Waste coal: how to avoid flow stoppages during storage and handling

Typically, waste coals are reclaimed from uncovered piles or ponds and transported to a power plant either to sit in another exposed pile or in a large storage silo before being conveyed into feed bunkers to feed the power boilers. The article explains how best to avoid problems related to flow stoppages such as spontaneous combustion when handling gob (bituminous and subbituminous) and culm (anthracite). Common problems are no-flow, due to arching (when an arch-shaped obstruction forms and prevents discharge) and rat-holing (when flow occurs in a channel above the outlet). To achieve mass flow, the sloping hopper walls must be steep enough and sufficiently low in friction for a particle to slide along them and the hopper outlet must be large enough to prevent arching. Equipment is best designed to satisfy flow properties of the particular materials being handled but if the plant is already built, problems can be solved by changing the bulk solid (by minimising moisture, increasing particle size etc.), changing the operating procedures or changing/modifying the equipment (hopper, chute or feeder). 1 ref., 4 figs.