June, 1913
T H E f O C R S A L OF I S D C-STRIAL .qLYD E.YGI-YEERI.VG C € I E a l I I S T R Y
which are movable around the axis of the rod. 3 . For supporting light condensers. 4. For holding separatory funnels. 5 . For supporting crucibles and small beakers.
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After using, the apparatus can be set aside and occupies no more space than a n ordinary reag-nt bottle This is of importance where space is a factor. RROOHLYN, N. Y .
ADDRFSES
PRODUCTION AND INDUSTRIAL APPLICATION OF BYPRODUCT COKE OVEN GASES’ By J , BECKIPR AND L. B . ROBERTSON
In a paper covering the production and industrial applications of coal gases you will all appreciate that this subject can be treated only in a general way, without taking up more than the allowed time. We shall therefore attempt to briefly outline the process of distillation of coal and the treatment and application of the resulting gases. The first distillations of coal were performed in bee-hive ovens for the purpose of making coke. No gas is recovered from this coke-making process, and the only application of the gas produced is its combustion in the bee-hive oven over the coal in order to supply the heat and maintain the temperature necessary for the coking process. Then coal was distilled in retort ovens, for the recovery of illuminating gas. Coal is charged into these retorts and the liberated gas collected in a so-called hydraulic main. The gas next passes through a washing and purifying system and is collected in gas holders from which it is distributed to consumers, either for illuminating or household purposes. These retorts vary in size as well as in their position in the retort benches: horizontal, vertical and inclined retorts are in present use; the coal-coked in these retorts must be of a very high grade, in order to produce the best gas. Usually the desired candle power of the gas governs the quality of the coal to be used. The fuel necessary to perform the distillation of coal consists of a part of the coke produced by this gas-making process. The first chamber ovens were waste heat ovens, and, like beehive ovens, were built for the sole purpose of producing coke from coal. We call them chamber ovens to distinguish between this type and other types of ovens and retorts. The chamber oven is built in the form of a long, narrow chamber varying in size from 4 to 15 tons capacity. The division walls between these chambers contain flues in which the gas produced from the distillation of the coal is burned so as to maintain the temperature necessary for the coking process. The gas received from waste heat ovens passes through openings in the top of the oven chamber and from there burns downward through the flues. Air necessary for the combustion of this gas is admitted from the outside. The waste gases from these ovens have a high temperature and are often utilized under waste heat boilers for generating steam. There are also built, especially in England, the Mond Gas producers. Low-grade coal is charged into these producers and the gas received is used for heating purposes after recovering the ammonia and tar. -4 large amount of steam is introduced in order to keep the gasifying zone a t a low temperature to prevent decomposition of the ammonia formed. The amount of ammonia recovered from this process amounts to about 20 to 80 pounds in form of ammonium sulfate. The recovery of the by-products makes this process a very economical one. Competition, and the desire to produce gas and”coke most economically, brought a n oven on the market, which, we are sorry to say, is not by any means used enough in this country 1 Paper presented before the Chicago Section of the American Chemical Society, Hotel Sherman, February 14, 1913.
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a t the present time for making gas and coke. This is the ByProduct Coke Oven. Long ago the wasteful bee-hive ovens disappeared from the plants of the coke and gas manufacturers in Germany. The by-product coke or gas oven is a chamber oven with a capacity of about 5 to I j tons of coal per oven chamber. These ovens are built in batteries varying from 2 5 to 70 ovens per battery. The division walls between the ovens serve as heating walls and contain either vertical or horizontal flues in which the combustion of the gas takes place. I n the improved by-product coke and gas ovens, the air used for the combustion of the fuel gases is preh:.ated in recuperators or regenerators placed under the oven chambers. The products of combustion of the fuel gases first pass through the recuperators or regenerators in order to heat them and are then collected in a larger flue and discharged through a chimney. In explaining the process of coal distillation we shall confine ourselves to the chamber oven The kind of coal to be used depends entirely upon the purpose for which the coal is being coked, whether for the production of gas only, coke only, or both coke and gas. I t coke p l a n s , the coke is considered the main product. At gas plants, gas is the main product, and the coke is considered as a by-product. The ideal way would certainly be, to consider both coke and gas as main products, which means making good gas and good coke from a given coal All this may be done in a chamber oven only, by coking certain coals or mixtures of certain coals. The chamber oven can produce a good illuminating gas as well as a valuable furnace coke, while retorts can produce a good gas but a n inferior coke which cannot be used for blast furnace purposes. The gas manufacturers must use a coal which gives a gas with a certain