LNG Container Recondenser Design to Reduce BOG Stratification
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Solution Overview
Problem
Existing methods for boiling-off gas (BOG) recondensation in liquefied natural gas (LNG) storage face inefficiencies due to high nitrogen content in BOG, leading to stratification and incomplete recondensation, as well as the need for cumbersome nozzle designs to enhance surface exchange for effective recondensation.
Innovation Solution
A method and apparatus for BOG recondensation using a recondenser that reintroduces subcooled LNG to directly mix with recondensed gas, minimizing stratification risks and achieving efficient recondensation by optimizing the recondensation process within a separated drum or integrated container setup, with control valves managing gas flow and temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If direct contact recondensation of BOG with LNG is used, then recondensation efficiency is improved, but stratification occurs due to high nitrogen content in BOG
Solution Approach 1:
The recondensation process is divided into two distinct stages: first, pre-cooling BOG in a separate section to reduce its temperature and nitrogen content; second, recondensing the pre-cooled BOG in another section. This segmentation prevents direct mixing of warm BOG with LNG, thereby avoiding stratification while maintaining recondensation efficiency.
Solution Approach 2:
A pre-cooling section acts as an intermediary between the BOG inlet and the main recondensation zone. This intermediate zone allows BOG to be partially condensed and cooled before entering the main LNG contact area, serving as a buffer that prevents the harmful direct mixing of high-nitrogen BOG with stored LNG.
2Productivity
If high surface exchange is achieved through complex nozzle designs, then recondensation effectiveness is improved, but device complexity increases
Solution Approach 1:
The complex nozzle design is completely removed from the system. Instead of using specialized nozzles to achieve surface exchange, the invention extracts the recondensation function to a separate pre-cooling section where simple direct contact between pre-cooled BOG and LNG occurs, eliminating the need for complex geometries.
Solution Approach 2:
Instead of using complex nozzles to increase surface area for heat exchange, the invention inverts the approach by using simple direct contact in a separated pre-cooling zone. The high surface exchange is achieved not through nozzle geometry but through the phase change process itself in a simplified configuration.
3Stress or pressure
If subcooled LNG is injected into container to control pressure, then pressure stabilization is improved, but stratification and flashing risks increase
Solution Approach 1:
The system performs preliminary recondensation of BOG in a separate pre-cooling section before the recondensed liquid is injected back into the container. This preliminary action ensures that the liquid returned to the container is already at a stable temperature and composition, preventing stratification and flashing upon injection while maintaining pressure control.
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 solution effectively reduces stratification and ensures complete recondensation of BOG, minimizing venting and enhancing the composition and temperature match of recondensed liquid with stored LNG, thereby stabilizing container pressure and preventing flashing.
Implementation Method 1
The recondenser has a first inlet for evaporated gas, a second inlet for subcooled liquefied gas and an outlet for recondensed gas
Implementation Method 2
A method and apparatus for BOG recondensation using a recondenser that reintroduces subcooled LNG to directly mix with recondensed gas
Implementation Method 3
means for withdrawing liquefied gas from one or more of the at least one container and supplying it to a refrigeration unit for subcooling the liquefied gas
Data Source
Figure 1a
Figure 1b
Figure 1c
AI summary
The present invention relates to a method and an apparatus for storing liquefied gas in at least one insulated container (1) while withdrawing evaporated gas from one or more of the at least one container (1), wherein at least a part of the evaporated gas is supplied to a recondenser (11) and wherein liquefied gas is withdrawn from one or more of the at least one container (1) and at least in part supplied to the recondenser (11) for recondensing the evaporated gas supplied to the recondenser (11) such that recondensed gas is obtained at a recondenser outlet, wherein before supplying the liquefied gas to the recondenser (11), the liquefied gas is subcooled by passing it through a refrigeration unit (8, 9), at least a part of the subcooled liquefied gas being supplied to the recondenser (11), and wherein at least a part of the recondensed gas obtained at the outlet of the recondenser (11) is reintroduced into one or more of the at least one container (1).