Damage Mechanism Of Chromia-aluminia-zirconia Bricks And Preparation Of Chromia-free Lining Materials

Gasification is a key process to use coal in a clean and efficient way. Gasifier is the high-temperature reactor of this process. Long service life of the lining materials is required to keep gasifier running safety and efficiency. To withstand the corrosion of gasifier lining from gasifier slag, phosphate bonded Cr2O3-Al₂O₃-ZrO2 ?CAZ? refractories with more than 75wt% chromia containing are conventionally used in the working surface of gasifier lining due to the low solubility of Cr2O3 in the gasifier slag. However, it has been reported that phosphate would be reduced under reducing atmosphere at high temperature. So, the corrosion mechanism of CAZ refractories has to be further studied. Besides, chromia is very expensive. More importantly,the formation of toxic hexavalent chrome in the manufacture or service would cause environmental problem. So, extending the service life of CAZ refractories and developing chromia-free lining materials for gasifier are indespensible.Based on the problems mentioned above, influence of sintering and simulative service atmosphere on the structure and properties of CAZ refractories were studied in the present work. Then CAZ castables bonded with CA-cement and organic polymer ?Isobam? were developed, corrosion resistance of these castables were studied. In order to developing chromia-free lining materials for gasifier, thermodynamic factors and kinetic factors were both taken into consideration to research the high temperature interactions between typical refractories and gasifier slag. Reaction mechanism between refractories and gasifier slag were analysed to provide theoretical basis for chromia-free lining research. Moreover, Al₂O₃-C, Al₂O₃-SiC-TiO2-C and Al₂O₃-MgAl₂O₄-C chromia free linings were developed. Sintering properties, microstructure, pore structure and corrosion resistance were studied to evaluate the possibility of these materials used as gasifier lining.The results showed that:when fired in coke bed, phosphate would be reduced and weakened the bonding system between aggregate and matrix, resulted in worse corrosion resistance of CAZ refractories.Cement and Isobam bonded CAZ castables showed better sintering properties and corrosion resistance when their fired in coke bed compared to that fired in air. Composites consist by Al₂O₃/MgAl₂O₄ and non-oxides might be used as chromia-free lining materials for gasifiers. Al₂O₃-C refractories showed better penetration resistance than CAZ ones both tested in air and in coke bed. The addition of 2wt% TiO2 could promote the formation of Ti?C,N? in the matrix of Al₂O₃-C refractories, which would increase the viscosity of slag during corrosion and improve the corrosion resistance of these materials. The addition of spinel in appropriate amount was benefit for the penetration resistance of Al₂O₃-MgAl₂O₄-C materials.