Jan., 1 9 2 1
T H E J O C R N A L OF INDL’STRIAL A N D ENGINEERING C H E M I S T R Y
carbon dioxide (7 t o 8 per cent in Texas lignites). It is this 3 2 t o 40 per cent incombustible volatile matter which causes briquets made from raw lignite t o explode in the fire. Hence lignite must be retorted to render it fit for briquetting. The question arises: What is the most economic extent of retorting? For our experimental study of this question, the lignite used was obtained in the open market in Austin, but all of it was from the same mine. The lignite thus obtained was of rather mediocre quality. To our knowledge better lignite can be obtained even a t this mine and certainly in other localities, but what we used is representative of much of the lignite now sold in Texas; hence, the figures presented below may be considered t o be safe for all commercial lignites in Texas, b u t low for specially good lignites. I n our first set of experiments we retorted lots of I O lbs. each in powdered form with constant stirring and fractionated the gas evolved as the temperature was raised. These experiments revealed : ( I ) The fact t h a t the evolution of carbon dioxide ceases abruptly a t about 525 C. ( 2 ) T h a t t h e per cent by volume of carbon dioxide in t h e gas collected u p t o this temperature is from 23 t o 33 per cent. , (3) T h a t t h e other constituents of t h e gas evolved up t o 525 C. have high calorific powers, so t h a t t h e mixture has a calorific power of 410 B. t. u. (4) T h a t all t h e t a r is evolved with this gas. These results were obtained also with a different kind of a lignite from a totally different field. The gas fractions obtained a t temperatures higher t h a n 5 2 j o C. have heating powers of 410 B. t. u. per cu. f t . or less, and the total amount of gas obtainable by retorting a ton of this lignite is not more than 6500 cu. it. (the lignite from another region gave 6900 cu. f t ) , with a n average heating power of t h e whole gas of 410 B. t. u. This result is in marked contrast with the 10,000cu. f t . of 400 B. t u. reported heretofore. The coke left after complete retorting has a n ash content of 25 t o 28 or even 30 per cent and a heating power of 10,000 B. t u. or below. The relatively poor quality of this coke and the fact t h a t the gas obtained with i t would have t o be enriched t o make i t fit for “city use” led us t o consider the feasibility of retorting the lignite with a maximum temperature of 525’ C. It was evident t h a t by removing as much as possible of t h e large per cent (about 30 per cent) of carbon dioxide from t h e gas obtained up t o 5 2 5 ’ C., its heating power could be raised substantially, and a simple trial showed t h a t this could be done readily t o such a n extent a s t o make t h e gas directly fit for “city use.” To t r y out this whole procedure on a sufficiently large scale, we constructed a n apparatus which retorted I IOO lbs. of lignite per 24 hrs. and purified all the gas. Theretort was a 6-in. castiron pipe placed vertically and surrounded by a brick furnace 7 ft. high, with gas burners a t the bottom. The low temperature required made i t easy t o operate in such a manner as not t o injure the iron retort; its life is likely t o be great. The amount of gas obtained was 2 2 j o t o 2500 cu. f t . per ton of raw lignite with a heating power of 525 t o 540 B. t. u . ; the yield of coke was goo lbs. of r1,ooo B. t. u. (or more!), and the yield of d r y t a r was z per cent. T h e carbon dioxide was removed down t o 2 per cent by means of potassium and sodium carbonate solution. Calculation shows t h a t the amount of lignite needed as fuel for retorting is about 7 . 5 per cent of the lignite retorted. The coke comes out of the retort a t a temperature just high enough for briquetting, and not so high as t o take fire on exposure to air. The advantages of this procedure are: ( I ) A coke of the highest heating power obtainable. ( 2 ) A gas immediately usable in city mains. (3) The maximum amount of tar obtainable. (4) A cheap retort with large capacity, operating under mild conditions, and yielding t h e coke a t a temperature a t which i t can be easily and immediately handled for briquetting.
