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Val. 19, No. t
INDCTSTRI.41, Ah'D BNCIArEERING CHEMISTRY
Low-Temperature Semi-coke in Briquetted Form By Chas. V. McIntire and Lesslie R. Thomson Co*s"i.xorri"s
CUAi. PXOL>II'TS
eo.,m w
YORY,
IIE priiiiary purpose of this paper is to sho~vthat tlie low-temperature semi-coke from a bituminous coal,
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after briquetting and secondary heat treatment, const.itutes an almost ideal fuel for domestic use. In presenting this aspect of the utilization of semi-coke, the authors draw alinost completely on the work done at Fairmont, W. Va., by the Consolidation Coal Products Company. A secondary purpose is to present a brief description OS the apparatus used at Fairmont, 'IV. i"a., to produce the semi-coke in smokeless briquetted form. In t,wo years nearly 22,000 net ions of coal have been processed at Pairmont and in the last year about 9000 tons of semi-coke hriqucts have been made and sold. Of this quantity of briquets 6000 tons have been raw semi-coke briquets and ahout 3000 tons have been carbonized. The scale of these figures shows that tile work has passed from the laboratory stage. What has been accomplished is on a commercial scale, and the products have been sold in the open market. The hazardous transfer from the laboratory to a full-size apparatus has beon made; and the difficulties alvays present at such a time have beeii met arid overcome successfully. Specifications for Ideal Fuel What are tire specifications of an idea1 fuel for domestic use? And by the term "ideal" the authors mean a fuel that is ideal within the realm of the practical. If any agreement can be reached in answer to this question, then it becomes easier to assess accurately the claims put forward by the authors as to the ability of low-temperature semi-coke in smokeless briquetted form to supply successfully the large and permaneut. demand in America for a high-class fnel for domiciliary use.
Figure l-General
N. Y.:CUNSULTINO sxon?e€!w, MONTNLI,,,.,
CAN*"*
hToN-PRlABLE--The degradation losscs and dustiness in handling are markedly reduced if the fuel be non-friable. The dealers cannot be expected to merchandise a fuel having high degradation losses, and the householder wishes to maintain his o m dwellins as free as pmsible from dust and dirt. SMOKELESS OR NSARLYSrr-The effect upon our city life of the gradual introduction of a smokeless fucl cannot bc oyerestimated or overemphasized. In addition, the individual purchaser has a natural desire for a "smokeless fucl." FRSEBURNINGBUT STILL RBTlSNTIYE OF FIRE-The public will oiily accept as a permanent substitute for anthracite, a fuel that is free burning and not difficult to ignite. On the other hand, once lighted, the fuel must have a reasonablc fire retention capacity. It is here that coke presents many of its difficulties as a domestic fuel. REASONABLY CHenr---Obviously no processed bituminous fuel can yieirl a semi-coke that can compete in price with raw bitnminous coal. The cost of processing is too high. But if semicoke can be made a true competitor of anthracite, the public is qiiitr willing to pay anthracite prices. SALABLE-A domestic fuel must be the sort of commodity that the public is willing to buy. The purchasing public is becoming increasingly addicted to buying on a "form value," and is willing to pay more for this characteristic, not only in coat but in all commodities which it consumes.
