Modern Gasworks Practice

118 MODERN GASWORKS PRACTICE (6) Mixture of half coal slack and half coke dust. Small coal at 10s. per ton . 9-0d. per ton of coal carbonized. Coke dust at !<$. 6tZ. per ton l-35rf. Boiler fuel .... . 2-15d. Labour .... . 3-84<Z. Repairs and depreciation . 8-53rf. Oil, etc. ..... . 0-34<Z. Sulphuric acid at 30s. per ton . l-30fZ. Sulphate bags, packing .... . 0-3CW. Gross cost ..... . 26-8 Id, per ton of coal carbonized. Less sale of sulphate ..... . 12-52<7. Net cost of heating .... . 14-2M. per ton of coal carbonized. More recently Chaney has given particulars which. show tliat the fuel usually employecl for producer work is a coal slack containing a proportion of nuts. It generally contains about 13 per cent, of ash; the calorific value of the slack being 12,500 B.Th.U. per pound (dry). The calorific value of the coke dust is approximately 10,000 B.Th.U. per pound. (dry), and the nitrogen content 1 per cent., the actual sulphate of ammonia recover-able being 45 to 50 Ibs. per ton. It may safely be assumed that 3 to 4 per cent, of the total coal carbonized for gas-making purposes in this country represents the quantity of coke dust made ; so that large quantities of sulphate of ammonia are available, and which at the present moment are neglected. Gasified alone, the coke dust yielded about 95,000 cubic feet per ton; the calorific value of the gas being 114 B.Th.U. per cubic foot. Unfortunately, the through-put per producer diminished to such, an extent as to jeopardize tlie heats of the coke-ovens, and the test had to be discontinued. By mixing 40 per cent, of coke dust with the producer coal, the heating value of the gas is increased to 130 B.Th.U. per cubic foot; and the average price of the mixture is correspondingly reduced. . O. U,, Assuming 17s. (id. to be the price of the producer coal, 60 per eent. of 17«. f'yl. . 10 6 Coke dust, 40 per cent, at (say) 15. per ton .... 05 Average prioe of mixture . . . 10 11 The additional revenue from the sulphate of ammonia recovered per ton of the mixture would be 69 Ibs. at £16 per ton = 9s. 10cZ.—reducing the cost of the producer fuel to Is. 1(Z. per ton. To this latter figure has, of course, to be added the increased expenditure of fuel due to heat losses, and to extra manufacturing charges. As regards. increased expenditure of fuel, 12 per cent, for the ordinary internal metliod of heating retorts would be practically increased to 24 per cent, with outside producers, using 40 per cent, of coke dust and 60 per cent, of producer coal. The manufacturing costs with outside producers are considerably higher than the ordinary method of heating retort settings; but the large margin between the cost of the producer fuel and the value of the coke displaced, warrants a careful consideration of this system of heating.