candle power. It is an undeserved handicap to the gas manufacturer to make gas on a candle power basis, since most of the gas is burned in mantles where the candle power of the gas means little or nothing. For this reason the quality of the gas should be judged on a B t u. basis. The Germans have long ago abolished the system of selling gas with a given candlepower. The requirements are certain heat units per cubic meter. Americans, considered as the most progressive people on earth, will undoubtedly do away with this antique law of judging qualities of gas by candle poner. If this requirement is done away with, gas, with a good heating value, could be made with a n inferior and cheaper kind of coal, which means that gas could be sold cheaper for public service. I n order to bring this about, Americans should continue their progress by adopting the mantle universally, which will allow a lower candle power gas to be used. I n the process of distillation, coal is charged into the chambers and the heat for coking this coal is transmitted from the heating flues to the coal charge. The gas evolved from the coal is conducted by means of ascension pipes to the collecting main and from there to the cooling, washing and purifying apparatus by means of a n exhauster which forces the gas through the pipes and apparatus into the holder. Immediately after the coal is charged into the oven, coking begins, forming a solid and thick mass on the surface of the coal. This mass on the outside of the charge consists of partly decomposed coal which is heated by radiation from the heating wall. The reversed side of this mass, that is, the side towards the center of the coal charge, is cooled by the coal which lays just behind it. The
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tar formed from this mass condenses, on account of the cooling effect of the cooler coal behind it, and is redistilled again as the heat travels towards the center of the charge. The coal in the center of the oven stays unchanged until the tar mass has traveled toward the center and in turn is decompbsed after it has reached the necessary temperature. I n other words, the tar travels in or condenses toward the center of the coal charge, and the gas passes out toward the oven walls and from there along the walls to the ascension pipes. This means that the temperature of the coal in the center of the charge may be very low for many hours, and that this temperature will not raise appreciably until the heat introduced through the oven walls has reached the center. The fact that the tar condenses toward the center of the charge, forming there a tight and solid mixture of coal and tar, proves that the gas must travel from the coal charge through the coke formed, to the walls, and that the gas does not pass through the coal mass; in other words, the gas
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I n
k,r'
Rir
Rir
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Air
(8
A Koppers Gross Reyeneratrve Gohe Oven.
travels in the opposite direction to the flow of heat. Tests were made on coke ovens in Germany, where coal was coked at a coking time of 30 hours. The coal was charged wet. The temperature of the center of the coal mass did not exceed 100' C. after 15 hours coking. This proves that the action of the heat is not to evaporate the moisture in the entire coal charge first, but is simply to evaporate the moisture of the coal nearer the walls, which moisture condenses toward the center of the mass and gradually evaporates as the heat travels to the center of the coal charge. The moisture remains in the coal during the first period and assists in the gradual condensation of the tar first formed. This is one reason why some coal when charged wet will give a better coke than when charged dry, for the moisture condenses the more heavy tar in the mass, which, after being redistilled, gives the coal the desired bonding substance to form good coke. This may possibly reduce the amount of
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tar somewhat, but, due to the redistillation of the tar leaving its carbon, a n increased coke yield will be obtained. The amount of gas as well as the amount of coke produced by this process is greater than in retorts. If a given coal is coked in a retort and in a chamber oven, the results will be that from the retorts will be obtained a larger amount of thick, inferior tar containing a high percentage of free carbon and a smaller amount of coke, on account of the carbon which forms on the roof of the retorts, whereas in the chamber oven a larger amount of coke and a smaller amount of light and fluid tar, containing a small percentage of free carbon, will be produced. The gas received from both is in quality practically the same, but the quantity is larger in a chamber oven. The amount of gas produced in the chamber oven is the maximum which can be obtained. The greatest difference in the principles of the distillation in chamber ovens and in retorts is, that by coking small amounts of coal as is done in retorts, the condensing and redistilling of the tar which takes place in the coking process of chambers does not occur in the retorts. The first formed tar gases cannot condense, but pass along the roof of the retort where they are decomposed, leaving a large amount of carbon as residue. P a r t of the carbon formed by the decomposition of these tar fumes is carried with the gas into the hydraulic main, where i t settles out and becomes mixed with the tar, thus increasing its per cent. of free carbon. In a retort, it is quite necessary to have considerable