The behavior of flame front with heating mechanisms in two entrained-bed coal reactors

Abstract

An experimental study was carried out in two laboratory-scale coal reactors to investigate the effect of heating rate on a pulverized coal flame. Each reactors had different heating mechanisms. For reactor A losing large heat through transparent quartz wall, pulverized coal particles were ignited by secondary air of 1050 K. Flame front could be visualized through the transparent wall. Reactor B was insulated with castable refractory to minimize the heat loss through the reactor wall and accompanied with secondary air of 573 K. Flame front was estimated from the gas temperature and species concentration measured using R-type thermocouple(Pt–Pt/Rh 13%) and gas chromatograph at various coal–air ratios and swirls. The flame front position was closely related with heating rate. The heating rate for lifted flame was of the order of 10 4–10 5 K/s and for ignition at least over 10 4 K/s. The heating mechanism had little impact on the extinction limits. The swirl forced the flame front to move toward the upstream by the rapid mixing of coal and air. However, it slightly increased the carbon conversion and the cold gas efficiency only below immediately fuel-rich conditions due to relatively low reactor temperature and a little increased residence time.