LNG Carrier Gas Return Line Spouting
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Solution Overview
Problem
LNG carriers face increased compressor power requirements when utilizing boil-off gas as fuel, especially when operating at low engine loads or when the tank is fully loaded, leading to potential pressure issues in the cargo tank.
Innovation Solution
A liquefied gas carrier design featuring a gas supply line, a compressor, a gas return line with an excess gas spouting portion positioned in the central region of the tank, allowing excess gas to be returned to the tank while minimizing compressor power and preventing pressure increases, by spouting excess gas into a liquid layer when full and into a gaseous layer when unloaded.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the boil off gas is compressed and supplied to the lower part of the cargo tank when the tank is fully loaded, then the excess gas can be returned to the tank, but the compressor power must be increased to exceed the high pressure head at full loading
Solution Approach 1:
The gas return line is positioned to discharge excess gas at a specific location (upper or middle portion) of the cargo tank rather than uniformly throughout. This localized discharge approach allows the compressor to overcome only the pressure head to that specific elevation, significantly reducing the required compressor power compared to forcing gas to the bottom of a fully loaded tank.
Solution Approach 2:
Instead of the conventional approach of supplying compressed gas to the lower part of the tank, this invention inverts the approach by discharging excess gas to the upper or middle portions of the tank. This reversal of the gas supply direction exploits the natural pressure distribution in the tank, allowing gas to be returned with minimal compression while still achieving effective pressure control.
2Reliability
If the excess gas is returned to the tank by increasing compressor power, then the tank pressure can be controlled, but the energy consumption increases
Solution Approach 1:
The invention changes the spatial parameter of gas discharge location from the lower part to the upper or middle portion of the cargo tank. This parameter change fundamentally alters the pressure head that the compressor must overcome, reducing the energy consumption while maintaining effective tank pressure control through the gas return mechanism.
3Reliability
If the gas return line discharges to the lower part of the tank, then the excess gas can be effectively returned, but the compressor must overcome the high pressure head especially when fully loaded
Solution Approach 1:
The gas return line is positioned to discharge excess gas at a specific location (upper or middle portion) of the cargo tank rather than uniformly throughout. This localized discharge approach allows the compressor to overcome only the pressure head to that specific elevation, significantly reducing the required compressor power compared to forcing gas to the bottom of a fully loaded tank.
Solution Approach 2:
Instead of the conventional approach of supplying compressed gas to the lower part of the tank, this invention inverts the approach by discharging excess gas to the upper or middle portions of the tank. This reversal of the gas supply direction exploits the natural pressure distribution in the tank, allowing gas to be returned with minimal compression while still achieving effective pressure control.
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 design effectively returns excess gas to the tank with reduced compressor power, avoiding rapid pressure increases in both full and unloaded states, thereby optimizing energy usage and tank pressure management.
Implementation Method 1
The gas return line includes an excess gas spouting portion provided with an excess gas spouting outlet positioned in a central region of the tank in a height direction, the excess gas spouting portion being configured to spout the excess gas from the excess gas spouting outlet into the central region of the tank
Implementation Method 2
a boil off gas is supplied as a fuel, the boil off gas being generated when the liquefied gas vaporizes in the tank
Implementation Method 3
a gas compressor disposed on the gas supply line and configured to pressure-feed the boil off gas to the gas fueled engine
Implementation Method 4
a boil off gas is generated due to heat that is transferred into the cargo tank from the outside
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
A liquefied gas carrier includes: a tank storing a liquefied gas; a gas fueled engine, to which a boil off gas is supplied as a fuel, the boil off gas being generated when the liquefied gas vaporizes in the tank; a gas supply line, through which the boil off gas is supplied from the tank to the gas fueled engine; a gas compressor disposed on the gas supply line and configured to pressure-feed the boil off gas to the gas fueled engine; a gas return line, through which an excess gas that has not been supplied through the gas supply line to the gas fueled engine is returned to the tank; and a gas return valve configured to open and close the gas return line. The gas return line includes an excess gas spouting portion positioned in a central region of the tank in a height direction and configured to spout the excess gas to the tank.