LNG (Liquefied Natural Gas) container ship gas supply system with BOG (Boil Off Gas) recondensation function

Abstract

The utility model relates to the field of ship construction, and provides an LNG container ship gas supply system with a BOG recondensation function. Comprising an LNG storage tank, the LNG storage tank is connected with a plurality of injection pipelines, an LNG pump is installed in the LNG storage tank, and the LNG pump is connected with a high-pressure fuel gas unit, a low-pressure fuel gas unit and a boil-off gas recondensation unit through control of pipelines and valves; the boil-off gas in the gas chamber and the boil-off gas injected into the pipeline enter the boil-off gas heat exchanger, the boil-off gas recondensation unit and the low-pressure buffer tank respectively under the control of the pipeline and the valve; the boil-off gas in the filling system and the LNG storage tank is compressed, low-temperature LNG is used as a heat exchange medium to be cooled and liquefied, and the liquefied boil-off gas is fed into the high-pressure fuel gas unit to be utilized or flows back to the LNG storage tank through control of a pipeline and a valve, so that emission waste and environmental pollution can be avoided; and the boil-off gas can also play a role in preheating the low-temperature LNG in the liquefaction process, so that the energy consumption is reduced.

Description

Technical Field

[0001] This utility model relates to the field of shipbuilding, specifically to an LNG container ship gas supply system with BOG recondensation. Background Technology

[0002] With the increasing global demand for clean energy dual-fuel vessels, LNG dual-fuel vessels are gradually becoming the mainstream ship type. Most dual-fuel vessels use LNG or methanol as fuel. LNG fuel tanks contain liquefied natural gas at -163°C. During operation, an LNG supply system is needed to vaporize the liquefied natural gas into gas at a specific temperature and pressure, which is then fed into the main engine and other gas-consuming equipment for combustion. Because liquefied LNG is highly volatile, a significant amount of boil-off gas (BOG) is inevitably generated during refueling and ship operation, resulting in a substantial difference between the actual BOG and theoretical calculations. Since LNG fuel tanks often use Type B or membrane-type non-pressurized tanks with lower design pressures, the actual BOG in the tank differs significantly from theoretical calculations. To ensure tank safety, excess BOG must be discharged, leading to energy waste and environmental impacts from methane escape. Summary of the Invention

[0003] To avoid the waste of BOG emissions from LNG ships and the environmental pollution caused by the emissions, this utility model provides an LNG container ship gas supply system with BOG recondensation.

[0004] The technical solution adopted by this utility model is as follows:

[0005] An LNG container ship gas supply system with BOG recondensation includes an LNG storage tank connected to multiple injection pipes. An LNG pump is installed inside the tank, and the pump outputs liquid LNG fuel through filters and pipes. A gas chamber is located at the top of the LNG storage tank, collecting the evaporated gas from the LNG. The LNG pump is connected to a high-pressure gas unit, a low-pressure gas unit, and an evaporated gas recondensation unit via pipes and valves. The high-pressure gas unit includes a high-pressure pump, a high-pressure heat exchanger, and a high-pressure valve group connected sequentially by pipes. The high-pressure valve group supplies gas for combustion to multiple main engines. The low-pressure gas unit includes a low-pressure heat exchanger and a low-pressure buffer tank, which supplies gas to the ship's low-pressure gas-using equipment. The high-pressure and low-pressure heat exchangers are each connected to a high-temperature liquid cooling source. The evaporated gas in the gas chamber and the evaporated gas in the injection pipes are controlled by pipes and valves to enter the evaporated gas recondensation unit. The system includes a heat exchanger, an evaporative gas re-condensation unit, and a low-pressure buffer tank. The evaporative gas heat exchanger is connected to a cryogenic liquid cooling source, and the gas after heat exchange is directly output to the ship's low-pressure gas-using equipment. The evaporative gas re-condensation unit includes a compressor and multiple evaporative gas condensers. The evaporative gas enters the compressor for compression and passes through multiple condensers in sequence. Liquid LNG is input into the multiple condensers by an LNG pump. The liquid LNG after heat exchange in the condensers and the liquid LNG after liquefaction of the evaporative gas are controlled by pipelines and valves to enter the high-pressure gas unit or the low-pressure gas unit.

[0006] Furthermore, the high-temperature liquid cooling source and the low-temperature liquid cooling source are ethylene glycol liquid cooling sources.

[0007] Furthermore, the evaporative gas re-condensation unit includes two parallel compressor stages.

