The Mechanical Handling and Storing of Material

CHAPTER XLI STORING OF COAL AND OTHER MINERALS IN STOCK HEAPS AND SILOS Coal and other minerals which do not materially deteriorate through the influence of the weather when stored in the open are generally accumulated in stock heaps or piles, over which mechanical equipments are erected for their deposition and withdrawal. Other materials, such as salt and chemicals, are similarly stored but under cover, as also is coal for household purposes. The mechanical equipment varies with the nature of the material. Coal and coke requiring gentle treatment to prevent breakage should preferably be deposited by con- tinuously working conveyors and elevators, and less frequently by intermittently working devices, such as grabs suspended from telphers and other mono-rails, or by the Hunt Automatic and other self-unloading railway trucks. This naturally also depends on the coal itself, whether it is in large or small pieces, and on the degree of friability ; American coal being less friable, for instance, than the average English coal. Materials such as ore, which are not affected in value by breakage, are generally handled by intermittently working devices. The withdrawal or reclaiming of the stock from the pile is likewise effected in various ways, which are principally influenced by the friability or otherwise of the materials. Those immune from deterioration by breakage are generally withdrawn by grabs or shovel-buckets, whilst the best method of withdrawing coal and coke is by continuously working conveyors located in culverts beneath the pile, and in such cases the mineral store is not infrequently heaped over a ferro-conqrete hoppered structure, from the lowest portion of which it is withdrawn through openings fitted with gates which com- municate with the culvert and its conveyor. There are, of course, exceptions to this, and friable materials are sometimes both deposited and withdrawn by grabs or shovel- buckets (suitable grabs of large capacity do not injure average coal more than some continuously working conveyors), as such installations are less costly in the first instance, the same appliance being used for both stocking and reclaiming. Local conditions also play an important part in the choice of the most suitable means to be employed. For instance, where coal is to be unloaded by grab from barges and delivered on to a stock heap, it may be better to retain the coal in the grab, telpher it to the pile and there gently lower it, than to transfer it to a conveyor, as this would cause more damage. On the other hand, if the coal arrives by rail and is unloaded by a tip, an elevator and conveyor, or combination of the two, would be chosen.. When varying levels of ground are available and favourable, or sufficient space, so as to run sidings up trestle-work or embankments at a gentle incline, it may be possible to bring the material in hopper wagons to rails above the store or silo and so discharge into them and withdraw from culverts, as already mentioned. Or if the store can be arranged on the hillside, both loading and unloading can be most conveniently and economically arranged. Whatever general arrangement may be chosen for storing coal, the most important 650