Effect of coal slag on the wear rate and microstructure of the ZrO2-bearing chromia refractories

The typical properties of slag and refractories for slagging coal gasifier were investigated. In the range of 0-25% CaO/ash, the characteristic ash-fusion temperatures (AFTs) and viscosity of a coal-ash slag decreased with an increase of CaO additive. When the CaO/ash ratio was greater than 25% in the mixture of the coal and limestone, AFTs no longer reduced. The slag viscosity for limestone addition with CaO/ash = 25% was very low and in a narrow range (4-13 Pa.s) at coal gasification temperatures between 1300 degrees C and 1500 degrees C. However, corrosion resistance of the ZrO2-bearing chromia refractories reduced with increasing CaO content in coal slag, especially for a slag with more than 30% CaO content. Increased chromia in three kinds of the ZrO2-bearing chromia refractories resulted in increased corrosion resistance. The higher the Cr2O3 content and the lower the SiO2 content, the less the deterioration of microstructures in the materials. Thermochemical spalling of the ZrO2-bearing 80% Cr2O3 refractory after 807 operating hours of a coal gasifier was considered as the primary attack mechanism. (C) 1997 Elsevier Science Limited and Techna S.r.l.