Case study of the conversion of tangential- and wall-fired units to low-NOx combustion: Impact on fly ash quality

Conversion of boilers to low-NOx combustion can influence fly ash quality in terms of the amount and forms of carbon, the overall fly ash fineness, and the relative amount of glass versus crystalline inorganic phases. All of these factors can influence the potential for a fly ash to be marketed for utilization. In this study, three coal-fired combustors, two tangentially fired and one wall-fired, all burning high-sulfur Illinois coal at the same power plant, were studied before and after conversion to low-NOx combustion. In all cases, the post-conversion fly ash was higher in carbon than the pre-conversion ash from the same unit. The fly ashes in at least two of the units would appear to have post-conversion ashes which still fall within the regional guidelines for the limit of carbon (or loss on ignition).