High-precision unloading metering device and unloading control method for LNG station

Abstract

This application discloses a high-precision unloading metering device and unloading control method for LNG stations. The high-precision unloading metering device includes a gas return interface, a liquid inlet interface, a liquid outlet interface, a gas outlet interface, a gas return pipeline, a liquid inlet pipeline, a liquid outlet pipeline, a gas outlet pipeline, and a gas-liquid separation buffer tank. The gas return interface is connected to the top gas return port of the gas-liquid separation buffer tank via the gas return pipeline, and a first control valve is installed on the gas return pipeline. The liquid inlet interface is connected to the liquid inlet of the gas-liquid separation buffer tank via the liquid inlet pipeline, and a second control valve is installed on the liquid inlet pipeline. The bottom medium outlet of the gas-liquid separation buffer tank is connected to the liquid phase port of the LNG storage tank via the liquid outlet pipeline, and a liquid phase flow meter and a third control valve are sequentially installed along the medium flow direction on the liquid outlet pipeline. The bottom medium outlet of the gas-liquid separation buffer tank is also connected to the gas phase port of the LNG storage tank via the gas outlet pipeline, and a fourth control valve, a gas phase flow meter, and a fifth control valve are installed on the gas outlet pipeline. This application can effectively improve the metering accuracy of LNG unloading at LNG stations.

Description

Technical Field

[0001] This application relates to the field of LNG station unloading metering technology, and in particular to a high-precision LNG station unloading metering device and unloading control method. Background Technology

[0002] LNG stations (including LNG refueling stations, L-CNG refueling stations, LNG vaporization stations, and LNG storage stations) need to regularly replenish LNG in their LNG storage tanks. Most LNG is transported by LNG tank trucks, and LNG stations need to be equipped with unloading devices to unload the LNG and measure the amount of LNG unloaded.

[0003] Currently, most LNG stations use weighbridges for weighing, measuring the weight of tank trucks before and after unloading and using the difference in weight. However, gas stations rarely have weighbridges; instead, trucks typically use nearby locations with weighbridges. This makes it difficult for gas stations to effectively control the weighing process, leading to violations by tank truck drivers regarding counterweights, water tanks, and weighing positions. This results in weighing errors ranging from 100-200 kg to 300-500 kg.

[0004] A few gas stations in China have installed mass flow meters at the liquid phase unloading port, but the actual error often exceeds 500 kg, rendering them ineffective and unusable for billing. The main reasons for this are as follows:

[0005] 1. The actual flow rate changes greatly during the unloading process, while the flow meter has a large range. In the low flow range, the accuracy of the flow meter cannot be guaranteed.

[0006] 2. The fluid phase is unstable during the unloading process: it is gaseous during the initial unloading pressure equalization; it is a two-phase gas-liquid mixture during the initial unloading stage; it is liquid during the middle stage of unloading; it is a two-phase gas-liquid mixture during the middle and later stages of unloading; and it is gaseous at the end of unloading. The accuracy of the liquid phase mass flow meter is inversely proportional to the gas content in the medium; the higher the gas content, the worse the accuracy. Summary of the Invention

[0007] To address the aforementioned technical problems, this application provides a high-precision unloading metering device and unloading control method for LNG stations, which can effectively improve the metering accuracy of LNG unloading volume at LNG stations.

[0008] The first objective of this application is to provide a high-precision unloading metering device for LNG stations capable of accurately measuring the unloading volume.

[0009] The aforementioned objective of this application is achieved through the following technical solution:

[0010] A high-precision unloading metering device for an LNG station includes a gas return port, a liquid inlet port, a liquid outlet port, a gas outlet port, a gas return pipeline, a liquid inlet pipeline, a liquid outlet pipeline, a gas outlet pipeline, and a gas-liquid separation buffer tank. The gas-liquid separation buffer tank is provided with a top gas return port, a liquid inlet port, and a bottom medium outlet.

[0011] The return gas port is used to connect to the gas phase port of the LNG tanker, the liquid inlet port is used to connect to the liquid phase port of the LNG tanker, the liquid outlet port is used to connect to the liquid phase port of the LNG storage tank at the LNG station, and the gas outlet port is used to connect to the gas phase port of the LNG storage tank.

[0012] The return gas interface is connected to the top return gas port of the gas-liquid separation buffer tank via the return gas pipeline, and a first control valve is provided on the return gas pipeline.

[0013] The liquid inlet is connected to the liquid inlet of the gas-liquid separation buffer tank via the liquid inlet pipeline, and a second control valve is installed on the liquid inlet pipeline.

[0014] The bottom medium outlet of the gas-liquid separation buffer tank is connected to the liquid phase port of the LNG storage tank through the liquid outlet pipeline. A liquid phase flow meter and a third control valve are sequentially installed along the medium flow direction on the liquid outlet pipeline.

