Modern Gasworks Practice

770 MODERN GASWORKS PRACTICE The coal used was a mixture of ordinary coal and brown coal. The former contained 11 per cent, of ash and 5-5 per cent, of moisture, while the brown coal contained 3-15 per cent, of ash and 55 per cent, of moisture. The yield of gas was 63,450 cubic feet per ton. of the mixed coal, its calorific valne being 315 to 338 B.Th.U. per cubic foot. The average composition of the gas was as follows :— Composition of Tri-Gas (Mixed Coal) Hydrogen________________________________________51-5 per cent. Methane 5-5 „ CnHm.................................................0-3 „ Carbon monoxide . . . . . . • . 23-9 „ Carbon dioxide 13-3 „ Nitrogen . . . . ... . • • . 5-1 „ Oxygen . . . . . . • • ■ . 0-4 „ Each of the producers put through from 12 to 15 tons per twenty-four hours ; but with coal not so highly caking a good deal more could be dealt with.. Producers are now being built of twice the capacity mentioned. The tar obtained was free from naplithalene, and met all the conditions laid down for good low-temperature tar. It is port-wine red when looked through, and has, when dry, a sp. gr. of 1 '04 at 15° C. 62 per cent, of it is soluble in benzene, and it is wliolly soluble in benzol. It gives, on distillation in a vacuum, 26-7 per cent, of lubricating oils, 32-5 of very viscous oils, 3'3 per cent, of hard paraffin, 11-5 per cent, of resin. and 26 per cent, of pitch. In amount it came to 5 to 6 per cent, of the material gasified ; but it is hoped to raise this percentage materially by avoicling the use of highly caking coal. The Vienna experiments gave 15 per cent, from brown coal, but there the coal was not a caking coal and the tar vapours got away freely, and, in addition, the heating of the coal in the upper part of the producers was, for the same reason, more uniform. The yield of ammonia was also good, but, in the same way, caking of the coal was found to interfere with. this. The Tri-gas plant consists of a producer at the base of which water gas is manufactured, thus gas ascends through the superimposed column of coal and transforms it into coke. The lower portion of the producer is divided into two by a partition, the higher part of which is below the zone in which the coal is coked. Two pipes coirtaining heated compressed air run. one to eacli side of the partition. Two superheated steam nozzles are also provided. The plant carries at the top the usual fittings for the discharge of waste gas and the run gases. The plant is worked by successive introduction of air and superheated steam. Düring the first period, all the valves are shut, except that for the intake of compressed air, and one for the discharge of waste gas into the chimney. The hot air thus blown in bums the coke; and the products of combustion rise through the column of coke on the right of the producer, to pass out through the waste-gas valve, after descending from top to bottom of the second half of the producer. In this way the coke bed is raised to a temperature of about 1,400° C. The run is then commenced. A current of steam is admitted to the plant, and