Modern Gasworks Practice

216 MODERN GASWORKS PRACTICE plants the generator linings are subjected at the top to abrasion by the descending fuel, and by the small particles whirled about by the blast, and also to the efl'ect of tools used for removing clinkers. The central combustion zone is very hot, owing to the preliminary combustion of the fuel. There is slagging action due to the ash of the fuel, some abrasion due to the fuel, and, with various kinds of fuel, serious abrasion caused in the removal of clinker. The lower portion of the generator, though not so hot, is subject to the effects of steam on the up-run, the hot gases nn the down-run, and the effect of tools in removing the clinker periodically. The connections between the generator and the carburettor are subjected to high temperature, erosion due to fuel particles passing through quickly, and some slagging action from the ash. The lining bricks of the carburettor are subjected to only moderate temperature ; but the chequer-bricks and the crown are exposed to a temperature of perhaps 1,200° C. during the biasting, and are then deluged with a spray of cold oil during the gasmaking period. This results in an accelerated spalling action 011 the chequer-bricks. The two important points in the selection of materials are the generator lining and the chequer-bricks. In the selection of material for the generator lining, the relatively high temperature (due to the combustion of fuel), and the action of the ■clinker as a slag, have to be considered. The fusing-points of the same askes ranged from 1,090° to 1,660° C. The very great variation results in the development of three distinct classes of clinker. The as lies with high fusing-points tend to build-out on the sides of the generator, thus considerably reducing the working area. This type of clinker does not seriously deteriorate the lining in a Chemical sense ; but the abrasion in barring-down the deposit is very destructive. The askes with. moderate fusing temperature for the most part collect on the grate, forming a compact mass which can be removed with-out much difficulty. Th.e hsIics with a low fusing-point—generally high. in iron and rather low in alumina—seriously attack the linings, and also collect on the grate to form a hard compact mass, which is difficult to remove when cold. In extreme cases they may even melt, and form stalactites in the ash-pit. The usual lining block is of fireclay. Silica materials have not been generally ■successful, because of extreme and very frequent changes in temperature during use. Experimental trials with magnesite have not been. very successful, because of spallmg. Recently, magnesite blocks enclosed in a thin iron casing seem to have been somewhat more successful. Chrome bricks have been tried ; but snfficipnf. ■data are not as yet available. Zirconia bricks are very expensive ; but their special properties may, perhaps, warrant more extensive trials. Carbonmdum materials have been tried. as solid bricks and as veneered. bricks. The solid brick is much stronger ; and its extra cost will probably be compensated by a longer life. With all these neutral materials the adhesioii of th.e slags to the sides is elimmated, along with possible corrosive action ; and consequently less time is required for Hüning the sets. For chequer-bricks to resist spalling action (due to alternate heating and cooling), it has been found that bricks with rather coarse grog and a minimum amount of