Feasibility Study of Vacuum Pressure Swing Adsorption for CO2 Capture From an SMR Hydrogen Plant: Comparison Between Synthesis Gas Capture and Tail Gas Capture

In this paper, a feasibility study was carried out to evaluate cyclic adsorption processes for capturing CO2 from either shifted synthesis gas or H2 PSA tail gas of an industrial-scale SMR-based hydrogen plant. It is expected that hydrogen is to be widely used in place of natural gas in various industrial sectors where electrification would be rather challenging. A SMR-based hydrogen plant is currently dominant in the market, as it can produce hydrogen at scale in the most economical way. Its CO2 emission must be curtailed significantly by its integration with CCUS. Two Vacuum Pressure Swing Adsorption (VPSA) systems including a rinse step were designed to capture CO2 from an industrial-scale SMR-based hydrogen plant: one for the shifted synthesis gas and the other for the H2 PSA tail gas. Given the shapes of adsorption isotherms, zeolite 13X and activated carbon were selected for tail gas and syngas capture options, respectively. A simple Equilibrium Theory model developed for the limiting case of complete regeneration was taken to analyse the VPSA systems in this feasibility study. The process performances were compared to each other with respect to product recovery, bed productivity and power consumption. It was found that CO2 could be captured more cost-effectively from the syngas than the tail gas, unless the desorption pressure was too low. The energy consumption of the VPSA was comparable to those of the conventional MDEA processes.

Hydrogen Purification Performance Optimization of Vacuum Pressure Swing Adsorption on Different Activated Carbons

Hydrogen purification is an important part of hydrogen energy utilization. This study aimed to perform hydrogen purification of multi-component gas (H2/CO2/CH4/CO/N2 = 0.79/0.17/0.021/0.012/0.007) by one-column vacuum pressure swing adsorption (VPSA) and pressure swing adsorption (PSA). AC5-KS was selected as the adsorbent for hydrogen purification due to its greater adsorption capacity compared to R2030. Furthermore, VPSA and PSA 10-step cycle models were established to simulate the hydrogen purification process using the Aspen Adsorption platform. The simulation results showed that the hydrogen purification performance of VPSA is better than that of PSA on AC5-KS adsorbent. The effects of feeding time and purging time on hydrogen purity and recovery were also discussed. Results showed that feeding time has a negative effect on hydrogen purity and a positive effect on hydrogen recovery, while purging time has a positive effect on hydrogen purity and a negative effect on hydrogen recovery. By using an artificial neural network (ANN), the relationship between the inputs (feeding time and purging time) and outputs (hydrogen purity and recovery) was established. Based on the ANN, the interior point method was applied to optimize hydrogen purification performance. Considering two optimization cases, the optimized feeding time and purging time were obtained. The optimization results showed that the maximum hydrogen recovery reached 88.65% when the feeding time was 223 s and the purging time was 96 s. The maximum hydrogen purity reached 99.33% when the feeding time was 100 s and the purging time was 45 s.

Enrichment and Separation of Methane Gas by Vacuum Pressure Swing Adsorption

In China, owing to the methane concentration being below 0.75%, the coal ventilation air methane (CVAM) is usually emitted directly into the atmosphere, rather than utilized, which not only causes huge waste of energy but also exerts potential hazards to the greenhouse effect. It is important and practicable to save costs of development and investment by simulating enrichment and separation of CVAM with an aim to improve the efficiency and recovery of adsorption separation. Above all, it will have important practical significance to the development of adsorption separation. In this paper, the experiment of the pressure swing adsorption process was carried out on double towers built by our laboratory, and the Aspen Adsorption was used to simulate the process. The effect of the operation parameters on the desorbed methane concentration was studied by altering the feed concentration, the adsorbed pressure, and adsorbed and desorbed time. The results of simulation and experiment are basically consistent. The ratio of methane was decreased following the increasing concentration of the feed. The optimum adsorption pressure and time were found to be 210 kPa and 120 s, respectively. The optimum desorption times of experiment and simulation were 150 s and 120 s, respectively. Because there was a man-made 30 s time lag between the experiment and simulation to protect the vacuum pump, the results show that the simulation and experiment were matched well. Therefore, we can make use of Aspen Adsorption to design separation and enrichment of CVAM, providing theoretical and practical guidance for the gas separation and saving resources and energy.