Fusion property prediction and mineral reaction mechanism of coal/ biomass ash blends upon in-situ tests in the gasification process

The co-gasification of coal and biomass serves as a pivotal strategy to tackle slagging challenges in entrained flow gasifiers. The pivotal factor in this process is the ash fusion characteristics. It is paramount to gain a profound understanding of mineral phase reactions and devise a rapid prediction method for key parameters. In this study, a comprehensive analysis was conducted through in-situ observation, quenched slag preparation and thermodynamic analysis. As the biomass addition increased, the introduction of alkaline components raised the ash system's basicity, leading to a notable reduction in ash fusion temperatures. The formation of K-based aluminosilicates in mixed ash was identified as the key reason. The transformation of refractory silica-aluminates in coal ash and K-silicates with an ultra-low melting point in biomass ash into leucite played a crucial role in alleviating slag blockage and slagging issues. The influence of K+ from biomass ash on the [SiO4]4- tetrahedral framework shifted the ash fusion range towards lower temperatures, expediting the ash melting process. Combining online monitoring with high-temperature thermal stage microscopy, it was implied that the ash melting process dominated by coal ash followed a softening-melting mechanism, while the process dominated by biomass ash followed a melting-dissolution mechanism. Furthermore, among the characteristic temperatures associated with ash fusibility, the deformation temperature indicated sintering behavior, and the hemisphere temperature represented slagging behavior. These characteristic temperatures are closely related to ash chemical composition, especially the acid-base ratio (Rb/a) and the iron-alkali metal ratio (Ra). Leveraging these chemically derived parameters, a highly accurate prediction of the ash fusibility index (AFI) was achieved. This approach can provide effective guidance for the selection and blending of fuels to ensure the long-term operation of gasifiers.