Test system for BOG reliquefaction device for LNG (Liquefied Natural Gas) ship

Abstract

The utility model discloses a test system for a BOG reliquefaction device for an LNG ship, which is provided with a gas supply main path, a gas supply branch path and a liquid return main path, the gas supply main path provides a stable gas source meeting conditions for the reliquefaction device, the reliquefaction device liquefies BOG to form liquid-phase LNG and gas-phase flash steam under the action of a refrigeration unit, the liquid phase and the gas phase are separated by a gas-liquid separator, and the liquid-phase LNG and the gas-phase flash steam are returned to the liquid return main path. Liquid-phase LNG flows into an LNG storage tank through a liquid return main path, gas-phase flash steam enters a gas supply branch path and is fully mixed with storage tank evaporation gas in a storage tank evaporation gas branch path in a branch path mixer, then a branch path air temperature type vaporizer is used for heating and vaporizing mixed gas, and the mixed gas enters the gas supply main path to be mixed with a main path gas source after being pressurized by a BOG compressor; and flowing into the reliquefaction device again. The test system adopts closed circulation, can effectively measure various performance indexes of the reliquefaction device, realizes recycling of a test working medium, improves the economy and safety of the system, realizes zero emission of carbon, and avoids resource waste.

Description

Technical Field

[0001] The utility model relates to the technical field of LNG boil-off gas reliquefaction, and further relates to a test system for an LNG ship-based BOG reliquefaction device. Background Art

[0002] The demand for natural gas is growing rapidly, leading to increased offshore natural gas production in various countries and increasing trade in liquefied natural gas (LNG). Against the backdrop of a "green transformation," LNG transportation demand and capacity deployment continue to maintain a healthy growth trend. Reliquefaction units, as key equipment at the heart of LNG carriers and LNG bunkering vessels, are used to liquefy and recover boil-off gas (BOG) generated during transportation, thereby reducing tank pressure and offering significant economic and environmental benefits. Before a product is put into use, it must undergo performance testing to simulate actual operating conditions and measure the device's performance indicators to ensure they meet performance specifications under actual operating conditions.

[0003] Currently, there are no specific standards for performance testing of reliquefaction units. Tests are generally conducted by manufacturers and shipowners according to a negotiated test outline. The test systems, test methods, and evaluation criteria used are not yet standardized. To meet the performance testing requirements of LNG ship BOG reliquefaction units, manufacturers use nitrogen and natural gas to simulate flash gas generated during ship operation. This gas is then transported to the reliquefaction unit to convert the test medium into liquid form, which is then converted into an equivalent liquefaction rate and equivalent cooling capacity. The resulting liquid test medium is then vaporized and either enters the pipeline network to the combustion device or is discharged into the atmosphere, or is returned to the storage tank via a return line. This generates boil-off gas, which increases the tank pressure and poses a risk to the tank's structural safety. Therefore, this type of test system has relatively low safety, accuracy, economy, and environmental performance. Utility Model Content

[0004] In response to the problems of low safety, economy, environmental protection and test accuracy caused by the discharge of test media in the open reliquefaction device test system in the existing technology, the purpose of the utility model is to provide a test system for LNG ship BOG reliquefaction device. The system is equipped with a gas-liquid separator, a gas supply branch and a tank boil-off gas branch. It adopts a closed circulation to accurately measure the liquefaction rate of the reliquefaction device while realizing the recovery of throttling flash gas and LNG tank boil-off gas, reducing the dependence on the pressure resistance performance of the tank, improving the safety of system operation, and achieving zero "carbon" emission in testing, energy saving and environmental protection.

[0005] In order to achieve the above purpose, the present invention provides the following technical solutions:

[0006] A test system for an LNG ship-mounted BOG reliquefaction unit comprises a gas supply unit, a reliquefaction unit, a gas-liquid separator, and a main liquid return line, which are connected in sequence. The gas supply unit comprises a main gas supply line and a branch gas supply line. The main gas supply line comprises an LNG storage tank, a main line air-temperature vaporizer, a main line mixer, a heater, and a buffer tank, which are connected in sequence through pipelines. The branch gas supply line is connected in sequence along the direction of flash gas flow to the gas outlet of the gas-liquid separator, the branch line air-temperature vaporizer, the BOG compressor, and the inlet of the main line mixer. The inlet of the main liquid return line is connected to the liquid outlet of the gas-liquid separator, and the outlet of the main liquid return line is connected to the liquid inlet of the LNG storage tank. The liquid LNG separated by the gas-liquid separator is injected into the LNG storage tank via a liquid return pump.

