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UNIVERSITY OF ILLINOIS BULLETIN
Vol. IX JUNE 3, 19f2 No. 30
fEntered Feb. 14 , 1902, at Urbana, 111. , as second-class matter under Act of Congress of July 16,1394]
BULLETIN NO. 60
THE COKING OF COAL
AT LOW TEMPERATURES
(WITH A PRELIMINAPvY STUDY OF THE BY-PRODUCTS)
BY
S. W. PARR
AND
H . L. OL1N
UNIVERS/iTV OF-' ILLINOIS
ENGINEERING ^XPSPtlMEISfT, STATION
URBANA, ILLINOIS
PUBLISHED BY THE UNIVERSITY
PBICB: TWENTY-FIVE CENTS
EUBOPEAN AGENT
CHAPMAN AND HALL, LTD., LONDON
TIHE Engineering Experiment Station was established by
I act of the Board of Trustees, December 8, 1903. It is
the purpose of the Station to carry on investigations
along various lines of engineering and to study problems
of importance to professional engineers and to the manu-
facturing, railway, mining, constructional, and industrial inter-
ests of the the State.
The control of the Engineering Experiment Station is vested
in the heads of the several departments of the College of Engi-
neering. These constitute the Station Staff, and with the
Director, determine the character of the investigations to be
undertaken. The work is carried on under the supervision of
the Staff, sometimes by research fellows as graduate work,
sometimes by members of the instructional staff of the College
of. Engineering, but more frequently by investigators belonging
to the Station corps.
The results of these investigations are published in the form
of bulletins, which record mostly the experiments of the Sta-
tion's own staff of investigators. There will also be issued
from time to time in the form of circulars, compilations giving
the results of the experiments of engineers, industrial works,
technical institutions; and governmental testing departments.
The volume and number at the top of the title page of the
cover are merely arbitrary numbers and refer to the general
publications of the University of Illinois; above the title is given
the number of the Engineering Experiment Station bulletin or
circular, which should be used in referring to these publications.
For' copies of ^bulletins, circulars or other information ad-
dress the Engineeri^jExn&Elm^it'SJation, Urbana, Illinois.
UNIVERSITY OF ILLINOIS
ENGINEERING EXPERIMENT STATION
BULLETIN No. 60 JUNE 1912
THE COKING OF GOAL AT LOW TEMPERATURES
'WITH A PRELIMINARY STUDY OF THE BY-PRODUCTS )
BY S. W. PARR, PROFESSOR OF APPLIED CHEMISTRY, AND H. L. OLIN,
RESEARCH FELLOW, DEPARTMENT OF CHEMISTRY
CONTENTS
PAGE
I. Introduction 3
II. Experimental Work 5
III. Gases 9
IV. Tar , 12
V. Coke 14
VI. The Formation of Coke 20
VII. Summary and Conclusions 26
Appendix 29
254958
THE COKING OF GOAL AT LOW TEMPERATURES
I. INTRODUCTION
1. Purpose of the Investigation.— The investigations dis-
cussed in this bulletin had two general purposes in view: (1)
to discover some fundamental facts pertaining to the properties
and characteristics of bituminous coals; (2) to determine the
feasibility of modifying the composition of raw coal in order
that a different type of fuel might be produced, or possibly an
alteration accomplished of the entire fuel content into forms bet-
ter suited to present-day requirements.
2., Scope of Previous Investigations. — In earlier experi-
ments1 (1907-1908), the information developed was mainly of
the type indicated under the first division; for example, the ex-
periments early indicated the important role played by small
amounts of oxygen in the gases surrounding the heated masses
of coal. The ease with which carbonaceous matter absorbed or
united with oxygen was so striking that it seemed desirable to
follow the matter into detail regarding the temperatures at
which oxidation takes place, and its effect upon the material in
hand. As a result, the whole matter of coal oxidation at low
temperatures was opened up as one of extreme importance. One
fundamental fact brought out in the study2 was the absorbent
power of freshly-mined coal for oxygen, and the part oxygen
played in producing certain changes in the coal and promot-
ing the initial form o,f deterioration in storage. Again3, the
prime element in all the phenomena was seen to be that of oxi-
dation. It will thus be seen that these preliminary studies on
low temperature distillation, while mainly bringing into view
what might be termed the scientific or fundamental properties
of the material, at the same time determined facts which have
had much to do with developing the practical application of
!The present investigations are a continuation of the work carried on in 1907-8 and presented
as a preliminary report under the title of "The Modification of Illinois Coal by Low Tempera -
ature Distillation", Bulletin No. 24, University of Illinois, Engineering Experiment Station,
by S. VV. Parr and C. K. Francis. 1908.
2 "The Occluded Gases in Coal", Bulletin No. 32, University of Illinois, Engineering Experi
ment Station, by S. W, Parr and Perry Barker.
3"The Weathering of Coal", Bulletin No. 38, University of Illinois, Engineering Experi-
ment Station, by S. W. Parr and W. P. Wheeler; also "The Spontaneous Combustion of Coal".
Bulletin No. 46, University of Illinois, Engineering Experiment Station, by S. W. Parr and
F. W. Kressmann.
4 ILLINOIS ENGINEERING EXPERIMENT STATION
the information in its relation to storage and spontaneous com-
bustion.
In the second phase of the earlier study, i. e., its industrial
side as related to the development of a special type of fuel, it
seemed to, be established that below a certain temperature, say
700° F., the heavy hydrocarbons, those chiefly responsible for
the formation of smoke, could be driven off, yielding a gas of
high illuminating power, a tar with high percentage of volatile
oil, and a solid which, while it could be burned without smoke,
was friable and not well adapted to ordinary use as a fuel.
3. Outline of Present Investigation. — In the present studies,
the friable or non-cokine- tendency of the earlier product has
been found to depend directly upon the amount of oxidation
that has occurred both in the preliminary exposure at ordinary
temperature arid in the process of heating to moderately high
temperatures.
The fact that a coke of good texture could be produced
when a careful exclusion of oxygen had been effected, has given
special interest to the present experiments. In addition, im-
portant facts have developed in connection with the study of
the various by-products. These by-products have also been
more or less modified in their characteristics by the exclusion
of oxygen.
Briefly outlined, the present studies have developed three
lines of industrial interest.
First: The possibility of developing a smokeless fuel of
good texture and admirably suited to domestic as well as to gen-
eral industrial use where absence of smoke is essential. The ac-
companying by-products promise to be of special value. These
consist of (a) Ammonia, though smaller in quantity than the
yield obtained at higher temperatures; (b) Illuminating gas of
high candle-power and high heat value; and (c) Tar, which is
composed almost entirely of oils, with a minimum amount of
pilch and free carbon. Some of the oils produced are of pecul-
iar structure and may have more than passing interest, two of
the fractions, for example, being readily oxidizable. The iodine
absorption numbers of the lighter fraction are found to be as
high as 165.
Second : They suggest a possible method for the manufac-
ture of producer gas which would be free from present difficul-
ties attending the use of bituminous coal, and would convert a
PARR-OLIX — COKING OF GOAL AT LO\V TEMPERATURES 5
much higher per cent of the fuel into the gaseous form. In
view of recent developments in the matter of combustion, effici-
encies are possible1 where gaseous fuel is available which are
almost revolutionary in character.
Third: There are opened up interesting possibilities in the
production of coke, briquettes or other forms of fuel in a dense
and stable form to meet certain requirements of shipping, stor-
ing, foundry, and other industrial uses. Certain facts developed
in these studies will be found to throw some light on the prob-
lem of coking, which is at present but little understood2.
It is not intended here to enter into a discussion of these
three main topics; they will be taken up again after the details
of the experiments have been set forth. The results of the ex-
periments may then with better understanding be made to enter
into the conclusions reached.
II. EXPERIMENTAL WORK
4. Apparatus. — The apparatus employed is illustrated in
Fig. 1. From the high pressure main at A, steam was admitted
to BB. a %-in. pipe 11 ft. long, fitted with twro return elbows.
The steam was then heated by a 26-burner combustion furnace,
CC. The retort D, 18 in. by 8 in., containing the coal, was fitted
with a head J held in place with set-screws and sealed with
asbestos. From the retort, the distillates were conducted by a
pipe to a condenser E connected in turn with a large wash
bottle F. Here the oils and tars were collected while the gases
passed on to the gasomeier G. A Hoskins nickel-nichromc
thermocouple,, inserted through a stuffing box 5 and joined to a
millivoltmeter K measured the temperature of the retort contents.
A battery of burners placed directly under the retort provided
a means for securing additional heat, which was retained
by means of, an asbestos-lined oven which entirely surrounded
both the retort and the furnace.
5. Cse of Superheated Steam. — Superheated steam was
used in this series of experiments as a medium for carrying1 the
iSurf ace Combustion. Proc. Am. Gas Inst.. 1911. By Prof. W. A. Bone. In this article
Prof. Bone gives data showing an efficiency in the generation of steam by use of the principle
of surface combustion of 94.2 per cent. It should be noted, however, that this efficiency is
based upon the net heating value of gas.
2"The question as to what really is the factor that produces the coking tendency character-
istic of some coals has been a matter of some speculation among manufacturers and users of
coke for two hundred years and we are no nearer to its solution now than were the investigators
of two centuries ago.''— Iron Age. 1907. F. C. Keighley.
ILLINOIS ENGINEERING EXPERIMENT STATION
FIG. 1
heat into the coal mass, in order to distribute the heat evenly
throughout the coal and thus obviate the necessity for revolving the
container. In the earlier experiments (1907-1908 , the carboniza-
tion was carried on in a cylinder heated externally and mounted
on hollow trunions in order to make possible the turning of the re-
ceptacle, while at the same time the hollow bearings permitted
the admission of various inert gases at one end and the discharge
of the distillates at the other. With that device, the frequent
turning over of the coal seemed to be unfavorable to the forma-
tion of coke having a homogeneous texture. Moreover, the
mechanical features were not easily installed. There was
positive evidence also of the activity of small quantities of oxy-
gen, which entered by leakage or as an impurity in the circula-
ting gas employed, thereby acting as a disturbing element.
There seemed sufficient reasons, therefore, for employing a
fixed retort and using superheated steam as the medium for con-
veying the heat and also for securing a suitable atmosphere for
the distillation. As will be seen later under the discussion of the
coking of coal, the use of steam in this manner has other
advantages which, while not fully appreciated at first, are
directly in line with the fundamental conditions upon which
depends the property of coke formation.
6. Coal Used. — Table 1 gives the data concerning the coals
used, it should be noted that since these studies were made for the
PARR-OLIN — COKING OF COAL AT LOW TEMPERATURES
purpose of testing the coking powers of the different coals and
not to determine their relative commercial values, many of the
samples selected were cleaner than the general run-of-mine.
The low ash and sulphur percentages result from the exclusion
of pyrites.
