PURPOSE: To ensure fuel gasification and the combustion of collected fine powder, by a method wherein a first dispersing plate for supplying solid fuel is provided outside a ring partition wall and a second dispersing plate for supplying collected fine powder is provided inside the wall, whereby a gasifying reaction zone and a combustion zone are formed.

CONSTITUTION: Solid fuel particles are dropped from a feeder 4 onto a first dispersing plate 28 and dispersed. Fine powder from a dust collector is mixed with air 36, and supplied through a nozzle 32 onto a second dispersing plate 29. Mixed gas 12 consisting of air, oxygen and steam is introduced into a tuyere box 10. The gasification of the mixed gas through pores 28A proceeds because of a high flow rate and a low air content, and a gasifying reaction zone L having a low air content is formed. Coarse particles which go over a partition wall 30 and are introduced onto the second dispersing plate 29, are returned through a communicating hole 31 to the first dispersing plate 28. Since the flow rate of the mixed gas through pores 29 is low and air content in the gas is high, the fine powder is rapidly oxidized and a combustion zone H having a high air content is formed. The fine powder is not flown off toward free board above a fluidized bed 7 immediately after the fine powder is blown into the bed. Gas streams from the gasifying reaction zone L and the combustion zone H are mixed together, and a gas stream-mixed zone M is formed.