[0008] Furthermore, the evaporation gas recondensation unit includes two condensers connected in series. The liquid LNG after heat exchange in the first-stage condenser enters the high-pressure heat exchanger through a pipeline. The liquid LNG after heat exchange in the second-stage condenser, as well as the liquefied evaporation gas, enter the high-pressure pump of the high-pressure gas unit or the low-pressure heat exchanger of the low-pressure gas unit through pipelines and valves.

[0009] Furthermore, a return pipeline is provided between the high-pressure gas unit and the LNG storage tank, and a control valve is installed on the return pipeline. The return pipeline is connected to the distribution pipe inside the LNG storage tank.

[0010] Furthermore, a gas-liquid separator is installed at the output end of the compressor.

[0011] After adopting the above technical solution, the beneficial effects of this utility model are as follows: by compressing the evaporated gas in the refueling system and LNG storage tank and then cooling it with low-temperature LNG as a heat exchange medium, the liquefied evaporated gas is sent to the high-pressure gas unit for use or returned to the LNG storage tank through pipelines and valves, which can avoid waste and environmental pollution from emissions; the evaporated gas can also preheat the low-temperature LNG during the liquefaction process, reducing energy consumption. Attached Figure Description

[0012] Figure 1 This is a system schematic diagram of the present invention.

[0013] In the diagram: LNG storage tank 1, injection pipeline 2, LNG pump 3, filter 4, high-pressure pump 5, high-pressure heat exchanger 6, high-pressure valve group 7, main unit 8, low-pressure heat exchanger 9, low-pressure buffer tank 10, low-pressure gas-using equipment 11, high-temperature liquid cooling source 12, gas chamber 13, evaporative gas heat exchanger 14, low-temperature liquid cooling source 15, compressor 16, first-stage condenser 17, second-stage condenser 18, return pipeline 19. Detailed Implementation

[0014] The specific embodiments of this utility model will be further described in detail below with reference to the accompanying drawings:

[0015] like Figure 1 As shown, an LNG container ship gas supply system with BOG recondensation includes an LNG storage tank 1 for storing liquid LNG at -163°C. The LNG storage tank 1 is connected to multiple injection pipes 2, which originate from chord-side injection pipes on both sides of the ship and refueling pipes from the refueling station. Multiple LNG pumps 3 are installed inside the LNG storage tank 1, and the LNG pumps 3 output the liquid LNG fuel from the tank.

[0016] The output liquid LNG, after being filtered by filter 4, is sent to the high-pressure gas unit, low-pressure gas unit, and evaporative gas re-condensation unit via pipelines and valves. The high-pressure gas unit includes a high-pressure pump 5, a high-pressure heat exchanger 6, and a high-pressure valve group 7 connected sequentially by pipelines. After being pressurized by the high-pressure pump 5, the liquid LNG enters the high-pressure heat exchanger 6 for heat exchange. The vaporized LNG gas after heat exchange is then supplied with high-pressure natural gas to the ship's main engine 8 via the control of the high-pressure valve group 7. The low-pressure gas unit includes a low-pressure heat exchanger 9 and a low-pressure buffer tank 10. The liquid LNG output from LNG pump 3 enters the low-pressure heat exchanger 9 for heat exchange. The vaporized LNG gas after heat exchange is buffered by the low-pressure buffer tank 10 and then supplied to the ship's various low-pressure gas-using equipment 11. The heat exchange medium for both the high-pressure heat exchanger 6 and the low-pressure heat exchanger 9 comes from a high-temperature liquid cooling source 12. The high-temperature liquid cooling source uses ethylene glycol as the medium. By heating the ethylene glycol, the high-temperature ethylene glycol exchanges heat with the low-temperature LNG and vaporizes it.

[0017] A gas chamber 13 is located at the top of the LNG storage tank. This chamber collects the evaporated gas from the LNG. The evaporated gas in the chamber 13, along with the evaporated gas in the injection pipe 2, is controlled by pipes and valves to enter either the evaporated gas heat exchanger 14, the evaporated gas re-condensation unit, or the low-pressure buffer tank 10, thus achieving secondary utilization. The evaporated gas heat exchanger 14 is connected to a cryogenic liquid coolant source 15, which also uses ethylene glycol as the heat exchange medium. The ethylene glycol is heated to a certain temperature and then exchanges heat with the evaporated gas. The resulting evaporated gas, with its increased temperature, is directly sent to some low-pressure gas-using equipment, such as for boiler combustion; or it is directly sent to the low-pressure buffer tank 10 for storage and later use. When the low-pressure gas-using equipment does not require gas, the evaporated gas is sent to the evaporated gas re-condensation unit.

