factor, and varies considerably according to the
type of screening surface employed. It is larger for woven
screens than for plate screens, but on the score of economy
a screen having a long life and a small opening factoi
is often chosen instead of one with a larger opening
factor and of less durable nature. In the case of silk
screens, it is essential that the threads should be even
and carefully twisted, so that they do not readily become
fuzzy, whereby the opening factor is considerably
reduced.
46 INTRODUCTION TO CHEMICAL ENGINEERING
If the screen remains at rest it is clear that the bulk
of the material remains on the screen supported upon
a number of arches formed in the material by the falling
away of the portion which has passed through the screen.
Further sifting is only obtained by causing motion
of the material relative to the screen, whereby these
arches are broken down. The type of motion and the
amount of power necessary cannot be estimated satis-
factorily, so that with any particular type of machine
the best method of obtaining efficiency is to conduct
a series of carefully checked trials.
The amount of relative motion required is small;
hence sifting machines which have a shaking or vibrating
screen form an efficient and important class of sifting
machinery.
It should be noted that during the period of vibration
not only is the screen sifting the material, but the material
is also sifting itself. Under the action of gravity the
smaller particles pass between the larger particles, each
grade of material acting as a screen for finer grades.
As the action proceeds it becomes more effective, until
a stage is reached when the material is composed of layers
of different fineness, the finest being at the screen and the
coarsest at the top. Any further action of the screen
will only pass the material through the openings until
a size of particle is reached which will just pass. At this
point choking becomes serious and the wear is excessive,
both of which are to be avoided as far as possible. In
addition to this, after the material has once become
separated into layers a certain amount of power has
been used up in uselessly agitating the coarse material
which never passes the screen. Hence, for economical
working, separation into layers should be carried out in
the first place, and then the coarser layers removed before
the finer portions are sifted.
Shaking Sifters.— This type of sifter is very effective
for grading most materials, into any sizes and number
SEPARATING AND MIXING MACHINERY 47
of grades. It consists of one or more screens supported
in a frame by flat springs slightly inclined to the vertical
and vibrated by means of a cam or crank having an
adjustable stroke. Owing to the fact that both the
speed and the length of the stroke can be varied as
desired, this machine can be adapted for a wide range
of material. Under the combined action of the crank
and the springs the screen travels on a small arc of a
circle, thus imparting an upward and forward motion
to the material and producing very efficient screening.
FIG. 31. — SHAKING SIFTER.
Fig. 31 shows a type of shaking sifter made by
J. Harrison Carter, Ltd., in different sizes up to 9 feet in
length and 1| feet in width. For dealing with materials
of a sticky or woolly nature a brush is provided to keep
the screen clean, and where the material has a tendency
to cake, the brush is also made to vibrate. When re-
quired, this machine is made with two or more screens
arranged one above the other.
Fig. 32 shows a similar type of machine made by Edgar
Allen and Co., which, however, finds its chief use as a
shaking conveyer. It is simple in design, strongly made,
and so arranged that no violent shocks come on any of
48 INTRODUCTION TO CHEMICAL ENGINEERING
the parts. A special feature of this machine is the
connecting rod, which automatically takes up any wear
and thus prevents any " knocking " from taking place.
The rod is also designed to eliminate any bending action
at the fixed end, which is the cause of many breakdowns
SEPARATING AND MIXING MACHINERY 49
in this type of machine. This is effected by means of a
toggle made of special steel, working on knife edges. The
supports, made of strong spring steel, are secured to the
bottom of the conveyer by means of pivots working on
a fixed spindle.
This machine can be used as a screen, a picking belt,
or as a conveyer.
A machine in common use in the gypsum and similar
industries, called the " Newaygo screen," consists of a
highly inclined screen tightly enveloped in metal sheeting
FIG. 33 — GRAVITY OB LEG SEPARATOR.
to prevent escape of dust, and jarred by many small
hammers automatically tripped on the upper surface of
the cover.
Air Separators. — The separation of materials such as
cement, phosphate rock, basic and other slags, coke,
ores, etc., which are of a cutting or wearing nature, and
therefore not suitable for reels or similar machines, is
often carried out by means of an air blast.
If such a material is free from dust a very simple
machine, known as a gravity or leg separator, can be used
with good results. Fig. 33 is an illustration of this type
50 INTRODUCTION TO CHEMICAL ENGINEERING
of machine made by J. Harrison Carter, Ltd., in which
the feed is delivered by a feed roll in front of the induced
air current when the lighter particles are drawn back and
fall into their respective divisions.
The air current is obtained from a fan or from an
existing air trunk. This machine can also be used for
separating iron from materials before they go to a grinding
or other machine. Any number of legs can be placed side
by side to deal with various grades of the same material,
and combined in one frame complete with the fan.
If, however, the material is dusty, the machine has to
be arranged so that the fan circulates the same air and
does not exhaust dust-laden air into the atmosphere.
Probably the best arrangement for separating powder
of any degree of fineness from dry materials is the
" Stag " air separator made by Edgar Allen and Co.,
Ltd., Sheffield.
Briefly described, this is a self-contained apparatus
in which a current of air circulating continuously through
a descending stream of ground material separates the
finer particles from the coarser, the latter being returned
to a pulverizer, mill-stones, or other grinding machinery,
to be further reduced. The result is a uniformly fine
product which can scarcely be obtained by any other
method.
Fig. 34 shows a sectional view of this machine, to
which the following details refer: The separator consists
of an outer casing of sheet iron A, circular in form,
together with an inner casing B, separate from each other,
for collecting the fine and coarse materials respectively.
Above the inner casing, and fixed on a vertical spindle,
is a fan E, with blades, which, when revolved, induces
a current of air. Fixed on the same spindle is a disc, E1,
which spreads the material being treated in a thin stream
all round towards a fixed hood directly below the fan.
The current induced by the fan passes upward and
carries with it the fine particles, which are thrown into
SEPARATING AND MIXING MACHINERY 51
the outer casing. The coarse particles, which are too
heavy to be lifted by the current of air, fall into the
"STAC" Al R SEPAR ATO R .
MAKERS,
EDGAR ALLEN & C? LTP
SHEFFIELD.
FIG. 34. — " STAG " AIR SEPARATOR.
inner casing, and return by the branch pipes 6 to the
grinding machine, to be further reduced. The degree
52 INTRODUCTION TO CHEMICAL ENGINEERING
of fineness of the finished material can be regulated by
the speed of the fan, also by the partial closing of a
damper fixed between the inner and outer casings, which
intercepts the current of air.
This machine occupies very little space and requires no
settling rooms, and at the same time does away with all
brushes, sieves, cloths, etc., in addition to the fact that it
can be run at slow speeds of 160 to 260 r.p.m.
It is made in sizes up to 9 feet in diameter and 16 feet
6 inches height over all, requiring about 5 b.h.p.
Among the materials which can be successfully treated
in this machine are cement clinker, raw shales, lime-
stone, burnt lime, basic slag, phosphate rocks, blacking,
charcoal, gypsum, cattle cake meal, cotton-seed meal,
clay and marl, coke dust, chrome ore, bauxite, aluminous
earth, fuller's earth, graphite, soda ash, soap powder,
gold quartz, etc.
Electro - Magnetic Machines. — Machines in which
material is sifted by means of electro -magnetic force are
of comparatively recent introduction. The earliest type
of machine and one which is in extensive use- to-day has
for its main object the separation of pieces of iron and
steel from material before it is fed into a crusher or
grinder, where its presence would cause a breakdown.
In its simplest form it consists of a magnet suspended
over a belt conveyer or shoot down which the material
slides. The pieces of iron and steel caught by the magnet
are periodically removed by a workman, who also picks
the material as it passes.
A safe and simple type of separator consists of a
pair or more of magnetized flat bars which are fixed in
the bottom of a spout or carried on a flat table, this
table being given a shaking motion or made a fixture.
These tables give a large magnetic surface, and conse-
quently the iron has a greater chance of being arrested
than it has in the case of some types of barrel and drum
separators.
SEPARATING AND MIXING MACHINERY 53
Fig. 35 shows an arrangement for carrying electro-
magnets in a spout.
Fig. 36 shows a type of machine made by J. Harrison
Carter, Ltd., which is suitable for bone grinders, cattle -
food makers, drug grinders, cake grinders, oil mills, etc.,
where it is essential that no iron or steel shall go to
the grinding machinery and that costly hand-picking shall
be avoided.
The extraction of the iron is effected by one or more
pairs of electro -magnetic bars placed in the bottom of
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FIG. 35. — ARRANGEMENT OF ELECTRO -MAGNETS IN SPOUT.
a reciprocative tray, which can be made of any desired
width and length and fitted with any number of magnets,
according to the nature of the material treated or the
quantity to be dealt with. An automatic cut-out valve
which opens when the current fails acts as a safety device
and prevents the feed entering the grinder.
A very simple and effective machine for separating
small particles of iron or steel from grain or seed is
formed by substituting a specially constructed magnetic
pulley for the driving pulley of a belt conveyer.
54 INTRODUCTION TO CHEMICAL ENGINEERING
Fig. 37 shows such an arrangement in action, the grain
being shot off by centrifugal force, which in the case of
the iron particles is overcome by the magnetic force,
and causes the particles to be carried round the pulley
to a point where they are discharged into a separate
receptacle.
The action of the magnetic pulley forms the basis for
SEPARATING AND MIXING MACHINERY 55
several types of complicated separating machines de-
signed for continuous working. By using several
magnetic drums rotating at different speeds it is possible
to grade material according to the magnetic properties
of the products present.
Separating machines which depend for their working
upon the different behaviour of materials to charges of
56 INTRODUCTION TO CHEMICAL ENGINEERING
static electricity have been developed within recent
years. These machines for their successful running
require much skilled attention and knowledge of the
principles involved, and on that account are not found
widely used by the chemical industry of to-day.
Water Separation. — One of the oldest and still most
widely used processes for obtaining separation of materials
consists of utilizing water as a medium for the separation
FIG. 38.— LEVIGATING MILL.
of bodies having different specific gravities or of different
sized particles having different rates of settlement. In
the mining industry this method has received great
attention, and the resulting developments have been
many, but in the chemical industry it has only limited
application.
In the case of barytes, oxides, ochres, coloured earths,
and similar substances, the material is first ground under
water in a special edge runner or levigating mill, a type
SEPARATING AND MIXING MACHINERY 57
of which is shown in Fig. 38, made by Follows and
Bate, Ltd.
This powerful machine is designed for crushing hard
oxides, etc., in water, and is conveniently arranged for
floating off the desired product by means of a tap fixed
at the top of the reservoir, inside which the runner
rotates. The sludge door is easily opened, by which
grit, sand, iron, and other suchlike particles, can be
speedily removed.
The mixture from the levigating mill is run into a
large vat or buddle, and after standing for some minutes
the upper portion, to a definite depth, is run off into
settling tanks, where it is allowed to stand for a longer
or shorter time, depending on circumstances. After
more or less complete settlement the clear supernatant
liquid is run off and the sludge removed for drying.
Very fine material of low specific gravity may take three
or four weeks to settle, but in the majority of cases the
operation is completed in a few hours. Sometimes the
settling tanks take the form of long troughs, through
which the mixture is made to flow at a definite rate. By
this means the coarser and heavier particles settle first,
the finest being deposited at the outlet, whilst all floating
impurities are carried beyond. This method can be
usefully adopted for large quantities of material which
does not take too long to settle. Many attempts have
been made to construct machines which will accelerate
the rate of settlement and provide a more compact
arrangement, but they can hardly be said to have received
much application in the chemical industry.
Fig. 39 gives a view of the interior of a settling tank
or subsider for cane juice. It is provided with a copper
decanting pipe and float having a limited travel. When
the decanting is finished the residue can be run off by
means of a separate cock. This type of tank, made by Blair,
Campbell and McLean, Ltd., Glasgow, ranges from 200 to
1,000 gallons in capacity, and is often used in a series.
iiii
11 «»«
-II II?
S3!
SEPARATING AND MIXING MACHINERY 61
Figs. 40 and 41 show in plan and elevation a design
for a levigating plant made by Follows and Bate, Ltd.,
Gorton. A careful study of this design throws con-
siderable light on the number and working positions of the
machines which are deemed necessary for the economical
working of one of the simplest operations in the chemical
industry.
Fig. 42 is interesting as representing the flow sheet of
the milling process used in preparing rock salt for market.
T/PPLE.
FIG. 42. — FLOW SHEET OF MILLING PROCESS.
Mixing Machinery. — Mixing operations may be roughly
divided into two classes — (1) the mixing of solids with
solids; (2) the mixing of solids with liquids. To obtain
ajuniform mixture of different solids is at present a
practical impossibility, because as soon as the mixture
is set in motion a sifting action takes place, as was
explained previously when dealing with the subject of
sifting. For this reason such mixing as is required is
done at the time of grinding by feeding the different
62 INTRODUCTION TO CHEMICAL ENGINEERING
solids, in the required amounts, together into the grinding
machine.
The tube mill and the ball mill are commonly used for
grinding and mixing at the same time, and when only
mixing is desired the balls are removed and projecting
arms substituted to assist in turning over the material.
This operation is common where different grades of
material are required to be mixed, or as a preliminary
to the grinding operation, in order to obtain a more
uniform product.
FIG. 43. — POSITIVE DRIVEN PUTTY MILL.
The edge runner mill is another machine which is
largely used for mixing, with more or less satisfactory
results, being limited in the extent of its output.
A special form of this type of machine, made by
Follows and Bate, Ltd., is shown in Fig. 43, and is
known as a " putty " mill. Besides being useful for
crushing to a fine powder, chalk, whiting, chrome, indigo,
Prussian blue, etc., it is also handy for mixing into smooth
pastes, red and white lead for steam joints, white lead
and borings into tough paste, etc. The taper roller
and the pan of this machine are caused to revolve by
SEPARATING AND MIXING MACHINERY 63
For Hand Power with Fly Wheel.
FIG. 44. — VERTICAL PUG MILL.
64 INTRODUCTION TO CHEMICAL ENGINEERING
gearing at different speeds, and to act independently
of the contents of the pan, no matter how slippery they
may be.
For the mixing of solids with liquids to form pastes or
semi-liquid products the ball mill is used for high-class
work, and the pug mill for paints, enamel varnishes, etc.
FIG. 45. — " POWERFUL " HORIZONTAL, MIXER.
A simple form of pug mill made by the above firm is
shown in Fig. 44, which gives a view of the interior,
showing the rotating arms used for mixing. This machine
is useful for small quantities of colours up to 6 gallons,
and the hopper is lined with white vitrified enamel to
allow of ease in cleaning.
SEPARATING AND MIXING MACHINERY 65
The pugging arrangement is strong enough to mix the
stiffest pastes, putty, and the like, and will also mix
semi-liquids in varnish or oil with equal facility.
A larger form of this machine is shown in Fig. 45,
which is largely used as an amalgamator for ready mixed
paints or for oil blending, etc. It is fitted with a steel
pan with double-riveted, lap-jointed vertical seam,
SECTIONAL VIEW OF THE " UNIVERSAL " CONE PAINT MILL.
FIG. 46. — CONE PAINT MILL: SECTION.
single riveted to cast-iron top and bottom rings, a heavy
vertical steel shaft carrying forged-steel mixing blades,
the angle of which can be adjusted to suit thick or thin
material, and a discharge door or cast-iron tap as shown.
A useful and handy type of machine made by this firm
for operating upon material of not too great specific gravity
is the horizontal mixer shown in Fig. 45. It may be
used for the blending of dry colours or powders, or for
66 INTRODUCTION TO CHEMICAL ENGINEERING
producing a liquid, semi-liquid, or paste like dough or
putty.
The open pan or hopper, of steel, brass, or copper,
swings between two heavy standards, and is firmly
locked or instantly released by the withdrawal of a stop
catch. The toughened steel beaters are detachable for
cleaning, and rotate in opposite directions, in such a
manner as to prevent the contents of the hopper from
gathering in a mass during the process of mixing. The
material may be discharged whilst the beaters are revolving
by swinging the hopper into any desired position.
FIG. 47. — DOUBLE MIXER FOR SEMI-LIQUIDS.
The " Universal " cone mill made by this firm, of
which a sectional view is shown in Fig. 46, is a combined
mixing and grinding machine used for paints, enamels,
varnish, stains, pulps, grease, lubricants, boot dressing,
match composition, antifouling composition, etc.
The cone has deep feeding and fine grooves, so arranged
as to force the material inside the hopper outwards to
the grinding surfaces, and .is balanced on a central
vertical steel shaft pivoted at the bottom in a conical
hardened steel bearing, being raised or lowered by means
of a handwheel at the side. The cone rotates inside an
annular trough which is broad and deep, with a square
SEPARATING AND MIXING MACHINERY 67
bottom, and is fixed on an incline, so that as grinding
proceeds the material flows steadily towards the outlet
provided.
For working up thick pastes detachable beaters are
provided, and the annular trough is removed, so that
the machine delivers on two sides simultaneously.
Sometimes it is necessary to keep the materials hot
whilst the mixing process is going on, and to this end
FIG. 48. — " OPEN-DRUM " MIXER.
mixing machines are sometimes provided with steam
jackets or with an arrangement for heating by gas. Fig. 47
shows a double mixer for semi-liquids or powder provided
with a steam jacket, made by J. Harrison Carter, Ltd.
This machine can be arranged to work as a charge or
continuous mixer with the outlet at the end or anywhere
in the length of the bottom.
Fig. 48 shows an " open -drum " batch mixer made by
the same firm, which is used for mixing either concrete
68 INTRODUCTION TO CHEMICAL ENGINEERING
or tar macadam. This machine is made in sizes weighing
up to 2 tons and capable of dealing with up to 20 cubic
yards of material per hour.
Fig. 49 shows another machine of this firm's make,
which is also useful for concrete and macadam. It is an
under-geared mixer which mixes thoroughly without the
pieces being crushed smaller than is desired, and from
which the material can be automatically discharged
FIG. 49. — UNDER-GEARED MIXER.
when desired. The pan is made up to 7 feet in diameter
and revolves up to 19 r.p.m., requiring up to 12 b.h.p.
The soap industry makes great use of mixing machines
which are known as " crutchers," from the fact that in
the early factories the mixing was done by hand with a
wooden stick or crutch.
The crutcher is surrounded by a jacket, into which is
introduced either steam for heating or cold water for
cooling. There are many different types of beaters, but
a common form consists of an Archimedean screw
working in a central cylinder, over which the soap passes
SEPARATING AND MIXING MACHINERY 69
during the mixing. Various materials, such as borax,
starch, carbonate of soda, sodium silicate, talc, sand,
perfume, etc., can be added and thoroughly incorporated
to produce the many types of soap marketed.
Fig. 50 shows a sectional view of a soap crutcher
such as is in common use.
FIG. 50. — CRUTCHIXG MACHINE : SECTION.
For dealing with plastic materials such as soap, india-
rubber, etc., and for the finishing of fine paints, enamels,
printers' inks, and suchlike, the fine roller mill is used.
In some cases it is necessary to provide the rolls with a
steam-heating arrangement, especially where a solvent
that has been used is required to be eliminated. These
fine rolls have already been treated in a previous chapter,
and reference should be made to them in connection with
the mixing of materials.
CHAPTER III
FILTERING APPARATUS
FILTRATION is the name given to the process of separating
solids from the liquids in which they are suspended, and
although a fairly simple operation when conducted en a
laboratory scale, it presents great difficulties when large
quantities of material have to be handled. Development
has been along the lines of speeding up the process, the
actual separation being still effected by the action of some
medium such as cloth, paper, asbestos, slag wool, glass
wool, unglazed earthenware, sand, or other fine porous
material.
The Bag Filter. — Although only capable of dealing
•with comparatively small quantities of material this
type of filter has a wide range of application. As its
name implies, it consists essentially of a bag of woven
cotton or similar material, into which the material to be
filtered is placed, the liquor being allowed to ooze through
the pores of the fabric, whilst the solid material is re-
tained.
In dealing with materials of a sticky nature the bag
filter has its advantages, and on this account it is found
in use particularly in the sugar industry.
Fig. 51 shows an improved type of bag filter for
filtering sugar liquors, made by Blair, Campbell and
McLean, Ltd., Glasgow.
The top is made loose so that, together with the dirty
bags, it can be lifted out of the filter casing and taken
by an overhead trolley or crane to a washing tank, and
another top ready with clean bags fixed in its place.
70
FILTERING APPARATUS
71
This arrangement saves much time and obviates the
necessity of having to get inside the filter casing to remove
the dirty bags. The above illustration shows a small
bag filter containing forty -nine bags. The casing is of
wrought iron, and is fitted with a steam coil and mount-
ings, discharge cock, etc.
FIG. 51. — BAG FILTER.
The Filter Press.— Filter presses are used in a great
variety of industries, and are generally recognized in their
present form as providing the most efficient means of
carrying out this of ten -required operation. By the
adoption of filter presses the following advantages are
obtained: (1) The greatest possible filtering surface is
secured, together with the minimum space; (2) a large
variety of materials can be treated, as they can be
72 INTRODUCTION TO CHEMICAL ENGINEERING
adapted so that the material can be fed into them at
pressures ranging from a slight gravitational pressure up
to 10 atmospheres; (3) the joints between the filtering
plates are under direct observation and control, and
access to the internal parts is a simple operation ; (4) the
solid matter can be washed free of any soluble matter
which may be deleterious or may be worth recovering.
There are two principal types of filter presses — viz., the
plate and frame type, or frame press, and the recessed
plate type, or chamber press.
The Frame Press consists of a series of filtering chambers
formed by placing alternately a number of solid plates
and hollow frames in a suitable framework. The solid
plates — which, like the frames, may be constructed of
iron, wood, gun-metal, hard lead, aluminium, etc.—
have both surfaces corrugated, to allow the filtered liquid
to escape easily and at the same time give adequate
support to the filtering medium, which usually takes the
form of a filter cloth spread over each surface. The
rectangular -shaped plate is the one most commonly
used, as it is the most economical of filter cloth, but the
efficiency of the presses depends upon the nature of the
plate surfaces. It is here that manufacturers differ in
their construction, each being guided by the results of
his own experience.
The Premier Filterpress Co., London, has found, after
many years' experience, that vertical corrugations or
ribs, with horizontal ribs at the top and bottom, are
the most efficient and provide ideal support for the filter
cloth, besides helping the filtered liquor to get away
easily and quickly.
In this type of filter plate the ribs are quite smooth,
so that they can be easily cleaned, and are deep enough
to prevent the cloth sagging to the bottom of the cor-
rugations and so prevent filtration. It has been found
by experience that a quarter of an inch is a minimum
satisfactory depth to which no filter cloth under pressure
FILTERING APPARATUS 73
can penetrate. Should the fibre of the filter cloth be
weakened under the action of the material filtered, a
perforated sheet is supplied to cover the ribs and give
additional support, whereby the life of the cloth is con-
siderably lengthened.
When this type of press is closed up there is formed a
series of hollow chambers, each of which forms in itself a
complete filtering chamber. Since all the chambers of
a filter press commence working simultaneously, it is
immaterial how many chambers are employed, except,
of course, as regards the quantities of materials to be dealt
with, so that, provided the means of feeding the presses
are suitable and adequate, a press with a filtering surface
of 1,000 square feet will fill in the same time as one having
only 100 square feet of filtering surface.
As a general rule solid matter does not form in a cake
gradually built up from the bottom of the press, but
forms on the surface of each plate and gradually builds up
towards the centre, finally forming a complete cake.
Where cakes are required having a thickness of over
1 J inches or require a thorough washing, the frame press
is the more suitable type to employ. A further advantage
is secured by the ease with which the filter cloth is fixed,
as all that is necessary is to cut a piece of filter cloth
rather more than double the length of the plate and simply
hang it over. This is possible owing to the feed passages,
etc., being arranged on the border of the plates with
ports leading to the interior of the chambers. Also, in
certain cases the frame and cake can be removed and
stored without breaking up.
It is often found necessary to wash the cake when
formed, either to remove deleterious substances or to
recover valuable soluble matter. For this purpose both
plates and frames are arranged with channels for feed
inlet, wash -water inlet and outlet, and a separate outlet
— or outlet taps — on each plate, for the filtrate. The
usual arrangement is for the channel for the wash -water
74 INTRODUCTION TO CHEMICAL ENGINEERING
inlet to be made at the bottom of the plates and frames ;
the three channels for feed inlet, wash -water and air
outlets at the top ; and the filtrate outlet at the bottom
corner, opposite the wash -water inlet.
The material to be filtered enters the chamber by means
of a port in each frame from the feed inlet A (see Fig. 52).
The wash-water inlets and outlets, also the air outlets, are
arranged so that the port to the chamber is made only in
alternate plates. By this arrangement the water enters
at B behind the cloth on one side of each cake, and as it
rises in the press expels any enclosed air, which can
escape through the air outlet C.
\
B B
FIG. 52.— FILTER PRESS PLATES AND FRAMES.
2213
The water forms in a vertical wall behind the filter
cloth, and passes evenly through the cake and away by
the special outlet channel E, on the opposite side of the
cake to which it enters. This action is sometimes
assisted by putting a siphon pipe on the wash-water
outlet, so that even at the top of the press the wash-water
is under a slight head.
A special attachment or control apparatus is often
placed on the wash-water outlet, in order that hydrometer
readings can be taken of the specific gravity of the wash
water, whereby the degree of washing can be checked.
Partial washing may be done in any filter press by
passing water through the feed pipe, but the above
arrangement of a frame press is the only method for
FILTERING APPARATUS 75
thorough washing. With this type a more even thick-
ness of cake is obtained and the feed passage being
arranged outside the actual cake, avoids the formation
of a core of material throughout the length of the press,
which is not subjected to the action of the wash -water.
The position of the feed channel is varied according to
circumstances. When the solid matter is so heavy that
the formation of the cake becomes abnormal, the feed
passage is placed at the top; whereas if the solid matter
is very fine and will not form a complete cake the feed
is placed at the bottom, to allow of drainage before
opening the press. For certain materials which require
to be pressed at temperatures above or below the normal,
plates are fitted having coils cast internally, through
which steam or brine may be circulated at will.
Sometimes steam is admitted into the material itself
by means of the cock on the feed inlet or the wash-water
inlet. In other cases, in order to produce a drying effect,
these passages are used for leading hot or cold air through
the cakes when they are formed. As a general rule it
is best to have a tap on each chamber, because it gives
control, so that if the cloth bursts the trouble can be
easily located.
Fig. 53 gives a diagrammatic view of a frame press
made by Blair, Campbell and McLean, Ltd., for use in
the sugar industry.
Fig. 54 shows a plate and frame type of filter press made
by Manlove, Alliott and Co., Ltd., Nottingham.
The Chamber Press, or recessed plate type, has plates
which are made with raised edges, so that when they are
placed together in a horizontal series each pair encloses
a chamber, the feed passage as a rule being in the centre.
This type is more suitable when materials are used which
are liable to clog the passages of a frame press ; moreover,
when the press is opened the cakes can easily be made
to fall out on to a conveyor, truck, or other arrangement
underneath the press.
FILTERING APPARATUS
77
Fig. 55 shows a recessed type of plate made by Manlove,
Alliott and Co., Ltd., Nottingham. The fixing of filter
cloths in this type of press is obviously a more difficult
operation than is the case in a frame press. As before,
the cloth is cut in pieces rather more than double the
length of the plate, but holes must be cut to correspond
to the feed channel and the cloth fixed at this point.
78 INTRODUCTION TO CHEMICAL ENGINEERING
This can be effected by means of clips of the " bayonet "
or " screw union " type, as made by the above firm
and shown in Figs. 56 and 57.
FIG. 55. — FILTER PRESS PLATE: RECESSED TYPE.
Another method frequently employed is known as the
" double cloth " system, which employs two cloths sewn
together where the feed-hole comes, one half being rolled
up and passed through the centre hole and the two corres-
FIG. 56.— FILTER CLOTH CLIPS: BAYONET TYPE.
ponding halves tied together by tapes at the top of the
plate. This process can be easily followed out by a
reference to Fig. 58. In this type of press the cloth forms
an efficient joint between the plates, which grip it
FILTERING APPARATUS
79
between their edges, whereas the frame press necessitates
cuffs being slipped over the lugs, or grooves cut round the
channel holes and india-rubber washers employed.
Fig. 59 shows a recessed type of filter press made by
the above firm.
FIG. 57. — FILTER CLOTH CLIPS: SCREW TYPE.
The materials used in the construction of a filter press
depend upon the nature of the materials to be filtered,
but where possible iron is used, on account of its greater
strength and durability. Wooden presses are made
equally as strong as iron ones, but they wear out more
i.
FIG. 58. — FILTER CLOTH: FIXING IN RECESSED TYPE.
quickly; they can, however, be easily replaced at a
small cost.
A quick and efficient method of closing a filter press
is one of the most important points in their design. There
are various methods of closing the presses and keeping
them tight during filtration and washing, but experience
80 INTRODUCTION TO CHEMICAL ENGINEERING
720'
FIG. 59. — FILTER PRESS: RECESSED TYPE
FIG. 60. — FILTER PRESS: CENTRAL SCREW CLOSING.
FILTERING APPARATUS 81
has shown that for presses up to 25 inches square a
central screw and hand wheel, as shown in Fig. 60, with a
lever or capstan bar for tightening up, is an effective
arrangement and the least likely to get out of order.
To avoid the long operation necessitated by a fixed screw
centre, the Premier Filterpress Co., Ltd., provide a
rotary screw which after a few turns can be swivelled
into any desired position.
FIG. 61. — FILTER PRESS: RACK AND PINION CLOSING
For presses having plates larger than 25 inches square
a single screw is hardly powerful enough, and it is here
that manufacturers differ in their designs.
The standard arrangement of Manlove, Alliott and Co.
is by rack and pinion, with wheels operated by levers for
tightening up, as shown in Fig. 61, the rack being con-
nected to the loose head by a flexible joint, by this
arrangement considerable simplicity and speed of opera-
tion being obtained.
Other types of closing gear, including pneumatic or
hydraulic means, as shown in Figs. 62 and 63, are em-
ployed in certain circumstances.
82 INTRODUCTION TO CHEMICAL ENGINEERING
The feeding of filter presses is most important, as in
order to produce the best results the flow of filtrate
must be as uniform as possible. As the operation pro-
ceeds, the resistance, owing to the formation of the cake,
increases: hence the pressure rises. This rise should be
slow and regular, and should not exceed a definite
pressure, depending on the nature of the machine. The
usual method of feeding is either by a pump, which may
be belt, motor, or steam driven, or by means of a forcing
ram worked by compressed air. If pumps are used, those
FIG. 62. — FILTER PRESS: COMPRESSED AIR CLOSING.
having either ball valves or wing rotating valves are
most suitable ; and whereas for small quantities a double-
acting single -plunger pump is good enough, yet for large
quantities the three-throw pump, which gives a regular
flow, is the one to be adopted .
