Simulation of Rayleigh convection during dichloromethane absorption by water using lattice Boltzmann method

Abstract

Developing dichloromethane (DCM) waste gas purification and absorption technology is consistent with the demand of the circular economy and contributes to the goals of achieving carbon peaking and carbon neutrality. In addition, Rayleigh convection generated during the absorption of DCM by water is of great significance for understanding the interfacial mass transfer mechanism and enhancing the mass transfer efficiency. Thus, the absorption process of DCM discrete diffusion sources was simulated using the two-dimensional lattice Boltzmann method (LBM) with external forces to visualize the effect of Rayleigh convection evolution law on the mass transfer of the absorption process in this study. The concentration and velocity distribution with single or multiple diffusion sources were respectively simulated at 298.15 K and 1.00 atm. The results show that the convection structure of the simulated plume is similar to that of comparable studies, and the convective structure on both sides suppresses the development of the intermediate convective structure when convection occurs. At a constant gas-phase concentration (CB,g), the more the number of diffusion sources, the faster the convective structures integration, and the rapid integration of convective structures is associated with the sharp increasing instantaneous mass transfer flux. Meanwhile, increasing the gas phase concentration can effectively shorten the convection onset time (tc), increase the instantaneous mass transfer flux (Nins,t), and enhance the mass transfer efficiency by calculating the simulated transfer mass data. Furthermore, the critical onset time of Rayleigh convection first lengthens and then shortens with the number of diffusion sources (n) increasing. And the more the number of diffusion sources, the more significant the final cumulative (Nt) absorption amounts are. The simulation results can provide theoretical guidance for enhancing the mass transfer efficiency in the DCM absorption process.