The effect of combustion conditions in a full-scale low-NOx coal fired unit on fly ash properties for its application in concrete mixtures

The wide implementation of low-NOx combustion technologies in pulverized coal combustion can lead to higher levels of carbon in fly ash and increase the adsorptivity toward surfactants of the carbon. Consequently, the air entraining agent (AEA) requirements of the fly ash used for concrete production increases, which can complicate the stabilization of entrained air. In this study, a low-NOx tangential fired 875 MWth power plant burning bituminous coal have been operated under extreme conditions in order to test the impact of the operating conditions on fly ash adsorption behavior and NOx formation. It was found that the AEA adsorption of the fly ash was reduced up to five times compared to reference operation, when the plant was operated with minimum furnace air staging, three levels of burners instead of four and without recycled flue gas. The lower AEA requirements of the fly ash at these conditions were primarily caused by a reduction in total carbon content, while the AEA adsorptivity of the residual carbon was lowered to about 60% of reference value. The tested operation mode, however, increased the NOx level in the flue gas before the DeNOx plant by 60% compared to reference operation.