Reverse Brayton LNG production process
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Solution Overview
Problem
Existing methods for liquefying natural gas using reverse Brayton cycles face inefficiencies due to the need for multiple refrigerant streams at different pressures and temperatures, which complicates the design and operation of heat exchangers, limiting the matching of cooling curves and overall process power.
Innovation Solution
The use of parallel coil-wound heat exchanger sections with the shell side of the first section operating at a different pressure from the second and third sections, allowing for improved cooling curve matching in the liquefaction section, and employing a closed-loop refrigerant cycle with methane as the primary refrigerant, enhances the specific power of the process while maintaining the robustness and high processing capacity of coil-wound heat exchangers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If multiple refrigerant streams at different pressures and temperatures are used in reverse Brayton cycles, then cooling capacity is improved, but heat exchanger design complexity increases
Solution Approach 1:
The heat exchanger is divided into multiple sections, each handling a different refrigerant stream at specific pressure and temperature levels. This segmentation allows each section to be optimized for its specific thermal conditions while maintaining overall system efficiency, resolving the contradiction between cooling capacity and design complexity.
Solution Approach 2:
The patent introduces a pressure dimension differentiation within the heat exchanger system by operating different sections at different pressures. This dimensional approach allows multiple refrigerant streams to coexist without requiring complex mixing or separation mechanisms, thereby improving cooling capacity while managing design complexity.
2Temperature
If multiple refrigerant streams at different pressures and temperatures are used, then cooling curve matching is attempted, but overall process power is limited
Solution Approach 1:
Different sections of the heat exchanger are assigned different local qualities in terms of pressure and temperature conditions to optimize cooling curve matching at each stage. This localized optimization allows better thermal matching without compromising overall process power, as each section operates at its optimal conditions.
3Ease of operation
If shell sides of heat exchanger sections are connected in fluid flow communication, then refrigerant circulation is simplified, but pressure equalization limits cooling curve matching
Solution Approach 1:
The shell sides of different heat exchanger sections are segmented into separate pressure zones rather than being connected in fluid flow communication. This segmentation enables each section to operate at its optimal pressure for cooling curve matching while maintaining independent refrigerant circulation paths, thus resolving the contradiction between operational simplicity and thermal efficiency.
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 configuration improves the specific power of the liquefaction process, reduces power requirements for the recycle flash gas compressor train, and enhances efficiency by aligning cooling curves, thereby reducing utility consumption and greenhouse gas emissions.
Implementation Method 1
The gaseous refrigerant may be a refrigerant circulating in a gas expander refrigeration cycle (also known as a reverse Brayton cycle)
Implementation Method 2
a gas expander refrigeration cycle
Implementation Method 3
cooling and liquefying a natural gas stream via indirect heat exchange with a gaseous refrigerant
Implementation Method 4
indirect heat exchange
Implementation Method 5
gaseous refrigerant flowing through the shell side
Implementation Method 6
liquefying natural gas via indirect heat exchange with a refrigerant
Implementation Method 7
cooling and liquefying a natural gas stream
Implementation Method 8
cold is recovered from the resulting flash gas streams by cooling and liquefying additional natural gas streams
Data Source
AI summary
Described herein are methods and systems for producing a liquefied natural gas (LNG) product by cooling and liquefying a natural gas stream via indirect heat exchange with a gaseous refrigerant and then flashing and separating the liquefied natural gas stream to obtain the LNG product. In particular, the gaseous refrigerant may be a refrigerant circulating in a reverse Brayton cycle. The gaseous refrigerant is warmed in the shell side first, second and third coil-wound heat exchanger sections each having a tube side and a shell side, the shell side of the first coil-wound heat exchanger section being separated from and operating at a different pressure to the shell side of the second and third coil-wound heat exchanger sections.