[0015] The bottom medium outlet of the gas-liquid separation buffer tank is also connected to the gas phase port of the LNG storage tank through the gas outlet pipeline. The gas outlet pipeline is equipped with a fourth control valve, a gas phase flow meter, and a fifth control valve in sequence according to the medium flow direction.

[0016] When unloading begins, the third control valve is opened and the fourth and / or fifth control valves are closed, and the LNG flowing into the liquid phase port of the LNG storage tank is measured by the liquid phase flow meter.

[0017] When the liquid phase flow meter detects that the proportion of gas phase in the LNG flowing through the liquid phase flow meter is lower than the preset BOG gas proportion threshold, the third control valve is closed and the fourth and fifth control valves are opened, and the LNG flowing into the gas phase port of the LNG storage tank is metered through the gas phase flow meter.

[0018] Preferably, the gas-liquid separation buffer tank is equipped with a level gauge, which is used to detect the liquid level inside the gas-liquid separation buffer tank.

[0019] Preferably, the high-precision unloading metering device for the LNG station further includes a first pressure detection module and a second pressure detection module, wherein,

[0020] The first pressure detection module is located on the return gas pipeline and near the return gas interface. The first pressure detection module is used to detect the pressure of the LNG tanker.

[0021] The second pressure detection module is located on the gas outlet pipeline and near the gas outlet interface. The second pressure detection module is used to detect the pressure of the LNG storage tank.

[0022] Preferably, the high-precision unloading metering device for the LNG station further includes a pressurization interface and a pressurization pipeline. The pressurization interface is used to connect to the pressurization liquid phase port of the LNG tanker. One end of the pressurization pipeline is connected to the pressurization interface, and the other end of the pressurization interface is connected to the return gas pipeline. The other end of the pressurization interface is located at the gas outlet of the first control valve. A sixth control valve, a pressurizer, and a seventh control valve are sequentially arranged on the pressurization pipeline along the medium flow direction.

[0023] Preferably, the high-precision unloading metering device for the LNG station further includes a pre-cooling return liquid pipeline, and the gas-liquid separation buffer tank is also provided with a return liquid port. One end of the pre-cooling return liquid pipeline is connected to the liquid outlet pipeline, and the one end of the pre-cooling return liquid pipeline is located between the liquid phase flow meter and the third control valve. The other end of the pre-cooling return liquid pipeline is connected to the return liquid port of the gas-liquid separation buffer tank, and an eighth control valve is provided on the pre-cooling return liquid pipeline.

[0024] Preferably, the high-precision unloading metering device for the LNG station further includes a controller. The first, third, fourth, fifth, seventh, and eighth control valves are electrically controlled valves, while the second and sixth control valves are manually controlled valves. The first, third, fourth, fifth, seventh, and eighth control valves and the booster are respectively connected to the signal output terminal of the controller. The liquid flow meter, gas flow meter, level gauge, first pressure detection module, and second pressure detection module are respectively connected to the signal input terminal of the controller.

[0025] The second objective of this application is to provide an unloading control method for the high-precision unloading metering device for LNG stations described in the first objective above.

[0026] The second objective of this application is achieved through the following technical solution:

[0027] A method for controlling the unloading of an LNG terminal using a high-precision unloading metering device, the method comprising the following steps:

[0028] S1, when unloading begins, open the first control valve and the second control valve to allow the LNG in the LNG tanker to enter the gas-liquid separation buffer tank through the liquid inlet pipeline, and the gas in the gas-liquid separation buffer tank to return to the LNG tanker through the gas return pipeline.

[0029] S2, when the level gauge detects that the liquid level in the gas-liquid separation buffer tank is greater than or equal to the preset upper limit of the liquid level, the first control valve is closed, the second control valve is kept open, and the third control valve is opened, so that the LNG in the gas-liquid separation buffer tank enters the LNG storage tank through the liquid outlet pipeline. At the same time, the liquid phase flow meter measures the LNG flowing into the liquid phase port of the LNG storage tank.

[0030] S3, when the liquid phase flow meter detects that the proportion of gas phase in the LNG flowing through the liquid phase flow meter is lower than the preset BOG gas proportion threshold, the third control valve is closed, the second control valve is kept open, and the fourth and fifth control valves are opened, so that the LNG in the gas-liquid separation buffer tank enters the LNG storage tank through the gas outlet pipeline. At the same time, the gas phase flow meter measures the LNG flowing into the gas phase port of the LNG storage tank.

[0031] Preferably, between step S2 and step S3, the unloading control method further includes the following steps:

[0032] S21, when the level gauge detects that the liquid level in the gas-liquid separation buffer tank is lower than the preset lower limit value, the third control valve is closed, the second control valve is kept open, the first control valve is opened, and a timer is started.

