Numerical Investigation of a Coal-Fired Power Plant Main Furnace under Normal and Reduced-Oxygen Operating Conditions

Abstract

This work simulates the Suralaya Power Plant Unit 6 boiler located at Cilegon, Banten, in Indonesia for two thermal loads, i.e., 600 and 400 MW under as-found (normal) and reduced-oxygen conditions, by means of computational fluid dynamics (CFD) using a sophisticated software package. The reduced-oxygen condition is an operational scheme that assumes lower mass flow rates of injected air and fuel compared with the as-found ones, but constant or slightly improved thermal efficiency with lower NOx emissions. The results of the CFD simulation were compared against thermodynamic results in the as-found condition cases regarding the overall heat flux and the species concentration, and overall show good agreement because the maximum percentage difference is approximately 14.5% regarding the O2 mole fraction in the 400-MW case. In general, the differences between the two subcases of each investigated thermal load are slight concerning the total heat transfer, the spatial distribution of the heat flux values, the CO2 emissions, and the overall char burnout. More important differences can be noted regarding the CO emissions because the mass and molar concentrations at the main furnace outlet surface almost double in the case of reduced-oxygen conditions in comparison with the case of the as-found ones. Furthermore, it is noted that in all four examined cases the front side of the boiler experiences the highest heat flux values among the boiler tube wall sides. This is attributed to the developed velocity field due to the inclined configuration of the rear boiler tube walls at the proximity of the main furnace outlet surface. In order to minimize the thermal loading of the front side walls and reduce the CO emissions, it would be beneficial to implement a more suitable swirl in the secondary air inlet ports and the development of an overfire air (OFA) system.