10 The Ohio State Engineer

KOPPERS COKE PLANTSLEE C. BlERY, Metal. Engr. '.21

The great increase in the demand for coke forthe metallurgical industries and especially for theiron blast furnace, in the last five years, alongwith the ever increasing demand for the by-products of the coking process, has caused theproduction of by-product coke to reach the40,000,000 ton per year mark as against15,000,000 tons produced in 1915. By far thegreatest portion of this coke is produced in Semet-Solvay, Otto Hoffman, and Koppers types ofovens, and the latter has the record of producingmore than any other one type of oven.

In the United States there are Koppers plantsoperating in seventeen States—Pennsylvania,New York, New Jersey, Maryland, Virginia, WestVirginia, South Carolina, Alabama, Ohio, Michi-gan, Indiana, Illinois, Wisconsin, Minnesota, Ken-tucky, Missouri and Colorado. The largest plantis situated at Clairton, Pa., and consists of twelvehundred ovens with a capacity of 5,600,000 tonsof coke per year. Pennsylvania leads in quantityproduction of coke by the Koppers process.

It is the purpose of the writer to outline brieflythe Koppers process for the coking of coal and therecovery of some of its by-products.

Not all coals have the properties necessary tomake them good coking coals and the choice sofar has been governed by experience alone. Itis usually conceded that the coking properties ofcoal are due to the resinous matter present and ithas been found that a mixture of Elkhorn, a highvolatile coal from Kentucky, and Pocahontas, alow volatile coal, mined in West Virginia, pro-duces the best quantity and quality of coke forblast furnace use and with the greatest yield ofby-products. A mixture of the two is necessarybecause Pocahontas expands greatly on cokingand could not be pushed out of the ovens if usedalone and because Elkhorn gives a low yield ofcoke. The mixture in most cases is about 65%Pocahontas and 35% Elkhorn, and other coals arealso included in the mixture at some plants.

When the coal is received from the mines it isstored in a stock pile from which the supply forthe ovens is taken. On the way to the ovens thecoal is conveyed to Bradford breakers and ham-mer-mills where it is crushed and pulverized toabout one-eighth inch size, and where all sticks,pieces of stone, and steel are removed. If morethan one coal is used the mixture is effected bymeans of continuous belt conveyors, the per-centage of each coal being governed by the speedof the belt or by adjustable gates. The pulver-ized coal then reacjy for coking, travels by meansof other conveyor belts to the hoppers or binsover the ovens.

The ovens are built in batteries with from 40to 120 ovens to one battery and each oven is about37'xll'xl7-21" (inside), one side being widerthan the other to make the pushing of the cokeeasier. The ovens are practically air tight andare heated on each side by a gas combustionchamber which gives heat to the silica walls ofthe ovens. These combustion chambers and

ovens alternate in the direction of the battery andbeneath each oven there is a brick checker workor regenerator for reheating the air that goes into aid in the combustion of the fuel gas in thechambers.

The coal is dropped from the storage bins intoa four-compartment larry car and charged thruthe four holes in the top of each oven. Thecharge runs about 24,000 pounds of coal to theoven.

The volatile matter or gas from the coal isdriven off by the heat thru a stand-pipe or riserand into a collector main, under a slight backpressure to prevent leakage of air into the ovens.The temperature of coking varies with the cokingperiod and the quality of coke desired. It usuallyaverages about 1800° F. with a coking period of17 or 18 hours.

The coke is pushed out of the ovens into atransfer car by means of an electrically operatedpusher ram, after the door on eacji end has beenremoved, the standpipe closed and the chargingholes opened. The car takes the hot coke to thequenching station where it is quenched with waterand then screened. The ovens are numbered andthe pushing is done in an order such as first No.1, then No. 5 and 9, 7, 2, 4, 10, 6, 8, 3, so thatthey will not cool off too much. The large sizecoke goes to the blast furnace, the pea-coke todomestic consumers and the coke breeze, or finecoke, to the power plant to be fired in the boilers.

