Heterogeneous reactions behaviors of pulverized coal MILD combustion under different injection conditions

Abstract

The behaviors of heterogeneous reactions during pulverized coal MILD combustion was quite different from that during conventional mode, which made an unclear effect on char burnout and NOx emissions. The present works aimed to numerically study the behaviors of pulverized coal combustion under different injection conditions, i.e., velocity and temperature. Results showed that, compared with preheating temperature, the effects of jet velocity on char combustion behaviors were more significant. As the jet velocity increased, the region of char burnout shrank and overall average burnout rate weakened, also the share of char consumed by O2 gradually raised up and by gasified agents fell down. For all cases, char reacting with H2O and CO2 accounted for >28%, and the peak values of Dat were below 0.65. The ranges of Da,O2, Da,CO2 and Da,H2O were 0.5–1.0, 0.002–0.012 and 0.0004–0.003 implying the diffusion/kinetics-controlled for char-O2 reaction while diffusion-controlled for char-CO2 and char-H2O. The location of the inflection points that the kinetics effect shifted to diffusion effect moved toward upstream with the velocity and temperature increasing. Further low NOx emissions could be realized by enhancing gasification reaction that were depended on the operational conditions.