Combustion characteristics of high ash coal in a pulverized coal combustion

The influences of ash content on pulverized coal combustion characteristics are experimentally and numerically studied under a staged combustion condition. The stage combustion ratio (the ratio of air volume of the staged combustion air to the total air) is 0 or 30%, and the coals tested are the three high ash coals with different ash contents of 36, 44 and 53 wt%, which were separated using the floatation method. The results show that as the ash content increases, gas temperature decreases and O-2 consumption and NOx formation becomes slow near the burner. Also, the increase of the ash content leads to the increase in NOx concentration and unburned carbon fraction at the furnace exit. The reasons being, for the high ash coal, the large heat capacity of the ash and the covering of combustible matter suppress combustibility with ash during the char oxidization. The numerical simulations designed to match the experimental setup for the staged combustion show that the numerical results are in general agreement with the measurements. (C) 2001 Elsevier Science Ltd. All rights reserved.