The next step is the recovery of the by-prod-ucts from the gas. In some plants the gas fromthe ovens is separated into rich and lean gas, therich coming aff during the first part of the car-bonization and the lean during the latter part.In that case there are two collector mains, but aseach goes thru practically the same processes forthe recovery of by-products that practice will beomitted here.

From the collector main the gas passes thrua cross-over main which contains a butterflyvalve, operated by means of a Northwestern gov-ernor, and from this point is drawn, usually byConnersville exhausters, thru the "down-comers"where some tar drops out, and thru the primarycoolers. In this last apparatus the tar and am-monia liquor, condensed from the gas on cooling,are removed and pumped to a separating tankand then to tar and liquor storage tanks. The taris marketed in that form and the liquor is chargedinto continuous ammonia stills. The ammoniavapor from these stills is either used in the satu-rators to make ammonium sulphate or is con-densed and sold as a concentrated product ofrefrigeration plants and manufacturers ofchemicals.

After the primary coolers the gas goes thruthe exhausters and P. & A. tar extractors, wherenearly all of the remaining tar is removed, nextthru the reheaters and then to the saturators.The saturator is a lead-lined cast iron cylinderwith a conical bottom, containing a bath of 5%

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24 The Ohio State Engineer

KOPPERS COKE PLANTS(Continued from Page 10)

sulphuric acid. The gas bubbles thru the acidand the remainder of the ammonia is absorbed,forming sulphate salt. The salt is ejected, bymeans of compressed air, out of the saturator,thru a vertical pipe, on to a draining table. Thebath drains off and runs back into the saturatorand the salt is shoved or paddled down into twocentrifugal driers where the free acid is washedout with water or ammonia liquor and the saltdried. From the driers the salt is weighed andconveyed to the stock pile. In some instances thesulphate is further dried in rotary driers and theammonia content increased by the application ofammonia vapor in this apparatus. The salt isshipped to fertilizer manufacturers. Sometimesthe pyridine is recovered by distillation from thesaturator baths, not so much because of its valuebut because, if left in, under some conditions, itcolors the salt. The reheater is inserted betweenthe tar extractor and saturator to increase thetemperature of the gas, thus increasing its watercarrying ability, increasing the speed of the reac-tion and the formation of salt and producing asalt made up of finer crystals.

After leaving the saturators the gas goes thruthe final coolers, where it comes in contact withwater and the napthalene is washed out, afterwhich it is sent up thru the scrubbers. In thisapparatus wash-oil is sprayed down from the topof the towers and absorbs the light oil from thegas as it passes countercurrent. The residual

gas then runs into the gas holder and from thereabout 50% goes to the combustion chambers be-tween the ovens and the same amount to the mu-nicipal lighting companies or to other markets.

The wash-oil from the scrubbers is pumped tostorage tanks at the benzol plant and then chargedinto wash-oil stills, distilling out the light oil.The residual wash-oil circulates back to the scrub-bing towers and is used over again.

The light oil is further distilled and benzol,toluol and solvent naphtha fractioned out. Theseproducts are purified by washing with acid andcaustic and by re-distillation.

The fractioning in the benzol plant is governedlargely by the market demand for the productswhich it can furnish. During the war there wasa great demand for toluol for the manufactureof T. N. T. and for benzol for motor fuel, and atpresent most of the plants are producing purebenzol, about 88%, to mix with a low grade ofgasoline to make a high test product, and refinedmotor benzol, a mixture of benzol and solventnaphtha, for consumption in automobile engines.

An increase in quantity production of ammonia,tar and light oil could be brought about by chang-ing the temperatures and coking periods on theovens, but such a practice would be at the expenseof the main product, coke.

Born to Mr. and Mrs. Alfred Halterman a sonon December 5th. Mr. Halterman is a memberof the class of 1921.

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