[0033] S22, when the timer reaches the preset buffer duration threshold, if the level gauge detects that the liquid level in the gas-liquid separation buffer tank is greater than or equal to the preset lower limit of the liquid level, execute S23; if the level gauge detects that the liquid level in the gas-liquid separation buffer tank is less than the preset lower limit of the liquid level, execute S24.

[0034] S23, continue to wait until the level gauge detects that the liquid level in the gas-liquid separation buffer tank is equal to the preset upper limit value, then close the first control valve, keep the second control valve open, and open the third control valve to continue unloading normally.

[0035] S24, close the first and second control valves and open the third control valve to unload the residual liquid in the gas-liquid separation buffer tank. When the liquid phase flow meter detects that the proportion of gas phase in the LNG flowing through the liquid phase flow meter is lower than the preset BOG gas proportion threshold, jump to S3.

[0036] Preferably, the unloading control method further includes the following steps:

[0037] During the execution of S2, when the liquid flow meter detects that the current flow rate is lower than the preset first flow threshold, the third control valve is closed and the liquid flow meter stops measuring. The first flow threshold is determined based on the rated flow rate of the liquid flow meter.

[0038] During the execution of S3, when the gas phase flow meter detects that the current flow rate is lower than the preset second flow threshold, the fourth control valve and / or the fifth control valve are closed to stop the gas phase flow meter from measuring. The second flow threshold is determined based on the rated flow rate of the gas phase flow meter.

[0039] Preferably, the unloading control method further includes the following steps:

[0040] During step 2, when the liquid flow meter stops measuring, if the level gauge detects that the liquid level in the gas-liquid separation buffer tank is greater than or equal to the preset lower limit of the liquid level, the sixth control valve and the seventh control valve are opened, and the booster is started to pressurize the LNG tanker. The LNG in the LNG tanker is vaporized after being pressurized by the booster and returned to the gas phase port of the LNG tanker through the booster pipeline.

[0041] During the pressurization process, the pressure of the LNG tanker and the pressure of the LNG storage tank are detected by the first pressure detection module and the second pressure detection module, respectively. When the pressure difference between the pressure of the LNG tanker and the pressure of the LNG storage tank is greater than or equal to the first pressure threshold, or when the pressure of the LNG tanker is greater than or equal to the second pressure threshold, the third control valve is opened to start liquid phase metering. At the same time, when the pressure of the LNG tanker is greater than or equal to the second pressure threshold, the pressurizer is turned off and the sixth control valve and / or the seventh control valve are closed to stop pressurizing the LNG tanker.

[0042] In summary, this application discloses a high-precision unloading metering device and unloading control method for LNG stations. By setting up a liquid phase flow meter and a gas phase flow meter, the liquid phase flow meter is used for metering in the initial stage of unloading. When the liquid phase flow meter detects that the proportion of gas phase in the LNG flowing through the liquid phase flow meter is lower than a preset BOG gas proportion threshold, the liquid phase flow meter is used to meter the LNG flowing into the gas phase port of the LNG storage tank. This avoids the problem of inaccurate unloading metering caused by poor metering accuracy of the liquid phase flow meter when the gas content is high, and effectively improves the metering accuracy of LNG unloading at LNG stations. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a schematic diagram of the structure of a high-precision unloading metering device for an LNG station according to one embodiment of this application;

[0045] Figure 2This is a block diagram illustrating the control principle of a high-precision unloading metering device for an LNG station according to one embodiment of this application.

[0046] Figure 3 This is a flowchart of an unloading control method for a high-precision unloading metering device at an LNG station, as described in one embodiment of this application. Detailed Implementation

[0047] To enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0048] In the embodiments provided in this application, it should be understood that the disclosed methods and systems can be implemented in other ways. The system embodiments described below are merely illustrative. For example, the division of units and modules is only a logical functional division, and in actual implementation, there may be other division methods, such as: multiple units or modules can be combined, or integrated into another system, or some features can be ignored or not executed. In addition, the coupling, direct coupling, or communication connection between the various components shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or modules, and can be electrical, mechanical, or other forms.

[0049] In addition, each functional unit in the various embodiments of this application can be integrated into a single processor, or each unit can be a separate device, or two or more units can be integrated into a single device; each functional unit in the various embodiments of this application can be implemented in hardware or in the form of hardware plus software functional units.

[0050] Those skilled in the art will understand that all or part of the steps of the following method embodiments can be implemented by program instructions and related hardware. The aforementioned program instructions can be stored in a computer-readable storage medium. When the program instructions are executed, they perform the steps of the following method embodiments. The aforementioned storage medium includes various media capable of storing program code, such as mobile storage devices, read-only memory (ROM), magnetic disks, or optical disks.

[0051] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "a plurality of" or "several" means two or more, unless otherwise explicitly specified.

