Nitrogen removal with ISO-pressure open refrigeration natural gas liquids recovery
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Solution Overview
Problem
Current natural gas recovery processes, particularly those using cryogenic expansion, face inefficiencies in separating nitrogen from natural gas streams, leading to higher operational costs and energy consumption, and often require multiple steps to meet pipeline specifications for nitrogen content.
Innovation Solution
The process involves fractionating gas streams containing nitrogen, methane, ethane, and propane into multiple fractions, using separators and membrane separation units to produce nitrogen-depleted and nitrogen-enriched streams, with a mixed refrigerant system providing process cooling and recycling of fractions to enhance separation efficiency, thereby reducing the need for additional nitrogen removal steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If cryogenic expansion processes are used for NGL recovery, then NGL recovery efficiency is improved, but nitrogen content in the natural gas exceeds pipeline specifications
Solution Approach 1:
The process segments the gas stream into multiple fractions using sequential separators. The first separator divides the stream into a first fraction (rich in C3+ hydrocarbons) and a second fraction (containing nitrogen and lighter hydrocarbons). A second separator further divides the second fraction into a third fraction (propane-enriched) and a fourth fraction (nitrogen-enriched). This segmentation allows selective recovery of NGLs while removing nitrogen to meet pipeline specifications.
2Manufacturing precision
If additional nitrogen removal steps are added, then nitrogen content is reduced to meet specifications, but device complexity and processing steps increase
Solution Approach 1:
The fractionation separators perform multiple functions simultaneously: they recover natural gas liquids (propane, butanes) as valuable products and remove nitrogen from the gas stream in the same processing train. The first separator recovers C3+ hydrocarbons while the second separator recovers propane and removes nitrogen, achieving both NGL recovery and nitrogen removal without requiring separate dedicated units for each function.
3Manufacturing precision
If conventional cryogenic separation is used for nitrogen removal, then nitrogen is separated from natural gas, but membrane area and power consumption increase significantly
Solution Approach 1:
The process utilizes parameter changes in the gas stream through controlled cooling and pressure reduction in the fractionation separators. By cooling the feed stream to temperatures where C3+ hydrocarbons condense while nitrogen remains gaseous, and by controlling pressure across the separators, the process achieves nitrogen separation without requiring high-power membrane units or additional compression stages.
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 membrane area and power consumption by up to 75% and 58%, respectively, while achieving high recovery of natural gas liquids and meeting pipeline nitrogen specifications with fewer processing steps, resulting in a more efficient and cost-effective natural gas processing system.
Implementation Method 1
cooling and refrigeration of gas, oil absorption, refrigerated oil absorption
Implementation Method 2
As the gas is cooled, liquids may be condensed and collected in one or more separators
Implementation Method 3
cryogenic expansion processes utilizing Joule-Thompson valves or turbo expanders
Implementation Method 4
The expanded stream, comprising a mixture of liquid and vapor, is fractionated in a distillation column. In the distillation column volatile gases and lighter hydrocarbons are removed as overhead vapors and heavier hydrocarbon components exit as liquid product in the bottoms.
Data Source
AI summary
A process for recovery of natural gas liquids is disclosed, the process including: fractionating a gas stream comprising nitrogen, methane, ethane, and propane and other C3+ hydrocarbons into at least two fractions including a light fraction comprising nitrogen, methane, ethane, and propane, and a heavy fraction comprising propane and other C3+ hydrocarbons; separating the light fraction into at least two fractions including a nitrogen-enriched fraction and a nitrogen-depleted fraction in a first separator; separating the nitrogen-depleted fraction into a propane-enriched fraction and a propane-depleted fraction in a second separator; feeding at least a portion of the propane-enriched fraction to the fractionating as a reflux; recycling at least a portion of the propane-depleted fraction to the first separator. In some embodiments, the nitrogen-enriched fraction may be separated in a nitrogen removal unit to produce a nitrogen-depleted natural gas stream and a nitrogen-enriched natural gas stream.