Study on the damage mechanism of high chromia refractory in the slag tapping hole of commercial entrained-flow gasifier

The service life of refractory brick in the slag tapping hole of gasifiers is a significant concern for long-term and stable operation. This study examined the damage mechanism of high chromia refractory of four commercial coal-water slurry gasifiers with their corresponding gasification coal samples and the corroded refractory bricks in the slag tapping hole of the gasifier. The slag characteristic, including crystallization and viscosity-temperature of four gasification coal samples were analyzed. The results revealed that the low viscosity slag could lead to more severe damage to refractory bricks. Given the risk of slag crystallization, it is recommended to establish a safe slag tapping temperature range should be set as tICT (initial crystallization temperature) − t2.5 when tICT is higher than t25. Upon examining interior morphology of these corroded refractory bricks, some cracks were observed within them. The chemical composition of molten slag was analyzed using SEM-EDS. However, XRD results found no spinel containing zirconium in these cracks. This suggests that the emergence of these cracks are mainly attributed to the molten slag penetration and the subsequent reaction with the refractory material. The difference in thermal expansion between the newly formed substances and refractory material is critical in forming these cracks. Furthermore, SEM-EDS analysis was also conducted on the slag-aggregate and the slag-matrix interface. The results reveal that the reduction in Cr2O3 content is the earliest characteristic of damage in high chromia refractories. A proposed damage mechanism of refractory brick suggests that the matrix and aggregate of high chromia refractory are initially compromised because of the reduced Cr2O3 content. Subsequently, the molten slag penetrates the interior of the refractory brick, forming new substances, leading to damage caused by the difference in thermal expansion between the new substances and the refractory brick. Understanding and preventing the reduction of Cr2O3 content is vital to prolonging the service life of refractory brick in the slag tapping hole of the gasifier based on this damage mechanism.