Abstract: Using CFD software to simulate different rates of overfire air NOx formation characteristics in furnance. According to the characteristics of the coal, select the appropriate NOx model. The simulation shows that the date can be consistent with the measured before and after transformation. It verifies the accuracy of the model. Base on this numerical model, a method called spatial distribution is used to analyze the results of different rates of overfire air by simulating. Describes the characteristics of NOx formation at different rate of overfire air. The results show that the spatial distribution method can describe the combustion conditions in the furnance and NOx formation in detail. Changing overfire air rate have a less affected on volatile release. In a high overfire air rate, the coke burn out will be postponed and the reducing atmosphere will be enhanced. In the primary combustion zone, the fuel and thermal NOx rates has declined. NOx concentration is reduced. But the unburned substances and the coke delays burn out makes more HCN to be oxidized to produce fuel NOx. This makes under the highest rate overfire air the furnace exit NOx concentration does not reach the minimum. The main idea to control export concentration of NOx is to choose a overfire air rate based on the characteristics of the coal so that can control the formation of fuel NOx in the main combustion zone and rebound in the burnout zone.

Key words: fuel NOx, numerical simulation, overfire air rate, spatial distribution, thermal NOx