Method and system for storage and transport of liquefied petroleum gases
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Solution Overview
Problem
Existing reliquefaction systems for liquefied petroleum gases (LPG) on LPG carriers face inefficiencies in energy recovery and condensation rates due to liquid pool cooling, leading to higher energy losses and limited coefficient of performance (COP).
Innovation Solution
The implementation of glide refrigeration technology, which utilizes a mixture of refrigerants with different saturation temperatures, allows for improved condensation and sub-cooling of boil-off gases through a counter-current heat exchange process, eliminating the need for separate intercoolers and vent gas condensers, and optimizing the piping arrangement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If liquid pool cooling is used in intercoolers and vent gas condensers, then the system structure is simple, but the temperature difference at equilibrium reaches up to 20°C which limits the condensation rate
Solution Approach 1:
The patent changes the thermal parameters by introducing a heat exchanger that enables continuous heat exchange between the refrigerant and the liquid pool, maintaining a smaller temperature difference (e.g., 5°C) compared to traditional liquid pool cooling (20°C), thereby improving condensation rate while keeping the system relatively simple
Solution Approach 2:
The patent introduces a heat exchanger as an intermediary component between the refrigerant circulation system and the liquid pool, enabling more efficient heat transfer without requiring complete system redesign, thus improving condensation efficiency while maintaining structural simplicity
2Reliability
If separate intercoolers and vent gas condensers are used, then the cooling function is comprehensive, but the equipment and piping arrangement become complex
Solution Approach 1:
The patent merges the intercooler and vent gas condenser functions into a single integrated system where the heat exchanger serves dual purposes: cooling compressed gas between stages and condensing non-condensable components, thereby reducing equipment quantity and piping complexity while maintaining comprehensive cooling functionality
Solution Approach 2:
The heat exchanger is designed as a multi-functional component that performs both intercooling and vent gas condensation functions, allowing a single piece of equipment to replace multiple separate components, thus simplifying the overall system structure without compromising cooling effectiveness
3Reliability
If traditional reliquefaction systems are used, then the system is established and reliable, but the energy losses are higher and the coefficient of performance (COP) is lower
Solution Approach 1:
The patent implements a feedback mechanism where the refrigeration effect is continuously optimized by adjusting the refrigerant circulation based on the actual cooling demand and temperature differential across the heat exchanger, thereby reducing energy losses and improving COP while maintaining system reliability
Solution Approach 2:
The patent optimizes thermal parameters by maintaining a smaller temperature difference in the heat exchanger compared to traditional liquid pool cooling, which improves the thermodynamic efficiency of the refrigeration cycle, reduces energy losses, and enhances the coefficient of performance
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 liquefaction capacity and COP of the reliquefaction system, reducing energy consumption and greenhouse gas emissions while simplifying the equipment and piping arrangement, leading to more efficient refrigeration and reduced operational time.
Implementation Method 1
a counter-current heat exchange process
Implementation Method 2
utilises a mixture of refrigerants with different saturation temperatures
Data Source
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AI summary
The present invention relates to a method and system for storage and transport of liquified petroleum gases (LPG) on LPG carriers where boil off gas from the LPG is compressed in a cargo compressor with minimum two stages of compression, condensed in a cargo condenser and any non-condensable gases can be separated and/or gas and liquid can be mixed in a liquid receiver. A warm and mixed two-phase condensate stream leaving the liquid receiver is heat exchanged by glide refrigeration in at least one condensate sub-cooler, and any droplets present in a stream leaving the at least one condensate sub-cooler is removed in at least one droplet separator before being returned to the cargo compressor thus forming a further cooled, compressed stream.