Membrane-Based Natural Gas Separation to Eliminate Amine Scrubbing
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Solution Overview
Problem
Existing processes for separating nitrogen and carbon dioxide from hydrocarbon-rich feed fractions, such as natural gas, require amine scrubbing and TSA drying, which are costly and complex, and result in water-saturated feed gas that needs additional processing.
Innovation Solution
A process utilizing permeative separation with rubber-like membranes to separate nitrogen-depleted and carbon dioxide-enriched fractions, followed by cryogenic separation of the nitrogen-enriched retentate, eliminating the need for amine scrubbing and often reducing the need for nitrogen enrichment columns and simplifying further processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If amine scrubbing is used to remove carbon dioxide, then carbon dioxide removal is achieved, but the feed gas becomes water-saturated requiring additional drying equipment
Solution Approach 1:
The patent changes the separation mechanism from chemical absorption (amine scrubbing) to physical permeation through rubber-like membranes. This parameter change in the separation method eliminates water saturation while achieving carbon dioxide removal, as the membrane process does not involve water-based chemistry
Solution Approach 2:
The patent replaces the mechanical/chemical amine scrubbing system with a membrane-based physical separation system. The rubber-like membrane selectively permeates carbon dioxide while rejecting nitrogen and hydrocarbons, eliminating the need for amine solution circulation and associated water saturation issues
2Quantity of substance
If TSA drying is installed upstream of NRU, then water content is reduced to acceptable levels, but process complexity and equipment requirements increase
Solution Approach 1:
The patent extracts the water removal function from the process by preventing water saturation at the source (amine scrubber). Since the membrane separation process does not produce water-saturated gas, the TSA drying unit becomes unnecessary, eliminating this equipment while still achieving the required water content reduction
Solution Approach 2:
The rubber-like membrane performs multiple functions simultaneously: it removes carbon dioxide while preventing water saturation, eliminating the need for separate drying equipment. The single membrane unit achieves what previously required both amine scrubbing and TSA drying
3Quantity of substance
If cryogenic separation is used to separate nitrogen from natural gas, then nitrogen removal is achieved, but carbon dioxide and other components must be removed first to avoid blockages
Solution Approach 1:
The patent performs preliminary carbon dioxide removal using the rubber-like membrane before the cryogenic separation step. This preliminary action ensures that carbon dioxide is already depleted in the retentate stream entering the NRU, preventing blockages while maintaining nitrogen removal effectiveness
Solution Approach 2:
The patent changes the sequence and method of component removal: instead of removing carbon dioxide after cryogenic separation or using amine scrubbing, it uses membrane permeation to selectively remove carbon dioxide first, creating a carbon dioxide-depleted stream that is then easily separated in the NRU
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
Reduces the complexity and cost of nitrogen and carbon dioxide separation by using rubber-like membranes, allowing direct feed to cryogenic separation and minimizing the need for additional drying steps, thus optimizing the separation efficiency and reducing equipment requirements.
Implementation Method 1
the permeative separation takes place by means of one or more membrane stages connected in series, rubber-like and/or glass-like membranes are used in the membrane stage(s)
Implementation Method 2
the nitrogen-enriched and carbon dioxide-depleted fraction, hereinafter referred to as retentate, is separated in a cryogenic separation process into a nitrogen-rich fraction and a methane-rich product fraction
Implementation Method 3
the nitrogen-enriched and carbon dioxide-depleted fraction obtained in the permeative separation is subjected to an adsorption process to separate carbon dioxide, water and/or C 2+ hydrocarbons before being fed to the cryogenic separation process
Data Source
Figure 1~2
AI summary
A process is described for separating a hydrocarbon-rich feed fraction (1), preferably natural gas, containing nitrogen and carbon dioxide, in which a) the feed fraction (1) is permeatively (M) separated into a nitrogen-depleted and carbon dioxide-enriched fraction (2) and a nitrogen-enriched and carbon dioxide-depleted fraction (3), b) the nitrogen-enriched and carbon dioxide-depleted fraction (3, 3') is separated in a cryogenic separation process (NRU) into a nitrogen-rich fraction (4) and a methane-rich product fraction (5), and c) the nitrogen-depleted and carbon dioxide-enriched fraction (2) is fed to the product fraction (5).