Optimization of Reburning for Advanced N0x Control on Coal-fired Boilers

This paper summarizes an experimental study which was conducted to investigate the chemical constraints of the reburning process and identify reburning configurations for optimal NO_x reduction in coal-fired boilers. Tests were performed on a bench scale tunnel furnace to characterize and optimize the fuel-rich reburning zone and the fuel-lean burnout zone independently. Detailed measurements ofunburned hydrocarbons, CO, NH₃, and HCN were made at the reburning zone exit. The influence of the concentrations of reactive species was examined as were temperature effects for both the reburning and burnout zone. Results indicated that reburning zone chemistry was not rate limiting. The impacts of temperature and burnout zone oxidation were of major importance. Integration of the optimum reburning and burnout zone configurations resulted in increased NO_x reduction. Over 85 percent reduction in NO_x emissions was achieved with ammonium sulfate injection in the burnout zone under optimum reburning conditions.