A two-stage swirl-flow fluidized bed combustor（FBC） has been devised to increase the combustion efficiency. The combustor consists of a first stage and a second stage with overflow drain, respectively. The combustion gas, including fine particles from the first stage, is tangentially introduced into the second stage through 4 nozzles, which are inserted into holes drilled in the second stage distributor, and secondary air is axially introduced through multiorifices drilled on the upper plate of the second distributor. The second stage is equivalent to a "axial-plus-tangential entry swirl generator", so that fine particles in the second stage are thrown to the wall under the influence of centrifugal forces in the swirl-flow, decended, collected on the second distributor, fluidized by the secondary air, and burnt within the second stage. Hot bed tests are carried out using low-grade anthracite (gross heating value=2,810 kcal/㎏, particle diameter<2 ㎜).
Due to the effect of swirl-flow, the amount of fines elutriated and the unburned carbon loss are considerably reduced in the two-stage swirl-flow FBC as compared with the same size single-stage FBC. Combustion efficiency is increased by about 20 % as compared with the same size single-stage FBC.