TABLE 1
COMPOSITION OF COAL
Mines
Counties— Illinois
Moisture
Ash
Volatile
Matter
Fixed
Carbon
Sulphur
B. t. u.
Vermilion
8.80
8.72
43.05
39.43
2 88
12673
Franklin
6 84
7.38
37 96
47 82
1 33
12770
Saline
3.93
5.80
37.86
52.41
1.54
13593
Macon
8 70
12.12
39 30
40 88
2 30
11 417
Perry
7 19
10 05
35 42
47 34
80
12153
Williamson
5 30
8.55
36 50
49 65
2.77
12640
7. Operation. — A quantity of coal sufficient for one run
only from 2500 to 3000 grams, was crushed at one time. In the
first experiments, the pieces ranged from Vi in. to buckwheat
size, the dust being removed by a sieve. At first the coal was put
directly into the retort, but it was found that the circulation of
the steam was retarded, delaying the heating of the mass. To
remedy this, a cylindrical sheet-iron container, 6 in. in diameter,
perforated with small holes, was made to hold the charge. This
shell (see Fig. 2) being smaller than the retort and having a sur-
O O O O O 0
O
o o o o e o
o
FIG. 2
rounding space of about 1 in., allowed a free distribution of heat.
It was used throughout the remaining runs of the series.
Steam was admitted from the main and allowed to blow
through the system until the air was entirely displaced. The
combustion furnace was next started and then the burners under
the retort. The coal was not stirred after heating had begun.
Table 2 exhibits the average working conditions. By im-
proving the facilities for applying external heat to the retort,
the time of the later runs was reduced to an average of about five
hours.
ILLINOIS ENGINEERING EXPERIMENT STATION
TABLE 2
TEST CONDITIONS : FIRST SERIES
Run No.
3
I
5
6
7
Weight of coaJi, grams
4800
5351
2195
3498
3398
Weight of residue, grams
4030
4112
1895
2810
2895
Max temp, (degrees C )
475°
515°
450°
410°
430°
Racio of coke
84$
76.8$
86.3$
80.3$
85.2$
JNineteen runs were made in the first series, using Williamson Co. coal for the first 10
tests. In the other tests, the coal came from the following counties in the order given. Ver-
milion, Williamson, Franklin, Saline, Macon, Vermilion. Vermilion, Williamson. Vermilion.
8. Distribution of Products. — Table 3 illustrates the distri-
bution of products.
TABLE 3
EXPERIMENT2 NO. 1 1
Coal used3 , Electric Mine. Danville, 111.
Temperature (average) 450°
Time of distillation 5hr.
Volatile matter in original coal not including moisture 43.00
Volatile matter in coke residue 27,95
Volatile matter in coke residue referred to original coal. . . 22.01
Loss in weight of original coal, volatile matter only, not
including moisture 20.28
Total volatile matter derived as above, not including mois-
ture 42.29
Total material, removed by distillation including moisture 29.10
2Selected as a typical example .
3For methods of calculating percentages of coal constituents in this and succeeding tables
see Bui. No. 16, p. 209, 111. Geol. Sur.
TABLE 4
YIELD OF PRODUCTS FOR DIFFERENT PERIODS OF HEATING
Time of Heating
3hr.
6hr.
Coal
3000 grams
4000 grams
Coke . .
2327 grams
3902 grams
77.50$
72.50$
Weight of tar , . ....
238.5 grams
316.0 grams
Per cent tar
7.93$
7.90$
Weight of total water
208.5 grams
348.4 grams
Per cent free moisture
3.38$ o oo<£
3.00$ nr.Q .,,<£
water constitution
3.55$ or6-93*
5.71$ Or8'7l#
Volume of gas at 760 mm and 0°
87 liters
134.7 liters
.46 cu. ft.
.54 CU. ft.
From the preceding tables a fair indication is given of the
ratio of distribution of the main products of decomposition. A
study of these three products, gas, tar and coke, has been made,
sufficient to determine their general characteristics and value.
PARR-OLIN — COKING OF GOAL AT LOW TEMPERATURES
9
III. GASES
9. Analyst of the Gas. — The methods of Hempel were used
in making all gas analyses. For absorbing the illuminants, bro-
mine water checked with the results from fuming sulphuric
acid and was free from the disagreeable properties of the latter.
The paraffin hydrocarbons were determined by the use of the ex-
plosion pipette. Hydrogen was determined separately with
palladium sponge, a variation from the ordinary industrial
method necessary when higher paraffins are present in the gas.
Calorific values were determined with the Parr gas calorimeter.
It is impossible to determine absolutely the paraffin content
of a gas by any methods now in general use, when more than
two of the homologues of methane are present. However, by
measuring the contraction of the gases and the amount of G02
produced in burning them in the explosion pipette, the total
volume of the hydrocarbons having the general formula Gn H2n+2
may be determined together with the average value for n. On
the assumption that the higher homologues are all ethane, the
percentages of methane and ethane may then be computed1.
Several analyses of the gases obtained early in the work
were made, but on account of air leakage in the gasometer, the
results obtained were misleading. Table 5 shows the average of
results obtained under satisfactory conditions, from gas evolved
at an average temperature of 400°.
TABLE 5
GAS FROM DANVILLE ELECTRIC MINE COAL
H2S
C02
Illuminants
CO
H2
C2H6
CH4
N2
B. t. u.
3.2
5.7
8.3
5.2
5.0
14.4
51.4
5.7
1032
The computed heat value of this gas was 1024 B. t. u. and
agrees closely with that determined directly. Heat values of the
different gases as given by Abady2 were used as the basis of cal-
culation.3
From the agreement between the observed heat value as
-shown by the gas calorimeter and the calculated value as derived
lAbady, Gas Analyst's Manual, p. 356, 1902.
2Qas Analyst's Manual, p. 521, 1902.
3According to J. H. Coste (Chemical Engineer, February, 1911) it has been found from
Julius Thomson's figures that the average calorific value of the unsaturated hydrocarbons is
•equivalent to that of propylene, C3H6.
10 ILLINOIS ENGINEERING EXPERIMENT STATION
from the constituents, indirect evidence is obtained as to the
correctness of the assumption concerning the composition of hy-
drocarbons assumed to be present in the higher forms.
10. Heat Value. — It will be noted that this gas is relatively of
high heating value, 1024 B. t. u. per cu. ft. Compared with ordi-
nary city gas at 600 B. t. u. per cu. ft., this gas has a heat value
about 70 per cent greater, i. e., 1 cu. ft. at 1024 B. t. u. would be
equal to nearly 1.7 cu. ft. at OuO B. t. u.
11. Sulphuretted Hydrogen. — The gas is practically free
from naphthalene but has a considerable content of H2S. The latter
feature is unexpected, since the temperature of decomposition of
FeS.2 is 1000° G. and above. Doubtless, therefore, the sulphur-
etted hydrogen present is in the main due to the breaking down
of the organic sulphur. It seems to be entirely in the form of
H2S and, therefore, easily removable by the usual methods of
purification. Some of the coke residue from a coal having orig-
inally 4 per cent of sulphur was examined to see if any of the
iron pyrites, FeS2, had been broken down by the temperature em-
ployed to ferrous sulphide, FeS. Five grams were treated with
a large excess of dilute hydrochloric acid. The mass was thor-
oughly washed and the percentage of sulphur remaining deter-
mined. Test No. 1 gave 3.55% ; No. 2, under identical conditions,.
3.70%. A quantity of the same residue kept well moistened wyas-
then exposed to air and sunlight for a period of twelve days in
order to oxidize any FeS present to a sulphate. After washing,
the sulphur content was 3.74%, indicating that FeS in the origi-
nal sample was absent.1 It is evident, therefore, that the pyritic
iron had been little affected by the temperatures of the retort.
12. Ammonia. — Any by-product process for the carboniza-
tion of coal would, of course, take account of the nitrogen liberated
in the form of NH3. At the temperature employed in these experi-
ments, it would not be expected that any considerable part of the
nitrogen organically present would be decomposed. The follow-
ing values are shown in a distillation2 varying in temperature
from 375°-400°G. In this work the entire distillate from a run of
3000 grams was retained and the total ammonia of the liquor de-
termined. It was found to contain ammonia as NH3 sufficient to
iQn the subject of the decomposition of pyrite, Peters, in Principles of Copper Smelting, p.
268, quotes Sticht as saying ' 'At dull red heat FeSs loses 3/7 of its sulphur and becomes Fe7S8.
At 1200°, it becomes for the first time FeS".
2Experimentsby Mr. E. C. Hull, Fellow in Chemistry, University of Illinois, Engineering-
Experiment Station, March, 1909.
PARR-OLIN— COKING OP GOAL AT LOW TEMPERATURES 11
represent a yield of 0.8 Ib. per ton of coal, somewhat less lhan ^
of the yield from high temperature distillation. It is not certain
that the value of this product would pay for its recovery.
13. Decomposition of Oxygen Compounds. — The oxygen
compounds upon decomposing form water. They are, therefore,
often referred to as the water of constitution. They are prop-
erly considered under this division, though not forming perma-
nent gases. It is a question of great interest whether any decom-
posing action in connection with the temperatures employed has
taken place. If such decomposition has occurred, it has by so
much enriched the fuel value of the remaining coke for the rea-
son that these compounds are inert and noncombustible and,
when present, by so much increase in effect the ash factor so far
as combustion is concerned. The fact of their decomposition
is shown by the increase of water content in the distillate over
and above that which would normally occur from a condensa-
tion of the hygroscopic moisture alone. While this fact was not
available in the case of distillation with superheated steam, the
point was well established in the previous experiments1, as also
by experiments conducted by Mr. E. G. Hull, not heretofore pub-
lished, in which careful measurement was kept of the amount of
water distillate recovered from the coal used.2 Thus, from the
work of the latter we have the following :
TABLE 6
3000 Grams
Coal Distilled
for3hr. Temp.
300° to 400°
•4000 Grams
Coal Distilled
for 6 hr. Temp.
300° to 400°
Weight of water in distillate
208.5
102.0
106.5
3.55
348.4
120 0
228.4
5.71
Weight of free moisture in original coal . .
Excess water from decomposition of oxygen compound in coal. ...
Per cent of water from decomposition of oxygen compound
14. Summary of Data Concerning the Gaseous Product.—
Distillation of Illinois coals at temperatures averaging 450° G.
and not exceeding 500° G. produces a gas having a heating value
exceeding 1000 B. t. u. per cu. ft. The yield approximates % cu.
ft. per Ib. of coal which, at the heat value present, would repre-
sent a yield of 1.00 cu. ft. per Ib. of a gas with a heat value of
500 B. t. u. per cu. ft. The ammonia yield is low, being approx-
imately 3 Ib. of ammonium sulphate per ton of coal. Decom-
iBulletin No. 24, University of Illinois, Engineering Experiment Station, Parr and
Francis.
2See also Porter and Ovitz. Bulletin No. 1, U. S. Bureau of Mines, p. 26-28.
12 ILLINOIS ENGINEERING EXPERIMENT STATION
position at this temperature extends to the oxygen compounds,
which are in the main carried off and appear in the condensate
instead of in the gaseous product. This feature will be referred
to again under the discussion of the composition and properties
of the coke residue.
IV. TAR
15. Composition. — As already noted, the amount of tar re-
covered from the distillations approximates ~y% of the yield of vol-
atile matter and in the sample noted where a direct weighing was
made (Table 6), this material represents very nearly 8% by
weight of the original coal. An exhaustive study of this ma-
terial would be an elaborate topic for research in itself. We
can, therefore, give only the general characteristics of the ma-
terial as found by fractional distillation as follows :
TABLE 7
FRACTIONS FROM Low TEMPERATURE TAR
Amount of tar (exclusive of water carried over).
