Abstract: A reactor for combusting fine-grained solid fuels in a circulating fluidized bed contains a combustion chamber, which is provided with lines which open in the lower portion of that chamber and serve to feed primary air, secondary air and solid fuel. The fluidized bed combustion chamber is divided into compartments by at least one partition provided in the upper portion of the fluidized bed combustion chamber. Each compartment communicates through a passage with at least one solids separator, which is connected to means for recycling solids and communicates with the compartment through a passage.