Effects of bluff-body cone angle on turbulence-chemistry interaction behaviors in large-scale semicoke and bituminous coal co-combustion

Abstract

During large-scale semicoke and bituminous coal co-combustion, the behaviors of turbulence-chemistry interactions were experimentally and numerically used to investigate the effects of char burnout and NOx emissions in a pilot-scale bias combustor at different bluff-body cone angles (α). The results show that with increasing α the main reaction zone moves upstream significantly, and a widened flame and uniform temperature profile are obtained due to enhancing the internal flue gas recirculation. An increase in α can improve the char-oxidation reaction, and further results in increased pore structures and char burnout ratios. For all cases, the Dat (homogeneous Damköhler number) maximum values are below 0.50. The Da,O2, Da,CO2 and Da,H2O (heterogeneous Damköhler numbers) values are within 0.670–1.207, 0.004–0.017 and 0.001–0.004, indicating that the char oxidation reaction is dominated by diffusion/kinetics, while the char gasification reactions are controlled by chemical kinetics. However, both reactions tend to be kinetically-controlled with increasing α. The NOx emissions decrease by 27% at the α = 34° value, because a large cone angle can enlarge the combustion reduction zone and enhance the oxygen diffusion rate. The findings can provide deep insight into the turbulence-chemistry interactions and its effect on NOx emission characteristics of semicoke co-combustion in a bluff-body tangential burner.