A Critical Review on the Impacts of Binder on Pellet Quality, Combustion Performance and Pollutant Emissions in Biomass-Coal Co-Fired Pellets

The objective of this review is to critically assess the impacts of binders on pellet quality, combustion performance, and pollutant emissions in biomass-coal co-fired pellets. The methodology involves synthesizing literature predominantly from 2010 to 2025, sourced from offline and online databases such as Elsevier journals, ScienceDirect, Textbooks, Chemical Abstracts, and Google Scholar. The findings indicate that co-firing biomass pellets with coal is an effective strategy to reduce CO₂ emissions from coal-fired power plants while utilizing existing infrastructure. Binders significantly enhance pellet mechanical stability; however, comprehensive evaluations of their influence on combustion behavior, optimal biomass-coal blending ratios, and pollutant emissions, particularly CO₂ and SO₂, are limited; hence, this critical review. The presence of binders alters the optimal biomass-coal blending ratios, which are generally 10–20% biomass in binder-free pellets. Complex interactions between binder types and their effects on emission trade-offs remain insufficiently understood. Co-firing with biomass can reduce CO₂ emissions by 75–90% compared to pure coal combustion, and sulphur-fixing binders further mitigate SO₂ emissions. This review identifies critical research gaps in optimizing binder-blend formulations and understanding long-term emission dynamics under real boiler conditions. It emphasizes the necessity for integrated experimental and modeling approaches, coupled with field demonstrations, to develop scalable, low-emission co-firing solutions, particularly in biomass-rich developing regions.