APPARATUS AND PROCESS OF MANUFACTURE.
In the generator-retort type of apparatus the water-gas is made in a generator, a steel shell lined with fire-brick, which after a fire has been kindled in it is filled with coal that is brought to incandescence by means of a forced blast of air.
a permanent gas. The crude carbureted water gas so formed is drawn from the retorts by an exhauster and condensed and purified, without being scrubbed, in the manner described under COAL: GAS.
In the generator-superheater type of appn ratus the water-gas is made and carbureted in one operation. In its most common form it consists of three brick-lined steel cylindrical ves sels connected together and called the generator, the carbureter, and the superheater. The genera tor contains the coal, and the carburetor and su perheater are filled with fire-brick piled in a checker-work. This checker brick is heated by the combustion of the producer gas formed in the generator while the coal is being brought to incandescence by a forced blast. When the proper temperature has been reached in all the vessels the blast is shut off, the stack-valve on top of the superheater, through which the prod ucts of combustion escape during the heating up period, or 'blow,' is closed, and steam is turned into the generator. As soon as the pro duction of water-gas is begun, oil is admitted at the top of the carbureter, is vaporized by the heat of the checker brick, and is taken up by the water-gas and carried through the checker work in the carbureter and superheater, being converted into a permanent gas by the exposure to heat to which it is thus subjected. After leav
ing the superheater the gas passes through a water seal, and is then condensed and run into a relief holder, the use of which is necessary for the reason given above. An exhauster draws the gas from this holder and forces it through the purifiers and station meter into the storage holder. The generator-superheater type is the one that is generally employed at present, having replaced almost all the earlier installations of the generator-retort type.
Carbureted water-gas is a mixture of essen tially the same gases as are found in coal-gas, though in different proportions, the following being representative analyses of each gas after purification by oxide of iron: In the case of carbureted water-gas, however, the crude gas contains no ammonia nor cyanogen, and a smaller amount of sulphureted hydrogen and sulphur compounds than are found in crude coal-gas. It is estimated that from 70 per cent. to 75 per cent. of the total amount of illuminat ing gas sold in the United States is carbureted water-gas, while English gas-works, in the year 1000, sent out only 8 per cent. of carbureted water-gas.