Modern Gasworks Practice

378 MODERN GASWORKS PRACTICE Under any circumstances, care should be taken to see that the store is not situated too near to the heat of the retort beuch. It is with stores of the closed type that particular care is necessary with regard to the use of water. When coal is stacked in a bin and takes fire, the application of water to the red-hot carbon will in all prob-ability be followed by the formation of water gas. This gas, in addition to being a source of danger to the men, owing to its poisonous nature, may mix with a sufficient quantity of air to form an explosive mixture, which might conceivably result in the destruction of the bin. When coal is stored in covered bins some arrangement should. be provided by means of which the affected. layers, which are frequently at the base of the heap, may be summarily removed. For this reason the more recent practice of constructing a small tunnel from end to end of the store and below floor level is to be strongly advised. The tunnel is made sufficiently large to take a conveyor, and by means of pouches fitted with sliding doors placed at frequent intervals the coal in the affected area can. be quickly removed and carbonized. An arrangement of this nature is seen in Fig. 260. The Storage of Coal under Water Owing to the tendency of stored coal to fire the practice of submerging the heaps in water has been adopted. In such, cases special reservoirs, usually con-structed of reinforced concrete, are required. The method has. so far, been confined almost solely to America and the Continent. When submerged, the coal is pro-tected more adequately than if it were housed; and no matter what the weather conditions, the variation in temperature of the mass will be comparatively small. It is now generally recognized that the gases occluded in the pores of the coal—more particularly oxygen—are indirectly the cause of heating and deterioration. The escape of the oxygen should therefore be arrested as far as .possible. By immersing coal and keeping it contimially sealed this condition is fulfilled, the gases being more or less confmed, whilst little or no oxidation takes place. Breaking up of lumps and pulverization are also considerably reduced, because the water forms a cushion between the various pieces, thus lessening the effect of the movement of the lumps one on another. The better physical condition of the coal is, however, probably due, in part, to the absence of heat, which in itself is to a great extent the cause of the opening out and disintegration of the larger pieces. There is no limiting depth for the heaps of coal when immersed, and accordingly a considerable saving of space can be effected ; in fact, by adopting the wet method the capacity per unit of ground area could be easily doubled. The most undesirable factor in comiection with the system is that of expense. One of the largest reservoirs for storing coal in this way is that on the banks of the Oder, at Stettin, where 20,000 tons may be submerged. Another series of tanks for storing coal, at Omaha, U.S.A., are 22 feet in depth, with the side walls carried on piles. Piles are also driven under the whole of the floor area at a pitch of 5 feet, and are capped with square slabs of concrete on which the floor rests. The side walls of concrete are about 2 feet thick at the top and 4 feet 6 inches at the bottom, whilst the concrete floor is protected from the bite of the coal “ grab ” by means of embedded rails.