To attain smooth and stable operation by eliminating melting of combustion ashes and coagulation (agglomeration) of a fluid medium, and eliminating adhesion of ashes into a boiler to improve the flow of the fluid medium in biomass fuel burning fluidized bed combustion with high alkali components in the combustion ashes.
The fluidized bed cross section of a combustion furnace is set to 1/2 of freeboard cross section, and an exhaust gas recirculation line is provided from the dust collector back wash of an exhaust gas line to a fluidized bed air box of the combustion furnace. Further, a fluid medium discharge port is provided in the lower part sidewall of the fluidized bed and connected to a fluidized bed grain size discriminator. A fluid medium charging port provided in the upper part sidewall of the fluidized bed is connected to the fluid medium grain size discriminator, and a fluidized bed combustion apparatus provided with a disposal opening is used to carry out fluidized bed combustion of biomass fuel. In the fluidized bed combustion, an air ratio in the fluidized bed is set within a range of 0.2-0.9, and the ratio of exhaust gas recirculation flow to the total air flow in performing exhaust gas recirculation is set within a range of 20-80%. A fluidized bed temperature is thereby controlled to 600-750°C while ensuring the ratio between superficial velocity and incipient fluidization velocity to 2-6.
OMURA YOSHITAKA
IKEDA KIYOTO
TANIGUCHI KOJI
MURAOKA TOSHINORI
