Mixed refrigerant system and method
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current natural gas liquefaction processes are complex, inefficient, and costly due to the difficulty in designing refrigeration systems that closely approximate the natural gas cooling curve, leading to high power consumption and mechanical complexity.
Innovation Solution
The process employs cold vapor separation to fractionate high-pressure vapor into cold liquid and vapor streams, which are then combined with sub-cooled liquids from a high-pressure accumulator to form a middle temperature refrigerant, reducing power consumption by operating near the dew point and minimizing thermodynamic losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If cascaded multilevel pure component refrigeration cycles are used to approximate the natural gas cooling curve, then the cooling efficiency is improved, but the mechanical complexity increases due to additional compressor trains
Solution Approach 1:
The refrigeration cycle is divided into multiple temperature levels (warm, cold, and transition zones) with dedicated heat exchanger sections, allowing each segment to operate optimally without requiring multiple compressor trains. The feed fluid cooling passage is segmented into zones handled by different refrigerant temperatures.
Solution Approach 2:
The system uses a single mixed refrigerant composition that dynamically adapts to different temperature zones through phase change and temperature-dependent heat transfer coefficients, eliminating the need for fixed-stage pure component systems with multiple compressors.
2Device complexity
If pure component refrigerants are used in cascaded cycles, then the refrigeration process can be structured in multiple levels, but thermodynamic efficiency decreases due to constant temperature vaporization not following the natural gas cooling curve
Solution Approach 1:
The system changes the refrigerant parameter from pure components to a mixed composition, which fundamentally alters the vaporization behavior to follow the natural gas cooling curve more closely, improving thermodynamic efficiency while maintaining structured refrigeration levels.
Solution Approach 2:
A composite mixed refrigerant composition is used instead of pure components, combining multiple hydrocarbons (methane, ethane, propane, butane, pentane) in specific proportions to achieve a vaporization curve that matches the natural gas cooling requirements across all temperature zones.
3Device complexity
If a single mixed refrigerant process is used to reduce mechanical complexity, then fewer compressors are required, but power consumption increases due to difficulty in finding a composition that generates a heating curve close to the cooling curve
Solution Approach 1:
The refrigerant composition parameters are optimized with specific hydrocarbon ratios and the system operates at specific pressure and temperature conditions to achieve a heating curve that closely matches the cooling curve, reducing the temperature driving force and improving heat transfer efficiency to lower power consumption.
Solution Approach 2:
The single mixed refrigerant system dynamically adapts to different temperature zones through phase equilibrium shifts and temperature-dependent properties, allowing one compressor to replace multiple compressors while maintaining efficiency through natural thermodynamic behavior.
4Device complexity
If single mixed refrigerant processes are used, then mechanical complexity is reduced, but power consumption increases due to large temperature differences at several points in the cooling process
Solution Approach 1:
Different sections of the heat exchanger are assigned different refrigerant temperatures (warm zone, cold zone, transition zone) to match the local cooling requirements of the natural gas at each stage, minimizing temperature differences and improving heat transfer efficiency throughout the process.
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 power consumption by up to 10% with minimal additional capital cost, improving the efficiency and operability of the liquefaction process while maintaining mechanical simplicity.
Implementation Method 1
cold vapor separation to fractionate condensed vapor obtained from high pressure separation into a cold liquid fraction and a cold vapor fraction
Implementation Method 2
heat exchange with refrigeration streams in the heat exchanger
Implementation Method 3
removal of heat via heat exchange with refrigeration streams
Implementation Method 4
the feed fluid stream is cooled and/or liquefied... a stream of product fluid such as liquid natural gas is produced
Implementation Method 5
combined with sub-cooled liquids from a high-pressure accumulator to form a middle temperature refrigerant
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Provided are mixed refrigerant systems and methods and, more particularly, to a mixed refrigerant system and methods that provides greater efficiency and reduced power consumption. The present invention generally relates to mixed refrigerant systems and methods suitable for cooling fluids such as natural gas. Natural gas and other gases are liquefied for storage and transport. Liquefaction reduces the volume of the gas and is typically carried out by chilling the gas through indirect heat exchange in one or more refrigeration cycles.