99/02298 Development of coal feeding system for coal gasifier: Kim, J. G. et al. RIST Yongu Nonmun, 1998, 12, (2), 146–153

Abstract

The particle size distribution (PSD) of feeding coal affects the solid concentration distribution, combustion fraction distribution and coal combustion behaviors in the circulating fluidized bed (CFB) boiler. In engineering, the particle size distributions for different feeding coals are determined empirically, such as the mean particle size of anthracite is smaller, and the mean particle size of lignite is larger. But the specific research on the PSD of different feeding coal is still lacking. In the operation of CFB boiler, the PSD of feeding coal is not adjusted. By optimizing the particle size distribution of feeding coal to adjust the mass ratio of fine particles in the dilute zone and coarse particles in dense zone, it is possible to obtain a good solid concentration distribution in the dilute zone and to improve coal combustion performance. This can assure the output of boiler and reduce the carbon content in ash, as well as reduce the friction of boiler and energy consumption of the fan. In this paper, an optimization model of the PSD of feeding coal of CFB boiler was developed, by setting the solid concentration of the furnace outlet and the mean retention time of coarse feeding coal in the furnace as the optimization goal. This procedure is based on the experimental results of primary fragmentation, burnout and ash formation of coal, using wen-chen hydrodynamic model. The optimized PSD of feeding coal had been calculated in some bed inventory, which results in an optimum solid concentration distribution in furnace and lower carbon content in bottom ash. Before and after optimization results showed that when the bed pressure drop was 11.3 kPa, the carbon content in bottom ash was reduced from 2.14% to 0.77%, and the solid concentration in the furnace outlet increased from 2.6 kg/Nm3 to 2.71 kg/Nm3. The calculation accuracy of the model was validated in a1060 t/h CFB boiler.