(771c) Post-Combustion Carbon Dioxide Capture Using Membrane Processes: A Sensitivity Analysis

Energy saving is the main challenge for post-combustion CO₂ capture technology. Membrane process has attracting growing interest for CO₂ capture applications.  This work focus on the potential of membrane processes for CO₂ capture for a wide range of process parameters in order to identify the right place and role of membrane processes in CCS technology.

 A broad range of CO₂ inlet concentration (5%-70%) corresponding to various emission sources has been investigated. In order to explore the influence of membrane material selectivity CO₂ over N₂ (a) on the process performances, three different membrane selectivities are simulated: a=50 corresponding to commercially available membranes and a=100 and 200 corresponding to prospective membranes. A large range of process performances in term of CO₂ purity and recovery ratio are investigated and the corresponding energy requirement is compared to the reference technology, MEA absorption. Furthermore, two compression strategies: feed compression with energy recovery system on the retentate and vacuum pumping are investigated. Their performances in term of energy requirement and membrane surface area are evaluated and compared. Hereafter are some important conclusions :

• For concentrated CO₂ inlet flue gas (x_in>0.2), a standalone membrane process can fulfill the target of CO₂ purity and recovery ratio with a lower energy requirement than a standard MEA absorption process.
• For more concentrated flue gas (x_in>0.3), it is shown that there is no significant interest to increase the membrane selectivity up to 100 because much higher membrane surface area will be required with almost the same energy requirement.
• For very concentrated CO₂ (x_in>0.5), a membrane process could play a role of polishing step with very low energy requirement (0.2-0.5 GJ/ton CO₂).
• Energy requirement decreases significantly for moderate CO₂ purity in the permeate suggesting that membrane process could play a role of a preconcentration process in a hybrid process. 
• For more diluted CO₂ flue gas (x_in<0.15), membrane process cannot fulfill the targets of CO₂ purity and recovery ratio (R=0.9 and y=0.9) whatever the membrane selectivity. In this case, a multistage membrane process is needed to achieve the capture target.
• Feed compression with ERS strategy leads to a much lower membrane surface area (a factor of ×6 could be attained) while energy requirement remains almost the same with the permeate vacuum energy being slightly lower.
•  A trade-off exists between membrane and surface area regarding the CO₂ recovery ratio, the membrane selectivity and the compression strategy. A technico-economic analysis is needed in order to determine the optimum operating parameters and configuration, taking into account both the CAPEX and OPEX of the process.