Modern Gasworks Practice

82 MODERN GASWORKS PRACTICE ampie room is left for the regenerator device, and the front wall area is comparatively small. This last is an important point, in that heat radiating through the wall is lost, whereas in the longer side walls it is partly picked up by the inflowing secondary air and recovered. Fürther considerations whicli must receive attention are the following (1) The producer lining should be entirely separate from the main body of the brickwork. The wear and tear on this portion of the setting is heavier than that on any other portion, and although a well-built and substantial lining will re-main in workable condition for about 600 to 800 days, minor repairs are often neces-sary every year. Shutting down and restarting, however, is to be avoided as far as possible, owing to the undesirable effect on the working life. The false cheeks to the producer may be built up of a 4J-inch or 9-inch wall. The latter is preferable, and the bricks should be laid all “ headers,” so that considerable wear can take place without the bond of the work being broken. (2) The lowest point of the charging door frame of the producer should be no higher than the soffit of the furnace arch, and the frame should be sloped at such an angle as to enable the coke at the back of the furnace to be seen, and to be reached with a rake. (3) The lower portion of the producer should be slightly narrower than the upper portion. That is, at a point about level with the top of the furnace frame the brickwork should be set back 2| inches at the sides. This will minimize the short- circuiting of primary air up the sides of the fuel-bed. (4,) The primary air if taken in by vacuum should be admitted through slides Fig. 33.—Arched Pboducek. in the furnace door, and not by means of channels passing through the brickwork at the side of the furnace. With the ordinary horizontal bar-grate, short-circuiting of the primary air up the front of the fuel-bed may be avoided by “ breez-ing up.” A later practice, however, as met with in the “ Grille ” grate, is that of impelling the primary air in throiigh special cast-iron duets arranged one on either side of the producer. The general practice is to build up the producer with parallel side walls, a semicircular furnace arch being thrown over these. In some cases additional strength. is given to the producer by arching out the side walls as in Fig, 33, but the advantages accruing from this arrangement can scarcely be said to be commensurate with the increased cost. The widening out of the furnace in this way also prevents the short- circuiting of air through the fuel-bed. Whatever the shape of the producer, the front wall should be of 18-inch thickness, and there should not be less than 9 inches solid work between the side walls of the furnace and the regenerator brickwork or tiles. (c) Grate Area For the common form of horizontal bar-grate the recognized modern rule is