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

摘要

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.