Ship BOG Reliquefaction System with Multistage Compression
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Solution Overview
Problem
Existing BOG reliquefaction systems face inefficiencies and maintenance challenges, particularly in low-pressure engine configurations, due to the need for multiple compressors and complex compression processes, which increase manufacturing costs and maintenance complexity.
Innovation Solution
A ship engine system that performs precooling of BOG through heat exchange with low-pressure, low-temperature BOG before multistage compression, using a single multistage compressor and additional self-heat exchangers to improve reliquefaction efficiency and simplify maintenance by using BOG as a refrigerant for heat exchange.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple compressors are used in BOG reliquefaction systems for low-pressure engines, then the reliquefaction capacity is sufficient, but the device complexity and maintenance requirements increase
Solution Approach 1:
The compression process is divided into multiple stages within a single compressor unit, with inter-stage cooling. The BOG is compressed in stages (e.g., first stage compression, inter-stage cooling, second stage compression) rather than using multiple separate compressors, achieving the same pressure increase with reduced complexity
Solution Approach 2:
A single multistage compressor performs multiple functions: it provides the necessary compression for reliquefaction, supplies compressed BOG to the engine, and works in conjunction with the cooling system to achieve temperature reduction. This multi-functional design eliminates the need for separate dedicated compressors
2Productivity
If complex compression processes are implemented, then reliquefaction efficiency improves, but maintenance complexity increases
Solution Approach 1:
The compression and cooling functions are merged into an integrated system where the multistage compressor works with inter-stage coolers and the final cooler in a unified process flow. This consolidation reduces the number of separate components that require maintenance while maintaining high reliquefaction efficiency
Solution Approach 2:
The system uses BOG itself as the refrigerant in a self-contained cycle. The compressed and cooled BOG is used to cool incoming BOG through heat exchangers, creating a self-sustaining cooling process that reduces external refrigerant requirements and simplifies maintenance
3Ease of repair
If a single multistage compressor is used, then maintenance complexity is reduced, but achieving sufficient compression for low-pressure engines becomes difficult
Solution Approach 1:
The multistage compressor is designed with adjustable parameters including variable compression ratios and controllable stage pressures. This dynamic capability allows the single compressor to adapt and achieve the required compression levels for low-pressure engines through optimized operational parameters rather than mechanical complexity
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 reliquefaction efficiency, reduces maintenance complexity, and allows for easier upkeep by utilizing a single multistage compressor, even in low-pressure engine configurations, thereby improving overall system performance and cost-effectiveness.
Implementation Method 1
a first self-heat exchanger performing heat exchange with respect to boil-off gas (BOG) discharged from a storage tank
Implementation Method 2
a multistage compressor compressing the BOG discharged from the storage tank and having passed through the first self-heat exchanger in multiple stages
Implementation Method 3
a first decompressor expanding some of the BOG compressed by the multistage compressor
Implementation Method 4
a second self-heat exchanger performing heat exchange with respect to the other BOG compressed by the multistage compressor with the BOG expanded by the first decompressor
Implementation Method 5
a second decompressor expanding the BOG precooled by the second self-heat exchanger and cooled by the first self-heat exchanger
Data Source
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AI summary
A ship comprising an engine is disclosed. The ship comprising an engine comprises: a first self-heat exchanger which heat-exchanges boil-off gas discharged from a storage tank; a multi-stage compressor which compresses, in multi-stages, the boil-off gas that passed through the first self-heat exchanger after being discharged from the storage tank; a first decompressing device which expands one portion of the boil-off gas compressed by the multi-stage compressor; a second self-heat exchanger which heat-exchanges the other portion of the boil-off gas compressed by the multi-stage compressor, with the boil-off gas expanded by the first decompressing device; and a second decompressing device which expands the boil-off gas pre-cooled by the second self-heat exchanger and cooled by the first self-heat exchanger, wherein the first self-heat exchanger uses the boil-off gas discharged from the storage tank as a refrigerant for cooling the boil-off gas that passed through the second self-heat exchanger after being compressed by the multi-stage compressor.