Influence of operating conditions and coal properties on NOx and N2O emissions in pressurized fluidized bed combustion of subbituminous coals

This experimental study is aimed at finding effects of operating conditions in PFBC on nitrogen oxide emissions for subbituminous coals differing in ash content/composition, combustion/gasification reactivities and in particle size distribution. The experiments have been done on a smaller laboratory apparatus with ID = 8 cm. The effects of operating pressure (0.1-1 MPa), temperature of the fluidized bed (800-900 degreesC), freeboard temperature and oxygen concentration (3-10 vol.%) on the nitrogen oxides emissions are relatively complex, coupled with temperature of burning coal particles. The coal ash content/composition (esp. CaO and Fe2O3) and fly ash freeboard concentration play an important role in formation/destruction chemistry of both NO and N2O. The NOx emissions decrease with increasing operating pressure at the same volumetric oxygen concentration and temperature. Temperature, volatile content, reactivities of coals and ash composition are the most important factors for N2O emissions. The N2O emissions are either almost constant or can exhibit a maximum at increasing operating pressure. Influence of increasing oxygen concentration on NOx and N2O emissions is more pronounced at lower operating pressures, esp. for the less reactive, medium ash coal. The particle size distribution of the coal (influence of coal dust) can cause characteristic changes in NOx and N2O emissions in PFBC, esp. at lower combustion temperatures (800-840 degreesC). The emission changes are dependent on ash properties/composition. (C) 2003 Elsevier Ltd. All rights reserved.