Semi-coke from bituminous coal can be produced in three forms: (a) as it comes from the ret.ort, (b) briquetted, (e) briquetted, but with secondary heat treatment. Semi-coke as a n Ideal Fuel Semi-cokein its raw state from low-temperature distillation processes is a friable residue in powdered and lump sizes. containing 10 to 15 per cent of vo1a.tile maiter. This semicoke is suitable for power plant or for domest,icuse, either raw or after further processing. It has a peculiar porous eel1 structure somewhat rcsembling charcoal. One of the authors has shipped more than 1000 tons of zemi-coke in its raw
View of Fsirmanf Plant
The authors believe that a fuel that is to achieve success in regions that have been accustomed to American nr Welsh anthracite must have the following characteristics:
state, and found that tlie degradation was very large. The semi-coke in raw state also lacks form value. Its appearance and handling qualities do not compare with those of good
I N D USTRI.4 I, A.VD E,VGINErERfNG CHEXISTR Y
January, 1927
briquets or good lump coal. Its density is far less than after briquetting, and this tends to increase the cost of transport, as more space is required for handling equivalent amounts. The lack of uniformity and size also militates against cheap mechanical handling. For these reasons semi-coke in its raw state from low-temperature retorts does not comply with the specificationslaid down for an ideal domestic fuel and cannot therefore become an acceptable fuel. Therefore, the next logical step in the development of a domestic fuel is to process the raw semicoke. Briquetting will correct cert.ain of t~hedisadvantageous features of the raw semi-coke, but unfortunately adds smokiness to the product unless the raw briquets are further carbonized. The amount of carbon dust deposited in any large city by smoke is a serious menace to t.he health and comfort of the community, and engineers, public leaders, etc., are practically unanimous in their support of the great desirability of placing in the homes of the citizens of all large cities an absolutely smokeless fuel. If smokiness is a bar to a successful domestic fuel, the next logical step is to render the briquet smokeless by a further heat treatment, which has, among other results, the effect of coking the binding agent. Subsidiary effects are increased hardness, greater density, and therefore better handling qua& ties. This final product is now able to meet the original specification for an ideal domestic fuel. It is non-friable, smokeless, free-burning, reaso cheap, and salable. Price is not the governing fact r for fuel for domestic heating. The public is willing to pay a higher rate for heating provided convenience and cleanliness are also given. Evidence of this is given in the table which shows the heat value received for the expen fuels at prices approximately western city.
~ Artificial gas Anthracite Cake Pocahontas coal Bifilmiiiour EO%/
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_
_
6 1.00perM
10.50 peg ton 14.60 per ton 1o.onperton 8.00 p a ton
600.000
1,56o.000 S,~ZO,OOO 2.900,0uo 3,580,000
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heated retorts the drum and the muffle types are probably the best known to the technical public. The drum types developed, principally in Germany, are from 50 to 90 feet long and from 4 to 7 feet in diameter. The shells are of steel, and the whole mechanism is slowly revolved with the coal on the inside and the heat applied on the outside much in the manner of the ordinary driers to which American industry is well accustomed. In comparison with their size and cost, the outputs are low and the maintenance costs are high, owing to mechanical difficulties and deterioration. The flexural stresses set up in the hot metal shell, with consequent sagging, ete., are not the least of the difficulties encountered in the operation of these retorts. The early forms of Carbocoal retorts, of which a grest number were built, consist of continnous horizontal muffles of carborundum brick with double intermeshing paddle agitators for stirring and conveying the coal.'
Figure +Secondary
Own
The McIntira retort., developed a t Fairmout, consists essentially of a horizontal steel cylinder, 8 feet in diameter and 15 feet long. It has a single agitator shaft extendGas is used by some particular housekeepers for domestic ing through the center of the cylinder on which are thirteen heating and recommended highly for that purpose by the gas radial paddles arranged in two rows 90 degrees apart. An companies; yet its cost per B. t. u. is nearly three times that oscillating motion given to the shaft by a reversing motor and of its smokeless competitor, anthracite. Obviously, gas is conventional gear train sweeps the radial arms or paddles the one ideal domestic fuel, but its present cost is much too over the heating surface, agitates the coal during distillation, high for the average consumer. and causes the coal and semi-coke as formed to progress continuously from the feed end to the discharge, where the Manufacture of Semi-coke latter passes out through an effective gas-sealed trap. The At the present stage of technical development, therefore, heating surface, composed of crosswise corrugated metal secany substitute for anthracite that will be acceptable to the tions, any one of which may be separately removed for republic on this continent must be manufactured by a three- newal, is heated by gas burners located in the flues formed by stage procesecarbonizing, briquetting of the semi-coke, the corrugations. This retort has been in continuous service since August, and secondary heat treatnicnt. The Consolidation Coal Products Company process to produce a low-temperature 1924, and is demonstrating a capacity of 50 tons of coal per semi-coke in briquetted form is based upon the threestage day.a.3 BRIQUEmING-The semi-coke is taken from the retort, method known as the Carboeoal process. ground, and then mixed with a cod-tar pit.ch binder of meltPrimary Carbonizing Retort ing point 180' F., about 11 per cent binder being used. The mixture is then passed through a fluxer and thcnce All sorts and conditions of ovens and retorts have been to a Belgian roll press, producing a pillow-shaped briquet, suggested and to some extent tried for the production of semi- weighing about 1.5 ounces. coke by low-temperature methods. They have been interThe procedure in the briquetting part of the Fairmont nally and externally heated. They have been in the form of plant is normal and needs no special elucidation. Operation ovens, drums, tubes, and screws. Of the internally fired I Curtis and Chapman. Chrn. & MB. En&, as, 11 (19231. ovens the MacLaurin and Hood-Ode11 (both in original * Melntire, Pawn P8onl EM., 80, 579 (1926). form and as subseouentlv develooed bv the Lignite Utiliaat American Gas A s o ~ . .October 11 to 15. 1926. Carbonization Comtion Board) are ;ell-known ex&nplek. Of the externally mittcER - ~ w ~p.. 82.
