Numerical Analysis of Loads Effect on Combustion Performance and NO x Emissions of a 220 MW Pulverized Coal Boiler

This paper presents numerical study on the combustion performance and NOx emissions of a 220 MW pulverized coal boiler. Three different loads have been simulated with combusting coal, 200, 170 and 140 MW, respectively. In order to get as precise as possible numerical analysis results, two-step simulation method has been adopted in this work, namely, air supply system simulation and furnace simulation. After air supply system simulation, the results have been taken as the initial and boundary conditions for furnace simulation. The comparison between the measured values and predicted results from 200 MW case shows much better agreement. According to the simulation results, the adopted two-step simulation method is reasonable and suitable for predicting the characters of the flow and combustion process. It is concluded that the distributions of temperature, O2 and CO concentration inside furnace with different loads shows good similarly. The total NOx emissions decreased with the boiler load reducing, and fuel NOx has the same trend as total NOx, and fuel NOx account for about 66% in total NOx in all the three cases. More important, thermal NOx slowly decreased with the rise of boiler load. More detailed results presented in this paper enhance the understanding of combustion processes and complex flow patterns of front-wall pulverized coal boilers.