375 grams
Light oil ( 20°-100°)
39 1 '
10 5%
Fraction (,b) (100°-200°j .. ...
109 1
29 1
" (c) (200°-240°)
111 8 '
29 8
(d) (240° -275°) .
20 6 '
5 5
Coke residue
80 0 '
21 3
From the results as given in Table 7, it will be seen that 75%
of the material classed as tar is in reality oils of different spe-
cific gravities and thus of much greater value than the pitch
proper. This latter product, moreover, is much smaller in
amount than is produced with high temperature distillation. In
the latter case over one-half of the tar is pitch, with a consider-
able content of free carbon suspended in the material. The low
temperature product is approximately one-fifth a pitch residue
with some suspended carbon present, seemingly depending on
the extent to which the temperature of the coal mass has been
carried above 400°.
16. Properties of Oils. — The further examination of the oils
distilled from the tar has developed the interesting fact that these
oils are readily oxidizable. As a measure of this property the
iodine absorption number was determined with results as given
in Table 8. It is realized, of course, that the iodine absorption
PARR-OLIN- — COKING OF GOAL AT LOW TKMPERATGtlE&vK X 13
must include or represent other activities than simple oxida-
tion especially in a complex mixture where members of the aro-
matic series are present.
TABLE 8
IODINE ABSORPTION OF OIL DISTILLATE
Fraction b. 100°-200° (29% ) . . .
Fraction c, 200°-240° (29.8% ).
Iodine No. 165
115-125
Further study of the oils recovered is necessary in order to
determine their specific values. Their ready oxidizability opens
up a very interesting and suggestive field. For example, this
feature is a marked characteristic of drying oils, turpentines, etc.,
used in paint mixtures. The question arises as to whether these
oils will have drying qualities, i. e., will they not simply evapo-
rate, leaving no residue, or will they oxidize in such a manner as
to produce a film-covering, which will serve as a paint vehicle.
Or, in a mixture with a drying oil such as linseed or similar
oil, will they promote the peculiar properties of such oils which
make them of value for paint mixtures? While only a few gen-
eral points in this connection have been developed, they indicate
characteristics of great interest and, possibly, value. It seems
fair to conclude that in some measure at least the iodine ab-
sorption numbers are an indication of the avidity of the oils for
oxygen. This is shown by the rapid discoloration of the oil
when exposed to the air and to the fact that the lighter fraction
will yield a dry film on glass at a 45° angle when exposed for 24
hr. under the usual standard requirements for such test. The
second fraction has also drying properties, but the process is
much slower. Or, rather, a fractionation appears to take place
in which the drying oil forms a hard gelatinous film while the
non-drying portion segregates into minute globules which are
more or less enveloped by the films of oxidized oil. At least, it
may be said of the oils which make up the element of the tar,
.they are available directly as fuel or for enriching or carburet-
ting water gas. For example, if the process were continued to
include the manufacture of water gas from the coke residue,
the oil of the tar would doubtless enter into the reaction in the
same manner as the crude petroleum now used, and thus would
furnish the needed enrichment without the clogging effect which
results when the attempt is made to use the raw coal directly in
the manufacture of water gas.
14
ILLINOIS ENGINEERING EXPERIMENT STATION
V. COKE
17. Yield of Coke. — The yield of coke, under average condi-
tions, as already noted in previous tables, is approximately 75% to
80%. This factor will, of course, vary greatly with the amount
of ash originally in the coal and on Ihe temperature at which the
distil lalion has been carried on. These Hems of variation are
shown in the following table where material of widely varying
composition was used.
TABLE 9
COMPOSITION OF COKE RESIDUES
Experiment No. 11
Vermilion Co.
Experiment No. 13
Franklin Co.
Experiment No. 14
Saline Co.
Moisture ...
34
40
.28
Ash
11.15
9.28
6.97
Volatile matter
27 61
26 60
23 50
Fixed Carbon
59.90
63.72
69.23
Sulphur
2 58
1 21
1.20
B. t. u
12892
13446
13746
TABLE 10
SHOWING THE YIELD OF COKE FROM VARIOUS COALS REFERRED TO
ORIGINAL COAL — DRY BASIS
Experiment
No. 11
Experiment
No. 13
Experiment
No. 14
Ash . . ...
9.56
7 92
6 04
Volatile matter expelled
25.48
18.00
19 12
Residual coke.
78 10
84 72
84 86
18. Reactions Involved. — In the transformation illustrated
by the change from the composition as given for the raw coal in
Table 1 and the residual coke as shown by the table above, No.
9, certain facts may be deduced as follows :
First : there has been, seemingly, a decomposition of the vol-
atile matter in a manner which would increase slightly the fac-
tor for fixed carbon. For example, if the fixed carbon be calcu-
lated as indicated in Table 11 to a percentage of ash correspond-
ing to that of the raw coal, comparisons will be obtained as
follows :
TABLE 11
COMPARISONS OF FIXED CARBON IN ORIGINAL COALS AND RESIDUES, DRY BASIS
Experiment No. 11
Vermilion Co.
Experiment No. 13
Franklin Co.
Experiment No. 14
Saline Co.
Fixed carbon in original coal . . .
Fixed carbon in coke residue re-
ferred to original ash
43.24
46.80
51.30
54.10
54.56
59.70
PARR-OLIN — COKING OF GOAL AT LOW TEMPERATURES
15
19. Oxygep Removed. — As has already been stated, the de-
compositions occurring at temperatures in the neighborhood of
400° G. include the liberation of oxygen, or, as it is frequently
designated, the water of constitution. Since this ingredient of
the raw coal is non-combustible1, it has the same function as so
much ash. Its removal, therefore, serves to make of the result-
ing material a richer or more concentrated fuel. This feature
is still further promoted by the removal of the hygroscopic or
free moisture which usually exceeds in amount the water of
composition. This point may be illustrated by the accompany-
ing table wherein the heat values per pound of the original coal
are compared with the heat values per pound of the residual
coke. There is also given an estimate of the amount of non-
combustible material removed in the form of water in the pro-
cess of decomposition.
TABLE 12
Estimated
Samples
B. t. u. per
Ib. As
Received
B. t. u.
After
Treatment
per Ib.
Gain
Thermal
Units
Gain
per cent
Loss of Total
Non-combusti-
ble Free and
Combined
Moisture
Williamson Co
12695
13150
455
3.60
10.30
Saline Co
13583
13746
163
1.63
8.93
Vermilion Co
12673
12892
219
1.72
13.30
20. Properties, Porosity, Hardness, etc. — The coke material
•obtained by this process varies in character somewhat with the
kind of coal used, and also the amount of pressure employed
during the carbonization. The Williamson Go. coal, for exam-
ple, gives a coke of much finer texture and less porosity than the
coal from Vermilion Go. With a view to determining the reason
for this greater porosity or to finding the conditions that would
modify it, the attempt was made to carry on a test with the coal
sample under pressure. To this end the following apparatus was
used :
21. Apparatus. — A, Fig. 3, is an iron cylinder, 8 in. by 4 in.,
fitted with screw caps B and B1, which received the coal. The
movable piston G to which is attached a long rod D, is pressed
against the charge by tightening the nuts EE. The cylinder is per-
forated with small holes to allow the escape of gases. This con-
trivance was fitted into the retort originally used and heat was
applied as before.
ifiulletinNo. 3, Illinois Geological Survey, p. 32-33.
16
ILLINOIS ENGINEERING EXPERIMENT STATION
Exhibit 1 shows the results obtained when pressure is
applied slowly during the entire heating period. The outer
portions passing through the temporary state of fusion soon
harden and form a wall which resists external pressure. The
inner core, therefore, is extremely porous. When sufficient pres-
FIG. 3
sure is applied, the outer part fractures and, as in this case, the
residue comes out broken up into small pieces. The coke shown
in the figure is from coal from Perry Go. The specific gravity
of the outer portions of the mass is .733 against .652 when
coked without pressure.
It was evident, therefore, that in order to get a firm block,
pressure must be constant. In the next run, the charge was
rammed into the cylinder and the piston was screwed up tightly
but not moved after heating had begun. The resulting column
cohered well and showed the same increase in specific gravity as
the one mentioned above.
22. Illustrations of Various Products. — An interesting fea-
ture of the product is the complete fusion of the mass, where
proper conditions exist, i. e., the individual particles of coal of
buck- wheat or pea size have completely lost their identity, the
resulting homogeneous mass showing no lines of demarcation
from the original pieces of coal. The texture, however, in some
cases is finer or closer than in others. These points are well
illustrated in photographs of typical masses as reproduced in
exhibits 2 and 3, for coals from southern Illinois. Exhibit 4
represents a somewhat coarser texture. It was made from Ver-
milion Go. coal. For the composition of these samples, reference
is made to Table 9, p. 14. Exhibit 2 from Saline Go. coal showed a
crushing strength of 750 Ib. persq. in1; exhibits from a Franklin
iJohn Fulton, (Coke, p. 331.) gives 1200 Ib. per sq. in. as the ultimate crushing strength
of standard Connellsville ooke; by-product coke is. in general, considerably stronger.
The crushing strength is important in reference to the load or burden the coke can with
stand in the furnace without crushing.
Exhibit 1
Exhibit 3
Exhibit 2
Exhibit 4
Exhibit 5
Exhibit
Exhibit 8
Exhibit 7
Exhibit 9
Exhibit 10
PARR-OLIN — COKING OF GOAL AT LOW TEMPERATURES 17
Go. sample crushed at 900 Ib. On account of its coarse cellular
structure, exhibit 4 showed little rigidity, and broke down at a
pressure of 300 Ib.
23. Resume Relating to the Coke Product. — It is evident up-
on examination of the coke product obtained, as above described,
that we have here a fuel of firm texture, not readily broken
down by handling and producible in the most convenient sizes
for handling and for efficiency in combustion. It is, moreover,
in a more concentrated form, in that for the most part, the free
moisture and the water of constitution have both been removed.
Thus in freshly mined coal there would be eliminated from 15 to
20 per cent of inactive material. Again, the heavy hydrocarbons
have been removed. These are the constituents most directly
responsible for the formation of smoke in the combustion of
untreated coal. It is to be noted further that because this coke
has been subjected to a temperature just approaching a red heat,
it will not begin to evolve volatile matter, when thrown upon the
iire, before it again comes up to or passes that temperature.
The effect of this point is twofold : first, there is obviated the
cooling effect! which must be necessary in the vaporization of
moisture in the raw coal which also lowers the temperature just
when a high temperature is needed for burning the heavy hydro-
carbons; and second, the remaining gases to be evolved consist
almost wholly of ethane or marsh gas (GH4) and hydrogen, both
of which are readily combustible. The hydrogen, of course,
burns with a non-luminous flame and is incapable of making
smoke. The marsh gas (GH4), though it has carbon in its com-
position, adds but little luminosity to the flame and is almost in-
capable of producing smoke in the process of combustion.
It may be well to analyze briefly the processes of combustion
as they occur in an ordinary hand-fired furnace. The first result
of throwing a mass of coal upon a fire is to lower the tempera-
ture during the time of volatilization of the moisture in the coal.
Theoretically, the temperature of the mass during this process
would remain at or slightly below 100° G.