A more expensive method of feeding is by Montejus
and air compressor, but it is not surpassed by any other
method for steadiness of pressure. When using a Montejus
the gauge will rise quite regularly all the way through,
and if an air receiver is used between the Montejus and
the compressor a sudden variation in pressure is almost
FILTERING APPARATUS 83
impossible. All pumps used for feeding filter presses
should be provided with air vessels both on the suction
and the delivery side, a pressure gauge in the top of the
delivery air vessel, a safety valve adjustable to blow
off at a definite pressure, and a stone trap to prevent
foreign substances reaching the suction valves.
To use the same pump for both washing and feeding
is not good practice, and separate pumps for these duties
will be found the most economical in the long-run.
FIG. 03. — FILTER PRESS: HYDRAULIC RAM CLOSING.
As a rule filter presses are square in section, although
many having circular plates are on the market. The
latter have an element of additional strength which is
discounted by the action of the safety valve on the
delivery side. Although the tendency to buckle is less
than in the case of square plates, and tight jointing is
easily obtainable, yet, as the duty of a filter press is to
filter, the great waste of filter cloth — nearly 25 per cent,
of the cloth needed for the same diameter square plate —
and the equivalent loss of filtering surface more than
balance any advantage the round type may have over
the square type.
84 INTRODUCTION TO CHEMICAL ENGINEERING
Provided presses are erected level, so as to avoid any
liability to leak, no special skill is required in their
assembly, and after a few runs any average hand becomes
quite competent to look after the plant in a satisfactory
manner.
Centrifugal Machines. — The work of this machine
differs from that of the filter press in that it mainly
consists of removing moisture which adheres to solids,
and not, as in the latter case, separating solids from an
excess of moisture.
It is included amongst filtering machines because
actual separation is effected by means of a filtering
medium, the action of centrifugal force being merely to
accelerate the operation. It finds its greatest use in the
drying of crystals by throwing off the adhering mother
liquor, and for this purpose is largely employed in the
sugar industry.
It is capable of very extended application, but as it
requires very careful workmanship, considerable skill, and
experience in running it if accidents are to be avoided, the
result is that many manufacturers are unable to take
full advantage of this means of separation.
The centrifugal machine consists essentially of a
cylinder with an adjustable perforated circumference,
fixed to a vertical shaft which is rotated at a high speed.
As the cylinder and its contents rotate, the latter is
driven by centrifugal force to the circumference, where
the perforated screens retain the solids and pass the
liquids.
Fig. 64 gives a section through a " Weston " type of
centrifugal basket and outer case, showing also the
central discharge with valve and inside and outside
steaming arrangement.
This machine is largely made by Pott, Cassels and
Williamson, Motherwell, Scotland, and Fig. 65 shows
the various types of linings which this firm supply for
use with the baskets. In actual practice three linings
FILTERING APPARATUS
85
are used: a 4-mesh plain woven iron lining next the
basket shell, then a 7-mesh plain woven brass lining, and
an inner lining of perforated copper sheet with conical
oblong holes.
For special work, linings of perforated copper sheet
with conical round holes, of 26 or 30 -mesh twilled woven
copper or of spiral woven brass (Lieberman lining), may
be used.
86 INTRODUCTION TO CHEMICAL ENGINEERING
The spindle bearing is perhaps the most important
part of the centrifugal, as it has to do continuous heavy
work at high speeds with a minimum of attention. In
some cases the load is about 1 ton with a speed of 750
revolutions a minute, and the machine has to work day
FIG. 65. — TYPES OF LININGS FOR BASKETS.
and night for months on end. It is essential, therefore,
that the wearing parts should last for a very considerable
time and that the cost of repairs should be small.
Figs. 66 and 67 show a solid spindle with compound ball-
bearing and a patent sleeve and ball-bearing spindle as
made by this same firm. In this latter case both sleeve
FILTERING APPARATUS 87
and ball-bearing run in an oil bath, and no adjustment
is necessary.
The actual power used in driving a centrifugal machine
is not only determined by the amount required when
running at speed — a comparatively small amount in the
392
FIG. 66.— BEARING FOR CENTRIFUGAL SPINDLE.
case of a well-balanced machine — but also by the time
allowed for acceleration. In practice the average time
allowed for acceleration is two minutes,* and the b.h.p.
required is calculated on this basis. If a shorter period
of acceleration is desired, there must be a corresponding
88 INTRODUCTION TO CHEMICAL ENGINEERING
increase of power available, and for a longer period a
smaller amount will suffice.
Power is usually transmitted to the centrifugal from
the prime mover, in most cases a steam engine, by either
a belt, electric motor, or water.
396
FIG, 67. — BEARING FOR CENTRIFUGAL SPINDLE.
With the belt drive the centrifugal counter -shaft is
driven by an engine or, as a variation, it may be driven
by an electric motor. A method which has been adopted
for many years for starting up centrifugals and other
high-speed machines is to transmit the power to the
FILTERING APPARATUS
89
90 INTRODUCTION TO CHEMICAL ENGINEERING
centrifugal through a friction pulley such as is shown in
Fig. 68.
By this means the machine is started without undue
strain on the driving belt, and may, within limits, be
adjusted to give different times for getting up speed.
Anyone who has the driving of a centrifugal in hand
must be thoroughly acquainted with the working and
adjustment of a friction pulley. The type of friction
pulley illustrated can be adjusted in the following
manner : First put the clutch in the off position close up
to the driving arm, screw the nuts behind the springs
toward the centre of the pulley as far as they will go, and
remove the loose caps from the ends of the driving arms.
Screw the arms into the leather-faced friction pieces until,
when each friction piece is pulled as far as it will go
toward the rim of the pulley there is a clearance of about
TV inch between the leather face and the inside of the rim.
This ensures that the frictions will come quite clear out
of gear when the clutch is in the off position. Replace
the loose caps, which are provided with toes between
which flats on the screwed arms slide and prevent the
rods turning. As adjusted above and without bringing
the small spiral springs on the arms into play, the friction
may grip too fiercely and throw off the belt or accelerate
the centrifugal too quickly. In such a case screw the
nuts on the rods towards the rim of the pulley so that the
springs take some of the centrifugal force off the arms, thus
reducing the friction and giving a lessened pull on the belt.
The amount of compression on each spring should be
approximately the same, and the travel of the clutch should
not exceed 1 inch, which is determined by the correct
setting of the loose collar.
In the case of electric -driven centrifugals the friction
pulley is used with a D.C. motor, but in the case of an
A.C. motor a flexible coupling is used to connect the
motor to the centrifugal spindle. This type of motor
has other advantages in that there are no commutators
FILTERING APPARATUS
91
or brushes to wear and the speed is constant. It is well
to note that in A.C. motors the available range of speeds
depends on the frequency, and it is necessary to bear this
in mind when deciding on the frequency. The table
FIG. 69. — " WESTON " CENTRIFUGAL MACHINE.
given below gives the possible synchronous speeds for
some common frequencies, the actual running speeds
being about 4 per cent, less than the synchronous
speeds.
92 INTRODUCTION TO CHEMICAL ENGINEERING
Frequency.
Synchronous
Speeds.
Diameter of Baskets of
Suitable Centrifugals.
25
40
50
60
1,500, 750
1,200, 800
1,500, 1,000, 750
1,200, 900
24, 48 inches.
30, 48, 30, 48 inches.
24, 36, 40, 42, 48 inches.
30, 40, 42 inches.
Fig. 69 shows a belt-driven centrifugal having a
42 -inch diameter basket, together with the necessary
steel framing, etc.
In the case of water -driven centrifugals, jets of water
under pressure are made to impinge on the cups of a
Pelton wheel which is coupled to the centrifugal spindle.
The pressure of the water is raised either by a direct-
acting steam-driven duplex pump, a turbine pump
driven by an engine or electric motor, or a high-duty
flywheel pumping engine. The duplex pump is the
cheapest and the one most commonly used; the turbine
has the advantage of simplicity, constant running, and
the ability to give out power approximately proportional
to the power consumed; the pumping engine is mcst
economical in steam consumption, but is the most
expensive in first cost.
Fig. 70 shows a sectional drawing of a water -driven
centrifugal made by Pott, Cassels and Williamson, and
the following details relative thereto will serve to illus-
trate the various points of centrifugal machines in
gen eral .
The motor case 3-4, fitted with a cover 1, into the
centre of which is secured a hollow axle 9, which does
not revolve, rests on the beams 40, which form part of
the framing. On the lower part of the axle a ball-bearing
10 is placed; the inner part of the ball-bearing is held
firmly to the hollow axle by the nut 12, and the outer part
is held in the eye of the water wheel 2 by the nut 11,
FILTERING APPARATUS
93
29! A
FIG. 70. — " WESTOX " CENTRIFUGAL MACHINE: WATER-DRIVEN
94 INTRODUCTION TO CHEMICAL ENGINEERING
and so revolves with it. The upper parts of the motor
case have flanges projecting towards each other, forming
diaphragms to prevent the water spray from getting
over the top, so that there is no possibility of the spent
water going anywhere except through the return pipe 39,
back to the water tank which supplies the pump for
driving the machine. The top of the water wheel, on the
face of which the water cups 5 are secured, revolves
between the diaphragms on the top of the motor case.
To prevent any alteration in the position of the cups, they
are fitted into a groove on the face of the wheel. To
obtain maximum efficiency they are carefully machined,
have knife edges, and are of parabolic form, properly
relieved on the bottom for the escape of the spent water.
Further, as the wheel does not oscillate, these cups always
maintain the same position relative to the water jets
6 and 7, which are screwed into the inlets 8, provided with
inspection plugs 41. The inlet bends 8 can be easily
and quickly removed and a choked jet readily cleaned.
On the bottom of the water wheel is bolted a driver 25,
which encloses the governor balls 19 in an oil-tight cavity
below the ball-bearing. This cavity is partly filled with oil
through the oil cup 43, which lubricates the governor pins
23 and the ball-bearings 21 and 10. The governor
spindle 24, which is a tube for the passage of the oil, has
a ball-bearing 21 at the bottom and a collar 14 at the top.
The governor balls are held in the " off " position by the
springs 20, which are of such strength that when the
machine attains full speed the centrifugal force causes
the balls to fly outwards and move up the spindle 24
by means of the levers 22. On the top of the motor case
cover is a fulcrum 16 for the lever 15, at the shorter end
of which is a swivelling cross-head 18, through which
passes the governor rod 17, adjusted and secured by
two nuts.
When the machine attains full speed the governor rod
is forced by means of the levers, and releases a trigger
FILTERING APPARATUS 95
which cuts off the water from the accelerating jet 6,
leaving the smaller jet 7 to maintain operations.
To the underside of the beam is attached the centrifugal
suspending block 37, into which are fitted india-rubber
buffer rings 35, separated by a loose cast-iron ring 36.
Thus top and bottom buffers support the weight of the
basket, which is attached to the lower end of the centri-
fugal spindle 38. By this means great resiliency and
steadiness are obtained when the machine is running
with either a balanced or an unbalanced load, and also,
as the buffers are separated by a loose ring, any wear on
the bottom buffer is compensated by the compression
caused and is self-adjusting.
The ball-bearing housing 34 fits inside the india-
rubber buffers and contains the compound ball-bearing 33,
secured by a nut 32; the inner part of the ball-bearing
is secured to the centrifugal spindle by the top nut 28
through the brake casting 29. To permit of the oscil-
lation of the centrifugal spindle and the basket, the water
wheel, which does not oscillate, is connected to the brake
pulley on the top of the spindle by leather links 27, the
eyes of which are slipped over the points of the driving
pins 26. Thus a strong flexible coupling is formed and
one which permits of the motor or centrifugal being
detached as desired by simply slipping off the links.
The brake band is supported by angle iron feet which
rest on a flange in the bracket 37, so there is no possi-
bility of the band drooping unequally. The feet on the
brake band are so arranged that when the brake is off
an equal space is left all round between the band and
the pulley.
As is well known, the power to accelerate a machine to
full speed quickly is much greater than is required to
maintain it at full speed ; consequently each centrifugal
is provided with two water jets, a large one and a small
one. When starting the machine both jets are required,
and when full speed is reached the small jet only is
96 INTRODUCTION TO CHEMICAL ENGINEERING
necessary to maintain full speed. It sometimes happens
that when the centrifugals are worked irregularly all
the machines may be accelerating at the same time,
requiring an amount of water largely in excess of normal
requirements, and for this reason pumps have hitherto
been made very large.
Fig. 71 shows two machines interlocked by a special
gear made by this firm, and so arranged that not more
than one half of the machines can be accelerated at the
same time, thereby reducing the size of the pump con-
siderably, without in any way reducing the output. In
FIG. 71. — INTERLOCKING GEAR FOR WATER-DRIVEN CENTRIFUGAL:
SECTION.
ordinary practice each pair of machines is interlocked,
so that when one machine is started the other machine
cannot be started until the first has attained full speed.
As the machines are usually arranged to accelerate
in two minutes, and the cycle of operations will occupy
at least six minutes, the interlocking gear ensures the
machines being worked in proper rotation without
interfering with the output. The advantages of this
method will be evident from the following comparison
of the maximum pump demand for a set of machines with
and without this interlocking gear.
FILTERING APPARATUS
97
For instance, a set of machines which are interlocked
in pairs, and require a pump 9f inches diameter, would
require a pump 12J inches diameter otherwise, provided
the maximum pump speed is the same in both cases. In
other words, the maximum pump demand is 55 per cent,
more. When a more rapid acceleration is required, three
machines are interlocked, in which case a pump 11 J inches
diameter would do the work instead of a pump 1 7 inches
diameter, which represents an increase of 130 per cent.
It should also be remembered that in most cases the
steam cylinder is at least twice the diameter of the
pump, and the smaller the pump the smaller the steam
cylinder.
The following cases extracted from a list given by this
firm affords useful comparisons.
Diameter and
Depth of Basket
(Inches).
R.P.M.
Average B.H.P.
Capacity
(Cubic Feet).
24 x 14
48x20
60x24
1,500
750
600
2
5-25
10
1-85
10-7
16-6
CHAPTER IV
DRYERS AND EVAPORATORS.
ALTHOUGH the bulk of the moisture in a material has been
removed by means of the filter press or the centrifugal
machine, a certain amount still adheres, which can only
be removed by evaporation in contact with air heated
to as high a temperature as is possible, consistent with
economy and the nature of the material.
The three systems of drying most commonly in use
are:
1. By direct heat from a fire.
2. By radiated heat from steam pipes.
3. By warm air circulation.
Machinery for using direct heat from a fire has only a
limited application, owing to fire risk and the liability
of damage to the material, although for substances such as
sand the method is very effective. Wherever possible
waste heat should be utilized, so that in the case of
materials which are not easily burned or scorched or
damaged by contact with gases the flue heater provides
an effective and economical drying means.
A common form of flue heater consists of a cast steel
or iron trough placed over a flue or furnace, the material
being propelled from one end of the trough to the other
by a worm, which is also made to act as a stirrer or turner
over. These troughs are of varying diameter and
lengths to suit the material to be treated, and can be
open or enclosed and connected with a fan if necessary.
The lack of any very effective control is one of the great
disadvantages of this method, so that it is not to be
98
DRYERS AND EVAPORATORS
99
wondered at that the ease of control of steam has rendered
that substance the principal heating agent in dryers and
evaporators, apart from the fact that it allows of the
utilization of much waste heat.
Steam may be used for drying or evaporating by being
passed through pipes immersed in the material to be
dried, by forming a steam jacket round the container,
by heating an inner drum round which the material passes,
or by a combination of these methods. Frequently
the drying process is combined with mixing and milling,
according to the nature of the material used.
FIG. 72. — '"FIRMAN" DRYER: LONGITUDINAL SECTION.
The rotary form of dryer is undoubtedly one which
finds the greatest application in the chemical industry.
In its simplest form it consists of a cylinder or drum,
steam-heated, containing the material, which can be
rapidly and uniformly presented to the steam heat by
rotating some part of the apparatus. Materials such as
slaughter-house refuse, blood, offal, condemned meat,
fish and vegetable matter can be turned into valuable
manure by means of a dryer as shown in Figs. 72 and 73.
This is a " Firman " type made by Manlove, Alliott
and Co., Ltd., Nottingham, which is designed for taking
semi-liquid material and delivering it mixed and dried
100 INTRODUCTION TO CHEMICAL ENGINEERING
ready for the market. It consists of a horizontal steam-
jacketed cylinder, the internal circumference of which is
continually swept by moving scrapers or paddles. The
material being treated is kept in constant motion, being
lifted up, turned over, and allowed to fall again, pre-
senting fresh portions to the heated surface and giving
the steam and vapour a better opportunity of escaping.
The temperature at which the material is dried can
be controlled by regulating the steam pressure, and so no
injury is caused by excessive temperature, as is frequently
'//////// /A
M.A.&C'l? 4
FIG. 73.— "FIRMAN" DRYER: CROSS SECTION.
the case with fire-heated machines. The body of the
machine consists of a double cylindrical shell suitably
stayed to withstand a working pressure of 40 pounds per
square inch, the space between the two shells forming
a steam jacket. A massive cast-iron plate at each end
of the drum is fitted with a gland, bracket, and plummer
block for supporting the central shaft of mild steel,
which carries cast-iron arms having knife-edge steel
scrapers at their outer ends. A charging door is fixed
in the top or one end of the machine, an outlet door in the
DRYERS AND EVAPORATORS
101
bottom, and a vapour outlet at the top. A draining valve
connected in two places and a steam inlet valve, together
with the usual pressure gauges and safety valve, complete
the equipment of the steam jacket.
Fig. 74 shows a cross-section of a dryer fitted with a
central steam drum extending the greater part of its
length, and Fig. 75 that of a combination of the steam
jacket and internal drum. These machines are suitable
for granular substances such as beer and distillery grains,
earthy and other colours, coal, sawdust, peat, etc., or
substances which have a low moisture content.
FIG. 74. — "HERSEY" ROTARY
DRYER: CROSS SECTION.
FIG. 75. — COMBINATION ROTARY
DRYER: CROSS SECTION.
In these cases the plan of operation is for a current of
air heated by passing through a steam-heated air heater
to be drawn through the cylinder by means of a fan.
The material is fed by hand or automatically, and is
lifted by the shelves and rained down through the hot
air, to which it gives up its moisture. Owing to the
cylinder being set at an angle, the material passes down
in the opposite direction to the air current, so that the
driest material comes in contact with fresh hot air,
effectively removing the last traces of moisture, while
before the air escapes it comes in contact with the fresh
102 INTRODUCTION TO CHEMICAL ENGINEERING
wet product, which cools it to the lowest temperature
consistent with the proper carrying away of the absorbed
moisture.
The temperature of the air used in this class of plant
is about 120° to 200° F. — the temperature in general
FIG. 76.— G. A. DRYING PLANT: PARALLEL DRIVE.
FIG. 77. — G.A. DRYING PLANT: RIGHT ANGLE DRIVE.
A, rotary dryer; B, air heater; (7, fan; D, feed apparatus;
J5?, air pipes; F, path rings; (r, discharge hood; //, driving
pulleys and gear; J, air inlet; K, air outlet; .L, rollers;
M, dust separator.
use being about 150° to 180°F. measured close to the
heater. In dealing with material of a powdery or dusty
nature the discharge from the fan may be led to a large
DRYERS AND EVAPORATORS 103
settling room, or a cyclone or other separator may be
used.
The main factors governing the size of plant for a given
output are — (1) The quantity to be dealt with per hour;
(2) the initial and final moisture percentages; (3) the
speed of the air current which can be employed without
carrying away too much material in the form of dust;
(4) the temperature which can be safely employed; and
(5) the ease with which the material gives up its moisture.
Where a very low final moisture is desired, or the material
dries slowly, it is better to have an extra long dryer.
Figs. 76 and 77 show the general arrangement of drying
plants with parallel and right-angle driving gear respec-
tively.
Drying by warm-air circulation forms the basis of the
Sturtevant system. A fan passes a volume of air through
a self-contained heater placed outside a drying room;
this air is led through a system of pipes and distributed
in the drying room, a positive circulation of warm air
being maintained, and the heat necessary for evaporating
the moisture in the materials is carried into every part
of the room. The advantages claimed for this system
are— (1) The temperature can be varied without affect-
ing the volume of the air circulated; (2) the humidity
of the air supply can be varied by recirculating part of the
moist air from the drying room; (3) the volume of air
circulated can be regulated by varying the speed of the
fan or by dampers.
This method is particularly suitable for the drying of
wool, flocks, rags, fibre, and similar substances, where
it is important that there should be no risk of fire.
When air is brought in contact with a wet substance
some portion of the moisture is absorbed by the air, which
has an increased capacity with increased temperature.
For any particular temperature there is a limit to the
amount of moisture the air will absorb, and when this
limit is reached the air is said to be saturated. Saturated
104 INTRODUCTION TO CHEMICAL ENGINEERING
air is obviously useless as a drying agent, but by raising
the temperature of the saturated air it becomes capable
of taking up more moisture before it again becomes
saturated. In other words, the higher the temperature
of the air, the better drying agent it becomes. The limit
of temperature usable depends, of course, upon the nature
of the material to be dried.
FIG. 78. — RECORDING HYGROMETER.
FIG. 79. — TYFICALTGUIDE CHART.
An important part of the Sturtevant system is the
recording of the humidity of the air in the drying rooms.
This is performed by a self-recording hygrometer which
has wet and dry bulbs (metallic expanding coils) which
actuate two pens against a revolving drum carrying a
guide chart, as shown in Figs. 78 and 79.
The following table is then found necessary in order
to calculate the humidity of the air used:
DRYERS AND EVAPORATORS
105
DIFFERENCE BETWEEN WET BULB AND DRY BULB IN
DEGREES FAHR.
10
12 14 16 18 20
Dn/Bnlb
'°F.
Percentage of Moisture in Air.
60
89 ! 78
68
58
49
40
31
22
14
6
70
90 j 81
72
64
56
48
40
33
26
20
80
91
83
76
68
61
51
47
41
35
29
90
92
85
78
71
65
59
53
47
42
37
100
93
86
80
74
68
62 57
52
47
42
110
94
87
81
76
70
65
60
55
50
46
120
94
88
82
77
72
67
62
58
54
49
130
04
89
84
78
74
69
65
60
56
52
140
95
89
84
80
75
71
66
62
58
55
150
95
90
85
80
76
72
68
64
60
56
160
95
90
86
81
77
73
69
66
62
58
170
96
91
87
82
78
74
70
67
63
60
The actual amount of water in a cubic foot of air can
then be found from a chart, as shown in Fig. 80.
For example :
The dry bulb thermometer registers 140° F.
The wet bulb thermometer registers 122° F.
Difference 18° F.
Percentage of moisture (from table), 58 per cent.
Moisture per cubic foot (from chart), 33 J grains.
The process of drying timber provides an example of
the method of working and flexibility of this system.
The seasoning of timber not only affects the moisture
content, but also goes deeply into the quality of the wood
— its workability, its cell strength, etc. — for in green
wood the moisture is divided between the cells and the
cell walls. The free water in the cells or pores can be
removed without affecting the physical structure of the
wood, but it is otherwise in the case of the water in the
cell walls. Successful drying of timber depends upon
the following fundamental conditions: Gentle heat in
combination with sufficient moisture to prevent case
106 INTRODUCTION TO CHEMICAL ENGINEERING
hardening ; an ample circulation of air, so that the humid
heat is carried to every part of the timber. The moisture
should be evaporated just as quickly as it conies to the
surface of the timber, and there should be no great
temperature drop throughout the pile or in each piece
of timber. By this system, when one particular kind of
wood has been dried, the particular guide chart — for the
same thicknesses of wood — can be used subsequently.
Percentage of Humidity,
/SO l
140
130
720-
-sol
8
£ 80\
bo
« J
60
SO
40
(00
10 ^O 30 4O SO 6O 7(7
_ _ Grains of Moisture per Cubic Foot.
FIG. 80. — HYGROMETRIC CHART.
All that need be done is to put the chart on the drum
of the hygrometer and manipulate the dampers so that
the pens of the recorder will follow the lines of the chart.
Warm and cold air dampers govern the top line of the
diagram, and the moist air damper and sprayers control
the bottom line.
For large and regular outputs of planks, barrel staves,
and suchlike, a progressive type of dryer is used. This
DRYERS AND EVAPORATORS 107
consists of one or more tunnels of brick or concrete to
reduce heat losses by air leakage to a minimum, with
rails running longitudinally, the wood being piled on
trucks which move through the tunnel against the air
current. The arrangement is such that whilst the wood
that is nearly dry is in contact with warm dry air from
the fan, the green wood at the other end meets moist
tepid air which has been cooled and moistened by passing
over the wood of the first waggons. Whenever a load is
taken out dry, a load of new wood is put in at the other
end, all the waggons moving one stage forward; thus,
progressively, the wood is dried in a suitable atmosphere.
The air ducts are usually placed underground and con-
structed with brick sides and concrete base, the top being
arched over with brick or covered with stone or concrete.
The drying apparatus consists of — (1) A fan for pro-
ducing circulation driven by a direct coupled steam
engine, electric motor, or belt; (2) a heater for heating
the air by live or exhaust steam or a combination of both ;
(3) a steam trap to prevent the passage of steam, or an
automatically controlled pump and receiver to return the
water of condensation to the boiler ; (4) steam and water
sprays for supplying such additional moisture to the air
as is necessary.
For drying different thicknesses and sizes of timber and
also different kinds of wood, especially hard woods, three
main distributing ducts are provided in the compartment
dryer for the supply of warm dry air, cold dry air, and
moist air. The supply to each compartment can be
controlled from a central board placed conveniently
outside, as shown in Fig. 81, which is a plan and eleva-
tion of the triple drying system.
The timber, if a hard wood, is first subjected to the
action of moist cool air, and the humidity is maintained
while the temperature is slowly raised, thus gradually
removing water from the heart of the timber without
drying the skin. The humidity is then gradually de-
108 INTRODUCTION TO CHEMICAL ENGINEERING
creased and the temperature raised, and when the drying
is nearly complete warm dry air is admitted to finish off.
In the above illustrated system the fan takes fresh
air, part of which is delivered through a by -pass valve,
into the cold air duct, the remainder passing through
a heater to the hot air duct. A second fan draws the
moist air from the drying chambers through the return
duct, and delivers any desired percentage of it to the moist
air supply duct.
DRYERS AND EVAPORATORS 109
By adapting the apparatus to suit the different
materials this system has been successfully used to dry
asbestos, casein, copra, explosives, fruit, glue, leather,
phosphates, rubber, soap, sugar, white lead, and wood
pulp, to mention but a few.
Vacuum Dryers. — A vacuum dryer is a machine in
which material is dried under reduced pressure, whereby
a considerable reduction in time and expense is effected.
The temperature at which a liquid changes rapidly and
violently into a vapour, or, in other words, boils, depends
upon the pressure upon its surface. By reducing the
pressure in a drying machine and maintaining it at any
desired level, the moisture, usually water, in the material
may be briskly evaporated at a convenient low tempera-
ture, so that waste steam of low temperature may be
usefully employed. Not only is this method quick and
economical, but it possesses the further advantage that
it is possible to dry rapidly substances which would be
decomposed or otherwise injured if raised above a certain
definite temperature.
There are three main types of vacuum dryers adapted
for different classes of materials, as follows : (1) The shelf
type for materials which do not require stirring; (2) the
rotary type for materials which require stirring; and
(3) the drum type for material which readily forms a
film on the drying surface.
Fig. 82 is an illustration of a vacuum shelf dryer,
made by Francis Shaw and Co., Ltd., Manchester. The
chamber itself is a heavily ribbed cast-iron box, in one
or more sections as necessary, having the faces where
the joints aie to be made, accurately machined. The
doors are also of cast iron, securely attached to the
body by double swing hinges and accurately balanced
for easy manipulation. To obtain an air -tight joint
when the door is closed, a rubber ring is fitted into a
groove on the inside skirting and makes contact with
the machined facing on the body. For the purpose
110 INTRODUCTION TO CHEMICAL ENGINEERING
of control, inspection windows are fitted so that the
material can be kept under observation during the
drying operation.
The heating chests or shelves are made of rolled mild
steel plates, flush-riveted at the edges through a wrelted
ring, and stayed all over to withstand a working pressure
of 60 pounds per square inch. Each shelf has its own
independent steam feed and exhaust connections, made of
J DRYERS AND EVAPORATORS 111
stout hydraulic piping bent to allow for expansion and
contraction and coupled to mains fitted in recesses.
These shelves are arranged to give complete drainage
and allow of uniform heating. A cast-iron vapour pipe
leads from the top of the stove to the head of the con-
denser, which is of the vertical multitubular type,, con-
taining copper, brass, or iron tubes expanded into end
plates at top and bottom. The condenser case is of cast
iron fitted with condensing water inlet at the bottom
and outlet at the top, together with all necessary valve
fittings. The receiver is a cast-iron vessel divided into
two compartments connected by a by -pass valve, by
which the liquid in the lower compartment can be drawn
off without breaking the vacuum throughout. Inspection
windows are also fitted to this vessel so that the drops of
water falling from the condenser can be seen during the
drying operation.
The method of working a shelf dryer first of all is to
warm up the shelves by admitting steam or hot water,
as the case may be. The material to be dried is placed to
a depth of 1 to 1| inches on trays of galvanized or
enamelled iron, wire netting, copper, aluminium, or
earthenware, having a depth not greater than 2 inches,
as the shelves are about 2J inches apart. The trays
are then placed on the shelves and the doors closed by
means of handwheels. Provided that the doors fit
perfectly, the handwheels can be swung clear as soon as
the gauge registers 10 inches, when the excess external
pressure is sufficient to hold the doors in place. The
vacuum pump is now started, and in a short time drops
of water can be seen through the inspection window
falling into the bottom chamber of the receiver. Cold
water is then admitted to the condenser, and a sufficient
flow maintained to keep the bottom of the condenser
cool to the touch. To obtain a constant drying tempera-
ture inside the stove the steam or hot water inlet must be
adjusted as required. The end point of the drying
112 INTRODUCTION TO CHEMICAL ENGINEERING
operation is indicated by the fact that no more drops of
water are observed falling into the receiver, or by a
decided rise of temperature registered by a thermometer
in the body of the stove. The operation is then stopped
by closing the vacuum valve and shutting down the
pump. To avoid loss of material the air must be ad-
mitted gradually through a vacuum break valve in the
door, until zero is recorded on the vacuum gauge, when
the material can be taken out and the stove lecharged
with a fresh set of shelves already prepared.
These stoves are made in all sizes from 10 square feet
up to 3,000 square feet of heating surface, and may be
combined in the form of a battery if required.
This type of machine is used for drying aniline dyes,
pigment colours, explosives, fine chemicals, malt extract,
carbon brushes, white lead, beta-naphthol, salicylic acid,
drugs, mica sheets, foodstuffs, etc.
