High-Pressure Expander Refrigerant Mixing for Make-Up Gas Variation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current high-pressure expander cycles for natural gas liquefaction are less efficient thermodynamically compared to refrigerant-based cycles, requiring external refrigeration for pre-cooling and resulting in high recycle gas stream flow rates, which reduces the benefits of expander cycles and increases logistical challenges, especially in remote LNG production sites.
Innovation Solution
The method involves using a high-pressure expander process with a primary cooling loop where a portion of the feed gas is compressed to a pressure greater than 1,500 psia, cooled, and expanded to produce a refrigerant stream that is then mixed with a make-up gas stream to condense heavy hydrocarbons, forming a cold primary refrigerant mixture used for liquefaction, thereby reducing the need for external refrigerants and improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If external refrigeration systems are used for pre-cooling in high-pressure expander cycles, then the liquefaction process can be maintained, but the system complexity and logistical requirements increase significantly
Solution Approach 1:
The feed gas itself is used as the refrigerant in a self-service manner. A portion of the feed gas is compressed, cooled, and expanded to produce cold refrigerant that pre-cools the remaining feed gas before it enters the expander. This eliminates the need for separate external refrigeration systems while maintaining reliable liquefaction operation.
Solution Approach 2:
The feed gas serves multiple functions: it is both the material to be liquefied and the refrigerant for pre-cooling. This multi-functionality reduces system complexity by eliminating dedicated refrigeration equipment while ensuring continuous reliable operation through the self-contained refrigeration cycle.
2Temperature
If high recycle gas stream flow rates are used in expander cycles, then cooling capacity is maintained, but the benefits of expander cycles are reduced and logistical challenges increase
Solution Approach 1:
The system changes the parameters of the refrigerant stream by compressing it to high pressure (e.g., 3000 psig), cooling it to ambient temperature, then expanding it to produce a cold stream at temperatures below -100°F. This parameter transformation allows effective pre-cooling with reduced recycle gas flow rates, improving overall liquefaction efficiency while maintaining adequate cooling capacity.
3Adaptability or versatility
If make-up gas with varying composition is used, then operational flexibility is improved, but control of refrigerant composition becomes difficult
Solution Approach 1:
The system incorporates composition monitoring and control mechanisms that detect variations in make-up gas composition and adjust operating parameters accordingly. This feedback control maintains stable refrigerant composition despite variations in make-up gas, allowing operational flexibility while preventing composition-related performance degradation.
Solution Approach 2:
The system dynamically adjusts compression ratios, flow rates, and cooling conditions based on real-time refrigerant composition measurements. This dynamic adaptation allows the system to maintain optimal performance and composition control even when make-up gas composition varies, balancing flexibility with stability.
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 enhances the thermal efficiency of the liquefaction process, allows for compact equipment design, and increases LNG production capacity by up to 30% for a given power input, while also reducing the size and cost of main cryogenic heat exchangers, thus addressing inefficiencies and logistical challenges in remote LNG production.
Implementation Method 1
cooling the compressed refrigerant stream by indirect heat exchange with an ambient temperature air or water
Implementation Method 2
expanding the compressed, cooled refrigerant stream in at least one work producing expander, thereby producing an expanded, cooled refrigerant stream
Implementation Method 3
mixing the expanded, cooled refrigerant stream with a make-up refrigerant stream in a separator, thereby condensing heavy hydrocarbon components from the make-up refrigerant stream
Implementation Method 4
passing the cold primary refrigerant mixture through a heat exchanger zone to cool the feed gas stream by indirect heat exchange
Data Source
AI summary
A method for liquefying a feed gas stream. A refrigerant stream is cooled and expanded to produce an expanded, cooled refrigerant stream. Part or all of the expanded, cooled refrigerant stream is mixed with a make-up refrigerant stream in a separator, thereby condensing heavy hydrocarbon components from the make-up refrigerant stream and forming a gaseous expanded, cooled refrigerant stream. The gaseous expanded, cooled refrigerant stream passes through a heat exchanger zone to form a warm refrigerant stream. The feed gas stream is passed through the heat exchanger zone to cool at least part of the feed gas stream by indirect heat exchange with the expanded, cooled refrigerant stream, thereby forming a liquefied gas stream. The warm refrigerant stream is compressed to produce the compressed refrigerant stream.