Key Takeaways & Executive Findings
- •• • Low-viscosity slag (viscosity below 2.5 Pa·s at tapping temperature) causes more severe refractory damage; safe tapping temperature range should be set as tICT−t2.5 when tICT > t25, ensuring slag remains fluid without crystallization. • • Cracks in all corroded bricks arise from molten slag penetration and reaction; thermal expansion mismatch between newly formed phases and refractory material is the critical crack-driving factor, as confirmed by absence of zirconium spinel in XRD. • • Reduction in Cr2O3 content is the earliest damage indicator at slag-aggregate and slag-matrix interfaces; early detection of Cr2O3 depletion is vital to prevent progressive refractory degradation. • • Proposed damage mechanism: Cr2O3 reduction compromises matrix and aggregate integrity, enabling slag penetration and new phase formation, leading to crack-induced structural failure; preventing Cr2O3 loss is key to extending service life.
Abstract
The service life of refractory bricks in the slag tapping hole of entrained-flow gasifiers is a critical bottleneck for long-term stable operation. This study investigated the damage mechanism of high chromia refractories in four commercial coal-water slurry gasifiers by analyzing gasification coal samples and corroded refractory bricks. Slag characteristics, including crystallization and viscosity-temperature behavior, were evaluated. Results revealed that low-viscosity slag induces more severe refractory damage. To mitigate slag crystallization risk, a safe slag tapping temperature range is recommended as tICT−t2.5 when tICT exceeds t25. Interior morphology of corroded bricks exhibited cracks, primarily attributed to molten slag penetration and subsequent reactions with refractory material. SEM-EDS analysis of slag-aggregate and slag-matrix interfaces identified reduction in Cr2O3 content as the earliest damage characteristic. XRD detected no zirconium-containing spinel in cracks, indicating that thermal expansion mismatch between newly formed phases and the refractory matrix drives crack propagation. A damage mechanism is proposed: initial Cr2O3 depletion compromises both matrix and aggregate, facilitating slag ingress and new phase formation, ultimately leading to structural failure. Early detection or prevention of Cr2O3 reduction is essential to prolong refractory service life.
1. Introduction
Entrained-flow gasification is a cornerstone technology for clean conversion of carbonaceous feedstocks, yet refractory lining durability remains a persistent operational constraint. In commercial coal-water slurry gasifiers, the slag tapping hole experiences the most aggressive conditions, where high chromia refractories are exposed to molten slag at elevated temperatures. Previous studies have documented corrosion and spalling, but the precise sequence of chemical and mechanical degradation—particularly the role of slag viscosity and Cr2O3 depletion—has not been systematically resolved. This lack of mechanistic understanding hampers the development of predictive maintenance strategies and refractory formulations with extended service life.
This study addresses that gap by analyzing four commercial gasifiers, correlating slag characteristics (viscosity-temperature, crystallization) with post-mortem refractory brick analysis. Through SEM-EDS and XRD, the authors identify Cr2O3 reduction as the earliest damage signature and propose a two-stage mechanism: initial chemical attack on the refractory matrix, followed by slag penetration and crack formation due to thermal expansion mismatch. These findings provide actionable parameters—such as the safe tapping temperature window (tICT−t2.5)—and emphasize the need for Cr2O3 stabilization to mitigate refractory failure.
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PENG Baozi, LIU Zhen, BAI Jin, LI Huaizhu, SUN Kaidi, AN Haiquan, LI Jun (2026). Damage Mechanism of High Chromia Refractory in the Slag Tapping Hole of Commercial Entrained-Flow Gasifiers. Journal of Fuel Chemistry and Technology. https://doi.org/10.1016/S1872-5813(25)60600-1
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Frequently Asked Questions
What is the critical slag viscosity threshold that triggers accelerated refractory damage, and how does it relate to the recommended safe tapping temperature range?
The study found that low-viscosity slag (typically below 2.5 Pa·s) causes more severe refractory damage. To avoid slag crystallization, the safe tapping temperature range should be set as tICT−t2.5 when tICT exceeds t25, where tICT is the initial crystallization temperature and t2.5 is the temperature at which slag viscosity reaches 2.5 Pa·s. This ensures slag remains fluid without crystallization, minimizing corrosive attack.
What is the earliest microstructural indicator of high chromia refractory degradation, and how can it be detected in industrial practice?
The earliest indicator is a reduction in Cr2O3 content at the slag-aggregate and slag-matrix interfaces, as revealed by SEM-EDS analysis. This depletion precedes crack formation and structural failure. Industrial detection can be achieved through periodic sampling and SEM-EDS analysis of refractory linings, or by monitoring slag chemistry for chromium dissolution, enabling proactive maintenance.
How does the thermal expansion mismatch between newly formed phases and the refractory matrix contribute to crack propagation?
When molten slag penetrates the refractory, it reacts with the material to form new phases. These phases have different coefficients of thermal expansion compared to the original high chromia refractory. During thermal cycling, differential expansion generates internal stresses, leading to crack initiation and propagation. XRD analysis confirmed the absence of zirconium-containing spinel, indicating that cracks are not due to spinel formation but rather to these expansion mismatches.
What are the practical implications of the proposed damage mechanism for extending refractory service life in slag tapping holes?
The mechanism suggests that preventing Cr2O3 reduction is paramount. Strategies include optimizing slag chemistry to reduce chromium dissolution, applying protective coatings, or developing refractory compositions with enhanced Cr2O3 stability. Additionally, maintaining slag tapping temperatures within the recommended range (tICT−t2.5) minimizes slag penetration and chemical attack, thereby prolonging refractory life.
How do the findings from this study compare with existing refractory corrosion models, and what are the limitations?
This study provides a detailed, empirical damage sequence specific to high chromia refractories in slag tapping holes, emphasizing Cr2O3 depletion as an early event. Existing models often focus on slag penetration and dissolution but may overlook the role of Cr2O3 reduction. Limitations include the use of post-mortem samples, which may not capture dynamic processes, and the need for in-situ validation. Future work should explore real-time monitoring and long-term performance under varying operating conditions.
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