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Full text of "Plant operation and control of North American Cement Corporation of Security, Maryland / by Thomas Eugene Watson."

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Submitted by: 

Thomas Eugene Watson, Jr. 

Tau Beta Pi, April 1940 



The Security, Maryland plant of the North American 
Cement Corporation is situated near a large limestone quarry 
which has been divided into sections according to the chemical 
analysis of the rock in each section. As the rock is needed it 
is dynamited, loa ded into rail cars and hauled to a crushing 
house on the edge of the quarry. Here it is crushed to about 
one inch or less and stored in a certain bin according to the com- 
position of the rock. If the rock is wa nted for commercial pur- 
poses it is stored in separate bins according to size. When the 
plant receives an order for cement of definite composition, the 
laboratory directs from which bins to remove the rock. This is 
done by automa tic hoppers. The mixed rock is carried to stor- 
age in the main plant by freight cars. As needed, it is conveyed 
to one of two rotary dryers. It is then stored again. At the 
same time crushed shale is dried in another rotary dryer and 
stored. As the laboratory directs the rock and shale are mixed 
a nd pulverized to the consistency of flour. This flour is then 
stored in one of twelve control tanks according to the composi- 
tion of the flour. As the flour is needed it is carried from one 
or more of the control tanks to a mixing tank where it is mixed 
to give the proper blend. The blend is elevated to a kiln tank 
and conveyed to a rotary kiln. The kiln is heated by burning 



pulverized coal at the opposite end to the feed. The fused 
clinkers are disclia rged at the hot end and earried to storage 
where they are quenched with a water spray. As the hot gases 
leave the cool end of the kiln they pass through boilers, the 
steam from which runs the power plant. The cooled gases then 
are cleaned by passing them through multiclones and Oottrell 
electric precipitators. The dust thus collected is lime and 
potash and is sold as such for agricultural purposes. In the 
meantime, the clinker, having been analyzed, is carried from stor- 
age and mixed with a prescribed amount of gypsum. This mixture 
is repulverized and the oversize particles separated from the 
correct-sized particles in an air separator. The rejects are re- 
pulverized. The cement is pumped to storage. Often it must re- 
main sealed in storage for 10 to 28 days in order to compete for 
government or private contracts. The cement is then conveyed to 
filling tanks from which sacks and barrels are filled. 

There are two control la boratories. One, the chemical 
laboratory analyzes all samples of crude, raw, and finished pro- 
ducts periodically for chemical composition. The other, the physi- 
cal laboratory analyzes all samples of raw, coal, clinker, and 
finished product for fineness, soundness, tensile strength, com- 
pression strength, time of set, and expansion. 

The process used at Security is the economical dry pro- 
cess, so called because no moisture is added to the mix as in the 
wet process. The Security plant operates very efficiently and 
safely and is very proud of its safety records. 



The quarry consists of two levels with faces ah out 50 
feet in height. Holes are drilled 25 feet back from the face and 
15 feet apart . These holes are 6 inches in diameter and 55 to 
60 feet deep. Samples are drawn up and sent to the chemical lab- 
oratory, where they are subjected to a complete analysis consist- 
ing of analyses for silica, lime, magnesia, and iron. In this 
fashion, the analysis of each section of the quarry is known and 
from this data can be determined the location from which to take 
rock in order to meet contract specifications. There is, at Secu- 
rity, one section that has remained untouched because the rock in 
that area contains an excess of magnesia. The magnesia over 5$ 
is harmful because it causes disintegration of the cement by hy- 
drating f rom MgO to Mg(OH) . 

As the laboratory gets the contract specifications, it 
orders the blast ing of a certain section or sections of the quarry. 
The rock is then loaded into rail cars and is taken to a dumping 
platform where it is dumped into a receptacle adjoining a jaw 
crusher. As the jaw crusher empties one charge, another charge 
is fed into it from the receptacle. In the crusher, the rocks 
are reduced to about nine inch sizes. A belt conveyor carries 
the crushed rocks up an incline to a hammer mill crusher to be 
reduced to about one inch or finer. The reduced rock is car- 
ried on a belt conveyor to a storage house. The storage house 
is divided into a series of bins, each bin containing reduced 
rock from a definite section of the quarry. The rock leaving 
the hammer mill is deposited in the bin containing rock of its 






^•^-v 1 .. 