[0007] In some embodiments, the test system of the BOG reliquefaction device is further provided with a tank boil-off gas branch and a branch mixer, wherein the inlet of the tank boil-off gas branch is connected to the gas outlet of the LNG storage tank, and the outlet of the tank boil-off gas branch is connected to the gas outlet of the gas-liquid separator, and the branch mixer is arranged on the pipeline between the gas outlet of the gas-liquid separator and the branch air-temperature vaporizer.

[0008] In some embodiments, the test system of the BOG reliquefaction device is further provided with a refrigeration unit, which is connected to the reliquefaction device and is used to provide sufficient cooling capacity for the reliquefaction device to cool the high-temperature working fluid and lubricating oil.

[0009] In some embodiments, a liquid cargo pump is further provided on the main gas supply line. The liquid cargo pump is arranged on the pipeline between the LNG storage tank and the main air-temperature vaporizer to control the flow rate of LNG in the main gas supply line.

[0010] In some embodiments, a flow regulating branch and a flow regulating valve are further provided on the main gas supply line. The inlet of the flow regulating branch is arranged on the pipeline between the liquid cargo pump and the main line air-temperature vaporizer, and the outlet of the flow regulating branch is connected to the liquid inlet of the LNG storage tank. The flow regulating valve is arranged on the flow regulating branch to stabilize the gas source flow entering the reliquefaction device.

[0011] In some embodiments, a pressure reducing valve is further provided on the gas supply branch, and the pressure reducing valve is arranged on the pipeline between the gas outlet of the gas-liquid separator and the inlet of the branch mixer, and is used to reduce the flash gas pressure at the gas outlet of the gas-liquid separator so that it can be mixed with the evaporated gas from the storage tank.

[0012] In some embodiments, a pressure regulating valve is provided on the tank boil-off gas branch line. The pressure regulating valve is disposed on a pipeline between the gas outlet of the LNG tank and the inlet of the branch mixer to regulate the pressure in the LNG tank.

[0013] In some embodiments, the test system of the BOG reliquefaction device is further provided with a throttle valve, which is arranged on the pipeline between the reliquefaction device and the gas-liquid separator and is used to reduce the pressure of the cooled and liquefied LNG to the return tank pressure.

[0014] In some embodiments, the test system of the BOG reliquefaction device further includes a monitoring unit, a monitoring element, and an actuator. The monitoring unit and the monitoring element are electrically connected to the gas supply unit, the reliquefaction device, and the refrigeration unit, respectively. The monitoring unit includes a master control cabinet, a power distribution cabinet, a centralized control console, and supporting data acquisition equipment and instruments. The master control cabinet is used to collect electrical signals from the monitoring element and electrical signals from the reliquefaction device monitoring system, and transmit them to the centralized control console. The master control cabinet and the centralized control console issue debugging instructions based on the collected electrical signals. The actuator receives the instructions and executes debugging actions to control the operation of the test system.

[0015] In some embodiments, the monitoring element includes a temperature sensor, a pressure sensor, a flow meter, and a gas composition analyzer, which are used to monitor the temperature, pressure, flow, and gas composition of the fluid in the test system in real time, and send the monitoring values ​​to the main control cabinet.

[0016] Compared with the prior art, the test system for LNG ship BOG reliquefaction device provided by the present invention has the following beneficial effects:

[0017] 1. The test system for the BOG reliquefaction device provided by the present invention is a closed cycle, consisting of a gas supply unit, a reliquefaction device, and a liquid return pipeline. The gas supply unit includes a main gas supply line and a branch gas supply line. High-pressure gaseous natural gas in the main gas supply line flows into the reliquefaction device, where it is cooled and liquefied to form high-pressure liquid LNG. The gas then flows into the storage tank along the main liquid return line to participate in the next cycle. At the same time, the flash gas generated enters the branch gas supply line, is vaporized and pressurized to a specified pressure, mixes with the main gas, and flows into the reliquefaction device again, forming a closed cycle. This eliminates the economic losses caused by direct emission and combustion of BOG, reduces carbon emissions, improves the safety and economy of the test system, and achieves zero carbon emissions, energy conservation and environmental protection for the test system.