[0052] This application provides a high-precision unloading metering device for LNG stations, such as... Figure 1-2 As shown, the device may include a return gas interface a, a liquid inlet interface b, a liquid outlet interface c, a gas outlet interface d, a return gas pipeline A, a liquid inlet pipeline B, a liquid outlet pipeline C, a gas outlet pipeline D, and a gas-liquid separation buffer tank 1. The gas-liquid separation buffer tank 1 is provided with a top return gas port, a liquid inlet, and a bottom medium outlet.

[0053] Gas return port a is used to connect to the gas phase port of the LNG tanker truck; liquid inlet port b is used to connect to the liquid phase port of the LNG tanker truck; liquid outlet port c is used to connect to the liquid phase port of the LNG storage tank at the LNG station; and gas outlet port d is used to connect to the gas phase port of the LNG storage tank.

[0054] The return gas interface a is connected to the top return gas port of the gas-liquid separation buffer tank 1 via the return gas pipeline A. The return gas pipeline A is equipped with a first control valve 2.

[0055] The inlet port b is connected to the inlet of the gas-liquid separation buffer tank 1 via the inlet pipe B, and a second control valve 3 is installed on the inlet pipe B.

[0056] The bottom medium outlet of the gas-liquid separation buffer tank 1 is connected to the liquid phase port of the LNG storage tank through the liquid outlet pipeline C. A liquid phase flow meter 4 and a third control valve 5 are sequentially installed on the liquid outlet pipeline C along the medium flow direction.

[0057] The bottom medium outlet of the gas-liquid separation buffer tank 1 is also connected to the gas phase port of the LNG storage tank through the gas outlet pipeline D. The gas outlet pipeline D is equipped with a fourth control valve 6, a gas phase flow meter 7, and a fifth control valve 8 in sequence according to the medium flow direction.

[0058] When unloading begins, the third control valve 5 is opened, the fourth control valve 6 and / or the fifth control valve 8 are closed, and the LNG flowing into the liquid phase port of the LNG storage tank is measured by the liquid phase flow meter 4.

[0059] When the liquid phase flow meter 4 detects that the proportion of gas phase in the LNG flowing through the liquid phase flow meter 4 is lower than the preset BOG gas proportion threshold, the third control valve 5 is closed and the fourth control valve 6 and the fifth control valve 8 are opened, and the LNG flowing into the gas phase port of the LNG storage tank is metered through the gas phase flow meter 7.

[0060] The high-precision unloading metering device for LNG stations in this embodiment connects the liquid outlet C and the gas outlet D of the LNG storage tank at the LNG station. A liquid flow meter 4 and a third control valve 5 are installed on the liquid outlet C, while a gas flow meter 7, a fourth control valve 6, and a fifth control valve 8 are installed on the gas outlet D. In the initial unloading stage, due to the low gas content in the LNG, the third control valve 5 is opened, and the fourth control valve 6 and / or the fifth control valve 8 are closed. Metering is performed by the liquid flow meter 4. When the liquid flow meter 4 detects that the gas ratio in the LNG flowing through it is lower than a preset BOG gas ratio threshold, the third control valve 5 is closed, and the fourth control valve 6 and the fifth control valve 8 are opened. The liquid flow meter 4 then measures the LNG flowing into the gas outlet of the LNG storage tank. This avoids the problem of inaccurate unloading metering caused by the poor metering accuracy of the liquid flow meter 4 when the gas content is high, effectively improving the metering accuracy of LNG unloading at the LNG station.

[0061] Specifically, in this example, both the liquid flow meter 4 and the gas flow meter 7 are mass flow meters.

[0062] In one embodiment, a level gauge 9 is provided on the gas-liquid separation buffer tank 1, which is used to detect the liquid level in the gas-liquid separation buffer tank 1.

[0063] In one embodiment, the high-precision unloading metering device for LNG stations further includes a first pressure detection module 10 and a second pressure detection module 11, wherein...

[0064] The first pressure detection module 10 is installed on the return gas pipeline A and near the return gas interface a. The first pressure detection module 10 is used to detect the pressure of the LNG tanker.

[0065] The second pressure detection module 11 is located on the gas outlet pipeline D and near the gas outlet interface d. The second pressure detection module 11 is used to detect the pressure of the LNG storage tank.

[0066] Specifically, in this embodiment, both the first pressure detection module 10 and the second pressure detection module 11 are pressure transmitters.

[0067] In one embodiment, the high-precision unloading metering device for LNG stations further includes a pressurization interface e and a pressurization pipeline E. The pressurization interface e is used to connect to the pressurization liquid phase port of the LNG tanker. One end of the pressurization pipeline E is connected to the pressurization interface e, and the other end of the pressurization interface e is connected to the return gas pipeline A. The other end of the pressurization interface e is located at the outlet of the first control valve 2. A sixth control valve 12, a pressurizer 13, and a seventh control valve 14 are sequentially arranged on the pressurization pipeline E along the medium flow direction.

