Flue gas recirculation (FGR), which is adopted to control the reheat steam temperature of double-reheat boilers, significantly affects the temperature, heat flux and NOx distributions. The effects of FGR on combustion characteristics and heat flux distributions were investigated by numerical simulation on 660 MW tower-type double-reheat boiler. The results show that, the FGR could reduce the temperature in the furnace under boiler maximum continuous rating (BMCR), 70% turbine heat acceptance (THA) and 50% THA loads. With the injection of recirculation flue gas (RFG), the heat flux in the combustion zone decreases, more heat is transmitted to the upper part of the furnace. The peak value of wall heat flux appears near the center line of furnace wall. The NOx emission increases with the decline of boiler load and the FGR technology could effectively reduce the NOx emission.
Keywords Flue gas recirculation, combustion characteristics, heat flux distribution, numerical simulation, double-reheat boiler