Grate firing

Grate firing was the first combustion system used for solid fuels. It now is used mainly for burning waste and biomass, but also for smaller coal furnaces.

• Capacities 0.3 to 175 MWth in industry and CHP
• Fuel fired per grate area 1-2 MW/m², maximum grate area 100 m²
• Grates are typical only suitable for coarse particles, for fine particles a spreader is required, increases max. capacity
• Primary air through the grate (also used for cooling) and secondary air

Types

travelling grate in an old steam boiler

Travelling grate

A moving grate which is covered with a fuel layer, 10-30 cm. Power control by means of varying the grate velocity

Reciprocating grate

For ash-rich, low calorific fuels like municipal waste, arrangement of stationary and moving grates -> conveying and mixing (forward-moving type or reverse-action grate)

Vibrating grate

Water cooled membrane wall, with holes for air. For burning coal or wood.

Grate area

The grate area is the area of the grate (length x width). The larger the grate area, the more fuel can be burned per hour. The amount of fuel burned also depends on the fuel or bed movement velocity.

See also

• Fluidised bed firing
• Pulverized fuel firing