Numerical Study of Co-firing Biomass with Lean Coal under Air-Fuel and Oxy-fuel Conditions in a Wall-Fired Utility Boiler

Co-firing biomass under oxy-fuel condition is one of the most attractive methods which is conducive to mitigating CO2 emissions by combining the advantages of these two respective technologies. The combustion characteristics of a wall-fired utility boiler operating in this mode have been seldom investigated. The burnout behavior of the blended fuel is still controversial. By using the newly proposed combustion mechanisms, a numerical study was carried out in a 600 MW wall-fired boiler to evaluate the influences of oxy-fuel working condition and biomass share on flow, temperature, O-2, distributions, and burnout behavior in this combustion mode. Besides, the effect of biomass injection position was also explored, which has yet to be fully understood. The simulation results show that oxy-fuel working condition affected the combustion characteristics to some extent. The introduction of biomass led to a lower temperature but a better burnout within the furnace. O-2 distribution was also correlated to the biomass share due to the difference in fuel properties. The injection position of biomass presented crucial impacts on particle trajectories, temperature distribution, and O-2 distribution. In addition, due to the increase in residence time and the reduction in trapped particles, an enhanced burnout could be achieved as the biomass inlet was moved down.