Effect of Minor Oxide and Residual Carbon on Coal Ash Crystallization Behavior and Slag Properties during Coal Gasification: Critical Literature Review and Thermodynamic Simulation.

Abstract

Coal-ash-associated problems seriously limit the industrial application of entrained flow coal gasification. There have been many studies of this issue. However, many problems still need to be fully understood, especially regarding the effect of minor oxides and residual carbon on the crystallization of slag in coal ash systems. Crystals formed in slag affect the slag properties, especially its viscosity. This article reviews the crystallization behavior of coal ash slag and its impact on ash fusion temperature (AFT) and temperature of critical viscosity (Tcv). A thermodynamic simulation using FactSage 7.3 thermochemical software was performed to study the effect of minor oxides (i.e., Na2O, K2O, and TiO2) and residual carbon at a temperature range of 1000-1700 °C on the phase transformation in the oxide system. The literature review reveals that the minor oxides and residual carbon in coal ash affect the AFT and the coal slag's Tcv. The thermodynamics simulation indicated that Na2O, K2O, and TiO2 tend to decrease Tcv, while the residual carbon increase Tcv.