Modern Gasworks Practice

386 MODERN GASWORKS PRACTICE of the oxygen of the coal substance is disposed of in other ways than by direct combination with hydrogen. The Nitrogen of Coal The element nitrogen, altliough of more or less subsidiary importance, enteis materially into the reckoning when the economics of carbonization come to be cou-sidered. The aim of the gas engineer must be to recover in the most valuable form the largest possible proportion of the total nitrogen present, which on further treat-ment forms the basis of one of his most valuable by-products, sulphate of ammonia. The amount of nitrogen, in bituminous coals is, on the whole, the least variable of any of the constituents, the figme fhictiiating but little on either side of 1-4 per cent. This percentage corresponds with a yield of about 34 Ib. of nitrogen per ton of coal employed, whilst the average yield of sulphate of ammonia, amounting to 27 1b. per ton, represents a quantity of ammonia equal to 7 lb., or about one-sixth of the total nitrogen. In addition, a small portion may be usefully recovered in the form of cyanide compounds; but comparatively few gasworks are provided with. the necessary plant for this purpose. For some years attention has been directed towards the possibilityof recovering a greater proportion of the original nitrogen, but although plants for the production of low-grade gas are operating successfully in this direction, the conditions under which the increased yield is obtained are scarcely consistent with ordinary gasworks methods. As an instance, mention may be made of the Mond gas apparatus, by means of which. an average yield of 96 1b. of sulphate of ammonia is obtained, this quantity representing nearly 25 1b. of recovered ammonia, or about 65 per cent, of the total nitrogen. One of the earliest attempts to determine the relative quantities in which nitrogen is distributed among the various products was made by Foster, in. 1883. This investigator employed a Durham coal containing 1-73 per cent, of nitrogen, and the conclusions arrived at are as follows :— Nitrogen remaining in coke ..... 48-68 per cent, of total. „ free in gas and combined in tar . . 35-26 „ „ „ as ammonia ...... 14-50 „ „ „ as cyanogen ...... 1-56 „ „ Investigation of this kind is attended by considerable difficulties, and several other workers have derived figures on the same lines, but in no case are they in close agreement. The researches of McLeod, conducted in 1907, are, however, considered most trustworthy, having been carried out under everyday conditions. McLeod’s figures are as follows :— Nitrogen in coke ......... 58-3 per cent. „ free in gas ........ 19-5 ,, „ as ammonia ........ 17*1 „ „ as tar ......... 3-9 „ „ as cyanogen . . . . . . . .1-2 „ The figures which Short obtained for conditions existing in coke ovens are