Modern Gasworks Practice

GAS-MAKING AND OTHER COALS 375 pile the less heat-dissipating surface there is exposed in proportion to the heat generating capacity of the pile. Twelve feet in height is a common limit. Dealing with a Burning Heap The undue heating of a coal heap is usually accompanied by “steaming ” and an offensive smell, due to the escaping hydrocarbon vapours. When these are noticed, the usual procedure is to turn the hose on to the apparent seat of the trouble and drown out the fire. When a fire does occur, however, it is necessary to avoid the use of water until the area actually affected has been located. The coal round about this area should then be dug out, and the smallest possible quantity of water made use of. By far the best practice is to get the afiected coal away to the retort house and carbonize it as soon as possible. A coal heap should be kept continually under observation. The most usual means of recording the temperature is thai of inserting 1| to 2-inch pipes, one end being knocked down to a point. A thermometer—attached to a cord—can then be lowered into the pipes and the temperature noted. As the drop in temperature while the thermometer is being withdrawn is likely to be somewhat considerable, a more accurate reading will be obtained if a maximum thermometer is used. When greater accuracy still is required, it is necessary to use a low-temperature pyrometer with electrical Connections. A great deal of trouble will be saved if the temperature pipes are suspended in position before the heap is made, for the task of forcing tliem down into an existing heap is certainly tedious. An idea from America is that of a coal auger, th.e head of which contains a small maximum thermometer. It is claimed that the point of the anger can be driven 20 feet in from three to five minutes, and about ten minutes is required for the thermometer to attain the tem- perature of the surrounding coal. Temperatures taken in this manner have been found to be several degrees higher than by the pipe method—the difference being ascribed to the circulation of air in the pipe. When the temperature rises above 36° C., the upper layers of coal at least should be removed. Disturbance of the heap by driving in rods, etc., to the seat of the fire should be avoided, for this merely has the effect of inducing air currents, and hence provides an additional supply of oxygen. When a fire actually breaks out, some prefer to use sand instead of water. While water cools the material and reduces the temperature below ignition point, sand smothers the fire and cuts ofl' the supply of oxygen. Sand certainly recom-mends itself for use in cases in which the action of water is known to have a dele-terious effect upon the surrounding coal. If the fire were large, however, it would afford but little check. In an investigation by the Experimental Station of the Illinois University into the storage and handling of coal many instances were supplied in reply to inqturies, that showed liow seldom water alone proves effective in subduing fires in coal-stores, chiefly owing to the difficulty of supplying it in sufficient quantities to cool the entire mass. The following example of the successful use of water is there-fore all the more interesting :—