By-product Ammonia from Coking

For decades this was an unwanted by-product of coking, as all gases from inefficient beehive ovens, which had been used since the substitution of coke for charcoal began in the United Kingdom after 1750, were simply released into the atmosphere.  

Section through a Semet-Solvay by-product recovery coking oven. This was one of the most common types of coking ovens during the late nineteenth and early twentieth centuries. Pusher machine is shown discharging coke into a coke car gases are recovered at the oven s top. Reprinted, by permission, from H. C. Porter, Coal Carbonization (New York The Chemical Catalog Company, 1924), 174. 

Process of ammonium sulfate production from coke-oven gas. 

With typical conversions of 15-20% of the original nitrogen into NH3, ammonia yields in the coke-oven gas are between 2.75 and 3.25 kg per tonne of charged coal. Although a considerable amount of research went into the means to increase the recovery yield, no satisfactory solutions were found. Such a low yield meant that even the potential output of by-product ammonia was relatively limited. Global production of pig iron was almost 40 Mt in 1900, and at that time even the most efficient blast furnaces needed at least 2 kg of coal to smelt 1 kg of the metal. 

In 1905 the U.S. used about 33 Mt of its coal (10% of the total) for coking, a potential source of between 75,000 and 88,000 t of fixed N in recovered NH3—but the actual output of ammonium sulfate was only about 14,000 t, equivalent of less than 4,000 t The United Kingdom was the largest producer of ammonium sulfate until the first decade of the twentieth century in 1900 it synthesized about 45% 

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Ammonium sulphate is traditionally produced by reaction of by-product ammonia from coke ovens with sulphuric acid ... 

Ammonium sulfate was originally manufactured by using sulfuric acid to scrub by-product ammonia from coke-oven gas, and much is still produced in this manner. Most of the ammonium sulfate produced is now made by reaction between synthetic ammonia and sulfuric acid. 

Haber s work on ammonia synthesis began during the summer of 1904 not because of any planned, determined effort to solve an elusive task, but because of an unexpected request from the Osterreichische Chemische Werke in Vienna, a company set up by the brothers O. and R. Margulies. Haber did not immediately take up the offer he advised the brothers to take what was at that time the easiest route and recover by-product ammonia from coking. As he knew something about Ostwald s earlier work on the problem (but not about his unsuccessful deal with BASF and about the withdrawal of Ostwald s 1900 patent application), he wrote to him hoping that he would cooperate with the Margulies brothers. 

L). During the late 1990s Haber-Bosch synthesis supplied more than 99% of fixed inorganic nitrogen the tiny remainder (about 0.7%) comes mostly from Chilean nitrates and by-product ammonia from coke ovens (appendix L). ... 

Recovering ammonia as a by-product from other processes accounted for less than 1% of the total U.S. ammonia production in 1987. The principal source of by-product ammonia is from the coking of coal. In the coking operation, about 15—20% of the nitrogen present in the coal is Hberated as ammonia and is recovered from the coke oven gas as ammonium sulfate, ammonia Hquor, and ammonium phosphates. The recovery product depends on the scmbbing medium employed, sulfuric acid, milk of lime, and phosphoric acid, respectively. Ammonium sulfate recovery by the so-called semidirect process, is most widely employed. 

Fixed atmospheric nitrogen and more especially the direct synthetic ammonia process is fast approaching the position once enjoyed by Chile nitrate, but it can never from present indications actuary achieve that position. Ammonia it is believed will always be produced as a by-product of the operation of the coke ovens. The production of by-product ammonia will increase, but it is believed its increase w lll be very slow. 

The Gray-King and Fischer assays determine the proportions of coke or char (carbonaceous solids), tar (organic liqnids), liquor (ammonia-rich solutions), and gas produced when the coal is carbonized (heated in the absence of air) under laboratory conditions. Hence, they provide a basis for estimating the yields of coke and coke by-products obtained from the coal in an industrial coke oven or oil shale-processing plant. 

The success of the Solvay process lay in the efficient use of the ammonia obtained as a by-product in the coke industry. The key step involves the reaction of ammonia gas and carbon dioxide gas in a saturated sodium chloride solution. That results in the formation of sodium hydrogencarbonate (bicarbonate) NaHCOj and ammonium chloride. The sodium bicarbonate precipitate is filtered from the solution, dried and heated to form sodium carbonate. Carbon dioxide is obtained by heating limestone CaCOj in a lime kiln. One noteworthy feature of the Solvay process is the effective use and recycling of materials. The only ultimate by-product is calcium chloride Ca-CI2, for which the demand is limited. To some extent it is used for deicing roads in winter and for dust control on dirt roads in the summer. 

The use of coal as a raw material started with the discovery of the first coal tar color by Sir William Perkins in 1856. Prior to this time the liquid by-products of coal coking were regarded as wastes. Perkins s discovery revealed that valuable materials could be isolated or made from coal tar and ultimately led to the establishment of the modern chemical industry. Coke ovens rapidly came to be important as sources of chemicals such as benzene, naphthatlene, ammonia, and hydrogen. Coal tar became an important source for aromatic and heterocyclic chemicals for the dye and pharmaceutical industries. 

Since 1960, about 95% of the synthetic ammonia made in the United States has been made from natural gas worldwide the proportion is about 85%. Most of the balance is made from naphtha and other petroleum Hquids. Relatively small amounts of ammonia are made from hydrogen recovered from coke oven and refinery gases, from electrolysis of salt solutions, eg, caustic chlorine production, and by electrolysis of water. In addition there are about 20 ammonia plants worldwide that use coal as a hydrogen source. 

Ammonium sulfate is produced as a caprolactam by-product from the petrochemical industry, as a coke by-product, and synthetically through reaction of ammonia with sulfuric acid. Only the third process is covered in our discussion. The reaction between anunonia and sulfuric acid produces an ammonium sulfate solution that is continuously circulated through an evaporator to thicken the solution and to produce ammonium sulfate crystals. The crystals are separated from the liquor in a centrifuge, and the liquor is returned to the evaporator. The crystals are fed either to a fluidized bed or to a rotary drum dryer and are screened before bagging or bulk loading. 

An electrostatic precipitator is used to remove more tar from coke oven gas. The tar is then sent to storage. Ammonia liquor is also separated from the tar decanter and sent to wastewater treatment after ammonia recovery. Coke oven gas is further cooled in a final cooler. Naphthalene is removed in a separator on the final cooler. Light oil is then removed from the coke oven gas and is fractionated to recover benzene, toluene, and xylene. Some facilities may include an onsite tar distillation unit. The Claus process is normally used to recover sulfur from coke oven gas. During the coke quenching, handling, and screening operation, coke breeze is produced. The breeze is either reused on site (e.g., in the sinter plant) or sold offsite as a by-product. 

F-S [Ferrous sulfate] A process for removing ammonia, hydrogen sulfide, and hydrogen cyanide from coke-oven gas by scrubbing with aqueous ferrous sulfate solution obtained from steel pickling. A complex series of reactions in various parts of the absorption tower yield ammonium sulfate crystals and hydrogen sulfide (for conversion to sulfur or sulfuric acid) as the end products. Developed in Germany by F. J. Collin A.G. 

Ammonia also may be produced as a by-product from gas liquor obtained from coal, gas, and coke ovens. Organic nitrogen in the coal converts to ammonium compounds which are separated from tar and distilled with an aqueous suspension of Ca(OH)2 to produce ammonia. 

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