Mercury speciation and removal during full-scale biomass–coal cofiring in a 242 MW pulverized-fuel unit

Mercury emissions from coal-fired power plants remain a critical challenge due to the toxicity, volatility, and limited capture efficiency of elemental mercury (Hg⁰) in conventional flue gas cleaning systems. Biomass–coal cofiring has emerged as a cost-effective mitigation strategy; however, its impact on mercury speciation and removal under full-scale operating conditions remains insufficiently quantified. This study presents an industrial-scale assessment of mercury behavior during coal–biomass cofiring in a 242 MW pulverized-fuel power unit equipped with SCR, ESP, and wet flue gas desulfurization. Three multi-day measurement campaigns were conducted under stable and comparable operating conditions, comparing coal-only combustion with cofiring of coal and 10% biomass (mass basis). Mercury concentrations and speciation were determined in fuels, solid residues, and flue gas using continuous online monitoring and mobile speciation analysis. Biomass cofiring reduced stack mercury concentrations from 1.5 ± 0.20 to 0.8 ± 0.12 µg·Nm⁻ 3 and shifted flue gas speciation toward oxidized mercury (Hg 2+ ), enhancing downstream capture efficiency. The results demonstrate that fuel-driven modification of flue gas chemistry governs mercury speciation and process-level removal performance. These findings provide statistically validated full-scale evidence that biomass cofiring enhances intrinsic mercury capture in existing pollution control systems without additional mercury-specific technologies.