Two-Stage Membrane Cooling for High-Purity Methane Separation
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Solution Overview
Problem
Existing gas separation systems for producing methane-enriched gas from a mixed gas containing CO2 and CH4 are inadequate in achieving high purity at low cost using a small membrane area.
Innovation Solution
A gas separation system comprising a first and a second gas separation membrane unit, where the second unit operates at a lower temperature than the first, with a higher gas permeation rate for CO2, and includes a cooling part to lower the operating temperature of the second unit, connected in series with a feedstock gas supply line and permeate gas reflux, using polyimide membranes for enhanced selectivity and throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a membrane with high gas separation selectivity is used to recover non-easily permeating gas at high purity, then the recovery rate is improved, but the membrane area must be increased or operating pressure must be increased due to low permeation rate
Solution Approach 1:
The gas separation system is divided into multiple stages (first-stage and second-stage membrane separation units) with different operating temperatures. The first stage operates at higher temperature for initial separation, while the second stage operates at lower temperature to further purify the retentate gas. This segmentation allows each stage to be optimized for its specific function, achieving high purity without requiring excessive membrane area in a single stage.
Solution Approach 2:
The invention changes the operating temperature parameter between stages - the first-stage membrane unit operates at a higher temperature while the second-stage membrane unit operates at a lower temperature. This parameter change optimizes the permeation characteristics at each stage, allowing the system to achieve high recovery rates and high purity simultaneously by matching temperature conditions to the specific separation requirements of each stage.
2Productivity
If a membrane with high gas permeation rate is used, then the membrane area and operating pressure do not need to be increased, but the recovery rate is low due to low gas separation selectivity
Solution Approach 1:
The system segments the separation process into two stages with different membrane units optimized for different functions. The first-stage unit handles the bulk separation with higher permeation requirements, while the second-stage unit focuses on achieving high purity of the retentate gas. This segmentation allows each stage to operate at optimal permeation rates for its specific separation task.
Solution Approach 2:
By changing the operating temperature parameter between stages, the system optimizes permeation rates at each stage. The first-stage unit operates at higher temperature to maximize permeation rate and productivity, while the second-stage unit operates at lower temperature to enhance selectivity and achieve high purity, thus resolving the contradiction between productivity and purity.
3Manufacturing precision
If multistage gas separation system is used to improve purity and recovery rate, then the separation performance is improved, but the system complexity and cost increase
Solution Approach 1:
The invention simplifies the multistage system by changing the temperature parameter between stages rather than using completely different membrane materials or complex control systems. The first-stage membrane unit operates at a higher temperature and the second-stage unit operates at a lower temperature, which is a straightforward parameter change that can be implemented with simple heating/cooling devices, thus improving separation performance without excessively increasing system complexity.
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
The system achieves high purity methane gas at low cost by reducing membrane area and power consumption, while maintaining high throughput and purity through controlled temperature differences and membrane selectivity.
Implementation Method 1
there is known a membrane separation method based on the difference between the gas permeation rates of the gases through a membrane
Implementation Method 2
The gas separation selectivity of the membrane can be defined as a ratio 'easily permeating gas permeation rate/non-easily permeating gas permeation rate'
Implementation Method 3
a cooling part for lowering an operating temperature of the second gas separation membrane unit, T2, below an operating temperature of the first gas separation membrane unit, T1
Implementation Method 4
a carbon dioxide gas permeation rate of the second gas separation membrane unit at the operating temperature T2, P1′CO2(T2), is larger than a carbon dioxide gas permeation rate of the first gas separation membrane unit at the operating temperature T1, P1′CO2(T1)
Data Source
AI summary
A gas separation system for producing a CH4-enriched gas from a feedstock gas containing CO2 and CH4, including a first gas separation membrane unit and a second gas separation membrane unit, in which the gas separation system includes a feedstock gas supply line connected to a gas inlet of the first gas separation membrane unit; a compression part disposed in the feedstock gas supply line; a first line connecting the retentate gas outlet of the first gas separation membrane unit and the gas inlet of the second gas separation membrane unit; a second line connecting the permeate gas outlet of the second gas separation membrane unit and the feedstock gas supply line; and a cooling part for lowering the operating temperature of the second gas separation membrane unit below the operating temperature of the first gas separation membrane unit.