Experimental Investigation on NO x Emission and Ash Deposition Characteristics of High-Alkali Coal Combustion Under Deep Peak-Shaving Conditions

Deep peak-shaving operation of thermal power units significantly alters the combustion environment in the furnace. However, the patterns and mechanisms of the influence of deep peak-shaving conditions on ash deposition and NOx emission characteristics during high-alkali coal combustion remain insufficiently understood. Hence, this study conducted experimental research on Zhundong high-alkali coal under air-staged combustion conditions using a vertical two-stage furnace system, systematically investigating the effects of combustion temperature, excess air ratio, and air-staged degree on ash deposition propensity and NOx emission characteristics under deep peak-shaving conditions. The findings reveal that an increase in combustion temperature promotes ash melting and fuel nitrogen release, exacerbating both ash deposition and NOx emissions. While an increase in the excess air ratio can suppress albite formation and alter ash deposition propensity, it simultaneously elevates the NOx conversion rate. Further analysis demonstrates that increasing the over-fire air (OFA) ratio significantly reduces the nitrogen conversion rate. However, under deep air-staged conditions, low load operation tends to promote the formation of albite in ash, potentially aggravating deposition issues. This study systematically clarifies the mechanisms through which key operational parameters in deep peak-shaving processes, a previously underexplored area, govern ash deposition and NOx emissions during high-alkali coal combustion. It thereby provides essential experimental evidence and theoretical guidance for achieving safe, clean, and flexible operation of high-alkali coal-fired units under deep peak-shaving conditions.