0,-uarry, showing the two levels and a drill in operation 

in the background 

Dumping the cement rock at the crusher house, 


If the rock is to "be used for commercial purposes such 
as road building, it is quarried from a section of the quarry 
containing almost pure limestone. It goes through the same opera- 
tions as the cement rock until it leaves the jaw crusher. From 
the ,iaw crusher this rock is carried by a belt conveyor to a 
gyratory crusher, then is sorted into sizes on a hummer screen. 
This rock is then stored with respect to sizes. 

At the bottom of each Din there is a hopper feeding 
onto a belt conveyor. As the laboratory directs different bins 
may be fed onto the conveyor to give a mixture of cement rock 
of desired composition. This mixing takes place on the conveyor 
and is automatically controlled by an oscillating bar to which 
the hoppers of the designated bins are attached. The mixture 
is carried to a bucket elevator on which it is elevated and 
dumped into a freight car to be carried to the main plant. This 
operation is carried on at night. 

Statistically about 1500 tons of stone are handled in 
a ten-hour day. The Crushers have a capacity of 200 tons/hr. 
The storage building has a capacity of 14,000 tons. 

(1) . Leighou, Chemistry of Snpiineerlnp; Materials 

Flow Sheet 

Commercial Rook 





Carrying to jaw crusher 

n J 


Reducing in gyratory crusher 



Cement Rock 



Carrying to jaw crusher 



Reducing in hammer mill 
Conveying to proper bin 

Mixing on belt 

Conveying and elevating 

Dumping into freight car 



The freight oars with the cement rock are taken to 
the main plant. There the rock is dumped into underground bins 
from which a bucket elevator takes the rock to stone tanks for 
storage. A stone tank has five hoppers beneath it in this fashion: 

The use of the five hoppers increases the useful area 
inside the tank and allows a more uniform feed onto the belt con- 
veyor beneath the hoppers. The hoppers are so controlled that, 
referlng to the diagram, feed from hopper "2" will fall on feed 
from hopper "1"; feed from hopper "3" will fall on feed from hoppers 
M l n and "2" and so on down the line. This gives uniform distribu- 
tion of rock. After the belt conveyor passes out from tinder hopper 
"5" it passes under a strong electromagnet which removes extraneous 
metal. The rock is then deposited on a bucket elevator and distri- 
buted to one of two rotary driers. These driers are 5& feet in 
diameter, 50 feet long and are slanted down toward the hot end. 
The driers are heated by burning pulverized coal and blowing air 
over the coal into the drier, counter our rent to the flow of the 
rock. The operation removes most of the moisture from the rocks. 
The dried rooks are deposited at the hot end and carried by an 
elevator belt to a shuts and belt, then deposited on a hummer 


screen to separate the rooks of the desired sizes of £ inch or 
less. Oversize rooks are returned to a crusher, reduced, and re- 
screened. The rocks of the correct size are conveyed to a raw 
storage tank, While this drying operation is going on, shale from 
a quarry in Williamsport is reduced and stored in a hopper at Secu- 
rity. The shale contains the silica, alumina, and iron necessary 
to bring the cement to the desired analysis. After this shale 
has been reduced in size it, too, is fed into a rotary drier, dried 
on the count ere urrent principle, and stored. From storage the dried 
rock is fed to belt oonveyors to mixing bins. The shale is con- 
veyed from storage to automatic scales and a weighed amount is 
conveyed to feed tanks to be fed into the rook. About 50 pounds 
of shale are added to 600 pounds of rock. The mixture of rock and 
shale is conveyed to a Hardinge ball mill. This mill is 10 feet 
in diameter, 5§ feet long and is loaded with 25 tons of steel 
balls from 3 Inches down which pulverize the mixture as the mill 
revolves. Air swept through the mill carries the powder from the 
Hardinge mill to 14 Puller mills where it is further pulverized 
to such an extent that 90% will pass a 200 mesh screen. The capa- 
city of the mills is about 1500 tons for a 24-hour day. In the 
Fuller mill the stone is pulverized between a steel die and four 
12 inch steel balls driven by centrifugal force around the periphery. 
The raw flour-like powder, as it leaves the Fuller mills is con- 
veyed to storage in one of twelve control tanks depending on the 
composition of the flour. These tanks are under laboratory control. 
The laboratory knows by analysis what each tank holds and can, by 
proper blending of the contents of several control tanks, obtain 


a mixture which will give a clinker within 0.2$ of laboratory 
prediction. Upon laboratory direction, flour from several con- 
trol tanks is conveyed to one of three feed tanks for mixing. 
The mixture is then conveyed and elevated to one of five kiln 
tanks each situated above the cool end of one of five kilns. 

