Numerical study of fractional combustion of pulverized solid fuel

Preparation for combustion of initial solid fuel by existing methods (crushing, mill grinding) results in burning polyfractional dust in the furnace due to the presence of particles whose sizes differ by one or two orders of magnitude in the flame. Also, the particle size distribution has a significant effect on all stages of the combustion process. Since at the beginning of the flame small fuel particles burn faster and consume a significant part of oxygen, large fuel particles, which determine incomplete combustion, burn in an oxygen-depleted atmosphere. This disadvantage can be eliminated by applying the technology of fractional solid fuel combustion, which consists in the separation of polyfractional dust into fractions of different sizes and their subsequent combustion under different conditions. This study is aimed to evaluate the efficiency of fractional combustion of pulverized solid fuel by comparing the results of numerical simulation for cases when burning polyfractional and fractionized coal dust. The comparative analysis indicates that the separation of polyfractional coal dust into "coarse" and "fine" fractions with their subsequent introduction into the furnace at different heights results in decreasing unburned carbon content by 0.7-1.36 % and simultaneous reduction of NOx concentration at the furnace outlet by 7.3-13.9 %. Moreover, the greater the distance between burner tiers, the better the found effect. Thus, the fractional combustion of pulverized coal can be effectively applied to reduce both unburned carbon and NOx emissions that can have a positive impact on reducing environmental pollution from thermal power plants.