Thermodynamic Modeling and Experimental Investigation of the System Fe–Ti–O-K for Ilmenite Used as Fluidized Bed Oxygen Carrier

The capability of ilmenite for potassium uptake in a simulated oxygen carrier-aided combustion environment has been investigated. The maximum uptake of potassium and the effect of potassium inclusion on the Fe–Ti–O system was analyzed. Through laboratory experiments and thermodynamic calculations, it was found that a molar ratio of 1:1 can be formed spontaneously for both the K–Ti-system (where the formation of K2Ti2O5 was found) and the K–Fe-system (where KFeO2 was found). K2Ti2O5 was identified as an unstable phase, undergoing decomposition into K2Ti4O9. The study demonstrates that the maximum K uptake, through forming K2Ti4O9 and KFeO2, reaches 25 wt %─a notably higher value than ilmenite exposed to biomass in a fluidized bed. The research concludes that the lifetime of ilmenite is therefore rather dependent on its mechanical integrity than its maximum potassium uptake.