Circulating fluidized bed boiler

The invention relates to a circulating fluidized bed boiler which comprises a hearth and a material returning device. The hearth is used for combusting granular fuel, a dense-phase zone and a dilute-phase zone which are communicated with each other are arranged in the hearth, and the dilute-phase zone is located above the dense-phase zone; the material returning device is provided with a material returning inlet end and a material returning outlet end, the material returning inlet end and the material returning outlet end are both communicated with the dilute-phase area, and the material returning inlet end is located above the material returning outlet end, so that the granular fuel in the area, away from the dense-phase area, in the dilute-phase area can be conveyed to the area, close to the dense-phase area, in the dilute-phase area through the material returning device. The fuel circulating through the material returning device can be directly introduced into the lean-phase area, the granular fuel can qui