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I N D USTEIAL AND ENGINBBRIA‘G C’HBMISTRY
Vol. 19, No. 1
was begun in kptember, 1926, and the product found a ready In developing these ideas, internally heated retorts, tunnel market during the winter of 1925, even though thc briquets kilns, and batch retorts were all suggested and tried. One (being raw) were not smokeless. of the difficulties encountered in attempting to operate an The hinder used a t Fairmont is taken entirely from the internally heated retort waa due to “channeling.” It was pitch distied from the low-temperatwe tars obtained from expected that the passage of hot inert gases around a batch the primary oven. There is 5 sufficient quantity of such pitch of briquets would carbonize each briquet uniformly without produced to supply the briquetting requirements. any shock or breakage. Actually, RS the hot gases began SECONDARY OVEN-M the preliminary work in the a t to circulate they did not flow evenly through the mass, hut tempt to develop a t Fairmont a successful secondary oven discovered special channels, probably due to minute difEerwas based on the work done previously by the Carbocoal ences of friction head, and once found nearly all the heating interests. The resulting product of Carhoeoal was an gases flowed through these special channels. As a result extremely dense briquet containing about 3 per cent or less of the briquets surrounding the channel were quickly carbonized volatile matter. The high density made it a very va1u:ible while all the others in the batch remained Inore or less unfuel from the point of view oi tranaportat,ion and handling, touched. but the low volatile content was a disadvantage from the Tunnel kilns were alii, given up on account of the difficnlstandpoint of burnties of repaifs and ing &ality. Both niecLanica1 mainthese qualities were tenace. Finally, a caused directly by basis intermittent the high temperahatch oven was deture to which the vised i n which a briquets were snblayer two briquets jected in thesecondthick was presented ary oven. Thereto radiant heat top fore, in the suhseand bottom for a p e n t development period of 30minutes. a t Fairmont a deciThis proved sound sion had to be made and practical and a to sacrifice some oC number of small the density in order ovens were built and to leave the volat.ile successfully opercontent a t 8 to 12 ated on this priuper cent in the finat eiple. T r i a l earproduct tu provide a freer burning fuel. thus carbonized were This decision necesshipped to distant sitated much lower Figure b C ~ ~ b o n i z eBriquets d in Stock Pile points and observed nmehllv temperatures in the . ~ ._~.” . ~ RF:to des-. secondary oven. The Carbocoal secondary ovon was a lCtinch radation in transit and combustion properties. The results inclined oven in which the briquets were intended to remain were very gratifying. for 6 hours exposed to a direct contact with surface temperaThis unit oven principle was applied to commercial-sized ture of about 2000’ F. In operation this oven developed cer- apparatus by building a bench of five individual ovens, one tain grave difficulties. Owing to the thickness of the charge, 6 above the other. Heating Bues were placed in the arches hours proved insufficient for the carbonization of the briquets. ns, aiid a simple method of regenerative fl The time actually taken was 8 to 10 hours. This reduced the stalled. The raw briquets are received from a capacity of the oven very markedly. Immediately upon traveling belt conveyor and dropped into a receiving bin charging a fresh batch of briquets into the oven, those bri- a t the top of a structural steel frame. The operating mechanquets which came in direct contact with the hot wall surface ism consists esseutialiy of an elevator cage which travels frequently disintegrated due to the shock of oorltact with the vertically between structural guides and discharges the followvery high temperature. Also as the heat gradually pene- ing functions for any one of the five ovens: It receives by trated the charge the inner briquets became at first soft and gravity a load of briquets from tlie fixed receiving bin, places pliable. The weight of the briquets above forced and these briquets in a layer two deep on the metal tray, pushes squeezed the mass of briquets