[0068] By setting up the booster 13 and the booster pipeline E, the LNG tanker can be pressurized when the pressure is low, thereby avoiding the low unloading flow rate when the tanker pressure is low, which would affect the metering accuracy of the liquid phase flow meter 4.

[0069] In one embodiment, the high-precision unloading metering device for LNG stations also includes a pre-cooling return liquid pipeline, and the gas-liquid separation buffer tank 1 is also provided with a return liquid port. One end of the pre-cooling return liquid pipeline is connected to the liquid outlet pipeline C, and one end of the pre-cooling return liquid pipeline is located between the liquid phase flow meter 4 and the third control valve 5. The other end of the pre-cooling return liquid pipeline is connected to the return liquid port of the gas-liquid separation buffer tank 1, and an eighth control valve 15 is provided on the pre-cooling return liquid pipeline.

[0070] By setting up a pre-cooling pipeline, the pipeline and gas-liquid separation buffer tank 1 are pre-cooled before unloading to avoid the LNG vaporizing and forming BOG due to excessively high temperature in the pipeline and gas-liquid separation buffer tank 1 during unloading. This reduces the gas content in the LNG during unloading and further improves the metering accuracy of the liquid flow meter 4 during unloading.

[0071] In one embodiment, the high-precision unloading metering device for LNG stations further includes a controller 16. The first control valve 2, third control valve 5, fourth control valve 6, fifth control valve 8, seventh control valve 14, and eighth control valve 15 are electrically controlled valves, while the second control valve 3 and sixth control valve 12 are manually operated valves. The first control valve 2, third control valve 5, fourth control valve 6, fifth control valve 8, seventh control valve 14, eighth control valve 15, and booster 13 are connected to the signal output terminals of the controller 16. The liquid flow meter 4, gas flow meter 7, level gauge 9, first pressure detection module 10, and second pressure detection module 11 are connected to the signal input terminals of the controller 16. By configuring some key control valves as electrically controlled valves and setting the controller 16 to automatically control each electrically controlled valve during the unloading process based on the detection data from the liquid flow meter 4, gas flow meter 7, level gauge 9, first pressure detection module 10, and second pressure detection module 11, the automation level of the device is improved.

[0072] Specifically, in this embodiment, the controller 16 is a PLC.

[0073] like Figure 3 As shown in the embodiments of this application, an unloading control method for the high-precision unloading metering device for LNG stations described in the above embodiments is also provided. This method may include the following steps:

[0074] S1, when unloading begins, open the first control valve and the second control valve to allow the LNG in the LNG tanker to enter the gas-liquid separation buffer tank through the liquid inlet pipeline, and the gas in the gas-liquid separation buffer tank to return to the LNG tanker through the gas return pipeline.

[0075] S2, when the level gauge detects that the liquid level in the gas-liquid separation buffer tank is greater than or equal to the preset upper limit of the liquid level, the first control valve is closed, the second control valve is kept open, and the third control valve is opened, so that the LNG in the gas-liquid separation buffer tank enters the LNG storage tank through the liquid outlet pipeline. At the same time, the liquid phase flow meter measures the LNG flowing into the liquid phase port of the LNG storage tank.

[0076] S3, when the liquid phase flow meter detects that the proportion of gas phase in the LNG flowing through the liquid phase flow meter is lower than the preset BOG gas proportion threshold, the third control valve is closed, the second control valve is kept open, and the fourth and fifth control valves are opened, so that the LNG in the gas-liquid separation buffer tank enters the LNG storage tank through the gas outlet pipeline. At the same time, the gas phase flow meter measures the LNG flowing into the gas phase port of the LNG storage tank.

[0077] In this example, during the initial unloading stage, due to the low gas content in the LNG, the third control valve is opened, and the fourth and / or fifth control valves are closed. Measurement is performed using a liquid phase flow meter. When the liquid phase flow meter detects that the proportion of gas phase in the LNG flowing through it is lower than the preset BOG gas proportion threshold, the third control valve is closed, and the fourth and fifth control valves are opened. The liquid phase flow meter then measures the LNG flowing into the gas phase port of the LNG storage tank. This avoids the problem of inaccurate unloading measurement caused by the poor measurement accuracy of the liquid phase flow meter when the gas content is high, effectively improving the measurement accuracy of LNG unloading at the LNG station.

[0078] Specifically, in this embodiment, the preset BOG gas ratio threshold is 2%, that is, the mass of the gas phase flowing through the liquid phase flow meter accounts for 2% of the sum of the mass of the gas phase and the liquid phase flowing through the liquid phase flow meter.

[0079] In one embodiment, between step S2 and step S3, the unloading control method further includes the following steps:

[0080] S21, when the level gauge detects that the liquid level in the gas-liquid separation buffer tank is lower than the preset lower limit value, the third control valve is closed, the second control valve is kept open, the first control valve is opened, and a timer is started.

