(226f) Optimizing Carbon Capture with Membrane Processes

Carbon capture and sequestration (CCS) is envisioned as one approach to mitigate the potential environmental impact of carbon dioxide emissions from fossil fuel power plants. The US Department of Energy (DOE) has set aggressive CCS targets of 90% CO₂ capture at 95% purity followed by compression to 140 bar for transport and storage without increasing the levelized cost of electricity (LCOE) more than 35%.

A promising approach utilizing a hybrid membrane-cryogenic process has been proposed by Membrane Technology and Research, Inc. (MTR). The process utilizes a two-stage membrane pre-concentration step followed by a cryogenic flash. The boiler feed air is used as a sweep in the second membrane stage to achieve capture targets. The improvement in capture comes at the expense of reduced oxygen concentration in the boiler feed air.

The design space for this process is systematically explored to identify an optimal design. Of special interest is the trade-off between capital and operating expenses associated with considering membrane materials that lie along the upper bound for transport.

Results are presented for designs that achieve carbon capture targets with a boiler feed air oxygen concentration of 18% - the lowest level being considered in proposed applications. A broad range of membrane materials, membrane operating pressures, and cryogenic flash conditions yield comparable LCOE near the minimum. This observation suggests that efforts to reduce membrane manufacturing costs may have the greatest potential to improve process economics.