Numerical Simulation of the OFA Effect on Combustion in a 600 MWe Boiler with Centrally Fuel Rich Burners

With the rapid development of renewable energy, the traditional coal-fired power generation plays an important role in peak regulation, which requires the boilers to operate at low load or even ultra-low load. In order to investigate the effect of over-fire air (OFA) ratio on the flow, temperature and component concentration distribution and the furnace exit parameters for utility boilers at ultra-low loads, a 600 MWe utility boiler with centrally fuel rich (CFR) burner technology is taken as the object of study, and numerical simulations are carried out for five operating conditions with different OFA ratios (0%–40%) at 25% of the boiler’s maximum continuous rating (BMCR) load. The results show that no obvious high-temperature region is formed in the furnace and the flow field distribution in the furnace exit area is not conducive to the stable combustion of pulverized coal when the OFA ratio is 0% and 10%. When the OFA ratio is 30%, the area of the high-temperature region in the furnace reaches its maximum. When the OFA ratio is 40%, the furnace exit NO concentration is only 94.54 ppm. With the increase of the OFA ratio from 0% to 40%, the temperature of the flue gas at the furnace exit decreases by more than 100 K, which may affect the stable operation of the Selective Catalytic Reduction (SCR) denitrification equipment. Taking into consideration the flow in the furnace, the combustion, the NO_x emission, and other factors, the recommended OFA ratio is 20% ~30%.