Analysis and prediction of slag-induced corrosion of chromium oxide-free refractory materials during fusion of coal and biomass ash under simulated gasification conditions

• Chromium oxide-free refractories are tested by three ashes simulating gasification.
• Optical microscopy and SEM/EDX reveal infiltration paths and mineral stoichiometry.
• Thermochemical modeling represents mineral formations during slag infiltration.
• SEM/EDX and thermochemical modeling have revealed promising candidates for the substitution of chromium oxides in gasifiers.

Four chromium oxide-free refractories based on spinel, alumina, and calcium aluminates are brought in contact with three ashes from coal and biomass with different base to acid ratios (B/A) and alkali contents under reducing atmosphere (simulated gasification). This investigation is performed in a lab-scale oven with a defined heat up to 1450 °C and a subsequent slow cool down to room temperature in H2/Ar atmosphere over a period of 3–4 h. Afterwards sample sections are prepared and analyzed by optical microscopy and SEM/EDX. The slag infiltration pathways are identified and the formed mineral phases in the sections are localized by SEM/EDX mapping. A stepwise model of thermochemical calculations of the interacting species using the FactSage™ software package is applied to reproduce the slag progression inside of the different refractory materials and to predict the formed mineral phases by equilibrium state calculations. The corrosion mechanisms and corrosion depths are concluded from the comparison between experiment and thermochemical calculations. A comparably good agreement between both experiment and calculation is shown. Aim of the present study is the identification of promising candidates of environmentally friendly and cheap substitutes for the commercially used chromium oxide-based refractory materials as well as the development of related methodical approaches for the evaluation/prediction.

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