Effect of Co-firing Straw with Two Coals on the Ash Deposition Behavior in a Down-Fired Pulverized Coal Combustor

摘要

This investigation examines the variation of ash deposit when co-firing wheat straw with both high-kaolinite, low-sulfur YanKuang (YK) coal and low-kaolintte, high-sulfur WenNan (WN) coal at different ratios. The experiment was carried out in a 25 kW lab-scale one-dimensional down-fired combustor, in which a temperature-controlled deposition probe was developed to collect deposit samples for further mass, morphology, or chemical analyses. The measured collection efficiencies are compared to the predicted ones by the "rule of mixtures", assuming no interaction between fuels. A significant increase in ash collection efficiency was observed in the cases of co-firing straw with WN but became insignificant when co-firing straw with YK. The formation of low-melting alkali-aluminum silicates instead of the sulfation of alkali chloride plays an important role in explaining the changing of two typical deposition mechanisms during ash deposition. The straw in blends or in pure streams brings a "shadow effect" that contributes to the increasing deposit height in contrast to pure coal combustion. Finally, the vital role of fine particles as the adhesive or glue between coarse ash residues was verified by scanning electron microscopy (SEM) pictures.