Other factors tending to lower the temperature would be the
specific heat1 of the coal and the heat necessary to effect the de-
composition, since it is probable that the decomposition reactions
are endothermic up to approximately 300° G2.
JBulletin No. 46. University of Illinois Engineering Experiment Station, Parr and Kress-
man, p. 34.
2Bulletin No. 24. University of Illinois, Engineering Experiment Station. Parr and
Francis, p. 46—47.
18
ILLINOIS ENGINEERING EXPERIMENT STATION
It is to be noted that during this depression of the general
temperature there is being distilled from the coal such volatile
substances as are liberated at these lower temperatures. This
point can best be illustrated by means of the accompanying dia-
gram. In Fig. 4, the region between the lines A £nd B may be
assumed to include those volatile constituents that are driven off
at a temperature below 400° G. This area includes the free
moisture of the coal, the combined moisture or water of con-
stitution, or as some prefer, the oxygen compounds of the coal,
shown on the chart as inert volatile; and, in addition, some of
the pure hydrocarbons which constitute a portion of the true
volatile combustible matter. It is, moreover, the nature of this
latter or volatile combustible material \vith which we are just
now concerned in this discussion of the processes of combus-
tion. It is to be noted first that this volatile matter contains the
FIG. 4
bulk of the heavy hydrocarbons. By this is meant that they be-
long to the higher series of any of the homologous compounds
present which in general are characterized by a higher percent-
age of carbon. For example, if the series is that of marsh gas
or methane GH4, i. e., Gn H?n+2, then the next higher order of
this series would be ethane or G2H6, and the next, propane or
G3H8. The carbon percentages, respectively, being 75, 80,81.8,
etc. Again a very considerable part of the volatile matter de-
livered at this temperature belongs to the methylene series
GnH2a, and the first known member of the series is ethylene or
olefiant gas, C2H4, with a carbon percentage of 92.92. Moreover,
PARR-OLIN — COKING OF GOAL AT LOW TEMPERATURES 19
this last compound may be made to break down under higher
heat into members of other series, as acetylene, C4H4, benzene,
G6H6, and naphthalene, G10H8. Other members of the ethylene or
paraffin series are found which ally the resulting complex
mixture quite closely to the very complicated compounds with
which we are familiar in petroleum.
The point to be noted in this phase of the discussion is the
fact that these compounds discharged at this relatively low tem-
perature, and having these high percentages of carbon, are the
most difficult of complete combustion without the formation of
smoke.
It is not necessary here to discuss the mechanics of com-
bustion of hydrocarbons. As a result of the researches of H. B.
Dixon1 and of Professor Bone2 the selective theory of oxygen for
hydrogen or the dogma of "preferential combustion of hydro-
gen" has beon obliged to give place to the theory of the inter-
mediate formation of "oxygenated" or "hydroxylated" mole-
cules. In any event, or whatever the theory finally developed by
Professor Bone in his most important researches on combustion,
the fact remains that these heavier hydrocarbons are the most
difficult of all with which to effect complete combustion, and
that even under favorable circumstances the tendency in their
combustion is to form condensation products in which free car-
bon largely predominates. The faulty reaction is thereby made
visible to the eye as smoke. A good illustration of this fact is
found in acetylene gas, which requires a special burner with
special provision for an extra oxygen supply in order to produce
a smokeless flarrie.
Smokeless combustion of raw coal is secured, therefore,
by observing the principles indicated above; i. e., there must be
uniform and gradual accession of fresh coal and a combustion
chamber maintained at a sufficiently high temperature, and the
same extending over a sufficient space to permit of ultimate
mixing and contact of the oxygen with the combustible gases.
Other conditions such as accelerating the reaction by introduc-
ing the principle of surface combustion, as developed by Pro-
fessor Bone, may at some time be added to the mechanical
and physical conditions now in vogue. But while these provis-
ions are readily adapted to large steam generating units, they
are impossible of application to the larger members of combus-
iPhil. Trans. 1893, 159; Trans. Chem. Soc. 61. 873 (1892);
2Chem. News, 102, 309(1911).
20 ILLINOIS ENGINEERING EXPERIMENT STATION
tion processes such as are common to the small plant, house
heaters, and possibly to locomotives. It is these latter cases es-
pecially that demand a modified fuel which can be burned with-
out the formation of smoke.
It will thus be seen that in the low temperature distillation
of coal, processes have been put into operation which have
taken out the heavy smoke-producing ingredients, and have also
removed the moisture, both free and combined, which are chiefly
responsible for the depression of temperatures under ordinary
conditions. There is left, moreover, as volatile matter, practi-
cally these volatile substances only; methane GH4 and hydrogen,
which most easily of all the gaseous products from coal, main-
tain a smokeless combustion.
VI. THE FORMATION OP COKE
The experiments as thus far conducted seem to throw some
light upon the matter of coke formation. In this discussion of
the theories involved, it may be helpful to formulate certain hy-
pothetical conditions which have had more or less confirmation in
these studies, as follows :
First: For the formation of coke there must be present cer-
tain bodies which Jiave a rather definite melting point.
Second: The temperature at which decomposition takes
place must be above the melting point.
Third: Where the compounds that satisfy the first and
second conditions]! are unsaturated, it is possible by subjecting
them to oxidation to so lower the temperature of decomposition
as to alter the second condition prescribed, in which case coking
will not occur.
Discussion of Conditions. — The first condition prescribed
above may be well illustrated by the behavior of sucrose or cane
sugar. This substance has a rather low melting point, say, 160°
G. This melting point, however, is just below the temperature
of decomposition. Where this point is reached, gaseous products
in the form of steam, etc., are delivered, leaving behind, if the
high temperature is continued, a mass of coke. On the other
hand, if starch is heated in a similar manner, it does not melt
but its first action is that of decomposition. When this is car-
ried to completion, there remains not a strongly coherent mass
but easily disintegrated particles of carbon. Pure cellulose be-
haves in a still more striking manner, showing no fusion pro-
perties whatever as maybe demonstrated by distilling in a closed
PARR-OLIN — COKING OF GOAL AT LOW TEMPERATURES 21
tube some cotton fiber, or other form of cellulose such as filter
paper beaten to a pulp and dried. Wood, however, if not disin-
tegrated, as in the form of sawdust, has enough resinous
material closely associated with the fibrous structure to bind
t|he carbon filaments resulting from the decomposition of the
cellulose by reason of the fact that these gums, or resins, have
a melting point below that of their decomposition temperatures,
and thus form . a binding film of carbon throughout the mass,
producing a sort of coking effect which we find in charcoal.
In the case of Illinois coals, we find the first prerequisite
formulated above, as present' in a marked degree. As an illus-
tration of the fact of a low melting point, reference is made to
exhibit 5, which is a photograph of a mass of such ma-
terial, which exuded from a sample of Vermilion Go. coal, sub-
jected to the usual treatment as described on p. 7. The lump
shown is a part of a mass that flowed out of the container,
forming a bubble-like puddle. It would seem, therefore, that
this type of coal from the north Danville field (Electric mine)
has the first essential for coke formation in a marked degree.
As illustrating the conditions which exist where oxidation
had been allowed to take place, an example is given in exhibit 6.
This was made from a weathered sample of coal from
Niantic. It had little if any tendency to fuse ; the individual
particles of coal still retain their form and the mass may be eas-
ily crumbled between the fingers. It should be noted that this
result is not due to, any inherent quality possessed by the original
coal; a Danville mine sample, for instance, weathered to a like
degree, gives the same results.
Test No. 9. — Another verification of this point, though in a
more marked manner, was the result of test No. 9. The coal
used was the fine material which had collected from the prepar-
ation of the previous tests, all of which had given excellent sam-
ples of coke in their freshly prepared condition. A quantity of
coal passing through a 10-mesh sieve had accumulated through a
period of about six weeks and had been stored in an ordinary
coal hod in the grinding room. After being heated for eleven
hours under conditions identical with those of the preceding
runs, it showed no signs of fusion and was entirely without cok-
ing properties.
It is evident from these tests that the very great avidity of
fresh coal for oxygen is evidence of the presence of those com-
pounds which satisfy the first of the hypothetical conditions,.
22 ILLINOIS ENGINEERING EXPERIMENT STATION
p. 17, and the subjection of the coal to oxidation destroys the
fusion property of the fresh coal and produces a condition cor-
responding to that described under the third proposition, in
which the coking property is lost.
Other studies on the nature of the coking process were car-
ried out as follows : The apparent plasticity exhibited by the
coal during certain stages of the treatment suggested the idea
of compressing it into a briquette at the time when it would most
easily yield to pressure and when it would presumably cohere
without requiring an artificial binder. Accordingly, a cupel
press with a pressure of 500 Ib. wras provided and the retort was
charged with Danville mine coal. At the time of maximum evo-
lution of gas, the heat was suddenly shut off and the retort
quickly opened. It was found at this point that the outer and
hotter portion of the mass was hard and unyielding. A soft in-
ner core was discovered, however, and portions of this were put
into the press. The resulting briquette is shown in exhibit 8. The
escaping gases have swollen it; considerably. Determinations of
the amount of volatile matter possessed by the coal when in the
plastic condition showed that this constituent had been reduced
very little, — from 38 % to 30 % . In short, the state of fusion seems
, to exist in early stages of distillation but disappears before the
process has proceeded far.
In one of the earlier tests with Danville mine coal using the
apparatus described in Fig. 3, the extreme fusibility of this type
was again demonstrated. As the piston was slowly forced in,
pencils of bituminous matter were squeezed out, through the
holes of the cylinder. Exhibit 5 includes some of these
nodules. The fact that there was a selective separation of bi-
tumen is proved by a comparison of the ash values, the residue
as a whole having 13 %, the nodules, 8 % of ash.
The readiness wTith which the cementing material ran to
waste seemed to indicate that the coal contained a superfluous
amount of it — mo're than was necessary for binding itself togeth-
er. The correctness of this view was shown by a series of runs
in which crushed gas house coke and anthracite were heated
with varying amounts of bituminous coal.
Exhibit 7 shows the hard firm product resulting from
the mixture of equal parts of Majestic bituminous coal and
gas house coke, both crushed to 20 mesh. Fairly good results
were obtained in the next run with 75 % of the coke and only
25 % of Danville Electric coal. In like manner, powdered an-
PARR-OLIN — -COKING OF GOAL AT LOW TEMPERATURES 23
ihracite and bituminous coal in ratios varying from 1 : 1 to 3 : 1
were firmly cemented together. Pitchy material no longer
exuded from the retort, being absorbed, seemingly, by the added
substance.
One of the essential factors in this scheme for briquetting
loose infusible material with bituminous coal is the use of the
press for keeping the two substances in close contact. On ac-
count of the difficulty of applying such a contrivance in indus-
trial work, attempts were made to attain the desired end by us-
ing temporary binders, i. e., substances which might hold the par-
ticles together clbsely until the permanent coal binder could
relieve them.
Mixtures of Danville mine coal and Danville mine coke resi-
due No. 17 in the proportion 3 : 1 were thoroughly moistened
with water and pressed (1) in the cupel machine and (2) in a
testing machine up to 1000 lb. per sq. in. Neither of the bri-
quettes survived the subsequent heating, being disintegrated,
seemingly, by tjhe escaping steam. The same effect, though to a
much less degree, was noted when coal tar was employed. The
resulting briquette retained its shape, but was rather soft and fri-
able. Crude molasses, of all the binding materials tride, proved to
be the best for this purpose. Different percentages of the molasses,
ranging from 5 to 15, were tested out at different times. Below
ten per cent the strength of the briquette was much diminished.