For substances which have a tendency to form a film
on the surface of the dryer, and for such substances as
sulphate of zinc, nitrate of ammonia, dyewood and
tannin extracts, glue solutions, albuminous substances,
milk, yeast, pastes, eggs, vegetable and meat extracts, etc.,
the drum dryer is the more suitable machine.
Fig. 83 illustrates a vacuum drum dryer as made by
J. P. Devine and Co., Buffalo, working under what is
known as the Passburg system. Briefly, the apparatus
consists of a cast-iron outer casing, in some cases tinned
inside or lined with copper or other suitable material,
inside which revolves a hollow drum or drums made
of cast iron, gun-metal, or bronze. This drum is care-
fully balanced, heated internally by hot water or steam,
and the outside is machined and polished. If hot water
is used as the heating medium, drying can be conducted
at as low a temperature as 63° F., and in the case of
steam T2 pounds of steam — including steam used for
motive power if the exhaust is used for heating the
chamber — will evaporate about 1 pound of water. The
DRYERS AND EVAPORATORS
113
inlet supply is regulated so that the material inside the
casing remains at a constant level, and shield rings
prevent the material from coming in contact with the
end of the drum.
A rapid and uniform drying is effected, because the
wet material is spread upon the steam-heated polished
FIG. 83. — VACUUM DRUM DRYER.
drum in a thin film of yi-^ inch or less. The conduction
of heat through the metal drum to the material on its
surface is very rapid, and the water is changed under
vacuum into vapour of about 104° F. to 122° F. Materials
containing as much as 88 per cent, of water are dried in
eight seconds without overheating, and the water is
evaporated from the material at a temperature of from
8
114 INTRODUCTION TO CHEMICAL ENGINEERING
117° F. to 96° F., according to the vacuum in the apparatus
of 26f inches to 28 J inches.
It is well known that the greater the difference in
temperature between two materials placed in contact,
the more rapid is the flow of heat from the hotter sub-
stance to the cooler, so that if the water in the material
is kept at a low boiling point by maintaining a high
vacuum, the heat from the steam is transmitted more
rapidly than if the boiling point be several degrees
higher. Even though the drum be heated by steam of
230° F. or over, the material being dried cannot get
higher than the temperature at which the water boils
FIG. 84. — VACUUM " JOHNSTONE " DRYER: SECTION.
under vacuum, because the heat is used to convert the
water into steam, and thereby rapidly evaporates it out
of the material.
The rotary vacuum dryer follows the lines of the non-
vacuum type previously described, but with the addition
of an evacuating plant. Here, again, the machine usually
combines the work of a ball mill or mixer, or both, with
that of drying.
Fig. 84 shows a section of the " Johnstone " dryer
made by Manlove, Alliott and Co., Nottingham. It
consists of an enclosed vacuum-tight vessel with a dome-
shaped cover which carries a scraper, agitator, and
DRYERS AND EVAPORATORS 115
driving gear. In the cover is placed a large circular
charging door, which is provided with shackles for
tightening on to a joint ring of asbestos or rubber. The
body of the machine has steam-jacketed parallel sides
and flat bottom capable of withstanding 40 to 60 pounds
per square inch. In the bottom of the machine is a
rectangular hinged and balanced door, opening down-
wards, for discharging the dried material as required.
A thorough and speedy drying is ensured, as the material
is continually broken up and turned over by revolving
scrapers and rakes, thus preventing an impervious crust
forming and hindering evaporation.
Fig. 85 shows a combined vacuum dryer, mixer and
ball mill, mace by Francis Shaw and Co., for treating
delicate chemicals, organic acids, and all substances
where metallic contamination is to be avoided. It
consists of a fixed steel casing designed for heating by
steam or gas, inside which is fitted a one-piece stoneware
vessel, supported in a steel cage having a hollow trunnion
at one end connected to the vacuum pump.
One of the disadvantages of many drying machines is
the loss of time in charging and discharging, and several
makers have evolved a more or less efficient continuous
apparatus.
Fig. 86 shows a continuous " cone " vacuum drying
plant made by this same firm. The body of the machine
consists of a steel cylinder, jacketed all round for steam
heating, and having a hopper fitted at the top of one end.
At the base of the hopper is a vacuum-tight rotary device
for receiving the wet material and delivering it to the
conveyor worm inside the dryer. A similar hopper is
provided on the underside of the machine, connected
through a wheel valve to a receiver provided with in-
spection windows and manhole door. The cone is made of
light sheet steel mounted on a hollow shaft extending
through stuffing box bearings 'in the ends of the outer
steel body to the driving gears and steam supply at one
116 INTRODUCTION TO CHEMICAL ENGINEERING
118 INTRODUCTION TO CHEMICAL ENGINEERING
end, and to the steam exhaust main at the other. Steel
chutes are fitted to the ends of the cone inside the body
for supplying the cone with the material to be dried,
and for guiding the material to the receiver. Both the
cone and the automatic feeding device are geared to the
same shaft, to ensure a uniform feed.
In working this machine steam is admitted, and then
as high a vacuum as possible is obtained throughout the
apparatus with receiver valve wide open. The material is
fed into the hopper, from which the worm conveyor
inside obtains a uniform feed; drying commences at once,
and continues as the material travels along the worm,
falls down the chute to the small end of the cone and
along to the wider end, where a chute delivers it to the
discharge hopper in a dry condition. When the receiver
is nearly full it can be discharged by cutting it off by
means of the wheel valve and admitting air until the
vacuum is gone.
One great advantage of vacuum dryers is that where
valuable solvents have been used they can be completely
recovered in the condenser. This part of the subject will
be more fully dealt with at a later stage.
Evaporators are machines used for recovering solids
which are dissolved in liquids by turning the latter into
vapour. The methods employed may be divided into
four classes, as follows: (1) Spontaneous evaporation;
(2) direct heating; (3) steam heating; and (4) reduced
pressure.
Spontaneous evaporation can be conducted successfully
in countries which have a definite period of hot dry
weather. Natural brines are frequently evaporated
by pumping them into ponds having a depth of about
2 feet and a surface of several acres, at a rate equal to
the rate of evaporation. In large installations as much
as 5,000 gallons per minute of fresh brine is required to
make up the evaporation losses, and the concentrate
is led into a separate pond and harvested.
DRYERS AND EVAPORATORS 119
In the direct-heat method, flames or hot waste gases
may be employed either to warm a vessel containing the
liquid, from underneath, or by being made to pass over
the surface of the liquid. Where the presence of a certain
amount of impurity does not matter, the latter method
can be adopted in preference to the former method,
which is not so economical of the available heat. Although
the open kettle is practically obsolete to-day, it is in-
teresting to note the evolution of the process and the
causes which led to its abandonment. From the simple
domestic copper heated by an open fire there evolved
the " block " or arrangement of as many as 100 kettles
of about 150 gallons capacity, arranged in one or more
rows in a flue or arches terminating in a chimney. To
prevent overheating of the kettles nearest the fire, arches
were built underneath them as a protection, thereby
causing a certain amount of heat to be wasted. Beyond
the grate the arches were built with air spaces between
them, which increased in size as the distance increased, and
the flues decreased in depth to about 6 inches under the
kettles next the chimney. Forced draught then became
necessary. Various difficulties arose which, combined
with the fact that it was found that for the fuel used
only about two -thirds of the amount of water was
evaporated as would be effected by a proper boiler, led
to the method being discarded.
Evaporation by means of direct heat is, however, still
employed, but the kettles are replaced by open pans
arranged as shown in Fig. 87.
The pans are of riveted wrought-iron plates J inch
thick, having flaring sides and divided into two or more
compartments, known as the front and back pans. The
pans are about 100 feet long, 25 feet wide, and 1 foot deep,
and the method of working is to run the liquid into the
back pan, where, after being heated by the hot gases
from the fire, it is siphoned into the front pan and
harvested, the solid being removed to the sides and allowed
120 INTRODUCTION TO CHEMICAL ENGINEERING
E
II
I
\-
I
to drain. Heating may be effected by oil, coal, or gas,
according to circumstances.
Evaporation by means of steam heating is very widely
DRYERS AND EVAPORATORS 121
used, owing to the ease of control and the absence of any
risk of damage to the product by overheating. In its
simplest form a steam-heated evaporator consists of a
vessel having steam pipes immersed in the liquid to be
evaporated.
In the salt industry brine is evaporated in a steam-
heated vessel known as a grainer — a long, narrow,
shallow vat built of wood or metal supported on a frame-
work, or of cement or concrete supported on a foundation
of sand. Wooden grainers made from white pine caulked
with oakum have been found to keep quite tight under
the great differences of temperature encountered.
The reinforced concrete type is monolithic, having no
expansion joints, and is usually provided with mechanical
raking devices. The walls are 5 to 7 inches thick, the
bottom 4 to 6 inches thick with J inch steel-bar rein-
forcement, the whole resting on a sand bed which gives
uniform support and reduces heat losses. An average
size grainer is about 150 feet long, 12 feet wide, and
2 feet deep, having four to eight steam pipes, 3 to 5 inches
in diameter, suspended about 12 inches above the
bottom.
The principle on which the grainer works is as follows :
If a solution of several salts is concentrated by evapora-
tion at a given temperature, the salts will be deposited
as they reach their saturation point. This will depend
upon their initial concentration and solubility and the
effects of the presence of other solutes. If, when the first
salt is deposited and before the second salt begins to form,
more of the original solution is added, the concentration
of the first salt is decreased less than that of the others.
Thus a thick deposit of the first salt can be formed by
the continuous addition and evaporation of the original
solution, until the concentration of the other salts reaches
saturation point and they also begin to form. This
method of separation should be carefully distinguished
from the method known as fiactional crystallization.
122 INTRODUCTION TO CHEMICAL ENGINEERING
Steam-Jacketed Pans. — For general use in the chemical
industry, steam-jacketed pans, such as shown in Fig. 88
and made by J. P. Devine and Co ; are built in every
size and shape, designed especially for the service under
which they are to operate. They are usually made of
DRYERS AND EVAPORATORS
123
sheet steel, but have been built of copper and cast iron,
rectangular or cylindrical, welded or riveted. Proper
openings are provided for steam inlets and condensed
water outlets. They are usually built shallow, to allow
for the greatest possible heating surface and to ensure
FIG. 89. — TILTING KETTLE.
maximum evaporation and facilitate the removal of
finished material. Where high -pressure steam is used,
the jacket must be properly stay -bolted '.
Steam- Jacketed Kettles. — A very convenient type of
apparatus, of which an example made by the above
firm is shown in Fig. 89, is known as the " tilting kettle."
These large kettles are usually arranged on a rigid struc-
124 INTRODUCTION TO CHEMICAL ENGINEERING
tural steel support of the necessary height to allow for
their emptying into a truck or similar device. They may
be equipped with a cover and a stirring gear of the horse-
shoe, grate, or propeller type, driven through bevel
gears and fixed and loose pulleys, which are rigidly
FIG. 90. — ASPINALL STEAM EVAPORATING PAN.
fixed to a heavy bridge on the top flange of the kettle.
The tilting device is formed of a worm gear and worm,
the latter operated by a handwheel. The kettle proper
is supported by hollow trunnions, which also provide
the steam inlet and condensed water outlet.
DRYERS AND EVAPORATORS 125
The common form of kettle is made of copper or cast
iron, with the jacket covering about half the kettle and
with provision made for the admission of thermometers
and for draininfir. In special cases kettles are made with
enamelled linings, or of special alloys for resisting corrosive
liquors or preventing contamination of the materials
by the metal of the kettle.
The method of working is to open the valve to the
drain pipe so that the first condensations can escape
and bumping be prevented. The exhaust valve is then
opened, and the steam gradually turned on at the inlet
valve until a good jet of dry steam issues from the drip,
which is then closed and the steam regulated to give the
desired temperature for evaporation.
This type of evaporator finds very great use in the
dye, paint, textile, and canning and preserving indus-
tries.
Fig. 90 shows a steam evaporating pan used in the
sugar industry, made by Blair, Campbell and McLean,
Ltd., Glasgow. The shell and conical top is of wrought
iron, and the bottom of cast iron fixed to the top by an
angle iron ring and bolts . The heating drum is of wrought
iron or brass, with solid drawn brass tubes expanded
into the same and beaded over, and with a large cir-
culating tube in the centre. The drum is designed for
a working pressure of 60 pounds per square inch, and is
fitted with an eye -bolt for lifting and cleaning.
Fig. 91 shows a Wetzel evaporating pan made by the
same firm, which is used for concentrating syrup. The
heating surface is obtained by a seamless copper helical
coil, the ends of which are attached to the cast-iron
trunnion pipe which admits and discharges the steam, and
is fitted with spur gearing driven by a pulley.
The Vacuum Pan. — The vacuum pan may be regarded
as a modification of the vacuum dryer which has been
considered previously. At the present time it is almost
universal practice to evaporate under vacuum those
126 INTRODUCTION TO CHEMICAL ENGINEERING
substances which are liable to damage either by a high
temperature or by the presence of air. Although the
temperature at which a liquid boils depends upon the
pressure to which it is subjected, in practice there are
limits to the range of temperature and pressure available.
As mere evaporation in a vacuum does not necessarily
mean economy, the utilization of exhaust steam fixes the
DRYERS AND EVAPORATORS 127
upper limit of temperature at about 225° F. ; the lower
limit, at about 125° F., is determined by the cost of
maintaining the required vacuum. Obviously, with a
given amount of heat available, better results are to be
obtained with a vacuum than with normal pressure,
and the greater the vacuum, the greater the amount of
liquid evaporated. Against this increase in evaporated
material must be reckoned the additional cost of the
special plant and the cost of maintaining the vacuum,
both of which must be taken into account when comparing
vacuum evaporation with the open pan process.
A vacuum-pan installation consists of three parts:
(1) The vacuum pan; (2) the condenser, and (3) the
receiver and pump. The vacuum pans are usually
vertical cylinders having conical ends, the whole being
constructed of iron, steel, or copper, and provided with
inlet and discharge holes, thermometers, vacuum gauge,
test cocks, liquor gauge, etc. These pans are seldom
less than 9 feet in diameter, and reach as much as 30 feet
in diameter, but from 10 to 20 feet is the most common
size. The smaller sizes are heated by means of a
steam jacket and the larger sizes by means of internal
steam coils or pipes. At the top of the pan is a dome or
large pipe connected with a " catch all," which serves
to trap all liquid carried along mechanically with the
steam and return it to the pan, while the steam passes
to the condenser. The condenser may be a coil of piping
surrounded with cold water or some special form of
surface or jet condenser.
Fig. 92 shows a copper vacuum pan made by Blair,
Campbell and McLean, Ltd., Glasgow, for concentrating
sugar solutions, a branch of industry in which vacuum
pans were used as far back as 1813.
This pan is 10 feet in diameter, and has a heating
surface arranged in seamless copper coils, each coil
having a steam inlet valve and pipe, pressure gauge, drain
pipe, and steam trap.
128 INTRODUCTION TO CHEMICAL ENGINEERING
FIG. 92.— COPPER VACUUM PAN.
DRYERS AND EVAPORATORS
129
FIG. 93. — CAST IRON CALANDRIA VACUUM PAN.
Fig. 93 shows a 12 -foot cast-iron calandria vacuum pan
made by the same firm, in which the heating surface
9
130 INTRODUCTION TO CHEMICAL ENGINEERING
consists of straight tubes of copper or brass expanded
into gun -metal or steel tube plates having a large cir-
culating tube in the centre to assist the circulation.
The steam belt is placed in the cylindrical part of the
pan or effect, as it is called, and contains several hundred
vertical copper tubes about 5 feet long and 2 inches in
diameter.
FIG. 94. — G.A. VACUUM PAN: JET CONDENSER.
Fig. 94 is a diagram showing the arrangement of a
vacuum pan having a jet condenser and wet vacuum
pump, and Fig. 95 is a similar diagram showing a vacuum
pan having a condenser with a barometric leg and
receiver, together with a dry vacuum pump.
There are many makes of vacuum pans ; but in general
the method of operation is for either live or exhaust
steam to enter the coils or steam belt, usually, but not
always, at low pressure. Any water which condenses
here is drained away to the boilers or used for boiling
out or thrown away.
As the liquor in the pan boils, the vapour passes to a
DRYERS AND EVAPORATORS
131
/S'///'''/W''"rs^^^^
FIG. 95. — G.A. VACUUM PAN: TORRICELLIAN CONDENSER.
condenser, which by condensing the vapour helps to
maintain the vacuum. Theoretically, the vacuum pro-
132 INTRODUCTION TO CHEMICAL ENGINEERING
duced by the pump at the commencement of operations
should be maintained by the action of the condenser,
but in practice it is found necessary to work the pump
FIG. 90.
-IN.TECTION CONDENSER :
SECTION.
FIG. 97. — SURFACE CON-
DENSER: SECTION.
throughout the process to an extent depending upon the
efficiency of the particular condenser used. As a general
rule the water from the condenser is allowed to go to
waste, and as its temperature is low — about 80° to 90° F.
DRYERS AND EVAPORATORS 133
— not much heat is wasted, but in some cases this water
may also be utilized.
In order to secure the highest efficiency, the vacuum
must be as high as possible, and for this reason both the
pump and the condenser must be as efficient as possible.
It is essential that the condenser should have a sufficient
cooling capacity to deal with the volume of vapour to
be condensed. There are two types of condensers in
common use — the jet type and the surface type, as shown
diagrammatically in Figs. 96 and 97 respectively.
With the surface condenser the evaporated liquid is
completely recovered and a pump of the dry type can be
used, but with the jet condenser the vapour is mixed
with the condensing water (equal to about forty times
the weight of vapour condensed) and a larger pump of
the wet type is required, but the operation is not so
costly.
In the case of the surface condenser the receiver is
usually directly connected, and arrangements are
provided for discharge from time to time without in-
terrupting the main process. Jet condensers are often
connected with a barometric leg 35 feet high in which
the condensing water stands and overflows into a well
without breaking the vacuum.
Multiple-Effect Vacuum Pans.— As far back as 1830
the suggestion was made of connecting vacuum pans
in series and regulating the pressure in each pan so that
the work done by the steam could be greatly increased,
but it took many years before the method was in general
use.
In the multiple effect system each vacuum pan acts
not only as an evaporator, but also as a boiler, producing
heated vapour for boiling in the next pan and acting as a
condenser for the preceding pan. Suppose, for example,
steam at about 212° F. is admitted to the first pan of a
series, and the vacuum maintained in that pan is 15 inches.
The vapour from the first pan will have a temperature of
134 INTRODUCTION TO CHEMICAL ENGINEERING
175° F., and passing into the second pan, which has a
vacuum of about 24 inches, produces more vapour at
140° F., which in turn passes to the third pan. having a
vacuum of 27 inches, and so on until the highest economical
vacuum attainable limits the process.
The varied applications of the vacuum -pan process have
produced a corresponding variety of makes, which differ
considerably in detail and operation, but which would
require more space than is available in this book for even
the briefest examination.
Nearly a hundred years ago an eminent authority
drew attention to the following points as constituting
the essentials of a good evaporator: (1) The liquor to be
evaporated as quickly as possible, so as to avoid any
alteration; (2) the movement of the liquor to be acceler-
ated by giving it great speed and spreading it out in the
form of a thin film.
These are the principles involved in the design of the
Kestner patent film evaporator, and hence show a great
departure from those embodied in the older types of
vacuum pan.
It is a truly continuous apparatus, the weak liquor
being fed by gravity or by means of a pump at a constant
rate into the bottom box of the evaporator, and the con-
centrated liquor at the predetermined density issuing
continuously from the separator. The heating surface
and the passage of the liquor through the tubes are so
disposed that the liquor to be concentrated passes over the
heating surface at high speed in the form of a thin film,
whilst the steam space surrounding the tubes is so
arranged that the outer surface of the tubes is swept
at high speed by the hot steam, so that not only is the
heat transfer improved, but the condensed steam is
rapidly brushed off the heating surface, thus preventing
any loss of efficiency from the tubes becoming water-
logged. In addition, the arrangement is such that
accumulation of air and non -condensable gases in the
DRYERS AND EVAPORATORS 135
steam space is entirely prevented, and so the whole of
the heating surface is able to exert the maximum
efficiency. The advantage of the high velocity of the
liquor and its short-time contact with the heating surface
is threefold: The physical properties of delicate liquors
remain absolutely undamaged, owing to the fact that
they are only in momentary contact with the heating
surface. Secondly, the rate of heat transfer is enormously
increased, owing to the fact that the presence of large
masses of water in feeble circulation is entirely eliminated.
Thirdly, the formation of scale on the internal surfaces
of the tubes is greatly reduced and in some cases pre-
vented, giving a great range of application to the
apparatus.
The design of the evaporator has a further advantage
in that the ground space occupied is exceedingly small
compared with that of many other pans, and that it lends
itself to the subsequent addition of effects, so as to
convert a single effect into a multiple, with the corres-
ponding steam economy.
Fig. 98 shows a sectional view of a Kestner single-effect
climbing film evaporator. It consists of two parts—
namely, the calandria and the separator, the former
being composed of a shell or casing containing the
evaporating tubes, which are about 23 feet long and
fixed into the upper and lower tube plates.
The liquor is fed into the apparatus at the lower inlet T,
and passes from the feed box into the tubes. The steam
or exhaust vapour, whichever medium may be employed
to heat the liquor, enters the calandria of the evaporator
at A. The liquor begins to boil in the tubes because they
are surrounded by steam, and as ebullition takes place
a column of vapour rises up the centre of the tube. This
vapour travels at a high velocity, and at the same time
draws up a film of liquor, which forms on the inner surface
of the tube continuously without dry patches, so pre-
venting any danger of burning any substances sensitive
136 INTRODUCTION TO CHEMICAL ENGINEERING
M
FIG. 98. — KESTNER CLIMBING
FILM SINGLE-EFFECT EVAP-
ORATOR.
FIG. 99. — KESTNER FALLING
FILM SINGLE-EFFECT EVAPOR-
ATOR.
to heat. Above the calandria is the separator S, which
consists of a cylindrical vessel containing a centrifugal
DRYERS AND EVAPORATORS 137
baffle placed immediately above the tubes, and so con-
structed that the liquor and vapour rising up the tubes
in the calandria strike against the curved vanes of the
baffle with such velocity that, due to centrifugal motion,
there is complete separation of liquor and vapour. The
concentrated liquor passes down the outlet L, and the
vapour, passing after through the save-all, leaves the
separator at B. The long shell of the Kestner gives two
important advantages over the calandria of the ordinary
type of vacuum pan: first, the distilled water can be
removed easily by running it off at the opening E ; and
secondly, all air and non -condensable vapours in the
heating system are removed at G ; thus all the tube
surface remains operative.
For such liquors as glue, gelatine, and the like, the
final concentration is made in a falling film evaporator,
of which a sectional view is shown in Fig. 99. The
apparatus consists of — (1) Tubes 18 to 23 feet long
secured in the upper and lower tube plates, divided into
two groups G and D, forming the climbing film and
falling film tubes respectively. (2) The separator, placed
below the lower tube plate, contains the feed box, and
is fitted with a centrifugal baffle and the necessary openings
for the concentrated liquor outlet and for the discharge
of the vapour. The liquor to be concentrated is delivered
into the feed box B, from which it passes into the tubes G ,
where the climbing film action takes place. The liquor
and the vapour arrive in the upper box above the tube
plate, where they are distributed to the tubes Z>, the
liquor running down as a thin film, and the high-speed
vapour forming a core in the centre of the tube. Both
liquor and vapour pass into the separator 8, where by
means of centrifugal action complete separation takes
place, so that the vapour passes at C and the liquor atP
By means of this apparatus substances such as
liquorice, gelatines, glue, dyestuffs, milk, fruit juice,
and sugar can be delivered in such a high state of
138 INTRODUCTION TO CHEMICAL ENGINEERING
concentration that the extract solidifying on cooling can
be run into drums or moulds ready for transit. Many
substances can be concentrated without a vacuum in this
;::ri §
apparatus^which require a vacuum in the older types of
apparatus. By this method all the steam required for
the auxiliaries is saved, and when multiple effects are
DRYERS AND EVAPORATORS
139
used great economy is obtained, as only a single feed
pump is required; moreover, where cooling water is
scarce, the possibility of avoiding the use of a condenser
is a great advantage.
FIG. 101. — KESTNER "SALTING" TYPE EVAPORATOR: SECTION.
Fig. 100 shows a direct-fired evaporator followed by a
quadruple effect, and a single -effect finisher which is
stated to produce caustic liquor of 60 per cent. Na^O.
Fig. 101 shows a section of a " salting " type evaporator
which is used for the concentration of dual solutions
and for the production of crystals direct in the separator
instead of in the usual trays. Separation of salts by
140 INTRODUCTION TO CHEMICAL ENGINEERING
crystallization, owing to difference of solubility, can be
effected in this apparatus — e.g., mixtures of NaCl and
NaN03, NaOH and NaCl, NH4N03 and Na2S04.
The separator is a cylindrical vessel round which
several calandrias can be grouped. Liquor is admitted
to the separator to above the opening B, at which point
the calandria can operate, the height being checked
through the sight glasses S. Steam is turned on in the
calandria, the liquor passing through B down into the
bottom box of the calandria through the tubes, and back
into the separator at A. The circulation is continuous,
and the crystals formed are by means of the circular
baffle deposited on the bottom of the cone, whilst the
liquor passes through B and the vapour formed passes
into the save-all, for further treatment as desired. At
the bottom of the separator is a valve capable of dealing
with liquors heavily charged with salt crystals, and
discharging into a salt box or filter box, which latter
has a bottom cover arranged with a balanced hinge
so that the filtering medium can be easily inspected.
By means of the isolating valves A and B, any one
of the heating units can be shut off from the system for
cleaning or repairs without interfering with the running
of the rest of the apparatus.
With multiple -effect apparatus there is an economy of
steam and condensing water amounting to one -half in a
double effect and two -thirds in a triple effect of that
consumed in a single -effect apparatus. Multiple -effect
evaporators have not been universally employed because
materials which are sensitive to high temperatures could
not be evaporated in such an apparatus without suffering
injury, as the operation of a multiple effect requires
evaporation temperatures up to about 176° F. in a triple
effect, and still higher for a larger number of effects.
For small and medium quantities of liquid, and where
work is done for an hour or two at a time, the use of a
multiple effect was precluded because of the difficulty of
DRYERS AND EVAPORATORS HI
starting and stopping it, the large space required, and the
very considerable first cost.
The " Multiplex " evaporator made by Blair, Campbell
and McLean, Ltd., Glasgow, overcomes some of these
objections, although high temperatures in the first effect
cannot be avoided. By special construction the quantity
of liquid contained in each effect is so small that the
liquid remains in it only one or two minutes at the
utmost, and is then drawn off into the next compartment,
which is at a lower temperature, and finally, after a
short time, is completely concentrated and discharged
from the apparatus.
Fig. 102 shows a view, and Fig. 103 shows a section
of a " Multiplex " triple -effect apparatus. When the
apparatus has been exhausted of air the liquid to be
concentrated enters at 1, into the double bottom 2,
and rises to a uniform height in the tubes 3, which are
surrounded with steam which enters at 4. The liquid
very soon boils, bubbles of steam first forming at the
underpart of the heating tubes and increasing to a
stream of high velocity. The liquid attaches itself to
the tube walls, and the steam drives it high up these,
so that the middle and upper parts of the tubes are no
longer filled with liquid, only the tube walls are wet
with it. The bubbles of froth formed in the lower part
of the tubes are thus broken up, so that the liquid leaves
the tubes in the form of drops which spring off the top
edges of the tubes. Close above the upper tube plate
another plate is fixed, between which the velocity of the
steam is so great that the drops have no time to sink down,
but are blown towards the tubular connection 5, and
through it into the separator 6. There the liquid sinks to
the floor, and thereafter it rises through the tube 7 into
the double bottom 2, and the heating tubes of the second
effect, whilst the vapour rises into the heating com-
partment 8, and there serves as heating steam. The
process of evaporation is repeated there in the same way
142 INTRODUCTION TO CHEMICAL ENGINEERING
FIG. 102.— " MULTIPLEX " FILM TRIPLE -EFFECT EVAPORATOR
DRYERS AND EVAPORATORS 143
FIG 103.— " MULTIPLEX " TRIPLE-EFFECT EVAPORATOR: SECTION.
144 INTRODUCTION TO CHEMICAL ENGINEERING
as in the first effect, and again in the third effect, from
which the liquid is drawn off at 9 after it has been con-
centrated to the desired degree. The vapour from the
last effect is then condensed in the condenser through
pipe 10.
Frothing interferes very much with the evaporation
in a vacuum apparatus, but in this case the liquid cannot
rush through the tubes in the form of froth, but adheres
to the walls and evaporates. The central entrance of the
steam into the heating space causes an energetic circu-
lation, so that all the heating tubes are heated with the
utmost possible uniformity, and no dead corners are
formed in which material that would generate deleterious
gases can collect. The apparatus is constructed in such
a way that the whole amount of liquid contained per
square foot of heating surface is only a few gallons.
Every particle of the liquid, therefore, only remains a few
minutes in the apparatus, and is then forced out by the
liquid following upon it, so that the material undergoing
concentration is very soon withdrawn from any de-
leterious action of high temperatures.
The mode of operation is very simple, and consists of
putting the vacuum pump in action and setting the valves.
It sucks in the liquid which is to be concentrated through
a pipe, and ejects it in the concentrated state through
another pipe, the degree of concentration being regulated
by the amount of the feed.
The sugar and the salt industries have had the longest
connection with the vacuum-pan process, and as both
these industries are widely represented on the American
continent, it follows that there are many types of pans
made by American firms. Among the most important
vacuum pans used in Canada and America are the
Manistee, Lillie, Brecht, Craney, Oscar Krenx, Swenson,
Sanborn, Wheeler, and Zaremba vacuum pans, each of
which is worth consideration by the chemical engineer.
CHAPTER V
DISTILLING APPARATUS
DISTILLATION is the term usually applied to the applica-
tion of the process of evaporation to the separation of a
solution into its components. There are three principal
parts which all types of distilling apparatus have in
common — viz., (1) a vessel or still in which the material
is heated; (2) a cooling apparatus for condensing the
evaporated material ; and (3) a receiver for collecting the
condensed material or distillate.
The process of heating materials and collecting the
bodies formed by the action of heat is termed destructive
distillation, and, when the main object of the process is
the residue in the still, so that this part of the apparatus
undergoes great modification, the terms roasting, burning,
glowing, and firing are used, and the apparatus termed a
muffle, furnace, kiln, etc., as the case may be.
It will be obvious from what has already been said about
vacuum pans that they are a form of still, and, indeed, they
are often used for this purpose in suitable cases, but the
separation of liquids of close boiling point demands
the type of apparatus usually termed a still.
The Column Still. — This commonly used apparatus,
of which a diagrammatic view is shown in Fig. 104,
derives its name from the column or dephlegmator A,
through which the vapours from the boiler are made
to pass before being condensed and collected in the
receiver. This column, which is fixed over the still or
boiler, contains a number of shallow cups or plates placed
at intervals, thus dividing the column into a series of
145 10
146 INTRODUCTION TO CHEMICAL ENGINEERING
chambers between which communication is maintained
by means of perforations in the plates or by small tubes
so arranged that a small quantity of liquid can be retained
in each cup.
