Modern Gasworks Practice

122 MODERN GASWORKS PRACTICE of the revolving grate, ensures uniform combustion over the whole grate area, the maximum gasification capacity per square foot of grate area, and perfect control of the fuel-bed. The charging platform of a battery of Kerpely producers is shown in Fig. 63. The gasification capacity of each producer is from 18 to 24 tons of coke per day. The producer is primarily employed on account of its ability to gasify extremely low-grade and dusty fuels—practically waste materials having a calorific power as low as 5,000 B.Th.U. per Ib. Äs in the Mond system, air and steam are supplied to the producer, in this case up to a pressur.e of 30 inches of water. The lower portion of the shell is water-jacketed, which. precludes the adhering of clinker to the side walls. SEMI-EXTERNAL PRODUCERS Of the semi-external producers an interesting example is that shown in Kg. 64. The producer dillers from the ordinary self-contained retort-bench type in that it is built out from the front face of the setting, thus providing an ampie fuel-bed, con-venience for charging, and ease of access. It is particularly suited to those retort houses in which hot-coke conveyors are employed, for the coke may be charged directly into the producers from the conveyor, the trough of which is provided with special sliding doors communicating with. the producer. From the illustration it will be seen that the gas duet is situated well below the level of the fuel. Accordingly, average variation in the depth. of the fuel-bed has no effeet upon gas quality. The arrangement does not necessitate the usual frequent charging of the producer, for the upper layers of fuel pro vide a storage which goes to replenish the fuel consumed in the active zone. It is claimed that the producer possesses the merit of being able to bum low-grade fuels such, as breeze and sweepings from the retort-house stage. Loss of Heat by Radiation In connection with the loss of heat due to radiation from the conduits of outside producers, Butterfield has pointed out that if the producer stands at some distance from the setting, and the gas has to travel through long pipes before reacliing the furnaces, or if it is stored for a short time in a gasholder, then 17 per cent, of the heating value of the fuel will be more or less completely lost. This amount of loss represents the heat which is expended in raising the producer gas to the temperature at which it leaves the furnace. With regard to the methods of insulation employed for maintaining the producer gas at the highest possible temperature, the author believes that the researches of Neumann on the reaction between gases after contact with. solid heated carbon have never been considered in. coiijunction with the working of outside producers of whatever type. Neumann has shown that at the furnace outlet there is a lower percentage of carbonic monoxide and a higher percentage of carbon dioxide in the gas than at the surface of the fuel, and that the total combustibles are less in percentage at the outlet than at a point just above the top of the fuel-bed. It is further pointed out that the change in composition of the gas after leaving the fuel-bed can be avoided by using an outlet pipe which is quickly