Investigation of mass transfer model of CO2 absorption with Rayleigh convection using multi-relaxation time lattice Boltzmann method |
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Authors: | Longyun Zheng Kai Guo Hongwei Cai Bo Zhang Hui Liu Chunjiang Liu |
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Affiliation: | 1.School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China;2.State Key Laboratory of Chemical Engineering, Tianjin University, Tianjin 300072, China |
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Abstract: | CO2 absorption into absorbents is a widely used method to reduce carbon emissions, in which the concentration gradient near the gas-liquid interface may induce Rayleigh convection (RC). Once RC occurs, the mass transfer rate will be significantly enhanced. Therefore, it is necessary to explore the mass transfer enhancement mechanism further and develop a penetration/surface divergence hybrid mass transfer model. In this study, we conduct research on the process of CO2 absorption into ethanol with RC. Firstly, we use a multi-relaxation time lattice Boltzmann method to simulate the absorption process and obtain the flow and concentration fields. And we also verify the reliability of the numerical simulation results by comparing with the experimental results. Then, we analyze the characteristics of non-uniform flow and concentration fields in RC. Moreover, we divide the near-interface region into diffusion-dominated and convection-dominated mass transfer zones by checking whether the horizontal average velocity is greater than 1.0×10-4 m·s-1. Furthermore, based on the differences in mass transfer mechanisms of the aforementioned two zones, we propose a penetration/surface divergence hybrid model to predict the instantaneous mass transfer coefficient. The prediction results demonstrate that the hybrid model can precisely predict the instantaneous mass transfer coefficient of the entire CO2 absorption process. Our proposed hybrid model provides a promising way to deal with the complex mass transfer problems with non-uniform flow and concentration fields. |
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Keywords: | Carbon dioxide Absorption Rayleigh convection Numerical simulation multiple-relaxation-time or generalized lattice Boltzmann model (MRT-LBM) Mass transfer |
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