503 / 2019-01-04 18:02:59

Process Simulations of CO2 Desorption by Direct Pentane Steam Stripping

CO2 capture, solvent regeneration, direct pentane stripping process, simulation

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Carbon capture, storage, and utilization (CCUS) are playing a significant role in the efforts of global carbon mitigation. CO2 capture by chemisorption is an effective approach to separate CO2 from the effluent gas mixture in large point sources. Recent progress in the fundamental research and demonstration of CO2 chemisorption has enabled this technology to be ready for commercialization. However, it is still challenged by high energy consumption arising from the water evaporation during solvent regeneration. A novel solvent regeneration process, direct steam stripping (DSS), was proposed and has been proved to be able to lower the energy consumption by over 20% compared with the conventional stripping process based on a reboiler (DRP). Further, the direct steam stripping process that uses pentane (DPS) as the stripping gas shows an even lower need in energy for solvent regeneration. This work uses simulation method to study the effects of solvents and operating conditions on the CO2 desorption rate and energy consumption of direct pentane stripping process. By using the VLE data under the actual regeneration conditions, the thermodynamic model of the Amine/CO2-Pentane/H2O is established in Aspen Plus. The rate-based model and two-film theory are utilized for the mass transfer calculation. For aqueous MEA, AMP and MDEA solutions, the DPS process shows a lower energy consumption, which is 15~25% and 38~60% lower than DSS and CRP respectively. The CO2 concentration, pressure and temperature profiles along the stripper illustrate a stronger flash process in DPS due to a stronger driving force of the stripping gas at the top of the stripper. The enhanced evaporation of water by pentane stripping results in the stronger perturbation in the gas-liquid interface, which helps break the gas-liquid boundary to gain enhanced kinetics. Because of the flashing phenomenon, the solvents (e.g., MDEA) with better VLE properties at rich loadings and less desorption heat show more significant potential in energy reduction for DPS. The lower temperature and loading of solvents illustrate the less consumption for the lean solvent cooler and absorber. Under the same CO2 removal efficiency of 90%, the required packing height in DPS is averagely 30% lower than that of DSS. As for the recovery system, the effects of the compression pressure and flashing temperature are significant for the recovery efficiency, but the influence of the H2O removal rate is insignificant.