Flow Sheet 













Storing in oontrol tanks 

Mixing in feed tanks 

Carrying to kiln tanks 

Cement Rock 

Freight Car 








From the kiln tanks the feed is carried continuously on 
a belt conveyor to the cool end of the kiln (about 1400°F) and de- 
posited in the kiln. There are five kilns at Security. Each is 
a revolving drum, 125 feet long. The diameter at the cool end is 
8 feet while that at the hot end (2800°F) is 10 feet. This differ- 
ence in diameters plus a slight slant towards the hot end allows 
the feed to drift counter currently to the heat. The kiln is heated 
by burning pulverized coal which is blown in by air- The coal is 
pulverized and analyzed at the Security plant. The plant uses about 
250 tons per day. After the feed enters the cool end of the kiln, 
it loses any moisture not removed In the driers. Then as the feed 
reaches a hotter section CO is freed from the limestone and goes 
off with the hot gases. At the hot end, the cement clinker is 
formed, 2 to 2i hours after charging. This clinker contains fused 
tricalcic silicate, tricalcic aluminate, and dicalcic silicate. 
These compounds are unstable and rearrange when wet. The tricalcic 
silicate forms a gelatinous calcium hydrate and silica to which is 
due the initial set. As the hydration continues, the gelatinous 
material binds the grains of sand which are added, and the stone 
filler, to a hard mass. The tricalcic aluminate and the dicalcic 

silicate are hardeners but are not as rapid as the tricalcic sili- 

cats. After the clinkers are formed and reach the discharge end, 

they are deposited into a pit from which a bucket elevator carries 

them to an opening in the wall through which they are dumped into 

an open-air storage. As they are dumped, they are quenched with a 

water spray. This sudden cooling gives a protective coating to 

One of five rotary kilns at Security 


the clinkers. 

In the meantime, the hot gases have passed out the cool 
end of the kiln into a boiler system of three 1000 Horsepower 
boilers. The gases make four passes through the system. The 
steam thus generated goes to drive the company's electric power 
plant which in turn drives all the oompany machinery. After the 
gases leave the boilers they are passed through multiclones where 
the suspended particles are separated and where most of the lime 
is collected. The gas then goes through a spray chamber In which 
water is sprayed over the gas to increase the ionization of the 
suspended particles. This increases the efficiency of the Cottrell 
electric precipitators through which the gases pass next. The 
cleaned gases are then allowed to escape to the atmosphere. The 
precipitators are periodically shaken down and the collected lime 
from the multiclones and potash from the precipitators are sold 
as such to fertilizer companies. 

Statistics on the kilns show that 1500 tons of raw 
material is fed into the kilns daily with formation of 940 tons 

of clinker, equivalent to 5000 barrels, and 560 tons of CO gas. 


As the clinker is needed, it is carried by an 8-ton 
crane to the clinker grinding department. Before grinding, gypsum 
is added in an amount designated by the laboratory. The proportion 
is controlled by automatic scales and Is generally 12 to 13 pounds 
gypsum for each barrel of clinker. The mixture is conveyed from 
the mixer to storage bins. Then, as needed, it is carried to 10 
Fuller mills for pulverizing. From these mills it is elevated to 
tube mill tanks. From these tanks the cement is let into 5 tube 

Air separator 


mills each of which Is charged with 15 tons of small steel balls. 
The action of the balls reduces the cement further. The powder is 
then conveyed and elevated to two air separators in which the centri- 
fugal force of an air current separates the large particles from 
the small. The large particles are sent out of the separator and 
are carried by screw conveyors to be reground in the Puller and tube 
mills from whence they are again separated. The powder which comes 
out of the separator is of such fineness that 96$ will pass a 
200 mesh screen. This fine powder is pumped by air into storage 
silos and 39 rectangular bins with a total capacity of 200,000 bar- 
rels. The effective oapacity is sometimes out down by contractors 
who require that the new cement remain in storage for 10 or 28 
days before it is allowed to be used in contract bids. As the ce- 
ment is required, it is withdrawn from storage and conveyed to the 
fillers from which cloth and paper bags, or barrels are filled, 
and then shipped to consumers as North American Portland Cement . 
One bag contains 94 pounds of cement while one barrel contains 
376 pounds. The cloth bags are reclaimed, cleaned, and patched 
when torn. Bags too badly worn are discarded. 

