The Mechanical Handling and Storing of Material

STORING OF COAL AND OTHER MINERALS 651 consideration is to deposit it gently with the minimum of drop, and when once deposited, break bulk as rarely as possible. It is impossible to prevent some breakage of the coal however gently it may be handled; mechanical handling, being inflexible, necessarily involves a numbei of transfers from hopper to shoot and from shoot to mechanical appliance, and so forth, but the fall at each point of transfer can and should be reduced to a minimum. Coal is handled with care at the colliery, and after journeys of often hundreds of miles is delivered in good condition containing, perhaps, only a small percentage of slack ; it is paid for at a rate proportionately high to its size and, if carelessly handled at the storage installation, it arrives at the furnace door at a greatly reduced value. American coal, as has already been mentioned, is harder than our average coal, and that used for railway engines in that country is also smaller, but notwithstanding this the breakage at some of the American coal stores is appalling. At the Session of the International Railway bud Association, held at Chicago in May 1913, this subject was discussed at great length, particularly in view of the modern locomotive coaling stores. Some details concerning a case of the Chicago Rock Island and Pacific Railroad revealed the fact that some coal which was delivered from the colliery with 42 to 45 per cent, of slack contained, after being handled by the coal plant, 72 to 75 per cent., and in the case of lump coal which contained only 25 per cent, of slack this was increased to 65 per cent. This incidentally shows how much lump coal suffers from rough treatment. Coal handled by grab or shovel-bucket must of necessity suffer some damage, and paiticularly.so if it has to be grabbed, twice,r on delivery and on withdrawal, as may be the case with a stock pile without subterranean facilities; if large grabs are chosen, however, and those with gentle action, it may be possible to effect no more breakage than if the coal were transferred with a shovel by hand. Spontaneous Ignition.—An important precaution when storing coal is to guard against spontaneous ignition, and to this end it is usual not to heap bituminous coal higher than from 15 ft. to 20 ft., but this must, however, depend upon the nature of the coal. Ihe Western 1*uel Co. on the great American lakes store bituminous coal 30 ft. high. Warm rain during or shortly after stacking coal, as well as the compression, and the effect of dumping from some height, are elements of danger. The height of storage does not apply so much to silos as to stock heaps, as in the former the coal is withdrawn from the bottom and the whole mass is, therefore, set in motion whenever some is withdrawn. 1 his also applies to piles with culverts beneath. Some useful points on this subject were given by Mr Irving, the President of the Southern Association of Gas Managers.1 At the Stapleton works of the Bristol Gas Co., of which Mr Irving has charge, all coal is stored in the open. The stores are 450 ft. long and 72 ft. wide, paved with blue brindle bricks and thoroughly drained. Coal is delivered into the stores by two sets of overhead rails, carried on steel girders, which are supported by iron columns. I he coal is dropped from hopper-bottomed railway trucks to the ground, and is stored to a depth of about 20 ft. During the past few years the Bristol Gasworks have been troubled with cases of spontaneous combustion. Great care has always been taken with the coal stocks, especially with those coals that were known to have any tendency to heating. A number of 1-in. pipes, to each of which a letter or number is attached, were usually inserted throughout the stock of coal, into which a thermometer could be lowered, and the temperature observed and daily recorded; and when any part of the stock gave indications of heating, that portion was worked out as soon as possible. It has rarely 1 From The Iron and Coal Trades' Review.