Experimental and simulation study on high-pressure V-L-S cryogenic hybrid network for CO2 capture from highly sour natural gas

Abstract Cryogenic carbon dioxide (CO2) capture technologies showed promising results for the purification of highly sour natural gas reserves. However, quantitative experimental data for solid and liquid CO2 formation during cryogenic separation is not adequately examined in the previous studies. Moreover, an economical and efficient cryogenic CO2 capture technology with reduced energy and hydrocarbon losses is necessary to make it attractive for commercial use. A high-pressure cryogenic hybrid network comprised of the packed bed and the cryogenic separator was developed for the cryogenic experimental study on CO2 capture from binary CO2-CH4 mixture to focus these areas. Feed containing 30, 50 and 70 % CO2 content were used and the separation study was conducted in vapor-solid (V-S), vapor-liquid (V-L), and vapor-liquid-solid (V-L-S) regions of phase equilibria. The packed bed was used in the V-S operational domain to quantify CO2 solid up to 20 bar because of the operational limitations. Separation characteristics and V-L isothermal flash measurements at 20, 30, and 40 bar pressure and temperature ranges from -20 to −60 °C were carried out in the cryogenic separator. The operation in the setups was carried out at different compositions of the CH4-CO2 binary mixture to define the boundaries of the hybrid cryogenic network. Liquid formation at 40 bar for 70% CO2 feed was 0.15 kg at -55 °C as compared to 0.03 kg for 30 % CO2 feed. The simulation study was carried out using Aspen Plus along with the Peng Robinson Equation of State (EoS), and the results were compared with the experimental data, which showed good agreement. The hybrid cryogenic network showed an energy reduction of 37 % compared to the conventional cryogenic distillation network with 90.6 to 97.3 % CH4 purity and 2.65 to 12.39 % methane losses with different arrangements of the hybrid cryogenic network.