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

Abstract

Ignition experiments regarding the combustion of Indonesian coal were performed in a reducing atmosphere using a bias combustion simulator with a thermal power of 250-kW. Flame spectra, gas temperatures and gas species were recorded, and coal combustion residues were sampled. The influences of exit velocity on the ignition mechanism, ignition delay distance, continuous flame boundary and fuel NOx formation of bias parallel pulverized-coal streams were investigated. The experimental results reveal that as exit velocity increased, the peak value of visible-light intensity, the combustion efficiency and the flame stability gradually decreased, while the ignition delay distance, the continuous flame boundary, and the formation of fuel NOx gradually increased. Furthermore, the ignition behaviors became worse. A transition of ignition mechanism occurred with increasing exit velocity, at an exit velocity of 16 m/s, the bias parallel pulverized-coal streams ignited in a hetero-homogeneous joint mechanism; at exit velocities of 20, 25 and 29 m/s, the bias parallel pulverized-coal streams ignited in a homogeneous mechanism. For different exit velocities, the fuel-rich stream ignited in advance of the fuel-lean stream, and the continuous flame boundary leaned evidently towards the fuel-rich stream side. According to the experimental findings in the present study, the horizontal bias combustion pulverized-coal burners were designed and applied to one-sixth of the total burners in a tangentially-fired pulverized-coal boiler. At the rated electrical load of 500 MWe, the NOx concentration prior to denitrification decreased by 11%, and the ammonium consumption for denitrification decreased by 42 kg/h. The results of the present study are also beneficial to further advance ignition concepts of low NOx bias combustion of pulverized-coal and enable the related numerical simulation work. © 2020 Elsevier Ltd