Modern Gasworks Practice

HIGH TEMPERATURE CARBONIZATION OF COAL 389 explained by the faet that if an unstable gas be diluted with some considerable quantity of inert gas the temperature necessary to bring about decomposition inereases rapidly in. proportion with the amount of dilution. Tlius the ammonia is quickly exhausted away from the retort before feeling the efiects of degradation. It is in this manner thai the high yield of ammonia in the Mond plant may be explained, for an excess of steam and air is admitted to the base of the fuel-bed and forms an enveloping gaseous mass (containing a high percentage of inert con-stituents) which shields the ammonia on its passage through the producer. The prochiction of the secondary ammonia, as disti net from that evolved .as a primary compound, has been explained by Tervet, who states that a portion of the nitrogen remainmg in th.e coke can be liberated in the form of ammonia, so long as the ammonia is brought into a state of strain which shall prevent it from sub-sequent degradation. This state is effeeted by subjecting the ammonia to the superior affinity which. exists between the combined nitrogen in the coke and free hydrogen at a particular temperature and in a diluting atmosphere. Thus synthesis between. the free hydrogen in the retort and the nitrogen evolved from the coke at higher temperatures is taking place. Important work on the question of the effeet of temperature and other con-ditions on the yield of ammonia has recently been carried out by Cobb and Hollings, who are still engaged in the research. In their experiments these investigators have stuclied the decomposition of the ammonia from coal when the products are subjected to differing conditions. In each case a small quantity of coal was distilled in a boat contained in a specially sealed and heated tube, and the ammonia present in the products was estimated. The gases evolved from the coal were first drawn away from a tube which was so designed and arranged that secondary reaction had no time to exert its influence ; in the second series of experiments they were drawn through a heated tube and subjected to radiant heat; whilst, thirdly, the tube was packed with coke, and the gases drawn through this. The results of their experiments may be briefly tabulated as follows :— (a) Minimum heat action . . . 22-5 per cent, of nitrogen in coal recovered as ammonia. (!> ) Gases subjected to radiant heat . 17-2 „ „ „ „ „ (c) Gases passed through hot coke . 9-4 „ From these figures conclusions can be drawn as to the effeet of high, temperatures and travel over heated surfaces on the yield of ammonia. The temperature of 800° C. (1,470° F.) was used throughout. The eflect of the heavy charge of long duration in ensuring the gases being swept from the retort before decomposition lias occurred to any extent is shown by the following figures given by Ferguson Bell1:— 6-hour charges of 6 cwts. of coal, yield of ammonia 7-26 Ib. per ton. 8-hour „ TI „ „ „ „ 8-26 „ „ 10-hour „ 9| „ „ „ „ 8-45 „ 12-hour „ U| „ „ „ „ 8-50 „ Proc. Inst. Gas Eng., 1909.