[0081] S22, when the timer reaches the preset buffer duration threshold, if the level gauge detects that the liquid level in the gas-liquid separation buffer tank is greater than or equal to the preset lower limit of the liquid level (which means that the LNG in the LNG tanker has not been completely unloaded and there is still LNG flowing from the LNG tanker to the gas-liquid separation buffer tank), execute S23; if the level gauge detects that the liquid level in the gas-liquid separation buffer tank is less than the preset lower limit of the liquid level (which means that the LNG in the LNG tanker has been completely unloaded), execute S24.

[0082] S23, continue to wait until the level gauge detects that the liquid level in the gas-liquid separation buffer tank is equal to the preset upper limit value, then close the first control valve, keep the second control valve open, and open the third control valve to continue unloading normally.

[0083] S24, close the first and second control valves and open the third control valve to unload the residual liquid in the gas-liquid separation buffer tank. When the liquid phase flow meter detects that the proportion of gas phase in the LNG flowing through the liquid phase flow meter is lower than the preset BOG gas proportion threshold, jump to S3.

[0084] In this embodiment, the above process is used to determine whether the LNG in the LNG tanker has been completely unloaded. The determination process is simple and reliable, and different unloading processes are executed according to the determination result. The liquid phase flow meter or gas phase flow meter is automatically selected for measurement. When the LNG in the LNG tanker has been completely unloaded and the residual liquid in the gas-liquid separation buffer tank is unloaded, the liquid phase flow meter is used for measurement first. When the liquid phase flow meter detects that the proportion of gas phase in the LNG flowing through the liquid phase flow meter is lower than the preset BOG gas proportion threshold, the measurement is switched to the gas phase flow meter, which effectively improves the measurement accuracy of the LNG unloading amount.

[0085] Specifically, the lower and upper limits of the liquid level in the gas-liquid separation buffer tank are set according to the specific model of the gas-liquid separation buffer tank, and the preset buffer duration threshold is set according to the specific situation, usually 5-10 seconds.

[0086] In one embodiment, the unloading control method further includes the following steps:

[0087] During the execution of S2, when the liquid flow meter detects that the current flow rate is lower than the preset first flow threshold, the third control valve is closed and the liquid flow meter stops measuring. The first flow threshold is determined based on the rated flow rate of the liquid flow meter.

[0088] During the execution of S3, when the gas phase flow meter detects that the current flow rate is lower than the preset second flow threshold, the fourth control valve and / or the fifth control valve are closed to stop the gas phase flow meter from measuring. The second flow threshold is determined based on the rated flow rate of the gas phase flow meter.

[0089] In this embodiment, by stopping the feeding of liquid into the LNG storage tank when the current unloading flow rate is lower than a preset flow rate threshold and stopping the flow meter measurement, the low flow rate can be effectively avoided from affecting the overall measurement accuracy of the device.

[0090] Specifically, in this embodiment, the first flow threshold is 5% of the rated flow of the liquid flow meter, and the second flow threshold is 5% of the rated flow of the gas flow meter.

[0091] In one embodiment, the unloading control method further includes the following steps:

[0092] During step 2, when the liquid flow meter stops measuring, if the level gauge detects that the liquid level in the gas-liquid separation buffer tank is greater than or equal to the preset lower limit of the liquid level, the sixth control valve and the seventh control valve are opened, and the booster is started to pressurize the LNG tanker. The LNG in the LNG tanker is vaporized after being pressurized by the booster and returned to the gas phase port of the LNG tanker through the booster pipeline.

[0093] During the pressurization process, the pressure of the LNG tanker and the pressure of the LNG storage tank are detected by the first pressure detection module and the second pressure detection module, respectively. When the pressure difference between the pressure of the LNG tanker and the pressure of the LNG storage tank is greater than or equal to the first pressure threshold, or when the pressure of the LNG tanker is greater than or equal to the second pressure threshold, the third control valve is opened to start liquid phase metering. At the same time, when the pressure of the LNG tanker is greater than or equal to the second pressure threshold, the pressurizer is turned off and the sixth control valve and / or the seventh control valve are closed to stop pressurizing the LNG tanker.

[0094] When the unloading flow rate is low, it is usually due to the decrease in pressure of the LNG tanker as the LNG inside the tanker is unloaded. At this time, the LNG tanker is pressurized by a booster and a booster pipeline to increase the pressure of the LNG tanker, thereby increasing the unloading flow rate and improving the metering accuracy of the liquid phase flow meter.

[0095] Specifically, in this embodiment, the first pressure threshold is 0.2 MPa and the second pressure threshold is 0.6 MPa.

