Method for reliquefying boil-off gas.
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Solution Overview
Problem
Existing partial re-liquefaction systems for boil-off gases in liquefied gas storage tanks have limitations in re-liquefaction efficiency and require additional compressor installations, leading to increased costs and reduced storage tank internal pressure management.
Innovation Solution
A vessel system incorporating a main compression unit, an extra compression unit in parallel, a heat exchanger, a decompressor, and a gas-liquid separator to enhance boil-off gas re-liquefaction efficiency, utilizing existing compressors to compress and cool boil-off gas, and then expand it for reliquefaction, with the option to bypass the gas-liquid separator in case of failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a separate refrigerant system is used for re-liquefying boil-off gas, then re-liquefaction can be achieved, but device complexity and cost increase
Solution Approach 1:
The system uses the boil-off gas itself as the refrigerant to cool and reliquefy additional boil-off gas, eliminating the need for separate refrigerant systems. The compressed boil-off gas flows through a heat exchanger where it is cooled by colder boil-off gas, achieving self-service re-liquefaction without external refrigerant infrastructure
Solution Approach 2:
The existing boil-off gas compression system serves dual purposes: it compresses gas for engine fuel supply and simultaneously provides the cold stream for re-liquefaction through the heat exchanger. This multi-functionality eliminates dedicated refrigerant equipment while maintaining re-liquefaction capability
2Productivity
If additional compressors are installed for re-liquefaction, then compression capacity increases, but cost and device complexity increase
Solution Approach 1:
The existing compressor that supplies boil-off gas to the engine is also used to compress boil-off gas for the re-liquefaction process. The compressed gas is directed to a heat exchanger where it is cooled and reliquefied, allowing the same compression infrastructure to serve both fuel supply and re-liquefaction functions
Solution Approach 2:
The system merges the fuel supply function and re-liquefaction function into a single integrated process using shared compression and heat exchange infrastructure. By combining these functions, the system achieves re-liquefaction without requiring separate dedicated compressors or refrigerant systems
3Quantity of substance
If boil-off gas is accumulated in the storage tank, then re-liquefaction amount increases, but internal pressure rises excessively
Solution Approach 1:
The system extracts boil-off gas from the storage tank and processes it through compression and heat exchange before reliquefaction. By removing gas from the tank for processing and then returning the reliquefied liquid, the system prevents excessive pressure accumulation while maintaining the ability to handle large quantities of boil-off gas
Solution Approach 2:
The system implements a feedback loop where boil-off gas is continuously monitored, compressed, cooled, and reliquefied, with the reliquefied liquid returned to the storage tank. This closed-loop process dynamically manages tank pressure by adjusting the rate of gas removal and reliquefaction to maintain optimal pressure levels
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 significantly increases re-liquefaction efficiency and reduces costs by utilizing existing compressors, maintaining optimal storage tank pressure and extending vessel operational periods by efficiently managing boil-off gas.
Implementation Method 1
a heat exchanger cooling compressed boil-off gas (hereinafter referred to as a 'first fluid') through heat exchange using boil-off gas discharged from the storage tank as a refrigerant
Implementation Method 2
a decompressor expanding the first fluid having been cooled through heat exchange with the boil-off gas discharged from the storage tank in the heat exchanger
Implementation Method 3
a main compression unit compressing a part of the boil-off gas discharged from the storage tank; an extra compression unit disposed in parallel to the main compression unit and compressing the other part of the boil-off gas
Implementation Method 4
Method for reliquefying boil-off gas... significantly increases re-liquefaction efficiency... efficiently managing boil-off gas
Data Source
Figure 1
Figure 2
AI summary
A vessel including a storage tank for storing liquefied gas is disclosed. The vessel comprises: a heat exchanger for heat-exchanging compressed boil-off gas (hereinafter, referred to as "first fluid") by using, as a refrigerant, the boil-off gas discharged from the storage tank, so as to cool the same; a main compression part for compressing a part of the boil-off gas discharged from the storage tank; a rest compression part provided in parallel to the main compression part so as to compress the other part of the boil-off gas discharged from the storage tank; and a decompression device for expanding the first fluid having been cooled by exchanging heat with the boil-off gas, which is discharged from the storage tank, in the heat exchanger, wherein the first fluid is: a flow in which the boil-off gas compressed by the main compression part and the boil-off gas compressed by the rest compression part join; or the boil-off gas compressed by the main compression part.