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

Abstract

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. Cr 2 O 3 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 Cr 2 O 3 into coal slag is calculated by FactSage software, and its impact on ash fusion temperatures and slag viscosity are investigated. The Cr 2 O 3 concentration of coal slag increases from 0.5 to 4 wt % as the operation temperature rises (1300−1600 °C). Cr 2 O 3 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 Cr 2 O 3 content. In addition, the slag viscosity increases with the Cr 2 O 3 content because of the increasing polymerization degree of the slag structure. Crystalline donathite formed by Cr 2 O 3 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 °C) for a long time to avoid the severe dissolution of refractory materials.

Influence of Ti3AlC2 addition on water vapor resistance of low‐carbon Al2O3–C refractories

“…3,4 Thus, Cr 2 O 3containing refractories are preferred materials for gasifiers' working linings because of their excellent resistance to gasifier slag corrosion. 5,6 However, Cr 2 O 3 -containing refractories cause a high risk of hexavalent chromium pollution during the production process and after handlining usage. 7,8 Therefore, Cr 2 O 3 -free refractories for coal-water slurry gasifier furnaces must be developed.…”

“…Lining refractories are key components of gasifiers and need to withstand complex and harsh conditions such as high temperature/pressure, reducing atmosphere, high‐speed scouring of solid–liquid–gas flow, and a chemical corrosion of liquid and acidic slag 3,4 . Thus, Cr 2 O 3 ‐containing refractories are preferred materials for gasifiers’ working linings because of their excellent resistance to gasifier slag corrosion 5,6 . However, Cr 2 O 3 ‐containing refractories cause a high risk of hexavalent chromium pollution during the production process and after handlining usage 7,8 .…”

Bio-Slag High-Temperature Corrosion on an Alumina Refractory under the Reducing Environment

“…A refractory brick wall as the lining is widely used in coal-water slurry gasifiers due to its stability. 5,9 There are also attempts on the Mg-aluminum base, Ti-aluminum base, and silicon carbide-based materials. 10,11 However, the high-chromia refractory material is widely used in the current gasifiers as the fire-resistant refractory because of its superior resistance.…”

“…The failure mechanism of refractory materials is due to chemical dissolution of the refractory by molten slags, chemical and structural spalling caused by molten slag penetration into the refractory. − Different materials have been evaluated as the refractory wall. A refractory brick wall as the lining is widely used in coal-water slurry gasifiers due to its stability. , There are also attempts on the Mg-aluminum base, Ti-aluminum base, and silicon carbide-based materials. , However, the high-chromia refractory material is widely used in the current gasifiers as the fire-resistant refractory because of its superior resistance. − Different studies have shown that Cr 3+ has the potential to be converted to Cr 6+ at high temperature, which is recognized as a human carcinogen and it is more hazardous than Cr 3+ . Recently, several researchers develop chrome-free refractories to reduce the gasification operation cost, as well as decreasing environmental pollution. , The silicon carbide material has been investigated as refractories in gasification reactors, and it has been proved to have high thermal shock resistance .…”