Fly ash characteristics and valorization pathways in paddy straw–coal co‐firing systems: A review

Abstract Open‐field burning of paddy straw and husk is a major environmental issue in India, driving efforts to use these residues as renewable co‐firing feedstocks in thermal power plants. This review synthesizes recent findings on the combustion behavior, fly ash formation, and valorization potential of paddy straw and coal blends, focusing on their compositional variability and operational implications. The study examines how variations in feedstock composition (notably SiO 2 , K 2 O, CaO, and Cl contents), pelletization parameters, and blending ratios impact fly ash fusion characteristics, slagging and fouling tendencies, emission formation, and power plant efficiency. Strategies such as additive use (kaolin, dolomite), controlled blending, and selection of coal types rich in alumina or sulfur are analyzed for their role in mitigating corrosion and deposit formation. Furthermore, the review examines the agricultural and construction reuse of CFA (co‐fired fly ash), highlighting its potential as a supplementary cementitious or soil amendment material when applied under controlled conditions. Additionally, operational aspects such as downstream impacts on electrostatic precipitator (ESP) performance and fly ash handling efficiency are evaluated to provide a comprehensive perspective on system‐level implications. Furthermore, the review highlights key research priorities, including pellet quality control, regional straw variability, supply chain logistics, and fly ash conveying performance, that warrant further investigation. The review offers operational guidance for utilities and policymakers aiming to scale co‐firing while maintaining boiler reliability and facilitating safe, value‐added fly ash reuse. It also highlights the research priorities necessary to ensure the technical feasibility and long‐term sustainability of integrating biomass into coal‐fired systems.