A review on release and transformation behavior of alkali metals during high-alkali coal combustion

High-alkali coal is abundant and can cope with the current energy supply and demand gap. However, the sustainable utilization of high-alkali coals is limited by their abundance of alkali metal species, which can lead to severe ash-related problems such as ash accumulation, slagging, and corrosion during its combustion in boilers. To explore the clean and sustainable utilization of high-alkali coal in coal-fired boilers, it is crucial to study the release and transformation behavior of alkali metals in the combustion process. First, this paper reviews the alkali metal measurement methods for high alkali-coal combustion processes. Further, the migration properties of alkali metals are summarized in terms of coal composition, temperature, and combustion atmosphere. Current co-combustion technologies for high-alkali coals with additives/other fuels and their effects on alkali metals are summarized and evaluated. Finally, the authors propose suggestions for the development of high-alkali coal combustion technologies based on current research on the behavior of alkali metals.