Membrane Biogas Upgrading Using Sweep Gas for CO2 Selectivity
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Solution Overview
Problem
Existing commercial gas separation processes for separating methane from carbon dioxide are inefficient and costly, requiring multiple steps and additional equipment to achieve desired purity, particularly due to the impact of operating pressures on gas permeation.
Innovation Solution
A system and method utilizing a sweep gas, sourced from within or outside the gas separation system, is applied to the permeate side of the membrane to enhance membrane CO2 permeance and selectivity, reducing the need for additional equipment and improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional gas separation processes are used to separate methane from carbon dioxide, then separation can be achieved, but multiple gas separation steps and additional equipment are required, increasing system complexity and cost
Solution Approach 1:
The patent divides the gas separation process into distinct functional zones within a single membrane system: a feed zone where biogas is introduced, a sweep gas zone where inert gas flows across the permeate side, and separate outlets for methane-rich and CO2-rich streams. This segmentation allows complex separation functionality to be achieved within a single integrated device rather than multiple sequential units
Solution Approach 2:
The patent introduces an intermediary sweep gas stream (inert gas such as nitrogen) that flows across the permeate side of the membrane. This sweep gas acts as a mediator to maintain low partial pressure of CO2 on the permeate side, enhancing the driving force for CO2 permeation while allowing methane to be recovered in the retentate stream without requiring multiple separation stages
2Productivity
If high pressure is applied to increase gas permeation rate, then separation efficiency improves, but energy consumption increases and system complexity increases due to additional compression equipment
Solution Approach 1:
The patent employs a self-service mechanism where the sweep gas stream automatically maintains the partial pressure gradient across the membrane without requiring external compression or vacuum systems. The flow of sweep gas across the permeate side continuously removes permeated CO2, sustaining the driving force for separation at low operating pressures and eliminating the need for energy-intensive compression equipment
Solution Approach 2:
The patent changes the operational parameters by operating at low feed pressures (near atmospheric or slightly above) while using the sweep gas flow rate as the controlling parameter to maintain effective separation. This parameter change replaces the traditional high-pressure operation with a low-pressure sweep-gas-driven mechanism, reducing energy consumption while maintaining productivity
3Manufacturing precision
If traditional membrane separation is used without sweep gas, then system simplicity is maintained, but CO2 permeance and selectivity are insufficient for efficient separation
Solution Approach 1:
The patent makes the single membrane separation device perform multiple functions simultaneously: it separates CO2 from methane, the sweep gas cools the membrane to enhance CO2 permeance, and the sweep gas flow pattern creates the necessary partial pressure gradient. This multi-functionality achieves high selectivity without adding separate equipment for each function
Solution Approach 2:
The patent uses pneumatic principles by introducing a gas flow (sweep gas) across the permeate side of the membrane to control the partial pressure of CO2. This pneumatic approach replaces the need for vacuum systems or high-pressure compression, achieving enhanced permeance and selectivity through gas flow dynamics rather than mechanical pressure changes
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 application of a sweep gas significantly increases membrane CO2 permeance and selectivity, allowing for more efficient and cost-effective separation of methane from carbon dioxide without increasing complexity or equipment.
Implementation Method 1
Gas permeation is driven by partial pressure differences of the gas components across the gas separation membrane
Implementation Method 2
Gas permeation is driven by partial pressure differences of the gas components across the gas separation membrane
Data Source
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AI summary
A system for separating a gas mixture is provided. The system includes a source of a gas mixture and a membrane separation stage including a gas separation membrane module. The membrane separation stage is in fluid communication with the source of the gas mixture, and the gas separation membrane module is configured to separate the gas mixture into a retentate stream and a permeate stream. The gas separation membrane module also includes a membrane having a permeate side and a retentate side. A sweep stream is provided to the permeate side of the membrane, the sweep stream comprising a portion of the retentate stream.