overhead heated surface, which is the roof of the retort, in order to produce a good gas yield. If this decomposition of the tar gases did not take place, the yield of the gas in the retort would be very low. The residue from this decomposition, the carbon found on the roof of the retort, is recovered in a chamber oven in form of coke, which has some value. The manner in which the heat is transmitted to the coal charge, as well as the temperature in the heating flues, has a great effect on the quality and quantity of the coke. Coal coked a t high temperature usually gives a higher coke and gas yield but a lower by-product yield. The gas received from coal coked a t a high temperature, which means in a short coking time, usually gives a gas with a lower candle power, but there is not much change in the heating value per cubic foot. The heating value of total gas produced per pound of coal distilled is higher when coking the coal a t high temperatures. The coke received from coking the coal a t high temperatures is usually smaller in size than that received by coking a t low temperatures. In order to produce the most uniform coke and gas a t any temperature of the heating flues, it is very important to have the heat in the heating walls distributed very uniformly. Thus, the rate of heat transmission to the coal charge is uniform and a n even coking of the charge will take place. Overheated or underheated spaces in the heating wall will show up in the quality of the coke. The coke nearer the overheated area will be of smaller size while the coke produced from the underheated urea will be undercoked, which means that it still contains uncoked coal particles and consequently too much volatile matter. Overheated areas in the oven walls affect the gas passing over these areas by decomposing the heavy hydrocarbons in the gas thus decreasing the candle power. From the above it is easily seen that for coking coal, only that oven should be used in which the combustion of fuel gases and consequently the transmission of the heat to the coal charge can be controlled in every heating flue. An oven which has many of these flues per heating wall and one in which every flue can be controlled and regulated individually would be the ideal oven to make the most uniform coke and the best gas. There is one great advantage of the coke oven over the retort. In a coke oven, illuminating gas can be made from a lower grade of coal than in retorts. Or, a high-grade gas coal, giving a poor quality of coke, can be mixed with a low volatile
June. 1913
T H E JOT;RSAL OF I S D C S T R I A L A,YD EAYGISEEKIL\-G C H E - I I I S T R Y
coal giving a high grade of coke. Such a mixture will produce a good coke, suitable for blast furnaces and foundries, and a good quality of illuminating gas. This is done by means of separating the gas received from the coking process. The gas. given off from coal during the first I O hours of the distillation has a higher heating value and a higher candle power than the gas produced towards the end of the process. The first gas may have 16 to 18 candle power and 650 to joo B.t u., while the gas received from the second part of the distillation may have 1 2 to 14 candle power and 560 to 600 B.t.u. These t r o gases are collected separately by means of two collecting mains, or by one collecting main divided by a longitudinal partition. Each gas passes through a serarate washing and purifying apparatus. The gas received from the first part of the distillation, the so-called “rich gas,” is sent to the rich gas holder, and that received from the second part of the distillation is burned under the ovens. The amount of each gas depends largely on the quality of the coal charged into the ovens. Also let us say here that ultimate and proximate analysis of a coal does not tell by any means what products would be obtained from the distillation. For determining the coking value of a coal as well as the quality and amount of distillation products, the coal must first go through a distilling process, either i n a laboratory or by coking the coal in a n oven chamber. The first process installed for treating the gases was by cooling, washing and purifying. The gas, after leaving the collecting main, passes through a cooler, where it is cooled to about 80° F. The water produced from the coal both from the condensation of the moisture and the water formed from the hydrogen and oxygen of the coal, and the tar is condensed in these coolers. They are usually tubular, the water passing through the tubes and the gas around them. After leaving the coolers, the gas passes through a number of washers, where it is brought in direct contact with water, which absorbs the ammonia in the gas. The gas then passes through boxes containing iron oxide for the removal of hydrogen sulfide and cyanogen and then is led to the gas holder. During the last few years the methods for treating the gases have been very much simplified. I t is easily understood that to wash out the ammonia requires a n enormous quantity of water, especially in larger plants. Also the floor space taken up by the ammonia washers is enormous. The percentage of the ammonia recovered in these washers depends t o some extent on the temperature of the water used. In summer time and especially in places where the temperature of the water supply is high, the washing of the gas is not perfect-losses of I O per cent. of the total ammonia produced are not unusual. Being Koppers men, we wish to explain the direct process for treating gases. This process was introduced by the H. Koppers Co., in practically all parts of the world in gas and