Modern Gasworks Practice

THE HORIZONTAL RETORT BENCH oo <1 usually ran iii the ratio of 1 to 36 or 1 to 40. A point to remem-ber is that the calculated cliirnney area refers to the area at the base of the shaft, and the design should be such that, in spite of the reduction of thickness of the brickwork, the cross-sec-tional area at the summit is the same. In Fig. 36 a batter of 1 in 40 gives an overall reduction in total width. of 3 feet, and at both. top and bottom the internal dimensions are similar, namely 3 feet 9 indies square. So far as the thickness of cliirnney walls is concerned, the following typical instances for various heights are given :— (a) 68 feet high. Brickwork: 1 foot I0J inches for 12 feet. 1 foot 6 inches for 16 feet. 1 foot 11 inches for 20 feet. 9 inches for 20 feet. (b) 63 feet high. Brickwork: 1 foot 10J inches for 12 feet, reducing to 9 inches at top. Outside batter 1 in 36. (c) 58 feet high. Brickwork: 1 foot 10| inches for 11 feet. 1 foot 6 inches for 14 feet. 1 foot inches for 16 feet. 9 inches for 17 feet. A small proportion of chimneys is now to be found in which the brickwork is reduced to 4|-inch for some distance in the upper length. It must be strongly emphasized, however, that such, design is to be rigidly avoided, the more so in. retort-house shafts, where wind and heat have both to be withstoocL Fig. 36.—Chimney with Extbknal Batter. Chimneys of this description are occasionally to be rnet with in which. no external batter has been. provided, the walls running up vertically from base to top. For instance, a group of retort-house shafts is known which are con.stru.cted as follows: The shafts are 70 feet in. height, the first 30 feet being 13|-inch brickwork, the next 20 feet 9-inch brickwork, and th.e final 20 feet 4|-inch work. In the 4J-inch. portions the corners are con.stru.cted of 6-inch. work for increased stability. The effect of such design on ch.imn.ey area is well illustrated by reference to Kg. 37. The efEective area at the base is 14 square feet; whereas at the 9-inch work it has been increased to 27| square feet, or nearly double. Retort-house chimneys are usually braced for their entire height, the most general method being to run angle-irons up each. corner, the irons being held in position. by tie-bars at intervals of about 6 feet. The shaft used in conjuiiction. with. regenerator settings should be centrally divided by a 4|-inch wall in the same manner as the main waste-gas flue. It is always advisable to leave mspection. doors at the base of the shaft, so that the condition of the waste-gas flue can be readily seen. during working, and a vacuum gauge inserted; whilst provision should. be made for a cleaning door, so that dust, etc., may be removed. during stoppage. The same