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

Abstract

The changes in microstructures of a high chromia refractory containing Al 2O 3 and ZrO 2 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 Cr 2O 3 and (Cr,Al) 2O 3; of Zr were ZrO 2 and Zr-silicate; of Si were silicates of Al 2O 3 and ZrO 2; and of Al were Al-silicate and (Cr,Al) 2O 3. As coal slag infiltrated a chromia refractory, FeO in the slag first reacted with Cr 2O 3 forming FeCr 2O 4 until there was no FeO remaining in the penetrating slag. Then, Al 2O 3 in the slag interacted with Cr 2O 3, forming (Al,Cr) 2O 3 from the outer edges of the particle. The slag resistance of Cr 2O 3 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 ZrO 2, 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.