Grate Firing

Grate firing is an industrial combustion system for solid fuels, used today mainly for waste and biomass and still found in some smaller coal furnaces. Fuel burns on a grate surface fed by primary air through the grate, which also cools it, and by secondary air above, and the grate's length and width set its hourly fuel capacity together with how quickly the fuel bed moves across the surface. Industrial installations range from about zero point three to one hundred seventy five megawatts of thermal output and can process one to two megawatts per square meter of grate, with the largest grates reaching about one hundred square meters. The three main configurations are travelling grates, which control power through the speed of a moving surface, reciprocating grates, which alternate stationary and moving sections for ash rich fuels, and vibrating water cooled grates, suited to coal or wood, and the technology performs best with coarser fuel particles, with finer material needing a spreader to reach full capacity.