Integrated LNG Nitrogen Removal Using Refrigerated Heat Pump Reflux
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Solution Overview
Problem
Existing methods for removing nitrogen from natural gas feeds with low nitrogen concentrations are inefficient, costly, and complex, especially in small and mid-scale LNG facilities, due to the need for extensive equipment and high capital costs, and struggle with meeting purity requirements for vented nitrogen products.
Innovation Solution
A method involving a natural gas feed stream passed through a main heat exchanger to cool and liquefy the stream, followed by expansion and separation in a distillation column, with reflux provided by condensing overhead vapor, utilizing a closed loop refrigeration system for efficient nitrogen removal and purification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a dedicated nitrogen rejection unit (NRU) is used to remove nitrogen efficiently and produce high purity nitrogen product, then nitrogen removal efficiency and product purity are improved, but capital cost and device complexity increase due to additional equipment
Solution Approach 1:
The main heat exchanger and distillation column are designed to perform multiple functions: natural gas cooling and liquefaction, nitrogen separation, and nitrogen product condensation all within the same integrated system. This eliminates the need for separate dedicated nitrogen rejection units while achieving both high purity nitrogen product and efficient removal.
2Manufacturing precision
If alternative solutions such as nitrogen recycle stream or dedicated rectifier column are used, then nitrogen removal capability is improved, but device complexity and capital cost increase due to large amount of equipment
Solution Approach 1:
The nitrogen separation function is merged with the existing natural gas liquefaction process. The distillation column integrates nitrogen rejection with the liquefaction train, and the main heat exchanger simultaneously performs cooling, liquefaction, and nitrogen product condensation, reducing equipment quantity while maintaining separation effectiveness.
Solution Approach 2:
Existing equipment is designed to perform multiple functions: the main heat exchanger cools natural gas, condenses nitrogen product, and provides refrigeration; the distillation column separates nitrogen from natural gas while producing liquefied natural gas. This multi-functionality reduces the need for additional dedicated equipment.
3Manufacturing precision
If strict purity specifications are required for vented nitrogen product, then environmental compliance is improved, but separation difficulty and energy consumption increase
Solution Approach 1:
The nitrogen product condensation process utilizes the cold natural gas stream as the cooling medium, and the refrigeration system provides cooling duty during off-peak periods. This self-service approach minimizes additional energy consumption while achieving high purity nitrogen product condensation.
Solution Approach 2:
The process utilizes phase transitions of nitrogen (condensation from vapor to liquid) and natural gas (liquefaction) to achieve separation and purification. The phase change processes occur within the existing temperature and pressure conditions of the liquefaction train, minimizing additional energy requirements while achieving strict purity specifications.
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 effectively removes nitrogen from natural gas feeds with low concentrations, achieving high purity nitrogen products while minimizing equipment and energy consumption, thus addressing the inefficiencies and costs of prior methods.
Implementation Method 1
passing a natural gas feed stream through a main heat exchanger to cool the natural gas stream and liquefy all or a portion of said stream
Implementation Method 2
expanding and partially vaporizing a liquefied or partially liquefied natural gas stream, and introducing said stream into a distillation column in which the stream is separated into vapor and liquid phases
Implementation Method 3
providing reflux to the distillation column by condensing a portion of the overhead vapor from the distillation column in a condenser heat exchanger
Implementation Method 4
refrigeration for the main heat exchanger and for the condenser heat exchanger is provided by a closed loop refrigeration system, refrigerant circulated by the closed loop refrigeration system passing through and being warmed in the main heat exchanger and passing through and being warmed in the condenser heat exchanger
Data Source
AI summary
A method for liquefying a natural gas feed stream and removing nitrogen therefrom, the method comprising passing a natural gas feed stream through a main heat exchanger to produce a first LNG stream, and separating a liquefied or partially liquefied natural gas stream in a distillation column to form nitrogen-rich vapor product, wherein a closed loop refrigeration system provides refrigeration to the main heat exchanger and to a condenser heat exchanger that provides reflux to the distillation column.