Study on ignition behaviors of bias parallel pulverized coal streams in a reducing atmosphere: Influences of exit velocity

•Experiments conducted in a 250-kW bias combustion simulator with an optical method and other multiple means.•The ignition behaviors became worse as exit velocity increased.•A transition of ignition mechanism occurred with increasing exit velocities.•Four horizontal bias combustion burners were designed and applied to a tangentially fired boiler.•At the rated electrical load of 500 MWe, the NOx concentration prior to denitrification decreased by 11%.