Mixed Refrigerant Phase Separation for Efficient Gas Liquefaction
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Solution Overview
Problem
Current gas cooling and liquefaction systems are costly and complex, with a need for improved refrigeration efficiency and reduced operating costs, particularly in systems using mixed refrigerants for natural gas liquefaction.
Innovation Solution
A mixed refrigerant system with a multi-stream heat exchanger and staged compression and expansion devices, including a primary refrigeration passage, pre-cool liquid, high and cold separator passages, and expansion devices, which allows for efficient cooling and liquefaction through countercurrent indirect heat exchange and phase separation processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a mixed refrigerant system with multi-stream heat exchanger and staged compression is used, then cooling efficiency is improved, but device complexity increases
Solution Approach 1:
The refrigeration system is divided into multiple streams (first stream, second stream, third stream) with separate heat exchangers and expansion devices for different refrigerant phases and temperatures. This segmentation allows each stream to be optimized independently for its specific temperature range and phase, improving overall cooling efficiency while managing complexity through modular design
Solution Approach 2:
Different portions of the system use different refrigerant phases and temperatures tailored to specific cooling requirements. The first expansion device handles high-pressure liquid refrigerant, the second handles vapor-phase refrigerant, and the third handles low-pressure liquid refrigerant. Each heat exchanger is positioned to provide cooling at specific locations along the cooling passage, matching local cooling demands with appropriate refrigerant properties
2Use of energy by moving object
If mixed refrigerant is used to match warming curve with cooling curve, then refrigeration efficiency increases, but equipment cost and operation cost increase
Solution Approach 1:
The system utilizes parameter changes in the mixed refrigerant by maintaining different phases (liquid and vapor) at different pressure and temperature levels throughout the system. The refrigerant composition and phase distribution are optimized to match the warming curve of the liquefied gas with the cooling curve, improving thermodynamic efficiency. The multi-stream design with staged expansion allows precise control of temperature and pressure parameters to maximize heat exchange effectiveness
3Productivity
If vapor and liquid phases are separated and directed to different heat exchanger portions, then cooling efficiency increases, but device complexity increases
Solution Approach 1:
The system separates the refrigerant flow into distinct streams based on phase and pressure: a first stream for high-pressure liquid refrigerant, a second stream for vapor-phase refrigerant, and a third stream for low-pressure liquid refrigerant. Each stream has its own heat exchanger and expansion device, allowing independent optimization of heat transfer surfaces and flow rates for maximum cooling efficiency
Solution Approach 2:
The heat exchanger is designed with multiple passages that serve different functions: some passages receive high-pressure liquid refrigerant for initial cooling, others receive vapor-phase refrigerant for intermediate cooling, and additional passages receive low-pressure liquid refrigerant for final cooling. This multi-functional heat exchanger design allows a single piece of equipment to handle multiple refrigerant streams with different properties, improving productivity while managing complexity through integrated design
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 system achieves increased cooling efficiency and reduced operating costs by optimizing the use of mixed refrigerants and phase separation, resulting in more practical and economical gas cooling and liquefaction processes.
Implementation Method 1
Liquefaction is typically accomplished by chilling the gas through indirect heat exchange by one or more refrigeration cycles
Implementation Method 2
The refrigeration cycle for the liquefaction system will typically include a compression system for conditioning or processing the mixed refrigerant
Implementation Method 3
Vapor exiting the compressor is cooled in the cooler, and the resulting two-phase or mixed phase stream is directed to the separation and liquid accumulator device
Implementation Method 4
A first expansion device has an inlet in fluid communication with the high pressure liquid passage of the heat exchanger and an outlet
Implementation Method 5
A cold vapor separator has an inlet in fluid communication with the high pressure vapor passage of the heat exchanger, a vapor outlet in fluid communication with the cold separator vapor passage of the heat exchanger and a liquid outlet in fluid communication with the cold separator liquid passage of the heat exchanger
Implementation Method 6
Natural gas, which is primarily methane, and other gases, are liquefied under pressure for storage and transport
Data Source
AI summary
A system for cooling a gas with a mixed refrigerant includes a heat exchanger that receives and cools a feed of the gas so that a product is produced. The system includes a mixed refrigerant processing system having compression devices and aftercoolers as well as a low pressure accumulator and a high pressure accumulator. A cold vapor separator receives vapor from the high pressure accumulator and features a vapor outlet and a liquid outlet. Vapor from the cold vapor separator vapor outlet is cooled, expanded and directed to a primary refrigeration passage of the heat exchanger. Liquid from the liquid outlet of the cold vapor separator is subcooled, expanded and directed to the primary refrigeration passage. Liquid from the low pressure accumulator is subcooled, expanded and directed to the primary refrigeration passage. Liquid from the high pressure accumulator is subcooled, expanded and directed to the primary refrigeration passage.