Exhibit 9 is a 3:1 mixture of Danville mine coke residue
and fresh Danville mine coal, both ground to 20 mesh, first
bound with 11 % of molasses and then pressed in the cupel ma-
chine. The cake was next heated in the retort under the atmos-
pheric conditions of all the preceding runs. This briquette 2 in.
high and 2 in. in diameter, has a crushing strength of5501b.
per sq. in. Exhibit 10 shows anthracite briquettes made
in the same way. They have a specific gravity of 1.02 and crush
at 650 lb. per sq. in.
These tests seem to show that the fusible substance of Illin-
ois coals is the true binding material in the coking process; that
it is present in such abundance as to produce a coke of too open
and spongy a character as a result of the evolution of the large
amount of gaseous products which result from its decomposi-
tion. In this respect, it is paralleled by the behavior of sugar in
the process of coking, which yields as a result of the large vol-
ume of escaping gases a very porous mass of sugar, coke or car-
bon. However, if the raw coal is mixed with a considerable
24 ILLINOIS ENGINEERING EXPERIMENT STATION
amount of material which has already gone through the coking
process, or which has at least given off the larger part of its
gases, and then has been reduced to a fine division like breeze,
the cementing material of the fresh coal is able to disseminate
throughout the mass, and the gases may also escape without
blowing it into a spongy mass, with the result that a coke of
good texture is formed. Exactly in a similar way, if molasses
or other sucrose or glucose material be substituted for the fresh
coal, we shall have again the formation of a dense coke capable
of retaining its shape under conditions of firing much better
than where a plastic binder is used. In both cases a strongly
cohering mass is produced which meets the requirements of
handling, storage, and combustion with the greatest efficiency
and the least formation of smoke. A small admixture of raw
coal may thus be made to serve the purpose of a binder for ma-
terial otherwise wasted as coke breeze at a cost which would
enable it to compete with the pitch binders now in use. It also
suggests a process of fractional coking, or coking in two stages.
The first result at the lower temperature furnishes a product
which, when ground to a moderate degree of fineness and mixed
with a small portion of fresh raw coal, would furnish the essen-
tial conditions for producing a coke of dense nature with a
binder so distributed as to give the material a strength quite
comparable with that produced by coals of the regular coking
variety. Moreover, an advantage would be evident in such ma-
terial, especially for use in household appliances, in that it
would be more lively in combustion and less difficult of manipu-
lation in the matter of maintaining a fire than coke made by the
usual methods.
One point further is to be noted in this connection. It was
said at the beginning of the discussion that superheated steam was
employed for the purpose of conveying heat into the material so
that it would not be necessary to revolve the apparatus in order
to secure an even distribution of heat. It is seen from the above
detail of the essential conditions to be observed in the coking of
coals, at least of this class, that an atmosphere free from oxygen
is of prime importance. Indeed following the indicated require-
ment, the coal should be fresh, or as recently mined as possible,
and in any event retained in larger sizes than in a broken down
or a fine state of division, in order that the least possible oppor-
tunity be given for the absorption of oxygen. Furthermore, by
first admitting steam or bringing the coal into an atmosphere of
PARR-OLIN — COKING OF GOAL AT LOW TEMPERATURES 25
superheated steam, the effect is to1 drive out such oxygen as has
been occluded or absorbed by the coal and as yet not chemically
combined. This is also brought about at temperatures and other
conditions least conducive to a reaction between oxygen and the
coal substance. Moreover, from former experiments,1 it has
been shown that no reaction at these temperatures takes place
between the steam itself and the coal. These principles have an
important bearing on certain recent tendencies to concentrate
gas production and coke manufacture in large unils and distri-
bute the gaseous products at high pressure. From the above, it
would seem that the nearer such units were located to the mine
or pit-mouth, the belter. If it is found, as seems probable, that
the coke residue is a suitable material for further continuation
of the gas-making process for the manufacture of producer gas,
then the above advantages and essential conditions would be
magnified.
A discussion2 by Prof. Lewes, relating to English co.als, bears
such a striking resemblance to the facts developed in o,ur own
work on Illinois coals that the references have especial interest in
this connection. Lewes develops his theories on the basis of the
existence in coals of four types of degradation products which
have all come from two original forms of \7egetation ; viz : cellulose
or lignose, and resinous bodies such as the spores of the lycopodia.
The first form of vegetation, i. e., the cellulose, has produced the
coal compounds of the humic and ulmic types, while the resinous
bodies have produced the other three, viz: (1) : resinous bodies
with but little alteration; (2) isometric or other slight modifica-
tions in form rather than of composition; and (3) decomposition
products from resins produced by the action of heat and pres-
sure and consisting of a long series of both saturated and unsat-
urated compounds, hydrocarbons of the hydro-aromatic series,
and saturated hydrocarbons, like hexane, pentane, etc.
"All these degradation- products of the original vegetation are to be
found in the bituminous coals, the residual body and humus forming
the basis, which is luted together by the hydrocarbons and resins, and
the characteristics of the various kinds of coal are dependent upon the
proportions in which the^four groups of the conglomerate are present.
The resin bodies and hydrocarbons which form the cementing
portion in the coal melt between 300° and 320°C, and if a coarsely pow-
dered sample of the coal becomes pa'sty or semi-fluid at this temperature,
iParr and Francis, p. 45, Bulletin No. 24, Engineering: Experiment Station.
2 A recent contribution to the theories of coke formation is made in a lecture by Vivian B.
Lewes. Professor of Chemistry, Royal Naval College. Greenwich. England, published in Pro-
gressive Age, Dec. 15, 1911. page 1030.
26 ILLINOIS ENGINEERING EXPERIMENT STATION
it is a strong inference that the coal will coke on carbonization, a fact
noted by Anderson, and which I have found very useful in practice as a
rough test. About these temperatures also the resin bodies and hydro-
carbons begin to decompose.
The resin bodies at low temperature yield saturated hydrocarbons,
unsaturated, chiefly hexahydrides or naphthenes, together with some
oxygenated compounds, while the hydrocarbons yield paraffins and liquid
products, all these primary constituents undergoing further decomposi-
tions at slightly higher temperatures. The liquids so produced begin to
distill out as tar vapors and hydrocarbon gases, and leave behind with
the residuum pitch, which at 500°G forms a mass already well coked to-
gether if the residuum from the humus is not too large in quantity; the
coke formed at this temperature is, however, soft, but if the heat be now
raised to 1000°G, the pitch residue undergoes further decomposition,
yielding gas and leaving carbon, which binds the mass into a hard coke."
He discusses further the action of oxygen upon certain of
the initial constituents, referring to the investigations of Bou-
douard.
"Boudouard has shown that when coal is weathered humus bodies are
produced and the coking power lessened or destroyed. In seven samples.
of various coals the humus constituents were increased by the oxidation,
which seems to show that the action of the absorbed oxygen is to attack
the resin compounds, and as we know that carbon dioxide and moisture
are the chief products of the earlier stages of heating of masses of coal,
it seems probable that the result is a conversion of resiriic into humus
bodies with evolution of these gases, and it is this change which leads to
the serious deterioration in the gas and tar made coal which has been
too long in store, while the fact that a cannel coal like Boghead or a shale
do not weather is partly due to their dense structure and also is an indi-
cation that the resin bodies of which they are chiefly composed are of a
different type, a fact borne out by their resistance to certain coal sol-
vents which freely attack the ordinary resin matter."
A continuation of studies along this line is being made.
Ptfention has been made concerning the adaptability of the coke
thus produced to use in suction gas producers for furnishing
fuel to gas engines. Its freedom from tar, oils, and the heavier
products of distillation, which clog and render impossible the
use of raw bituminous coals of this type, would seem to offer
a solution of these fundamental difficulties. Further studies
along this line are also being made.
VII. SUMMARY AND CONCLUSIONS
1. Goals of the Illinois type can be coked at a temperature
approximately 400° or -450° G.
2. The gaseous products consist chiefly of illuminants of
high candle-power, and represent, together with the condensible
PARR-OLIN — COKING OP COAL AT LOW TEMPERATURES 27
material under (3) following, the chief elements involved in for-
mation of smoke in the ordinary combustion of raw coal. The
nitrogen of the coal is liberated as NH3, at these temperatures,
in amounts representing approximately 20% of the total nitrogen
present.
3. The cordensible distillate consists largely of oils with
the minimum amount of tar and free carbon. The oils repre-
sent positive values for fuel, for carburetting water gas, or for
other specific uses on account of their chemical characteristics-
as unsaturated compounds.
4. The coke residue has special characteristics which seem
to make it o,f value as a concentrated fuel, capable of combus-
tion without the formation of smoke, suitable for storing with-
out the possibility of spontaneous combustion, and presumably
adapted to the manufacture of gas for use in the suction gas
producer.
5. Certain facts seem to have been developed concerning
the principles involved in the formation of coke which may
open the way to the production of a kind of coke of such texture
and strength as to make it acceptable for uses that are not now
possible with coke made from similar coal, but formed under
ordinary conditions, such as are found in the ordinary gas-
house retort practice, or that of the by-product coke-oven.
Other considerations1 are pertinent in this connection, such
as losses and pollution of the atmosphere which accompany the
production of smoke2.
!As illustrating the present-day appreciation of matters connected with fuel economy and
activity of thought concerning remedial measures, a quotation is here made from the presi-
dential address of Sir William Ramsey before the British Association for the Advancement of
Science at York, Eng., July, 1911. (Science, Vol. 34, p. 302, Sept., 1911.)
"The domestic fire problem is also one which claims our instant attention. It is best grap-
pled with from the point of view of smoke. Although the actual thermal loss of energy in the
form of smoke is small, still the presence of smoke is a sign of waste of fuel and careless stoking.
In works, mechanical stokers, which insure regularity in firing and complete combustion of
fuel are more and more widely replacing hand-firing. But we are still utterly wasteful in our
consumption of fuel in domestic fires. These considerations would point to the conversion at
the pit-mouth of the energy, using as intermediary, turbines or preferably, gas-engines; and
distributing the electrical energy to where it is wanted. The use of gas engines may, if desired,
be accompanied by the production of half-distilled coal, a fuel which burns nearly without
smoke, and one which is suitable for domestic fires.
2It is not necessary to multiply arguments for the prevention of smoke- However, a recent
article in the Journal of the Society of Chemical Industry, December 15, 1911. by Prof . J. B.
Cohen and A. G. Ruston, contains some very striking facts developed in their study of the
smoke problem. A few extracts may be given as follows:
"The average per cent of soot passing up the chimney, in 12 analyses including eight of
Yorkshire coals, two of Durham coals, and two of Wigan coals, amounted to 6.5 per cent on the
carbon burnt. This quantity 6.5 per cent seems a very high figure, representing an annual loss
of nearly two million tons on the estimated domestic consumption of 32 million tons. The
average deposit of soot over the whole of Leeds will therefore correspond to at least 280 tons
per square mile per annum. The tar contained in the soot adheres so tenaciously to everything
that it is not easily removed by the rain. The leaves of trees and evergreens in particular get
coated with this black deposit. Unfortunately, it does more than blacken the vegetation; it
covers the whole leaf over with a kind of varnish, and fills up the pores or stomata, thus check-
ing the natural process of transpiration and assimilation. It is in fact no uncommon thing to
find in the case of leaves of conifers grown in Leeds that 80 per cent of the stomata are choked
up with tar."
