Straw feeding system for grate firing

BWE has developed an innovative and efficient system for grate firing of straw in biomass boilers.

Depending on the size of the boiler, the firing system consists of one or more firing lines fed by a bale distribution system which receives the bales from a straw barn with automatic cranes. The firing line ends at the inlet to the grate.

The straw bales are conveyed through the fire barriers to the scarifiers. From here the scarified straw is fed on to the water cooled vibration grate where it is burned.

The system is designed for large bales with the following bale size (l x w x h): 2.5 – 3.2 m x 1.2 m x 0.7 – 1.3 m which corresponds to most large square bale makes on the market. A water content in the straw bales of up to 25% is acceptable.
 

A firing line has a capacity 40 bales pr. hour, maximum 10 tph corresponding to approximately 30 MJ/s fuel and includes the following equipment or functions:

• Weighing and moisture measurement of single bales
• Inlet seal gates
• Chain conveyors including a conveyor for feed control
• A bale opener
• A screw stoker for fuel transport to the inlet of the grate
• A water cooled inlet duct
• Dampers inclusive of a water cooled damper close to the furnace
 

BWE designs standing natural circulation boilers for up to 4 straw firing lines. Steam data of up to 120 bar and 540 °C is possible upon request.

A similar system can be applied for other types of biomass.