Modern Gasworks Practice

86 MODERN GASWORKS PRACTICE to the special material from which. it is manufactured. It shoulcl, thcrefore, be rigidly avoided. The grate area required when sloping grates are employed is much. less than that demanded by the horizontal bar-grate. For step-grates the minimum area allofrted should be 0-8 square foot per ten lineal feet of retort in the setting. With. Grille grates the allowance may be reduced to 0-6 square foot per ten lineal feet of retort. (d) Flue and Chimney Area The retort-house chimney in large houses varies from 50 to 70 feet in height,. The chief considerations to be kept in mind are that of taking it well above any adjoining buildings, and that down-draughts and varying winds are avoided. With direct-fired and generator furnaces it is usual to support the chimney from the top of the beuch and to run the main waste-gas flue directly into it. With. the regenerator setting, however, the chimney is usually sprang from foundation-level, and should preferably be entirely distinct from the beuch. So far as its constructional features are concerned, the cross-sectional area is the most important, and must in all cases be adequate. The usual rule, which may be applied with. perfect reliance, is to allow 1| square inches of area per lineal foot of retort in all settings dependent upon the flue and chimney. Thus, suppose a bench consisting of eight settings of “ tens ” is to work on to a common flue and chimney— The length. of retort in each setting is 200 feet. The length of retort in eight settings is 1,600 feet. The chimney area required is 1,600 X 1| square inches, i.e. 2,400 square inch.es, or 16| square feet. With. large units of through settings 75 per cent, of this is sufficient Another rule (due to Herring) is that of allowing 40 square inches per ton of coal carbonized per diem by the whole beuch, of retorts dependent on the chimney The following formula (Brooke) is also sometimes used:—■ Wherc A = area of chimney, in square feet. H = licight of chimney, in feet. W = weight of fuel burnt per minute, in Ibs. In any case, when a skaft is to be erected it should be based upon the first of the rules b.ere given, and th.e last named may be used as a means of ch Peking. It is inadvisable to connect a chimney to a greater number of beds th.an ten, as above this (at any rate, for settings of 10 s or 12’s) its dimensions become somewhat un-wieldy. Circular shafts, except for some vertical installations, may qow be said to be th.in.gs of the past, and the rectangular chimney with extemal batter is most commonly seen. A typical design of this style of shaft is seen in Fig. 36. It will be noticed that a square base 10 feet in. height is provided. Some ornamentatioa (such as oversailing courses, plinths, or panelling in different coloured bricks) is usually added. The batter cominences immediately above tlie square base, and is