[0018] 2. The BOG reliquefaction unit test system provided by the present invention is equipped with a gas-liquid separator that can separate the flash gas generated by throttling, making it easier to measure the flow rate of liquid LNG, calculate the liquefaction rate and refrigeration capacity, and evaluate the performance of the reliquefaction unit, thereby improving the accuracy of the test system. At the same time, the throttling flash gas is recycled into the circulation to prevent the flash gas from flowing back into the storage tank with the liquid LNG, causing the storage tank to continue to be pressurized.

[0019] 3. The utility model also incorporates a tank boil-off gas branch for recovering boil-off gas from the tank, reducing reliance on the tank's pressure resistance and improving system safety. Boil-off gas from the LNG tank is mixed with BOG flash gas through the tank boil-off gas branch before entering the main gas supply line. This maintains the tank pressure within the set range, reducing reliance on high-pressure tanks and eliminating the risk of LNG being unable to flow into the tank due to excessive tank pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The preferred embodiments will be described below in a clear and understandable manner with reference to the accompanying drawings to further illustrate the above-mentioned characteristics, technical features, advantages and implementation methods of the present invention.

[0021] Figure 1 This is a schematic diagram of the overall structure of the test system for the BOG reliquefaction device for LNG ships of the present invention;

[0022] Figure 2 It is the flow regulation control logic of the gas supply unit.

[0023] Description of Figure Numbers:

[0024] 1—LNG storage tank; 2—pressure regulating valve; 3—liquid cargo pump; 4—flow regulating valve; 5—main line air-temperature vaporizer; 6—main line mixer; 7—heater; 8—buffer tank; 9—reliquefaction device; 10—refrigeration unit; 11—gas-liquid separator; 12—pressure reducing valve; 13—branch line mixer; 14—branch line air-temperature vaporizer; 15—BOG compressor; 16—liquid return pump; 17—master control cabinet; 18—power distribution cabinet; 19—central control console. DETAILED DESCRIPTION

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without inventive work.

[0026] To simplify the drawings, only the parts relevant to the utility model are schematically shown in each figure; they do not represent the actual structure of the product. Furthermore, to simplify the drawings and facilitate understanding, in some figures, only one of the components with the same structure or function is schematically depicted or labeled. In this document, "one" not only means "only one" but also "more than one."

[0027] It should be further understood that the term "and / or" used in this specification and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0028] It should be noted that, unless otherwise specified or limited, the terms "mounted," "connected," and "connected" should be understood broadly. For example, they can refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediary; and internal communication between two components. Those skilled in the art will understand the specific meanings of these terms in this utility model based on the specific circumstances.

[0029] Reference Manual Figure 1 The test system for an LNG ship-based BOG reliquefaction device provided by the present invention includes a gas supply unit, a reliquefaction device 9, a gas-liquid separator 11, and a liquid return main line connected in sequence, wherein the gas supply unit includes a gas supply main line and a gas supply branch line, the gas supply main line includes an LNG storage tank 1, a main line air-temperature vaporizer 5, a main line mixer 6, a heater 7, and a buffer tank 8 connected in sequence through pipelines; the gas supply branch line is connected in sequence to the gas outlet of the gas-liquid separator 11, the branch line air-temperature vaporizer 14, the BOG compressor 15, and the inlet of the main line mixer 6 along the flow direction of flash gas; the inlet of the liquid return main line is connected to the liquid outlet of the gas-liquid separator 11, and the outlet of the liquid return main line is connected to the liquid inlet of the LNG storage tank 1, and the liquid LNG separated by the gas-liquid separator 11 is injected into the LNG storage tank 1 through the liquid return pump 16.

