Modern Gasworks Practice

HIGH TEMPERATURE CARBONIZATION OF COAL 391 ammonia -are passed over spongy platinum a small quantity of hydrocyanic acid is formed, and this has led to the supposition (probably erroneous) that cyanogen may be formed in some degree by the double decomposition of carbon monoxide and ammonia. Otters support the theory that ammonia and carbon disulphide react to form the product. It must be remembered that, like ammonia, hydrocyanic acid itself is liable to decomposition at the higher temperatures, and that the quantities in which it is ultimately found probably depend to some extent upon the amount of diluent gases which are present to conduct it from the retort. As regards the decomposition of ammonia, Bueb carried out a series of ex-periments which showed that at temperatures of about 750° C. approximately 4 per cent, of the nitrogen of the ammonia was converted into cyanogen, whcreas at 980° C. nearly one-quarter of the amount had undergone this change. A some-what remarkable result was obtained by Cobb and Hollings in conuection with hydrocyanic acid. In the experiments previously quoted, after decomposition of ammonia had taken place the products were tested for cyanogen, but in no case could- the presence of this compound be detected. This is probably explained, however, by the faet that the conditions favourable to the production of cyanide were absent. Several attempts have been made to inerease the recoverable proportion of the total nitrogen, in coal, but their measure of success has been such, that the suggested. methods have only been adopted on. gasworks in isolated in.stan.ces. Among them may be mentioned the liming of coal, originated by Cooper, and operated at the Cheltenham gasworks. In this process lime is charged with the coal into the retorts. In order that tliorough admixture may take place the coal is slightly damped on. the surface by a steam jet, thus causing the lime to cling to the lumps. The quantity of lime intermixed witli the coal is usually about 2 per cent. As a result of its employmen.Li the sulphate of ammonia recovered per ton of coal carbonized showed an average inerease of nearly 2 Ib. The improvement in the yield of ammonia in this case may be due to the faet that admixture of a caustic alkali has some tendency to convert the residual nitrogen of the coke into ammonia. Some thirtyyears ago a method1was introduced for extracting nitrogen in the form of ammonia from the coke of shak retorts, by passing steam through the fuel-bed whilst in a highly heated condition. In this way the recovered ammonia in-creased by about 200 per cent. Several suggestions were made for the application of the same principle to the recovery in the form of ammonia of the nitrogen left behind in the coke produced on gasworks. One promising suggestion provided for dropping the red-hot coke as it came from the retorts into special chambers maintained at a high, temperature into which—for a short period—steam could be blown. A certain quantity of blue water gas was thus obtained, and at the same time a large additional yield of ammonia. Another means was based on. the faet that when. hydrogen, or a gas rieh in. hydrogen, is passed through highly heated. coke the hydrogen combines with. the latent nitrogen to form ammonia. Such conditions are obtained 1 Compafe West arid Wild’s system, p. 109.