[0018] The evaporative gas re-condensation unit comprises two parallel compressors 16 and two series-connected evaporative gas condensers. The evaporative gas is compressed within the two compressors 16, reaching approximately 45°C. After separation by a gas-liquid separator, the gas enters the first-stage condenser 17. Low-temperature LNG from an LNG storage tank is introduced into the first-stage condenser 17 as a heat exchange medium. After heat exchange, the temperature of the evaporative gas decreases to approximately -106°C, and then it enters the second-stage condenser 18. The liquid LNG after heat exchange in the first-stage condenser 17 is piped to the high-pressure heat exchanger 6; or to the low-pressure heat exchanger 9 of the low-pressure gas unit. The second-stage condenser 18 also uses cryogenic LNG liquid from the LNG storage tank as a heat exchange medium. The evaporated gas after heat exchange can be reduced to approximately -154°C, achieving condensation and liquefaction. The liquid LNG and liquefied evaporated gas after heat exchange in the second-stage condenser 18 are controlled by pipelines and valves to enter the input end of the high-pressure pump 5 of the high-pressure gas unit. After vaporization, they are sent to the main unit for use, or they can be returned to the LNG storage tank through the return pipeline 19 between the high-pressure gas unit and the LNG storage tank and the control valve on the return pipeline. The return pipeline is connected to the distribution pipe in the LNG storage tank, and the gas is evenly distributed into the LNG storage tank 1 through the distribution pipe.

Claims

1. An LNG container ship gas supply system with BOG recondensation, comprising an LNG storage tank, the LNG storage tank being connected to multiple injection pipes, an LNG pump installed inside the LNG storage tank, the LNG pump outputting liquid LNG fuel through a filter and pipes, and a gas chamber at the top of the LNG storage tank for collecting LNG vapors, characterized in that... The LNG pump is connected to the high-pressure gas unit, the low-pressure gas unit, and the evaporative gas re-condensation unit via pipelines and valves. The high-pressure gas unit includes a high-pressure pump, a high-pressure heat exchanger, and a high-pressure valve group connected in sequence by pipelines. The high-pressure valve group supplies gas for combustion to multiple main engines. The low-pressure gas unit includes a low-pressure heat exchanger and a low-pressure buffer tank. The low-pressure buffer tank supplies gas to the ship's low-pressure gas-using equipment. The high-pressure and low-pressure heat exchangers are each connected to a high-temperature liquid cooling source. The evaporative gas in the gas chamber and the evaporative gas injected into the pipeline are controlled by pipelines and valves to enter the evaporative gas exchanger. The system includes a heat exchanger, an evaporative gas re-condensation unit, and a low-pressure buffer tank. The evaporative gas heat exchanger is connected to a cryogenic liquid cooling source, and the gas after heat exchange is directly output to the ship's low-pressure gas-using equipment. The evaporative gas re-condensation unit includes a compressor and multiple evaporative gas condensers. The evaporative gas enters the compressor for compression and passes through multiple condensers in sequence. Liquid LNG is input into the multiple condensers by an LNG pump. The liquid LNG after heat exchange in the condensers and the liquid LNG after liquefaction of the evaporative gas are controlled by pipelines and valves to enter the high-pressure gas unit or the low-pressure gas unit.

2. The LNG container ship gas supply system with BOG recondensation according to claim 1, characterized in that, The high-temperature liquid cooling source and the low-temperature liquid cooling source are ethylene glycol liquid cooling sources.

3. The LNG container ship gas supply system with BOG recondensation according to claim 1, characterized in that, The evaporative gas recondensation unit includes two parallel compressor stages.

4. The LNG container ship gas supply system with BOG recondensation according to claim 1, characterized in that, The evaporation gas recondensation unit includes two condensers connected in series. The liquid LNG after heat exchange in the first-stage condenser enters the high-pressure heat exchanger through a pipeline. The liquid LNG after heat exchange in the second-stage condenser, as well as the liquefied evaporation gas, enter the high-pressure pump of the high-pressure gas unit or the low-pressure heat exchanger of the low-pressure gas unit through pipelines and valves.

5. An LNG container ship gas supply system with BOG recondensation according to claim 1, characterized in that, A return pipeline is provided between the high-pressure gas unit and the LNG storage tank. A control valve is installed on the return pipeline, and the return pipeline is connected to the distribution pipe inside the LNG storage tank.

6. The LNG container ship gas supply system with BOG recondensation according to claim 1, characterized in that, A gas-liquid separator is installed at the output end of the compressor.

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