[0030] In this embodiment, a liquid cargo pump 3 is further provided on the main gas supply line. The liquid cargo pump 3 is arranged on the pipeline between the LNG storage tank 1 and the main air-temperature vaporizer 5 to control the flow rate of LNG in the main gas supply line.

[0031] Furthermore, the test system of the BOG reliquefaction device is further provided with a refrigeration unit 10 , which is connected to the reliquefaction device 9 and is used to provide sufficient cooling capacity for the reliquefaction device 9 to cool the high-temperature working fluid and lubricating oil.

[0032] In the above embodiment, since LNG throttling and pressure reduction will generate flash gas (calculated at 5%) which will flow back to the storage tank along with the liquid LNG, causing the storage tank to continue to be pressurized. In order to avoid the LNG backflow caused by excessive tank pressure, the system is also provided with a tank boil-off gas branch and a branch mixer 13. The inlet of the tank boil-off gas branch is connected to the gas outlet of the LNG storage tank 1, and the outlet of the tank boil-off gas branch is connected to the gas outlet of the gas-liquid separator 11. The branch mixer 13 is arranged on the pipeline between the gas outlet of the gas-liquid separator 11 and the branch air-temperature vaporizer 14. The boil-off gas in the storage tank enters the branch mixer 13 along the tank boil-off gas branch and is fully mixed with the flash gas. After being heated and vaporized, it is introduced into the main gas supply line to participate in the circulation.

[0033] Furthermore, a pressure regulating valve 2 is provided on the tank boil-off gas branch. This valve is located in the pipeline between the gas outlet of the LNG tank 1 and the inlet of the branch mixer 13, and is used to regulate the pressure within the LNG tank 1. To ensure the smooth return of liquid LNG to the LNG tank 1, the return liquid pressure must be higher than the pressure within the LNG tank 1. A pressure regulating valve 2 is provided at the tank boil-off gas outlet. When the tank pressure reaches the upper limit of the pressure-limiting pressure, the valve opens, allowing the tank boil-off gas to flow out of the tank and mix with the throttled flash gas from the gas supply branch. When the tank pressure reaches the lower limit of the pressure-limiting pressure, the valve closes, and the fluid in the gas supply branch is now the throttled flash gas.

[0034] Preferably, a pressure reducing valve 12 is also provided on the gas supply branch, and the pressure reducing valve 12 is set on the pipeline between the gas outlet of the gas-liquid separator 11 and the inlet of the branch air-temperature vaporizer 14. Since the pressure of the throttling flash gas flowing out of the gas-liquid separator 11 is approximately the return tank pressure, and the tank evaporation gas pressure at the gas outlet of the LNG storage tank 1 is lower than the return tank pressure, the pressure reducing valve 12 is set to reduce the flash gas pressure to facilitate the mixing of the tank evaporation gas and the flash gas.

[0035] This test system is also provided with a monitoring unit, monitoring elements and an actuator. The monitoring unit and the monitoring elements are electrically connected to the gas supply unit, the reliquefaction device 9 and the refrigeration unit 10 respectively. The monitoring unit includes a main control cabinet 17, a power distribution cabinet 18, a centralized control console 19 and supporting acquisition equipment and instruments. The monitoring elements include temperature sensors, pressure sensors, flow meters and gas component analyzers, which monitor the temperature, flow, pressure and gas composition of the fluid in the system in real time, and send the monitoring values ​​to the main control cabinet 17 in real time, and transmit the electrical signals to the centralized control console 19. The centralized control console 19 issues debugging instructions based on the collected electrical signals. The actuator accepts the instructions and performs debugging actions to realize the operation of the control test system.

[0036] The power distribution cabinet 18 can distribute electrical energy to various power lines to meet the power requirements of the above-mentioned various devices.

[0037] Reference Manual Figure 1 and attached Figure 2The main gas supply line is also provided with a flow regulating branch and a flow regulating valve 4. The inlet of the flow regulating branch is arranged on the pipeline between the liquid cargo pump 3 and the main line air-temperature vaporizer 5. The outlet of the flow regulating branch is connected to the liquid inlet of the LNG storage tank 1. The flow regulating valve 4 is arranged on the flow regulating branch to stabilize the gas source flow entering the reliquefaction device.

