Method and system for the re-liquefaction of boil-off gas
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Solution Overview
Problem
The existing methods for re-liquefying boil-off gas in LNG infrastructure are energy-intensive and costly, especially during unfavourable market conditions when cold energy from re-gasification is not available, limiting the flexibility and efficiency of LNG import terminals and leading to significant losses and degradation of LNG stock.
Innovation Solution
A method that involves storing and controlling the flow rate of a cryogenic fluid to recover and recycle cold energy from re-gasification, allowing its use for re-liquefying boil-off gas independently of the re-gasification process, thereby reducing the energy required for re-liquefaction and enhancing the flexibility of LNG export management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional re-liquefaction methods are used for boil-off gas, then the boil-off gas can be converted back to liquid form, but the energy consumption is very high and the process is costly
Solution Approach 1:
The invention converts the harmful heat ingress that causes boil-off into a beneficial resource by capturing the cold energy from LNG regasification and using it to re-liquefy the boil-off gas. The heat that would otherwise be wasted is now utilized to drive the re-liquefaction process, transforming an energy loss into an energy recovery opportunity.
Solution Approach 2:
The invention recovers the cold energy that would be discarded during LNG regasification operations. By capturing and storing this cold energy in a cryogenic storage medium, the system prevents energy waste and makes it available for subsequent re-liquefaction operations, thereby reducing overall energy consumption.
2Loss of energy
If cold energy from re-gasification is used directly for re-liquefaction, then energy efficiency improves, but the process is limited to times when re-gasification is occurring
Solution Approach 1:
The invention performs preliminary action by capturing and storing cold energy from regasification operations in advance, during periods when cold energy is abundant. This stored cold energy is then available for later use during periods when regasification is not occurring, ensuring continuous operational flexibility and energy efficiency.
Solution Approach 2:
The invention introduces a cryogenic storage medium as an intermediary between the regasification process and the re-liquefaction process. This intermediary stores the cold energy temporarily, decoupling the two processes in time and allowing re-liquefaction to occur independently of current regasification status, thereby enhancing operational versatility.
3Ease of manufacture
If boil-off gas is vented or flared instead of re-liquefied, then energy costs are reduced, but significant losses of LNG stock occur
Solution Approach 1:
The invention enables the system to serve itself by using the cold energy generated from its own regasification operations to re-liquefy its own boil-off gas. This self-service approach eliminates the need for external energy inputs or complex external systems, while simultaneously preventing LNG stock losses through continuous re-liquefaction capability.
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 significantly reduces the energy needed for re-liquefying boil-off gas, potentially by half, making it cost-effective and allowing for better management of hydrocarbon gas exports and storage longevity, while maintaining continuous cooling without losing hydrocarbon gas.
Implementation Method 1
The method involves mixing a stream of hydrocarbon gas with a stream of cryogenic fluid from a fluid store, and condensing the boil-off gas to form a liquid
Implementation Method 2
LNG is pumped to high pressure, warmed and vaporised before being exported on the gas network
Implementation Method 3
cold energy from re-gasification (i.e. changed from its liquid state following liquefaction back into its gaseous state)
Data Source
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AI summary
A method for liquefying boil-off gas comprises storing a liquefied hydrocarbon gas in a store; processing streams of gaseous cryogenic fluid and liquefied hydrocarbon gas by transferring heat, such that the liquefied hydrocarbon gas becomes gaseous and the gaseous cryogenic fluid becomes liquefied;storing the liquefied cryogenic fluid in a store;processing streams of gaseous boil-off gas and liquefied cryogenic fluid by transferring heat, such that the liquefied cryogenic fluid becomes gaseous and the gaseous boil-off gas becomes liquefied; and storing the liquefied boil-off gas in the store. The method further comprises controlling the flow rate of the gaseous cryogenic fluid based in part on the flow rate of the liquefied hydrocarbon gas and independently controlling the flow rate of the liquefied cryogenic fluid based in part on the flow rate of the gaseous boil-off gas. A corresponding system is provided.