When the process has been continued for a sufficient
time for the column to take up a steady state there is a
definite drop in temperature from the top of the column
FIG. 104. — DIAGRAM OF STILL COLUMN.
downwards, and each cup contains a small quantity of
liquid with a correspondingly higher boiling point
through which the oncoming vapour from the boiler
must bubble. In each, the partial pressure of the con-
stituents depends upon the temperature and the com-
position of the liquid therein, so that the higher boiling
constituents, as they fall back down the column, enrich
DISTILLING APPARATUS 147
themselves at the expense of the ascending vapours, until
only the lower boiling or more volatile bodies issue from
the top of the column. From the top of the column
the vapours pass through a series of U -tubes B, which are
surrounded by a bath kept at a definite temperature.
From the bottom of these U -tubes draining pipes lead
back to the column, and are so arranged that they dis-
charge into it at various points, depending upon the
boiling point of the condensate, progressively from the
bottom of the column with the highest boiling point to
the top with the lowest.
By this means the vapour which issues from the
U -tubes and is condensed in the coils C is comparatively
free from foreign substances, and has a constant boiling
point. By continuing the process this constituent may
be generally entirely recovered, and the apparatus
taking up a fresh steady state, the next higher boiling
constituent may be recovered, and so on.
This is the method known as fractional distillation,
and it should be noted that it is not applicable to all types
of liquid mixtures, of which a short account is given in
the Appendix.
Fig. 105 shows a patent rectifying still made by John
Dore and Co., London. It is designed for the strengthen-
ing of weak alcoholic liquors and the recovery and
purification of solvents, such as ether, acetone, and the
like, and it is claimed that in one operation it will produce
alcohol of 0-815 specific gravity from weak liquors of
about 0-967 specific gravity.
Fig. 106 is a diagram illustrating a continuous still
made by George Adlam and Son, Ltd., Bristol. This
still consists of —
1. A boiling or analyzing column made in sections of
cast iron and fitted with copper plates between each
joint, on which are fitted copper bell plates and dip
pipes. In the bottom chamber is placed a steam heating
coil for heating the liquor.
148 INTRODUCTION TO CHEMICAL ENGINEERING
2. A rectifying column constructed of strong copper
and made in flanged sections. This is also fitted with
copper bell plates, bells and dip pipes similar to those
FIG. 105. — RECTIFYING STILL.
in the analyzing column, but with four plates to each
section.
3. A rectifier or reflux condenser.
4. A condenser with tube plates and tubes.
5. Sight glasses or still watchers.
DISTILLING APPARATUS
149
The liquor is fed into the still at the seventh section
of the analyzing column, and exhausted, waste, or spent
liquor is run off from the bottom chamber.
The vapours pass from the analyzing column to the
rectifying column through the connecting pipe, and
ftect-ifier. Condenser
FIG. 106. — CONTINUOUS DISTILLATION APPARATUS: DIAGRAM.
from the rectifying column to the rectifier through the
bent pipe shown. Portions condensed here are returned
to the rectifying column through a draining pipe at the
bottom, and the rest of the vapour passes on for con-
densation in the spirit condenser, where it can be observed
and discharged as required.
150 INTRODUCTION TO CHEMICAL ENGINEERING
FIG. 107. — CONTINUOUS STILL: DIAGRAM.
Fig. 107 shows a continuous still made by George
Scott and Son, Ltd., London.
The Coffey Still. — This particular type of still, named
after the original maker, ^Eneas Coffey, whose successors
DISTILLING APPARATUS
151
are John Dore and Co., London, has found a most varied
application in many of the branches of chemical industry.
To trace out the application of the principles of the Coffey
still to the various branches of industry is impossible
for the purposes of this book, but the student should make
himself acquainted with the main outlines of the process,
and always be on the look-out for its practical applicaticn
in the industrial world.
Fig. 108 is a diagram which gives a rough idea of the
principal parts of a Coffey still. It consists of two columns
FIG. 108. — DIAGRAM OF COFFEY STILL.
or towers A and B, known as the analyzer and rectifier
respectively. The internal arrangement of the analyzer
is similar to that of a column or dephlegmator on a large
scale. The rectifier consists of a column which contains
a tubular coil, through which the liquor is pumped and
discharged at the top of the analyzer over the perforated
plates or trays. Steam or some other suitable vapour
is admitted at the bottom of the analyzer, and, rising
through the descending stream of liquor, is partially
condensed whilst vaporizing the volatile constituents of
the liquor. The action of this tower is exactly similar
152 INTRODUCTION TO CHEMICAL ENGINEERING
to the action of the column of an ordinary still, so that
from the top of the analyzer a pipe leads away a heated
mixture of steam and vapour of the volatile portions of
the liquor. This hot vapour is in turn delivered to the
bottom of the rectifier, where it gradually rises through
the coils of the liquor tube, heating the contents and at
the same time condensing out the higher boiling portions,
including the steam, which run down to the bottom.
The most volatile portions pass out of the rectifier at the
top, and are led to a condensing apparatus and receiver.
The liquid which collects at the bottom of the rectifier
is pumped up to the top of the analyzer, and there
discharged over the plates, together with the liquor from
the tank. With proper working, by the time the liquor has
reached the bottom of the analyzer all the volatile portion
has been extracted, and it may be drawn off and discharged
as spent liquor. It will be noticed that the apparatus
practically consists of two columns arranged on the
counterflow system.
It need hardly be mentioned that the success of the
process depends both upon the design of the parts and also
upon the experience and skill of the operator.
Among the many applications of this apparatus a very
interesting one is its use in the liquefied gases industry
for the separation of the constituents of mixtures such
as liquid air, liquid natural gas, etc., whereby formerly
rare gases, such as argon, neon, and helium, are obtained
in commercial quantities.
Extraction Plant. — One of the most interesting modi-
fications of distilling apparatus is found in its application
to the extraction of oils and drugs.
Fig. 109 shows a continuous extraction apparatus made
by John Dore and Co., London, which is designed for the
extraction of drugs by means of alcohol, ether, acetone,
petrol, benzene, etc., and is so arranged that there is
little or no loss of the solvent used. It consists of three
vessels — viz., an evaporator, extractor, and condenser,
DISTILLING APPARATUS
153
FIG. 109. — EXTRACTION APPARATUS.
154 INTRODUCTION TO CHEMICAL ENGINEERING
all mounted on a self-contained stand with the necessary
cocks and connections. The method of operation is
for the extractor to be filled with the plants or roots to be
treated, while the evaporator is filled with the solvent.
This latter vessel, heated by a steam jacket, vaporizes
the solvent, which is conveyed to the overhead condenser,
where it is condensed and allowed to flow or percolate
through the material in the extractor and back into the
evaporator again, together with the dissolved substances.
Here the solvent is again vaporized and returned for
extraction, and so the process is carried on until the
material in the extractor is completely extracted. At
this stage the solvent is again vaporized and drawn off
from the condenser, while the product is collected from
the lower vessel as required. The centre extraction
vessel is also fitted with a steam jacket which can be
used for driving off any solvent remaining in the ex-
hausted mass, or for heating the drug during the process
of extraction. Both vessels are fitted with removable
covers for cleaning purposes and for charging.
Fig. 110 is a diagram showing the arrangement of an
oil extraction plant made by George Scott and Son,
Ltd., London.
The distillation of such substances as crude petroleum
and coal tar involves both distillation proper and des-
tructive distillation. The plant used is comparatively
simple in nature, although in most cases of huge size.
For the fractional distillation of crude petroleum, cylin-
drical steel shells up to a size of 15 feet in diameter
and 42 feet in length are set horizontally in brickwork,
leaving the upper half exposed except for an iron cover.
Of the two methods of firing — end firing and side firing —
the latter is preferred on account of the greater control
of the still which ensues. The stills are fitted with
the usual dome, from which the vapour main of 12 inches
to 18 inches in diameter leads to the condensers, which
are very often simple coils immersed in a water bath.
DISTILLING APPARATUS
155
In this type of still the various fractions are collected
until about 10 per cent, of the original oil is left as a
tarry residue, which is removed and distilled in tar
stills.
156 INTRODUCTION TO CHEMICAL ENGINEERING
Sometimes the distillation of the oil is carried on till
the residue is destructively distilled to coke. In this
case the vapours are led through a kind of column, which
takes the form of a number of towers each of which
corresponds to a chamber of the smaller column. These
DISTILLING APPARATUS
157
towers consist of two chambers connected by tubes,
around which the air circulates and in which the vapours
are condensed and run down into the bottom chamber,
whence they are drawn off as a separate fraction after
passing through water coolers. The towers are connected
to the still in series, the vapour entering at the bottom
of the fir?t and passing out at the top to the bottom
FIG. 112. — LUBRICATING OIL DISTILLING PLANT: PLAN.
of the second, and so on. In certain cases steam is
blown into the still, which has the effect not only of keeping
the mass agitated and preventing overheating of the
bottom portion, but also, by its additional pressure on
the surface, lowers the partial pressure necessary for any
constituent to boil, and so causes that substance to boil
off at a lower temperature. It need hardly be mentioned
158 INTRODUCTION TO CHEMICAL ENGINEERING
that some manufacturers obtain the same effect by
working the process under a vacuum.
On account of the fact that a high distilling temperature
is injurious to the product, in the case of lubricating oils,
the process of vacuum distillation is in common use.
Figs. Ill and 112 give a view in elevation and plan
of a continuous vacuum oil distilling plant for lubricating
and paraffin oils made by W. J. Fraser and Co., Ltd.,
Dagenham, Essex.
The plant is so designed that a high vacuum is main-
tained in the entire system by means of a vacuum pump
under a continuous or periodical distillation, the dis-
tillates being collected in their respective receivers.
This plant may be advantageously connected direct
with the crude oil distillation plant, effecting thereby
a further saving in fuel and labour. Among the advan-
tages of this type of plant are (1) a high quality product
due to low temperature and high vacuum ; (2) no cracking,
as the vapours do not have contact with highly heated
plates in the still.
For the distillation of tar, similar stills having a
capacity of about 5,000 gallons are in common use, but
very often the still is of the vertical type, having a con-
vex top and concave bottom. Constructed of J-inch
boiler plate with a bottom of Ij inches set in a brick
arch over the fire, the lower half is heated by the hot
gases from the fire being made to circulate round it by
means of flues. The vapours are led away to the usual
type of condensing coil, and provision is made for running
off the pitch from the still into a vessel for cooling.
Retorts. — The greater part of the labours of the early
chemists was devoted to the heating of all manner of
materials in an alembic or retort and investigating
the nature of the resulting products. This form of
distilling apparatus in some cases yielded important
results of commercial value, so that industries were
started and the retort was developed in accordance with
DISTILLING APPARATUS 159
the particular needs. The term " re tori " is now generally
used to indicate that part of the apparatus in which
the heating of the material is carried on. The construc-
tion of a retort depends entirely upon the particular
industry in which it is used and the requirements of the
individual manufacturer.
In the nitric acid industry a retort is required in which
sulphuric acid and nitrate of soda can be mixed and
heated, resulting gases collected, and provision made
for removing the nitre cake.
These retorts are usually cast-iron cylinders about 5 feet
in diameter and 10 feet in length, closed at either end by
stone or cast-iron plates, one of which is pierced for the
separate feeding of the acid and the soda, and the other
for the exit of the gases and the discharge of the nitre
cake. These retorts are fixed in a brickwork setting and
only require a comparatively small fire area.
Another common form is known as the pot still, which
consists of a pot made up of three sections luted together
with an acid-resisting cement. The upper sections are
lined with bricks, but the bottom section is unlined, as
it is not so liable to corrosion, and to allow of easy heat
transfer. The bottom section is provided with an outlet
for the discharge of the nitre cake, and the top section is
provided with a charging door and gas exit tube. As a
rule the pots receive a charge of about 1 ton of material
a day, which is gradually distilled.
The retorts used in a by-product coke oven are long
narrow structures of firebrick about 30 feet long, 6 feet
high, and 1J feet wide, arranged side by side, separated
by flues. The ends are closed by sliding iron doors,
which are luted during operations, and which can be
raised at the end of a run and the whole of the contents
pushed out by mechanical means.
The retorts used in the coal-gas industry are of three
kinds — viz., (1) horizontal, (2) inclined, and (3) vertical.
There is considerable variation in the length and
160 INTRODUCTION TO CHEMICAL ENGINEERING
cross-section of these retorts and in the method of heating,
although the use of producer gas is growing in favour.
Horizontal retorts are usually provided with mechanical
stokers, and are charged to about two -thirds of their
capacity. Inclined retorts are charged by feeding in at
the top, and discharged from a door at the bottom,
thus saving a certain amount of labour. The gas is
drawn off at the bottom of the retort, but it is said that
the yield is smaller than in the case of other types of
retorts. Vertical retorts are arranged in groups for
filling at the same time, and the gas is drawn off at the
top, while the coke is removed from the bottom and
used directly for making producer gas for heating the
retorts.
An exceedingly important modification of the gas
retort is that designed by Mr. Dowson for the production
of a cheap gas fuel for driving gas engines and for heating
work of all kinds where cocks and burners are used.
Briefly, the gas is made by passing superheated steam,
mixed with air, through red-hot fuel in a vertical gas
producer. The steam is decomposed, the oxygen com-
bining readily with the carbon of the fuel, and the com-
bustible constituents of the gas consist of hydrogen,
carbon monoxide, and a small percentage of marsh gas.
The process is continuous and automatic, and there is no
outside fire, as there is with an oidinary retort; the
cost of repairs is low, and the apparatus is simple and
easy to work. The gas is made as quickly as it can be
consumed, and its production being governed auto-
matically to suit a varying rate of consumption, it can be
stopped completely for meal-times or when laying off.
The gas is cooled, washed and scrubbed, and passed
into a gasholder when required, although in many cases
the latter operation is found not to be necessary.
The original Dowson plant is worked with a jet of
steam at pressure, acting as an air injector, and is known
as the pressure plant, but in the more recent plant the
DISTILLING APPARATUS 161
suction plant, air and steam are drawn in by means
of a fan or gas engine, the only difference in the result
being that pressure gas has a little higher calorific power
and is more useful for heating work than the suction
gas.
Both types are worked with anthracite (peas, beans,
or nuts), charcoal, or gas coke, which latter should be
in pieces of £ to f inch cube, and should not contain
more than 10 to 12 per cent, of ash. Owing to the forma-
tion of tar, special plants are needed for using bituminous
coal and for the utilization of wood refuse, shavings,
sawdust, etc.
FIG. 113. — "DOWSON" STEAM JET PRESSURE GAS PLANT.
Fig. 113 shows a diagrammatic sectional view of a
Dowson pressure plant. A jet of steam at pressure from
a small independent boiler, or from a factory or other
boiler near the gas plant, plays in an open air pipe,
and the mixture of steam and air is forced into the fire
in the producer, the fuel being put in through the hopper
on the top. The gas is made continuously so long as the
jet of steam is working, and if shut off the production
of gas ceases at once. On the steam pipe there is a
governing valve and lever actuated by the rise and fall of
the gasholder, so that the rate of production is governed
automatically to suit a varying rate of consumption.
11
162 INTRODUCTION TO CHEMICAL ENGINEERING
After the gas leaves the producer it passes through a
water seal, and then through coke and sawdust scrubbers.
The consumption of anthracite or charcoal is about
13 pounds, or of coke about 14 pounds per 1,000 cubic
feet of gas, and it may be taken for the purposes of costs
comparison that 4,000 cubic feet of this gas are equivalent
to 1,000 cubic feet of town gas.
FIG. 114. — " DOWSON " SUCTION GAS PLANT.
This type of plant is suitable when there are two or
more gas engines, when there are engines and heating
work, or when there is heating work only. The gas
mains are then simplified, and it is also more easy to start
two or three engines from a pressure plant than from a
suction plant.
When this type of plant is used for engine work the
consumption of anthracite or charcoal of average quality
is about 1 pound per b.h.p. hour, the actual consumption
DISTILLING APPARATUS 163
depending somewhat on the efficiency of the engine.
With coke the consumption is a little higher.
Fig. 114 gives a sectional view of the Dowson suction
plant. In this case the steam is formed in a vaporizer
inside the producer, near the top, and the steam and
air are drawn into the fire at the bottom by means of
a fan or by the suction of the engine, which works in
combination with the plant. Every plant has a small fan
for blowing up the fire at the start, and when the engine
is started this fan is stopped and the engine itself governs
the rate of producing the gas to suit its own varying
consumption. After the gas leaves the producer it passes
through a water seal, and then through coke and saw-
dust, as in the pressure plant.
Fig. 115 is taken from a photograph of a 30-h.p.
plant. The chemical process of making the gas is the
same as in the pressure plant, but as there is no inde-
pendent boiler, no allowance need be made for raising
the steam required, so that with a good engine the
consumption of anthracite or average charcoal is about
| pound per b.h.p. hour. From tests which were made
on a 40-h.p. plant the heat efficiency was found to be as
high as 90 per cent.
For plants of about 200 h.p. and upwards it is found
that bituminous coal is cheaper than anthracite, and so
a special type of plant is used.
Fig. 116 gives a sectional view of a Dowson bituminous
plant for making gas without tar. The special feature
of the producer is that it is double acting — i.e., air is
drawn in through the top and through the bottom of the
fuel column, as indicated by the arrows. The producer
is open at the top, and coal is put in there, but there
is no escape of smoke as air is drawn inwards by an
exhaust fan. The upper part of the fire burns down-
wards, the hydrocarbons are distilled off, and the coke
which remains sinks downwards into the lower part
of the producer, where it meets an upward current of
164 INTRODUCTION TO CHEMICAL ENGINEERING
steam and air and is converted into ordinary producer
gas. The mixture of gases leaves the producer through
FIG. 115.— 30 H.P. SUCTION GAS PLANT.
an outlet about halfway between the top and the bottom.
The producer has a water bottom, so that clinker and ash
can be drawn out while the plant is working, and almost
DISTILLING APPARATUS
165
any kind of coal can be used which does not contain more
than 31 to 35 per cent, of volatile matter. After leaving
the producer the hot gas passes through a vaporizer to
cool and also assist to raise the steam required. It then
passes through special scrubbers to remove dust, scot, etc.,
but in this process there is no tar, as it is converted into
gas in the producer, and no mechanical or other tar
extractor is required.
The calorific value of this gas is nearly the same as that
made from anthracite, and under good conditions the
166 INTRODUCTION TO CHEMICAL ENGINEERING
consumption of coal of fairly good quality in pieces of
about J to 1 inch cube is a little over 1 pound per b.h.p.
hour.
During the last few years the great development of the
oil-hardening industry has created a demand for large
quantities of pure hydrogen. In the Lane process this
gas is produced by means of a special retort which is the
result of the research work of Mr. Howard Lane during
the past fourteen years. The retorts used are of the
vertical type, and consist of cast-iron tubes 1 J inches
thick, 9 inches internal diameter, and 9 feet 9 inches long,
having end covers for charging and discharging, and
arranged in a brickwork casing. The basis of the process
is the alternate oxidation and reduction of iron by
steam and water gas respectively, and the purification of
the hydrogen formed. The retorts are first charged
with spathic iron ore, which on heating parts with its
carbon dioxide and yields ferrous oxide. This oxide
is then reduced by heating in a stream of purified town
gas or water gas, and then subjected to the action of
steam, whereby the iron is oxidized and hydrogen
liberated. Although the process is chemically simple,
the successful results obtained depend largely upon the
inventor's mode of working. Since the production pro-
cess takes twice as long as the oxidation process, Mr. Lane
arranges three groups of retorts, so that two groups are
reducing while one is oxidizing. In the experimental
plant at Ashford the control valves are operated every
10 minutes, so that each retort produces hydrogen for
10 minutes every half -hour. From time to time it is
found necessary to burn out the iron in a current of air,
in order to restore its activity, the iron becoming poisoned
by the accumulation of sulphur and other impurities
which find their way past the scrubbers. Owing to
the conditions of the reaction, an excess of water gas
is needed to obtain complete reduction; hence a certain
amount of this gas passes from the retorts unused, but at
DISTILLING APPARATUS 167
a later stage it is dried and used for firing the retorts.
The purity of the hydrogen produced by this process
is stated to be from 99 to 99 J per cent., and the cost,
depending upon local conditions, is low enough for its
production on a commercial scale.
Kilns. — This type of apparatus is used when it is
necessary to subject material to the action of a high
temperature in order to drive off moisture or some
volatile constituent. They are mostly used in the cement
and gypsum industries, and may be divided into the
stationary and rotary types. Of the former type the
primitive limekiln needs only a mention, but a modified
form consists of a vertical steel cylinder lined with
firebrick up to 10 feet in diameter and 50 feet in height.
The fuel is kept apart from the limestone in two fire-
places built in the sides, and so arranged that the hot
gases pass through the kiln and the ashes fall into a
separate ashpit below.
In the chamber type of kiln a series of chambers aie
built round a central stack and connected to it by flues.
The chambers, which are alternately charged with fuel
and limestone, are so arranged that any one may be
disconnected from the flue and separated from the other
chambers by partitions as required. Thus the lime may
be removed and the chamber recharged and set into
operation with considerable saving of fuel. In the gypsum
industry the kiln takes the form of a beehive with a
flat floor resting on a cylindrical base in which are
doors, each opening into a furnace. The kiln, which is
built of brick, is about 16 feet high and 30 feet in dia-
meter, and is arranged so that the hot gases are led
through flues on the inner side of the kiln down through
the material to an underground flue to the stack. As
a rule a white heat is maintained for three days, when the
lumps are removed and reduced to a fine powder for the
purposes of cement.
The rotary calciner (Fig. 117) used in the gypsim
168 INTRODUCTION TO CHEMICAL ENGINEERING
industry consists of an inclined cylinder 30 to 70 feet long
and 5 feet or more in diameter, set at a small angle to the
horizontal and caused to revolve slowly, having roller
bearings and trunnions and a heavy geared driving
wheel at one end. The cylinder is housed in a brick
DISTILLING APPARATUS 169
casing, in one part of which is situated the furnace, the
bottom part consisting of chambers with perforated
tops, about 2 feet above which is a perforated arch.
Through these perforations cool air passes, and mixes with
the hot gases, which are drawn by a fan connected
to the top end of the cylinder through the bottom chamber
and up the cylinder as the material passes down. A
certain amount of the gases passes through the arch into
the cylinder through ducts arranged in the length of the
cylinder and protected on the inside to prevent any loss
of material. Lifting blades running the entire length of
the cylinder keep the material in motion during the ten
minutes or so that it takes to travel the whole length.
By the use of a recording thermometer at the outlet
and the operation of the cool air damper a steady tempera-
ture can be maintained throughout the operation.
In the Portland cement industry rotary kilns are used
up to 150 feet in length, made of J-inch steel plates with
single strap butt joints and lined with some refractory
material. The cylinder, which has an inclination of
about 1 in 15, is driven near its middle by a train of
gears at a speed of from 25 to 55 revolutions an hour.
The top of the kiln, where there is a water-cooled feeding
device, projects into a flue connected with a firebrick-
lined shaft provided with a door or damper. The lower
end of the kiln has a removable firebrick cover having
openings for the discharge of clinker and for the heating
apparatus, which may consist of a jet of powdered coal,
worked by a fan or compressor, which partly supplies
the air necessary for combustion.
The Muffle Furnace. — When it is necessary to calcine
material without having contact with the hot gases the
muffle furnace is employed. The muffle itself is usually of
firebrick, and the flues are arranged so that the hot gases
first pass beneath the bottom of the muffle and then over
the top back to a point near the grate, and thence to the
chimney. In cases where any gas has to be discharged
170 INTRODUCTION TO CHEMICAL ENGINEERING
from the muffle a pipe is fixed to the top to allow of its
ready escape.
The Reverberatory Furnace. — In this type of furnace,
which has extensive application, the material treated is
exposed to the direct action of the gases from the fire.
It consists of an arched brick chamber lined with fire-
brick, at one end of which is placed a grate for heating,
and at the other end a chimney to carry off the waste
gases. The material is placed on the floor of the arched
FIG. 118. — SIEMENS REGENERATIVE FURNACE: DIAGRAM.
chamber and heated directly by the hot gases from
the grate, which are deflected upon it by the arched
roof. By regulating the supply of air an oxidizing or
reducing action can be obtained at will. To obtain the
former effect the firebars must be set well apart and the
fuel fed in a thin layer, and for the latter effect the
firebars must be set closer and the fuel fed in so as to form
a thick layer.
The Regenerative Furnace. — Fig. 118 is a diagrammatic
illustration of this type of furnace, which owes its in-
DISTILLING APPARATUS 171
ception to Siemens. The object of this furnace is to
recover as much heat as possible from the flue gases.
To effect this the furnace is connected with a number
of chambers or flues filled with firebrick, through a
certain number of which the hot waste gases pass, thus
(riving up their heat to the firebrick packing. After
about twenty minutes to half an hour the waste gases are
diverted by means of dampers to a fresh set of cool flues,
and at the same time the incoming gas and air is made
to pass through the heated flues and recover the heat
therein. In the glass -making industry the pot furnaces
are frequently of this type, although the recuperative
furnace, in which there is no reversal of draught, but
the incoming gas is made to pass over fireclay tubes
heated by the waste gases, is also in use.
Roasting Furnaces.— The chemical industry of this
country requires enormous quantities of sulphuric acid,
the production of which depends upon the oxidation of
huge quantities of sulphur. A great proportion of this
sulphur is obtained by heating ores which contain sulphur,
in specially constructed furnaces, which aim at producing
sulphur dioxide gas in as pure a state as possible.
Fig. 119 is an illustration of a mechanical roasting
furnace for copper and iron pyrites, spent oxide, gold
ores, silver lead ores, concentrates, zinc ores, etc., made
by the Harris Furnace Co., Ltd., Sheffield.
The furnace is built in vertical sections separated by
division walls, and each section is divided into the desired
number of tiers by arched floors. In each section there
are two vertical rabble shafts mounted on substantial
ball-bearing pedestals, which are adjustable for height
and separated from the interior of the furnace by an
arched opening accessible from the outside at any time.
There are two types of shafts used, known as the " A "
and " B " types, illustrations of which are shown in
Fig. 120 and Fig. 121 respectively. The " A " type is
so constructed that it can be easily taken to pieces, or any
172 INTRODUCTION TO CHEMICAL ENGINEERING
one arm can be replaced without interfering with any
other part of the shaft, by simply removing the bolts
in the top and bottom joints. The shaft has a separate
flow of water to each arm, and a return to the centre of the
FIG. 120. — " A " TYPE SHAFT FOR ROASTING FURNACE.
174 INTRODUCTION TO CHEMICAL ENGINEERING
shaft, through which water is carried up, whence it is
taken off at a lower level than the feed into the pan,
and is then conveyed through suitable piping, to be
disposed of as desired.
When only hard water is available for cooling, type
" B " shaft is used, as the " A " type is liable to become
choked with lime deposit, which, stopping the flow of
cooling water, allows the arm to become red hot and
possibly be burnt off, thus necessitating the closing
down of the whole section. In the " B " type the arm is
detachable from the shaft by removing the first rake
in the arm, which rake also acts as a locking piece to the
cover plate on the front of the boss. The cover plate
not only holds the arm in position, but also prevents
any gases from the furnace entering the shaft, or air in the
shaft reaching the furnace. The arm can be either air
or water cooled on any or all of the hearths, and in the
latter case the water pipes are lowered into the arms
from the top of the shaft, the joint thus being inside
the shaft and obviating the possibility of water getting
inside the furnace. The very simple construction on
the top of the shaft is so arranged that no arm but the
one to be operated on need be interfered with, the water
pipes being lifted from the arm projection inside the
shaft. The first rake and cover plate having been re-
moved (working from the furnace door), the arm is then
free of the shaft and can be drawn out and replaced,
and the necessary repairs to the defective arm carried
out as desired. Each arm has at least a 1 J-inch water way
and a separate flow and return governed by valves at the
top of the shaft, so that the heat from each arm can be
tested and the growth of deposit observed. The water
is taken off at the bottom of the shaft, thereby causing
a current of cold air to travel up the shaft, and also
relieving the arms of any pressure. When air-cooling
is used the air enters the shaft at the bottom, and, passing
through an opening in the bottom of the arm, it travels
, Water-
cooled
Arm.
Air-
cooled i
Arm.
FIG. 121. — "B" TYPE SHAFT FOR ROASTING FURNACE.
176 INTRODUCTION TO CHEMICAL ENGINEERING
along and returns overhead; thence it re-enters the shaft
from the top side of the arm and travels upwards, finding
its exit at the top of the shaft. The illustration shows
the lower arm being air-cooled and the upper arm water-
cooled.
The rakes are of the slip-on type, and can be easily
changed in a few minutes; consequently the pattern or
pitch of the rakes can be so arranged that different
depths of mateiial can be maintained on each bed without
interference with the discharge. Thus on the top bed,
where the combustion is most rapid, a shallow working
load can be maintained, while on the lower beds, where
the sulphur is partly burnt off and it becomes necessary
to retain all the heat possible, a deeper load can be
kept with advantage. This interchangeability of the
rakes is a great advantage in the roasting of spent oxide
and different grades of copper or iron pyrites.
The ore to be roasted is fed through a suitable feeding
arrangement in the roof of the furnace, adjacent to the
centre of one of the shafts in the uppermost tier. The
rakes on the first arm are so arranged that the ore is
gradually moved towards the circumference of the arm
path, whence it comes under the control of the other arm
in that tier, the rakes on which are arranged to move
the ore towards the centre of the arm path, whence the ore
passes through a feed opening to the next tier. This
operation is repeated in each tier until the ore is finally
delivered from the lowermost tier into a discharge spiral
conveyor or other suitable arrangement for dealing with
burnt ore. The gas apertures are arranged at alternate
ends of the hearths, and rakes are provided on the roof
of the furnace for utilizing waste heat for drying damp
ore or other material. In the event of repairs or renewals
being necessary, the section affected is cooled by stopping
the feed to the same and opening fully all its air doors,
without interfering with the work of the remaining
sections.
DISTILLING APPARATUS
177
Driving belts are dispensed with throughout the whole
furnace, and the separate sections are driven by claw-
I I i ' i i i lii'i
i I i J_J J._i 1 J.-I l__l__w
FIG. 122. — H.H. TYPE MECHANICAL ROASTING FURNACE.
clutch gears from a main shaft, which is in turn driven
from the engine, motor, or existing line shafting. The
12
178 INTRODUCTION TO CHEMICAL ENGINEERING
sections which are independent of one another require
about 1 b.h.p. per vertical shaft, and the additional heat
obtained in the Glover tower through having no separate
dust chamber enables the whole make of the plant to be
concentrated in the tower into acid of from 145° to
150° (T.).
