Effect of Two-Level Over-Fire Air on the Combustion and NOx Emission Characteristics in a 600 MW Wall-Fired Boiler

This paper accomplishes a numerical investigation on the effect of two-level over-fire air (OFA) on the combustion and NOx emission in a supercritical 600MW wall-fired boiler. Different arrangements of two-level OFA nozzles and different airflow ratios between the two layers are set to examine NOx emission and the carbon content in fly ash. According to the simulation results, the two-level OFA case releases the NOx between the single upper layer and the single lower layer of the two-level OFA nozzles in operation. Moreover, the two-level OFA arrangement gives a lower carbon content in fly ash than the single-level OFA cases. In addition, both low NOx emissions and low carbon content in fly ash can be obtained simultaneously when the two levels of OFAs are injected from Layers 1 and 4 with r(lower) at 0.5.