[0096] To prevent LNG from vaporizing and forming BOG (Boiled Ocean Gas) due to excessively high temperatures in the pipelines and gas-liquid separation buffer tank during unloading, thereby reducing the gas content in the LNG and further improving the metering accuracy of the liquid flow meter, the pipelines and gas-liquid separation buffer tank can be pre-cooled before unloading. The specific process is as follows:

[0097] First, the gas-liquid separation buffer tank is filled. At this time, the liquid flow meter is still at room temperature and needs to be pre-cooled. The eighth control valve is opened, and the LNG in the gas-liquid separation buffer tank returns to the gas-liquid separation buffer tank for pre-cooling after passing through the liquid flow meter and the eighth control valve. When the liquid flow meter detects that the proportion of gas in the flowing LNG is less than or equal to the preset BOG gas proportion threshold, the pre-cooling is completed. The eighth control valve is closed, and the third control valve is opened to start feeding liquid into the LNG storage tank of the LNG station. At the same time, the liquid flow meter starts metering.

[0098] It should be noted that the measurement data of the liquid flow meter is not included in the unloading volume before the precooling is completed.

[0099] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0100] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0101] The steps of the methods or algorithms described in conjunction with the embodiments disclosed herein can be implemented directly using hardware, a software module executed by a processor, or a combination of both. The software module can be located in random access memory (RAM), main memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art.

[0102] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A high-precision unloading metering device for LNG stations, characterized in that, It includes a return gas interface, a liquid inlet interface, a liquid outlet interface, a gas outlet interface, a return gas pipeline, a liquid inlet pipeline, a liquid outlet pipeline, a gas outlet pipeline, and a gas-liquid separation buffer tank. The gas-liquid separation buffer tank is provided with a top return gas port, a liquid inlet, and a bottom medium outlet. The return gas port is used to connect to the gas phase port of the LNG tanker, the liquid inlet port is used to connect to the liquid phase port of the LNG tanker, the liquid outlet port is used to connect to the liquid phase port of the LNG storage tank at the LNG station, and the gas outlet port is used to connect to the gas phase port of the LNG storage tank. The return gas interface is connected to the top return gas port of the gas-liquid separation buffer tank via the return gas pipeline, and a first control valve is provided on the return gas pipeline. The liquid inlet is connected to the liquid inlet of the gas-liquid separation buffer tank via the liquid inlet pipeline, and a second control valve is installed on the liquid inlet pipeline. The bottom medium outlet of the gas-liquid separation buffer tank is connected to the liquid phase port of the LNG storage tank through the liquid outlet pipeline. A liquid phase flow meter and a third control valve are sequentially installed along the medium flow direction on the liquid outlet pipeline. The bottom medium outlet of the gas-liquid separation buffer tank is also connected to the gas phase port of the LNG storage tank through the gas outlet pipeline. The gas outlet pipeline is equipped with a fourth control valve, a gas phase flow meter, and a fifth control valve in sequence according to the medium flow direction. When unloading begins, the third control valve is opened and the fourth and / or fifth control valves are closed, and the LNG flowing into the liquid phase port of the LNG storage tank is measured by the liquid phase flow meter. When the liquid phase flow meter detects that the proportion of gas phase in the LNG flowing through the liquid phase flow meter is lower than the preset BOG gas proportion threshold, the third control valve is closed and the fourth and fifth control valves are opened, and the LNG flowing into the gas phase port of the LNG storage tank is metered through the gas phase flow meter.

2. The high-precision unloading metering device for LNG stations according to claim 1, characterized in that, The gas-liquid separation buffer tank is equipped with a level gauge, which is used to detect the liquid level inside the gas-liquid separation buffer tank.

3. The high-precision unloading metering device for LNG stations according to claim 2, characterized in that, It also includes a first pressure detection module and a second pressure detection module, wherein, The first pressure detection module is located on the return gas pipeline and near the return gas interface. The first pressure detection module is used to detect the pressure of the LNG tanker. The second pressure detection module is located on the gas outlet pipeline and near the gas outlet interface. The second pressure detection module is used to detect the pressure of the LNG storage tank.

4. The high-precision unloading metering device for LNG stations according to claim 3, characterized in that, It also includes a pressurization interface and a pressurization pipeline. The pressurization interface is used to connect to the pressurization liquid phase port of the LNG tanker. One end of the pressurization pipeline is connected to the pressurization interface, and the other end of the pressurization interface is connected to the return gas pipeline. The other end of the pressurization interface is located at the gas outlet of the first control valve. A sixth control valve, a pressurizer, and a seventh control valve are sequentially arranged on the pressurization pipeline along the medium flow direction.

5. The high-precision unloading metering device for LNG stations according to claim 4, characterized in that, It also includes a pre-cooling return pipeline, and the gas-liquid separation buffer tank is also provided with a return port. One end of the pre-cooling return pipeline is connected to the liquid outlet pipeline, and the one end of the pre-cooling return pipeline is located between the liquid flow meter and the third control valve. The other end of the pre-cooling return pipeline is connected to the return port of the gas-liquid separation buffer tank. An eighth control valve is provided on the pre-cooling return pipeline.

