Membrane CO2 Separation With Permeate Sweep for Combustion Exhaust
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Solution Overview
Problem
Current membrane-based gas separation processes for removing carbon dioxide from combustion exhaust gases are inefficient and economically impractical, particularly in large-scale industrial applications like power plants, due to low carbon dioxide concentration in the exhaust streams and high energy costs associated with pressure-driven separation methods.
Innovation Solution
A membrane-based gas separation process using a sweep gas on the permeate side to enhance the driving force for transmembrane permeation, specifically utilizing membranes with high carbon dioxide permeance and selectivity, and recycling the carbon dioxide-enriched permeate stream back to the combustor to increase carbon dioxide concentration and reduce the volume of gas needing further processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If membrane-based gas separation is used to remove carbon dioxide from combustion exhaust, then carbon dioxide removal capability is improved, but the process becomes economically impractical due to low carbon dioxide concentrations and high transportation costs
Solution Approach 1:
The patent applies preliminary action by concentrating the carbon dioxide stream before it enters the membrane separation unit. A pre-concentration step using absorption or adsorption removes a portion of the carbon dioxide, creating a more concentrated feed stream that reduces the size and cost of the subsequent membrane separation system and lowers transportation costs.
Solution Approach 2:
The patent segments the carbon dioxide removal process into multiple stages: a pre-concentration stage using absorption or adsorption, followed by a membrane separation stage. This segmentation allows each stage to operate under optimized conditions and reduces the overall system complexity and cost compared to using membrane separation alone.
2Productivity
If a sweep gas is used on the permeate side to enhance driving force for carbon dioxide removal, then separation efficiency is improved, but device complexity increases
Solution Approach 1:
The patent applies self-service by using the permeate stream itself as the sweep gas. The permeate, which is already separated carbon dioxide-rich gas, is recycled back to the feed side to provide the sweeping action needed to maintain the partial pressure gradient. This eliminates the need for an external sweep gas source and associated equipment.
Solution Approach 2:
The patent recovers and reuses the permeate stream as the sweep gas instead of discarding it. The permeate, containing concentrated carbon dioxide, is recycled to the feed side where it serves as the sweeping gas, thereby recovering a useful resource and eliminating the need for additional sweep gas supply systems.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces the carbon dioxide content in exhaust gases to less than 5 vol %, minimizing environmental impact and lowering transportation and processing costs by concentrating carbon dioxide for more efficient capture and sequestration, while maintaining energy efficiency.
Implementation Method 1
membranes selectively permeable to carbon dioxide over nitrogen and oxygen, with a carbon dioxide/nitrogen selectivity of at least 10
Implementation Method 2
passing a sweep gas across the permeate side of the membranes, thereby lowering the partial pressure of a desired permeant on that side
Data Source
AI summary
A gas separation process for treating exhaust gases from the combustion of gaseous fuels, and gaseous fuel combustion processes including such gas separation. The invention involves routing a first portion of the exhaust stream to a carbon dioxide capture step, while simultaneously flowing a second portion of the exhaust gas stream across the feed side of a membrane, flowing a sweep gas stream, usually air, across the permeate side, then passing the permeate/sweep gas back to the combustor.