GENERATION AND DEPOSITION OF FLY-ASH IN THE COMBUSTION OF PULVERIZED COAL

The development of two experimentally tested models is discussed, of which one relates to the generation, and the other the impaction, of fly ash. The first is capable of yielding the size and mineral-composition distributions of fly ash from microscopic examination of coal. Computer-controlled scanning electron microscopy, combined with automated image analysis, was used to determine the size and composition distributions of individual mineral inclusions in coal samples graded for size and density. The information thus obtained was used as input to the generation model. The output of the generation model was used as input to the impaction model, to predict the fraction of fly ash impacting, relative to that approaching, a heat-exchanger tube. This latter model, which is based on considerations of particle mechanics, has been tested experimentally in the flame tunnel of the MIT Combustion Research Facility.