23
PROF. PARR:I would like t o ask Mr. French if he expects sufficient binder for his briquet t o come from the tars One of his numerical factors especially interests us H e says 7 per cent of heat is lost in the final accounting for the heat. If he finds it possible t o locate, with sufficient accuracy, those percentages of heat in the various constituents, and then say pretty accurately here is 7 per cent of heat unaccounted for, we would like t o know about it. It is one method of getting a t the exothermic quantity of heat. Seven per cent of 4000 cal would be somewhere within the range where we think the measurement of quantity of exothermic heat resides. T h a t factor, 7.6, is exceedingly interesting t o our work. MR. FRENCH:A remark of Prof. Schoch’s reminds me I should mention some things myself. We found exactly the same things in the beginning of our work t h a t he did. We never got 10,000 cu f t of gas or anything like it. I suggest t h a t some of those high figures may be due t o the method of carbonization, because I know of one case where a man was actually operating The a carbonizer so designed t h a t they fed moist coal t o i t moisture t h a t was driven off passed through the hot charge and what you got was a gas producer on a small scale. This person may have got IZ,OOO or 20,ooo cu. f t . of gas, but he was getting it a t the expense of his residue. I judge from Prof Schoch’s remarks t h a t he was primarily after gas. We were after residue, and i t appears t h a t with our own carbonizers we had just about enough t o operate the carbonizers, and not much more. M r . Stansfield ran a series of experiments in t h e small retorts under pressure, vacuum, and with a steam atmosphere, b u t none of these seemed t o show any advantage, and he went back t o practically atmospheric pressure. In answer t o Prof. Parr’s question on tars, we took the t a r and distilled i t a t 325’ C. On t h a t basis, we got what we called “available binder,” a quantity of pitch representing 2 . 5 t o 3 per cent of the carbonized residue, and t h a t is not sufficient. It is probably not a quarter of what is required. It takes a large quantity of binder t o make residue briquets, because physically the residue more nearly resembles charcoal than i t does coke. I imagine i t will be similar t o some coke which Prof. Parr has here. Answering Dr. Porter, the water is the water of constitution. It is dry coal. It is dried a t 105’ C., and t h a t is the water left after drying. Returning t o Prof. Parr, so far as loss of heat is concerned, I would prefer t h a t *Vr. Stansfield should answer t h a t question himself, because I do not know very much about his calculations, except t h a t I have a number of them, and I know t h e loss of heat always runs around t h e figures given. T H E COMMERCIAL REALIZATION OF T H E LOW-TEMPERATURE CARBONIZATION O F COAL By Harry A. Curtis INTERNATIONAL COALPRODUCTS CORPORATION, IRVISGTON, NEWJBRSBY
The’ p r o c e s s h e r e i n d e s c r i b e d w a s d e v e l o p e d f o r c o n v e r t i n g b i t u m i n o u s c o a l into a u n i f o r m , s m o k e l e s s f u e l r e s e m b l i n g a n t h r a c i t e in p r o p e r t i e s . It was r e c o g n i z e d at the outset t h a t the problem was one i n w h i c h small-scale t e s t s a l o n e would n o t yield the necessary data f o r p l a n t d e s i g n , and while m u c h v a l u a b l e i n f o r m a t i o n has b e e n s e c u r e d i n s m a l l a p p a r a t u s , t h e d e v e l o p m e n t of the p r o c e s s has b e e n very l a r g e l y t h r o u g h u s e of commercial-size u n i t s . F o r the past f o u r and a half years large-scale e x p e r i m e n t a l w o r k has b e e n c a r r i e d on in p a r a l l e l w i t h l a b o r a t o r y tests. The e x p e r i m e n t a l plant, as finally d e v e l o p e d , has a c a p a c i t y of a b o u t roo t o n s of r a w c o a l p e r d a y , b u t
24
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
GENERAL VIEW OB
since it was built only for experimental work, no attempt has been made t o operate all units a t capacity. I n the course of experimental tests, t h e conversion of coal has, however, frequently reached 40 tons per day, and recently one of t h e commercial units was r u n continuously for 5 . 5 mo. without a shutdown. T h e experimental plant is fully equipped t o handle all t h e by-products, and includes a t a r distilling unit of I O O , O O O gal. per month capacity t o work u p t h e t a r into t h e usual crude products. During the World War construction of a commercial plant was begun, as a government war project. This plant was eventually completed and half of t h e retorts put into operation in June 1920. The usual minor difficulties of a new plant have been overcome without trouble and t h e balance of t h e retorts are now being put into operation. DESCRIPTION O F PROCESS
The essential steps in t h e process are briefly as follows : The raw coal is crushed and subjected t o low-temperature distillation in horizontal retorts, t h e coal being continually stirred and advanced through t h e retort b y paddles mounted on two heavy paddleshafts running lengthwise through t h e retort. The retort is heated externally i n a gas-fired furnace, and t h e by-products are collected essentially as in cokeoven practice. During this low-temperature distillation, 8;oo t o 950' F. in t h e gas phase, the volatile matter in t h e coal is reduced from, say, 3 5 per cent t o about I O per cent, the resulting semi-coke, being a soft, porous material considerably different from ordinary coke in structure. It can be used directly in a water-gas producer or as a boiler fuel, either hand-fired or with mechanical stokers. The material is not, however, in good shape for transportation and marketing away from t h e plant. The next step consists in grinding
Vol. 1 3 , No.
