LNG Refueling System Using Boil-Off Gas Heating
Solution Overview
Problem
Current systems for refueling ships with liquefied natural gas (LNG) face challenges in efficiently heating LNG to optimal storage pressure and temperature, which limits the rate of refueling and increases technical complexity and safety risks due to the need for multiple connections and potential leaks.
Innovation Solution
A method and system that actively heats LNG by mixing boil-off gas with liquid gas and using a heat exchanger to raise the temperature from below -161°C to around -140°C to -150°C, allowing for overpressure in the ship's tank to facilitate fuel removal without pumps and reducing the number of connections, thereby enhancing safety and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If LNG is heated actively using heat exchangers and boil-off gas mixing, then the refueling speed and storage pressure are improved, but the device complexity and safety risks increase due to additional heating components and connections
Solution Approach 1:
The system uses boil-off gas (natural gas that evaporates from the LNG tank) as the heating medium itself, turning a waste product into a useful resource. This eliminates the need for external fuel sources or complex heating systems, as the LNG tank's own evaporated gas provides the heat needed for refueling operations.
Solution Approach 2:
Instead of venting or wasting the boil-off gas that naturally occurs during LNG storage, the system recovers this gas and utilizes it as a heating medium in the heat exchanger to warm incoming LNG during refueling, thereby improving efficiency while reducing waste.
2Adaptability or versatility
If multiple connections and sockets are provided on the tank for fuel delivery, temperature control, and gas displacement, then the functionality is improved, but the reliability decreases due to increased leak risks and safety hazards
Solution Approach 1:
The system combines multiple functions into integrated components. The heat exchanger serves both as a heating device and as a pathway for boil-off gas utilization. The single-phase and two-phase outlet lines are strategically positioned to enable both fuel delivery and temperature control through selective usage, reducing the need for separate dedicated lines for each function.
Solution Approach 2:
The outlet lines are designed to serve multiple purposes: they can deliver liquid fuel, control tank temperature through regulated gas release, and work in conjunction with the heat exchanger for both heating and cooling operations. This multi-functionality reduces the total number of separate connections required on the tank.
3Quantity of substance
If LNG is stored at cryogenic temperatures below -161°C, then the energy density is improved, but the ease of operation worsens due to the need for complex heating systems to reach optimal storage pressure
Solution Approach 1:
The system leverages the natural boil-off phenomenon of stored LNG to provide the heating required for refueling operations. The evaporated gas, which would otherwise be wasted, is captured and used as the heating medium in the heat exchanger, eliminating the need for external heating systems or additional energy inputs.
Solution Approach 2:
The system exploits the phase transition of LNG from liquid to gas (boil-off) as a natural heat source. By capturing the evaporated gas and using it in the heat exchanger, the system converts the phase change process into a useful heating mechanism that simplifies operations while maintaining high energy density storage.
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
Enables quick and safe refueling by creating sufficient storage pressure for immediate fuel supply, reducing the risk of leaks, and minimizing the need for complex pump systems, allowing ships to continue operation immediately after refueling.
Implementation Method 1
The removed liquefied gas is heated by a heat exchanger
Implementation Method 2
actively heats LNG by mixing boil-off gas with liquid gas
Data Source
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AI summary
The invention relates to a method for storing cryogenic liquid gas in a tank (1) of a transport means, in particular of a ship, having the following steps: removal of liquid gas from a storage tank, heating of the removed liquid gas, filling of the tank (1) of the transport means with the heated liquid gas by pumping the liquid gas into the tank (1) of the transport means. Moreover, the invention relates to a system, by way of which this method can be carried out, and to a ship having a system of this type.