Co-firing characteristics of rice husk and coal in a cyclonic fluidized-bed combustor (Ψ-FBC) under controlled bed temperatures

This study extensively investigated temperature and emission characteristics, and the performance of co-firing rice husk with coal in a cyclonic fluidized-bed combustor (Ψ-FBC) of 125 kWth nominal capacity. The Ψ-FBC integrated the distinct features of cyclonic/vortex and fluidized-bed combustion. Fluidization, without any inert material, can be accomplished by the stirring blades and vortex ring. The combustor was equipped with a multi-passes water coil to regulate the bed temperatures, varying 800-900 °C. Rice husk was co-fired with coal, a supplementary fuel, with coal blending ratios of 0-25% by thermal basis. The radial temperature profiles displayed vortex combustion along the wall, while the axial temperature profiles suggested a well-mixed condition in the lower part. The large depletion of O2 and proliferation of CO in the lower part revealed vigorous combustion beneath the vortex ring. A reducing atmosphere appeared unfavorable to NOx formation. The combustor showed satisfied Ec, mostly >98.5%. The optimum operating conditions with respect to NOx emissions were: (1) the thermal percentage of coal not >20%, and (2) bed temperatures between 800 and 850 °C. Otherwise, NOx emissions would exceed the regulations; even CO and SO2 emissions were well acceptable.