Industrial experiments were performed on a down-fired pulverized-coal 300 MWe utility boiler with swirl burners. Gas temperature, concentrations of gas components (O(2), CO, CO(2) and NO(x)) in the burning region and carbon content in the fly ash were measured with outer secondary-air vane angles of 25 degrees, 32.5 degrees and 50 degrees. Results indicate that with increasing vane angle, NO(x) emission and boiler efficiency decrease. Overall evaluation boiler efficiency and NO(x) emission, the vane angle of 32.5 degrees is optimum. Using an IFA300 constant-temperature anemometer system, cold air experiments on a quarter-scaled burner model were also carried out to investigate the influence of various outer secondary-air vane angles on the flow characteristics in the burner nozzle region. No central recirculation zone appeared for vane angles of 25 degrees and 32.5 degrees. Most of the pulverized-coal was ignited in the external recirculation zone. For vane angles of 45 degrees and 55 degrees, a central recirculation zone could be observed, and air flow rigidity and axial velocities decreased rapidly. (C) 2009 Elsevier Ltd. All rights reserved.