Influence of staged-air on combustion characteristics and NO_x emissions of a 300 MWe down-fired boiler with swirl burners

Using an IFA300 constant temperature anemometer system, cold air experiments on a quarter-scaled burner model sited in a 300MWe down-fired boiler were carried out to investigate the influence of various relative secondary air ratios on the flow characteristics in the burner nozzle region. With decreasing secondary air ratio, axial velocities and entrained flue gas decreased, as well as tangential velocities and rates of jet diffusion. However, the more that secondary air obstructs the diffusion of primary air, rates of primary air diffusion increased. Industrial-sized experiments were performed on a 300MWedown-fired boiler with swirl burners. Gas temperature, concentrations of gas components (O₂, CO, and NO_x) in the burn region and combustible content in the fly ash were measured over a range of staged-air damper openings of 15, 25, and 35%. With openings of 15 and 25%, the level of pulverized-coal burnout is high, although NO_x emissions were also a little higher. The level of burnout degree decreased for a 35% opening, and exhaust gas temperatures increased. Although the boiler efficiency decreased, NO_x emissions also decreased.