[0038] When the flow rate supplied to the reliquefaction unit 9 remains unchanged, the flow rate of the main gas supply line is determined by the flow rate of the branch line: that is, the flow rate of the main gas supply line is the difference between the total flow rate and the branch flow rate. The flow rate of the branch gas supply line is determined by the throttling flash gas flow rate and the tank boil-off gas flow rate. The throttling flash gas flow rate is determined by the liquefaction performance of the test piece, the gas supply parameters, and the throttling pressure. Under certain operating conditions, its fluctuation is small. The flow rate of the tank boil-off gas is determined by the pressure limiting pressure. When the pressure limiting pressure is low, the amount of boil-off gas generated by the pressure reduction of LNG entering the tank is large. When the pressure limiting pressure is high, the amount of boil-off gas generated by the pressure reduction of LNG entering the tank is small. The opening and closing of the pressure regulating valve 2 is determined by the boil-off gas pressure in the LNG storage tank 1. The intermittent opening of the pressure regulating valve 2 will cause pressure fluctuations in the gas supply branch line, which in turn affects the stability of the pressure in the main gas supply line. Therefore, a flow regulating branch line is added to the main gas supply line to stabilize the gas source pressure in the main gas supply line. The specific method is as follows: when the flow of the gas supply branch fluctuates, the collected flow signal is transmitted to the main control cabinet 17 and the centralized control console 19, and the main control cabinet 17 and the centralized control console 19 issue adjustment instructions to the actuator to roughly adjust the flow in the gas supply main line by adjusting the speed of the liquid cargo pump 3. When fine adjustment is required, that is, when the gas source flow entering the reliquefaction device 9 needs to be fine-tuned, the flow regulating valve 4 is opened, and the excess LNG will flow back to the storage tank through the loop, so that the sum of the flow of the gas supply branch and the main line is stabilized within an appropriate range.

[0039] The working principle of this utility model is as follows:

[0040] When the system starts operating, the cargo pump 3 draws LNG from the LNG storage tank 1 and pressurizes it to the set pressure (8 barG to 13 barG). After being vaporized in the main air-temperature vaporizer 5, BOG of equal mass flow is generated. The BOG is then reheated to 0-50°C by the heater 7 and enters the buffer tank 8 for pressure stabilization, providing a stable gas source of 8 barG to 13 barG and 0-50°C for the reliquefaction device 9.

[0041] After the reliquefaction unit 9 pressurizes the natural gas provided by the system to a specified pressure, it is gradually cooled and liquefied, producing liquid natural gas at a temperature of -150°C to -165°C and a pressure of 1.0 barG to 6 barG (adjustable by a throttle valve). This produces some flash gas, which is separated into gas and liquid phases by a gas-liquid separator 11. The liquid LNG is then injected from the bottom of the storage tank via a return line, ready for the next stage of circulation. The flash gas enters the gas supply branch, where it is reduced in pressure by a pressure reducing valve 12 and then merges with the tank boil-off gas in the tank boil-off gas branch in a branch mixer 13. After thorough mixing, the gas is returned to a temperature 10°C below room temperature by a branch air-temperature vaporizer 14. The gas then enters the BOG compressor 15, where it is pressurized to the specified pressure and mixed with the main gas, completing the branch boil-off gas cycle.

[0042] The test system provided by the present invention adopts a closed circulation process of natural gas, which meets the conditions for the performance test of the reliquefaction device. At the same time, it can accurately measure the liquefaction flow rate of the reliquefaction device 9, recycle and utilize high-pressure LNG throttling flash gas and LNG storage tank boil-off gas, achieve zero "carbon" emission in the test, save energy and be environmentally friendly, and at the same time reduce the pressure bearing capacity of the LNG storage tank 1, thereby improving the safety of the test system operation.

