Simulation of aggregation effects on co-fired biomass-coal ash in an electrostatic precipitator

Abstract

Aggregation of fine ash into larger particles benefits fly ash removal in an electrostatic precipitator. Thermal aggregation, turbulent aggregation, and electrical aggregation of fine ash (derived from co-firing of biomass fuel and anthracite coal) was simulated under different conditions in an electrostatic precipitator. A population balance model and user-defined function in Fluent were assumed to obtain aggregation kernel functions and calculate the aggregation effects on the co-combusted particles. The results show that electrical aggregation had an obvious effect on both micron- and submicron-sized particles. For submicron particles, the effect of thermal aggregation is about ten times greater than turbulent aggregation. Meanwhile, for micron-sized particles, turbulent aggregation is about seven times greater than thermal aggregation. Therefore, particle aggregation in the electrostatic precipitator mainly occurs because of electrical aggregation, supplemented by thermal aggregation and turbulent aggregation. When the flow velocity is 1.0m/s, particle volume fraction is 1.4%, and biomass co-firing ratio is 10%, the effects of all three aggregation processes on ash particles are optimized.