Three-Stage Membrane Gas Separation Without Interstage Compression
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Solution Overview
Problem
Current membrane separation technologies for removing carbon dioxide and nitrogen from natural gas face challenges due to low selectivity, leading to unacceptable methane losses and increased capital and operating costs, particularly due to the need for multistage systems with interstage compression.
Innovation Solution
A three-stage membrane separation process using membranes selective for carbon dioxide or nitrogen over methane, where the permeate from one stage is compressed and fed to the next without compression, optimizing pressure ratios and minimizing methane loss without additional compressors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multistage membrane systems are used to improve separation performance and reduce contaminant content, then carbon dioxide or nitrogen removal efficiency is improved, but capital cost and operating cost increase due to interstage compression requirements
Solution Approach 1:
The system is divided into multiple membrane stages (first, second, and third stages) with different pressure ratios, allowing each stage to operate optimally without requiring interstage compression. The first stage operates at high pressure ratio, the second at intermediate pressure ratio, and the third at low pressure ratio, collectively achieving high separation performance without additional compressors.
Solution Approach 2:
The invention introduces a pressure ratio dimension by operating membrane stages at different pressure ratios rather than uniform compression. This dimensional approach allows the system to achieve the same separation effect as compressed multistage systems but without the mechanical compression equipment, thereby reducing device complexity while maintaining separation performance.
2Manufacturing precision
If membranes with high ideal selectivity are used to improve contaminant removal, then carbon dioxide selectivity is improved, but methane loss increases due to plasticization effects under real operating conditions
Solution Approach 1:
The invention changes the operating parameters by using different pressure ratios across different membrane stages. The first membrane stage operates at a high pressure ratio to achieve initial separation, while subsequent stages operate at lower pressure ratios. This parameter variation prevents the plasticization effect that occurs at uniformly high pressures, maintaining both selectivity and reducing methane loss.
Solution Approach 2:
The separation process is segmented into multiple stages with different pressure ratios rather than using a single high-pressure stage. This segmentation allows the system to achieve high overall selectivity while distributing the pressure stress across stages, preventing membrane plasticization and reducing methane loss in the permeate stream.
3Power
If compression is applied between membrane stages to maintain driving force, then permeation driving force is improved, but power requirements and operating costs increase
Solution Approach 1:
Instead of compressing the permeate stream between stages as in conventional systems, the invention inverts the approach by using expansion or pressure reduction. The first stage operates at high pressure ratio, and subsequent stages operate at progressively lower pressure ratios, eliminating the need for compression while maintaining adequate driving force through the pressure differential across each membrane.
Solution Approach 2:
The system uses the pressure differential naturally established by the membrane separation process itself to provide the driving force for subsequent stages. The permeate from one stage naturally feeds into the next stage at an appropriate pressure, eliminating the need for external compression equipment and reducing power requirements while maintaining permeation driving force.
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 achieves high methane recovery and purity while reducing capital and operating costs by eliminating the need for interstage compression, effectively addressing the limitations of existing technologies.
Implementation Method 1
passing the gas stream as a first feed stream at a pressure of at least about 400 psia across the first feed side of the first membrane; withdrawing from the first permeate side a first permeate stream enriched in carbon dioxide compared with the gas stream
Data Source
AI summary
A process for removing carbon dioxide or nitrogen from gas, especially natural gas. The process uses three membrane separation stages without compression between the second and third stages.