High-precision unloading metering device for LNG (Liquefied Natural Gas) station and unloading control method

Abstract

The invention discloses an LNG station high-precision unloading metering device and an unloading control method.The LNG station high-precision unloading metering device comprises a gas return connector, a liquid inlet connector, a liquid outlet connector, a gas outlet connector, 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 connector is connected with a top gas return opening of the gas-liquid separation buffer tank through a gas return pipeline, a first control valve is arranged on the gas return pipeline, the liquid inlet connector is connected with a liquid inlet of the gas-liquid separation buffer tank through a liquid inlet pipeline, and a second control valve is installed on the liquid inlet pipeline. A bottom medium outlet of the gas-liquid separation buffer tank is connected with a liquid phase opening of the LNG storage tank through a liquid outlet pipeline, a liquid phase flowmeter and a third control valve are sequentially arranged on the liquid outlet pipeline in the medium flowing direction, and the bottom medium outlet of the gas-liquid separation buffer tank is further connected with a gas phase opening of the LNG storage tank through a gas outlet pipeline. And a fourth control valve, a gas phase flowmeter and a fifth control valve are arranged on the gas outlet pipeline. The metering precision of the LNG unloading amount of the LNG station can be effectively improved.

Description

Technical Field

[0001] The present application relates to the technical field of unloading metering at LNG stations, and in particular to a high-precision unloading metering device and an unloading control method at LNG stations. Background Art

[0002] LNG stations (including LNG filling stations, L-CNG filling stations, LNG gasification stations, and LNG reserve stations) need to regularly replenish LNG in the LNG storage tanks on the station. LNG is mostly transported by LNG tank trucks. LNG stations need to be equipped with unloading equipment for unloading and measure the LNG unloading volume.

[0003] At present, most LNG stations use weighbridges for measurement, which are to weigh the weight of the tank truck before and after unloading, and measure the difference. However, few gas stations have weighbridges, and they usually weigh at nearby places with weighbridges. It is difficult for gas stations to effectively control the weighing process, and tank truck drivers have made some illegal operations in terms of counterweights, water tanks, and weighing parking positions, resulting in a final weighing error of 100-200kg or 300-500kg.

[0004] There are also a few gas filling stations in China that have installed mass flow meters at the liquid phase port of the unloading truck, but the actual error is often more than 500kg, which is useless and cannot be used for settlement. The reasons are mainly the following:

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

[0006] 2. Fluid phase is unstable during unloading: it is gaseous when unloading is flat; it is gas-liquid two-phase in the initial unloading; it is liquid in the middle of unloading; it is gas-liquid two-phase in the middle and late stages of unloading; it is gaseous at the end of unloading. The accuracy of liquid mass flowmeter is inversely proportional to the gas content in the medium. The higher the gas content, the worse the accuracy. Summary of the invention

[0007] In order to solve the above technical problems, the present application provides a high-precision unloading metering device and an unloading control method for an LNG station, which can effectively improve the metering accuracy of the LNG unloading amount at the LNG station.

[0008] The first objective of the present application is to provide a high-precision unloading metering device for an LNG station that can measure the unloading amount with high precision.

[0009] The above-mentioned application objective 1 of the present application is achieved through the following technical solutions:

[0010] A high-precision unloading metering device for an LNG station, comprising a return air interface, a liquid inlet interface, a liquid outlet interface, a gas outlet interface, a return air pipeline, a liquid inlet pipeline, a liquid outlet pipeline, a gas outlet pipeline and a gas-liquid separation buffer tank, wherein the gas-liquid separation buffer tank is provided with a top return air port, a liquid inlet port and a bottom medium outlet;

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

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

[0013] The liquid inlet interface is connected to the liquid inlet of the gas-liquid separation buffer tank through 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 arranged on the liquid outlet pipeline along the medium flow direction.

[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 medium flow direction of the gas outlet pipeline is sequentially provided with a fourth control valve, a gas phase flow meter and a fifth control valve.

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

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

[0018] Preferably, a liquid level meter is provided on the gas-liquid separation buffer tank, and the liquid level meter is used to detect the liquid level in the gas-liquid separation buffer tank.

