The Mechanical Handling and Storing of Material

STORING OF COAL AND OTHER MINERALS 655 coal storage plant consists of a number of these groups, which may be of equal or of varied capacities. The shear trusses are fixed to correspond with the angle of repose of the coal, the front truss of each group, i.e., the truss adjacent to the track-hopper or receiving point, containing the conveyor. This conveyor runs in a trough, having for a bottom a continuous steel ribbon about 12 in. wide, which is wound upon a drum at the foot of the truss, and is paid out only as demanded by the formation of the pile ; this feature provides a gentle discharge of the coal and prevents breakage. Modifications of the standard “Dodge” system have been made to meet local conditions. Hillside storage has been increased by mounting the trimmer conveyors on cantilever trusses, so as to fully command the storage area after the initial and com- paratively small gravity capacity has been reached. Where a continuous or oblong pile of maximum capacity is needed, instead of a conical one, a travelling trimmer is used, supported at the lower end on a power-driven truck, and at the upper end on a column-supported track. Stocking or reclaiming is accomplished as in the standard group plant; the reloading machine being of the traversing instead of the pivotal type. Where climatic severity makes covering of the coal necessary, the “ Dodge ” system has been found especially adaptable. A prominent installation of this kind employs a circular building with trussed dome-shaped roof. The coal is brought to the dock by boat, and unloaded by a tower hoist, from which it is spouted by gravity to the chute of the trimmer conveyor. The construction of the trimmer permits it to be mounted on one of the roof trusses of the building. The reclaiming from the pile is effected by means of the pivotal reloader, which commands the inner circumference of the building, and delivers through floor openings to a push-plate conveyor running horizontally in a tunnel, from a position beneath the centre of the pile to a point outside the building. From here it rises on an incline to the reloading tower from which its discharge is transferred through screening chutes to cars. No exterior bracing is required for these buildings, as they are strengthened against bursting pressure from the mass of coal by a continuous circular bulkhead, which is supported free of the floor by anchor bolts extending inwardly from the I-beam posts of the annular wall. In another type of covered storage plant the house area is of rectangular form, the building being divided to store equal quantities of egg, stove, and nut coal, the aggregate capacity totalling up to 100,000 tons. The equipment consists of three standard “ Dodge ” trimming conveyors for stocking the coal; three open-top carriers running in underground tunnels for reloading; three reloading towers provided with screens; three gravity discharge transfer conveyors; and three screenings conveyors. The three trimmer conveyors and three transfer conveyors, or three reloading conveyors and three transfer conveyors can be operated simultaneously. Each machine handles 1,500 tons per day of ten hours. The power plant for a “ Dodge ” system installation may include steam or electrical equipment, the generating outfit comprising a central unit from which distribution may be effected through a piping or wiring system to convenient points for direct operation. The equipment of a large plant of eight piles of 60,000 tons each includes four 16-in. by 20-in. 150 H.P. engines, so located that one engine drives the machinery of each two-pile group. In a 240,000-ton plant two 225 H.P. alternating current, 440-volt, 25-cycle, 3-phase motors drive the machinery of the 60,000-ton piles, while that of the 30,000-ton piles is controlled by motors of 150 H.P. In 1906 a 200,000-ton covered anthracite storage plant on this system for stocking coal 60 ft. high was installed on Section 2 of the North-Western Fuel Co.’s Superior