Four-Stage Membrane Biogas Upgrading with Internal Sweep Gas
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Solution Overview
Problem
Existing membrane-based gas separation systems for upgrading biogas to biomethane face inefficiencies due to unpredictable performance in the retentate stage, particularly when recycling CO2 reduction streams, leading to high costs and inefficiencies.
Innovation Solution
A four-stage membrane system where the third retentate stream is purified further in a fourth stage to generate a sweep gas for the second stage, eliminating the need for external sweep gases and optimizing the permeate side efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the third retentate stream is recycled into the feed stream in a three-stage arrangement, then product recovery is improved, but performance becomes unpredictable due to high CO2 reduction conditions
Solution Approach 1:
The system divides the retentate processing into separate stages: the third retentate stream is separated from the main feed recycling loop and directed to a fourth membrane stage for further CO2 removal. This segmentation isolates the problematic high CO2 reduction conditions from the main recycling loop, improving performance predictability while maintaining product recovery through the fourth stage's purified stream recycling.
Solution Approach 2:
The fourth membrane stage acts as an intermediary between the third retentate stream and the feed stream recycling. It processes the third retentate stream to reduce CO2 concentration to acceptable levels before recycling, thereby mediating the conflict between maintaining high product recovery and ensuring predictable performance by preventing excessive CO2 buildup in the recycled stream.
2Productivity
If external sweep gas is used in the second membrane stage, then permeate side efficiency is improved, but system complexity and cost increase
Solution Approach 1:
The system generates its own sweep gas internally through the fourth membrane stage, which produces a CO2-reduced retentate stream suitable for use as sweep gas in the second membrane stage. This self-service approach eliminates the need for external sweep gas sources, reducing system complexity and cost while maintaining permeate side efficiency.
3Productivity
If valuable product streams are used as sweep gases, then permeate side efficiency is improved, but product loss increases
Solution Approach 1:
The fourth membrane stage changes the composition parameters of the third retentate stream by further removing CO2, transforming it into a suitable sweep gas with acceptable CO2 concentration. This parameter change allows the use of what would otherwise be a waste stream as a valuable sweep gas resource, improving efficiency without causing product loss.
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 enhances the efficiency of the gas separation process by generating its own sweep gas, reducing costs, and improving the purity and recovery of methane and CO2 streams without recycling valuable product streams as sweep gases.
Implementation Method 1
a first gas separation membrane that is more permeable to the second component than the first component, the first gas separation membrane separating the feed stream to form a first retentate stream and a first permeate stream
Data Source
AI summary
Disclosed herein are membrane-based gas separation methods and systems. The methods and systems may, in particular, be used for separating a feed stream comprising methane and carbon dioxide (such as for example a biogas feed stream) in order to provide a methane product stream (such as for example a biomethane stream).