28 ILLINOIS ENGINEERING EXPERIMENT STATION
Further studies have in mind the carrying out of the pro-
cesses as indicated with apparatus involving the continuous
feature, subjecting the mass at the point of greatest fusibility to
the pressure of the oncoming material and producing the coke
in amount sufficient for testing its properties in the gas pro-
ducer and for combustion in oiher ways which would test its
properties as a smokeless fuel.
APPENDIX
PARR-OLIN— COKING OF GOAL AT LOW TEMPERATURES 31
APPENDIX
I. INTRODUCTION.
HISTORICAL1
STUDIES IN THE Low TEMPERATURE DISTILLATION OP COAL.
Researches in the low temperature distillation of bituminous
coals have been carried on at the University of Illinois since
19022. In a series of preliminary experiments, on heating coal
to temperatures ranging from 250° to 500° for periods of less
than an hour, it was found that the percentage of fixed carbon
was increased by more than 25% and that there was a corre-
sponding decrease in volatile matter to a point where the forma-
tion of smoke was prevented altogether.
In order to eliminate as far as possible those variables which
would result from oxidation, Parr and Francis in continuing
this work heated Illinois coals in non-oxidizing atmospheres.
Choosing nitrogen first as the most suitable medium for this pur-
pose, a careful study was made of the quantity and composition
of the gases and heavy residues produced at different tempera-
tures below 400° G. With a view to securing an absolutely inert
atmosphere, after finding that the ordinary commercial nitrogen
was contaminated with oxygen, the air in the retort] was dis-
placed by steam.
The coals heated in these media underwent changes which
rendered them smokeless in ordinary combustion. Howrever, on
account of the rotary motion given the retort in order to equalize
the temperatures, the coke product came out in a loose granular
state much like that of the original coal.
In the course of some of the experiments, while using oxygen
as the atmospheric medium, rises in the thermometer readings
were observed at unexpectedly low temperatures, seemingly inde-
pendent of the amount of external heat supplied. This suggest-
ed the idea of a second series of tests entirely separate from the
first, to determine the temperatures at which oxidation begins.
The method of procedure was to allow the retort to cool slowly
iln assembling the literature relating to the carbonization of coal, it has been planned to
bring together first, all of the references to low temperature distillation including the studies
of the by-products, followed by references to the theories concerning coke formation and the
carbonization of coal in general.
2111. Gteol, Surv., Bull. No. 4. by S. W- Parr. p. 97, 1906.
32 ILLINOIS ENGINEERING EXPERIMENT STATION
until a drop of say 50° had been recorded. Oxygen was then ad-
mitted and the resulting temperature was noted. A rise was
considered proof of oxidation. This was repeated until a point
was reached where no rise in temperature occurred on the read-
mission of oxygen. In this way it was found that pulverized bitu-
minous coals in pure oxygen began to oxidize at about 125° and
that they ignited at about 160°. With diluted oxygen the tem-
peratures were somewhat higher.
While making some of their tests with atmospheres of steam
it was observed that near the temperature of 315° the mercury
made an abrupt rise incommensurate with the amount of exter-
nal heat added. After allowing the coal to coiol to 300° and then
again heating up to 315° the same phenomenon was observed.
No appearance of carbon dioxide accompanied this sudden rise.
A tentative explanation is that it was due to the exothermic
character of decompositions occurring at that stage.
In considering the subject of oxidation temperatures,1 it was
found that freshly-mined coal immediately begins to exude hy-
drocarbons and to absorb oxygen and that it retains its avidity
for oxygen for an indefinite length of time. The exact result of
this absorption was not fully determined, but it seems probable
that under favorable temperature conditions it would tend to
hasten combustion.
Gonstam and Schlapfer2 publishing "Studies in the Gasify-
ing of the Principal Types of Goal" report that the percentage
o,f oxides of carbon included in the gases given off in distilling
coal varies with the oxygen content of the coal itself.
R. T. Chamberlain3, studying the causes of mine dust explo-
sions, found that fresh coal absorbs a large quantity of oxygen
but that even under a vacuum it gives off very little. He deter-
mined further that coal bottled in air for several weeks yields
some carbon dioxide but an amount equivalent to only a small
part of the oxygen absorbed. This he thought, might be due to
the presence of unsaturated compounds in the coal, which form
addition products with oxygen.
Mahler and Gharion4 found that when dry air was passed
over pulverized coal at temperatures below 100°, measurable
quantities of water, carbon dioxide and carbon monoxide were
iBulletin No. 32, By Parr and Barker, Engineering Experiment Station, University of
Illinois. (1910).
2jour. Gasbel. 49, 741. 774. (1906).
3Bulletin No. 383. U. S. Geol. Sur. (1909).
4Compt. rend. 150, 1521, 1604. (1910).
PARR-OLIN-^-COKING OF GOAL AT LOW TEMPERATURES 33>
given off. Between 125° and 200° the liberation of water was
so greatly accelerated as to indicate the" splitting oiT of water of
constitution. Above 150° the water contained considerable-
quantities of acetic acid, from 20% to 40% of the total conden-
sate, and showed, in addition, traces of acetones, aldehydes, and
methyl alcohol. The upper limit of temperature in their studies*
was 200°.
Porter and Ovitz1 made an extended study of the volatile-
matter of coal' with a view to determining the influence of the
gas composition factor on the efficiency in the use of coal in
various industrial processes with special reference to gas pro-
ducer, coke oven and gas retort operation.
Their investigations show that the composition of the vola-
tile matter of a coal depends largely upon the character of the
coal itself. The gases from the younger coals of the West com-
pared with those from the coals of the Appalachian region have
high percentages of carbon dioxide and carbon monoxide. Be-
cause of the readiness with which these gases are given off even
at comparatively low temperatures (300°-500°) , the writers con-
clude that these western coals contain compounds having a di-
rect carbon linkage such as the complex alcohols, aldehydes
and acids. They show, further, that contrary to the theory of
Dulong, who assumed that in combustion all the oxygen of a
coal combined with hydrogen, in the case of certain low grade
highly oxygenated coals nearly two-thirds of the oxygen ap-
pears in the volatile products in union with carbon, and that
this fact accounts for the discrepancy between the determined
heat value and that calculated by Dulong's method.
Higher hydrocarbons such as ethane are produced in great-
est abundance from the eastern coals and they, consequently,
yield more smoke in combustion. In general, however, the gas
evolved from any coal subjected to moderate heat only, is rich
in the higher paraffins such as ethane and propane. In the case
of Gonnellsville coal, at furnace temperatures of 500° and 600°
these higher hydrocarbons constitute about 50% of the total
paraffin content. At about 800° the percentage reaches a maxi-
mum, when it rapidly falls on account of decomposition by heat.
They conclude that the nature of the volatile products dis-
tilled from coal in the early stages of heating varies in accord-
ance with the smoke producing tendencies of that coal. They
iThe Volatile Matter of Coal. Bull. 1, Bureau of Mines. 1910.
34
ILLINOIS ENGINEERING EXPERIMENT STATION
include among the smoke-producing constituents, tar, benzene,
ethylene, and the higher homologues of methane.
E. Boernstein1, subjecting eight Westphalian coals to a max-
imum temperature of 450°, reports that the gaseous products of
distillation did not exhibit differences corresponding with those
shown by the coals themselves. Compared with ordinary coal
gas, they were characterized by a higher content of heavy hydro-
carbons (5% to 14%) and of methane and its homologues (55%
to 76%), and a lower content of hydrogen (5% to 16%). The
tars had a specific gravity between .95 and .98, began to distill at
about 70° to 80°, and were found to contain no aniline, thio-
phene, naphthalene, or anthracene. He states that the solid
paraffin content ranged from .3% to 2% (m. pt. 55° to 60°).
Inasmuch as in modern gas retort operation portions of the
coal do not reach their maximum temperature for one or two
hours, the subject of low temperature distillation is of real
importance to the gas industry. In a paper read before the
Michigan Gas Association, White, Park and Dunkley 2, report the
results of their studies of the primary reactions involved in heat-
ing American coals to 500°.
Gas evolution commences only above 300° and that given off
in the 300° to 350° interval contains from 25% to 40% of ethane.
Above the latter point the yield of ethane diminishes and very
little is produced between 450° to 500°. The illuminants de-
crease with increasing temperature starting with 8% at 300° and
going down to zero at 500°. Methane starting with small
amounts reaches its maximum in the 400° to 450° interval.
They call attention to the similarity of the gases produced at low
temperature to natural gas and suggest that the latter was also
produced at low temperature. They give the following results
of analyses :
TABLE 13
AVERAGE YIELD AND COMPOSITION OF GAS FROM COAL HEATED FOR Six TO
EIGHT HOURS AT TEMPERATURES OF 300°-500°
Coal
Volume in cu. ft. per Ib. of
Pittsburgh ,
Penna.
Bay City,
Mich.
Zeigler
111.
Coal. ..
1.42
1.15
0.63
CO2
2 9
16.2
13.1
Ilium ..
2.2
4.1
1.6
CO.
6.2
5.0
5.8
H2
26.3
16.4
13.9
CH4 * . ,
47 0
37.8
38.0
C2H
13 2
11 8
19.5
N2
2.7
9.1
7.8
Calculated B t u ,
902
778
871
1 Jour. Soc. Chem. Ind. 25-213.
2 Am. Gas Light Jour. 89-621.
(1906).
(1906).
PARR-OLIN— COKING OF GOAL AT LOW TEMPERATURES
35
The apparent similarity between the gases evolved from
coal at low temperatures and natural gas, gives interest to the
work of Gady and McFarland1 on the composition of the natural
gases of Kansas. They proved the presence of paraflins heavier
than methane and ethane, by condensing higher boiling hydro-
carbons along with the methane in a bulb surrounded with liquid
air. Some of these remained liquid up to ordinary temperatures
and had an odor similar to that of light boiling petroleum distil-
lates. The quantity of this residue varied in the different gases.
Professor V. B. Lewes2 in discussing the relative merits of
high and, low temperatures for gas distillation, gives parallel
tables showing the net cost of 1000 cu. ft. of gas produced by
each of the two processes.
TABLE 14
COST OF 1000 cu. FT. OF GAS
(1) Hig
h (900°)
(2) Low (400°)
•Coal
pence
13 30
pence
26 50
•Operating expenses
6 74
5 50
20.04
32.00
LESS VALUE OF RESIDUALS PRODUCED
•Coke
82 cwt
6 11
2 4 cwt
17 64
Tar
9 gal
1 30
4 6 gal
6 90
NH4 products
2 11
2 80
9.52
27.34
NET COST OF GAS
10.52 4.66
B. t. u. of gas 592 750.
He points out that although the coke residues are figured at
the same price, coke (2) is really more valuable since it contains
15% of volatile matter which increases its calorific value. He
states also that the low temperature tar distillates contain valu-
able fractions of a character different from those obtained from
ordinary gas tar, one of which is especially suitable for use in
motors as a fuel.
