Modern Gasworks Practice

172 MODERN GASWORKS PRACTICE charging of the coal into the retort is eftected by opening a large cock or valve having an upright plug, the lower opening of which connects with the retort and the upper opening with the coal hopper. The amount of free space in the retort (usually abont 3 per cent, of the total volume) is regulated by a rod which projects into the top of the retort for the required distance. The movement of this rod indicates when the proper quantity of coal has been delivered, and the charging cock is then closed. For the benefit of the quality of the coke the coal charge may, if desired, be subjected to a small amount of stearning. The producers, which. are fed with cold coke, are carried right up to the top of th.e setting, this giving an ampie reserve of fuel, and thereby minimizing the amount of attention required. The producer gas is admitted around the tipper portions of the retort, so that the maximum heat is concentrated here; the gases then circulate downwards, leaving the setting at the base. The coal hoppers are of large capacity in order to allow for sufficient storage to carry the work over Sundays without refilling. The following are the more important features in Connection with the design of the system:— Retorts: Length......................... Breadth and width. At top. At base . Coal carbonized per retort per 24 hours . Average yield per retort per diera . . . . Number of retorts in eaoh setting .... Grate area of producer___________________ Approximate time taken by coal in travelling from entrance into and exit from retort . 23 feet. 40 inches by 10 inches. 48 inches by 18 inches. 3 to 5 tons. 31,500 to 55,000 cubio feet, according to dass of coal. 4, 6, or 10. 4 square feet per retort per bed. 18 hours. HERRING’S SYSTEM Mr. W. R. Herring’s system of vertical retorts, erected some years ago at Edinburgh, differed from the majority of installations at work in this country in that the retorts were fired by means of outside producers. The system was designed to work on either the contimious or intermittent principle. When working continuously the coke extractor was devised to act as a cutter, whercwith the size of the coke could be reduced as required. The retorts were built up of tongued and grooved bricks, they were of rectangular shape, and received their coal charge through a special closure apparatus (Fig. 91) which was designed to maintain a gastight joint while permitting the passage of the coal. The coal finds its way into the retort through an upper cylindrical pouch, to which the gas outlet is also affixed. The coke extractor (Fig. 92) is varied in speed in accordance with the dass of coal under-going carbonization, and the coke on passing this is confined in special chambers, where it is slowly quenched. The outlet of the coke hopper is closed by a special gastight device similar to that through which the coal is admitted to the retort. Heating of the retorts takes place from the top downwards, so that the newly charged coal passes at once into the highest temperature zone. Pyrometrie tests conducted by Mr. Herring showed that the temperature varied from 1,130° C. towards