together, so that within a couple the tray into an oven, closes the oven door, moves itself by of hours the charge had been transformed from a batch oi vertical travel into position opposite another oven. withindividual briquets into a mass of formlms, sticky portions of draws therefrom a tray full of carbonized briquets, dumps broken and fused briquets, quite difficult, if not impossible, t,hese briquets into a quenching chamber, and reloads the to discharge from the oven. The problem, therefore, was empty tray with a iayer two deep of the raw briquets. This to devise an apparatus that would carbonize these briquets completesa well-defined cycle. The withdrawing and reloadwithout on the one hand, breakage due to heat shock or, on ing of any one tray require less than a minute and the sensible the other, any tendency to fuse the soft briquets by the dead heat of the tray is not entirely dissipated. From the quenchweight oi other briquets above them. ing device the finished briquets are dumped to a cooling The danger from breakage due to temperature shock could wharf, from which they are taken by conveyor to the railroad he obviated by heating t.he briqucts gradually in an inert car. Figure 2 gives a general view of the new secondary oven. atmosphere by passing hot gases around them, and one way to It will be remembered that the time of exposure of any one prevent the mass of briquets from being squeezed together tray of briquets to the heat is 30 minutes. The completion due to pressure of upper briquets would be to carbonize them of one discharging and charging cy& is about one minute. in very thin layers so that no briquet would have t o snpport Therefore, since the eondrol of the operating mechanism more t.han the weight of one other briquet. is by one man, the iabor costs will not be increased by en~
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January, 1927
INDUSTRIAL AND ENGINEERING CHEMISTRY
larging the oven considerably above its present capacity of five ovens per bench. No unusual mechanical difEculties have been encountered with the operating mechanism, in spite of the fact that it is almost entirely home-made. The trays now used are composed of structural angles for the side and end members with steel wire cloth for carrying the briquets. They give good service, and replacement costs are very reasonable. Trays have also been fabricated of some of the cheap heatresisting metals, and the results have been encouraging. The main advantages of this secondary oven are obvious. The briquets are well carbonized with practically no breakage. The temperatures are under close control both by the regulation of gas burners and by the amount of time allowed for the briquets to remain in the ovens. There is a minimum loss from heat radiation: the heat in the trays is conserved and there is the smallest possible amount of outside radiating surface. All ovens are accessible through the doors for patching or repairs or for the removal of carbon, which has a tendency to collect on the floors. Any oven can be removed from service while the balance of the bench is in operation,
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and trays can be removed and set aside for renewal or repairs. The carbonizing capacity is high-about 10 pounds of raw briquets per square foot of heating surface per hour, as compared with 2 pounds per square foot per hour, the general capacity of high-temperature coke ovens. This very striking fact can be accounted for by the extremely efficient manner in which the heat is transmitted to each briquet. No transference of heat through the semi-coke itself is necessary because of the thin layers in which the briquets are exposed to the source of the heat. Thus is avoided any dependence on the heat conductivity of coal or coke-notoriously bad thermal conductors. I n order to collect the gases evolved during carbonization of the briquets, the ovens are connected by a gas suction main to the condensing system of the primary retort. The byproducts are 2000 cubic feet of 450 B. t. u. gas and about 8 gallons of high-gravity tar per ton of briquets. The unit has been in operation almost continuously since March, 1926, with an average throughput of about 30 tons of briquets per day. Part of the output of carbonized briquets is shown in Figure 3.
