Study of NO Emission from a Pilot Scale Vortexing Fludized Bed Combustor Using Response Surface Methodology

Abstract

All the experiments were conducted in a pilot scale vortexing fluidized bed combustor (VFBC), an integration of circular freeboard and rectangular combustion chamber. The dimension of the freeboard is 0.75 m LD. and 4.6 m in height. The cross section of the combustion chamber is 0.8×0.4 m2 and the height of the combustion chamber is 1.35 m. The secondary air injected nozzles were installed tangentially at the bottom of the freeboard. Coal was used as the fuel. Silica sand was employed as the bed material. Acetic acid was used as the reductant to reduce NO emissions. The operating conditions, such as the stoichiometric oxygen in the combustion chamber, the bed temperature and the injecting location of acetic acid, were determined by means of response surface methodology (RSM), which enables the examination of parameters with a moderate number of experiments. In RSM, the NO emission concentration at the exit of the VFBC is used as the objection function. A mathematical model for the NO emission as a function of the operating conditions was empirically proposed. The results show that NO emission increases with the stoichiometric oxygen in the combustion chamber and the bed temperature. NO emission can be decreased by injecting the acetic acid into the combustion chamber. The NO emission decreases with the height of the acetic acid injecting location above the distributor. Meanwhile, the bed temperature has more important effect on the NO emission than the other two factors.