(2). Reigel, Industrial Chemistry 


Flow Sheet 


Kiln tank 

K ll n gafiS3^. Boi i er ^Multlclonea— -~ Spray 


J \ I 

Clinker storage Power plant Lime 





Quenching Plant operation ^^-""""^ Flue gas 


Mixing with gypsum 



Pumping to storage 




Conveying to fillers 

Filling containers 




The control and testing is carried on in two laboratories, 
the chemical laboratory and the physical laboratory. All tests are 
standard according to the American Society for Testing Materials 
and the Cement Reference Laboratory. 

The Chemical Laboratory runs all chemical analyses. It 
receives samples from the quarry and runs complete analyses for 
lime, silica, magnesia, and iron. Tests are run for lime on the 
cement rock in the stone tank. The shale is tested for iron, alu- 
mina, and silica. The blend is analyzed for lime before entering 
the kiln. Samples are drawn from the control tanks and are placed 
in eleotric furnaces to simulate conditions in the kiln, The labora- 
tory clinker is analyzed after 45 minutes in the furnace and from 
these data and similar data on the other control tanks the labora- 
tory can control the blend to be taken from each tank. The theo- 
retical analysis and the actual analysis of the kiln clinkers varies 
no more than 0.2$. Clinker samples are subjected to complete analy- 
sis every hour. The gypsum is analyzed for SO content. A complete 


analysis is run on the 24-hour run of the finished product. Among 
the qualities not desired in cement are high magnesia and free 
lime because these compounds tend to disintegrate the eement by hy- 

The physical laboratory runs the physical analyses. Sam- 
ples are collected each hour of the raw material, the clinker, the 
coal, and the finished cement and analyzed for fineness. The ce- 
ment must pass a 200-mesh and a 325-mesh screen test. A continuous 
sample is taken from the pump leading from the separators to the 


bins and silos. 

On the finished product tests are run on time of set 
with the use of the Gillmore needle. For initial set a quarter- 
pound needle must sink no more than 1/1 2 of an inch while at final 
set the pound needle must sink no more than 1/24 of an inch. 

The cement is tested for tensile strength. It is made 
up with 20 to 30 mesh sand and placed in molds in a constant hu- 
midity box. After setting for 1, 3, 7, or 28 days, the tensile 
strength is tested on a standard machine. 

For soundness, the cement is made up with water and kept 
at 70 •p and 94 to 96$ humidity for 24 hours. It is then subjected 
to steam for 15 minutes and inspected for soundness. The cement 
must be sound. 

The compression test is run on cement made up with a 
2.77 mix with C-107T34 sand. The. cement is molded as a cube and 
allowed to set . It is then subjected to a standard compression 

The autoclave test measures the expansion of the cement. 
The cement is molded in bar form and its length calibrated with a 
meter. The bar is then subjected to 300 pounds steam pressure for 
three hours. It then cools for 15 minutes by placing in water at 
80 °F. Then it is regaged. The difference in readings is the per- 
cent expansion, the maximum limit of which is 0.5$. 

The tests run at Security are all analytical and control. 
The research laboratory is situated in New York State. 

Chemical control laboratory 



The Security plant is very modern and efficient. Proud 
of its safety record, the plant has operated for over seven months 
without a lost-time accident. 

The method employed to make cement is that known as the 
"Dry Process", used almost exclusively in the United States. 

The industry is one of great importance to our country 
and to the world at large. With the Industry as well organized 
as it is today, we need never lack that valuable product- Cement. 





(1) Mr. Zaiser, general plant guide 

(2) Mr. Samuels on, chemistry laboratory guide 

(3) Mr. Eiler, physical laboratory guide 

THE STORY OF CEMENT , published by North American Cement