I
PLANT
t h e semi-coke, mixing it with hard pitch and briquetting. The resulting briquets are somewhat like t h e ordinary coal briquets on the market, except t h a t they burn with but little smoke. The final step consists in charging these briquets into an inclined retort and carbonizing them a t about 1800' F. for 6 hrs. During this carbonization t h e pitch is coked and t h e volatile matter in t h e briquet reduced t o about 3 per cent. There is a shrinkage of approximately 30 per cent in t h e size of the briquet and t h e final product is a hard, uniform fuel, which burns with an entirely smokeless flame. I t s structure is still markedly different from t h a t of metallurgical coke, and t h e fuel burns more freely t h a n coke. " COALS S U I T A B L E F O R T H E P R O C E S S
A t the experimental plant more t h a n a hundred coals have been put through t h e process, and in no case has i t been found impossible t o make a satisfactory product. The procedure in briquetting has had t o be varied considerably with different coals, but t h e hard, smokeless briquet has finally been produced in every case. Since t h e ash in the coal is accumulated in t h e product, i t is desirable, although not imperative, t h a t the ash in t h e coal be low. Also, if a high yield of byproducts is desired, a bituminous coal of high volatile content should be used. The process, however, can be applied t o any coal. It is, perhaps, of interest t o .mention t h a t several lignites have been successfully treated, including those of Texas, Wyoming, Colorado, Saskatchewan, Japan, and Brazil. BY-PRODUCT YIELDS
The yield of by-products in any carbonizing process will, of course, depend on t h e kind of coal used. In Table I is given t h e average yield of various by-products from twenty-nine different bituminous coals in which the volatile matter ran from 3 2 t o 41 per cent, averaging
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
Jan., 1 9 2 1
per cent. These results are from small-scale testing, charging about 3 3 lbs. of coal in t h e retort and making three t o six charges t o each test. I n comparing these results with those obtained b y others working on t h e problem of low-temperature carbonization, it must be remembered t h a t in t h e process under consideration both low- and hightemperature carbonization are used, and t h e yields obtained in t h e primary or low-temperature carbonization are augmented by those from t h e subsequent high-temperature carbonization of the briquets. It must also be borne in mind t h a t t h e pitch, which is one of the usual by-products, is returned t o t h e process, and yields, on carbonization, some by-products in addition t o t h e pitch coke which remains in t h e briquet. 37
TABLE I-AVERAGE
RESULTS F R O M TWENTY-NINE COALS RUNNINGOVER 32 PER CENT VOLATILE MATTER Avevage A n a l y s i s of Coal ( D r y ) Per cent 36.9 56.0 7.1
TOTAL ............................
~
100.0 1.1 13,783 Per cent 3.8 85.1 11.1 __ 100.0 0.68 12,874 66.1 Coal 34 8457 21 1.87 19.3 43
................ TOTAL ............................
....
.... rodu Dry tar, gal.. ........................... Gas, cu. f t . .............................. Ammonium sulfate, lbs.. Light oil from gas, g a l . . Other t a r oils gal.. ...................... Pitch, per cerk of t a r . .
.............
..............
TABLE!11-PRODUCTS FROM ONE TONOB DRY COAL(35 per cent volatile, 7 per cent ash) Coke or Carbocoal.. . . . . . . . . . . Gas, cu. f t . . . . . . . . . . . . . . . . . . . Light oil from gas, g a l . . . . . . . . Ammonium sulfate, lbs.. . . . . . . T a r oils, g a l . . . . . . . . . . . . . . . . . Pitch, gal.. . . . . . . . . . . . . . . . . . .
