Solid Precipitation Behaviors in Coal Slag from Different Primary Phases and Their Effects on Slag Viscosity from Thermochemistry and Experimental

Abstract

Undesired solid precipitation in coal slag at high temperatures can cause serious blockages, or even the shutdown of coal gasifiers, due to a rapid increase in slag viscosity. In this study, the solid precipitation behaviors of coal slag from different primary phases and under different atmospheres were both experimentally and theoretically investigated. Our results demonstrated that the viscosity of the coal slag in the primary phase of mullite was strongly influenced by the atmosphere at a typical tapping temperature of 1300 °C because of the high content of network formers. The viscosity of the partially crystallized slag was significantly affected by solid precipitation behavior. Iron was converted to magnetite and hematite in air and was reduced to metallic iron under a reducing atmosphere. Increasing CaO content improved both the iron reduction reaction and the slag crystallization behavior. Anorthite precipitation was largely inhibited under a mild reducing atmosphere, leading to a large difference in the viscosity of coal slag under different atmospheres. In contrast, the viscosity of the coal slag in the primary phase of mullite was slightly influenced by the atmosphere due to the weak crystallization tendency of mullite, as well as its high slag viscosity.