The Insight into the Ash Fusion Process and Sintering Behaviour by Gasification of Blended Coal and Biomass Feedstock

Abstract

Biomass is considered as promising carbon-neutral fuel that can partially replace coal in gasification processes. The significant variation in the ash composition of blended feedstocks leads to the complex ash fusion behaviour, which is crucial for the stable operation of slagging gasifiers. Therefore, further research on the ash fusion process and sintering behaviour of blended feedstocks is required to support industrial applications in China. In this study, two distinct types of blended ash, denoted as HC-CS and LC-CS, were prepared by combining corn stalk (CS) with two kinds of coal (HC and LC) in different ratios. The fusion processes of the blended ash were divided into three stages similar to coal ash, including sintering-shrinkage, melting-swell, and melting-collapse. The sintering and swelling behaviour changed the fusion process significantly. The CS inhibited mullite generating in the blended ash, significantly reducing the degree of solid-phase sintering. Furthermore, two different liquid phases are formed during the fusion process, facilitating liquid-phase sintering and swelling. In the melting-swell stage, the liquid phase shows the dominant effect on apparent swelling, which can be quantified by flow index: FI= Δ(ϑslag i/ηslag i).  After the swelling, the melt content reaches 90% for HC-CS and 60% for LC-CS, determined by the end of FI fluctuation. In the last stage, the remaining refractory minerals dissolve rapidly in the initial liquid phase, causing a swift collapse of the blended ash. It is interested that the temperature range of the melting–collapse stage closely corresponds to the fusion interval (DT - FT), although obtained in very different conditions.

Keywords: co-gasification, biomass, Blended ash, Fusion, Sintering, Liquid phase