[0043] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A test system for an LNG ship BOG reliquefaction unit, characterized in that: It includes a gas supply unit, a reliquefaction device, a gas-liquid separator, and a liquid return main line connected in sequence, wherein: The gas supply unit includes a main gas supply line and a branch gas supply line, wherein the main gas supply line includes an LNG storage tank, a main air-temperature vaporizer, a main mixer, a heater, and a buffer tank connected in sequence through pipelines; The gas supply branch is connected in sequence along the flash gas flow direction to the gas outlet of the gas-liquid separator, the branch air-temperature vaporizer, the BOG compressor and the main mixer inlet; The inlet of the liquid return main path is connected to the liquid outlet of the gas-liquid separator, and the outlet of the liquid return main path is connected to the liquid inlet of the LNG storage tank. The liquid LNG separated by the gas-liquid separator is injected into the LNG storage tank through the liquid return pump.

2. The test system for LNG ship BOG reliquefaction device according to claim 1, characterized in that: The test system of the BOG reliquefaction device is further provided with a tank boil-off gas branch and a branch mixer, wherein the inlet of the tank boil-off gas branch is connected to the gas outlet of the LNG storage tank, and the outlet of the tank boil-off gas branch is connected to the gas outlet of the gas-liquid separator. The branch mixer is arranged on the pipeline between the gas outlet of the gas-liquid separator and the branch air-temperature vaporizer.

3. The test system for LNG ship BOG reliquefaction device according to claim 1, characterized in that: The test system of the BOG reliquefaction device is further provided with a refrigeration unit, which is connected to the reliquefaction device and is used to provide sufficient cooling capacity for the reliquefaction device to cool the high-temperature working fluid and lubricating oil.

4. The test system for LNG ship BOG reliquefaction device according to claim 1, characterized in that: The main gas supply line is also provided with a liquid cargo pump, which is arranged on the pipeline between the LNG storage tank and the main air-temperature vaporizer to control the flow of LNG in the main gas supply line.

5. The test system for LNG ship BOG reliquefaction device according to claim 4, characterized in that: The main gas supply line is also provided with a flow regulating branch and a flow regulating valve. The inlet of the flow regulating branch is arranged on the pipeline between the liquid cargo pump and the main line air-temperature vaporizer. The outlet of the flow regulating branch is connected to the liquid inlet of the LNG storage tank. The flow regulating valve is arranged on the flow regulating branch to stabilize the gas source flow entering the reliquefaction device.

6. The test system for LNG ship BOG reliquefaction device according to claim 2, characterized in that: The gas supply branch is also provided with a pressure reducing valve, which is arranged on the pipeline between the gas outlet of the gas-liquid separator and the inlet of the branch mixer, and is used to reduce the flash gas pressure at the gas outlet of the gas-liquid separator so that it can be mixed with the evaporated gas from the storage tank.

7. The test system for LNG ship BOG reliquefaction device according to claim 2, characterized in that: A pressure regulating valve is provided on the tank boil-off gas branch line. The pressure regulating valve is arranged on the pipeline between the gas outlet of the LNG storage tank and the inlet of the branch mixer, and is used to regulate the pressure in the LNG storage tank.

8. The test system for LNG ship BOG reliquefaction device according to claim 1, characterized in that: The test system of the BOG reliquefaction device is further provided with a throttle valve, which is arranged on the pipeline between the reliquefaction device and the gas-liquid separator and is used to reduce the pressure of the cooled and liquefied LNG to the return tank pressure.

9. The test system for LNG ship BOG reliquefaction device according to claim 1, characterized in that: The test system of the BOG reliquefaction device is further equipped with a monitoring unit, monitoring elements, and an actuator. The monitoring unit and monitoring elements are electrically connected to the gas supply unit, the reliquefaction device, and the refrigeration unit, respectively. The monitoring unit includes a master control cabinet, a power distribution cabinet, a centralized control console, and supporting data acquisition equipment and instruments. The master control cabinet is used to collect electrical signals from the monitoring elements and electrical signals from the reliquefaction device monitoring system, and transmit them to the centralized control console. The master control cabinet and the centralized control console issue debugging instructions based on the collected electrical signals. The actuator receives the instructions and executes debugging actions to control the operation of the test system.

10. The test system for LNG ship BOG reliquefaction device according to claim 9, characterized in that: The monitoring elements include a temperature sensor, a pressure sensor, a flow meter and a gas composition analyzer, which are used to respectively monitor the temperature, pressure, flow and gas composition of the fluid in the test system in real time and send the monitoring values ​​to the main control cabinet.

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