Biomass circulating fluidized bed boiler

The utility model provides a biomass circulating fluidized bed boiler, which comprises a hearth of the fluidized bed boiler, a cyclone separator, a treatment tower, a bag-type dust collector and a chimney, a flue gas circulating pipe is connected between an exhaust fan and the chimney, a flue gas circulating valve and a circulating fan are arranged on the flue gas circulating pipe, an air inlet is arranged at the lower end of the hearth, and an air outlet is arranged at the lower end of the circulating fan. A flue gas recirculation nozzle is arranged on the inner wall of the hearth on the upper side of the air inlet; and an air outlet of the circulating fan is connected with the flue gas recirculation nozzle. By means of tail smoke circulation, on one hand, the emission amount of smoke is reduced, emission of nitric oxide is reduced, on the other hand, circulating smoke is introduced into the hearth again, the amount of air entering the hearth is reduced through the smoke, and due to the fact that the content