The following are the capacities for a twenty -four hours'
roast of various sizes of the Harris furnace :
Copper Pyrites or
Ground Space.
44 feet x 20 feet. 28 tons.
33 „ x20 ,, 21 „
23 „ x20 ,, 14 ,,
12 „ x20 „ 7 „
Australian Zinc Blende.
22 feet 6 inches x 22 feet. 12 to 14 tons.
One man can easily attend to two or three furnaces,
roasting from 45 to 60 tons of ore per twenty-four
hours.
Fig. 122 illustrates the type of furnace made by
Huntington, Heberlein and Co., Ltd., London. It has
a capacity of 5 to 5J tons of 48 per cent, pyrites in
twenty -four hours, according to the composition of the
ore, and has an air-cooled shaft with natural draught
and a top drying shelf. The furnace has a diameter of
13 feet, requiring 370 square feet of floor space, and has
seven hearths giving a total hearth area of 624 square
feet. The power required is f h.p. and a dust-proof dis-
charge and funnel are also provided when necessary.
CHAPTER VI
WATER TREATMENT PLANT
THE attempt to obtain a universal solvent engaged the
major portion of the time of a great many alchemists.
Had they been content with a comparatively slow action
and with dilute solutions, they would have found that
water was the nearest approach to their ideal that it was
possible to find. This solvent property of water, to-
gether with the operation of the laws of mass action,
should always be present in the mind of the chemical
engineer. All natural waters are more or less impure,
and the nature and extent of the purification required
depends upon the uses to which they are put, which may
be roughly classified as follows: (1) Food purposes;
(2) the manufacture of industrial products; and (3)
steam raising.
The method of removing insoluble material and matter
held in suspension has already been dealt with in con-
sidering filtering apparatus, so that the matter of concern
at the moment is the removal of those dissolved substances
by methods other than those of distillation, also previously
mentioned.
The presence of dissolved minerals in natural waters
is the cause in boiler-room practice of the trouble of
scale formation, corrosion, and foaming.
From the nature of the substances concerned, waters
containing a certain amount of inorganic impurities are
termed hard, and the process resorted to for their purifica-
tion is called water-softening.
When hard water is evaporated the mineral impurities
dissolved in it are precipitated, and settle upon the sbeJJ
179
180 INTRODUCTION TO CHEMICAL ENGINEERING
and tubes of boilers as hard scale, the rate of incrustation,
its composition, hardness, and density, depending upon
the quality of the water, the steam pressure, and other
circumstances.
If we take the steam requirement of the average
engine as being equivalent to 2 gallons of water per
horse -power indicated per hour, and that the water
contains 15 grains of scale-forming salts per gallon, which
is less than is commonly the case, the scale deposited
in a working day of ten hours amounts to about f ounce
per i.h.p.
Calcium and magnesium in the form of carbonates and
sulphates form about 90 per cent, of the scale commonly
found in boilers, which forms an insulating medium
with a high power of resistance to heat. Professor
Rarikine estimates that the heat resistance of carbonate
of calcium is seventeen times that of iron, and of sulphate
of calcium forty -eight times that of iron. He therefore
calculates that J inch of average scale necessitates the
expenditure of 16 per cent., J inch of 50 per cent., and
| inch of 150 per cent., extra fuel to generate the same
amount of steam, as compared with a clean boiler.
It has been ascertained in this connection that, whereas
the temperature of a clean boiler plate is only 350° F.,
the temperature of the same plate covered with | inch
of scale is 750° F.— i.e., 400° F. above the temperature
actually required to convert the water into steam, in-
volving the danger of collapse of the furnace crowns.
Corrosion or pitting is mainly caused by the presence of
free acids in the original water or formed by the inter-
action of the solutes under certain conditions of tem-
perature and pressure obtained in the boiler. Chlorides
of the metals are particularly ready to dissociate and form
hydrochloric acid in the presence of moisture, and the
results of mass action become apparent wherever different
phases of iron of the boiler are in contact, such as at the
rivets. The most abundant chloride found in watei
WATER TREATMENT PLANT 181
is that of magnesium, and it is the frequent cause of
serious trouble in boilers. Nitrates are also found, and
also exert a similar corrosive action.
Foaming is essentially the formation of large masses
of bubbles on the surface of the water in the boiler and
in the steam space above, which do not break readily
and release the steam. The strength of the film is
dependent upon the nature of the water in the boiler, the
steam pressure, and other conditions present, but as a
rough guide the tendency to foam is measured by the
concentration of sodium and potassium salts in the
water. It is obvious that since surface tension is so
readily a variable quantity, the prevention of foaming
largely depends upon the skill and experience of the
operators.
The following mineral impurities are of common
occurrence in water:
Calcium Carbonate. — In its pure state it is only slightly
soluble in water. It, however, dissolves freely in water
containing carbonic acid, forming calcium bicarbonate.
When water containing calcium bicarbonate is heated,
the carbonic acid is driven off and the normal carbonate
is precipitated. Calcium carbonate by itself forms a
comparatively soft scale, but with other ingredients in the
water forms a hard scale.
Cakium Sulphate. — This forms a hard flinty scale, and
attaches itself very firmly to the boilers.
Calcium Chloride. — This substance is very soluble in
water, and will not cause incrustation or deposit, but,
being a chloride, it will readily react to form calcium
sulphate, and also cause corrosion.
Calcium Nitrate. — This has a similar action to the
chloride, and readily forms the sulphate, and also causes
corrosion .
Magnesium Carbonate. — Has a similar action to calcium
carbonate, its normal carbonate being sparingly soluble,
while its bicarbonate is much more soluble.
182 INTRODUCTION TO CHEMICAL ENGINEERING
Magnesium Sulphate. — It is very soluble in water and
does not form a scale, but in the presence of calcium
carbonate both calcium sulphate and magnesium car-
bonate are formed as scale.
Magnesium Chloride. — This does not form a scale, but,
being a chloride, it readily forms hydrochloric acid,
which causes corrosion .
Sodium Sulphate. — Is a very soluble alkaline salt
which does not form a scale, but increases the tendency
to foaming.
Sodium Chloride. — It behaves similarly to the sulphate,
and is fairly stable at boiler temperatures, but, being a
chloride, must be reckoned with accordingly.
Iron. — This is usually present in the form of the
bicarbonate, which readily gives up its carbon dioxide
and is oxidized to the hydroxide, forming a gelatinous
scum. In acid water the sulphate may be present,
but it is very readily treated.
Alumina. — Is found in small quantities in most
waters .
Silica. — Is found in nearly all waters, and when
present in appreciable quantities it unites with other
ingredients to form an extremely hard scale.
Carbon Dioxide. — This is found in all natural waters
in excess of that required to form the bicarbonates
found in solution, and is the cause of a certain amount
of corrosion.
Hardness which is caused by the presence of such
substances as the bicarbonates which are precipitated
on boiling is known as temporary hardness, the other
salts producing permanent hardness, the two together
making up the total hardness of the water.
Messrs. Sofnol, Ltd., Greenwich, who are experts in
water- softening, very truly remark that softening is not
so much a mechanical as a chemical process, and too
much attention is generally paid to the mechanical part,
whilst the chemistry is allowed to take its chance. The
WATER TREATMENT PLANT 183
function of the machine is to bring the water into in-
timate contact with the proper amount of the chemicals,
to remove the precipitates formed, and to deliver a clear
effluent.
The chemistry of the process is the formation of new
combinations, which, being insoluble, allow the machine
to perform the mechanical part and deliver a clear,
softened effluent.
The chemicals must be —
1. In a fine state of division.
2. As light as possible.
3. Quickly soluble.
4. In proper proportions.
5. Uniform in composition.
Further, they must act immediately, do their work
as quickly as -possible, and yield precipitates which
readily settle.
If these conditions are fulfilled and the machine brings
the chemicals into intimate contact with the water, then
the water will be properly softened; but if these con-
ditions are not fulfilled the process is a haphazard one,
and the results are neither concordant nor satisfactory.
The process of softening a carbonate water is essentially
different from that required by a sulphate water. In
the first case the withdrawal of the free carbonic acid
removes the solvent of the carbonates ; they thus become
insoluble and the water loses its hardness. On the other
hand, the sulphates, being dissolved by the water itself,
are not eliminated by the removal of the carbonic acid,
and some other material requires to be added to cause
them to become insoluble. Carbonate of soda is gener-
ally used for this purpose, but this cannot act so long
as free carbonic acid remains in the water. Each grain
of free carbonic acid means that every 1,000 gallons of
the water will put 5 ounces of carbonate of soda out
of action and prevent it doing its work as a destroyer of
184 INTRODUCTION TO CHEMICAL ENGINEERING
sulphate of lime and its analogues. Hence, unless the
free acid is removed there is a great waste of soda, and the
softened water has a high residual alkalinity, which will
render it unfit for many purposes and manifest itself un-
pleasantly in the boilers.
Water -softening being a chemical operation, the factors
of proportion, time, and temperature apply, and practical
experience serves to show the many difficulties to be
overcome. A great deal depends upon the selection of
the proper type of plant for the work in hand, and when
the water exceeds a moderate hardness the lime and soda
type becomes a necessity. This type of plant, when
properly designed and with due attention, will give satis-
factory results.
There are two general types of lime-soda water -softening
plants — the intermittent and the continuous types. The
intermittent type, which possesses several advantages,
usually consists of two large tanks, each tank holding
at least four hours' supply of water. The process works
intermittently, so that when one tank of water is being
softened the other tank is being filled with hard water.
The volume of water in the tank is known, and to this
measured volume of water of known hardness a weighed
quantity of lime and soda is added — the lime in the form
of milk of lime and the soda in solution form. The
contents of the tank are then thoroughly mixed and
allowed to settle, when the calcium and magnesium
compounds fall to the bottom of the tank. The clear
softened water may then be drawn off for direct use or
into a store tank, and the precipitated solids drawn
off by an outlet in the bottom of the tank.
Owing to the facilities for control, this is probably the
most exact method of water-softening, and, with an
ordinary hard water, practically the whole of the hard-
ness-forming salts can be removed, and the softened
water contains the minimum excess of lime and soda.
In a works where there is sufficient room for tanks, and
WATER TREATMENT PLANT 185
first cost is not essential, it forms probably the most
satisfactory plant.
The continuous -process plant, taking less room and
requiring less attention, has been more developed. For
successful working it must conform to the following
conditions :
1. The lime and soda control system must work
accurately.
2. The tank capacity must be large enough to enable
the chemical reaction to complete itself fully.
3. The lime and magnesia sludge must be easily
removable from the plant.
Fig. 123 gives a view of a rectangular form of the
" Lassen-Hjort " automatic water-softener made by the
United Water Softeners, Ltd., London.
This apparatus is designed to perform the following
functions :
1. Measurement and proportioning of the water.
2. Measurement and proportioning of the chemicals.
3. Settlement and filtration of the precipitate.
4. Regulation of the supply of both untreated and
softened water.
The main parts of the apparatus are the mixing and
measuring apparatus and the settling tanks and filters.
The measuring apparatus (Fig. 124) operates by leading
the hard water into the plant by a pipe which alternately
fills each of the compartments of a two -chambered tipper
oscillating on a shaft carried in bearings. When one of
these compartments is full of water the disturbance
of equilibrium causes the tipper to overbalance, and, by
doing so, to discharge its contents into the tank in which
it is suspended. At the same time the other compart-
ment of the tipper is brought under the orifice of the
inlet pipe and filled in its turn with hard water, to be
discharged in the same manner when full. As a definite
quantity of water is passed at each oscillation, by at-
taching a counter to the tipper shaft, the quantity of water
186 INTRODUCTION TO CHEMICAL ENGINEERING
passing through the plant can be accurately deter-
mined. *
At each discharge of water from the tipper into the
tank a corresponding amount of water is displaced from
this tank through a standpipe and shoot into the re-
action chamber, and here it receives at the same moment
WATER TREATMENT PLANT
187
the requisite charge of chemical solution from the
circular container affixed to the side of the tipper
semi-
tank.
This is effected by the positive discharge valve placed
in the bottom of the chemical container, which is opened
188 INTRODUCTION TO CHEMICAL ENGINEERING
at every movement of the tipper, and caused to deliver
into the reaction chamber the exact amount of softening
reagent (in the majority of cases a mixture of lime and
soda ash) required to soften it to the guaranteed figure.
The valve can be adjusted to deliver any specified
quantity of reagent required by the volume of water
in the tipper.
In the illustration of this valve (Fig. 125), A is a
cylinder fixed to the bottom of the chemical reservoir,
into which screws an adjustable cylinder B, secured in any
desired position by the back nut C. Within these two
cylinders work two valves, D and E, the latter screwing
on to a tail piece F, projecting from the valve D. The
pitch of the threads on this tail piece and the adjustable
cylinder being the same, any movement of the cylinder
B results in a corresponding movement of the valve E,
owing to the valve E having a feather G working in a
key -way H cut into the cylinder B. The valve D is
provided with a flat face and a piston body, which latter
prevents any chemical solution being admitted into the
adjustable cylinder until the lower valve E has closed
the outlet ports J. The operating gear consists of a
double lever K fixed to the rocking shaft L of the tipper.
These levers are fixed to the vertical valve spindle by
two loose links M and trunnions N, clamped against a
screwed sleeve 0 by the lock nut P. These levers, when in
operation, impart an up-and-down motion to the valve.
The screwed sleeve O works between rollers Q carried
on to the bridge R. The object of the weight 8 is to keep
the valve D tight on its seat.
The oscillating receiver is prevented from tipping
until it contains a predetermined quantity of water by
means of a locking gear constructed as follows: To the
end plate of each compartment of the tipping bucket
is attached a bracket carrying a ball float and lever,
and a vertically sliding rod actuated by these, which
latter at a certain height of the water lifts a lever
WATER TREATMENT PLANT
FIG. 125. — POSITIVE DISCHARGE VALVEJFOR WATER-SOFTENING
APPARATUS.
190 INTRODUCTION TO CHEMICAL ENGINEERING
fulcrumed on the angle -iron edge of the tank, and
engaged with a notch provided on the bracket before
mentioned. On further rising, the lever is disengaged
from the notch and the bucket tips. A link from the end
of the tipper shaft operates a counter, which registers
the number of tips.
The heavier portion of the precipitate produced by the
addition of the measured quantities of softening reagents
to the water settles to the bottom of the reaction chamber,
whence it is removed daily by opening the sludge cocks.
The finer precipitate, which will not settle, is retained in
filters consisting of wood fibre packed between two rows
of wood bars. The filters require cleaning, on an average,
about every two months, which operation is effected
by removing the top bars, by loosening the fibre, and
washing it through with water.
The chemical container of the softener is designed, in
the majority of cases, to hold eight to twelve hours'
supply, when it can be refilled from a mixing tank
situated in any convenient position.
Fig. 126 shows a cylindrical type of softener which is
useful where soft water is required to be delivered at a
height. The operations involved are the same as pre-
viously described, but the water from the measuring
apparatus passes down a central tube, depositing preci-
pitate as it slowly rises up the tank and through the
filters to the storage tanks.
Permutit. — This is the name given to an artificial
zeolite having the formula A^Og.lOS^.lONagO, and
marketed by the United Water Softeners, Ltd.,
London.
The valuable property of this substance is the readiness
with which it will exchange its sodium for calcium and
magnesium, the reaction being reversible, and therefore
solely a question of mass action. Therefore, if hard water
is passed through a bed of Permutit, a calcium-magnesium
Permutit is formed, and only sodium salts pass through ;
WATER TREATMENT PLANT
191
but although the hardness is removed, the total amount
of solids remains the same.
When the sodium of the Permutit is exhausted by the
FIG. 126. — CYLINDRICAL WATER-SOFTENING APPARATUS.
replacement with calcium and magnesium, it is treated
with a solution of salt, which by mass action converts
the Permutit back to its original condition.
192 INTRODUCTION TO CHEMICAL ENGINEERING
FIG. 127.— PERMUTIT WATER-SOFTENING APPARATUS: DIAGRAM
WATER TREATMENT PLANT 193
The simplicity of the chemical reaction finds its
counterpart in the extreme compactness and convenience
of the apparatus requisite for the softening process.
A Fermutit softener, of which a sectional view is given
in Fig. 127, consists simply of a cylinder to contain the
Permutit, connected with a receptacle holding the salt
solution for regeneration, and fitted with the necessary
valves for controlling the water flow.
The design of the plant and the nature of the Permutit
process favour the carrying out of the softening under the
ordinary pressure of the water mains, thus giving this
system the great advantage that it can be connected to
the water main in any position without the necessity of
pumping twice, or of arranging for a gravity flow of
softened water.
The removal of iron from water is accomplished by a
Permutit in wrhich the sodium is replaced by an oxidized
product of manganese which oxidizes the iron to the
hydrate which is retained by the filter. When the
oxidizing properties of the Permutit are exhausted they
are restored by means of a solution of potassium per-
manganate.
The Permutit process will give water of zero hardness,
which is of inestimable advantage in many industries,
such as silk and cotton dyeing and bleaching, wool
scouring, laundry work, etc.
For food and drinking purposes water is sterilized by
injecting liquid chlorine and removing the excess by
sulphur dioxide, and the plant is mostly of the nature
with which the chemical student is already familiar.
CHAPTER VII
THE CONTROL OF TEMPERATURE
IN most chemical industries reactions have to be carried
out at definite temperatures, and as these temperatures
are in most cases well above the normal atmospheric
temperature, some means of temperature control is
necessary, so that the process may be worked efficiently
with the least possible consumption of heat units. The
commonest form of heating is by means of steam, and
James Baldwin and Co., Keighley, have devised a system
of temperature control which, applied to steam, acts
independently of the boiler and controls the steam supply
during boiling and other processes. This device is known
as the "Isothermal " (electric -mercury thermometer -con-
trol) valve, which is claimed to regulate automatically
temperature to within 1°F.
In the case of steam the supply is controlled by elec-
tricity, so that the parts of the control, consisting of
the valve, thermometer, and the transformer, may be
separately fixed in suitable positions.
The control valve, of which a section is shown in
Fig. 128, is fixed in a horizontal position, on the steam
pipe on the outlet side of the usual steam stop valve, the
internal parts operating vertically, so that when not
in use the valve is free from pressure. As illustrated
in the section the valve is in the normal position, closed,
there being no pressure. Instantly steam is admitted
the action of the pressure upon piston C lifts the piston
valves D D full open, allowing a full-bore passage for the
steam at any or varying pressures. The valves D D are
of the equilibrium type, and are cast on the same stem
194
THE CONTROL OF TEMPERATURE
195
as the pistons B and C, the piston C being smaller in
diameter than the piston B. In the cover of the valve-
FlG. 128. " ISOTIIERMAL " STEAM VALVE.
body is a small valve A, which is in the centre of a
solenoid. There is a connecting pipe F to the valve A
196 INTRODUCTION TO CHEMICAL ENGINEERING
from the inlet or pressure side of the pistons C, D D.
When pressure is admitted to the valve the pistons
C, B are forced up against the cover or end of the cylinder
which forms the outlet side of the small valve A, and
the valves D D are fully opened. If the valve A be
FIG. 129. — "ISOTHERMAL," THERMOMETER.
raised from its seating, the inlet pressure passes along
the pipe F, and, acting on the large piston B, forces down
into their seatings the valves D D, shutting off the
steam supply. If the small valve A be allowed to fall
on to its seating, the pressure upon the large piston B
is removed (a small escape for this pressure is situated
THE CONTROL OF TEMPERATURE
197
between the valve A and pis ton B), and the boiler pressure
acting on the piston C opens the valves D D full bore.
It will be noted that the pistons B, C and the valves D D
are operated by steam pressure, while the valve A in the
solenoid is operated by electricity.
A mercury -column thermometer acts as an electric
switch, and is specially constructed, having terminals
for connections, as shown in Fig. 129. The thermometer,
suitably calibrated, is fixed in a selected position on the
vessel of which the temperature of the contents is to be
THtRMOMEUR
TRANSFORMER ft KELAV
FIG. 130.
G.A. " ISOTHERMAL " TEMPERATURE CONTROL
APPARATUS.
controlled. The bulb of the thermometer is connected
to one terminal, and the top is closed by a cork carrying
a platinum wire which can be adjusted so as to make
contact with the mercury at any desired temperature.
This switch operates the solenoid in the valve through
a transformer and relay connected up as shown in Fig. 130,
the current required for each valve being about 0'6
ampere at 110 volts, and for the thermometer 15 milli-
amperes at 1 volt.
In case of failure of the current supply the valve is
free to open, and the steam supply can be manipulated by
198 INTRODUCTION TO CHEMICAL ENGINEERING
hand in the ordinary manner, or the valve can be con-
structed to shut off automatically the steam supply
until the current is again restored.
The very wide range of application of this system of
temperature control includes the steam heating of factories.
oz:
STILL
FIG. 131. — " ISOTHERMAL " CONTROL OF STILL.
etc., hot water heating, and the cooling of vessels, by passing
cold water to maintain a lower temperature required in
many chemical processes. Fig. 131 is a diagram showing
its application to a still, and Fig. 132 its application
to a jacketed pan. An exceedingly important application
is its use in a dye vessel for dyeing piece goods, to which
THE CONTROL OF TEMPERATURE
199
it is connected as shown in Fig. 133. It can also work
as a reducing valve for maintaining an exhaust steam
pressure at a constant pressure of, say, 5 pounds per
square inch, by admission of high-pressure live steam as
shown in Fig. 134. Applied to a vulcanizing press, pan,
or cylinder, as shown in Fig. 135, it will maintain a constant
temperature and reduced steam pressure, or, as shown
in Fig. 136, maintain the blast to gas producers at
FIG. 132. — '* ISOTHERMAL " CONTROL OF STEAM-JACKETED PAN.
constant temperature and composition. Fig. 137 shows
how this apparatus can be used for the automatic regu-
lation of the temperature and humidity of cotton-spinning
and other rooms. Fig. 138 is a diagram of the valve used
for regulating the temperature of superheated steam by
the admission of saturated steam, and Figs. 139 and 140
illustrate in section the valve for regulating the gas
supply for. sizes -fa inch to J inch bore and f inch to
200 INTRODUCTION TO CHEMICAL ENGINEERING
FIG. 133. — " ISOTHERMAL " CONTROL OF DYE VESSEL.
MAIN STEAM PIPE
120 LBS PRESSURE.
FIG. 134. — "ISOTHERMAL" CONTROL OF EXHAUST STEAM.
THE CONTROL OF TEMPERATURE 201
FIG. 135. — " ISOTHERMAL " CONTROL OF VULCANIZING PAN
»
FIG. 136. — "ISOTHERMAL" CONTROL OF BLAST FOR GAS PRODUCER.
202 INTRODUCTION TO CHEMICAL ENGINEERING
FIG. 187. — " ISOTHERMAL " CONTROL OF COTTON-SPINNING ROOMS
ii
I
f
'
—
/M
-'
/
hi/////////
Ess
S^-
->
1
/,//////////
3 i
s^n
i
FIG. 138. — " ISOTHERMAL " SUPERHEATED STEAM VALVE.
THE CONTROL OF TEMPERATURE
203
2 inch bore respectively for gas-heating systems, and
automatically regulating the temperatures up to 600° F.
It may be used to regulate a fan so that it operates at any
desired temperature, or as a steam main isolating valve,
or for winding engines and for other purposes too numerous
to mention.
FIG. 139. — " ISOTHERMAL " GAS
VALVE.
FIG. 140. — " ISOTHERMAL, " GAS
VALVE.
Refrigerating Machines. — The problem of maintaining
temperatures below the normal atmospheric temperature
demands the use of refrigerating machinery such as is
made by the Lightfoot Refrigeration Co., Ltd., London.
The cold storage of food is familiar to all, but this
forms only a portion of the field of application of the
mechanical production of cold. In dyeworks refrigerating
machinery is indispensable for producing fast colours
and even for colouring with certain dyes. The supply
of natural silk is considerably augmented by its use to
regulate the hatching out of the eggs to suit the supply
of food available for the silkworms, while artificial silk
204 INTRODUCTION TO CHEMICAL ENGINEERING
also depends upon it in the process of converting pulp
into silky fibre. It forms an essential part of the equip-
ment of the bacon -curing factory, the brewery, and the
margarine factory, to name but a few.
In the Lightfoot system of refrigeration cold is produced
by the evaporation of liquid ammonia or carbon dioxide,
the vapour formed being afterwards condensed and used
over again. Fig. 141 is a diagram illustrating the
principal parts of which each machine consists.
REFRIGERATOR
COJNDEINSER
_J
RELGULATiMG VALVE
FIG. 141. — DIAGRAM OF LIGHTFOOT REFRIGERATION SYSTEM.
The refrigerator consists of a series of coils of special
welded tube wound each in one length so as to avoid
inaccessible joints, inside which the liquid ammonia
or carbon dioxide, entering through a regulating valve,
is vaporized, thus reducing the temperature of the liquid
or material surrounding the coils.
The condenser, of which a normal open type is shown
in Fig. 142, consists of a series of coils of special welded
tubes, inside which the compressed vapours are cooled
and liquefied, the liquid being returned to the refrigerator
THE CONTROL OF TEMPERATURE 205
through the regulating valve. In order to cool the
vapours the condenser coils are either completely im-
mersed in water contained in a wrought-iron tank, or a
spray of water is caused to trickle over the surface of the
coils. The ammonia compressor, of which a small
horizontal type is shown in Fig. 143, consists of a cylinder
of tough, close-grained cast iron, with back and front
covers of the same material. These covers contain the
suction and delivery valves, which are turned out of solid
steel, each fitted into a box in which is formed the seat,
FIG. 142. — OPEN CONDENSER.
the arrangements being such that any valve can be readily
withdrawn and replaced without disturbing the con-
nections. The piston rod is of polished steel, secured
to the piston, and arranged to work through a special
stuffing box formed in the front cover. The cross-head
is of wrought iron, provided with a slipper with large
wearing surface fitted with bronze bearings, and the
connecting rod of polished wrought iron is fitted with
white metal bearing at the large end. The bed plate is
206 INTRODUCTION TO CHEMICAL ENGINEERING
of cast iron, upon which are formed the guides for the
cross-head and the bearing for the crank-shaft, which is
ring lubricated. Special oiling arrangements are pro-
vided for lubricating the piston and for preventing the
oil from passing over into the coils of the condenser and
refrigerator.
The carbonic acid compressor, of which a vertical type
is shown in Fig. 144, has a cylinder machined out of a
billet of solid steel, as also are the covers and all the
fittings. In the delivery valve cap is placed a safety
valve, which will relieve the pressure in the event of the
machine being started up with the delivery stop valve
shut, but which will only allow just sufficient gas to escape
to keep the pressure within safe limits. Cup leathers,
which are a frequent source of trouble, are avoided by
having a metallic packed piston and gland. In some
cases the cast-iron frame forms a casing in which are
contained the condenser coils, thus making a compact
machine.
Ice-making. — The appearance of the ice produced is
dependent on the water used and on the method of
freezing — e.g., ordinary fresh water frozen without agita-
tion produces opaque ice.
There are three systems on which ice is made viz.,
(1) the can ice system; (2) the cell ice system; and (3) the
plate ice system.
The can ice system employs a number of cans of lead-
coated steel, of rectangular section, tapering slightly from
top to bottom, in which the water to be frozen is placed.
These cans are placed in a tank containing brine sufficient
to immerse them to within 2 or 3 inches of their tops.
The brine is maintained at a temperature of 16° to 20° F.
by means of the refrigerator coils of the machine, and
circulated round the cans until all the water in the latter
is frozen. The cans are then removed in rows and dipped
in warm water for a short time to loosen the ice, so that
it may be tipped out.
FIG. 143. — HORIZONTAL, AMMONIA COMPRESSOR.
FIG. 144. — VERTICAL CARBON DIOXIDE COMPRESSOR.
208 INTRODUCTION TO CHEMICAL ENGINEERING
The can system of ice-making is the least expensive
in first cost, and also the most economical to work,
and the ice formed is either opaque or, by the adoption
of agitation gear, may be rendered clear to within about
5 per cent.
In the cell system a wooden tank is used, in which are
placed a number of galvanized iron cells from 10 to 14
inches apart, through which cold brine is circulated.
The space between the series of cells is filled with water
which, during freezing, is made to oscillate gently up and
down. Ice forms on the sides of the cells, gradually
increasing in thickness until the two plates of ice on
opposite cells join in the centre to make a single block.
Warm brine is then circulated through the cells to loosen
the blocks, which are lifted out of the tank by means of
hooks or ropes frozen into them . Cell ice is made in blocks
weighing from 4 to 6 cwt., and from 9 to 14 inches thick,
which are of convenient size for handling.
The plate ice system consists of placing flat hollow
walls of galvanized sheet iron in a large wooden tank
which is filled with the water to be frozen. Brine or
ammonia is circulated through the hollow walls, causing
a plate of ice to form on each side of them, the water
being agitated by means of compressed air. When the
plates of ice are of the desired thickness — say, 12 or 14
inches — warm brine or ammonia is pumped through the
walls, so as to loosen the ice and permit of its being
withdrawn from the tank. Plate ice is transparent, and
is the finest quality obtainable.
Cold Storage- — There are three systems in use, known
as — (1) The brine pipe system; (2) the direct expansion
pipe system; and (3) the air circulation system.
The brine pipe system may be used with advantage
for certain purposes, such as for cooling, fermenting and
storage cellars in breweries, bacon-curing beds, etc. The
pipes are placed under the ceilings and sometimes on the
walls of the rooms to be cooled, and cold brine from a
THE CONTROL OF TEMPERATURE 209
brine refrigerator is pumped through them. An advantage
of the brine system is that the large volume of cold brine
in the pipes will maintain the low temperature in the
rooms for a considerable time after the refrigerating
machine has stopped.
The direct expansion pipe system consists in placing
the ammonia or carbonic acid refrigerator coils directly
in the cold rooms, these coils being arranged in a similar
manner to the pipes in the brine system. The refrigerat-
ing agent is vaporized in these coils, thereby reducing
the temperature of the chamber.
The air circulation system consists in circulating a
current of pure, cold dry air at the desired temperature
through the cold rooms. There is entire absence of snow,
moisture, or drip in the rooms, and they are kept dry
and free from smell. The apparatus is simple and less
costly than the brine system, and owing to its compact
arrangement much larger cooling surfaces are obtainable,
with a consequently much increased efficiency. The
apparatus being external to the rooms, its full power
can be applied to any room without loss of efficiency,
whereas with the pipe system the pipes in the rooms that
are not being cooled are useless.
Lubrication is one of the practical difficulties of re-
frigerating machinery, and great care should be exercised in
the choice of a suitable lubricant. The condenser coils
of every machine should be examined at least once every
year, and should the slightest sign of corrosion or pitting
be discovered at any part of the coil, this part should be
carefully cleaned and painted with two coats of some
reliable bitumastic solution or protective paint.
