Modern Gasworks Practice

HIGH TEMPERATURE CARBONIZATION OF COAL 431 efiect upon the rich gases takes place without loss or absorption of heat; moreover, the speed of travel towards the gas outlet is greatly, accelerated, thus curtailing secondary action. So far as the yield of B.Th.U. per ton of coal is concemed. some remarkable results have been obtained at Truro gasworks, the main features of which are shown below:— Carbonizing Results from Downward Steaming I. II. Steam pressure, Ib 20 25 Gas yield per ton of coal 16,860 17,483 Calorific power (B.Th.U. gross) 489 503 Coke made per ton of coal, cwts 12-94 12-97 B.Th.U. in gas per ton of coal (in millions) 8-242 8-805 Type of coal Whitwood Wigan Arley ATMOSPHERE IN VERTICAL RETORTS The modern vertical retort lends itself admirably to an adjustment of “ atmo-sphere.” This faet has led to important attempts to modify both liquid and gaseous products by adjusting the conditions of atmosphere in accordance with the results desired. Hydrogen may be readily brought into the retort, either in the form of debenzolized coal gas, as blue water gas, or by the generation of water gas in situ by the injection of steam. J. W. Cobb 1 has said that the action of a scouring gas in the retort may be regarded in two ways. Even an inert gas, such as nitrogen, would not be without effeet, because it would wash the volatile products out of the pores of the coke, assist their volatilization by lowering their concentration in the vapour phase, and hurry them away from the region of decomposition. So light a gas as hydrogen has a great power of diffusion, and it is therefore even better able to penetrate the pores and perform these duties. The general effeet of the ascending stream of gas to be anticipated is that of inereasing the yield of gas and of the lighter constituents in the tar. In so far, however, as the secondary products of carbonization are concerned (in which are included benzene, toluene, and other valuable products for the manufacture of dyes and drugs), the plant which. excels in the rapid removal of products without any considerable decomposition may have its disadvantages. The suggestion is made, therefore, that carbonizing plant might be so modified that, whereas conditions would prevail which would ensure a high yield of gas and paraffinoid Condensed products, the gas should be accorded secondary heating, which would ensure the volatile hydrocarbons being obtained in the benze-noid form. The tendency for paraffins to predominate when ordinary grades of gas coal 1 Wm. Young Memorial Lecture, Sept., 1918.