Modern Gasworks Practice

390 MODERN GASWORKS PRACTICE Sommer1 states that in practice the yields of ammonia from a given coal vary according to the rate of increase in temperature, the maximum temperature reached by the prochicts of distillation, and the time the products are in contact with the hot walls. The following table illustrates how the above-named factors vary according to the type of carbonizing apparatus employed:— Influence of Time and Temperature on Ammonia Yield Type of Carbonizing Chamber. Weight of Charge. Carbonizing Period. Temperature. Glowing Wall Area. Per ton coal. Time of Action. Tons. Hours. ° c. Sq. ft. See. Horizontal retort .... 0-118 5 1165 290 112-3 Vertical retort 0-50 7 1150 176 2-4 Horizontal chamber . 10-3 24 1100 68-3 3-4 Sloping chamber .... 6-6 24 1050 83 2-3 Coke oven (6-4 coal ) \0-88 water ) 30 1000 84 - 8-4 Sommer says that no definite conditions can be given as most favourable for all classes of coal, as these dopend upon the properties of the individual ooals. Thus for a Silesian or English coal ratter higher temperatures give the best yields of ammonia, so that vertical retorts or coke ovens will give good results. In these ovens the time and temperature factors balance one another. Ä Westphalian coal requires a lower temperature or much faster cooling, and will, therefore, give better results in a horizontal or sloping chamber, more especially if wet coal be used. Gas retorts are poor in. every respect for all classes of coal from the point of view of ammonia recovery—e.g., high, temperatures and slow cooling. The small portion of the original nitrogen of the coal which is found. as cyanides is almost wholly in the form of hydrocyanic acid, although small quantities of free cyanogen are also present. Hydrocyanic acid is essentially a high, temperature product, and probably makes no appearan.ee in the retort below temperatures of 870°. to 925° C. When higher temperatures were first introduced in conjimction with. the light 6-cwt. coal charge a distinct increase in the yield of cyanogen was noticeable, whilst the yield of ammonia showed some falling off. There seems little doubt that the greater portion of the cyanogen. is produced at the later stages of the charge, when the temperature is at a maximum, and the traces of syntheti-cally produced ammonia which may be coming away have few dilueat gases to shield them from decomposition. It is at these higher temperatures that a portion of the ammonia is split up into its elements hydrogen and nitrogen which react with. carbon and yield hydrocyanic acid. It does not necessarily follow, however, that a high yield of cyanogen. means a decreased production of ammonia, and in many cases a high yield of both products is obtained. Some iavestigators, such as Kulmann, have shown that if carbon inonoxide and 1 Stahl und Eisen, 1919, pp. 294, 349.