Method and system for at least partially converting methane-containing gas, in particular boil-off gas, retained in a container, to a liquid state
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Solution Overview
Problem
Existing methods for converting boil-off gas to a liquid state in containers, such as LNG, face inefficiencies in energy use and composition changes over time, particularly when using liquid nitrogen for subcooling, and require phase separators for batch processes.
Innovation Solution
A method involving compressing, cooling, and then decompressing methane-containing gas to produce liquid and flash-off gas, with the flash-off gas reintroduced at the bottom of the container to dissolve into the liquid, and utilizing heat exchangers to enhance cooling without mixing, allowing for a continuous process without phase separators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If liquid nitrogen is used for subcooling to reduce evaporation, then the boil-off gas is reduced, but energy efficiency deteriorates
Solution Approach 1:
The system uses the boil-off gas itself as the cooling medium to re-liquefy more boil-off gas, creating a self-service cycle. The gas is compressed, cooled using heat exchangers that utilize the cold boil-off gas, expanded through a Joule-Thomson valve to achieve further cooling and liquefaction, and the resulting cold liquid is returned to the container to cool the remaining LNG and reduce further evaporation.
Solution Approach 2:
The system changes the parameters of the boil-off gas by compressing it to high pressure, cooling it through heat exchange, and then expanding it through a Joule-Thomson valve. This series of parameter changes transforms the warm boil-off gas into a cold liquid that can effectively reduce evaporation when returned to the container.
2Stability of the object's composition
If phase separator is used to separate flash-off gas from liquid, then separation is achieved, but device complexity increases
Solution Approach 1:
The system extracts only the necessary components (compressor, heat exchangers, Joule-Thomson valve) for the re-liquefaction process while eliminating the phase separator. The flash-off gas is directly reintroduced into the container without mechanical separation, as the system relies on the gas dissolving into the cold liquid phase in situ.
Solution Approach 2:
The cold methane-containing liquid acts as an intermediary medium that absorbs the flash-off gas through dissolution. Instead of using a phase separator to mechanically divide gas and liquid, the cold liquid serves as a mediator that naturally absorbs the flash-off gas components, achieving separation through phase interaction rather than mechanical means.
3Stability of the object's composition
If flash-off gas is reintroduced at bottom of container, then dissolution into liquid is enhanced, but residence time increases
Solution Approach 1:
The system introduces flash-off gas at the bottom of the container where the liquid is coldest and has the highest capacity to absorb gas. This localized introduction at the optimal position (bottom) maximizes the dissolution efficiency by utilizing the temperature gradient within the container, with the coldest region providing the best absorption conditions.
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 improves energy efficiency, reduces composition changes, and enables a compact, continuous process for converting boil-off gas to liquid, enhancing the conversion of methane-containing gas to a liquid state while maintaining a stable composition.
Implementation Method 1
feeding methane-containing gas from said container to a compressor, and increasing, by said compressor, a pressure of said fed methane-containing gas
Implementation Method 2
feeding said increased pressurized methane-containing gas to a cooling unit for cooling said pressurized methane-containing gas
Implementation Method 3
decreasing said pressure of said pressurized and cooled methane-containing gas, thereby obtaining methane-containing liquid and flash-off gas
Implementation Method 4
said flash-off gas is inputted into said container at or near a bottom part of said container for at least partly dissolving said flash-off gas into said methane-containing liquid
Implementation Method 5
exchanging heat in a heat exchanger via said heat exchanger between said methane-containing gas and said methane-containing liquid and said flash-off gas
Data Source
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AI summary
Method for at least partially converting methane-containing gas, in particular boil-off gas, retained in a container, to a liquid state, the method comprising the subsequent steps of: - feeding methane-containing gas from said container to a compressor, and increasing, by said compressor, a pressure of said fed methane- containing gas; - feeding said increased pressurized methane-containing gas to a cooling unit for cooling said pressurized methane-containing gas; - decreasing said pressure of said pressurized and cooled methane- containing gas, thereby obtaining methane-containing liquid and flash-off gas; - feeding said methane-containing liquid and said flash-off gas to said container, wherein said flash-off gas is inputted into said container at or near a bottom part of said container for at least partly dissolving said flash-off gas into said methane-containing liquid. System for at least partially converting methane- containing gas, in particular boil-off gas,retained in a container, to a liquid state.