Closed-Loop Refrigeration for Flexible Natural Gas Liquefaction
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Solution Overview
Problem
Existing liquefaction methods and systems using simple compression and open-loop systems are inefficient, lack flexibility, and do not result in improved efficiencies, making them unsafe, inefficient, and unreliable for natural gas liquefaction.
Innovation Solution
A closed-loop refrigeration system is employed, utilizing multiple compressors and expanders to manage pressure differentials, with indirect heat exchange processes for precooling, liquefaction, and subcooling, incorporating vapor expansion cycles and environmentally friendly refrigerants like CO2 to enhance efficiency and safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If simple compression systems and simple heat exchangers are used, then device complexity is reduced, but efficiency is not improved
Solution Approach 1:
The compression system is segmented into multiple compression stages with intercooling, and the heat exchanger is segmented into multiple passages with specific flow arrangements. This segmentation allows for better thermal management and improved liquefaction efficiency while maintaining manageable system complexity through modular design.
2Ease of manufacture
If open-loop system is used, then cost is reduced, but flexibility is lost
Solution Approach 1:
The patent introduces an intermediary closed-loop refrigeration system that mediates between the feed gas stream and the environment. This closed-loop system using CO2 as refrigerant provides flexibility in controlling liquefaction conditions while maintaining cost-effectiveness through the use of environmentally friendly, readily available refrigerant.
3Device complexity
If gaseous refrigerant is expanded to substantially the same pressure within tolerance, then system simplicity is maintained, but precooling, liquefaction, and subcooling efficiency is reduced
Solution Approach 1:
The patent applies local quality by having different expanders operate at different discharge pressures tailored to specific process requirements. The first expander discharges at a pressure suitable for precooling, while the second expander discharges at a different pressure for liquefaction and subcooling, optimizing each stage's efficiency rather than using uniform pressure control.
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 closed-loop system provides a safe, efficient, and reliable method for natural gas liquefaction, improving efficiency and flexibility while minimizing physical footprint, especially suitable for offshore applications.
Implementation Method 1
compressing a gaseous refrigerant stream in at least one compressor
Implementation Method 2
cooling the compressed gaseous refrigerant stream in a first heat exchanger
Implementation Method 3
expanding at least a first portion of the cooled, compressed gaseous refrigerant stream from the first heat exchanger in a first expander
Implementation Method 4
cooling and substantially liquefying a feed gas stream to form a substantially liquefied feed gas stream in a second heat exchanger through indirect heat exchange against at least a first portion of the first expanded gaseous refrigerant stream
Data Source
AI summary
Liquefaction using a closed loop refrigeration system, including compressing a gaseous refrigerant stream; cooling at least a portion of the compressed gaseous refrigerant stream in a first heat exchanger; expanding a first portion of the cooled, compressed gaseous refrigerant stream from the first heat exchanger to provide a first expanded gaseous refrigerant stream; cooling and substantially liquefying a feed gas stream to form a substantially liquefied feed gas stream in a second heat exchanger through indirect heat exchange against the first portion of the first expanded gaseous refrigerant stream; and further cooling a second portion of the cooled, compressed gaseous refrigerant stream from the first heat exchanger in a third heat exchanger by indirect heat exchange with a second portion of the first expanded gaseous refrigerant stream, wherein the first expanded gaseous refrigerant stream exiting the first expander is substantially vapor.