6. The high-precision unloading metering device for LNG stations according to claim 5, characterized in that, It also includes a controller, wherein the first, third, fourth, fifth, seventh, and eighth control valves are electrically controlled valves, and the second and sixth control valves are manually controlled valves. The first, third, fourth, fifth, seventh, and eighth control valves and the booster are respectively connected to the signal output terminal of the controller, and the liquid flow meter, gas flow meter, level gauge, first pressure detection module, and second pressure detection module are respectively connected to the signal input terminal of the controller.

7. A method for controlling the unloading of an LNG station high-precision unloading metering device as described in any one of claims 4-6, characterized in that, The unloading control method includes the following steps: S1, when unloading begins, open the first control valve and the second control valve to allow the LNG in the LNG tanker to enter the gas-liquid separation buffer tank through the liquid inlet pipeline, and the gas in the gas-liquid separation buffer tank to return to the LNG tanker through the gas return pipeline. S2, when the level gauge detects that the liquid level in the gas-liquid separation buffer tank is greater than or equal to the preset upper limit of the liquid level, the first control valve is closed, the second control valve is kept open, and the third control valve is opened, so that the LNG in the gas-liquid separation buffer tank enters the LNG storage tank through the liquid outlet pipeline. At the same time, the liquid phase flow meter measures the LNG flowing into the liquid phase port of the LNG storage tank. S3, when the liquid phase flow meter detects that the proportion of gas phase in the LNG flowing through the liquid phase flow meter is lower than the preset BOG gas proportion threshold, the third control valve is closed, the second control valve is kept open, and the fourth and fifth control valves are opened, so that the LNG in the gas-liquid separation buffer tank enters the LNG storage tank through the gas outlet pipeline. At the same time, the gas phase flow meter measures the LNG flowing into the gas phase port of the LNG storage tank.

8. The unloading control method of the high-precision unloading metering device for LNG stations according to claim 7, characterized in that, Between step S2 and step S3, the unloading control method further includes the following steps: S21, when the level gauge detects that the liquid level in the gas-liquid separation buffer tank is lower than the preset lower limit value, the third control valve is closed, the second control valve is kept open, the first control valve is opened, and a timer is started. S22, when the timer reaches the preset buffer duration threshold, if the level gauge detects that the liquid level in the gas-liquid separation buffer tank is greater than or equal to the preset lower limit of the liquid level, execute S23; if the level gauge detects that the liquid level in the gas-liquid separation buffer tank is less than the preset lower limit of the liquid level, execute S24. S23, continue to wait until the level gauge detects that the liquid level in the gas-liquid separation buffer tank is equal to the preset upper limit value, then close the first control valve, keep the second control valve open, and open the third control valve to continue unloading normally. S24, close the first and second control valves and open the third control valve to unload the residual liquid in the gas-liquid separation buffer tank. When the liquid phase flow meter detects that the proportion of gas phase in the LNG flowing through the liquid phase flow meter is lower than the preset BOG gas proportion threshold, jump to S3.

9. The unloading control method of the high-precision unloading metering device for LNG stations according to claim 7 or 8, characterized in that, The unloading control method further includes the following steps: During the execution of S2, when the liquid flow meter detects that the current flow rate is lower than the preset first flow threshold, the third control valve is closed and the liquid flow meter stops measuring. The first flow threshold is determined based on the rated flow rate of the liquid flow meter. During the execution of S3, when the gas phase flow meter detects that the current flow rate is lower than the preset second flow threshold, the fourth control valve and / or the fifth control valve are closed to stop the gas phase flow meter from measuring. The second flow threshold is determined based on the rated flow rate of the gas phase flow meter.

10. The unloading control method of the high-precision unloading metering device for LNG stations according to claim 9, characterized in that, The unloading control method further includes the following steps: During step 2, when the liquid flow meter stops measuring, if the level gauge detects that the liquid level in the gas-liquid separation buffer tank is greater than or equal to the preset lower limit of the liquid level, the sixth control valve and the seventh control valve are opened, and the booster is started to pressurize the LNG tanker. The LNG in the LNG tanker is vaporized after being pressurized by the booster and returned to the gas phase port of the LNG tanker through the booster pipeline. During the pressurization process, the pressure of the LNG tanker and the pressure of the LNG storage tank are detected by the first pressure detection module and the second pressure detection module, respectively. When the pressure difference between the pressure of the LNG tanker and the pressure of the LNG storage tank is greater than or equal to the first pressure threshold, or when the pressure of the LNG tanker is greater than or equal to the second pressure threshold, the third control valve is opened to start liquid phase metering. At the same time, when the pressure of the LNG tanker is greater than or equal to the second pressure threshold, the pressurizer is turned off and the sixth control valve and / or the seventh control valve are closed to stop pressurizing the LNG tanker.

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