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Solution Overview
Problem
Existing boil-off gas re-liquefaction systems, such as the partial re-liquefaction system, face inefficiencies in re-liquefying boil-off gas and can lead to increased internal pressure in storage tanks, potentially damaging them, and require separate refrigerants, which increases costs and complexity.
Innovation Solution
A ship-based system that includes a boil-off gas heat exchanger, compressors, a refrigerant heat exchanger, and decompressing devices to re-liquefy boil-off gas using the boil-off gas itself as a refrigerant, with an extra compressor and boost compressor to enhance efficiency and pressure, allowing for flexible control of refrigerant flow and cold heat supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a separate refrigerant is used for re-liquefying boil-off gas, then the re-liquefaction process can be implemented, but the system complexity and cost increase
Solution Approach 1:
The system uses the boil-off gas itself as the refrigerant for re-liquefaction, eliminating the need for separate refrigerants. The boil-off gas is compressed, heat-exchanged, and expanded to create a refrigeration cycle that liquefies additional boil-off gas and returns it to the storage tank, making the system self-sufficient and reducing complexity
Solution Approach 2:
The boil-off gas serves multiple functions: it is used as fuel for the engine, as a refrigerant for re-liquefaction, and as a working fluid for heat exchange. This multi-functionality eliminates the need for dedicated separate refrigerant systems and reduces overall system complexity
2Productivity
If boil-off gas is accumulated in the storage tank, then the re-liquefaction efficiency can be improved, but the internal pressure of the tank rises excessively
Solution Approach 1:
The system extracts boil-off gas from the storage tank through a discharge line and processes it externally through compression, heat exchange, and expansion. This prevents excessive accumulation and pressure buildup in the tank while still enabling efficient re-liquefaction of the extracted gas and its return to the tank
3Productivity
If the refrigerant flow rate is increased to improve cooling capacity, then the re-liquefaction amount increases, but the system requires larger compressors and heat exchangers
Solution Approach 1:
The system dynamically adjusts the refrigerant flow rate, compressor speed, and heat exchange parameters based on the boil-off gas generation rate and cooling requirements. This allows the system to achieve high re-liquefaction amounts when needed without requiring oversized equipment that would be necessary for continuous maximum-capacity operation
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 system significantly increases re-liquefaction efficiency and amount, reduces the need for separate refrigerants, and flexibly controls refrigerant flow and cold heat supply, enhancing the economical efficiency and safety of boil-off gas management.
Implementation Method 1
a boil-off gas heat exchanger which is provided on the downstream of a storage tank and is for heat exchanging a compressed boil-off gas (hereafter referred to as 'a first fluid') by means of a boil-off gas discharged from the storage tank as a refrigerant, thereby cooling same
Implementation Method 2
the refrigerant heat exchanger may heat exchange and cool both the first fluid and the second fluid by means of the boil-off gas, which has passed the refrigerant decompressing device, as the refrigerant
Implementation Method 3
a refrigerant decompressing device which expands the second fluid, which is sent to the refrigerant heat exchanger (hereinafter, the fluid sent to the refrigerant heat exchanger being referred to as 'second fluid') and cooled by the refrigerant heat exchanger, and then sent the expanded second fluid back to the refrigerant heat exchanger; and a first decompressing device which expands the first fluid cooled by the boil-off gas heat exchanger and the refrigerant heat exchanger
Data Source
AI summary
A ship includes: a boil-off gas heat exchanger installed on a downstream of a storage tank and heat-exchanges a compressed boil-off gas (“a first fluid”) by a boil-off gas discharged from the storage tank as a refrigerant, to cool the boil-off gas; a compressor installed on a downstream of the boil-off gas heat exchanger and compresses a part of the boil-off gas discharged from the storage tank; an extra compressor installed on a downstream of the boil-off gas heat exchanger and in parallel with the compressor and compresses the other part of the boil-off gas discharged from the storage tank; a refrigerant heat exchanger which additionally cools the first fluid which is cooled by the boil-off gas heat exchanger; and a refrigerant decompressing device which expands a second fluid, which is sent to the refrigerant heat exchanger, and then sends the second fluid back to the refrigerant heat exchanger.