Modern Gasworks Practice

 424 MODERN GASWORKS PRACTICE tures will tend to increase the benzene, while lower temperatures produce paraffins and olefines. The recovery of light oils from water gas in this country, though attempted in the early days of the war, has not been followed up, partly owing to the paraffins present in the recovered spirit, and also on account of the attenuated nature of the carburetted water gas which has resulted from the shortage of gas-oil. Willian’s figures show that, with thorough scrubbing, the crude spirit recovered from carburetted water gas amounts to about 10 per cent, of the oil used, and ■consists of benzol 35 per cent., toluol 25 per cent., solvent naphtha 10 per cent., heavy naphtha and wash-oil 30 per cent. The loss of candle-power due to scrubbing was 50-8 per cent., and of calorific valne 4-2 per cent. Snme interesting figures relating to the effect of tar on the proportion of benzene, etc., in the gas have been given by Sainte Claire Deville,1 who shows that the tar tends to absorb the benzene at the commencement of the carbonizing period but throws it off towards the end of the charge Gas prior to entering Gas at outlet of Condensers and Condensers and Purifiers. Purifiers. First hour of carbonization. Benzol in grains per cubic foot. . 21-4 17-3 Second „ „ . 19-3 15-4 Third „ „ . 12-3 18-8 Fourth ,, „ . . . 4-0 19-1 The extent to which the benzol recovered. from coal is enhanced by the process •of stripping the gas is illustrated by the following figures :— Pounds per ton of coal carbonized. Benzene. 0-4 1-5 10-0 Töluene. 0-130 0-75 3-50 Recovered from tar . Recovered by tar-washing process „ „ oil-washing process CHARGE THE EFFECT OF STEAMING THE COAL Opinion as to the relative economy of producing a mixed gas in two operations ■or of generating it in a single operation by producing water gas in situ is still divided. The process of steaming the coal charge was in its early days almost solely confined to the intermittent system of vertical retorts when it became customary to admit steam during the last two hours of a 12-hour charge. In recent years, however, ideas as to the essential qualities of towns-’ gas have been considerably modified, with the result that a remarkable advance has been made with the system as applied ta continuously operated vertical retorts. The operation of steaming is particularly ■elastic, it being possible to Control the results obtained within a wide range by regu-lating the quantity of steam admitted and the temperature of the retorts. In general, it may be said tliat the arrangement consists of passing superheated steam into the coke-extractor chamber through a |-inch nozzle and at a pressure of 40 Ib. per square inch. 1 Gas J., CXLVII, p. 392.