The Heat of Distillation of Coal By S. P. Burke and V. F. Parry CONBUSTION U T I L I l l E S CORP.,
RESEARCA LABORATORIES,
HE thermal reactions occurring during the carbonization of coal have been the subject of extensive literature.” There is, however, a pronounced lack of agreement in the various determinations of the thermal reactions occurring during the distillation of coal, which are collectively included under the descriptive term “heat of carbonization.” These differences are largely due to the variety of experimental methods employed. This “heat of carbonization” per se-that is, the integrated thermal quantities resulting from exothermic or endothermic chemical reactions, or both, which occur during coal distillation-while of considerable importance to the chemist in his endeavor to elucidate the chemical phenomena occurring during carbonization, is of relatively slight importance to the engineer, who is concerned with the design or operation of apparatus for effecting carbonization. The reason is the trifling magnitude of the thermal quantities involved even in the most extreme cases, although in certain critical cases they may be of real importance in the mechanism of the carbonization process. Of more vital concern to the engineer is the total heat required to distil coal and separate it into the final products-tar, water, gas, and coke-under the conditions he proposes to use in commercial practice. Such information is necessary in order adequately to plan the flow of materials and energy in any proposed process of carbonization. This total heat of distillation includes, of course, in addition to the heat of carbonization, the latent heats of vaporization of water, tar, etc., and the sensible heat required to raise the gases and vapors to the exit temperature of these products on leaving the retort. Previous published attempts to determine the thermal quantities involved in the total heat of distillation of coal have for the most part employed the application of the heat balance method to commercial scale retorts. Because of the errors inherent in this method the results are widely
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1 For survey of previous work see Davis and Price, THISJ O U R N A L , 16, 589 (1924), Davis, Ibrd.. 16, 726 (19241, Fuel S c i e n c p Practsce, 6, 12 (1926).
L O N G ISLAND CITY, N.
Y
divergent.2 With the objects of obtaining in the laboratory accurate data of this character, which would be directly comparable with commercial practice, and of checking available data, the apparatus and method to be described were developed. The scope of the present paper is limited to carbonization by the sensible heat of a current of hot gases and is concerned only with so-called low-temperature carbonization, However, suitable modifications should readily extend the applicability of the method and the equipment. Apparatus The principle involved in this apparatus is the passage of a hot inert gas through a charge of coal with means for measuring the heat content of this gas before and after passage through the coal, when no heat is lost by radiation. Figure 1 gives a diagrammatic cross section of this apparatus. Starting at the left of the diagram we have (I), a small-surface combustion tube furnace 2 inches in diameter. Gas and air are burned in proper proportions (under-ventilated) to supply an inert gas of the desired composition. The hot gas is passed through the coke column t o remove oxygen, which might have escaped combustion, and thence passes to (2), which is a cooling tank t o reduce the temperature and saturate the gas a t room temperature. The gas is then drawn through the meter and the control flowmeter (3), which has a a/,-inch orifice. Leaving the pump (4), the inert cooled gas is passed directly to the superheating coil ( 5 ) . This coil is made up of S/c-inch calorized pipe, 30 feet long. The gas is heated t o the desired temperature by regulation of surface combustion burners in the furnace ( 6 ) . Leaving the heating coil, the gas is passed through a well insulated and electrically heated iron tube, containing thermocouples in the union at (8),and thence into retort (IO). The retort is held in the adiabatic furnace, which prevents loss of heat during carbonization by supplying heat at the electrically heated wall (9), which acts as a n adiabatic shield. Heat is prevented from escaping at the top by the hot plate (11). The space between the retort and the adiabatic shield and the space outside of the shield are filled with Sil-0-Cel powder. After the gas leaves
* Euchene, “Thermic Reactions Occurring during Distillation of Coal.” Transactions International Gas Congress, Paris, 1900 : Wilson, Forest, and Herty, THISJ O U R N A L , 16, 251 (1923J; Otto, Stahl Eisen, 86, 477 (1915).
