Ignition temperature of pulverized coal particles: Experimental techniques and coal-related influences

Abstract

Laboratory measurements of the visual and combustion sequences during the ignition of pulverized coals, chars, and petroleum coke are reported. Two experimental techniques—the first using a pulse of coal and the second, a continuous flow of coal and air in near stoichiometric proportions—are shown to give similar gas temperatures for the onset of flashing. The first flash temperature, commonly referred to as the minimum gas temperature for ignition, is shown to decrease with an increase in the volatile matter content of coal, particle size, and ambient oxygen concentration. However, little oxygen is consumed during this initial visual event. At a gas temperature, about 100°–200°C higher than the first flash temperature, the oxygen consumption is seen to increase rapidly and this is accompanied by the rapid generation of NO x . This characteristic temperature decreases with an increase in the ambient oxygen concentration but appears to be independent of particle size. It is found to be very close to the flame formation temperature. These two temperatures appear to be better indicators of the ignitability of pulverized coals in combustors than the first flash temperature.