Modern Gasworks Practice

HIGH TEMPERATURE CARBONIZATION OF COAL 393 assist very considerably in augmenting the yield of ammonia is the process of Perkin and West, whereby a stream of moderately low quality gas is passed in at the base of the vertical retort at such a rate as to carry the volatile matter away before degradation has time to occur. Although the method has primarily for its obj eet the preservation of the hydrocarbons there can be little question that it must also reflect on the ammonia, for conditions of a thoroughly shielding nature are introduced, while synthesis is encouraged. Some extremely interesting results have recently been published by Salmang,1 ■who endeavoured to inerease nitrogen recovery during the gasification of coke by ad ding chalk or oxide of iron to the bed of fuel in the generator. Varying mixtures of steam and air were passed through the fuel-bed, and under the most favourable conditions 59 per cent, of the free nitrogen was recovered as ammonia, a figure which agrees very closely with the yield obtained with the Mond gas plant. When, however, 5 per cent, of chalk was intermixed with. the coke the proportion of nitrogen recovered inereased to so high a figure as 96-3 per cent., and with 5 per cent, of oxide ■of iron added the figure was 70 per cent. Salmang says that under given conditions of ammonia concentration and duration, of heating the rate of decomposition of ammonia in the presence of steam is only about an eighth. to a twentieth of what it is in a nitrogen atmosphere and without steam. In faet, the yield of ammonia is inereased by the presence of steam in conjunction with a considerable excess of air. The effeet of lime, too, was to inerease the nitrogen obtained as ammonia up to 12 per cent, in the case of coke derived from coal, and up to as mueh as 100 per ■cent, when coke derived from peat was experimented with. Unfortunately, so long as towns’ gas of the present description is made, it is not possible to arrange for the atmosphere which is most amenable to maximum ammonia output—namely, a mixture of steam and air, and with the air excliided the maximum recovery obtained by Salmang was 20 per cent, less tlian with a steam-.air mixture. Sommer 2 corroborates the faet thai the presence of steam has a tendency to •conserve ammonia, and he accounts for this by suggesting that the ammonia under .such conditions is present as the hydroxide (NH40H), which is comparatively stable. Moreover, he is of the opinion that the inclined chamber oven is productive of better results than can be obtained with the vertical retort, for the necessary conditions— i.e., shortened time of contact with the hot charge through rapid removal of the gas— are more readily obtained. therein. A similar advantage is obtained by inereasing the size of coke ovens and by lowering the level of the upper collecting flue so as to avoid undue heating of the gas as it passes out. Benzol, in addition to the ammonia, is thereby conserved, particularly towards the closing period of carbonization when all the moisture has been. driven from the coal. Speaking of moisture in the original coal, it may be mentioned that although dry coal is looked upon as essential m the ordinary gasworks process there can be no doubt that, whatever the effeet ■of moisture in other directions, it is certainly helpful in the way of ammonia recovery, 1 Z. Angew. Chem., 1919, 32, p. 148. 2 Stahl und Eisen, 1919, 39, pp. 261, 294, 349.