Fluidized bed combustion of some woody biomass fuels

In this study, the experiments of comparing cedar pellet, cypress pellet, and cypress sawdust combustion in a bubbling fluidized bed combustor (BFBC) was carried out. To improve the combustion efficiency and avoid the agglomeration, the porous alumina sand was used as bed material instead of conventional silica sand. Experimental results indicated that pellet can be sufficiently burned in the BFBC, and the CO emission was only 50-188 ppm. Meanwhile, the unburned carbon in fly ash was considerably limited even neglected; both the unburned carbon in fly ash and CO emission (3,700 ppm) was significantly high during sawdust combustion. Moreover, it was difficult to operate the BFBC above 650 degrees C with the sawdust. Therefore, direct combustion was not a good utilization method for sawdust. It was also observed that volatile matter released from pellet volatilized and mostly burned in the dense zone due to the porous alumina. The effect of operation parameters like temperature and fluidized velocity on the pollution emission and combustion characteristic was also evaluated. High temperatures can promote the combustion efficiency, while SO(2) and NOx emission is independent to temperature. As for fluidized velocity, the optimum fluidized velocity in the tests is about 0.07 m/s.