Review and Perspectives of Ash Slag Fluidity during Co-gasification of Industrial Solid Waste and Coal: Characteristics, Chemistry, Controlling Mechanisms, and Regulation

The stable fluidity of slag at a high temperature is crucial for the long-period operation of an entrained-flow gasifier. The diversity and difference of coal ash make it difficult to meet the requirements for stable slagging in a gasifier. Consequently, coal blending or adding flux has been employed in the industry to improve the fluidity of coal ash slag. As a carbon-containing matrix, industrial solid waste is a kind of energy substance. Utilizing existing industrial gasifiers to blend combustion of industrial solid waste can not only transform industrial solid waste into fuel but also improve the entrained-flow gasifier slagging performance using the unique ash chemical composition of industrial solid waste. Therefore, sorting out the effect of industrial solid waste on coal ash slag fluidity can not only clarify the regulating mechanism of coal ash slagging but also provide some theoretical support for the large-scale consumption of industrial solid waste. In this review, the effects of acid- and alkali-rich industrial solid wastes and coal co-gasification on coal ash slag fluidity were reviewed from the perspectives of ash melting characteristics and viscosity–temperature characteristics, and the effect mechanism of SiO2, Al2O3, SiO2/Al2O3 (S/A), CaO, Fe2O3, and CaO–Fe2O3 (Ca–Fe) compound fluxes on coal ash slag fluidity were elaborated from the viewpoint of mineral evolution and microstructure. Meanwhile, studies on the ash slag fluidity during the co-gasification of industrial solid waste and coal were prospected, which could afford theoretical guidance for the stable slagging of an entrained-flow gasifier and the resourceful treatment of industrial solid waste.