A coal stacker that handles loads as high as 7,000 tons per hour (normal operating rate is 6,000 tons per hour) was installed recently by FMC at Ontario Hydro's Nanticoke, Ontario, generating station on the north shore of Lake Erie. This capacity allows it to keep pace with the highest unloading rates of any self-unloading coal carrier on the Great Lakes. Said to be one of the largest stackers of its kind, it has a maximum slew angle of 250 degrees and produces a crescent-shaped pile of coal 60 feet high representing storage of about 80,000 tons.
This is one of two unloading systems serving a highly complex coal-handling facility. FMC of Canada's Material Handling Systems Division in Scarboro, Ontario, designed and built the new coal-handling and stockpiling system, which includes a dock hopper with dust hood, two 84-inch-wide belt conveyors totaling 1,750 feet, and FMC's massive luffing and slewing coal stacker.
The stacker is unique in many respects. It is impressive for its dimensions as well as the 7,000-tph capacity. It stands 92 feet high, and the base covers an area of 2,403 square feet. The boom is 173 feet overall, and the 84-inch-wide boom belt can be luffed from a 12½-degree declined position to an 11-degree incline. The belt travels at a speed of 750 feet per minute.
With the exception of the conveyor drive, the stacker is entirely hydraulically driven. Luffing action is by hydraulic cylinder, and slew action by variable-speed drives transmitting torque to a rotating mast structure.
The operator's cabin is located on the rotating mast structure, well above the luff axis, providing a wide field of view. Cabin controls provide for either manual or automatic operation. Control also can be transferred to the central control room, but mandatory manual control is established during critical phases of the stocking-out operation — for example, where the pile is reaching maximum height.
Automatic control is achieved by a programmable controller that is linked to all safety devices and monitoring systems. It is capable of initiating sequential startup or shutdown of the entire system or portions of it. Telephone communication is available from all main points to the self-unloading vessel.
Safety devices and detectors include plugged chute detectors, motion sensors to insure correct sequencing, belt side-travel switches, and belt penetration devices to detect possible belt damage. The integrity of the hydraulic systems is monitored by a series of temperature and pressure detectors.
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