Modelling of the combustion process and NOx emission in a utility boiler

This paper presents numerical simulation of the flow and combustion process in the furnace of a pulverized coal fired utility boiler of 350 MWe with 2 4 swirl burners installed at the furnace front wall. Five different cases w ith 100, 95, 85, 70 and 50% boiler full load are simulated. The comparison between the simulation and the plant data is stressed in this study. The he at flux to furnace walls between the measured values and the calculation re sults is compared. It is found that increasing the load leads to consistent variations in the properties presented and the exception is observed for t he full load case where the predicted exit gas temperature is lower than th e 95% one and the total heat to the boiler walls is smaller. This might be due to the fact of considering a linear scaling of the input parameters bet ween the 70% and 100% load. The increase of the air flow rate led as expect ed to a reduction of the furnace outlet temperature and to a small decrease in NOx emissions. It shows that the NOx model used shows a higher sensitiv ity to temperature than to oxygen level in the furnace. The model used cons idered the De Soete mechanism for the nitrogen from volatiles and the contr ibution of char was considered in a similar way. The agreement for all case s except the one of 50% boiler load between the calculation results with th e plant data validates the models and algorithm employed in the computation . The furnace performance under different boiler loads is predicted and com pared in order to meet the requirements of NOx abatement and avoiding some negative side effects on the furnace. (C) 2000 Elsevier Science Ltd. All ri ghts reserved.