Numerical Simulation of Combustion Characteristics and Heat Flux Distribution in a 600-MW Arch-Fired Boiler with Different Primary Air Injection Angles

A CFD model of a 600 MW supercritical arch-fired boiler (SC-AFB) was established and applied to investigate the combustion characteristics and heat flux distribution with three primary air injection angles of 0°, 5°, and 10°. The results showed that in general, the primary air streams barely penetrate the secondary air in the lower furnace, and thus, no strong combustion occurs in the hopper zone. A smaller injection angle results in a longer penetration distance and longer residence time of the coal particle, but it generates a larger reducing zone in the lower furnace. When the injection angle varies from 0° to 5°, high-temperature zone (T > 1800 K) expands, but it becomes narrower when the injection angle further increases to 10°. Coal particles burnout ratio at furnace exit is highest when injection angle is 5°. It was also found that coal particles move and gather near the two side walls by the thermal expansion in the near burner zone, resulting in intense combustion and heat transfer near the side walls and a two-peak heat flux profile on the front wall. When the burner injection angle increases, less coal particles move toward side walls and their residence time is shorter in the lower furnace. The injection angle of 5° is suggested based on the optimal flux distribution and burntout ratio of the coal particles.