Process Design of Hydrate-Membrane Coupled Separation for CO₂ Capture from Flue Gas: Energy Efficiency Analysis and Optimization

Natural gas hydrates, as a novel gas separation technology, hold significant promise for the separation of CO₂ from flue gas. In this study, a comprehensive analysis integrating hydrate-based technology and membrane separation technology is conducted to establish a post-combustion CO₂ capture process. The heat calculation of the hydrate unit in the separation process is performed based on experimental CO₂/N₂ hydrate separation data, leading to a heat value of 1,104,662 MJ/h for the formation and decomposition of hydrates. In the membrane separation unit, the mathematical model of hollow fiber membranes is employed to conduct an optimization process for the membrane area and inlet pressure. The optimization objectives focus on attaining a product gas with a CO₂ concentration of 90 mol% and a CO₂ recovery rate of 95%. As a result, the first-stage membrane area is determined to be 8000 m² and the inlet pressure to be 1.45 MPa, while for the second-stage, the optimal values are found to be 5000 m² for the membrane area and 2.00 MPa for the inlet pressure. Finally, following the optimization of the energy consumption throughout the entire process, a comprehensive analysis is carried out to assess the energy consumption and energy efficiency of the process. The findings reveal that the most significant energy losses in the process occur during the initial pressurization phase of the feed gas and the subsequent formation and decomposition stages of the hydrates. Additionally, the unit energy cost for CO₂ capture is calculated to be 0.4416 kWh/kg CO₂. In comparison to alternative post-combustion CO₂ capture technologies, this process exhibits distinct advantages.