Vessel BOG Reliquefaction Using Self-Heat Exchange and Expansion
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Solution Overview
Problem
The reliquefaction of ethane BOG with a low boiling point in liquefied gas storage tanks requires a separate independent cold heat supply cycle, increasing installation and operational costs due to the need for additional equipment and energy consumption.
Innovation Solution
An apparatus and method for reliquefaction of BOG that utilizes self-heat exchange between compressed and expanded BOG, eliminating the need for a separate cold heat supply cycle by controlling pressure and temperature through a multistage compressor and heat exchanger system, allowing for efficient reliquefaction without additional refrigeration cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a separate independent cold heat supply cycle is added to reliquefy ethane BOG, then reliquefaction of low boiling point BOG is achieved, but installation cost and device complexity increase
Solution Approach 1:
The patent merges the cold heat supply function with the BOG compression system by using the compression process itself to generate the necessary cold heat through expansion. Instead of adding a separate refrigeration cycle, the system utilizes the BOG compressor and expansion valve to create cold heat in-situ, thereby achieving reliquefaction without increasing device complexity
Solution Approach 2:
The system performs self-service by using the BOG itself as the working fluid for generating cold heat. The compressed BOG is expanded to produce cold heat that then cools and reliquefies the remaining BOG, eliminating the need for external refrigeration systems and reducing installation costs
2Reliability
If a separate independent cold heat supply cycle is added to reliquefy ethane BOG, then reliquefaction of low boiling point BOG is achieved, but operation cost and energy consumption increase
Solution Approach 1:
The patent converts the harmful effect of BOG expansion (which normally causes temperature drop and potential freezing) into a beneficial cold heat source. By strategically expanding a portion of the compressed BOG, the system generates cold heat that is then used to reliquefy the remaining BOG, turning what would be a waste into a useful resource and reducing energy consumption
Solution Approach 2:
The system recovers the cold heat generated during BOG expansion instead of discarding it. The expanded BOG that would normally be vented or wasted is instead used as a cooling medium to reliquefy the main BOG stream, thereby recovering energy and reducing overall operation costs
3Productivity
If compression ratio is increased to improve reliquefaction efficiency, then reliquefaction efficiency is improved, but discharge temperature increases excessively
Solution Approach 1:
The patent segments the compression process into multiple stages with intercooling. Instead of single-stage compression that leads to excessive discharge temperatures, the system uses multi-stage compression with cooling between stages, maintaining manageable temperatures while achieving the necessary compression ratio for efficient reliquefaction
Solution Approach 2:
The patent introduces an intermediary cooling process between compression stages. This intermediary cooling step acts as a mediator that removes excess heat generated during compression, allowing the system to achieve high compression ratios without excessive discharge temperatures that would compromise reliquefaction efficiency
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 reduces installation costs, energy consumption, and maintains high reliquefaction efficiency by optimizing the coefficient of performance (COP) through self-heat exchange, achieving comparable results to traditional systems without the need for additional refrigeration cycles.
Implementation Method 1
a compressor (20) compressing the BOG discharged from the storage tank (10)
Implementation Method 2
a heat exchanger (30) performing heat exchange between the BOG compressed by the compressor (20) and the BOG discharged from the storage tank (10)
Implementation Method 3
a first expansion unit (71) expanding some of the BOG compressed by the multiple compressors (20a, 20b, 20c, 20d)
Data Source
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AI summary
The present invention relates to an apparatus and a method for reliquefaction of boil-off gas generated in a liquefied gas storage tank applied to a vessel. The apparatus for reliquefaction of boil-off gas for a vessel, according to the present invention, which is a reliquefaction apparatus for reliquefying boil-off gas generated in a liquefied gas storage tank installed on a vessel, comprises: a compression unit for compressing the boil-off gas discharged from the storage tank; and a heat exchanger for heat-exchanging the compressed boil-off gas compressed by the compression unit with the boil-off gas discharged from the storage tank, wherein the apparatus for reliquefaction of boil-off gas for a vessel further comprises: a first expansion means for dividing the boil-off gas passing through the heat exchanger into at least two flows including a first flow and a second flow, and expanding the divided first flow; a first intercooler for cooling the second flow remaining after the division of the first flow by using the first flow expanded by the expansion means as a refrigerant; and a receiver for receiving a second flow having passed through the first intercooler, in which a downstream pressure of the compression unit is controlled by a flow discharged from the receiver.