[Objective] High-ratio co-combustion of biomass with coal is an effective strategy for reducing greenhouse gas emissions. However, the release of gas-phase potassium during this process frequently induces operational issues such as ash deposition and slagging. These issues not only drastically reduce heat transfer efficiency and increase maintenance costs but also may lead to unscheduled boiler shutdowns and safety hazards. Therefore, it is of paramount engineering importance to develop reliable online detection methods for gas-phase potassium concentration and systematically investigate the potassium release characteristics and combustion behaviors of biomass-coal blended fuels under different mixing ratios. 

[Methods] In this study, a single-particle combustion experimental setup was established to investigate coal and biomass blends at various ratios using emission spectroscopy. This system achieved the simultaneous detection of flame temperature, gas-phase alkali metal concentration, and thermal radiation energy, thereby facilitating an in-depth analysis of the gas-phase potassium release characteristics of the blended fuels. Bituminous coal and corn stover were mixed using an isocalorific method, based on the heat content of 0.5 mg of bituminous coal as a benchmark. The blended fuels were compressed into structurally stable single pellets under a pressure of 13 MPa using a hydraulic press and subsequently combusted on the custom-built experimental platform. 

[Results]The experimental results demonstrate that the variation characteristics of gas-phase alkali metal concentration and thermal radiation energy can clearly distinguish three distinct combustion stages of the blended fuels: the devolatilization stage, the fixed carbon combustion stage, and the ash stage. Every stage could be distinctly identified through the variation characteristics of gas-phase alkali metal concentration and thermal radiation energy. As the biomass blending ratio increased from 0% to 100%, the peak concentration of gas-phase potassium rose significantly from 2.59 mg/m³ to 16.8 mg/m³, exhibiting a trend consistent with the duration of volatile pyrolysis. Conversely, the char combustion duration shortened by approximately 330 s, the average flame temperature decreased by 237 K, and the thermal radiation energy declined by 31.2%. These findings elucidate the promotional effect of biomass co-combustion on alkali metal release and quantify the significant alterations in fuel combustion characteristics. 

[Conclusion] Biomass cocombustion exerts a pronounced promoting effect on the release of gas-phase potassium and significantly alters the overall combustion characteristics of the fuel, including accelerating fixed carbon burnout, lowering flame temperature, and reducing thermal radiation output. The findings of this research provide crucial experimental data and theoretical support for the optimal design of biomass-coal co-firing boilers, the adjustment of operational parameters, and the development of effective alkali metal-related problem prevention and control strategies in industrial applications.