Ash thermomechanical properties and combustion characteristics during Co-combustion of anthracite and biomass for CFB combustors

Co-firing biomass with coal in circular fluidized bed combustors is a promising method to reduce carbon emissions. In this study, the ash behavior and combustion characteristics of anthracite, wood pellet (WP) and their blends were thoroughly investigated by thermomechanical and thermogravimetric analysis, respectively. The results show that the fusibility of anthracite ash is significantly enhanced with the addition of WP ash due to the formation of low-melting-point KAlSi₂O₆, as a result of the interaction between SiO₂ and Al₂O₃ from anthracite ash and K₂O in WP ash. The thermomechanical analysis demonstrated that T25 decreased from 1227 °C to 1108 °C for the ash blend formulated with 50 % WP ash. The addition of WP reduced the combustion initial and final temperature of anthracite. Antagonism was minimized when WP was added at 25 %, whereas synergism was strongest around 580 °C when added at 50 % WP. The apparent activation energies calculated via four iso-conversional methods (Flynn-Wall-Ozawa [FWO], distributed activation energy model [DAEM], Starink, and Kissinger-Akahira-Sunose [KAS]) exhibited minimum values of 91 kJ/mol, 82.23 kJ/mol, 86.07 kJ/mol and 82.23 kJ/mol at 25 % WP addition across all blending ratios, corresponding to the respective models. This paper provides fundamental guidances for biomass co-firing technology.