Mass transfer in molten salt and suspended molten salt in bubble column

Recently, the practical uses of bubble columns and slurry bubble columns at elevated temperature have attracted much attention. However, there is less knowledge of mass transfer in high temperature slurry bubble column, even though mass transfer data is essential to design bubble column and slurry bubble column. In this study, the CO₂ mass transfer in eutectic mixtures of molten carbonate in bubble column at elevated temperature was investigated. CO₂ was chosen as gas species, eutectic mixtures of Li₂CO₃-K₂CO₃ (38:62mol%) binary molten carbonate and Li₂CO₃-Na₂CO₃-K₂CO₃ (43.5:31.5:25mol%) ternary molten carbonate were used as liquid phase. In those eutectic mixtures, CO₂ solubilities were determined at the temperature from 673K to 1173K. The values of solubilities increased with increasing temperature. It was suggested that CO₂ dissolved into binary and ternary molten carbonate with chemical interaction, CO₂+CO₃^2-↔C₂O₅^2-. Increasing the temperature shifted this equation to the right and then more CO₂ chemically dissolved into molten carbonates as C₂O₅^2-. From the CO₂ gas absorption rate in molten carbonates, CO₂ liquid phase volumetric mass transfer coefficients, k_La were determined and the influence of temperature and superficial gas velocity on k_La was also investigated. The k_La decreased with increasing temperature. And the k_La increased linearly with increasing superficial gas velocity. Regardless of unusual conditions in molten salt in bubble column at high temperature, where viscosity, surface tension and gas diffusivity were relatively high, it was suggested that the superficial gas velocity was most important operation condition in common with aqueous bubble column at ambient temperature.