Gas Separation Membrane System for Natural Gas Purification
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Solution Overview
Problem
Conventional natural gas processing methods for offshore applications are hindered by the large footprint, high cost, and performance deterioration of molecular sieve dehydration systems, especially when dealing with C3+ hydrocarbons and CO2 removal in gas separation membranes.
Innovation Solution
A method and system utilizing gas separation membranes with selective layers for C3+ hydrocarbons and CO2, combined with a compressor and dehydration unit to produce a dry conditioned natural gas, reducing the need for molecular sieve dehydration and minimizing equipment size and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If molecular sieve dehydration is used to treat the entirety of the feed gas stream, then water removal is effective, but the equipment becomes too heavy, bulky, and occupies too large a footprint
Solution Approach 1:
The gas stream is divided into two separate processing paths: a first gas separation unit treats the feed gas to remove water and C3+ hydrocarbons, while a second gas separation unit treats only the CO2 removal. This segmentation allows each unit to be optimized for its specific function, reducing the overall size and weight compared to treating the entire stream through a single molecular sieve system.
Solution Approach 2:
The invention extracts and removes C3+ hydrocarbons and water from the feed gas stream before the CO2 removal step. By taking out these components in a dedicated first separation unit, the subsequent second separation unit only needs to handle CO2 removal, significantly reducing its size and the overall system footprint compared to treating the full feed gas stream through molecular sieves.
2Measurement precision
If glassy polymer membranes are used for CO2 removal, then CO2/methane selectivity is high, but membrane performance quickly decreases due to C3+ hydrocarbon condensation
Solution Approach 1:
The first gas separation unit performs preliminary removal of C3+ hydrocarbons and water from the feed gas stream before the gas enters the second gas separation unit for CO2 removal. This preliminary action prevents C3+ hydrocarbons from condensing on the glassy polymer membranes in the second unit, thereby maintaining their high CO2/methane selectivity and performance stability over time.
3Reliability
If conventional hybrid process with molecular sieve and gas separation membrane is used, then specifications for both conditioned gas and reinjected gas are met, but footprint, volume, and mass are relatively high
Solution Approach 1:
The system is segmented into two specialized gas separation units: the first unit handles water and C3+ hydrocarbon removal, while the second unit handles CO2 removal. This segmentation allows each unit to be compact and optimized for its specific function, reducing the overall system footprint compared to the conventional hybrid process while still meeting all specifications for both conditioned and reinjected gas.
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 significantly reduces the weight, size, and footprint of the dehydration process by up to 90%, while maintaining compliance with pipeline specifications and reducing compression energy requirements, thus providing a more efficient and cost-effective solution for natural gas purification.
Implementation Method 1
gas separation membranes with selective layers for C3+ hydrocarbons and CO2
Implementation Method 2
The gaseous reject stream is compressed so as to cause condensation of least some of the water contained therein
Implementation Method 3
The gaseous reject stream is compressed so as to cause condensation of least some of the water contained therein to produce a biphasic stream having liquid and gaseous phases
Implementation Method 4
The gaseous phase is fed to a dehydration apparatus so as to remove at least some of the water contained therein
Data Source
AI summary
Natural gas may be purified by removing C3+ hydrocarbons and CO2 in respective one or more separation units to yield conditioned gas lower in C3+ hydrocarbons and CO2 in comparison to the un-conditioned natural gas. Notably, the feed gas need not be subjected to joule-thomson expansion and molecular sieve dehydration performed by conventional processes. Rather, any water-rich reject stream from the separation unit(s) is dried downstream with a smaller compressor and smaller molecular sieve or gas separation membrane dehydration unit before it may be re-injected deep underground or deep under the sea bed.