Biogas Membrane Separation Unit with Recycle Loop
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Solution Overview
Problem
Current membrane separation systems for biogas purification, particularly those with three stages, suffer from high electricity consumption due to unnecessary recompression of CO2-rich retentate from the third membrane stage, leading to increased methane losses and operational costs.
Innovation Solution
A plant with a compressor and a membrane separation unit comprising two modules, where each module separates the biogas stream into permeates and retentates, with the second retentate and third permeate recycled back to the compressor inlet, utilizing membranes more permeable to CO2 than methane, to optimize methane recovery and reduce costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a three-stage membrane separation system is used, then methane purity is improved, but electricity consumption increases due to unnecessary recompression of CO2-rich retentate
Solution Approach 1:
The membrane separation unit is divided into two functional modules: a first module for initial CO2 removal and a second module for final methane purification. This segmentation allows the system to achieve high methane purity (97-99%) while avoiding the need for a third compression stage, thereby reducing electricity consumption compared to traditional three-stage systems.
Solution Approach 2:
The system changes the operating parameters by recycling the CO2-rich retentate from the second module back to the compressor inlet instead of discarding it or requiring additional compression stages. This parameter change in the process flow allows the same purification effect to be achieved with lower energy input.
2Productivity
If three membrane stages are used, then methane recovery is improved, but operational costs increase due to intermediate compression requirements
Solution Approach 1:
Instead of discarding the CO2-rich retentate from the second membrane module, the system recycles it back to the compressor inlet. This recovery approach maintains high methane recovery rates (95-98%) while eliminating the need for intermediate compression equipment and reducing operational costs associated with multiple compression stages.
3Quantity of substance
If conventional biogas upgrading is used, then methane production is achieved, but methane losses occur due to inefficient separation processes
Solution Approach 1:
The system implements a feedback mechanism by recycling the CO2-rich retentate from the second module back to the compressor inlet. This feedback loop ensures that any methane present in the retentate stream is recovered and reprocessed, minimizing methane losses while maintaining high methane production output.
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 configuration enhances methane yield and purity while minimizing methane losses and operational costs by reducing the need for intermediate compression and recycling CO2, thus improving the overall efficiency and economic viability of biogas upgrading.
Implementation Method 1
Each module comprises at least one membrane that is more permeable to carbon dioxide than to methane
Data Source
AI summary
Process and plant for membrane permeation treatment of a carbon dioxide and methane-containing biogas stream in which the biogas stream is compressed with a compressor and the compressed biogas stream is fed to a membrane separation unit comprising first and second modules each containing at least one membrane selective for carbon dioxide over methane. The first module separates the compressed biogas stream into a first, second, and third methane-deficient permeates (in comparison to the biogas stream) and a first methane-enriched retentate (in comparison to the biogas stream). The first permeate being richer in methane than the second or third permeates. The second module separates the first permeate into a fourth methane-deficient permeate and a second methane-enriched retentate. The second and third retentates are recycled back to an inlet of the compressor.