Multi-Stage Membrane NGL Recovery for Hydrocarbon Dew Point Control
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Solution Overview
Problem
Conventional membrane-based processes are inefficient for capturing and utilizing flare gas due to the contradictory effects of stage cut on natural gas liquids (NGL) recovery and compressed natural gas production, leading to significant gas flaring worldwide.
Innovation Solution
A two- or three-stage membrane-based process that separates natural gas using membranes selective for C2+ hydrocarbons over methane, followed by chilling and recycling of permeates to enhance NGL recovery and produce compressed natural gas with minimal energy consumption, utilizing rubbery or glassy polymer membranes with high free volume for efficient separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a high stage cut is used in membrane separation to obtain high pressure compressed gas meeting pipeline specification, then the compressed natural gas quality is improved, but the C3+ concentration in the permeate decreases reducing NGL recovery efficiency
Solution Approach 1:
The single membrane separation stage is divided into multiple sequential stages. The first stage operates at high stage cut to produce compressed natural gas meeting pipeline specifications, while subsequent stages process the permeate at lower stage cuts to maximize C3+ recovery. This segmentation allows each stage to be optimized for its specific function, resolving the contradiction between gas quality and NGL recovery.
Solution Approach 2:
The stage cut parameter is varied across different separation stages rather than maintaining a fixed value. The first stage uses high stage cut (0.6-0.8) for compressed natural gas production, while subsequent stages use lower stage cuts (0.2-0.4) for NGL recovery. This dynamic parameter adjustment resolves the contradiction by allowing optimal performance for both compressed gas quality and NGL recovery in different stages of the process.
2Device complexity
If a single membrane separation stage is used to simplify the process, then the device complexity is reduced, but the ability to simultaneously achieve high compressed gas quality and high NGL recovery is compromised
Solution Approach 1:
The separation process is segmented into multiple stages with different optimization goals. The first stage focuses on producing compressed natural gas meeting pipeline specifications, while subsequent stages focus on maximizing NGL recovery from the permeate stream. This segmentation enables simultaneous high productivity for both products without excessive complexity, as each stage has a dedicated function.
Solution Approach 2:
The multi-stage membrane system serves multiple functions: the first stage produces compressed natural gas for pipeline delivery, while subsequent stages recover NGLs from the permeate. The reject streams from each stage are recycled back to the feed, creating a multi-functional system that maximizes both compressed gas production and NGL recovery efficiency.
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
The process effectively recovers NGL and produces compressed natural gas while minimizing energy consumption, allowing for the utilization of reject gas as fuel for on-site power generation, thereby reducing environmental emissions and generating significant energy value.
Implementation Method 1
A flow of associated gas is fed to a first gas separation membrane-based separation stage comprising one or more gas separation membranes selective for C2+ hydrocarbons over methane to produce a flow of a first permeate enriched in C2+ hydrocarbons and a flow of a first retentate enriched in methane
Implementation Method 2
The first permeate is chilled to provide a flow of chilled first permeate. The flow of chilled first permeate is separated to produce a flow of a first gaseous phase deficient in C3+ hydrocarbons and a flow of a first liquid phase enriched in C3+ hydrocarbons
Data Source
AI summary
An energy efficient process for NGL recovery and production of compressed natural gas (CNG) in which natural gas is fed to a first gas separation membrane-based separation stage where it is separated into a permeate and a retentate. The high C3+ concentration first stage permeate is chilled and separated to provide liquid phase NGL and a gaseous phase. The first stage retentate is separated at a second gas membrane-based separation stage to produce a retentate meeting pipeline specifications for CNG (including hydrocarbon dewpoint) and a permeate that is recycled to the first stage. The gaseous phase, constituting a low BTU fuel, may be used in on-site power generation equipment and/or in internal combustion engines. The second stage permeate (and optionally the third stage retentate) is (are) recycled back to the first stage to enhance the production of NGL and CNG. The gaseous phase may instead be fed to a third stage to produce a third permeate and a third residue, in which case the third permeate is recycled to the first stage and the third retentate is a low BTU fuel which may be used in on-site power generation equipment and/or in internal combustion engines.