Investigation of non-uniform characteristics in a 300 MWth circulating fluidized bed with different coal feeding modes

Abstract

Circulating fluidized bed (CFB) has been practised in many engineering fields, but the non-uniform characteristics deteriorate combustion performance and system control. In this study, the improvement of external-loop and in-furnace non-uniformity of a 300 MWth industrial-scale CFB with multiple cyclones by a dual-side coal feeding mode was numerically quantified. The results show that the pressure is non-uniformly distributed among three external loops, where the pressure in the middle loop seal is lower than that in the corner loop seals by 4.5 %. The pressure gradient positively correlates with the solid holdup. As compared with the traditional single-side coal feeding mode, the dual-side coal feeding mode: (i) promotes the final mixing degree by 11.15 %; (ii) extends the residence time of coal particles by 10.3 %; (iii) reduces the magnitude and fluctuation of the horizontal solid flux by 28.5 % and 77%, respectively; (iv) narrows the temperature range and reduces the mean temperature by 7 °C; (v) enhances the combustion of coal particles by consuming more O2; (vi) decreases the concentrations of SO2 and NO by 3 % and 5 %, respectively. The present study shows the superiority of the dual-side coal feeding mode to the traditional single-side coal feeding mode in the optimization of CFBs in practical industrial processes.