Coke Oven 66% (1% volatile) 10,000 1 20
Carbocoal 68 % (3% volatile) 9,000
3.8 8.2
.
2
26 15 None
While there are a few coals of 35 per cent volatile which can be coked in an ordinary coke oven, such as, for example, the Illinois coal recently used in a test conducted by t h e Bureau of Standards a t St. Paul, coke-oven practice in general calls for a much lower volatile coal. Instead of comparing the by-products from a high volatile coal, as is done above, it is probably far more significant, economically speaking, t o compare the actual average by-product yields from coke ovens the country over, with t h e yields which the process secures, assuming logically t h a t each process will use coals t o which i t is particularly well adapted. If we take the coke-oven data as the average of 7800 by-product coke ovens operating in the United States in 1g:7, the following figures obtain: Coke Oven Coke or Carbocoal, per cent. . . 71. Gas, cu. f t . , . . . . . . . . . . . . . . . . . 11,000 (Estimated) Light oil gal . . . . . . . . . . . . . . . . 2.4 Ammonidm sulfate, lbs.. . . . . . 19 T a r oils, gal.. . . . . . . . . . . . . . . . . 2.3 Pitch, g a l . . . . . . . . . . . . . . . . . . . 4.8
Aoevage A n a l y s i s of Finished Briquets
Sulfur, ..................................
25
Carbocoal 6a 9 , ooa 2
20 15 None
I n speaking of yields from the process, the particular coal in question must always be considered. I n coke-
...................
The by-product yields from t h e commercial retorts are a little different from those obtained in t h e small apparatus, due in part, a t least, t o the fact t h a t t h e primary distillation in t h e small apparatus is carried out in an iron retort, whereas t h e commercial retort is lined with carborundum, and in order t o get capacity i t is necessary t o carry a higher shell temperature in t h e retort. This results in a little less primary t a r and a little more primary gas t h a n found in t h e smallscale tests. COMPARISON
WITH
COKE-OVEN
BY-PRODUCT
YIELDS
Since coke-oven practice is established and well known, i t is of interest t o compare t h e by-product yields from this process with those from the ordinary coke oven. If t h e two processes be compared for a high volatile coal, say, 35 per cent, it must be assumed t h a t t h e coke oven could handle such a coal, and t h e yields given in Table I1 will, therefore, appear a little unusual for a coke oven. A further point must be considered in t h a t while t a r is a normal by-product of the coke oven, i t is not, strictly speaking, a by-product of t h e other process, since the t a r in the lat$er case is distilled and t h e pitch returned t o the process. I n order t o compare t h e two processes, then, i t must be assumed t h a t in each case t h e t a r is distilled, and t h e pitch in t h e Carbocoal process charged against t h e process. I n Table I1 this is done, the pitch being taken as 68 per cent of' the coke-oven t a r and 50 per cent of t h e other t a r , these being representative figures in each case.
FEEDMECHANISM. PRIMARY RETORTS
oven practice, the range of coals is rather narrowly limited and it is, therefore, permissible t o refer t o average yields, b u t in the other process, where t h e range of coals is not limited a t all, no average or standard yields can be considered. It is, for example, quite possible t o use a coal yielding 2 0 gal. of t a r oils per ton, or one yielding 7 5 per cent of carbonizedproduct. I n t h e tables above a coal of 3 5 per cent volatile has been taken as one t o which t h e process is particularly well adapted. I N D U S T R I A L PLANT
The industrial plant was p u t into operation in June 1920. It has a capacity of joo tons of raw coal per
26
T H E J O U R N A L O F I N L I L T S T R I A L AiVD E X G I N E E R I N G C H E M I S T R Y
day and, besides t h e main plant, includes equipment for working u p t h e by-products into the usual crude products for t h e market. The coal is mined b u t a few miles away, and is a good grade of high volatile bituminous coal. As t h e coal comes from t h e cars i t is dumped into a track hopper and elevated t o a crusher, where i t is crushed t o pass a three-eighthsinch screen. It is then delivered t o six 80-ton bins in t h e primary retort building. There are 2 4 primary retorts, arranged in four batteries of six each. Each retort is about 7 ft. in diameter and 20 f t . long, with a capacity of a ton a n hour. The crushed coal is fed into t h e retorts by self-sealing screw conveyors and is stirred and advanced slowly through t h e retorts by a paddle mechanism. The by-products are led off t h e discharge end of the retorts and handled as in coke-oven practice.
