Identifying the multi-ion effects on the phase flow, mass and heat transfer in amine absorption of CO_2

摘要

Carbon dioxide mitigation strongly supports the greenhouse gas control. Amine absorption of CO_2, as a method to mitigate the CO_2, is a typical multi-ion system with obvious multi-ion effects. However, there is little information about the multi-ion effects on the phase flow, mass and heat transfer in amine absorption of CO_2. The multi-ion effects have previously to be neglected to simplify the absorption process description, which produces unknown deviations from the realistic absorption process. According to experiment data, a multi-ion mass transfer, heat transfer and phase flow model is here developed to describe the realistic amine absorption of CO_2. The turbulent diffusivity, turbulent thermal diffusivity, turbulent viscosity, CO_2 concentration, liquid temperature and velocity are analyzed under the multi-ion conditions. It was found that there is 6-22% CO_2 concentration difference between the multi-ion effects case and the neglect of the multi-ion effects (NME) case. The positive ions show the better synergy effects compared with the negative ions. Under the ion concentration of 0.001 kmol/m~3 to 0.02 kmol/m~3, 0.2 kmol/m~3 to 2 kmol/m~3 and 4 kmol/m~3 to 7 kmol/m~3, the multi-ion mass transfer, heat transfer and phase flow model provides an accurate description of the realistic CO_2 absorption against the NME case. Finally, Nusselt number and mass transfer coefficient models revised by synergy angles are developed to include the multi-ion effects for engineering application. Adding the amine salt and Na_2CO_3 respectively reduce the liquid film thickness and liquid film depth, which increases the Nusselt number by 9.5% and 9.3%, respectively. Adding the metal Cu increases the Nusselt number by 11.57%, which helps to reduce the energy consumption by 7.8%.