Dissolution of Cr2O3 into Coal Slag and Its Impact on Slag Flow Properties

In an entrained-flow coal gasifier, gasification slag derived from the melting of mineral matter in coal flows along the refractory wall and is tapped out. The refractory of spallation and dissolution enters into coal slag and can affect the slag flow properties, which are crucial for the entrained-flow gasifier's smooth operation. Cr2O3 is one of the most common compositions of refractory materials and is selected to research the effect of refractory on the flow properties of slag. In this work, the dissolution of Cr2O3 into coal slag is calculated by FactSage software, and its impact on ash fusion temperatures and slag viscosity are investigated. The Cr2O3 concentration of coal slag increases from 0.5 to 4 wt % as the operation temperature rises (1300-1600 degrees C). Cr2O3 reacts with FeO to form the high-melting point mineral donathite during the ash melting process, and the retention of FeO reduces the formation of low-melting point clinopyroxene, leading to the increase of ash fusion temperatures with the Cr2O3 content. In addition, the slag viscosity increases with the Cr2O3 content because of the increasing polymerization degree of the slag structure. Crystalline donathite formed by Cr2O3 is precipitated first during the cooling process, and the precipitated donathite acts as the heterogeneous nucleus, promoting the precipitation of troilite and anorthite and thus increasing the critical viscosity temperature. This suggests that the high-chromia refractory material corrosion can cause the fluctuation of slag flowability and even lead to slag blockage. Therefore, the gasifier cannot be operated beyond the upper limit of operation temperature (1600 degrees C) for a long time to avoid the severe dissolution of refractory materials.