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

Abstract

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+CO32−↔C2O52−. Increasing the temperature shifted this equation to the right and then more CO2 chemically dissolved into molten carbonates as C2O52−. From the CO2 gas absorption rate in molten carbonates, CO2 liquid phase volumetric mass transfer coefficients, kLa were determined and the influence of temperature and superficial gas velocity on kLa was also investigated. The kLa decreased with increasing temperature. And the kLa 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.