Boil-Off Gas Reliquefaction Using Immersed Heat Exchange Lines
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Solution Overview
Problem
The existing methods for reliquefying boil-off gas from liquefied gas tanks are costly and wasteful, as they often require specialized facilities and result in incineration or disposal of the gas, and direct injection of bubbles into the tank leads to inefficient reliquefaction.
Innovation Solution
A boil-off gas processing apparatus with a discharge line and a reliquefaction line that immerses in the liquefied gas tank, maintaining necessary pressure and length for heat transfer, allowing for reliquefaction and return of the gas without external reliquefying apparatuses, and includes a pressure holding device to condense and trap the gas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If boil-off gas is removed by compressor to external processing apparatus, then tank pressure is maintained, but facility cost and operating cost become enormous
Solution Approach 1:
The invention extracts the reliquefaction function from external processing apparatus and relocates it directly into the storage tank through immersed heat exchange pipes. This eliminates the need for external compressors and processing facilities, thereby maintaining tank pressure while dramatically reducing facility and operating costs.
Solution Approach 2:
The storage tank performs its own reliquefaction operation using its stored liquefied gas as the cooling medium. The system is self-sufficient, using the cold liquefied gas already present in the tank to cool and reliquefy the boil-off gas, eliminating dependence on external energy sources or complex processing equipment.
2Productivity
If boil-off gas is directly injected as bubbles into liquefied gas tank, then reliquefaction occurs, but bubbles quickly rise and return to gas phase
Solution Approach 1:
The invention introduces heat exchange pipes as an intermediary structure between the boil-off gas and the liquefied gas. Instead of direct bubble injection, the gas is cooled through the pipe walls by the immersed pipes, providing a controlled and efficient heat transfer pathway that ensures complete reliquefaction.
Solution Approach 2:
The invention replaces the mechanical bubble injection method with a thermal field-based heat exchange system. By using the temperature difference between the cold liquefied gas and the warmer boil-off gas through immersed pipes, the system achieves reliable reliquefaction without relying on bubble dynamics that cause gas to rise and re-evaporate.
3Productivity
If external reliquefying apparatus is used, then boil-off gas can be reliquefied, but facility cost becomes enormous
Solution Approach 1:
The invention merges the reliquefaction function with the storage tank itself by immersing heat exchange pipes directly into the tank. This integration eliminates the need for separate external reliquefying apparatus, combining storage and processing functions into a single system, thereby maintaining full reliquefaction capability while dramatically reducing facility costs.
Solution Approach 2:
The immersed heat exchange pipes serve multiple functions: they act as both cooling elements for reliquefaction and structural components within the tank. This multi-functionality eliminates the need for dedicated external processing equipment, reducing overall system complexity and cost while maintaining effective boil-off gas处理能力.
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 solution reduces facility and operating costs by allowing reliquefaction within the tank, preventing pressure buildup, and minimizing gas incineration or disposal, while maintaining tank pressure below predetermined limits.
Implementation Method 1
a boil-off gas reliquefaction line configured to immerse at least part of the boil-off gas discharge line in the liquefied gas within the liquefied gas tank
Implementation Method 2
the boil-off gas reliquefaction line maintains a pressure necessary for reliquefaction of the boil-off gas and has a length sufficient to be able to release an amount of heat necessary for reliquefaction of the boil-off gas
Implementation Method 3
the boil-off gas reliquefaction line maintains a pressure necessary for reliquefaction of the boil-off gas
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
A boil-off gas processing apparatus for reliquefying a boil-off gas (22) generated within a liquefied gas tank (2) storing a liquefied gas (21) and returning the reliquefied gas to the interior of the liquefied gas tank (2) includes a boil-off gas discharge line (3) configured to discharge the boil-off gas (22) from the liquefied gas tank (2) to outside, and a boil-off gas reliquefaction line (4) configured to immerse at least part of the boil-off gas discharge line (3) in the liquefied gas (21) within the liquefied gas tank (2), wherein the boil-off gas reliquefaction line (4) includes a pressure holding device (42) configured to maintains a pressure necessary for reliquefaction of the boil-off gas (22) and has a length (L) sufficient to be able to absorb an amount of heat necessary for reliquefaction of the boil-off gas (22).