CFD investigation on combustion and NOx emission characteristics in a 600 MW wall-fired boiler under high temperature and strong reducing atmosphere

In this paper, a modified air staging technology for pulverized coal boilers was proposed, to notably reduce NOx emission by creating a zone with high temperature and strong reducing atmosphere (HT&SRA) in furnace. Here, the conventional air staging technology was employed in combination with increasing O-2 fraction of feeding gas in primary zone (O-2.p). The new technology was numerically verified in a 600 MW wall-fired boiler and the temperature distribution, the char burnout and the effectiveness in NOx reduction were mainly examined. The results indicate that a sufficiently low stoichiometric O-2 ratio in primary zone (SRp) is essential to reduce NOx emission by increasing O-2.p. The effectiveness in NOx reduction by increasing O-2.p also depends greatly on the injection position of over fire air (OFA). Under the condition of 0.7 SRp and a relatively high OFA position, the NOx emission could be reduced by 27.6% when O-2.p is increased from 21% to 33%, while the incomplete combustion heat loss only shows a slight rise. In addition, the NOx reduction ratio could reach to >60% through the proposed low-NOx combustion technology compared with the current operation condition. (C) 2017 Elsevier Ltd. All rights reserved.