Vessel
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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 and an extra compression unit in parallel, with a heat exchanger using boil-off gas as a refrigerant, a decompressor, and a gas-liquid separator to enhance re-liquefaction efficiency and manage boil-off gas effectively, allowing for the reuse of boil-off gas as fuel or return to the storage tank.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a separate refrigerant is used for re-liquefying boil-off gas, then re-liquefaction can be achieved, but device complexity and cost increase due to additional components
Solution Approach 1:
The system uses the boil-off gas itself as the refrigerant for re-liquefaction, eliminating the need for separate refrigerant systems. The compressed boil-off gas is cooled by heat exchange with the cold liquid phase from the decompressor, and the expanded boil-off gas provides the cooling effect needed for re-liquefaction, making the system self-sufficient.
Solution Approach 2:
The boil-off gas serves multiple functions: it is compressed for re-liquefaction, used as a refrigerant for cooling, and the cold liquid phase from decompression is used to cool the compressed gas. This multi-functional use of the same substance eliminates the need for separate dedicated refrigerant systems.
2Productivity
If additional compressors are installed to increase re-liquefaction capacity, then re-liquefaction efficiency improves, but device complexity and installation cost increase
Solution Approach 1:
The compression function is divided into two separate compression units, each handling a portion of the boil-off gas flow. This segmentation allows the system to process larger volumes of boil-off gas more efficiently while distributing the compression load across multiple units rather than requiring a single large compressor.
Solution Approach 2:
The compressed gas from both compression units is merged into a single flow that enters the heat exchanger. This combining of flows allows the system to utilize the cold liquid phase from the decompressor to cool both compressed streams simultaneously, increasing overall re-liquefaction capacity without proportionally increasing system complexity.
3Device complexity
If boil-off gas is accumulated in the storage tank, then re-liquefaction is simplified, but internal pressure rises excessively causing safety risks
Solution Approach 1:
The system extracts boil-off gas from the storage tank through compression units and removes it from the tank environment. By continuously compressing and processing the boil-off gas, the system prevents excessive accumulation and pressure buildup in the storage tank while maintaining safe operating conditions.
Solution Approach 2:
The compression units operate continuously to compress boil-off gas as it is generated, maintaining a continuous removal process. This continuous action prevents pressure buildup by ensuring that boil-off gas is constantly being processed and re-liquefied rather than accumulating in the storage tank.
4Use of energy by moving object
If boil-off gas is used as fuel in engines, then energy utilization improves, but re-liquefaction efficiency decreases due to gas consumption
Solution Approach 1:
The system dynamically balances the allocation of compressed boil-off gas between the heat exchanger (for re-liquefaction) and engine fuel supply. By adjusting the distribution of compressed gas based on system needs, the system can optimize both re-liquefaction efficiency and energy utilization without compromising either function.
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 increases re-liquefaction efficiency, reduces the need for additional compressor installations, and effectively manages internal tank pressure by efficiently re-liquefying boil-off gases, thereby enhancing storage tank stability and reducing operational costs.
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
Data Source
AI summary
A vessel includes 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 a storage tank, 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. 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.