EXPERIMENTAL STUDIES OF IGNITION BEHAVIOR AND COMBUSTION REACTIVITY OF PULVERIZED FUEL-PARTICLES

A pulse ignition technique, whereby a small mass of fine coal or char particles is fed into a drop-tube furnace, was used to evaluate the ignition characteristics of pulverized fuel particles. Combustion rates were estimated from the ignition temperatures and were compared with rates determined experimentally using a fixed-bed reactor, DTG, and an entrained-flow reactor. Three Australian coals, two chars prepared from these coals and a petroleum coke were used. Coal rank and particle size were found to influence the ignition temperatures of the coal and char particles. However, these effects were reduced at high oxygen concentrations. In pure oxygen, the ignition temperatures of the chars and their parent coals were similar. Heterogeneous and homogeneous ignition theories indicated that at low O2 concentrations ignition was controlled by a homogeneous mechanism, whereas at high O2 concentrations heterogeneous ignition became dominant. The combustion rates of the chars determined by the four techniques were compared at an oxygen partial pressure of 10.1 kPa. The results of the fixed-bed, DTG and entrained flow experiments were consistent with each other and spanned the range of kinetic control from regime I at low temperature (fixed bed) to regime II at high temperature (entrained flow). The drop-tube experiments indicated consistently higher combustion rates than did the other techniques. The pulse ignition measurements therefore, while providing a valid means of characterizing coal and char ignition behaviour, result in overestimation of the char combustion rate.