Reactivity of coke ash on aluminosilicate blast furnace hearth refractories
Blast furnace hearth refractories are a key component in achieving long furnace lives. These refractories can be degraded by among other things reactions with coke ash products. Recent studies have shown that these coke ash products could be calcium aluminate based. To understand and characterize the effects of these calcium aluminates on hearth refractories a study has been carried out that investigates the reaction kinetics of CaO.Al2O3, CaO.2Al2O3 and CaO.6Al2O3 in contact with an aluminosilicate blast furnace hearth refractory. The experimental program covered the temperature range 1 450° to 1 550°C. The temperatures were chosen to represent the hot face temperatures of the hearth refractories. From this study it was found that the rate of reaction with the aluminosilicate refractory and CaO.6Al2O3 was much slower than that of CaO.Al2O3 and CaO.2Al2O3. The prevailing kinetics of the aluminosilicate refractory with CaO.Al2O3 and CaO.2Al2O3 was found to be consistent with the linear rate law. The slow rate of reaction of the refractory with CaO.6Al2O3 prohibited identification of the prevailing kinetic regime. In characterizing the reaction interface between the aluminosilicate and the calcium aluminates it was found that there was significant reaction between the refractory and CaO.Al2O3 and CaO.2Al2O3 but little reaction with the CaO.6Al2O3. The reaction layers formed at the interface between the couples were found to consist of CaO.2Al2O3, CaO.6Al2O3, corundum (Al2O3), plagioclase (CaO.Al2O3.2SiO2) and melilite (2CaO.Al2O3.SiO2). The formation of a layer with these phases could result in spalling/wear of the hearth refractory.
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