coke oven plants. After the gas leaves the collecting main it is drawn through tubular condensers, where it is cooled down to the desired temperature. The exhauster then forces the gas through a tar extractor where the last traces of the tar are removed. The gas leaving the tar extractor is naturally saturated with water vapor. After leaving the tar extractor, it passes through a reheater where the temperature of the gas is raised about 1 5 C. ~ and is no longer saturated for that temperature. I t next passes through saturators, containing a saturated solution of ammonium sulfate and about j per cent. of sulfuric acid. All the ammonia in the gas is combined with the sulfuric acid in the saturators forming ammonium sulfate, which precipitates out instantly. The salt crystals are removed from the saturator by means of a n ejector which discharges into a draining table, and pass from there to centrifugal driers, then to the storage pile. This process works continuously and all the ammonia in the gas is recovered. After the gas leaves the saturators it may be used for any purpose. If used as illuminating
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gas it must pass through the purifier and from there to the gas holder from which it is distributed to consumers for household and heating purposes. The sulfate received from this process is perfectly white and contains a t least 2 5 per cent. of ammonia and only 0 . I to e.2 per cent. of free sulfuric acid. The condensates received from the coolers are collected and the small amount of ammonia water distilled in a still passing the ammonia vapors back into the gas again SO that they finally reach the saturators. This direct process is already installed in a great many plants and works with great success. The advantages over the wash processes are: I . Smaller amount of labor required. 2 . Less floor space. 3 . No water for washing is necessary. 4. No pumps for wash water. j . Less steam consumption by the stills. 6. More complete recovery of ammonia. 7. Can be installed in any climate because it is independent of the temperature of water supply.
“B” Hoppers C r e e Regenerative Gas Oven The application of coal gases, with which we are all more or less familiar, is in cooking and lighting. We have already explained that with the proper coal, and with the distillation taking place under the proper conditions, the requirements regarding candle power can be easily met. This statement is borne out by the fact that millions of feet of gas for household uses are now produced from chamber ovens and delivered to the consumers in the same condition as it leaves the purifiers. Among the industrial applications of by-product coke oven gases, vie wish to take up its use as fuel for boilers, gas engines, open hearth furnaces, heating furnaces, its various uses in foundries, etc. By-product coke oven gas has a n average heating value of 450 to 550 B.t.u. per cu. ft. I t s comparison with other fuels
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will be based on a heating value of 500 B.t.u. We shall also assume a coal of 12,000B.t.u. and fuel oil of 18,000B.t.u. per pound as a basis of comparison. By-product coke oven gas has proved its value as fuel for open hearth furnaces only in the last five or six years. I t is now considered as one of the best fuels for this purpose on account of the higher temperature obtainable, a better economy both in the use of heat and in the construction of the furnace, a n increased tonnage and lower operating costs as compared with producer gas. The gas was first used in the same m a n n a as producer gas, being passed through regenerators before meeting with the preheated air in the combustion chamber. This was found unnecessary, as its high heating value enabled sufficiently high temperatures to be maintained without preheating; besides, the gas actually loses approximately g per cent of its heating value by
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Cdmbinatlbn Oven.
preheating. Therefore, the gas is now' introduced cold and only the air passed through the regenerators, which allows 0 , smaller regenerators and thus cheaper furnace construction. On account of the high heating value of this gas a temperature may be maintained considerably higher than with producer gas, allowing a greater tonnage for the furnace. The output in some cases has been known to increase 15 to 2 0 per cent Also by using the fuel which is already a gas, operating costs will be reduced by the amount of the operating costs of the producers. It has been claimed by some that the life of the furnace was shortened by the higher temperatures obtained with this gas, also, that the light gas had a tendency to rise and burn along the top of the furnace instead of just over the bath. These difficulties are being rapidly overcome and cases have been cited where the roof has actually stood more heats than with producer gas before repairing was necessary, while the life of
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the checkers was greatly increased. This is due more perhaps t o the more skilful handling of the furnace as the workmen become better acquainted with the peculiarities of the gas. *
