LNG Transfer Line Residual Gas Return System
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Solution Overview
Problem
In the supply of liquefied natural gas (LNG) from a source tank to a consumer tank, especially on ocean-going tankers and barges, there is a challenge in efficiently purging the transfer line to prevent LNG vaporization and manage boil-off gas, which requires rapid and safe handling to avoid delays and regulatory issues.
Innovation Solution
A method and system where residual LNG in the transfer line is drained into a liquefied gas holding tank, and pressurized inert or boil-off gas is used to return the LNG back to the source tank, eliminating the need for pumps and simplifying the process with valve control and a holding tank to manage the residual gas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If residual LNG is allowed to vaporize in the transfer line, then the LNG can be contained in the source tank, but the source tank cannot contain the volume of boil-off gas resulting from vaporization
Solution Approach 1:
The system divides the transfer line into segments by introducing an intermediate holding tank. The transfer line is segmented into: source tank to holding tank, holding tank to consumer tank, and holding tank to source tank (for return). This segmentation allows the hold tank to serve as a temporary repository for vaporized LNG, preventing overflow in the source tank while maintaining system reliability.
2Productivity
If a pump is used to return residual LNG to the source tank, then the LNG can be efficiently returned, but pump-related issues and complexity arise
Solution Approach 1:
The patent replaces the mechanical pump system with a pneumatic system. Instead of using a pump to force LNG back to the source tank, compressed gas (inert gas or boil-off gas) is introduced into the holding tank to create pressure that pushes the LNG back through the return line to the source tank. This substitution eliminates mechanical moving parts, reduces complexity, and improves reliability.
3Ease of operation
If the transfer line is not completely drained before disconnection, then the disconnection process is simpler, but LNG vaporization causes delays and regulatory issues
Solution Approach 1:
The system performs preliminary draining action by automatically draining residual LNG from the transfer line into the holding tank before disconnection is attempted. The drain line is positioned to utilize gravity and pressure differential to drain the line completely. This preliminary action ensures the line is empty before disconnection, eliminating the need for time-consuming purging operations and ensuring regulatory compliance.
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 the need for additional boil-off gas handling, avoids pump-related issues, and ensures complete drainage before vaporization, enhancing operational efficiency and compliance with regulations by using simple valves and compressed gas to return LNG to the source tank.
Implementation Method 1
a pressurized gas is then fed into the liquefied gas holding tank in order to return at least a part of the residual liquefied gas in the holding tank via a return line back into the source tank
Implementation Method 2
residual liquefied gas remaining in at least a part of the transfer line is drained into a liquefied gas holding tank
Data Source
AI summary
The present invention relates to a method and a system for supplying liquefied gas source tank (110) to a liquefied gas consumer tank (200) and/or liquefied gas consumer, wherein the liquefied gas is supplied via a transfer line (130, 140, 210) to the liquefied gas consumer tank (200) and/or the liquefied gas consumer, and wherein after having supplied liquefied gas to the liquefied gas consumer tank (200) and/or liquefied gas consumer, residual liquefied gas remaining in at least a part of the transfer line (130, 140, 210) is drained into a liquefied gas holding tank (120) and a pressurized gas is then fed into the liquefied gas holding tank (120) in order to return at least a part of the residual liquefied gas in the holding tank via a return line (160) back into the liquefied gas source tank (110).