YOI, 1 3 , N O .
I
DISCUSSION
PROF.PARR:Mr. Chairman, I would like t o ask Dr. Curtis how nearly the pitch residue from the oil or t a r in the process met the requirements of the binder for the briquets. DR. CURTIS:It is about an even break on most high volatile coals. T h e point is not one which bothers us a t all. Having a t a r plant as a part of the equipment, we can if necessary bring in outside t a r and distil i t a t a profit, giving t h e required additional pitch. I n the case of one plant there is a small shortage and this is being done. The question ol pitch yield depends, of course, on the coal which is being used in t h e process. MR. SPERR: I should like t o ask about the amount of gas produced. As I understand it, t h e comparison of t h e yields of this process with those obtained in by-product coke-oven practice was made on the basis of the entire gas prodltction. T h a t is evidently why the figure of 10,000 t u . f t . was given lor coke-oven production. Have you any figures t h a t we could use t o compare t h e surplus gas produced by this process with t h a t obtained from the by-product coke oven? DR. CURTIS:The plant a t Clinchfield has not been ruiuiiiig long enough t o give a n accurate figure, but judging from results obtained a t the Irvington plant i t takes about 7000 cu. ft. of gas per ton of coal to run t h e process. At Clinchfield we do not consider gas as one of the salable products of t h e plant, but in case a plant were located near a city or industrial center, there would be a few thousand cubic feet of gas which could be disposed of. The gas yield depends, of course, on t h e coal used in the process, and with most high volatile coals is somewhat more than necessary for the retorts. BY-PRODUCT COKING By F. W. Sperr, Jr., and E. H.Bird THEKOPPERS C O M P A N Y LABORATORY, 3fELLON
T O P VIEW O F
SECONDARY RETORTS
The semi-coke which is discharged continuously from the primary retorts is carried by covered conveyors t o storage bins in t h e briquet building. Here it is ground, fluxed with pitch, and briquetted. There are two of these roll presses having a combined capacity of about 24 tons of briquets per hour. The raw briquets are carried slowly up a long cooling conveyor t o t h e storage bins a t t h e secondary retorts. From these bins they are drawn into larry cars and charged into t h e secondary retorts. The secondary retorts are built in two batteries of six and four, t e n retorts in all. Each retort consists of six rectangular chambers, 2 1 ' f t . long and inclined a t about 30°, with six charging and three discharging doors per retort, t h e capacity of t h e retort being approximately I 5 tons of raw briqueks. The finished briquets are discharged into steel quench cars and carried t o a quenching and loading station from which they are finally loaded into railroad cars. The by-products from t h e secondary carbonization are combined with those from t h e primary, after a preliminary cooling. The usual by-product equipment is provided, including a light oil plant, and a tar-distilling plant.
INSTITUTE, Pl'l"rSBU1Z(;H,
L'A.
For nearly two years t h e production of by-product coke in America has held t h e lead over t h a t of beehive coke. By-product coke manufacture is now firmly established and continually growing, while beehive coke is certain t o decline t o a position of minor importance. Although t h e bulk of t h e coke and gas manufactured i n by-product ovens is now consumed by iron and steel plants, there is a n increasing tendency for t h e by-product coke industry t o assuine t h e position of an independent fuel industry, and its relations are broadening t o such a n extent t h a t they must be considered i n t h e study of almost every phase of fuel economy. I S C X E A S I N G S H O R T A G E O F h-ATUR.4L F U E L S
Among t h e underlying causes of t h e many-sided development of this comparatively new industry, there is, first of all, t h e increasing shortage of t h e important natural fuels-anthracite, natural gas, and petroleum. The difficulty of obtaining adequate supplies of anthracite and t h e inferior quality of t h e material have combined t o favor t h e substitution of coke. Natural gas finds its most satisfactory supplement i n coke-oven gas and has a further accessory in water gas made from by-product coke. Fuel oil is being replaced t o a n increasing extent with t a r and t a r oils, while benzene has been successfully introduced as a motor fuel distinctly superior t o gasoline, although on account of t h e comparatively limited amount of t h e former available, there is n o question of competition between t h e two. The high price and poor quality of t h e gas oils now available are having