Blast furnace gas is too low in heating value for use as a n open hearth fuel, but when mixed with coke oven gas in the ratio of 3 or 4 to I volume of coke oven gas, sufficiently high temperatures have been maintained. The gas required per ton of open hearth product will vary with the size of the furnace and the nature of the charge. For a liberal estimate let us take the results reported from a 4-ton open hearth furnace design for producer gas but now using coke oven gas. In this furnace 880 pounds of coal per ton of product were replaced by 15,400 cu. f t . of coke oven gas per ton, making the gas equivalent of a net ton of coal as open hearth fuel, 35,000 cu. ft. Next to its use as open hearth fuel, coke oven gas is probably best adapted to heating furnaces. Here again the operating cost is reduced and the tonnage of the furnaces greatly increased. The gas required per ton of product varies greatly according to the size of the material to be heated, ranging from 1,500 cu. f t . per ton in large ingot heating furnaces to 33,000 cu. ft. per ton of smaller material, such as bolt and nut rods. Part of this great difference is due also to the ingots being charged directly from the stripper while the small rods are charged cold. In this capacity the gas equivalent of a net ton of coal will average approximately 29,000 cu. ft. As a boiler fuel, coke oven gas has proved economical for replacing coal. The lower repair and labor costs for gas-fired boilers are just as great a saving as where producers are replaced by coke oven gas. The efficiency of the boiler is also increased approximately IO per cent. Under a boiler approximately IOO cu. ft. of gas are required per boiler horse power, or the gas equivalent of one net ton of coal as boiler fuel is 35,400 CU. ft. Since we have no reliable information a t present for a comparison of coke oven gas with fuel oil, if we assume that the two fuels are used with the same efficiency, we find the gas equivalent of I gallon of oil to be 264 cu. f t . In the foundry, the coke oven gas adapts itself to various uses, all of which tend to make the work of the foundry lighter and more pleasant and to decrease the cost of the products. I n many foundries, where it is available, it has replaced coal and coke as fuel in every use except the cupolas and even there it is often used for kindling. It lends itself very readily to drying molds and ladles, and to firing coke ovens. To these foundry applications already mentioned, must be added the furnaces for melting brass and other alloys as well as pits for crucible heating. , Last, but not least, of the industrial applications of coke oven gas is in the gas engine. It has not as yet come into general use in gas engines, owing principally to the effect of the sulfur and cyanogen compounds upon the piston, the interior of the cylinder, and the valves. These difficulties are overcome by purifying the gas and with rapid improvement in design; there is no doubt but coke oven gas engines will come into common use. Much of the progress in the development of these engines has been made in Germany, where there are many power plants now using by-product coke oven gas in gas engines. One of the most interesting ones of these is described by C. A. Tupper, in Mining and Engineering W o r l d for Dec. 23, 1911. This plant was located in Rhenish, Prussia, and consisted of two electrical generator stations operated in parallel, one equipped with steam turbines and the other with gas engines operated on by-product coke oven gas. Power was developed by the gas engine with 30 cu. f t . of 5 0 0 B.t.u. gas per kw. hr., by the steam turbine with 13.6pounds of steam per kw. hour. This amount of steam would require in the neighborhood of 40 cu. ft. of gas to develop
June, 1913
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it in steam boilers, to say nothing of losses in steam lines and condenser auxiliaries. Let us see what we may do with a ton of coal. First we may coke it in a bee-hive oven and get in return 65 per cent or 1300 lbs. of coke with which we may produce something less than 1200 pounds of pig iron. Again, let us put it in a by-product coke oven. We get inreturn 1500 lb. of coke which will produce over 1350 lbs. of pig iron, about 17 c. worth of tar, 60 c. (net) worth of ammonium sulfate and still have sufficient surplus gas to replace 286 pounds of coal in the open hearth furnace or under boilers, or produce 224 electrical horse power. I n other worlds, our saving by the by-product ovens over the bee-hive is zoo lbs. of coke, 77 c. worth of tar and ammonia and 2 2 4 electrical horse power. As mentioned before, i t is very important to have the best possible heat distribution on the oven in order to get the most by-products in the gas as well as the best coke, and we wish to explain to you a coke oven which has all the features required to obtain this even distribution of the heat. This is the Koppers Regenerative Coke and Gas Oven. A battery of Koppers regenerative cokeovens (Fig. “A”) consists of a series of oven chambers placed side by side. The wall between two ovens serves as a heating wall. This heating wall consists of about 28 to 30 vertical flues in which the combustion takes place Underneath these vertical flues is a gas distributing flue. Every vertical flue is connected to this gas flue by a gas nozzle through which the gas is introduced into the vertical flues for combustion. These nozzles are interchangeable, so that a nozzle with any desired size of opening can be used Directly underneath each oven chamber is a regenerator where the air used for combustion in the vertical flues is preheated. I t enters the regenerators a t the bottom and passes up through the hot checker work and then to each individual flue, where the combustion of the gas takes place. The amount of air admitted to the regenerator can be regulated by means of individual dampers for each oven. During one period the gas burns in one-half of the vertical flues of the oven walls and the products of combustion