The effect of residual carbon on ash deposition behavior

One of the major effects of staged combustion of pulverized coal is the presence of partially burned char during the reducing stage. The effect of partially burned char, also present at short residence times in conventional pc boilers, on the deposition behavior of ash is not well understood. In this work several experiments were performed to explore the effect of unburned carbon on ash stickiness. In the first set of experiments ash stickiness and carbon content were measured as a function of residence time for one coal. In the second set of experiments each of the five study coals were combusted under a range of stoichiometric ratios and ash stickiness and carbon content measurements were taken at each condition. The data from these experiments suggest that carbon decreases the effective ash stickiness by physically preventing the sticky ash particles from contacting the tube surface. A simple model was developed based on this premise and found to be in good qualitative agreement with the data.