Experimental study of the high-temperature slagging characteristics of coal ash-biomass ash blends under different atmospheres

Abstract The blends of coal ash and straw ash with the proportion of 50%, 30% and 10% were selected for high-temperature slagging experiments under different atmospheres (Air/N 2 /CO 2 ). The main components of the slags were the mixtures of Si-Al-Ca-O. The straw ash in low proportion was first to melt and then bonded slags. The eutectic reaction of blend ashes were facilitated by increasing the proportion of straw ash, which enhanced the effect of slagging. Slagging in oxygen-containing atmospheres (Air, CO 2 ) was much more serious than that in N 2 atmosphere. The formation of iron glass was promoted under air atmosphere, and K, Na, Cl elements in straw ash volatilized significantly while few of them existed in the form of feldspar compounds or sulfates. Mullite in coal ash was consumed and then produced calcium feldspar because of the eutectic reaction with CaO. However, the slagging characteristics were not the same in reducing atmospheres. In CO 2 atmosphere, the surface was eroded into gully apertures because of the gasification, and Fe 2 O 3 was reduced to FeO which enhanced slagging. But the effect of N 2 atmosphere on the blend ashes was weak. The mineral decomposition and reorganization made the slag present fragmented, while the element Fe was present in the form of Fe 2 O 3 under N 2 atmosphere. In this case, the strong polarity of Fe 3+ weakened the melting of the slag.