Natural Gas Liquefaction With Supplemental Expander Cooling
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Solution Overview
Problem
Current LNG liquefaction processes face inefficiencies due to high ambient temperatures, which increase power requirements and costs, especially when ambient air or water cooling is insufficient, and the complexity of multi-refrigerant cycles adds to equipment and operational costs.
Innovation Solution
A process that uses a high-pressure expander cycle with supplemental cooling, where a portion of the gas stream is compressed, cooled indirectly with ambient temperature fluids, and then expanded to further cool the refrigerant, optimizing thermodynamic efficiency by minimizing horsepower requirements through strategic placement of external refrigerant cooling units.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If ambient temperature cooling is used for natural gas liquefaction, then the process is simpler and costs are lower, but at high ambient temperatures the cooling efficiency decreases and power requirements increase
Solution Approach 1:
The cooling process is divided into two distinct segments: (1) ambient temperature cooling for initial cooling of the refrigerant stream, and (2) supplemental cooling for additional temperature reduction when ambient cooling is insufficient. This segmentation allows the system to use the simpler ambient cooling method when possible while having a backup supplemental cooling mechanism activated only when needed, thus maintaining process simplicity while managing power requirements at high ambient temperatures
Solution Approach 2:
The system performs preliminary cooling of the refrigerant stream using ambient temperature cooling before the supplemental cooling stage. By pre-cooling the refrigerant as much as possible using the free ambient temperature source, the system reduces the cooling load that must be handled by the powered supplemental cooling system, thereby reducing overall power requirements while maintaining effectiveness even at high ambient temperatures
2Productivity
If multiple refrigerants are used in cascade cycles to match cooling curves, then liquefaction efficiency improves, but equipment complexity and costs increase
Solution Approach 1:
The invention extracts and eliminates the need for multiple refrigerants and complex cascade cycle equipment by using a single refrigerant stream that is cooled through a combination of ambient temperature cooling and supplemental cooling. The complex multi-refrigerant system is replaced with a simplified single-refrigerant system that achieves comparable liquefaction efficiency through strategic cooling placement
Solution Approach 2:
The single refrigerant stream performs multiple functions that would traditionally require multiple refrigerants: it provides both the cold end cooling and warm end cooling requirements for natural gas liquefaction. By cooling this single refrigerant stream to different temperatures through the combination of ambient and supplemental cooling, the system achieves the temperature matching function of multi-refrigerant systems with simpler equipment
3Temperature
If deep water is used for cooling when surface temperatures are high, then cooling efficiency improves, but piping costs and structural support requirements increase
Solution Approach 1:
Instead of always using deep water cooling, the system applies supplemental cooling partially - only to the extent necessary when ambient temperature cooling is insufficient. The supplemental cooling is applied selectively based on ambient conditions, providing additional cooling capacity when needed (at high ambient temperatures) while avoiding the complexity of deep water piping when ambient cooling is adequate
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 reduces overall horsepower requirements by approximately 20% and net horsepower usage by 10%, improving process efficiency and reducing costs, while maintaining efficient operation even in high ambient temperatures.
Implementation Method 1
cooling said compressed refrigerant by indirect heat exchange with an ambient temperature cooling fluid to a process temperature above about 35 degrees Fahrenheit
Implementation Method 2
expanding the refrigerant of (e) to further cool said refrigerant, thereby producing an expanded, supplementally cooled refrigerant
Data Source
AI summary
The invention relates to a process for liquefying a gas stream rich in methane, said process comprising: (a) providing said gas stream; (b) withdrawing a portion of said gas stream for use as a refrigerant; (c) compressing said refrigerant; (d) cooling said compressed refrigerant with an ambient temperature cooling fluid; (e) subjecting the cooled, compressed refrigerant to supplemental cooling; (f) expanding the refrigerant of (e) to further cool said refrigerant, thereby producing an expanded, supplementally cooled refrigerant; (g) passing said expanded, supplementally cooled refrigerant to a heat exchange area; and, (h) passing said gas stream of (a) through said heat exchange area to cool at least part of said gas stream by indirect heat exchange with said expanded, supplementally cooled refrigerant, thereby forming a cooled gas stream. In further embodiments for improved efficiencies, additional supplemental cooling may be provided after one or more other compression steps.