Performance assessment and emission implications of an ammonia co-combustion power system with various coal ranks

Ammonia (NH₃)-coal co-combustion has been identified as a key strategy for decarbonizing coal-fired power generation. Large-scale implementation requires a comprehensive investigation into co-combustion behaviour, considering the influence of coal properties on system performance. The variability in coal composition and the resulting flue-gas characteristics necessitate detailed analysis, as their direct effect on system efficiency and emissions is significant. This study presents a simulation of NH₃ co-combustion in a 1 GW ultra-supercritical power cycle, evaluating five different coals (bituminous, sub-bituminous, and three lignite coals) with co-combustion ratios ranging from 0 to 0.5. The findings of this study demonstrated a decline in net efficiency, concomitant with a decrease in calorific values of coal and an increase in co-combustion ratios. The variation in coal compositions also significantly influenced the combustion-temperature trends and thereby the flue-gas composition (especially the NO_x emission). In addition, the properties of the flue-gas had a discernible impact on boiler efficiency and heat-exchange performance. A distinct correlation was observed between boiler efficiency and the primary flue-gas constituents, H₂O, CO₂, and N₂ across different coal ranks, both in terms of molar-flow rate and concentration. A general decrease in the log mean temperature difference (LMTD) was observed as the coal rank shifted from bituminous to lignite. However, with rising co-combustion ratios, a trend reversal was observed in all the lignite coals, with LMTD profiles transitioning from decreasing to increasing, in contrast to the behaviour seen with higher-rank coals. This study provides a comprehensive analysis of NH₃ co-combustion with various coal ranks—offering insights that lay the foundation for the widespread large-scale adoption of relevant technologies.