Advances in Efficient Utilization of Low-Rank Fuels in Coal and Biomass-Fired Systems: A Comprehensive Review

While coal–biomass cocombustion has gained considerable attention as a climate-sensitive power generation strategy, the detrimental impact of inorganic species present in low-rank fuels can lead to counterproductive outcomes in combustion systems. Low-rank solid fuels negatively affect heat transfer efficiency and energy conversion during steam generation, resulting in adverse environmental consequences. However, a combination of improved combustion technology and fuel quality improvements can enable the safe utilization of these fuels. This review highlights the pressing need for research in fuel quality improvement as an effective climate change mitigation strategy during the global transition to renewable energy sources. Identifying the problematic species in solid fuels and understanding the mechanisms of ash formation are critical steps toward designing effective strategies to control ash aerosol-induced fouling. The paper discusses methods for promoting clean combustion, including fuel pretreatment and cocombustion. Additionally, the review examines recent advancements in fuel improvement strategies, such as CFD-targeted-in-furnace injection (CFD-TIFI), intelligent soot blowing, and fuel additive technology, with a focus on mineral additives. Due to its high efficiency, low cost, and minimal retrofit requirements, additive technology holds promise for large-scale applications, paving the way for fuel flexibility in utility-scale power generation. The current study emphasizes the importance of fuel ash mineral transformation and characterization techniques for evaluating the effectiveness of fuel additives. Assessing the viability of utility-scale applications economically and the feasibility of a large-scale demonstration requires further research.