Experimental studies on a novel swirling fluidized-bed combustor using an annular spiral air distributor

This work reports studies on hydrodynamics as well as combustion and emission characteristics of a conical swirling fluidized-bed combustor (SFBC) using an annular spiral air distributor as the swirl generator. In the experimental study on a ‘cold’ SFBC model, hydrodynamic regimes and characteristics of an air–sand bed were investigated for variable bed particle size and static bed height. Depending on the superficial air velocity, the bed exhibited four operational regimes. Based on the results from the ‘cold’ hydrodynamic study, optimum bed characteristics (sand particle size and bed height) and the range of primary air were determined prior to the combustion tests. In the second part of this work, a conical SFBC was tested for firing 80 kg/h rice husk. During the combustion tests, swirl motion of a fluidized bed was induced by primary air injected into the bed through the air distributor and, also, sustained by tangential injection of secondary air into the bed splash zone. Radial and axial temperature and gas (O2, CO, NO) concentration profiles in the reactor were obtained for 20–80% excess air. Effects of operating conditions on formation and decomposition of major gaseous pollutants (CO and NO) in the reactor are discussed. Both CO and NO were found to be reduced significantly in the bed splash zone, resulting in quite low CO and moderate NO emissions from the reactor. High combustion efficiency, 99.4–99.5%, is achievable when burning rice husk in the proposed conical SFBC at 80 kg/h feed rate and excess air of 40–80%.