Membrane Dehydration Using PSA Waste Gas Sweep
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Solution Overview
Problem
Current methods for generating a sweep gas for dehydration membrane modules are costly due to the need for energy-consuming compression steps or refrigeration, which increase operational expenses.
Innovation Solution
A system comprising a dehydration membrane module connected to a pressure swing adsorption (PSA) unit, where the waste stream from the PSA unit acts as a countercurrent sweep gas, and an air ejector unit that entrains supplemental gas to create a sweep stream without requiring additional compression, thereby reducing energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a compressor is used to compress the sweep gas before using it to sweep the permeate gas from the module, then the sweep gas can effectively remove permeate gas, but the operating cost increases due to energy consumption
Solution Approach 1:
The system uses the dried product gas from the membrane module itself as the sweep gas, eliminating the need for external compression. The product gas flows through the shell side of the membrane fibers, naturally carrying away permeate water vapor without requiring additional energy input from a compressor
Solution Approach 2:
The dried product gas serves dual purposes: it is both the desired output of the dehydration process and the sweep gas that removes permeate from the module. This multi-functionality eliminates the need for separate sweep gas generation and compression systems
2Productivity
If a refrigeration dryer is used to remove water from air, then dehydration can be achieved, but power consumption increases
Solution Approach 1:
The system replaces the mechanical refrigeration drying process with a membrane-based separation process. The polymeric membrane fibers selectively permeate water vapor from the feed air, using the inherent selective transport properties of the membrane rather than mechanical cooling and condensation
3Device complexity
If ambient air is used as sweep gas, then no compression is needed, but the sweep gas must still be compressed or vacuum applied to flow through the module
Solution Approach 1:
The dried product gas from the module provides its own driving force to flow through the shell side and carry away permeate. The pressure differential naturally present in the system drives the sweep gas flow without requiring external compressors or vacuum systems
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 minimizes energy costs by utilizing waste gas as a sweep stream and eliminating the need for separate compression, enhancing the efficiency and cost-effectiveness of the dehydration process while maintaining the productivity of the membrane module.
Implementation Method 1
a pressure swing adsorption (PSA) unit connected to receive product gas from the dehydration membrane module, the PSA unit providing a product stream and a waste stream
Implementation Method 2
an air ejector unit that entrains supplemental gas to create a sweep stream without requiring additional compression
Implementation Method 3
Polymeric membranes have been shown to be effective for the removal of condensable gases, especially water, from otherwise desirable gas streams
Data Source
AI summary
An air dehydration membrane module is provided with a sweep gas which is taken from the waste gas of a pressure swing adsorption (PSA) unit. No additional compressor is required, other than the compressor forming part of the PSA unit. In another embodiment, the sweep gas includes the combination of dried product gas, taken from the dehydration membrane module, and a supplemental gas, which may be ambient air, or permeate gas from an air separation membrane, or waste gas from a PSA unit. An air ejector combines the streams, without the use of an additional compression step, and the combined gas is used as a sweep stream for the dehydration module. The invention also includes the method of selecting an optimum point at which the sweep gas is injected into the module.