Burgess and Wheeler3 working on the problem of the pre-
vention of mine dust explosions, and recognizing the relationship
iJour. of Am. Chem- Soc. 29. 1523. (1907).
2Engineering. 85-410. (1908).
3Jour. Chem. Soc. 97-1917. (1910).
36
ILLINOIS ENGINEERING EXPERIMENT STATION
that exists between the character of the volatile matter escaping-
from a heated coal, and its degree of inflammability, studied the
composition of the gases evolved at different temperatures.
They found that with all coals whether bituminous, semi-
bituminous, or anthracite, there was a well-defined decomposi-
tion point at a temperature between 700° and 800° which corre-
sponds to a marked increase in the quantity of hydrogen evolved.
This increase they attribute to the thermal decomposition of one
or more of the higher homologues of methane yielding hydrogen
and carbon. Ethane, propane, butane, and, probably, higher
members of the paraflin series, form a large percentage of the
gases given off at temperatures below 450° ; above 700° they no
longer appear.
They believe that the smoke producing elements consist al-
most entirely of the higher paraffins and differ from Porter and
Ovitz in excluding ethylene and the related unsaturated gases
from this class. This view is based upon experiments made-
showing that elhylene decomposing at 600°, deposited very little-
carbon.
A typical analysis of the gases obtained is given below.
TABLE 15
GAS FROM COAL FROM ABERTILLERY, SOUTH WALES (BITUMINOUS)
Coal (C)
Temp.
Ilium.
COS
CO
H2
CH4
C2H6
500°
5.8
3.9
4.7
8.0
64.5
11.0
600°
4.9
3.2
6.4
25.0
47.8
12.4
700°
2.8
3.4
7.4
34.7
46.2
4.2
800°
2.8
2.5
9.8
50.8
28.6
4.7
1100°
4.2
1.4
13.0
60.7
18.8
1.8
In a second paper2 they discuss the results obtained by sub-
jecting coals to a series of fractional distillations in a vacuum
and determining the compositions of the gases evolved within
well defined limits of temperature. They succeeded by pro-
longed exhaustion at a low temperature, in removing entirely
the paraffin-yielding constituents and leaving behind a compound
which decomposed at a comparatively high temperature, yield-
ing only hydrogen. They conclude, therefore, that coal is com-
posed largely of two types of compounds, the one unstable, giv-
ing no hydrogen, the other more stable yielding hydrogen only.
iJour. Soc. Chem. Ind. 5. 2. (1886).
2Jour. Chem. Soc. April, 1911, p. 649.
PARR-OLIN— COKING OF GOAL AT LOW TEMPERATURES 37
G. E. Davis1, discussing the tars formed under different con-
ditions, says that at low temperatures are produced mainly such
hydrocarbons as belong to the paraffin series having the general
formula Gn H2n + 2> along with the olefines Gn H2n. The lower
members of these series are liquid, and, furnished in the pure
state, are illuminating and lubricating oils ; the higher ones are
solid and form commercial paraffin. They are always accom-
panied by phenols. Liquid products prevail and among the
watery substances acetic acid predominates.
If, on the other hand, the coal has been decomposed at a very
high temperature, the molecules are grouped quite differently.
While olefines and acetylenes occur more or less the paraffins
disappear almost entirely with the resultant deposition of carbon.
Some of this carbon set free is deposited in the retort in a
compact graphitoidal form; some occurs in a state of extremely
fine division in the tar and forms a constituent of the pitch oir
coke remaining behind. At the same time the action of heat
effects molecular condensations by which process compounds of
a higher molecular weight are formed, such as naphthalene,
anthracene and phenanthrene.
Behrens2 found that the tar obtained in the distillation of
ooal in the ordinary fire-clay gas-retorts (operated at high tem-
peratures) was much richer in benzene, toluene, naphthalene, etc.,
than the tar made inPauwel's coke ovens (operated at low tem-
peratures) from the same kind of coal.
Lunge3 thinks that at low temperatures most of the nitrogen
of the tar is in the form of aniline and fatty amines (ethylamine,
propylamine, amylamine) ; at high temperatures in the form of
pyridine bases, picoline, lutidine, viridine, etc. He admits that
the statement needs verification by more detailed investigations.
In general, at high temperatures the tendency to complete disso-
ciation becomes far more pronounced; the products approach
more and more to free carbon on the one hand and free hydrogen
on the other.
Watson Smith4 states that naphthalene increases with rise
of temperature. This is true also of anthracene, which is then
found in the creosote oil coming over before the anthracene oil
proper. Carbolic acid is also an important constituent.
iJour. Soc. Chem. Ind. 5. 2. (1886).
2Dingler's Polyt. Journal 208, 362.
3Coal Tar and Ammonia, p. 26, (1900).
4Jour. Soc. Chem. Ind. 8, 950, (1890).
38 ILLINOIS ENGINEERING EXPERIMENT STATION
II. STUDIES IN GENERAL ON THE CARBONIZATION OF COAL
F. C. Keighley1 argues that since the chemical constituents
of coals from any horizon are not necessarily indicative of their
coking properties, it is reasonable to assume that an important
factor determining the coking quality must be one of a physical
character and not altogether chemical.
It is known, he says, that the finest coking coals not only are
of the bituminous class, but their structure is such that upon
fracture they exhibit a fingery or prismatic form and separate
vertically, while the more difficult coking coals and the ones of
a bituminous character that cannot be coked at all, are of a lam-
inated structure and upon fracture break into cubical form and
have a tendency to separate horizontally instead of vertically.
This he thinks would indicate that the coking property depends
very largely upon the arrangement of the small particles of coal
composing the seam. If these lie in the seam with their longer
axes horizontal to the bedding of the seam they are unfavorable
to the coking process. On the other hand, if they are perpendic-
ular to the strike of the seam, i.e., at right angles with its bed-
ding, the coking tendency is much more pronounced. He sug-
gests that the superiority of Connellsville coke may be due to the
structure given it in the process of formation by the peculiar
geological movements of the region in which it is found.
M. A. Pishel2 suggests a simple practical test, for coking coal.
Pulverize the coal to 100 mesh in an agate mortar. Pour out the
dust and observe its condition. If it adheres strongly to the
mortar, it will probably make ^ood coke, he says. If there is
little adhesion, coking properties are absent. In his experimen-
tal work he tested more than 150 different specimens. Of the
four Illinois coals tried, none stuck to the mortar while most of
the Eastern coals adhered. He offers no theory to account for
this phenomenon.
Groves and Thorp3 classify coals with respect to their coking
properties as sand coals, those devoid of coking powers; sinter
coals, those possessing it to a relatively slight degree; coking
coals, those which produce a good quality of coke, and anthra-
cite.
Jiron Age. 80-364. Aug. 1907. Mines and Minerals Oct. 1907-
2Econ. Geol. June-July 1908. p. 265-270.
3Chem. Tech. Vol. 1, p. 122 (ed. 1889)
PARR-OLIN— COKING OF GOAL AT LOW TEMPERATURES
39
They give the following analytical table made up from the
wrork of Richardson. Regnault and others:
TABLE 16
(
Percentage
)
c
H
0
77
5
18
Sinter coal •
83
5
12
87
5
g
Anthracite
95
3
2
TABLE 17
Anthracite
Blanzy sinter
Lancashire cannel sinter . .
Mons coking
Grand Croix-highly coking,
80C + 88H +0
80C + 128H +60
80C + 128H +30
80C + 24CH + 50
80C + 112H +30
It will be observed from Table 16 that the amount of hydro-
gen in the first three varieties is identical, while the oxygen di-
minishes as the coking property is developed. The Grand Groix
coal (Table 17) has only half the amount of hydrogen contained
in the coking coal from Mons. Anthracite, consisting almost
entirely of carbon, may be considered a kind of natural coke.
They state in conclusion, however, that Stein of Dresden has.
shown that coking and non-coking coals may have the same ul-
timate composition and that simple analyses, therefore, cannot
determine absolutely the coking property of the coal. They sug-
gest that the real source of coking lies in a resinoid body or
bedies identical in composition with the coke itself.
White and others1 mention the work of Ste. Glare Deville,
consulting chemist of the Paris Gas Company, who, on the basis
of results of nearly 2000 tests, divided coals into groups according
to the relations of their percentages of oxygen to hydrogen. He
found that all coking coals contain a percentage of oxygen ap-
proximately twice that of hydrogen.
They reasoned that possibly the artificial application of heat
which gives as its first products water and other compounds
rich in oxygen, would lower the relatively high oxygen of the
non-coking coals and possibly bring them into the coking class.
They found, however, that coals which were originally non-cok-
ing were not improved in this respect even though the oxygen-
lAm. Gas Light Jour. 89-621. (1906)
40 ILLINOIS ENGINEERING EXPERIMENT STATION
hydrogen ratio was brought down to 2 to 1. The coking coals
tested sintered together during the heating and if the resultant
mass was heated to redness it retained its shape and gave a good
coke. If, however, it was powdered before being heated, it re-
mained a powder.
Dr. Haberman1, in studying the spontaneous heating of coals,
noted the fact that long storage tends to destroy both gasifying
•and coking properties. He found that those coals that oxidized
the most and gave the greatest rise in temperature absorbed the
largest quantities of bromine.
Professor Fischer2 of Gottingen, working on the same prob-
lem, mentions the loss of coking suffered by oxidized coals. He
too suggests the bromine absorption test for determining the
•chemical activity of the fuel.
Parr and Lindgren3 doing work on the weathering of coal at
the University of Illinois observed that in volatile matter deter-
minations, samples exposed for several months gave powdery
residues instead of coke as in the case when fresh coals were
used.
David White4, in his bulletin "The Effect of Oxygen in Goal,"
-after discussing the negative calorific value of the oxygen and
the transition between various grades of coal due to progressive
devolatilization brought about more or less directly by dynamic
forces, takes up a study of the relative proportion of oxygen,
hydrogen, and carbon, in coking coals with special reference to
a theory framed to explain the coking quality.
He mentions the work of Regnault8 and Bertrand,6 who
found that the high percentage of volatile matter and the high
illuminating value of certain bogheads and oil shales are due to the
presence of immense numbers of supposed gelatinous algae
which, in these coals, seem to have exercised a selective attrac-
tion for certain bituminous compounds. Likewise, the condi-
tions of accumulation and deposition attending the origin of
many coals were doubtless favorable for the mingling of algee
and different animal remains with the debris of higher plant
types.
Mr. White thinks it is more than probable that the sub-
stances of these lower organisms contributed as ingredients to
iSchillingrs Jour, fur Gasbel. 49-419, (1906)
2The Gas World. April 13, 1901.
^Unpublished reports of supplementary studies to Bulletin No. 17, University of Illinois,
Engineering Experiment Station. (1911)
4Bull. U. S. G. S. 382 (1909)
5Regnault, B. Les micro organismes des combustibles fossiles. St. Etienne, 1903.
. Soc.d'hist. Nat. Antun. Vol. 9, 1897, p. 193.
