The Need

Post-combustion carbon capture (PCC) provides an option to mitigate CO₂ emissions from large stationary sources, followed by compression, transport, and geological sequestration; the captured CO₂ may be used for enhanced oil recovery. Because of the system compactness and energy efficiency, CO₂-selective membranes have been suggested to be a promising candidate for PCC. Typically, a stripping cascade is not suitable for separation requiring high product purity and recovery simultaneously. An enriching cascade is capable of achieving at least 90% CO₂ recovery with 95% purity, but the capture cost and energy penalty are unfavorable. The air-sweep process, however, utilizes the combustion air as a “free” driving force, thereby resulting in a reduced capture cost.

The Technology

Researchers at The Ohio State University, led by WS Winston Ho, have developed a 2-stage enriching cascade membrane process for capturing CO₂ from flue gas in a power plant. In the process, the flue gas flows to the first enriching membrane stage using a membrane with high CO₂ permeance and low CO₂/N₂ selectivity. The CO₂-enriched permeate gas then flows to the second enriching membrane stage employing another membrane with high CO₂/N₂ selectivity but modest CO₂ permeance. This stand-alone hybrid membrane process shows a comparable capture cost to the state of the art membrane processes using power plant combustion air as membrane sweep gas. More importantly, the risk of affecting the power plant efficiency caused by air sweep is eliminated.

Commercial Applications

• Carbon capture from power plants
• CO₂ emissions mitigation

Benefits/Advantages

• The risk of affecting the power plant efficiency caused by air sweep is eliminated
• This particular process is more cost effective than traditional membrane processes