Modern Gasworks Practice

114 MODERN GASWORKS PRACTICE generated at some distance from the point at whiich it is to be consumed. Outside producers as now employed on gasworks may be classified as follows :— 1. Coke-fired. (a) External types. (6) Semi-external types. 2. Coal fired (or mixture of coke and coal), with plant for recovery of by-products. 3. High-pressure producers. External producers of all types are entirely confined to the largest of gasworks. Although they cannot compete with the self-contained furnace on the score of fuel economy, their chief recommendations lie in a somewhat reduced Capital outlay, if the producer is of a simple type, comparatively low labour charges, and little wear and tear. The working conditions for the men are also better. A distinct advantage, Fig. 59.—Simple Fokm of Outside moreover, is the finer regulation of temperature in the settings owing to the possibility of passing the gas on its way to the settings through metal cocks. The simplest form of coke-fired external producer is very similar in appearance and construction to a water-gas generator, the outer casing being made of mild steel plates, with. a lining of firebricks and thin. layer of slag wool. In all cases a forced air-blast is provided, consequently a comparatively fine fuel may be made use of. A certain amount of steam is usually ad-mitted below the grate in order to curtail clinker formation. One of the largest installations of outside producers is that laid down at tKe Provan works of the Glasgow Corpor- Pboducer. ation, some fifteen years ago. These pro- ducers designed on. the lines of that shown in Fig. 59, are rectangular (not circular) in section, and twelve of them were erected, to be used. in conjunction with sixty beds each. of twelve retorts. The steel casings are 13 feet 3 mch.es high by 9 feet 4 inch.es long and 6 feet 4 inches wide, and are lined with 9 inches of firebrick work, with a 2-inch. cavity filled in with slag wool. The gas is led away from each. producer by a lined flue casing measuring 2 feet by 3 feet 6 inches, this passing into a round main flue pipe of 4 feet 10 inches diameter. Owing to the forced draught made use of with this type of producer it is essential that an efficient dust chamber should be provided, so that the gas is thoroughly cleansed before reaching the combustion chambers of the settings. In the Provan installation the main flue is mtercepted by dust chambers measuring 22 feet high by 11 feet 4 inches long by 6 feet 10 inches wide. At the Old Kent Road works there are four retort bortses (having a total capacity of 10 million cubic feet of gas per diem) heated by outside producers. There are two producers to each hou.se, having a capacity of 30 tons, the coke used per day being about 35 tons per house. Tlie caloriflc value of the gas is approximately