METHOD OF FLUIDIZED BED COMBUSTION FOR BIOMASS FUEL BURNING AND APPARATUS THEREFOR

摘要

In a fluidized bed combustion for biomass fuel burning in which the alkali content in combustion ash is high, any fusion of combustion ash and agglomeration of bed material are avoided and further any ash sticking to boiler internal parts is avoided so as to increase the fluidity of bed material and to realize smooth and stable operation. Fluidized bed combustion of biomass fuel is carried out by the use of a fluidized bed combustion apparatus including a combustion furnace which has its sectional area of fluidized bed portion set so as to be smaller than the sectional area of free board portion but not smaller than 1/2 thereof; an exhaust gas recirculation line extending from a rear stream of a dust collector of exhaust gas line to a fluidized bed wind box of the combustion furnace; a bed material discharge opening disposed on a side wall of fluidized bed lower part, which bed material discharge opening is connected to a bed material particle diameter sorter, the bed material particle diameter sorter having, connected thereto, a bed material charging opening disposed on a side wall of fluidized bed upper part; and a disposal opening. In this fluidized bed combustion, not only is the air ratio within the fluidized bed set so as to range from 0.2 to 0.9 but also an exhaust gas recirculation is conducted to thereby set the ratio of exhaust gas recirculation flow rate to total air flow rate so as to range from 20 to 80% with the result that while ensuring a ratio between, within the fluidized bed, superficial velocity and fluidization initiation velocity of 2 to 6, the fluidized bed temperature is controlled at 600 to 750°C.