A three-dimensional numerical investigation is presented on the coal combustion and NO x emission in a supercritical 600 MW wall fired utility boiler fed with lean coal. The distributions of velocity, temperature, and species were obtained using a finite volume method and some validated submodels. The influence of air staging condition, i.e., overfire air (OFA) ratio and OFA port position, on combustion and especially on NO x emission was studied. The temperature of the burner zone and the carbon content in fly ash increased with increasing OFA ratio, while the NO x emission decreased with increasing OFA ratio. An increase of the OFA port position resulted in a decrease of NO x emission and an increase of carbon content in fly ash. In addition, high burnout rate of pulverized coal and low NO x emission can be achieved in the present boiler, in which OFA was injected from Port 3 with a ratio of 34.2%. This study provides new insights into the physical and chemical processes in a wall fired utility boiler fed with lean coal and also illustrates a method to reduce NO x emission.

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