Numerical investigation on the flow, combustion and NO x emission characteristics in a 500 MW e tangentially fired pulverized-coal boiler

Abstract

The characteristics of the flow, combustion, temperature and NO x emissions in a 500 MW e tangentially fired pulverized-coal boiler are numerically studied using comprehensive models, with emphasis on fuel and thermal NO x formations. The comparison between the measured values and predicted results shows good agreement, which implies that the adopted combustion and NO x formation models are suitable for correctly predicting characteristics of the boiler. The relations among the predicted temperature, O 2 and CO 2 mass fractions are discussed based on the calculated distributions. The predicted results clearly show that NO x formation within the boiler highly depends on the combustion processes as well as the temperature and species concentrations. The results obtained from this study have shown that overfire air (OFA) operation is an efficient way to reduce the NO x emissions of the pulverized-coal fired boiler. Air staging combustion technology (OFA operation) adopted in this boiler has helped reduce fuel NO x formation as well as thermal NO x formation under the present simulated conditions. The decrease in the formation of fuel NO x is due to the decreased contact of the nitrogen from the fuel with the oxygen within the combustion air, while the decrease in thermal NO x formation is caused by a decrease in temperature. The detailed results presented in this paper may enhance the understanding of complex flow patterns, combustion processes and NO x emissions in tangentially fired pulverized-coal boilers, and may also provide a useful basis for NO x reduction and control.