Integrated LNG Nitrogen Rejection Using Shared Refrigeration
Find Innovative SolutionsGenerate Solutions
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 high capital costs and operational difficulties, and fail to meet strict purity requirements for vented nitrogen products.
Innovation Solution
A method involving a main heat exchanger for cooling and liquefying the natural gas feed, followed by expansion and separation in a distillation column, with reflux provided by condensing overhead vapor, and a closed loop refrigeration system for efficient nitrogen removal, allowing for the production of high-purity nitrogen streams with minimal equipment and energy consumption.
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 used for natural gas liquefaction is made to serve dual purposes: providing refrigeration for the liquefaction process and serving as the refrigeration source for the nitrogen rejection distillation column. This multi-functionality eliminates the need for separate refrigeration equipment, reducing capital costs while maintaining high nitrogen product purity through efficient separation
Solution Approach 2:
The refrigeration systems for the natural gas liquefaction process and the nitrogen rejection unit are merged into a single integrated system. The main heat exchanger handles both liquefaction cooling and distillation column refrigeration, consolidating equipment and reducing overall system complexity while achieving the required nitrogen separation efficiency
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 main heat exchanger is designed to perform multiple functions simultaneously: it provides refrigeration for the natural gas liquefaction process and serves as the cooling source for the nitrogen rejection distillation column. This eliminates the need for dedicated rectifier columns and separate refrigeration systems, reducing equipment quantity while maintaining high nitrogen product purity
Solution Approach 2:
The system uses its own internal resources efficiently - the refrigeration capacity generated during the natural gas liquefaction process is self-utilized to power the nitrogen rejection distillation column. This self-service approach eliminates external equipment requirements and reduces overall capital investment
3Manufacturing precision
If processes with additional equipment are used for nitrogen removal, then nitrogen separation capability is improved, but power consumption increases
Solution Approach 1:
The refrigeration requirements for both the natural gas liquefaction process and the nitrogen rejection distillation column are merged into a single thermal system. The main heat exchanger handles both cooling loads simultaneously, eliminating duplicate equipment and reducing overall power consumption while achieving the required nitrogen product purity
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 methane loss and operational complexity, thus addressing the inefficiencies and costs of existing 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 the stream
Implementation Method 2
cool the natural gas stream and liquefy all or a portion of the stream, thereby producing a first LNG stream
Implementation Method 3
expanding and partially vaporizing an at least partially liquefied nitrogen-enriched natural gas stream
Implementation Method 4
expanding and partially vaporizing an at least partially liquefied nitrogen-enriched natural gas stream, and introducing said stream into a distillation column in which the stream is separated into vapor and liquid phases
Implementation Method 5
introducing said stream into a distillation column in which the stream is separated into vapor and liquid phases
Implementation Method 6
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 7
condensing a portion of the overhead vapor from the distillation column in a condenser heat exchanger
Implementation Method 8
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
Figure 1
Figure 2
Figure 3
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.