Effects of biomass blending, ashing temperature and potassium addition on ash sintering behaviour during co-firing of pine sawdust with a Chinese anthracite

When biomass and coal are co-combusted, the ash sintering behaviour cannot be directly predicted on the basis of the properties of individual fuel ash. Knowledge of the ash sintering behaviour can help understanding the subsequent ash fouling and slagging. Herein, the ash sintering characteristics during co-combustion of Jincheng coal (JC) and pine sawdust (PS), together with the effects of biomass blending ratio, ashing temperature and K2CO3 catalyst addition were investigated in depth. The results indicated that for a given JC/PS blend, the ash slagging degree expressed by different decision indices was different, but the tendency was consistent. No obvious fusion phenomenon was observed among the individual particles from the blends without K2CO3 addition. Both types of the particles from individual fuel could be separately identified with obvious difference from their respective particles. When K2CO3 was added to the blends, the ash surface structure varied from unmelted to slightly adhesion. The formation of potassium silicates made great contributions to slagging. The molten and solidified zone on the agglomerate surface featured high contents of K, Si, O and Al, and the coating on the melting surface was composed of the mixture of K-bearing aluminosilicates, potassium chloride and smaller amounts of Ca-bearing aluminosilicates.