Vacuum Acquisition System for Cryogenic LNG Tanks
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Solution Overview
Problem
Conventional vacuum acquisition systems for cryogenic containers, such as LNG tanks, are unable to achieve the high vacuum levels required for efficient storage and transport of liquefied natural gas, as they typically maintain a vacuum level of about 1×10−3 torr, which is not sufficient for LNG vehicular fuel tanks.
Innovation Solution
A method and system involving a series of pumping and purging cycles using a combination of roughing pumps, turbo pumps, and cryogenic pumps, controlled by a system that evacuates, purges, and condenses air within the insulation space of the container to achieve a vacuum level of 1×10−6 torr or lower, utilizing a vacuum manifold and a controller to manage the process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional vacuum acquisition systems are used, then the system complexity is low, but the vacuum level achieved is insufficient (1×10−3 torr)
Solution Approach 1:
The vacuum acquisition system is divided into multiple stages with different pump types: roughing pumps for initial evacuation, turbo pumps for intermediate vacuum levels, and cryogenic pumps for final high vacuum achievement. Each stage handles a specific vacuum range, allowing the system to reach 1×10−6 torr while managing complexity through functional segmentation.
Solution Approach 2:
A vacuum manifold is introduced as an intermediary component that coordinates between multiple pumps and the insulation space. The manifold integrates the operations of roughing pumps, turbo pumps, and cryogenic pumps, enabling them to work sequentially and achieve the target vacuum level of 1×10−6 torr.
2Manufacturing precision
If multiple pumping and purging cycles are implemented, then the vacuum level reaches 1×10−6 torr, but the acquisition time increases
Solution Approach 1:
The system employs periodic pumping and purging cycles where roughing pumps operate intermittently with purging phases. This periodic operation allows the insulation space to be evacuated, purged with inert gas, and re-evacuated in cycles, progressively removing contaminants and achieving the target vacuum level of 1×10−6 torr through repeated iterations.
Solution Approach 2:
Cryogenic pumps utilize phase transition of residual gases from vapor to liquid state at extremely low temperatures. This phase change mechanism enables the cryogenic pump to efficiently capture and condense remaining gas molecules, achieving the final high vacuum level of 1×10−6 torr that other pump types cannot reach alone.
3Loss of substance
If the vacuum level is increased to 1×10−6 torr, then LNG evaporation is reduced, but the device complexity increases
Solution Approach 1:
The insulation space is segmented into a vacuum environment separated from the LNG storage compartment. By achieving and maintaining a high vacuum level of 1×10−6 torr in the insulation space, heat transfer to the LNG is minimized, reducing evaporation losses while the segmented structure allows independent vacuum management.
Solution Approach 2:
The vacuum manifold serves as an intermediary system that maintains the high vacuum environment in the insulation space, acting as a barrier between the external atmosphere and the cryogenic LNG storage. This intermediary vacuum system reduces thermal conduction and convection, thereby minimizing LNG evaporation without requiring direct contact between pumps and LNG.
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 effectively maintains a high vacuum level of 1×10−6 torr within the insulation space of LNG tanks, reducing LNG evaporation and extending the time between maintenance cycles, thereby improving storage and transport efficiency and reducing maintenance costs.
Implementation Method 1
evacuating air from a space between double walls of the container
Implementation Method 2
purging the space by supplying a gas into the space
Implementation Method 3
condensing the air within the space for a third predetermined time period
Implementation Method 4
control the cryogenic pump to condense air in the insulation space and remove water vapor from the air
Data Source
AI summary
A method for generating an insulating vacuum in a container is provided. The method includes evacuating air from a space between double walls of the container for a first predetermined time period. The method also includes after the first predetermined time period, if a vacuum level within the space has not reached a first predetermined vacuum level, purging the space by supplying a gas into the space and subsequently evacuating the air from the space for a period of time equal to the first predetermined time period. The method also includes repeating the evacuating and purging until the vacuum level within the space reaches the first predetermined vacuum level. The method also includes when the vacuum level within the space reaches the first predetermined vacuum level, evacuating the air from the space for a second predetermined time period.