The Absorption System. — In this system the cooling
effect is also produced by the evaporation of liquid
ammonia, but the cycle of operations is more extensive.
Aqueous ammonia is boiled by means of steam-heated
coils in a still, and the vapours pass upwards through
an analyzing column, where they meet a descending
14
210 INTRODUCTION TO CHEMICAL ENGINEERING
stream of strong liquor which robs them of some of their
moisture. The vapours pass thence to a dehydrator,
where complete drying is effected, and the ammonia
passes to the condenser to be liquefied and used for
cooling purposes. The expanded gas then enters an
absorber containing weak ammonia solution, which,
when strengthened, flows into a tank, and is thence
pumped to a heat exchanger, where it is raised to within
30° or 40° F. of the still temperature. It is then dis-
charged down the analyzer into the still, and is again
boiled and the cycle of operations repeated.
CHAPTER VIII
TRANSPORT
THE method adopted for the movement of material
from one part of a chemical works to another depends
upon the nature of the material, whether it is a solid or
a fluid. Fluids possess inherent advantages for trans-
portation, and it may be stated, in a general way, that
the development of the methods of transporting solids
has been along the lines of obtaining mechanical fluidity.
Conveying Solids. — The simplest, least efficient, and
most common method adopted for the conveying of
solids takes the form of the man-handled wheelbarrow.
A barrow weighs from 60 to 70 pounds, and with this a
man can move about J ton of material 100 yards per hour
over a level or slightly inclined surface . The proportion of
shovellers to wheelers is determined by the nature of the
particular job, but it may be taken that on an average
a man can wheel a barrow having a capacity of 2 cubic
feet about 200 feet a minute, and that it takes from
one to two minutes to fill the barrow and about the same
time to unload it. Barrows weighing up to 250 pounds,
and having a capacity of 9 cubic feet, are sometimes used,
and these are provided with two wheels as a rule. Steel
plate ways are frequently provided to ease the running
and to save the track when much barrow work is done
in any area.
Tipping Waggons.— For dealing with heavy loads a
more efficient method is to use light four-wheeled cars
provided with tyres suitable for running on steel rails
and drawn by a small locomotive or electric motor. The
211
212 INTRODUCTION TO CHEMICAL ENGINEERING
shape of the cars and the method of dumping vary
considerably, but the commonest forms are the V-shaped
FIG. 145. — SIDE-TIPPING WAGGON.
cars tor side tipping, as shown in Fig. 145, and end-tipping
cars, of which a sample is shown in Fig. 146.
FIG. 146. — END TIPPING WAGGON.
A cheap and efficient method is to run the cars on
runways or overhead rails carrying a small trolley,
from which the skip or bucket is suspended by means of
TRANSPORT
213
a hook. This method, which is illustrated in Fig. 147, has
a very wide range of application.
Aerial Wire Ropeways. — During the last decade there
has been a great development of this means of transport,
and there is a constantly increasing field of employment
for these ropeways, which are now designed with great
efficiency in working, combined with largely reduced
working costs, provided that care be exercised in adopting
the best type of ropeway for any given duty.
FIG. 147. — RUNWAY FOR MINE.
To give an account of this system even in outline
would take up more space than is available at the
moment. It may be very inadequately described as
consisting of a cable or wire rope, usually endless, whicli
is suspended from towers, and along whicli are run
carriages to which skips or buckets are attached. Fig. 148
illustrates the sectional portable ropeway, for inter -
works traffic, made by R. White and Sons, Widnes, who
are specialists in aerial wire ropeways.
Among the various systems of aerial ropeways reference
must be made to the single and the double rope system,
the former in which the single rope acts both as the
214 INTRODUCTION TO CHEMICAL ENGINEERING
hauling and the carrying rope, and the latter where one
rope does the hauling and the other the carrying of the
load.
FIG. 148. — INTERWORKS TRAFFIC: PORTABLE ROPEWAY.
In the single-rope system an endless rope passes round
a grooved driving wheel 6 to 12 feet in diameter at
one end, and at the other end round a similar wheel
TRANSPORT 215
kept up by a tension weight so that a constant tension
is put on the rope. About every 100 yards the wire is
supported by standards with cross -heads having four
sheaves on the loaded side and two sheaves on the empty
side. These sheaves are fixed to arms pivoted finally
at the centre of the cross -head itself, so that each sheave
as it receives the load is depressed and the weight of the
rope is distributed over the other three sheaves. This
arrangement can be clearly seen in the illustration of
FIG. 149. — STANDARD FOR SINGLE-ROPE SYSTEM.
one of the standards of a single-rope installation in
Fig. 149. Cars are attached to the rope by means of a
saddle, of which there are many types designed for quick
engaging and disengaging and for maintaining a firm grip
on inclines.
This type of ropeway is simple and efficient, and
for straight lines with easy gradients and moderate
loads is the best form, as it requires little attention
and is practically fool-proof. The defects are that it
216 INTRODUCTION TO CHEMICAL ENGINEERING
cannot automatically negotiate horizontal angles, nor
can the carriers be automatically carried round the return
terminal, from the outwards to the return rope.
The double -rope system has been greatly developed
to deal with severe gradients, heavy loads, automatic
angles, automatic tipping, and automatic return of the
carriers.
In this system two separate fixed ropes are used,
stretched from one terminal to the other, and supported
FIG. 150. — STANDARD FOR DOUBLE-ROPE SYSTEM.
on standards, as shown in Fig. 150, placed usually from
100 to 200 yards apart. One end of each rope is generally
fixed, whilst the other is led over guiding sheaves and
terminates in a heavy tension weight. Saddles are
fixed to the cross -heads about 6 to 12 feet apart, each
saddle being long enough to support 2 to 3 feet of the
rope, which lies in a groove. A fixed curved rail at each
terminal connects the ends of the fixed ropes and com-
pletes the circuit. The carriers travel along these
TRANSPORT 217
ropes by means of two or more wheels fixed into the
head of the carrier, and a separate and lighter rope is
used to haul the carriers along. This haulage rope is
driven and kept tight as in the single rope system, and is
supported at the standards by rollers.
Elevators. — The bucket elevator is the machine
commonly used when it is desired to lift material any
distance. It consists of a number of buckets fastened
to an endless belt or link chain which passes over a wheel
in the hood at the top and another wheel in the boot
at the bottom. Power for driving is applied to the top
wheel in order to keep the loaded side taut, and the
whole machine is lightly boxed in with wood or sheet
metal in order to prevent the dispersal of dust. Ac-
cording to the nature of the material operated upon,
the buckets are made of steel, copper, or malleable iron,
and may be perforated to admit of drainage or have a
toothed edge to assist in raising fibrous materials. For
working with pasty material L-shaped buckets are
the best, as they are readily emptied, but the V-shaped
bucket is more commonly used, as it has a larger capacity ;
in any case the buckets must be so arranged on the
chain or belt that at a given speed they discharge the
whole of their contents by centrifugal force as they go
over the top pulley. The material is discharged through
a spout in the hood, and the machine is capable of being
inclined so that the buckets give a clean discharge. When
the material to be lifted is in small particles and not of
a wearing nature, webbing or leather belts are used,
to which the sheet steel buckets are riveted. Such
machines are used in sizes having a bucket from 3 to 10
inches wide with an internal pulley from 9 to 24 inches
in diameter, driven at 90 to 40 revolutions per minute
When the material is in a rough condition a link chain,
such as is shown in Figs. 151 and 152, is used, and the
machine is driven at a slower speed than is the cast when
webbing or leather bands can be used. Some form of
218 INTRODUCTION TO CHEMICAL ENGINEERING
tightening device is located at either end, according to
whether interference with the feed or the drive is of
lesser moment. The boot is usually constructed so that
TRANSPORT
219
Jj
LL!
UJ
CO
i/)
LU
o
» D
-\CD
(f) -
"1
_i g
< r
2
O
D
CD
oc
O
220 INTRODUCTION TO CHEMICAL ENGINEERING
FIG. 153. — DUST-PROOF ELEVATOR.
the buckets can fill themselves by scraping up the
material as they travel round the bottom pulley, but it
is very desirable to give the buckets a direct and positive
TRANSPORT 221
feed when practicable. Owing to the slow speed, it
is found that with this type of elevator it is necessary
to give it a considerable inclination in order to get a
proper discharge, and for this reason the gravity type of
bucket is employed, so as to obtain a full load.
FIG. 154. — BOOT FOR ELEVATOR.
Fig. 153 shows a view of a dust-proof elevator made
by Edgar Allen and Co., Ltd., Sheffield, and Figs. 154
and 155 show the boot and hood on a larger scale.
Conveyors. — These machines are used for the continuous
transport of material, and are of various types, such as
worm, scraper, belt, apron, vibrating, and bucket, to
meet the need of transport of various classes of
material.
222 INTRODUCTION TO CHEMICAL ENGINEERING
Worm Conveyor. — The worm or screw conveyor con-
sists of a shaft carrying an endless screw formed by bolting
on metal nights. It rotates in a trough having a loose
lid, which will lift in case the material as it is carried along
should accumulate at any one spot and cause choking,
which would damage the screw. During the progress of
the material a certain amount of mixing takes place,
FIG. 155. — HOOD FOR ELEVATOR.
depending upon the type of worm employed, the selection
of which will be regulated by the nature of the material
conveyed. In some cases the worm is made of separate
blades or paddles bolted to the shaft, or a continuous
helix is made up of cast-iron sections threaded on.
The more modern form consists of a spiral attached to
the shaft at a few points, as shown in Fig. 156. This
TRANSPORT 223
is the type of worm employed in the spiral conveyor shown
in Fig. 157, made by the above-mentioned firm in all
sizes from 4 inches to 24 inches in diameter, and for
conveying from 1 ton to 200 tons per hour. These
machines are suitable for conveying cements, lime,
chalk, coal, ores, flour, phosphates, wheat, barley, seeds,
sugar, and other ground material, over distances up to
about 100 feet. The nature of the material transported
determines the pitch, which on an average is about half
the diameter of the screw, and the speed, which is highest
for the small sizes, which are driven at about 100 revolu-
tions per minute. The output of a spiral conveyor
depends upon the size of the machine, and the power
FIG. 156. — SPIRAL FOR WORM CONVEYOR.
required to drive is obviously a function of the length
of the machine, amount of the output in unit time, the
efficiency of the worm, and the coefficient of friction of
the materials used.
There are various other types of screw conveyors having
the worm fixed to the inner surface of the cylinder, which
itself revolves, but these are often combined with sifters,
mixers, and suchlike machines, which have already been
dealt with.
Scraper Conveyor. — In this type of machine, also known
as a drag or flight conveyor, the material is pushed along
by means of scrapers fixed to an endless rope or chain.
In this simple form it finds many applications in factories
where sludges have to be transported which would
TRANSPORT
225
rapidly settle and choke a trough through which they
flow.
A typical scraper conveyor is the suspended draw
type, which consists of a trough along which the material
is dragged by flights attached to cross-bars fitted with
shoes at the ends for sliding on iron tracks at each side.
By this means lateral motion is prevented and the scrapers
given the necessary clearance from the sides and bottom
of the trough. Fig. 158 illustrates this type as made by
Pott, Cassels and Williamson, Motherwell.
FIG. 158. — SCRAPER CONVEYOR.
In another type of machine the wearing shoes are
replaced by rollers, which also serve to give the necessary
clearances and to reduce friction.
A form of scraper known as a mechanical raker is
used for removing salt crystals as they are formed during
evaporation in large pans. It consists of a framework
suitably braced, and supported on both sides by sliding
shoes on tracks provided for that purpose. On this
framework, feathering blades are placed at intervals of
about 8 feet, and the whole is given a to-and-fro move-
15
226 INTRODUCTION TO CHEMICAL ENGINEERING
ment of about 9 feet, so that there is about 1 foot of
overlap in the travel of the blades. The engine used
has a cylinder of about 8 inches diameter, and with a
9-foot stroke, which it makes about every two minutes,
thus bringing up a load every four or five minutes.
Belt Conveyor. — The belt or band conveyor forms
a very efficient means of transportation, for it can be
erected in almost any position, and there is a great saving
in power over that required for worm conveyors for large
quantities over long distances .
It consists of endless belts of rubber (rubber -coated
cotton duck), cotton, or metal (wire mesh, etc.), which
may be flat or troughed, supported at intervals on rollers,
and motion is imparted by a head pulley and the slack
taken up by a foot pulley.
Although these machines were originally used for light
materials, they are now adapted for heavy work, and for
this purpose the rubber belt is designed for rough usage,
whereas the cotton belt is more often used for carrying
boxes and packages. The capacity of a belt conveyor is
determined by its width, which is usually from 10 to 20
inches, and its speed, a troughed belt being capable
of transporting two or three times that of a flat belt.
Fig. 159 shows the rollers for a three-pulley belt carrier
made by Edgar Allen and Co., the upper rollers on the
loaded side making the belt into a trough, and the lower
roller supporting the belt on the unloaded side. In the
ordinary way the material is discharged over the head
pulley by centrifugal force, but very often it is required to
tap off the material at some intermediate spot. This
function is performed by a travelling throw-off carriage
such as is shown in Fig. 160, which makes an S-bend
in the belt, so that the material is delivered over the top
pulley into a hopper placed alongside. With such an
arrangement it is necessary to keep the proper tension
on the belt, and this is usually effected in the ordinary
way of running the belt round a weighted pulley on the
TRANSPORT
227
228 INTRODUCTION TO CHEMICAL ENGINEERING
TRANSPORT
229
unloaded side. Material is fed to the belt by means
of a shoot, which is so adjusted that there is the minimum
relative motion between the material and the belt at the
point of feed, thus reducing the wear on the belt.
Apron Conveyor. — This machine, which is largely used
for handling light packages, consists of light slips of
wood or metal attached to link chains. An ordinary type
of conveyor will not work satisfactorily at a greater
inclination than about 25°; hence there are many
modifications of the belt to enable greater elevations
FIG. 161. — ELEVATOR AND CONVEYOR.
to be used. For packages and such-like the belt may be
provided with raised crossbars which prevent any back-
slip or tendency to overturn.
Fig. 161 shows a conveyor and elevator made by
R. White and Sons, Widnes.
Fig. 162 shows a slat-conveyor made by Pott, Cassel,
and Williamson.
A modification of the belt conveyor is becoming familiar
to most people in the form of the moving staircase,
which is installed in railway stations and other places.
Bucket Conveyor. — Sometimes it is necessary to trans-
port material which from its rough or heated nature is
230 INTRODUCTION TO CHEMICAL ENGINEERING
unsuitable for the belt conveyor. For such purposes
the bucket conveyor is used, and it consists of buckets
carried on rollers and joined together by a roller chain.
TRANSPORT 231
Shaking Conveyors. — These machines have already been
dealt with under the heading of shaking sifters.
There are various modifications of these machines,
but the underlying principles are the same. They require
considerably more power than belt conveyors, but this
is somewhat compensated by balancing one shaking
conveyor against another, thus securing a comparatively
smooth action.
Fig. 163 shows the grasshopper conveyor made by
this same firm.
Conveying Liquids. — liquids are transported from one
place to another through pipes under the action of
gravity — that is, by maintaining a certain head of liquid.
Apart from the means used to obtain a head of the liquid,
the main problem in a chemical works consists of selecting
a pipe which will remain more or less unaffected by
the liquids which flow through it.
For conveying water, pipes are used made of wrought
iron, plain or galvanized, cast iron, lead, copper, tin,
alloys, and ebonite. Earthenware and cement pipes are
commonly used for waste liquids of all kinds. For dilute
acids, organic acids, beer, and vinegar, wrooden pipes
made of staves held together by metal bands are widely
used. Lead pipes are useful for resisting corrosion, but
they are not satisfactory under heat or pressure, so that
lead-lined iron pipes are frequently employed.
Tin pipes are used for conveying liquids which are
used in food or for drinking purposes, but a cheaper
article is produced by tinning a copper or iron pipe.
Copper and brass pipes have as wide an application as
any material used in the construction of pipes.
The conveying of strong acids and other chemically
active liquids is a problem to the solution of which
there have been many attempts. Silicon compounds, in
the form of iron alloys or ceramic materials, form the
bulk of the acid-resisting substances which are placed
on the market under various trade names, such as Ironac,
232 INTRODUCTION TO CHEMICAL ENGINEERING
Tantiron, Vitreosil, Vitreon, Ceratherm, and Vitresoate
stoneware, and intended to replace the regulus metal
which has been so commonly used.
TRANSPORT 233
Tantiron is the name given to a ferro -silicon alloy
manufactured by the Lennox Foundry Company, Ltd.,
London. It is a hard, close-grained, silvery white alloy,
melting at about 1,200°C., which does not rust or
oxidize, nor is it attacked by ordinary corrosives to any
extent. It can be treated exactly like cast iron, and
castings varying from a few ounces to many tons in
weight can be made with equal ease. It differs from other
non-corrosive alloys in that its resistance to corrosion is
general and not specific. Muntz metal, for instance,
is not attacked by sea water, and nickel alloys do not
rust, but all such metals are easily attacked by acids.
Again, truly non-corrosive bodies such as carbides are
quite unfitted for the manufacture of plant, as they
cannot be cast in the foundry nor be machined. Although
in the earlier stages Tantiron was found difficult to
machine, and all finished surfaces had to be ground from
the rough casting, it can now be drilled, turned, planed,
or screwed, and still retains its non-corrosive properties.
By immersing weighed samples of Tantiron in different
corrosive liquids for periods of one to three days, and
carefully weighing the washed and brushed samples at
intervals, the table on p. 234 of corrosive actions, giving
percentage loss, has been obtained.
As regards physical properties it has been found, as a
result of many experiments carefully conducted, to
possess practically twice the thermal conductivity of
lead and four to five that of stoneware or quartz — an
immense gain in either heating or cooling fluids. Its
hardness is some fifteen times that of regulus metal,
which, together with its lower density, allows lighter
and more practical apparatus to be designed than is
possible in the case of lead-antimony alloys.
Tantiron has been used in the manufacture of nitric
acid and sulphuric acid plants, acid pumps, cocks,
valves, pipes, fittings, and various vessels required to
withstand exposure to corrosive materials.
234 INTRODUCTION TO CHEMICAL ENGINEERING
First
24 Hours.
Second
24 Hours.
Third
24 Hours.
Sulphuric acid 98 per cent.
0-10
0-02
0-02
„ 30
0-07
nil
nil
Nitric acid 1-4 sp. gr.
0-03
0-01
nil
„ 1-1 ,,
0-01
nil
nil
Acetic acid 60 per cent.
0-03
0-01
nil
Chromic acid 10 ,,
0-07
nil
nil
Tartaric acid 25 ,,
0-05
0-03
0-03
Iodine, saturated solution
nil
nil
nil
Bromine water, saturated
0-01 0-01
nil
Bleaching powder, saturated
solution
0-04
0-01
0-01
Copper sulphate, acid . .
nil
nil
nil
,, ,, alkaline
nil
nil
nil
Ferric sulphate solution
0-06
nil
nil
Zinc chloride 30 per cent.
0-03
nil
nil
Ammonium chloride solution . .
0-05
0-02 0-01
Fused sulphur
0-06
0-01
nil
Fused ammonium nitrate
nil
nil nil
The following physical constants, contrasted with
those of cast iron, will be of use to the designer of plant
where a non-corrosive metal is required.
Cast Iron. Tantiron.
Density
7-3
6-8
Tensile strength, tons per square
inch
9 to 10
6 to 7
Transverse strength, 12 inch x
1 inch bars
2,500 pounds 1,600 pounds
Crushing, 1-inch cubes . . . . 40 tons 34 tons
Melting-point
1,150°C.
1.200° C.
Hardness
1
1-6
Thermal conductivity
10
8
Electrical resistance
8
10
Corrosion resistance
1
1,000
Contraction allowance in casting
| inch per
Jg inch per
foot
foot
Ironac is a similar product manufactured by Houghton's
Patent Metallic Packing Co., Ltd., London, which is
TRANSPORT 235
chiefly used in the construction of special types of nitric
acid and sulphuric acid plants. It resists the action of
nitric acid and sulphuric acid of all densities, and has
sufficient strength, both tensile and transverse, to with-
stand the necessary handling to which such plants are
subjected, and it will resist varying changes of tempera-
ture. The conductivity of this material is nearly twenty
times that of pottery and similar material, and conse-
quently tubes may be made quite thin in section and
cooling effected very rapidly where required.
Owing to the increased efficiency thus gained, a very
great saving in space is effected as compared with that
required for the old-type pottery installations.
Vitreon ware is made by Shanks and Co., Barrhead,
Scotland. It is a pure white, dense body, vitreous
throughout, homogeneous in texture, and free from
laminations and from iron. It can be used unglazed,
as it is vitreous throughout, and has therefore a very low
absorption. It resists the action of heat and chemicals
equally as well as Berlin porcelain, but it has a very
much greater strength. Its compression strength is
24 tons to the square inch, and its tensile strength,
calculated by the Nielsen and Garrow formula, is more
than 1,800 pounds per square inch, as against 842 pounds
for the best German stoneware. A 2-inch diameter pipe
with J-inch walls has successfully withstood a test
pressure of 900 pounds per square inch of internal
pressure. Pipes of all sizes are made, those of 6 inches
diameter being 6 feet long and small bores up to 9 feet
in length. Owing to the hardness and fine texture of
the material, a fine surface can be obtained by grinding,
so that it can be used for the manufacture of acid taps
of all descriptions.
Vitreosil is a pure fused silica made by the Thermal
Syndicate, Ltd., Wallsend-on-Tyne, and used for the
construction of all kinds of appliances used in the acid
industries.
236 INTRODUCTION TO CHEMICAL ENGINEERING
It has great resisting powers to high temperatures and
the action of chemicals, and is readily made into all
kinds of pipes, basins, stills, etc.
Ceratherm is an earthenware composition made by
Guthrie and Co., Accrington, and used for the con-
struction of all kinds of chemical machinery. It is un-
affected in the slightest degree by corrosive liquids, and,
unlike porcelain and earthenware, sudden changes of
temperature will not crack it. This material has a much
higher thermal conductivity than porcelain or stoneware,
and even violent variations of temperature do not crack
it, also it can be made of considerable strength without
showing the brittle nature of porcelain. Its specific
gravity is about one -third that of cast iron, and it has an
exceedingly high thermal conductivity and emissivity,
and by using a special cement it can be used for lining
iron vessels where great strength is required.
Vitreosate is another earthenware composition made
by the same firm, and largely used for lining iron pipes
and acid cocks.
Elevating Liquids. — Liquids are elevated by the direct
action of a plunger pump, centrifugal pump, pulsometer,
or hydraulic ram, constructed of non-corrosive material,
or indirectly by the use of compressed air in the acid egg
system and the Pohle air lift system.
The Acid Egg. — This apparatus is almost universally
used for lifting strongly corrosive liquids, despite the
fact of its low efficiency and the labours of chemical
engineers to perfect automatic elevators. Its simplicity
is a great point in its favour, but its limitation up to the
present has been its corrodibility if made of iron or steel,
and its weakness if made of earthenware or similar non-
corrodible substances.
Fig. 164 is an illustration of an acid egg, as made
by The Lennox Foundry Co., in Tantiron, and is formed
of two cups joined by their top flanges to form a horizontal
cylinder with hemispherical ends. These eggs are filled
TRANSPORT
237
with the liquid through a pipe which contains a check
valve to prevent its return, and air is pumped in through
a second pipe having an automatic or manually operated
valve. The liquid is then forced out through a third pipe
which goes to the bottom of the egg, and at each discharge
the liquid is followed by a rush of the air used for raising
the liquid and so becomes wasted. Various devices for
FIG. 164. — TANTIRON ACID EGG.
automatically charging and discharging the eggs have
been made and successfully put into operation at acid
plants throughout the world.
The Air Lift or Pohle System. — In this system air under
pressure is forced down, a pipe within the tubing of a well
containing the liquid. The air is broken up into small
bubbles, which rise up the tube, accompanied by a
certain amount of the liquid, which is discharged at the
238 INTRODUCTION TO CHEMICAL ENGINEERING
top in a steady stream. In this system the air escapes,
but the amount required is only about half that con-
sumed in the working of an acid egg. The successful
working of these pumps demands considerable practical
experience, but in general the deeper the submersion
of the air pipe, the higher the air pressure, and consequent
greater efficiency, which also increases with increase of
temperature of the liquid pumped. The absence of moving
parts and the freedom from wear makes this pump
compare very favourably with positive-acting steam
pumps, which suffer from corrosion, except in the case of
low lifts of 75 feet and under, when the centrifugal pump
is probably more economical.
For practical working it is found that the velocity
of the air should not exceed 20 feet per second, that the
submersion should be about 1*5 times the lift, measured
from the working water level, and the cross-sections
of the air tube and the rising tube should be in the ratio
of 1 to 6-25. As a rough estimate it takes 1 cubic foot
of air to raise 1 gallon of water, but this amount of air
can be considerably decreased in the case of an efficient
pump. The average air pressure used is 60 pounds per
square inch, and at the commencement of operations,
owing to the unbroken column of liquid in the tube, a
larger pressure is required than is subsequently needed for
steady working.
Plunger Pumps. — These pumps exist in all forms and
sizes, and are too well known to need any description
here. In the design of these pumps for chemical work
care should be taken to render all valves easily ac-
cessible and to proportion each part to withstand rough
usage.
Fig. 165 shows a standard horizontal pump made of
Tantiron by the Lennox Foundry Co. specially for acid
work. It is a single-acting ram pump with a ram 2 inches
in diameter and 6 inches stroke, and when run at 80
revolutions per minute has a capacity of about 280
TRANSPORT
239
gallons per hour. The diameters of the suction and
delivery pipes are each lj inches.
Fig. 166 shows a Tantiron standard vertical pump
made for the same duties as the horizontal pump, the
dimensions of the cylinder and pipes being exactly the
same.
This type of pump is also largely used for pumping
wort, molasses, sugar juice, oil, glue, varnish, and other
thick liquids. In the case of liquids of heavy density or
FIG. 165. — TANTIRON HORIZONTAL PUMP.
of a sticky nature the output of such pumps is somewhat
reduced, and for such cases it is advisable to have large
pipe connections, the suction and delivery pipes being of
the same diameter as the pump barrel.
Centrifugal Pumps. — The moving of highly corrosive
liquids is principally effected by compressed air, but this
method is being seriously threatened by the latest types
of centrifugal pumps. The manufacture of centrifugal
pumps for this purpose, however, raises a variety of very
complicated questions, and that is the reason why the
240 INTRODUCTION TO CHEMICAL ENGINEERING
development in this direction has been so slow. Lead and
regulus metal have been used for strong sulphuric acid,
but are not satisfactory for weak acid, and quite useless
for nitric and hydrochloric acids or sulphuric acid con-
taining certain common impurities. In addition, all
, FIG. 166. — TANTIRON VERTICAL PUMP.
metal pumps are unsuitable for many chemicals and for
a large range of solutions of metallic salts. For example,
an iron pump could not be used for a solution of chloride
of copper. Pumps made from ferro -silicon alloys are not
satisfactory when organic acids are used, and the brittle-
TRANSPORT
241
ness of the alloy and the difficulty in making suitable
castings have prevented its development as a material
of which to make pumps .
It is out of the question to use enamelled iron for making
pumps, however good the enamel may be, as the enamel,
in all probability, will be scratched off the impeller or
the casing. In fact, for a number of corrosive liquids no
metallic substance is a suitable material from which to
make the centrifugal pump, as at every revolution of the
impeller the casing and impeller are washed by the
FIG. 16 T. — CERATHERM BODY IN IRON CASTING.
contained liquid. Porcelain is inert, but is not suitable
for the preparation of pumps because of its brittle nature.
Stoneware pumps have been produced, but they have the
disadvantage that if used with boiling liquids they are liable
to crack. They are also very fragile, and are hardly
safe to use above 30 pounds pressure or 40 feet acid
head. •
Cera therm is the material used by Guthrie and Co.,
Accrington, as the basis for the construction of centri-
fugal pumps of all kinds.
Taking first of all the case where only low lifts are
required and small pumps, a thin casing of Ceratherm
16
242 INTRODUCTION TO CHEMICAL ENGINEERING
FIG. 168. — CERATHERM IMPELLER.
i
FIG. 169. — CERATHERM PUMP: INTERIOR
TRANSPORT
243
is set into an outer casing of cast iron by means of an
acid-resisting cement, which will withstand continued
treatment with nitric acid, and affixes the lining to the
casing in a permanent fashion, as shown in Fig. 167.
Fig. 168 shows an impeller screwed on to a steel shaft
which is protected by a Cera therm boss, after which the
Cera therm is machined and ground accurately. Fig. 169
shows the interior of a pump where the liquids passing
through only meet the Ceratheim and do not touch
FIG. 170. — CERATHERM PUMP: SMALL SIZE.
any metal, and in Fig. 170 the complete pump is
shown. These pumps are suitable for a number of
purposes, and will handle 20 to 100 gallons per minute
to a head of 15 to 20 feet without trouble, and they are
not affected by boiling corrosive liquids. Stronger
pumps are made by using a Ceratherm lining up to 2f
inches in thickness.
No matter how generous the stuffing box of an acid
centrifugal pump may be, it is most desirable that the acid
at this point should not be under pressure but rather
under suction, so as to avoid leaks with high heads,
244 INTRODUCTION TO CHEMICAL ENGINEERING
H.!'
FIG. 171.— CERATHERM PUMP: SUCTION SIDE INTERIOR.
FIG. 172.— CERATHERM PUMP: PRESSURE SIDE INTERIOR.
TRANSPORT 245
especially in the case of liquids of high specific gravity.
Fig. 171 shows the interior of the suction side of the
pump containing the feed chamber, inlet, and race, and
Fig. 172 shows the pressure side of the pump containing
the race.
The Ceratherm impellers are tested by running to about
3,000 revolutions, and as the pumps are designed in such
a way as to give the desired head at about 1,000 revolu-
tions, it will be seen that the safety factors in these pumps
are high. The factors are based on a calculation of the
tensile strength, and are probably somewhere in the
neighbourhood of 14 to 15. The distribution of thrust
in a pump of this description is quite different from that
of the normal centrifugal pump, and this is catered for
by the strong casing. It is clear from the above that
the thicknesses of the material found to be desirable
lead to certain modifications in the feed and in the design
of the impellers, but by careful experimentation thoroughly
efficient combinations have been attained. The mechani-
cal efficiency of these pumps is much higher than that
of their only possible competitor in most cases — namely,
the compressed air system. It is not so high as that
attained in metallic pumps, for certain definite reasons—
for instance, 75 per cent, efficiency in a metallic pump
is quite easy to attain, given sufficient quantity. In the
armoured Ceratherm pump a small amount of horse-
power is deliberately spent in preventing the pump from
leaking at the gland, in doing away with troublesome
stuffing boxes, and permitting such contrivances as will
avoid any rubbing surfaces or bearings within the
chemicals. It is fatal practice in chemical pumps to
have bearings running in acids, as this soon causes the
pump to be scrapped.