pass into a horizontal flue which is placed just above the vertical flues and from there to the other half of the vertical flues of the oven walls, then down to the regenerator on the other side, where it gives off its heat to the checker brick and passes into a common flue leading to the chimney. The draft in each regenerator can be regulated by means of a damper a t the entrance to the regeneratorsand in eachvertical flue by sliding bricks which are placed a t the outlet of each vertical flue just where they connect to the horizontal flue. With these sliding bricks, the combustion in each vertical flue as ne11 as the length of the flame and the draft in each individual flue can be regulated. The setting of these sliding bricks can be regulated through openings from the top of the battery which means that each individual flue can be easily inspected. hfter the gas is burned on one side for a period of one-half an hour, Lhis process is reversed and the gas is burned in the vertical flues through which the waste gases passed.beforc reversing. Reversing of gas and air is done automatically by means of cables which are connected to the covers of the individual flue boxes on each regenerator as wdl to the gas cocks in the connections leading to the gas distribliting flue underneath the vertical flues. It is easily seen that with this design of oven absolutely uniform heats can be maintained over the entire oven wall, for the operator is able to inspect every part of the oven wall and regulate the combustion accordingly. The amount of gas uscd to coke a coal in these ovens amounts to but 45 or 50 per cent of the gas produced, afigurewhichis not reached by any other coke oven construction. The remaining j o to j 5 per cent of the gas produced
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from these ovens is received in form of gas and not in form of waste heat, as is the case in some other oven designs where the waste heat is used for raising steam- in boilers. By using waste heat for raising steam, the utilization of the B.t.u. is not as economical as when surplus gas is burned under a boiler. By using surplus gas in a boiler, one is able to regulate the amount of gas and air so as to obtain the most efficient and economic operation of the boilers. The temperature of the waste gases after they leave the regenerators on the Koppers ovens is so low that they can be discharged directly through the chimney. The advantage of the regenerators over the recuperators is well known. I n gas plants, where the main product is illuminating gas, and where there is no market for coke, the H. Koppers Co. has constructed a gas oven (Fig. “B”)which is similar to the coke oven. Instead of using half of the gas as fuel, all the gas made can be used as illuminating gas, the oven being heated with producer gas. Coke breeze and small coke from the ovens can be utilized as fuel for the producers. The regenerators on the gas ovens are divided into two parts by means of a vertical wall which extends the entire length of the oven chamber and no gas distributing flue connected to the vertical flues is used. The producer gas as well as the air necessary for combustion is preheated in these regenerators and meets in the vertical flues where combustion takes place. The amount of underfiring, that is, the amount of fuel used in the producers in order to gasify the coal in the oven chambers, is much less than that used for gasifying coal in retorts. The amount of underfiring in retorts is 16 to 20 per cent, whereas in Koppers gas ovens it amounts to I O to 1 2 per cent. The underfiring, of course, depends to some extent on the kind and efficiencies of the producers installed. The Koppers Co. has also constructed a combination oven (Fig. “C”) which can be used either as a coke oven heated with gas produced in the ovens, or as a gas oven heated with gas generated in gas producers. This oven is similar to the gas oven just described with the addition of the gas distributing flue underneath the vertical flues as on coke ovens. When operating on producer gas, the gas is sent through half the regenerators before entering th ’ vertical flues, which allows the use of all the gas produced in the ovens for illuminating gas. If only half the amount of illuminating gas is desired, this oven can be heated with a separated fuel gas, passing this fuel gas to the gas distributing flue, ihe air being preheated in all the regenerators. This oven is one of the most flexible ovens ever constructed. A plant having these combination ovens can be first operated as a coke plant by separating half of the gas and using the other half as fuel gas. The plpnt can be btiilt large enough to operate on a long coking time arid with the increase of illuminating gas consumption, the coking time can be lowered gradually so as to produce more gas corresponding to the amount of illuminating gas desired. After the limit of the coking time is reached, then gas producers can be installed and the oven heated with producer gas made from coke breeze. This allows all the gas made in the oven to be used as illuminating gas, and the coking time can be increased again. With the increasing demand for illuminating gas the coking time can be then decreased until the limit of coking time is again reached. A further increase on the demand of illuminating gas naturally would mean building additional ovens. 1307 5fALLERS BLDG CHICAGO,ILL
SYNTHESIS O F PRECIOUS STONES’ By I. H. LEVIS
Our present success in reproducing the precious stones makes 1 Presented a t the meeting of the New York Section of the American Chemical Society, May 24. 1912.
