Membrane Gas Separation with Adjustable Compressor
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Solution Overview
Problem
Existing gas permeation devices for separating mixtures of gases into product and off gases suffer from low product gas quality and yield, high energy demand, and high investment costs, particularly due to the need for highly selective membranes and oversized plant dimensions.
Innovation Solution
A device with a membrane unit and a rotational speed-adjustable compressor, featuring a pressure control unit that allows for adjustable operation in co-current flow, reducing methane concentration in off gases and increasing product gas recovery by controlling the rotational speed and pressure of the compressor, and using a specific gas mixture of CH4/CO2 to limit methane concentration and provide resistance in the retentate space.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a one-step membrane separation is used, then the device complexity is low, but the product gas quality and yield are low
Solution Approach 1:
The patent divides the membrane separation process into multiple stages with different flow patterns. The first membrane unit operates in counter-current mode for initial separation, while the second membrane unit operates in co-current mode for further purification. This segmentation allows each stage to optimize for specific separation objectives, achieving high product gas yield (over 98% CH4 recovery) without requiring overly complex multi-column systems.
2Manufacturing precision
If highly selective membranes are used to improve product gas quality, then the manufacturing precision increases, but the investment costs increase
Solution Approach 1:
The patent applies different operational modes (counter-current and co-current flow) to different membrane units based on their specific separation objectives. The first unit uses counter-current flow for bulk separation where high selectivity is less critical, while the second unit uses co-current flow for final purification where higher effective selectivity is needed. This local optimization allows using moderately selective membranes overall, reducing investment costs while achieving high product gas quality (99.6% CH4).
3Productivity
If the permeate is recirculated to increase product gas yield, then the productivity increases, but the plant dimensions must be oversized
Solution Approach 1:
The patent dynamically switches between counter-current and co-current operational modes in different membrane units to optimize separation efficiency. The co-current mode in the second membrane unit allows effective utilization of recirculated permeate without requiring excessive plant capacity. This dynamic operational strategy achieves high product gas yield (over 98% CH4 recovery) with appropriately sized equipment, avoiding the need for oversized plants that would be required with simple recirculation approaches.
4Use of energy by moving object
If the compressor pressure is increased to improve separation, then the use of energy increases, but the product gas quality improves
Solution Approach 1:
The patent segments the compression and separation process into two distinct stages. The first membrane unit operates at lower pressure differential in counter-current mode for bulk separation, consuming less energy. The second membrane unit operates at higher pressure differential in co-current mode for final purification, achieving high product gas quality (99.6% CH4). This segmented approach minimizes total energy consumption while achieving the required product specification, avoiding the need for high-energy single-stage high-pressure compression.
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
Achieves a high recovery rate of over 98% of CH4 as product gas, with methane concentration in off gases limited to 0.2% by volume, reducing energy consumption and investment costs while maintaining high product gas yield.
Implementation Method 1
separating a mixture of gases into product gas and off gas by means of gas permeation
Implementation Method 2
a pressure control unit (2) is provided at or downstream of the retentate outlet (1b)
Implementation Method 3
the permeate outlet (1c') of the membrane unit (1) is connected via conduits to the compressor (3) or the gas supply leading into the compressor (3) on the suction side thereof
Data Source
AI summary
The invention relates to a device for separating a gas mixture into a product gas and an offgas by gas permeation, having a membrane unit (I) and a compressor (3) that is connected upstream of the membrane unit (I) and is preferably adjustable in terms of rotational speed, which membrane unit (I) has a gas inlet (I a), an outlet (I b) for retentate or product gas, and an outlet (I c) for permeate or offgas, wherein the membrane unit (I) has at least one other permeate outlet (1c′) that is downstream of the gas inlet (1a), and the permeate outlet (1c′) of the membrane unit (I) is connected by lines on the suction side to the compressor (3) or to the gas supply leading into the compressor, and wherein a pressure-regulating device (2) is provided at or downstream of the retentate outlet (Ib), and use is made of a gas mixture, consisting primarily of CH4/CO2 and having a methane concentration of not greater than 30% by volume; and to the use of such a device and to a corresponding method.