According to De Laval, until recently 40 per cent, was
considered the highest efficiency for a metal centrifugal
pump of ordinary volute type, and for the quantities
which are generally dealt with in the chemical practice —
246 INTRODUCTION TO CHEMICAL ENGINEERING
namely, below 250 gallons per minute — 55 per cent, is as
high efficiency as can be attained. It is only when
quantities reach the neighbourhood of 500 to 600 gallons
per minute that efficiency can be attained up to 70
to 75 per cent. For practical purposes these pumps
are at least three times as efficient as the compressed
air system, and are greatly superior to metallic pumps
which lose their efficiency owing to rapid corrosion. It
will be noticed that only single-stage impellers are used,
as it has been found that for corrosive liquids, one -stage
pumps with very large impellers, which at low revolu-
tions will give the head required in chemical practice,
will give the best results.
These pumps are used in bleaching and dyeing works
where chemicals must be circulated without any impurity
being yielded to the liquors; in acid factories; for the
circulation of weak acid in nitric towers; for improved
methods of absorbing hydrochloric acid; for electro-
chemical purposes, in the wool carbonizing trade, the
dope trade, and the fermentation industries.
To maintain freedom from corrosion in the plant
actuated by these pumps, armoured Vitreosate piping,
another form of earthenware, is used, and armoured
Vitreosate acid cocks, of which latter a sample is shown
in Fig. 173.
Conveying Gases. — The gases which are met with in the
chemical industry may be classified as — (1) Those which
are circulated because they are valuable, and (2) those
which are exhausted into the air because at present they
are of no value. Transportation is effected through
pipes which are of various materials, such as iron, in the
cast, wrought, galvanized, or sheet form, copper, and
for large pipes or flues, bricks, concrete, and similar
materials are used.
A chimney is the simplest means of exhausting waste
gases to the atmosphere and at the same time providing
a draught for promoting the combustion of fuel, but it
TRANSPORT 247
may be confidently expected that the future will see
the abolition of chimneys and the economical use of
present waste gases — a subject up to the present sadly
neglected. For the removal of noxious gases the size of
the chimney is more important than height, which latter
is of importance for draught, a height of 400 feet giving a
draught pressure equal to about 2J inches of water.
For low pressures and rarefactions, fans and blowers
are used, and for high pressures and rarefactions com-
pressors and vacuum pumps are employed.
FIG. 173. — VITREOSATE THREE-WAY TAP.
Fans. — These consist of a number of blades fixed on a
rapidly revolving shaft, the design of the impeller and
casing depending upon the nature of the work to be done.
For large volumes of air up to 4 inches water pressure
shallow blades are required; for pressures up to 10 inches
side plates are provided and the blades are deeper ; up to
15 inches the wheel is narrower and deeper and the
scroll casing has to be carefully designed; high -pressure
fans for cupolas, etc., are provided with a greater number
of blades.
For hot or corrosive gases a water-cooled steel fan
248 INTRODUCTION TO CHEMICAL ENGINEERING
may be employed, or the fan may be made of regulus
metal or stoneware.
For supplying the air to a producer -gas apparatus
the radial-flow fan is frequently employed. It consists
of a shaft carrying a spider of six T-iron arms, each having
a sheet-iron paddle with annular discs riveted at the
sides. The paddle has a radial direction at the inlet,
but is curved back at the tip at an angle of about 50
degrees. The side clearance of the impeller is about
f% inch, and the tip clearance varies from 3 inches at
the beak to 12 inches at the discharge orifice. A vortex
chamber is provided for by the eccentric setting of the
impeller in the casing.
For large and varying volumes of gases these fans are
particularly useful, and in spite of losses due to eddy
currents and other causes they have an efficiency of
from 50 to 70 per cent.
For circulating large volumes of gases at comparatively
high pressures a mixed-flow fan, where the inlet flow is
axial and the outlet flow radial, such as in the Rateau
fan, has come into common use. The shaft of the im-
peller has a conical boss on which are riveted up to twenty-
four specially designed blades having an angle at the
tip of about 45 degrees opposite to the direction of
rotation, and the vortex chamber is of rectangular cross-
section. Delivery is taken from the now usual conical-
shaped funnel, and the bearings are of the high-speed
type, while carbon rings are provided to prevent leakage
at the impeller. This type of fan has a much higher
efficiency than the radial -flow type, and with a single
impeller can maintain a head of from 35 to 40 inches
of water, so that by using several impellers, through
which the gas passes in series, large volumes may be
passed against high heads.
When a centrifugal fan is run at constant speed the
power increases as the pressure falls and the volume of
air increases,
TRANSPORT 249
Rotary Blower. — This machine is designed to maintain
constant blasts of small capacity, and is chiefly used for
forge-smiths' fires, furnaces, heating and drying stores,
glass blowing, brass smelting and gas exhausting, besides
the circulation of gases where high pressures up to
15 pounds per square inch are required. The action is
positive, and when run at constant speed the power
increases directly with the pressure, while the volume
remains practically constant. These machines will run
for years without repair, as their mechanism is simple,
being designed to scoop the gas at the inlet and discharge
it at the outlet, and they are made in large sizes.
Compressors. — These machines are used for pressures
considerably above that of the atmosphere, and as such
are the development of the last fifty years. All com-
pressors operate by first allowing the gas to flow into
a cylinder under its own pressure on the so-called suction
stroke of the piston, and then on the return stroke, by
closing the inlet valve compressing the gas until the
desired pressure is reached, when the delivery valve
opens. The following conditions* should be fulfilled in
a good compressor : (1) On the suction stroke the cylinder
should be filled with the maximum mass of gas. (2) On
the compression stroke there should be no loss of gas by
too late closing of the inlet valves, nor should there be
any leakage back, but the whole contents of the cylinder,
less the minimum clearance, should be discharged through
the outlet valves. (3) The outlet valves should have
ample area of opening, should open automatically on the
pressure in the receiver being reached in the compression
cylinder, and the gas should be discharged at a pressure
as little above that in the receiver as possible, as excess
pressure causes a rise in temperature, with increase in
volume, requiring a corresponding increase in the work
necessary to compress and discharge the air. (4) The
discharge valves should have sufficient width of seating
to ensure their keeping quite tight, so that no loss by
250 INTRODUCTION TO CHEMICAL ENGINEERING
leakage back into the cylinder may take place. (5) The
valves should be self-adjusting under all speeds and
pressures. (6) Highest volumetric efficiency should be
obtained. (7) All valves and pistons should be easily
accessible for examination and renewal. (8) Wear and
tear should be reduced to a minimum.
Compressors are usually of the horizontal type for
slow speeds and of the vertical type for high speeds,
both requiring very heavy foundations. The horizontal
type is more accessible than the vertical, but needs a
larger flywheel; but at slower speeds the more even
turning of the horizontal type is most marked.
When compressing in a single cylinder to the final
pressure desired, the water jacket of a single-stage
compressor is not sufficient to extract the heat of com-
pression, and the compound compressor, with intercooler,
should always be adopted when the most economical
results are required. The rise in temperature not only
represents the loss of work in compression, but, should
it exceed the ignition temperature of the lubricating oil,
an explosion may result. To prevent this, and to obviate
the serious loss of efficiency in compression at high terminal
pressures which would be caused by the heating of the
air, the compression is carried out in stages in a compound
compressor, with intercoolers to cool the air between each
stage of the compression. The intercooler should be of
sufficient capacity to reduce considerably the temperature
of the gas before it is admitted to the second-stage cylinder.
Provided the work is equally distributed between the
cylinders and the intercoolers are properly designed, the
final temperature in each cylinder will be the same,
and the final temperature of compression very much lower
than if the compression were done in one cylinder, with
corresponding direct saving in power, as the resistance
due to compression is directly proportional to changes in
temperature. The compounding of the air cylinders
should be so proportioned as to divide the work of
TRANSPORT
251
compression equally between them, and thus distribute
the load more equally throughout the stroke, thereby
admitting of an earlier cut-off on the steam cylinders,
with attendant economy in steam consumption.
Compressors may be classified according to the manner
in which their inlet and discharge valves are actuated:
(1) Inlet and outlet poppet valves arranged (a) in the
252 INTRODUCTION TO CHEMICAL ENGINEERING
cylinder covers; (6) partly in the cylinder covers and
partly in the cylinder walls ; (c) with inlet valves in the
piston and discharge valves either in the cylinder covers
or walls. (2) With large hinged flap valves in the
cylinder covers, and actuated similarly to poppet valves.
(3) With mechanically operated valves which open and
close gradually. (4) With mechanically operated inlet
FIG 175. — VERTICAL, OPEN-TYPE AIR COMPRESSOR.
valves and poppet discharge valves. (5) Direct air con-
trolled and balanced inlet and discharge valves. (6) Light
automatic disc valves with small lift.
The first four types have a low efficiency and output,
owing to the limitations of speed of the pistons due to
the heavy valves in motion, and the air -con trolled system,
although admitting of high speeds and increased efficiency,
has not been generally adopted owing to the cost of
maintaining the complicated valve gear in good order.
TRANSPORT 253
The automatic disc valve is the best valve for practical
purposes, as it is silent, simple, and gives great efficiency
at high speeds.
Fig. 174 shows a horizontal type two -stage belt-driven
air compressor made by Robey and Co., Lincoln, and
Fig. 175 a vertical open- type compressor made by the
same firm.
FIG. 176. — BELT-DRIVEN THREE-STAGE COMPRESSOR.
Probably the largest field for compressed air is for
pressures up to 6 atmospheres, but the rapid progress of
the chemical industry has called for higher pressures
and for the compression of many other gases. The pro-
duction of oxygen for welding, etc., of nitrogen for ammonia
and nitrates, of argon for electric lamps, depends upon
the liquefaction of air demanding up to 200 atmospheres.
Hydrogen, chlorine, carbon dioxide, and sulphur dioxide
are also stored under pressure.
254 INTRODUCTION TO CHEMICAL ENGINEERING
Fig. 176 shows a belt-driven 3 -stage stationary type
of small air compressor for simple working made by Peter
Brotherhood, Ltd., Peterborough, in which the cylinders
are water-cooled and control is effected by an automatic
governor.
Fig. 177 shows an oxygen compressor made by this
same firm. It is a four -stage machine (2,000 cubic feet
per hour, 250 atmospheres at 200 r.p.m.) with forced
FIG. 177. — FOUR-STAGE OXYGEN COMPRESSOR.
lubrication, driven by a two -crank compound steam
engine. This type of compressor has lubrication suited
to the chemical nature of the gas compressed, and the
materials of construction are also adapted to the same
end. Generally, the pump is made of bronze of great
strength and non-corrodible, except by acetylene and
similar gases. There is a minimum number of joints to
give trouble, and the piston packing is easily renewable
TRANSPORT 255
without the use of moulded leather or special piston
rings.
Vacuum Pumps. — These machines have been dealt with
from time to time in connection with other types of plant
already mentioned, and are of the wet and the dry type
designed to give what the ordinary engineer terms a
perfect vacuum. However, the production of the ionic
valve, the latest forms of electric lamps, vacuum vessels
for holding liquefied gases, etc., require a high vacuum,
which is only limited by the nature of the materials
used for construction. For these purposes the high-speed
rotary or molecular pump, such as the Gaede, which
has a porcelain grooved disc half -immersed in mercury,
or the Siemens or Langmuir pumps, which are completely
immersed in oil, will give when working alone up to a
vacuum equal to 10100 mm. Hg. They are usually worked
in series with a large capacity vacuum pump known as
a roughing pump and followed by a diffusion pump,
which consists of a vessel surrounded by a hot -water bath
and containing mercury, which is vaporized continu-
ously, thus providing a wall of vapour through which
the attenuated gases diffuse to the rotary pump, a liquid-
air cooled trap holding back any straying mercury vapour.
By this means much higher vacuums than 10100 mm. Hg.
can be obtained on an industrial scale.
CHAPTER IX
APPENDIX
Distillation of Liquid Mixtures. — If the liquids do not
mix to any appreciable extent, each exerts its own vapour
pressure independently of the other liquids which may be
present. The vapour pressure is the sum of the vapour
pressures of the liquids contained in the mixture. Such
a mixture will boil lower than the lowest boiling con-
stituent, since the sum of the vapour pressures becomes
equal to that of the atmosphere at a lower temperature
than is required for any one constituent. The vapour
of such a mixture will contain all the constituents in the
same proportions as the relative vapour pressures of the
liquids present. On distillation the distillate will contain
all the liquids present in the proportions depending on the
relative vapour pressures at the temperature of distil-
lation.
If the liquids are partly miscible, the vapour pressure
of the mixture is less than the sum of the vapour pressures
of the constituents. The boiling point may be below
that of the lowest boiling constituent, or coincident with it,
or even above it. The composition of the distillate remains
constant so long as there are two layers present, and the
effect of distillation is to diminish the lower boiling
more rapidly than the higher boiling solution. During
this period the boiling point remains constant until one
layer has disappeared.
If the liquids are soluble in one another in all pro-
portions, the vapour pressure of the mixture is always less
than the sum of the vapour pressures of the constituents
at the same temperature. The composition of the
256
APPENDIX 257
vapour from this mixture bears no close relation to the
composition of the mixture, but the vapour contains a
preponderating amount of the most volatile constituent,
and upon this fact rests the possibility of separating such
mixtures by fractional distillation. No general relation-
ship exists between the boiling point of such a mixture
and the boiling points of the constituents.
Air Compression. — When air is subjected to pressure its
volume is reduced and its temperature is raised. If
during compression air neither loses heat to, nor gains
heat from, any outside source it is said to be adiabatically
compressed. In this case the temperature does not
remain steady, but rises throughout the operation. In
the case where the heat due to compression is removed
as quickly as it is formed, so that the temperature of the
air remains steady throughout the operation, the com-
pression is said to be isothermal. When the operation is
reversed and the air is expanded instead of being com-
pressed, the above holds true, but in the reverse direction
— e.g., the volume is increased and the temperature is
decreased. The rate of increase of temperature of
air during compression decreases as the compression
increases, and also — what is very important in practice —
it depends upon the initial temperature of the air before
compression.
The rate of increase of temperature due to compression
increases not only as the initial temperature increases,
but also increases throughout the compression when com-
pared with the rates of increase of temperature throughout
compression, of air compressed at a lower initial tempera-
ture. For a considerable range of temperatures and
pressures of air, the relation pressure x volume = constant,
provided the temperature is unaltered, holds sufficiently
accurately. The effect of increase of temperature is to
increase the volume of the air if the pressure is kept
unaltered, and hence it follows from the above relation
that increase of temperature will increase the pressure of
17
258 INTRODUCTION TO CHEMICAL ENGINEERING
air if : the volume is kept unaltered. The final volume or
pressure of air under the conditions just mentioned
depends directly upon the final absolute temperature
of the air- — e.g., a certain volume V of gas under pressure
P at ^°C. is heated to Z2° C. If the pressure is kept
T7 . V(273+^)
constant its volume increases irom V to * +^ . -,
and if the volume is kept constant its pressure increases
from P to ^fJ3 + \^- If the Fahrenheit scale is used>
then 461 must be used in place of 273. The impor-
tant facts to be known in connection with air com-
pression are the temperature when any given pressure
is reached, and the relative volume of the air at that
pressure. It will be seen from the above that as during
compression the temperature rises, so the pressure
rises also; that is, the back pressure of the air on the
piston of the compressor during compression is due
in part to the heat generated by the compression. Since
air is required to be delivered at a definite temperature
and pressure, any rise of the temperature of the air above
this definite temperature during compression results in
setting up a back pressure which has to be overcome
by the prime mover, which is a distinct disadvantage.
The required temperature of delivery is usually that of
the free air at the intake, hence the ideal compressor
should compress free air isothermally. This means that
in a compressor the heat produced by compression must
be taken away as quickly as it is produced. In any
compressor some heat is removed by radiation and by
conduction through the metal parts in contact with the
air, and usually this operation is assisted by a flow
of cold water round the parts wherever possible. The
cold-water jacket is more effective on the cylinder head,
because that portion is longer exposed to the heated
air than any other part; and it should be noted that,
apart from other reasons, cooling is a necessity for obtaining
APPENDIX 259
proper lubrication and preventing firing in the cylinders.
Further, it is obviously an advantage to have a slow-
running compressor, for, apart from purely mechanical
considerations, the longer the time allowed for the air
to cool, the greater will be the cooling effected, and the
less the power required for compression. There are two
distinct operations in air compression which should be
noted — viz., (1) the compression of the air to a given
pressure, and (2) the delivery of the air from the cylinder
after the given pressure is reached. It will be seen that
these operations are the inverse of those occurring in a
steam-engine cy Under. In making any calculations as
to the h.p. required to compress a given quantity of air
to a definite pressure, it is best to take values for adiabatic
compression and allow a small percentage for friction of
the apparatus, as a part of the friction loss is set off by
the reduction of power required due to cooling in actual
practice. Assuming there is no clearance in a cylinder
of volume % to which air is admitted at a pressure plf
and that the air is compressed to a volume vz at a pressure
Pz adiabatically, the following relations can be deter-
mined :
1. Work done by external air in filling the cylinder —
foot-pounds.
/p\o-29 i
2. Work of compression = 2*463^% -j — J — 1 !• foot-
pounds.
/P \0-29
3. Work of expulsion = PiV^--} foot-pounds.
The total work done "is the algebraic sum of these
( /« x 0-29 \
three, and equals 3.463^^1 ( — j — 1 1 foot-pounds, and
from this the mean effective pressure (M.E.P.) during the
f/#2\°'29 )
stroke equals 3.463^M ( — J - 1 1 in pounds per square
foot.
The question of clearance cannot be avoided in practice,
260 INTRODUCTION TO CHEMICAL ENGINEERING
but as the compressed gas in the clearance is expanded
on the back stroke of the piston, it serves as an additional
source of cooling. For pressures above 100 pounds per
square inch compressors work in two or more stages,
according to the ultimate pressure desired, and inter -
coolers between the stages are provided to assist in the
cooling required. In such cases the stroke in each
cylinder except the last stage is a complete compression
stroke, without any work of delivery being done, as each
cylinder compresses its air into the volume of the cylinder
of the next stage. This will modify any calculation for
the h.p. required for a multistage compressor. Since in
an air compressor the back pressure on the piston is
greatest at the end of its stroke, the compressor must
be kept in motion by other means than that of the prime
mover, and so far this has been effected by heavy fly-
wheels and reciprocating parts. The efficiency of the
compressor largely depends upon securing the largest
possible mass of air in the first cylinder, which should be
at as low a temperature as possible, as it is found that a
difference of 5° F. of the air at the intake secures a
saving of 1 per cent. The inlet should have an area not
less than 50 per cent, of the area of the air piston.
Belt Conveyors. — The power required varies very
much with the design, but the following formula may
be taken as giving an average result:
33,000
where V= speed of belt in feet per minute; 6 = weight
of belt; h— height of elevation in feet; Wi = maximum
weight of material on the belt at any one time; W2 =
weight of material delivered per minute.
Belting. — The power transmitted by any belt:
HP =£?-*)*
" 33,000'
APPENDIX 261
T = tension in pounds on pulling side ; £= tension in pounds
on slack sides; v= speed of belt in feet per minute.
Size of pulley and area of contact of belt have no effect
on the power transmitted ; centrifugal force reduces
power by 10 per cent, at 3,000 r.p.m. and 30 per cent,
at 5,000 r.p.m.; the arc of contact of belt has consider-
able influence; the greater the arc, the greater the power
transmitted.
A simple rule for belts is that 1 foot per minute of belt
speed per inch of width of belt is safely equal to the
transmission of 1 watt of electrical energy; add 25 per
cent, for light double bands and 60 per cent, for heavy
double bands. This fixes a constant for working tensions
of 44-24 pounds pull per inch width of belt. The extra
pull on the tight side is obtained by dividing the total
output in watts by the velocity in feet per minute and
multiplying by this number.
Rubber belts transmit 25 to 40 per cent, more power
than leather for the same arc of contact, but should not
be used for temperatures above 90° F.
Shafting. — For ordinary light shafting carrying pulleys,
H.P.=0-013xD3xN; for shafts carrying gears, H.P.=
0-01xD3xN; for heavy shafting, H.P. = 0*008 x D3x N
where D = diameter of shaft in inches and N = speed of
shaft in r.p.m.
For wrought-iron shafts, the diameter in inches at the
/ TT T* x1
bearings = 5 x ( — - — ~ j3. Distance between supports, when
no power is taken off between, = 5 %Jd2, where d =
diameter in inches. In other cases the distance is from
7 to 12 feet.
Maximum safe loads in pounds per square inch on
ordinary bearings for shafting: Wrought iron on cast
iron = 250; wrought iron on gun -metal or mild steel
on cast iron = 300; mild steel on gun -metal = 3 70; cast
steel on gun -metal = 600; flywheel shaft=250.
262 INTRODUCTION TO CHEMICAL ENGINEERING
Refrigerating Machines. — 25 h.p. will cool 15,000
cubic feet of air per hour; 20,000 cubic feet of air
saturated at 90° F. contains 42 pounds of water, and
at 60° F. contains 17 pounds. The amount of cooling
water required for air -compression machines in gallons1
TT
per minute =-—= — where H=heat to be withdrawn
1UV1l~ J-2)
from the water, Tx and T2 inlet and outlet temperatures
respectively.
Low Boiling-Point Liquids. —
Boiling-Point. \ Melting-Point.
Ammonia
Carbon dioxide
Ethyl chloride
Liquid air. .
-38-5°C.
- 78-2° C.
-19-5° C.
- 190° C
- 77-34° C.
-65-0° C.
-141-6° C.
Nitrogen
Oxygen
Sulphur dioxide . .
- 195-5° C.
- 182-7° C.
- 10° C.
-210-5° C.
-227° C.
-76-l°C.
Freezing Points of Common Salt Brine. —
Freezing-Point,
Specific Gravity at
15° C.
1-037
1-073
1-111
1-150
1-191
- 3-7
- 7-4
-11-0
-13-9
-17-2
Freezing Points of Calcium Chloride Solutions. —
Specific Gravity at
20° C.
1-100
1-125
1-150
1-175
1-120
1-225
1-250
Freezing - Point,
0 C.
- 7-8
- 10-8
-14-2
- 18-9
-24-7
- 30-8
- 38-0
APPENDIX
263
Freezing Mixtures-
Alcohol 77: Snow 73 gives - 30° C.
Alcohol and C02 solid gives - 72° C.
Ammonium chloride 30: Water 100 gives - 5-1° C.
Ammonium chloride 25: Snow 100 gives - 15-5° C.
Ammonium nitrate 100: Water 131 gives - 17-5° C.
CaC]2 2HaO 100: Snow 70 gives - 50° C.
Chloroform and C02 solid gives - 77° C.
Ether and C02 solid gives - 100° C.
S02 liquid and C02 solid gives - 82° C.
66 per cent. H2S04 100: Snow 110 gives - 37° C.
Table Showing CaO in Milk of Lime at Varying Density
(Mateczel)
Degree
Beaumc.
Per Cent.
CaO.
100 Litres.
§
Per Cent.
CaO.
100 Litres.
Weight
Kilos.
CaO
Kilos.
Weight
Kilos.
CaO
Kilos.
10
10-60
125-9
13-3
38
19-72
149-8
29-5
11
11-12
127-4
14-2
39
19-80
149-9
29-6
12
11-65
129-2
15-2
40
19-88
149-9
29-8
13
12-16
130-8
16-1
41
19-95
150-0
29-9
14
12-68
132-6
17-0
42
20-03
150-0
30-1
15
13-20
134-5
18-0
43
20-10
150-0
30-2
16
13-72
136-3
18-9
44
20-16
150-1
30-3
17
14-25
138-2
19-8
45
20-22
150-1
30-4
18
14-77
139-9
20-7
46
20-27
150-1
30-5
19
15-23
141-7
21-6
47
20-32
150-2
30-6
20
15-68
143-6
22-4
48
20-37
150-2
30-7
21
16-10
145-1
23-3
49
20-43
150-3
30-7
22
16-52
146-2
24-0
50
20-48
150-3
30-8
23
16-90
146-9
24-7
51
20-53
150-3
30-9
24
17-23
147-4
25-3
52
20-57
150-4
31-0
25
17-52
147-8
25-8
53
20-62
150-4
31-1
26
17-78
148-1
26-3
54
20-66
150-4
31-1
27
18-04
148-4
26-7
55
20-70
150-5
31-2
28
18-26
148-6
27-0
56
20-74
150-5
31-3
29
18-46
148-8
27-4
57
20-78
150-5
31-3
30
18-67
149-0
27-7
58
20-82
150-5
31-4
31
18-86
149-1
27-9
59
20-85
150-6
31-4
32
19-02
149-2
28-2
60
20-89
150-6
31-5
33
19-17
149-3
28-4
61
20-93
150-6
31-5
34
19-31
149-4
28-7
62
20-97
150-6
31-6
35
19-43
149-5
28-9
63
21-00
150-6
31-6
36
19-53
149-6
29-1
64
21-03
150-7
31-7
37
19-63
149-7
29-3
65
21-05
150-7
31-7
264 INTRODUCTION TO CHEMICAL ENGINEERING
Comparison of Thermometer Scales.
n Degree Celsius — ^n Degree Reaumur = 32 + f n Degree Fahrenheit,
n Degree Reaumur =%n Degree Celsius = 32 + %n Degree Fahrenheit,
n Degree Fahrenheit = §(n — 32) Degree Celsius =f (n — 32) Deg. E.
c.
E.
F.
\j .
E.
F.
/->
E.
F.
ri
E.
F.
-20
-16
_4
20
16
68
60
48
140
100
80
212
-19
-15-2
-2-2
21
16-8
69-8
61
48-8
141-8
101
80-8
213-8
-18
-14-4
-0-4
22
17-6
71-6
62
49-6
143-6
102
81-6
215-6
-17
-13-6
1-4
23
18-4
73-4
63
50-4
145-4
103
82-4
217-4
-16
-12-8
3-2
24
19-2
75-2
64
51-2
147-2
104
83-2
219-2
-15
-12
5
25
20
77
65
52
149
105
84
221
-14
-11-2
6-8
26
20-8
78-8
66
52-8
150-8
106
84-8
222-8
-13
-10-4
8-6
27
21-6
80-6
67
53-6
152-6
107
85-6
224-6
-12
- 9-6
10-4
28
22-4
82-4
68
54-4
154-4
108
86-4
226-4
-11
- 8-8
12-2
29
23-2
84-2
69
55-2
156-2
109
87-2
228-2
-10
- 8
14
30
24
86
70
56
158
110
88
230
g
- 7-2
15-8
31
24-8
87-8
71
56-8
159-8
111
88-8
231-8
- 8
- 6-4
17-6
32
25-6
89-6
72
57-6
161-6
112
89-6
233-6
- 7
- 5-6
19-4
33
26-4
91-4
73
58-4
163-4
113
90-4
235-4
- 6
- 4-8
21-2
34
27-2
93-2
74
59-2
165-2
114
91-2
237-2
K
- 4
23
35
28
95
75
60
167
115
92
239
- 4
- 3-2
24-8
36
28-8
96-8
76
60-8
168-8
116
92-8
240-8
f\
- 2-4
26-6
37
29-6
98-6
77
61-6
170-6
117
93-6
242-6
2
1-6
28-4
38
30-4
100-4
78
62-4
172-4
118
94-4
244-4
1
- 0-8
30-2
39
31-2
102-2
79
63-2
174-2
119
95-2
246-2
0
0
32
40
32
104
80
64
176
120
96
248
1
0-8
33-8
41
32-8
105-8
81
64-8
177-8
121
96-8
249-8
f
1-6
35-6
42
33-6
107-6
82
65-6
179-6
122
97-6
252-6
t
2-4
37-4
43
34-4
109-4
83
66-4
181-4
123
98-4
253-4
^
3-2
39-2
44
35-2
111-2
84
67-2
183-2
124
99-2
255-2
r
«.
4
41
45
36
113
85
68
185
125
100
257
6
4-8
42-8
46
36-8
114-8
86
68-8
186-8
126
100-8
258-8
7
5-6
44-6
47
37-6
116-6
87
69-6
188-6
127
101-6
260-6
8
6-4
46-4
48
38-4
118-4
88
70-4
190-4
128
102-4
262-4
(
7-2
48-2
49
39-2
120-2
89
71-2
192-2
129
103-2
264-2
10
8
50
50
40
122
90
72
194
130
104
266
11
8-8
51-8
51
40-8
123-8
91
72-8
195-8
131
104-8
267-8
12
9-6
53-6
52
41-6
125-6
92
73-6
197-6
132
105-6
269-6
13
10-4
55-4
53
42-4
127-4
93
74-4
199-4
133
106-4
271-4
14
11-2
57-2
54
43-2
129-2
94
75-2
201-2
134
107-2
273-2
15
12
59
55
44
131
95
76
203
135
108
275
16
12-8
60-8
56
44-8
132-8
96
76-8
204-8
136
108-8
276-8
17
13-6
62-6
57
45-6
134-6
97
77-6
206-6
137
109-6
278-6
18
14-4
64-4
58
46-4
136-4
98
78-4
208-4
138
110-4
280-4
19
15-2
66-2
59
47-2
138-2
99
79-2
210-2
139
111-2
282-2
APPENDIX
265
Temperature, Pressure, and Total Heat of Steam, with
Corresponding Vacuum, reduced to a 30-inch Barometer.
Vacuum in
Inches.
Absolute Pres-
sure, Pounds
per
Square Inch.
.fc
H°
•^ OQ OTOJJ H
1*911 TOOJ,
Vacuum in
Inches.
Absolute Pres-
sure, Pounds
per
Square Inch.
Temperature
Degrees F.
Total Heat
H from 0° F.
