Circulating fluidized bed boiler

The invention discloses a circulating fluidized bed boiler, which comprises an air distributor and a hearth surrounded by water cooling walls, wherein the air distributor comprises an air distributing plate, a plurality of air pipes passing through the air distributing plate to extend and air caps arranged on each air pipe, and a hole is formed on each air cap and communicated with the air pipe; in the central region of the air distributing plate, the flow area of the air distributor is smaller than those of other regions; a transition layer is arranged on a corner part between two adjacent water cooling walls and generates arc transition between the adjacent water cooling walls. By reducing the flow area in the central region with a thinner bed material, the aims of grading air distribution and uniform fluidizing are fulfilled, so that the efficiency of the circulating fluidized bed boiler is improved and the problems of air cap wear and slag leakage can also be solved radically. Moreover, the arc-shaped tra