Modern Gasworks Practice

oo MODERN GASWORKS PRACTICE Charges to be met (annual):— £ s. d. Interest, depreciation, repairs, and renewals, 11 per cent, on £200 . . 28 0 0 Gas consumed by engine, say 3,000 cubic feet per week at 4s. (id., oost into holder....................................................................... 35 2 0 Oil, stores, etc., per weck 4a. . . . . . . . 10 8 0 £73 10 0 Resultant Swing :— £ s. d. 45 tons of coal at net costprice (after allowing for residuals) of 32s. . 72 0 0 Wear and tear on carbonizing plant, owing to reduced quantity of coal used, at 4s. per ton _________________________________...... ....900 £81 0 0 The balance, it will be noticed, is extremely small, although a good deal will ■depend upon the distance of the works from a point of delivery for materials, and consequently the price at which coal can be obtained at works. No saving of labour ■can be contemplated, for on works of such a size a single man only is employed for carbonization. Moreover, the question of labour may operate against the em-ployment of the exhauster, owing to the necessity for the man in charge to have some knowledge of mechanical plant. On the other hånd, the exhauster offers undoubted advantages in such directions as the control of gas quality, the reduction of scurf, etc. Exhausters now employed on gasworks are almost universally of the rotary type, although those operating on. the reciprocating principle and designed on the lines of an. ordinary steam pump were in. common use in. days when the rotary machine had not been brought to its present stage of perfection. Primarily, the function of the exhauster, in wha te ver form it may be used, is that of withdrawing the gas from the retorts by the creation of a vacuum, to avoid the formation of an excessive pressure Hierein, and eventually to propel the gas through, the remainder of the apparatus and into the holders, thus causing the latter to rise. So far as the conditions of the operation of the exhauster are concerned the vacuum induced on the inlet must be sufficient— (a) To overcome the seal on the dip-pipe, if a seal is employed. (b) To overcome frictional losses arising from the passage of the gas along the foul main. (c) To overcome the resistance offered to the gas by the condenser. In normal working and when dry mains are not in use, the hydraulic seal amounts to about half an inch, whilst the frictional losses in the foul main may be equal to 1 inch. of water pressure, and the resistance of the condensers to 2 inches. Accord-ingly, on the larger works it is usual to maintain an average vacuum of about 4 inch.es of water at the exhauster inlet. On the outlet, the pressure to be overcome varies in accordance with the resistance ofEered by the apparatus following and the ■quantity of gas passing at the time. In the aggregate, it may vary between. 8 inches to 10 inches on a small country works to as mucli as 50 inches of water on the largest ylant-s, but in average cases it will be accounted for somewhat as follows:—