Reactive additives for alkali capture in biomass combustion

Biomass, as a renewable and CO₂ neutral fuel, is combusted in fluidized bed, grate and pulverized fuel-fired boilers for heat and power production. The gaseous alkali species released from biomass combustion, such as KCl and KOH, can cause several operation problems in the boilers, including ash deposition, corrosion, bed agglomeration, and deactivation of SCR catalysts. To address these problems, reactive additives that can convert the harmful gaseous alkali species to less harmful species, have been studied extensively through experiments and modelling. This paper aims to provide a discussion of the current understanding and applications of reactive additives for alkali capture in biomass combustion. The focus is on the thermodynamics, reaction mechanism, kinetics, and application aspects of sulfur based additives and Al-Si based additives.