Changes in microstructure of a high chromia refractory due to interaction with infiltrating coal slag in a slagging gasifier environment

The changes in microstructures of a high chromia refractory containing Al2O3 and ZrO2 due to interaction with penetrating coal slag under slagging gasifier conditions were investigated. The unused chromia refractory was an inhomogeneous mixture of microstructures of varying shape, size, composition and degree of densification. The chemical structures of Cr were Cr2O3 and (Cr,Al)2O3; of Zr were ZrO2 and Zr-silicate; of Si were silicates of Al2O3 and ZrO2; and of Al were Al-silicate and (Cr,Al)2O3. As coal slag infiltrated a chromia refractory, FeO in the slag first reacted with Cr2O3 forming FeCr2O4 until there was no FeO remaining in the penetrating slag. Then, Al2O3 in the slag interacted with Cr2O3, forming (Al,Cr)2O3 from the outer edges of the particle. The slag resistance of Cr2O3 varied with the particle size and the extent of densification, and the higher resistance was observed in the larger and more densified particles. There was no chemical change in ZrO2, but it may have dissolved in the slag. The same interaction products were observed in both laboratory-tested and spent refractories from a pilot scale gasifier. The composition and the crystalline phase analyses also support chromite formation at the interface and subsequent depletion of Fe. When the temperature and time were varied, the percent of slag penetrated increased with the exposure time and temperature, though changes in microstructures were difficult to quantify.