Fuel gas supply system
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Solution Overview
Problem
The existing methods for managing boil-off gas in liquefied natural gas storage tanks on ships are inefficient in terms of re-liquefaction efficiency and heating value regulation, leading to energy inefficiencies and potential equipment damage due to the high nitrogen content in the boil-off gas.
Innovation Solution
A fuel gas supply system that includes a compression unit, a re-liquefaction line with a cooling unit and expansion valves, and a heating value regulator with flow rate regulation valves to optimize the re-liquefaction and utilization of boil-off gas, separating gas and liquid components, and regulating the heating value for efficient fuel gas supply to engines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If boil-off gas with high nitrogen content is supplied to the engine as fuel gas, then the energy efficiency is improved by utilizing the boil-off gas, but the heating value of the fuel gas deteriorates due to the low heating value of nitrogen
Solution Approach 1:
The boil-off gas is segmented into two separate supply lines: a first fuel gas supply line that supplies boil-off gas to a first engine, and a second fuel gas supply line that supplies boil-off gas to a second engine. This segmentation allows different portions of the boil-off gas to be utilized by different engines, optimizing the overall system efficiency while managing the nitrogen content issue.
Solution Approach 2:
The invention changes the parameters of the boil-off gas by pressurizing it through a compression unit before supply. The compression unit increases the pressure of the boil-off gas, which changes its physical parameters and makes it suitable for engine injection. This parameter change allows the boil-off gas to be effectively utilized as fuel while maintaining proper combustion characteristics.
2Productivity
If a compression unit is added to pressurize boil-off gas for engine supply, then the fuel gas supply capability is improved, but the device complexity increases
Solution Approach 1:
The compression unit is designed to serve multiple functions: it pressurizes the boil-off gas for engine supply, and also provides pressurized gas to the re-liquefaction apparatus. This multi-functionality reduces the need for separate compression systems, thereby limiting the increase in device complexity while maintaining improved fuel gas supply capability.
Solution Approach 2:
The system utilizes the compression unit to not only supply fuel gas to engines but also to provide pressurized boil-off gas to the re-liquefaction apparatus, which then re-liquefies a portion of the gas and returns it to the storage tank. This self-service approach allows the compressed gas to serve multiple purposes within the system, improving productivity without proportionally increasing complexity.
3Productivity
If re-liquefaction apparatus is added to re-liquefy boil-off gas, then the utilization of boil-off gas is improved, but the device complexity and energy consumption increase
Solution Approach 1:
The re-liquefaction apparatus acts as an intermediary between the boil-off gas and the storage tank. It receives pressurized boil-off gas, re-liquefies a portion of it, and returns the re-liquefied gas to the storage tank. This intermediary function improves boil-off gas utilization by converting it back to liquid form for storage, while the system is designed to minimize the complexity increase through integrated control and existing infrastructure utilization.
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
Improves re-liquefaction efficiency, effectively manages boil-off gas, and maintains a stable heating value of fuel gas, enhancing energy efficiency and equipment operation with a simple structure.
Implementation Method 1
a compression unit pressurizing boil-off gas of the storage tank
Implementation Method 2
a cooling unit for cooling the pressurized boil-off gas
Implementation Method 3
a first expansion valve for primarily depressurizing the pressurized boil-off gas
Implementation Method 4
a first gas-liquid separator for separating boil-off gas which has passed through the first expansion valve and is in a gas-liquid mixed state into gas components and liquid components
Implementation Method 5
liquefied natural gas which is a colorless transparent cryogenic liquid with its volume reduced to 1/600 by cooling the natural gas at about -162 °C
Implementation Method 6
a heating value regulator for measuring and regulating a heating value of fuel gas supplied to the second engine
Data Source
Figure 1
Figure 2
AI summary
Disclosed is a fuel gas supply system. The fuel gas supply system includes a storage tank for receiving liquefied gas and boil-off gas, a first fuel gas supply line provided with a compression unit pressurizing boil-off gas of the storage tank and supplying boil-off gas pressurized through the compression unit to an first engine, a second fuel gas supply line branched from an intermediate portion of the compression unit and supplying boil-off gas partially pressurized by the compression unit to a second engine, a re-liquefaction line for receiving and re-liquefying a part of the pressurized boil-off gas, and a heating value regulator for measuring and regulating a heating value of fuel gas supplied to the second engine, wherein the re-liquefaction line comprises a cooling unit for cooling the pressurized boil-off gas, a first expansion valve for primarily depressurizing the pressurized boil-off gas that has passed through the cooling unit, a first gas-liquid separator for separating boil-off gas which has passed through the first expansion valve and is in a gas-liquid mixed state into gas components and liquid components, a boil-off gas circulation line for supplying the gas components separated in the first gas-liquid separator to the second engine, and a liquefied gas circulation line for receiving the liquid components separated in the first gas-liquid separator.