Variations in the temperatures of coal-char particles during combustion: A consequence of particle-to-particle variations in ASH-content

Abstract

Experimental evidence is provided that supports our hypothesis that the wide variations in the temperatures and burning rates of pulverized-coal char particles of nominally the same size are primarily a consequence of particle-to-particle variations in ash-content. In situ size, temperature, and velocity measurements on the char particles of two uncleaned, run-of-mine coals and on the char particles of their physically-cleaned products are presented. The cleaning process reduced the total mineral matter content of the coals. It is shown that the variations in particle temperatures are reduced with cleaning. The higher the mineral matter content of the coal, the wider the variations in the ash-content of individual particles and hence, the wider the variations in the temperatures of particles of nominally the same size. Wide variations in particle temperatures lead to wide variations in particle burning rates. It is also shown that the temperature-dependence of the chemical reactivity of the particle material remains unchanged throughout the early to late stages of burning. Further, the data indicate that catalysis by mineral matter is negligible at particle temperatures exceeding 1500 K.