0
14-7
212
1178-6
24-4
2-744
138-2
1156-2
1
14-21
210-4
1178-2
24-6
2-646
136-8
1155-8
2
13-72
208-4
1177-6
24-6
2-548
135-7
1155-4
3
13-23
206-9
1177-1
25-0
2-450
133-8
1154-9
4
12-74
204-9
1176-5
25-2
2-352
132-3
1154-4
5
12-25
203-0
1175-9
25-4
2-254
130-7
1153-9
6
11-76
201-0
1175-3
25-6
2-156
129-1
1153-4
7
11-27
198-7
1174-6
25-8
2-058
127-3
1152-8
8
10-78
196-8
1174-1
26-0
1-960
125-6
1152-3
9
10-29
194-4
1173-4
26-1
1-911
124-6
1152-0
10
9-8
192-5
1172-7
26-2
1-862
123-6
1151-7
10-5
9-555
191-3
1172-4
26-3
1-813
122-7
1151-4
11
9-31
190-0
1172-0
26-4
1-764
121-7
1151-1
11-5
9-065
188-8
1171-6,
26-5
1-715
120-7
1150-8
12
8-82
187-1
1171-1
26-6
1-666
119-7
1150-5
12-5
8-575
185-9
1170-8
26-7
•617
118-6
1150-2
13
8-33
184-7
1170-4
26-8
•568
117-5
1149-8
13-5
8-085
183-5
1170-0
26-9
•519
116-4
1149-5
14
7-84
182-0
1169-6
27-0
•470
115-2
1149-2
14-5
7-595
180-6
1169-1
27-1
•421
114-0
1148-8
15
7-35
179-1
1168-7
27-2
•372
112-8
1148-4
15-5
7-105
177-6
1168-2
27-3
•323
111-6
1148-0
16
6-86
176-0
1167-7
27-4
1-274
110-2
1147-6
16-5
6-615
174-4
1167-2
27-5
1-225
108-9
1147-2
17
6-37
172-8
1166-7
27-6
1-176
107-3
1146-8
17-5
6-125
171-0
1166-2
27-7
1-127
105-9
1146-3
18
5-88
169-3
1165-7
27-8
1-078
104-5
1145-9
18-5
5-635
167-4
1165-1
27-9
1-029
103-1
1145-4
19
5-39
165-6
1164-5
28-0
0-980
101-3
1144-9
19-5
5-145
163-5
1163-9
28-1
0-931
99-6
1144-4
20
4-9
161-5
1163-3
28-2
0-882
97-7
1143-8
20-5
4-655
159-3
1162-6
28-3
0-833
96-1
1143-3
21
4-41
157-1
1162-0
28-4
0-784
94-1
1142-7
21-5
4-165
155-7
1161-6
28-6
0-735
91-8
1142-0
22
3-92
152-2
1160-5
28-6
0-686
89-7
1141-4
22-2
13-822
151-2
1160-2
28-7
0-637
87-4
1140-6
22-4
3-724
150-3
1159-8
28-8
0-588
84-9
1139-9
22-6
3-626
149-1
1159-5
28-9
0-539
82-5
1139-2
22-8
3-528
148-0
1159-2
29-0
0-490
79-3
1138-2
23-0
3-43
146-9
1158-8
29-1
0-441
76-1
1137-2
23-2
3-332
145-7
1158-5
29-2
0-392
72-3
1136-1
23-4
3-234
144-5
1158-1
29-3
0-343
68-8
j 1135-0
23-6
3-136
143-3
1157-7
29-4
0-294
64-2
1 1133-6
23-8
3-038
142-1
1157-4
29-5
0-245
59-5
1132-2
24-0
2-94
140-8
1157-0
29-6
0-196
53-3
1130-3
24-2
2-842
139-6
1156-6
29-7
0-147
45-5
1127-9
266 INTRODUCTION TO CHEMICAL ENGINEERING
Specific Gravities of Soda Solutions at 15 C., with Beaume
Degree and Percentages of Dry and Crystallized Soda.
Specific
Gravity.
Beaume
Degree.
Dry Cryst. Soda
Soda. 10 Aq.
1 Cubic Me
conta
Dry Soda
(Kilos).
tre Solution
ins —
Cryst. Soda
(Kilos).
1-007
I
0-67 1-807
6-8
18-2
1-014
2
1-33 3-587
13-5
36-4
1-022
3
2-09 5-637
21-4
57-6
1-029
4
2-76
7-444
28-4
76-6
1-036
5
3-43
9-251
35-5
95-8
1-045
6
4-29
11-570
44-8
120-9
1-052
7
4-94
13-323
52-0
140-2
1-060
8
5-71
15-400
60-5
163-2
1-067
9
6-37
17-180
68-0
183-3
1-075
10
7-12
19-203
76-5 206-4
•083
11
7-88
21-252
85-3
230-2
•091
12
8-62
23-248
94-0
253-6
•100
13
9-43
•25-432
103-7
279-8
•108
14
10-19
27-482
112-9
304-5
•116
15
10-95
29-532
122-2
329-6
•125
16
11-81 31-851
132-9
358-3
•134
17
12-61 34-009
143-0
385-7
•142
18
13-16 35-493
150-3
405-3
•152
19
14-24 38-405
164-1
442-4
Liquids.
Specific
Density
Specific
Boiling-
Gravity
in Pounds
Heat
Point in
Substance.
(Water =
per
(Water =
Degrees
1-00).
Cubic
1-00).
Cent.
Foot.
Alcohol
0-791
49
0-673
78
Benzine
0-85
53
0-395
Ether
0-723
45
0-516
35
Mercury
13-596
848
0-033
357
Turpentine (oil of ). .
0-865
54
0-463
160
Water (almost boil-
ing)
0-958
60
1-013
100
APPENDIX
Solids.
267
Substance.
Specific
Gravity
Water =
1-00).
Density
n Pounds
per
Cubic
Foot.
Specific
Heat
(Water =
1-00).
Melting-
Point in
Degrees
Cent.
Aluminium (cast) . .
2-6
162
0-212
625
Antimony
6-7
417
0-051
435
Arsenic . .
5-9
368
0-081
Bismuth
9-82
613
0-031
260
Brass
8-4
525
0-094
900
Cadmium
8-6
539
0-057
320
Charcoal
0-36
22
0-241
Coal (anthracite) . .
1-43
89
0-241
— .
Cobalt
8-5
530
0-161
1500
Coke
1-0
62
0-203
Copper
8-8
550
0-092
1090
Fluorspar
3-15
196
—
900
Glass
2-89
181
0-198
1100
Gold
19-3
1200
0-032
1050
Ice(atO°C.)
0-92
57
0-504
0
Iridium
22-4
1400
0-033
1950
Iron (cast)
7-2
451
0-130
1100
Iron (wrought)
7-7
485
0-114
1600
Lead
11-4
710
0-031
325
Limestone
3-16
197
0-217
. —
Magnesium
1-74
109
0-250
500
Manganese
8-0
499
0-122
—
Nickel
8-7
542
0-107
1500
Oak
0-86
54
0-57
Palladium
11-4
710
0-059
1500
Pine
0-55
34
0-65
Platinum
21-5
1340
0-032
1775
Silver
10-5
653
0-056
950
Steel
7-85
490
0-116
1500
Sulphur
2-07
127
0-203
115
Thallium
11-8
736
0-034
290
Tin
7-3
455
0-056
230
Zinc..
7-12
445
0-095
415
i
INDEX
ABSORPTION system of cold storage,
209
Acid egg, 236
— retort, nitric, 159
Aerial wire ropeways, single wire,
213
_ double wire, 216
Air circulation system of cold
storage, 209
Air compression, 257
— drying, 103
— lift system, 237
— separators, 49
— gravity leg, 50
— "Stag," 51
Ammonia compressor, 205
Apron conveyor, 229
Armoured ceratherm pumps, 241
Aspinall evaporating pan, 125
" Atlas " pebble grinding mill, 31
B
Bag filter, 70
Ball mill, 29
Bearing for centrifugal spindle, 86
Belt conveyor, 226
power for, 260
Belting, 260
Blower, rotary, 249
Boiler, corrosion, 180
— foaming, 181
Brine-pipe system, 208
Bucket conveyor, 229
— " Weston " centrifugal, 84
Buhrstone mill, 24
By-product coke oven retort, 159
Calciner, rotary, 169
Can ice system, 206
Cane-juice subsider, 57
CaO in milk of lime, 263
Carbon dioxide compressor, 206
Cast-iron calandria, 129
Cell ice system, 208
Central screw closing of filter press,
81
Centrifugal machines, 84
Centrifugal machines, basket for, 84
— basket linings, 85
— bearings for spindle, 86
— electric- driven, 90
— friction pulley for, 90
— interlocking gear, 96
"Weston" type, 84
dressing, 44
Centrifugal pumps, 239
Ceratherm ware, 236
Chamber kiln, 167
Chamber press, 75
Chaser, 10
Climbing film vacuum pan, 135
Coal-gas retorts, 160'
Coffey still, 150
Cold storage system:
air circulation, 209
brine pipe, 208
direct expansion, 209
Column still, 145
Combination tube mill, 37
Comparison of thermometer scales,
264
Compression of air, 257 i
Compressors :
— ammonia, 205
— carbon dioxide, 206
— oxygen, etc., 253
Cone paint mill, 65
Continuous cone vacuum dryer, 115
Continuous still, 147
Continuous water- softening plant,
cylindrical, 188
— rectangular, 185
Control of temperature, 194
— of dye vessel, 200
of gas producer, 201
— of jacketed pan, 199
of spinning rooms, 202
of still, 198
Control steam valve, 194
Conveying gases:
— blowers, 249
— chimneys, 246
— compressors, 249
— fans, 247
— liquids:
— acid egg, 236
pipes, 231
268
INDEX
269
Conveying liquids:
— Pohle system, 237
— solids:
bucket elevators, 217
— runways, 212
— tipping waggons, 212
wheelbarrows, 211
wire ropeways, 213
Conveyors :
— apron, 229
— belt, 226
— bucket, 229
— scraper, 223
— shaking, 231
— worm, 222
Corrosion of boilers, 180
Cracker, 10
Crusher, fine rotary, 10
— jaw-, 1
Crushing rolls, 5
high speed, 6
fine, 8
Crutcher, 68
D
Direct heat evaporators, 118
Discharge valve, Lassen-Hjort, 188
Disintegrators, 14
— sifter for, 18
— fixing of, 20
Distillation of liquid mixtures, 25C
Double mixer for semi-liquids, 66
" Dowson " gas producers:
pressure, 161
suction, 163
bituminous, 163
Drag conveyor, 223
Dresser, powder, 44
Dressing machine, centrifugal, 47
Dryer, mixer, and ball mill, 115
Dryers, non- vacuum:
combination, 101
"Firman," 100
— " Hersey," 101
— rotary, 99
Sturtevant, 107
— vacuum:
continuous cone, 115
drum, 112
" Johnstone," 114
— rotary, 114
shelf, 109
E
Edge runner mill, 10
granite, 13
iron, 12
overhead- driven, 14
Electric control, " Isothermal," 197
Electro-magnetic separating ma-
chines, 52
Elevating liquids :
acid egg, 236
Pohle system, 237
Elevators, 217
Evaporating pan, "Aspinall," 124
open type, 121
"Wetzel," 125
Evaporators, 118
— direct heat, 119
Extraction plant, 152
Fans:
— mixed flow, " Rateau," 248
— radial, 248
Filter, bag, 70
Filter press:
frame type, 72
— plates for, 74
recessed type, 75
clips for, 78
double cloth system, 79
— plates, 79
methods of closing, 79
central screw, 81
hydraulic, 81
pneumatic, 81
— rack and pinion, 81
methods of feeding, 82
" Firman " dryer, 100
Flight conveyor, 223
Flue heater, 98
Freezing-point of brine, 262
CaCL,, 262
— mixtures, 263
Friction pulley for centrifugals, 90
Furnaces :
— "Harris," 171
— shafts for, 172
— " H. H." mechanical, 178
— muffle, 169
— regenerative, 170
— reverberatory, 170
— roasting, 171
G
Gas compressors, 254
— conveyance, 246
— retorts, coal, 160
*' Dowson " bituminous, 163
pressure, 161
suction, 163
hydrogen, 166
Gas valves, " Isothermal," 203
Grainer, 121
270 INTRODUCTION TO CHEMICAL ENGINEERING
Grasshopper conveyor, 234
Grizzly, 40
Hand-driven portable screen, 42
Harris roasting furnace, 171
— shaft, 172
Heater, flue, 98
"Hersey" dryer, 101
" H. H." mechanical roasting fur-
nace, 178
Horizontal mixer, 65
Hydraulic closing of filter press, 81
Hydrogen retorts, Lane process, 166
Ice making :
— can ice, 206
cell ice, 208
— plate ice, 208
Interlocking gear for centrifugals, 96
Intermittent water-softening plant,
184
Ironac, 231
" Isothermal" :
— control apparatus, 197
— gas valve, 203
— steam valve, 195
— superheated steam valve, 199
— thermometer, 196
Jaw-crusher, 1
Jet condenser, 133
" Johnstone" dryer, 114
K
"Kestner" evaporators:
climbing film, 135
falling film, 137
— quadruple effect, 139
— salting type, 139
Kilns:
— chamber, 167
— lime, 167
— rotary, 168
Lane hydrogen retorts, 166
Lassen-Hjort water plant:
— cylindrical, 190
rectangular, 185
Levigating mill, 56
— plant, 61
Lightfoot refrigeration system, 204
Lime kiln, 167
Lime-soda water softening plant:
continuous, 185
intermittent, 184
Liquid mixtures, distillation, 256
Linings for "Weston" basket, 85
Low boiling-point liquids, 262
Lubricating oil stijl, 158
M
Machines :
— centrifugal, 84
dressing, 44
— crutching, 68
— electro-magnetic separating, 52
— mixing, 61
— vibration, 45
Magnetic pulley, 55
Measuring apparatus, Lassen-Hjort,
185
Mechanical raker, 225
Methods of closing filter press, 81
— feeding filter press, 82
Milk of lime, 263,
Mill:
— ball, 29
— Buhrstone, 24
— combination tube, 37
— cone paint, 65
— edge runner, 10
granite, 13
iron, 12
— levigating, 56
— overhead- driven, 14
— pebble, 31
— pug, 64
- putty, 62
— roller, 27
— triple roller, 28
— tube, 34
— vertical runner, 26
Mixer:
— double, 67
— horizontal, 65
— open drum, 67
— undergeared, 68
Mixing machinery, 61
Muffle furnace, 169
Multiple effect vacuum pan, 133
"Multiplex" evaporator, 141
N
" Newaygo " screen, 49
Nitric acid retort, 159
Open drum mixer, 67
— evaporating pan, 121
INDEX
271
Paint mill, 65
Pans:
— "Aspinall," 125
— steam- jacketed, 122
— vacuum, 125
— "Wetzel," 125
Pebble grinding mill, 31
Permutit, 190
Petroleum stills, 154
Plant:
— extraction, 152
— levigating, 61
— lime-soda, continuous, 185
intermittent, 184
Lassen-Hjort, cylindrical,
190
rectangular, 185
— Permutit, 190
Plate ice system, 208
Pohle air system, 237
Portable hand-driven screen, 42
Pot still, 159
Powder dresser, 44
Press filter, 71
chamber, 75
frame, 72
plates, 74
recessed type, 77
clips, 78
double cloth system, 78
- plates, 79
methods of closing :
central screw, 81
— hydraulic, 81
pneumatic, 81
rack and pinion, 81
methods of feeding, 82
Pug mill, 64
Pulley, magnetic, 55
Pumps, acid, centrifugal, 239
plunger, 238
— vacuum, Gaede, 255
— Langmuir, 255
mercury, 255
Siemens oil, 255
Putty mill, 62
•so
Quadruple effect evaporator, 139
R
Rack and pinion closing of filter
press, 81 "
Rectangular water- softening plant,
185
Rectifying still, 147
Reels, sifting, 43
Refrigerating machines, 203, 262
ammonia, 204
absorption system, 209
carbon dioxide, 206
Regenerative furnaces, 171
Retorts:
— by-product coke-ovens, 159
— coal-gas, 160
— " Dowson " bituminous, 163
pressure, 161
suction, 163
— hydrogen, 166
— nitric acid, 159
Reverberatory furnaces, 190
Roasting furnace, 171
Roller mills, 27
triple, 28
Rolls, crushing, 5
— fine, 8
— high-speed, 6
Rotary blower, 249
— calciner, 169
— fine crusher, 10
— vacuum dryer, 114
Runway for mine, 212
Salting type evaporator, 139
Scraper conveyor, 223
Screen, " Newaygo," 49
— portable hand- driven, 42
Self-recording hygrometer, 104
chart, 106
Separation by water, 56
Separators, air, 49
— electro-magnetic, 53
— gravity leg, 5J
— " Stag," 5
Settling tank, 57
Shafting, 261
Shafts for roasting furnace, 172
Shaking sifters, 47
Sifters for disintegrators, 18
Sifting reels, 43
Slat conveyor, 229
Soap crutcher, 68
Softening of water, 183
plant, continuous, 185
intermittent, 184
lime-soda, 184
Lassen-Hjort, cylindrical,
190
discharge valve, 188
measuring apparatus,
185
rectangular, 185
Permutit, 190
272 INTRODUCTION TO CHEMICAL ENGINEERING
Spindle, centrifugal bearing, 86
"Stag" ball mill, 33
Stamps, 38
Steam- jacketed kettle, 123
— pans, 122
— temperature, pressure, and total
heat, 265
— valve, " Isothermal," 195
Still:
— Coffey, 150
— column, 145
— continuous, 147
— lubricating oil, 158
— petroleum, 154
— pot, 159
— rectifying, 147
— tar, 158
" Sturtevant," drying system, 103
— hygrometer, 104
guide chart, 104
— triple duct dryer, 107
Superheated steam valve, 199
Surface condenser, 133
Synchronous speeds for centrifugals,
86
T
Tables:
— common liquids, 266
• solids, 267
— comparison of thermometer
scales, 264
— specific gravity of soda solutions,
266
— total heat of steam, 265
Tantiron, 233
- pumps, 238
Tar stills, 158
Thermometer, "Isothermal," 196
Three-way tap, 247
Throw-off carriage, 226
Tilting kettle, 123
Tipping waggons, end, 211
— side, 212
Triple duct dryer, 107
— roller mill, 28
Trommel, 40
Tube mills, 34
Typical guide chart, 106
U
Undergeared mixer, 68
" Universal" cone mill, 66
Vacuum dryers:
continuous cone, 115
drum, 112
Vacuum dryers:
— " Johnstone," 114
mixer and ball mill, 115
— rotary, 114
- shelf, 109
— pan:
cast-iron calandria, 129
copper, 127
jet condenser, etc., 130
"Kestner" climbing film, 135
falling film, 137
— quadruple effect, 139
salting type, 139
— multiple effect, 133
- "Multiplex," 141
— Torricellian condenser, etc.,
130
— pumps, diffusion, 255
dry, 130
Gaede, 255
Langmuir, 255
Siemens oil, 255
- wet, 130
Valve, " Isothermal "gas, 203
steam, 195
superheated steam, 199
Vertical runner mill, 26
Vibration machines, 45
Vitreon ware, 235
Vitreosate, 236
Vitreosil, 235
W
Warm air drying, 103
Water separation, 56
— softening plant :
discharge valve, 188
Lassen-Hjort, cylindrical,
188
lime-soda, continuous, 185
intermittent, 184
measuring apparatus, 185
Permutit, 190
— rectangular, 185
— treatment, 179
chemistry of process, 183
— impurities, 181
" Weston" centrifugals, 84
— basket, 84
basket linings, 84
electric- driven, 91
— — friction pulley, 90
— interlocking gear, 96
spindle bearing, 85
water-driven, 91
" Wetzel" evaporating pan, 125
Worm conveyor, 222
BILLING AND SONS, LTD., PRINTERS, OUILDFORD, ENGLAND
53T6
A LIST OF BOOKS
PUBLISHED BY
Sir Isaac Pitman & Sons, Ltd.
(Incorporating WHITTAKER & CO.)
I AMEN CORNER, LONDON, E.C. 4
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ARCHITECTURAL HYGIENE, OR SANITARY SCIENCE AS
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ART AND CRAFT OF CABINET MAKING. D. Denning . .60
ASTRONOMY, FOR GENERAL READERS. G. F. Chambers . 4 0
ATLANTIC FERRY: ITS SHIPS, .MEN AND WORKING, THE.
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BAUDOT PRINTING TELEGRAPHIC SYSTEM. H. W. Pendry 3 0
CALCULUS FOR ENGINEERING STUDENTS. J. Stoney .36
CARPENTRY AND JOINERY: A PRACTICAL HANDBOOK FOR
CRAFTSMEN AND STUDENTS. B. F. and H. P. Fletcher 7 6
CENTRAL STATION ELECTRICITY SUPPLY. A. Gay and C. H.
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COLOUR IN WOVEN DESIGN: A TREATISE ON TEXTILE
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DYNAMO: ITS THEORY, DESIGN AND MANUFACTURE, THE.
C. C. Hawkins -and F. Wallis. In two vols.. .Each 12 6
ELECTRIC LIGHT FITTING: A TREATISE ON WIRING FOR
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ELECTRO PLATER'S HANDBOOK. G. E. Bonney >V . .3 6
ELECTRICAL ^EXPERIMENTS. „ :,«, . 3 0
ELECTRICAL INSTRUMENT MAKING FOR AMATEURS. S. R.
Bottone . . . . . . . .36
ELECTRIC MOTORS: HOW MADE AND HOW USED. S. R.
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ELECTRIC BELLS AND ALL ABOUT THEM. S. R. Bottone . 2 6
ELECTRIC TRACTION. A.T.Dover. ., . . . 21 0
ELECTRICAL ENGINEERS' POCKET BOOK. K. Edgcumbe . 6 0
ELECTRIC MOTORS AND CONTROL SYSTEMS. A. T. Dover. 16 0
ELECTRIC MOTORS— CONTINUOUS, POLYPHASE AND SINGLE-
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ELECTRIC LIGHTING AND POWER DJSTRIBUTION. Vol. I.
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ELECTRIC WIRING, FITTINGS, SWITCHES AND LAMPS. W.
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ELECTRIC WIRING DIAGRAMS. W. Perren Maycock v* • 3 0.
ELECTRIC WIRING TABLES. W. Perren Maycock .: 4 0
ELECTRIC CIRCUIT THEORY AND CALCULATIONS. W.
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ELECTRICAL MEASURING INSTRUMENTS. Murdoch and
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ELECTRIC TRACTION. J. H. Rider . \^' • 12 6
ELECTRIC LIGHT CABLE! S.A.Russell. 10 6'
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ELECTRICITY IN HOMES AND WORKSHOPS. S. F. Walker . 6 0
ELECTRIC LIGHTING FOR MARINE ENGINEERS. ,, .56
ELECTRICAL ENGINEERS' POCKET BOOK. Whittaker's . 6 0
ELEMENTARY GEOLOGY. A. J. Jukes-Browne . . .30
ELEMENTARY TELEGRAPHY. H. W. Pendry . . .36
ELEMENTARY AERONAUTICS, OR THE SCIENCE AND PRACTICE
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ELEMENTARY GRAPHIC STATICS. J. T. Wight . . .50
ENGINEER DRAUGHTSMEN'S WORK: HINTS TO BEGINNERS IN
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ENGINEERING WORKSHOP EXERCISES. E. Pull . .26
ENGINEERS' AND ERECTORS' POCKET DICTIONARY: ENGLISH,
GERMAN, DUTCH. W. H. Steenbeek . . .26
ENGLISH FOR TECHNICAL STUDENTS. F. F. Potter . .20
EXPERIMENTAL MATHEMATICS. G. R. Vine
Book I, with Answers ..... 9
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EXPLOSIVES INDUSTRY, RISE AND PROGRESS OF THE BRITISH 18 0
FIELD. WORK AND INSTRUMENTS. A. T. Walmisley . 60
FIRST BOOK OF ELECTRICITY AND MAGNETISM. W. Perren
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GALVANIC BATTERIES: THEIR THEORY, CONSTRUCTION AND
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GAS SUPPLY, IN PRINCIPLES AND PRACTICE: A GUIDE FOR
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GEOMETRICAL OPTICS. T. H. Blakesley . . . .30
GERMAN GRAMMAR FOR SCIENCE STUDENTS. W. A.
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HANDRAILING FOR GEOMETRICAL STAIRCASES. W. A.
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HIGH-SPEED INTERNAL COMBUSTION ENGINES. A. W. Judge 18 0
HISTORICAL PAPERS ON MODERN EXPLOSIVES. G. W.
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How TO MANAGE THE DYNAMO. S. R. Bottone . .10
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INDUCTION COILS. G. E. Bonney . . . .60
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LEKTRIC LIGHTING CONNECTIONS. W. Perren Maycock . 9
LENS WORK FOR AMATEURS. H. Orford *4v>^'> /*?/•*; 3 Q
LIGHTNING CONDUCTORS AND LIGHTNING GUARDS. Sir O.
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LOGARITHMS FOR BEGINNERS. ; ^ --VM-I £i£ r«*: ^.^ ,-. j g
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MANAGEMENT OF ACCUMULATORS. Sir D. Salomons . A '.•'" 7 6
MANUAL INSTRUCTION — WOODWORK. Barter, S. . ' . . ' 7 6
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MECHANICAL TABLES, SHOWING THE DIAMETERS AND CIR-
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MECHANICAL ENGINEERS' POCKET BOOK. Whittaker's . 5 0
MECHANICS' AND DRAUGHTSMEN'S POCKET BOOK. W. E.
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METAL WORK — REPOUSSE. C. G. Leland '.'.'.,' :* C""' ',. * 5 0
METRIC AND BRITISH SYSTEMS OF WEIGHTS AND MEASURES.
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MINERALOGY: THE CHARACTERS OF MINERALS, THEIR
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MINING MATHEMATICS (PRELIMINARY). G. W. Stringfellow 1 0
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MODERN PRACTICE OF COAL MINING. Kerr and Burns.
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MODERN OPTICAL INSTRUMENTS. H. Orford . f"ft :'v^... 3 0
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MOVING LOADS ON RAILWAY UNDER BRIDGES. H. Bamford 5 6
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v , '* Lanbolt . . ; .''11 yi " .' .'..'.,•; '^ '•+)?'. ,-. 5 6
OPTICS OF PHOTOGRAPHY AND PHOTOGRAPHIC LENSES.
J.T.Taylor . ' ^ :'\'l '.* ,.s ' .'t ,/fl'V " :. 4 0
PIPES AND TUBES: THEIR CONSTRUCTION AND JOINTING.
P. R. Bjorling v,. -^ ' > ^;v'., . l^j -'^j ^ V'- 4 0
PLANT WORLD: ITS PAST, PRESENT AND FUTURE, THE. G.
Massee . ;*<v . '". .•;'••'•'; " •';." ' ;'* ^ -™. '" '' .'';";*' 30
POLYPHASE CURRENTS. A. Still . ''••{• ,'*J : v^.lii*'V iOir* 7 6
POWER WIRING DIAGRAMS. A. T. Dover ir-pr '*+ •'< <«/>-.> '• 7 ^
PRACTICAL EXERCISES IN HEAT, LIGHT AND SOUND. J. R.
Ashworth 2 6
s. rf.
PRACTICAL ELECTRIC LIGHT FITTING. F. C. Allsop . 6 0
PRACTICAL EXERCISES IN MAGNETISM AND ELECTRICITY.
J. R. Ash worth ... 2* 6
PRACTICAL SHEET AND PLATE METAL WORK. E. A. Atkins 7 6
PRACTICAL IRONFOUNDING. J. G. Homer . . .60
PRACTICAL EDUCATION. C. G. Leland . . .".50
PRACTICAL TESTING OF ELECTRIC MACHINES. L. Oulton
and N. J. Wilson . . ..60
PRACTICAL TELEPHONE HANDBOOK AND GUIDE TO THE
TELEPHONIC EXCHANGE. J. Poole ....
PRACTICAL ADVICE FOR MARINE ENGINEERS. C.W.Roberts 3 6-
PRACTICAL DESIGN OF REINFORCED CONCRETE BEAMS AND
COLUMNS. W. N. Twelvetrees . . . ..76
PRINCIPLES OF FITTING. J. G. Homer . . .60
PRINCIPLES OF PATTERN-MAKING ,, ... 4 0
QUANTITIES AND QUANTITY TAKING. W. E. Davis . . 40
RADIO-TELEGRAPHIST'S GUIDE AND LOG BOOK. W. H.
Marchant .... .56
RADIUM AND ALL ABOUT IT. S. R. Bottone . . .16
RAILWAY TECHNICAL VOCABULARY. L. Serraillier . .76
RESEARCHES IN PLANT PHYSIOLOGY. W. R. G. Atkins . 9 0
ROSES AND ROSE GROWING. Kingsley, R. G. . .76
ROSES, NEW ........ 9
RUSSIAN WEIGHTS AND MEASURES, TABLES OF. Redvers
Elder . —
SANITARY FITTINGS AND PLUMBING. G. L. Sutcliffe . .60
SIMPLIFIED METHODS OF CALCULATING REINFORCED CON-
CRETE BEAMS. W. N. Twelvetrees . . . 9
SLIDE RULE. A. L. Higgins ..... 6
SMALL BOOK ON ELECTIC MOTORS, A. C. C. AND A. C. W.
Perren Maycock. . . . . . . .50
SPANISH IDIOMS WITH THEIR ENGLISH EQUIVALENTS. R.
D. Monteverde 30
SPECIFICATIONS FOR BUILDING WORKS AND How TO WRITE
THEM. F. R. Farrow 40
STEEL WORK ANALYSIS. J. O. Arnold and F. Ibbotson . 12 6
STRESSES AND STRAINS: THEIR CALCULATION, ETC. F. R.
Farrow . . . . . . . . .60
STRUCTURAL IRON AND STEEL. W. N. Twelvetrees. . 7 6
SUBMARINES, TORPEDOES AND MINES. W. E. Dommett . 3 6
SURVEYING ANP SURVEYING INSTRUMENTS. G. A. T.
Middleton . . . .. . . . .^60
TABLES FOR MEASURING AND MANURING LAND. J. Cullyer 3 0
TEACHER'S HANDBOOK OF MANUAL TRAINING: METAI, WORK.
J. S. Miller . ( " ./tt>,, ' '"j..,J, / * -\V 4 °
TELEGRAPHY: AN EXPOSITION OF THE TELEGRAPH SYSTEM
OF THE BRITISH POST, OFFICE. T. E. Herbert '( .,' 10 6
, TEXT BOOK OF BOTANY. Part I — THE ANATOMY OF
FLOWERING PLANTS. M. Yates •t/;i*< ''".'* " "'"V" ' ' '.il 2 0
TRANSFORMERS FOR SINGLE AND MULTIPHASE CURRENTS.
G. Kapp . ". M£ " •' '• r ;'' . \ '' V 12 6
TREATISE ON MANURES. A. B. Griffiths . » . . .7 6
VENTILATION OF ELECTRICAL MACHINERY. W. H. F.
%' Murdoch . .". ^ . , _. ._ \ 'f, . ; , -\ '.** . 3 6
VENTILATION, PUMPING, AND HAULAGE, THE MATHEMATICS
OF. F. Birks . ' ''.' .". A," \ . « $ .L . 3 0
VILLAGE ELECTRICAL INSTALLATIONS. W. T. Wardale . 2 6
WIRELESS TELEGRAPHY AND HERTZIAN WAVES. S. R.
Bottone . .'. . . . . , , . . 30
WIRELESS TELEGRAPHY: A PRACTICAL HANDWORK FOR
OPERATORS AND STUDENTS. W. H. Marchant . . 60
WIRELESS TELEGRAPHY AND TELEPHONY. W. J. White . 4 0
WOODCARVING., C. G. Leland . . . . .50
Catalogue of Scientific and Technical Book* pott free.
LONDON: SIR ISAAC PITMAN & SONS, LTD.,! AMEN CORNER^. C.4
UNIVERSITY OF CALIFORNIA LIBRARY
BERKELEY
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