Simultaneous particle morphology and temperature measurements of burning pulverized coal

Abstract

Simultaneous, in situ measurements of the morphology, temperature and velocity of individual pulverized coal particles are presented. Particle temperatures are measured using two-color pyrometry and shapes are obtained from two-diemnsional images. From these images, estimates of particle external surfac area and volume are obtained using a discrete revolution technique. This method provides more accurate determination of the surface area of irregularly shaped particles than the equivalent sphere method typically referred to in the literature. The results of simultaneous morphology, temperature and velocity measurements obtained for a Pittsubrgh seam coal (35% volatile matter by weight) 30 msec after particle ignition in various bulk gas oxygen concentrations are presented. At oxygen concentrations of 10 and 15% by volume, two types of particles are observed: low temperature particles with large, irregular shapes and high temperature particles with more compact shapes. Examination of collected particles using scanning electron microscopy showed the low temperature particles to be lacy, soot-like formations and the high temperature particles to be partially burned coal particles. A comparison is made between calculated particle burning rates (μg/s) obtained using the discrete revolution technique and those obtained using the equivalent sphere method. Burning rates obtained from the images are approximately 30% higher than those obtained from the equivalent sphere method. The two-dimensional images provide a better estimate of the higher surfaces areas associated with irregular shaped particles and hence the higher calculated particle burning rates (μg/s) are more accurate.