Numerical Simulation On CO Emission Characteristic Of Coal-fired Boiler

Advanced low-NOx burners and the combustion technology of air staging have been applied to reduce the NOx emissions on modern coal-fired power plant.The main burner zone is kept under anoxic and fuel-rich conditions to control NOx emissions.However,this may lead to higher CO emission concentration in the boiler and high CO peaks in local areas,which may cause incomplete combustion or delayed combustion,and reducing of the combustion efficiency of the boiler.Studying the formation mechanism and control method of CO in coal-fired boilers has important engineering value for improving the economical and environmental protection of thermal power units.FLUENT is applied to simulate the combustion process in a 400t/h tangentially fired pulverized-coal boiler with an improved multi-step coke reaction model.Theimpact on the furnace temperature field,CO mass fraction and NOx emission is analyzed in details.In order to reduce the CO concentration without significantly increasing NOx emission,two combustion schemes are designed to simulate and analyze the flow and combustion characteristics with different transformation plans.The first scheme is to change the horizontal swing angle of a single burner and to analyze the change about the furnace temperature field,CO mass fraction and NOx emission.The second scheme is to increase the separated overfire air(SOFA)in the upper part of the existing closed-coupled overfire air(CCOFA)and to analyze variation about temperature,NOx concentration and CO concentration in furnace by changing the wind ratio and arrangement height between CCOFA and SOFA.The results show that both schemes reduce the temperature of the boiler outlet,and effectively reduce the CO mass fraction and the NOx emission concentration of the furnace.The incomplete combustion and high temperature corrosion phenomenon are eliminated to some extent which indicate the adjustment of the horizontal swing angle of the burner and adding the separated burnout wind is an effective means to improve the economic and safety of the unit.