The effect of primary measures for controlling biomass bed temperature on PM emission through analysis of the generated residues

Flue gas recirculation and the use of cooled beds are novel strategies for controlling the biomass bed temperature and are currently under investigation for domestic applications. This paper explores their effect on the chemical composition of the deposits and emitted particles during biomass combustion and aims to study whether these techniques influence fouling, slagging and PM release. Tests were performed in an experimental plant, and samples were taken from three different zones of the facility. The results revealed a low ash-melting hazard in grate and wall residues due to the low Si content and the predominant presence of Ca-Mg-Mn-based minerals (accounting for values closer to 50% and 30% respectively in grate and wall samples). Chimney-filter particles were mainly composed of K-Cl-S (> 85%), which implied high fouling and corrosion potential. The cooled bed allowed for the retention of these alkali compounds on the refrigerated surfaces, which prevented the formation and emission of fine particles.