PARK-OLIN— COKING OF GOAL AT LOW TEMPERATURES 41
the mass of coal-forming material, and that they, therefore, ex-
erted some influence on the character and quality of the final res-
idues. He considers the higher percentage of bituminous matter
in the older and more altered condition of the fuel, due to con-
centration as the result of devolatili/ation of the coal by dyn-
amochemical processes, the larger part of the concentration be-
ing the result of loss of oxygen, this loss being disproportionately
.great as compared with that of hydrogen. Thus, the progressive
-deoxygenation of the organic matter accomplishes bituminiza-
tion.
Now, he continues, the qualities of fusibility and swelling
•concurrent with bituminization which appear to characterize
fuels known to contain quantities of gelatinous micro-alga3, are
also necessary to the coking quality in coals, and he thinks it
permissible;, therefore, to inquire whether the coking property
may not be due to some unascertained proportion of gelatinous
algal matter entering into the original mass from which the coal
was formed and imparting to it this fusibility and tendency to
swell.
While the presence of micro-algal ingredients has been
noted in peats and even in some brown coals, yet it is very evi-
dent that their detection by microscopical means in the highly
metamorphosed coking coals, is so difficult as to be practically
impossible. The evidence of chemical analysis must therefore,
be called into service. The coals, he says, whose large volatile
combustible matter contains relatively the highest hydrogen and
the lowest o,xygen, thus approaching nearest the bitumen analy-
ses, are those in which the organic remains described as micro-
algae are most predominant and best preserved. If then, in the
high volatile coals high bituminization and gelatinous algal in-
gredients go together and the presence of the latter causes the coal
to fuse and swell, we may conclude that high volatile coals that
show sufficiently high bituminization will coke by the ordinary
process. The degree of bituminization is indicated by the rela-
tive excess of hydrogen as compared with the diminished oxy-
gen in dry coal and is expressed by the ratio H :0.
Data covering the tests of over 300 coals from different lo-
calities furnished by the U. S. Geological Survey are given. It
was found that those coals having a H:0 ratio of 59 or more,
coke by the ordinary commercial process. Nearly all below 59
and above 55 so far as tested, make a coke. Those below 55 us-
42
ILLINOIS ENGINEERING EXPERIMENT STATION
ually give a poor and dark product. The best cokes obtained by
the ordinary process were made from coals having a ratio of
60 or over. It was noted however that with coals with a fixed
carbon value of over 79 per cent the rule breaks down.
He remarks that his hypothesis appears to harmonize with
the tendency of coking coals to cohere when reduced to fine
powder, discussed by M. A. Pishel.
0. Boudouard1 took up the study of coals with the specific
purpose of delermining the causes of coking and selected for
experiments samples of (1) English anthracite, (2) Gourrieres
(y± bituminous), (3; Belgian forge coal, (4) Forge coal of un-
known origin which has lain in the laboratory several years,
(5) Bruay (% bituminous). (6) Goal of unknown origin, (7)
Lignite.
The following table gives the results of the approximate
analyses :
TABLE 18
COMPOSITION OF COALS BEFORE TREATMENT
i
2
3
4
5
6
7
Fixed carbon
88 6
89 5
70 5
79 1
39 3
51 4
37.3
Ash
Volatile matter
Character of coke
Hardness2
2.5
8.8
powdery
0
1.6
8.8
powdery
o
4.6
21.8
hard
3
2,6
18.1
hard
3
3.1
37.6
hard
3
2.3
46.2
slightly
caked
0
4.2
58.4
powdery
0
These coals were successively subjected for periods of 105 hr,
each to the action of air at 15° and 100°. After the first treat-
ment little change in the coal and in the appearance and char-
acter of the coke was noted except that No. 6 and 7 showed
traces of hurnic acid. In contrast with this, after being heated
at 100°, none had retained their coking powers and all but (1)
and (2) contained humic acid. A marked increase in weight due
to oxygen absorption was observed, amounting in some cases to
nearly 5 per cent.
He further treated 25 grains of each of the coals studied with
150 grams of concentrated nitric acid for a period of 2l/2 months.
Analyses of the residues gave the following results :
JBull de Ca. Sec. Chim. 5 (series 4) 365-39-) (1909\
2The relative hardness of the coke is indicated by the figures 3, 2, 1 , 0.— 3 denoting a hard
compact coke, 0. a powdery residue.
PARR-OLIN- — COKING OF COAL AT LOW TEMPERATURES
43
TABLE 19
COMPOSITION OF GOALS AFTER TREATMENT WITH NITRIC ACID
1
2
'
i
5
6
7
Per cent
change in
weight . . .
Fixed carbon.
Ash
+ 15.6
68.1
1 8
+ 26.0
54.7
41
+ 6.4
56.5
1 5
+ 20.4
51.5
6 1
+ 17.2
49.6
1 6
— 14.0
43.2
72
- 36.8
39.4
61
Vol. matter ..
Appearance of
coke
Humic Acid . .
30.1
powdered
0
44.8
powdered
0
41.9
powdered
15 per cent
42.2
powdered
8 per cent
48.7
traces of
agglome-
rate
50 per cent
56.0
traces of
agglome-
rate
40 per cent
59.9
powdered
27 per cent
Organic solvents such as ligroin, pyridine, benzene, carbon
disulphide, carbon tetrachloride and the like, modified in no
appreciable way the quality of the coke produced. Concentrated
sulphuric acid destroyed the coking power; concentrated hydro-
chloric acid had no effect.
In none of these coals did humic acid exist before treatment
and since iis presence was always constant in the same oxidized
coals which had in the process lost their coking powers, work-
ing on the theory that the carbohydrates were responsible for
the origin of the acid, he found that starch or sugar treated with
bromine water, for instance, yielded humic acid much like that
obtained from coal.
It is probable, he thinks, that the hydrocarbonaceous sub-
stances giving rise to this acid do not exist in a single form but in
a state of great condensation, and polymerization is a result of the
decomposition of the living matter, the principal characteristics
of this series of processes being the disintegration of the plant
tissues and the accumulation of carbon at the expense of hydro-
gen and oxygen.
In his comparative studies of natural and oxidized coals, he
noted that the production of a very small quantity of humic
acid (less than 1 per cent) marked the disappearance of the
coking qualities of the original sample.
In this connection the theories advanced by Professor
Lewes, already referred to, on page 25, are of interest, harmon-
izing as they do with Boudouard's work and presenting some of
the most modern lines of thought on this subject.
Dennsledt and Bun/1 hold with Boudouard that humic acids
JZeitsch. f. ang. Chem. 21, 1825. (1908).
44 ILLINOIS ENGINEERING EXPERIMENT STATION
are the ultimate oxidation products of coals and the most in-
flammable coals are those that produce the largest quantities of
the acid.
The exact nature and composition of the so-called humic
acids, however, seem to be unknown. Boudouard1 quotes the re-
sults of several experimenters who produced the substance by
treating sugar with acids. The empirical formulas (no struc-
tural formulas are attempted,) range from C24H1809 (Stein) to
C40H<24012 (Mulder). He himself proposes G18H1409 as the compo-
sition of humic products he obtained by extracting oxidized
coal with potassium hydroxide.
W. G. Anderson in studying the varying coking tendencies
of a number of Scotch coals, concluded that cementation is
caused by the decomposition of two classes of substances;. (1)
resinous materials soluble in caustic potash, which break down
on rapid ignition; and (2) non-saponifiable substances, some of
which were volatile at 300°, others being stable at this tempera-
ture.
III. SUMMARY OF OPINIONS
A very brief review of the literature covering the decompo-
sition that takes place at low temperatures in the distillation of
coal, is sufficient to prove to the student that the problem in all
its phases is distinctly modern. A glance at the bibliography
will show (hat few, if any, references date back more than ten
years and that most of the publications on the subject have ap-
peared within the last two or three. Indeed, Burgess and Wheel-
er2 writing in 1910, remark that "previous work has been very
scanty". Furthermore, almost without exception, those inves-
tigators who have already made reports announce that their
first articles are more or less incomplete and that they expect to
continue along the same lines of study.
While the development of the subject is evidently still in its
infancy, yet results from different sources are in many cases en-
tirely consistent. Of particular interest in that it bears a close
relationship to the problem of smoke prevention, is the fact, men-
tioned by nearly all authorities, that the heavy smoke-producing
benzines and paraffins of high carbon content are given off at
iBull. de la Soc. Chim. 5 (series 4) 378. (1909).
Jour. Soc. Chem. Ind.. 17-1013. Nov., 1898.
2Jour. Chem. Soc. 97— 1917 (1910)
PARR-OLIN-^-GOKING OF GOAL A:P Ea.TEElliCRfiS 45
low temperatures and are practically eliminated at 500°. At-
tempts to separate and estimate the higher homologues of me-
thane contained in early distillates, however, have not been en-
tirely successful on account of a lack of adequate methods of gas
analysis. Gady and McFarland1, using liquid air, got perhaps
the best results but even their scheme leaves much to be desired.
Writers reporting the paraffin content of the gases studied there-
fore have been obliged to estimate the heavier members as
"ethane", or, using the formula Gn H2n + 2, to give average val-
ues of n.
It is generally agreed further, that as temperatures rise above
500°, methane and hydrogen are the principal gas constituents,
being decomposition products of not only the coal itself but of
some of the gases given off at the lower temperatures. Below
400°, hydrogen is present in very small amounts. It seems fair-
ly well established, therefore, that the density and, consequently,
the calorific value of a gas varies inversely with the temperature
at which it is evolved and that a very moderate heating of the
coal is sufficient to remove enough of the smoke producing ele-
ments to make the combustion of the residue clean and econom-
ical.
With a very small amount of work done in determining the
character of the low temperature tar distillates, a fruitful field is
left for future investigation. Paraffin oils, valuable for lubri-
cating and power generating, seem to predominate, while the
equally important aromatic derivatives, as anthracene, are pre-
sent to a less extent than in the high temperature runs.
The investigations of Parr and Francis prove that coal, mod-
ified by the application of moderate heat gains valuable prop-
erties and that it retains a high calorific vfilue. In the use of cer-
tain types of coal, however, such as those of the central west, the
problem of putting the residues into marketable condition de-
mands a solution before the process can be made an economic
success.
Much has been written in attempts to explain the causes of
coking, or at least to define the conditions that govern it. From
the work of Parr, Chamberlain, Boudouard, and others, who
have studied the reactions taking place at low temperatures,
it has been proved that oxygen absorption goes on rapidly when
fresh coal is exposed to the atmosphere. It has been shown
ijour. Am. Chem. Soc. 29—1523 (1907)
46 : : ill.iK@IS^N(rLNaEaiNG EXPERIMENT STATION
further that this absorption weakens or destroys altogether any
coking properties that the original coal may have. In other
words a high oxygen-hydrogen ratiio marks the absence of fusi-
bility and cementation.
The structures of the organic compounds of the coal which
furnish the cementing material for coke and which are appar-
ently attacked by oxygen, have not been determined and seem to
vary somewhat in different types of coals. However they yield,
on oxidation, humic acids of varying composition which decom-
pose into powdery residues. Because of the complex nature of
these substances and the difficulty experienced in isolating and
identifying them, the matter of coking is still an open problem
and the explanations advanced are largely hypothetical.
PUBLICATIONS OF THE ENGINEERING EXPERIMENT STATION
* Bulletin No. 1. Tests of Reinforced Concrete Beams, by Arthur N. Talbot. 1904.
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