THE PRELIMINARY PURIFICATION OF COAL GAS 533
Ammonia Recovery at Gaswobks, 1918
Pounds of Sulphate of Ammonia per ton of Coal. Number of Works. Coal Carbonized (tons per annum).
Between 40 and 45 Ib „ 35 „ 40 „ 30 „ 35 „ „ 25 „ 30 „ 20 „ 25 „ ......... „ 15 „ 20 „ 10 „ 15 „ 5 „ 10 Below 5 Ib 2 3 12 41 119 119 98 28 4 14,228 32,766 623,328 2,492,311 3,984,768 2,835,001 1,714,941 322,481 12,401
Highest average yield for the year 43 -0 Ib. Lowest average yield for the year 3 -7 Ib.
So far as tlie prevention of ammonia loss in. storage wells is concerned it has been shown that evaporation may be considerably reduced by covering the surface of tlie liquor with. a very thin. film of oil. Those undertakings making carburetted water gas may readily employ ordinary gas oil for the purpose, but the precaution must be taken to ensure that the suction from the liquor pump is always well below the surface of the liquor, otherwise the oil film may be drawn off. Once the surface has been covered the oil will remain effective for a considerable period, thus requiiing very infrequent renewal.
LIQUOR PURIFICATION
Attempts have been made to dispen.se with dry purification plant by making use of the alkaline impurity (ammonia) for removing the whole of the remain-ing acid substancés. As previously pointed out, liowever, the available ammonia in coal gas (after the condensers have been. passed) amounts, theoretically, to very much less than the quantity necessary for extracting the acid impurities. It has been proposed to overcome the difficulty of this deficiency by causing the ammonia to perform its duties twice; in otlicr words, having absorbed the acid impurities the resultant salts are decomposed in special apparatus, wh.cn the acid gases are expelled and the ammonia rendered available for further use. Purification. systems based on such principles were introduced by Claus, also Laming, Livesey, and Hills. Although theoretically ingenious, their complicated nature prevented any develop-ment on a practical scale. During the war, liowever, renewed attention was given to th.e subject, owing to the faet tliat a demand arose for concentrated ammoniacal liquor ; and in the preparation of this the liquor was treated in such, a manner that, while tlie ammonia was retained, the sulphuretted hydrogen, and carbon dioxide were expelled. Thus, the first condition necessary for complete liquor purification of the gas was fulfilled.