Modern Gasworks Practice

132 MODERN GASWORKS PRACTICE RETORT-BENCH EXPLOSIONS Though serious damage resulting from the explosion of producer gas in retort settings is, fortunately, rarely met with on gasworks, it is, perhaps, surprising that this is the case, considering the singularly small amount of attention which is often given to the matter. The infrequency of these explosions is partly due to the fact that a large element of hick enters into the question, but chiefly because they are only likely to occur during the period when. newly constructed settings are under “ slow fixes, ” or when benches are being picked up again for work. Mishaps of the kind, however, are particularly to be guarded against; for, in addition to endangering the limbs of those members of the retort-house staff who may be in the vicinity of the beuch at the time, the resulting damage to the structural work of the s^ting-may be considerable, entailing extensive rebuilding, and, consequently, expense. It is somewhat puzzling to account definitely for the actual source of explosions of this nature, but in the greater number of instances they are the outcome of a. mixture of carbon monoxide and oxygen Unding its way into the setting at a time when the prevailing temperature is insufficient to bring about ignition. What has to be recognized, of course, is that during the time when a setting is undorgoing its preliminary heating up prior to being put into full work, the gaseous firing principle of the furnace is not brought into play, and the fuel is burnt merely as in the old type of “ direct ” fire. That is to say, primary air is admitted, the object being to burn the fuel to carbon dioxide in the furnace, and not in two steps, as is eventually to be done. If this could be ensured, th.en an incombustible gas would alone be circulating in the setting; but what usually takes place is that the primary air during its passage through the shallow bed of fuel is only partially converted into CO 2, whilst some CO is afterwards formed. At the same time air may pass through (particularly if the fuel-bed is very uneven) entirely unchanged. Thus we have a mixture of CO and oxygen travelling throughout the setting. The general practice adopted during “ slow fires ” is to shut off the secondary-air slides completely ; but in some cases it is preferred to admit a small supply through these ports, for it is claimed that in this way a better draught is created, which ensures the more thorough. removal of steam from new brickwork, etc. If secondary air is admitted, however, it certainly adds to some extent to the possibilities of an explosion in the setting itself. How Danger is Avoided Explosions of producer gas, botli minor and severe, are usually the outcome of carelessness on the part of the man responsible for the supervision of the settings, or are due to the non-observance of certain practical rules which have come to be recognized as the result of everyday experience. The usual cause to which the trouble can. be traced is that of sealing up the producer charging door before the setting has reached a sufficient degree of heat. Some explanation of this is, perhaps, necessary. First, when the charging hole is uncovered any CO resulting from the com-bustion of the fuel, instead of travelling onwards through the nostrils and thence