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

[0020] The first pressure detection module is arranged on the return air pipeline and close to the return air interface, and the first pressure detection module is used to detect the pressure of the LNG tank truck;

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

[0022] Preferably, the high-precision unloading metering device of the LNG station also includes a boosting interface and a boosting pipeline, the boosting interface is used to connect the boosting liquid phase port of the LNG tank truck, one end of the boosting pipeline is connected to the boosting interface, and the other end of the boosting interface is connected to the return air pipeline, and the other end of the boosting interface is located at the air outlet end of the first control valve, and the sixth control valve, the boosting valve and the seventh control valve are sequentially arranged on the boosting pipeline along the medium flow direction.

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

[0024] Preferably, the LNG station high-precision unloading metering device also includes a controller, the first control valve, the third control valve, the fourth control valve, the fifth control valve, the seventh control valve and the eighth control valve are electrically controlled valves, the second control valve and the sixth control valve are manual valves, the first control valve, the third control valve, the fourth control valve, the fifth control valve, the seventh control valve, the eighth control valve and the supercharger are respectively connected to the signal output end of the controller, and the liquid flowmeter, the gas flowmeter, the liquid level gauge, the first pressure detection module and the second pressure detection module are respectively connected to the signal input end of the controller.

[0025] The second object of the present application is to provide a method for controlling unloading of the high-precision unloading metering device of an LNG station as described in the first object above.

[0026] The second application objective of the present application is achieved through the following technical solutions:

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

[0028] S1, when unloading starts, the first control valve and the second control valve are opened to allow the LNG in the LNG tank truck to enter the gas-liquid separation buffer tank through the liquid inlet pipeline, and the gas in the gas-liquid separation buffer tank returns to the LNG tank truck through the gas return pipeline;

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

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

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

[0032] S21, when the liquid level meter detects that the liquid level in the gas-liquid separation buffer tank is lower than the preset liquid level lower limit, 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 timing time of the timer reaches the preset buffer time threshold, if the liquid level meter detects that the liquid level in the gas-liquid separation buffer tank is greater than or equal to the preset liquid level lower limit, execute S23; if the liquid level meter detects that the liquid level in the gas-liquid separation buffer tank is less than the preset liquid level lower limit, execute S24;

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

[0035] S24, close the first control valve and the second control valve, 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 gas phase ratio in the LNG flowing through the liquid phase flow meter is lower than the preset BOG gas ratio threshold, jump to S3.

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

[0037] During the execution of S2, when the liquid phase flow meter detects that the current flow rate is lower than a preset first flow rate threshold, the third control valve is closed to stop the liquid phase flow meter from measuring, wherein the first flow rate threshold is determined according to the rated flow rate of the liquid phase flow meter;

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

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

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

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

[0042] In summary, the present application discloses a high-precision unloading metering device and unloading control method for an LNG station. By setting a liquid phase flowmeter and a gas phase flowmeter, in the initial stage of unloading, metering is performed by the liquid phase flowmeter. When the liquid phase flowmeter detects that the gas phase ratio in the LNG flowing through the liquid phase flowmeter is lower than the preset BOG gas ratio threshold, the LNG flowing into the gas phase port of the LNG storage tank is metered by the liquid phase flowmeter, thereby avoiding the problem of inaccurate unloading metering caused by poor metering accuracy of the liquid phase flowmeter when the gas content is high, and effectively improving the metering accuracy of the LNG unloading amount of the LNG station. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0044] Figure 1 This is a structural schematic diagram of a high-precision unloading metering device for an LNG station in one embodiment of the present application;

[0045] Figure 2This is a control principle block diagram of a high-precision unloading metering device for an LNG station in one embodiment of the present application;

[0046] Figure 3 This is a flow chart of a method for controlling a vehicle unloading of a high-precision vehicle unloading metering device at an LNG station in one embodiment of the present application. DETAILED DESCRIPTION

[0047] In order 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 part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

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

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

[0050] A person skilled in the art can understand that all or part of the steps of the following method embodiments can be completed 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, the steps of the following method embodiments are executed; and the aforementioned storage medium includes: a mobile storage device, a read-only memory (ROM), a magnetic disk or an optical disk, and other media that can store program codes.

[0051] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, "multiple" and "several" mean two or more, unless otherwise clearly and specifically defined.

[0052] The present application embodiment provides a high-precision unloading metering device for an LNG station, such as Figure 1-2 As shown, the device may include a return air interface a, a liquid inlet interface b, a liquid outlet interface c, a gas outlet interface d, a return air 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, wherein the gas-liquid separation buffer tank 1 is provided with a top return air port, a liquid inlet port and a bottom medium outlet;

[0053] The return air interface a is used to connect the gas phase port of the LNG tank truck, the liquid inlet interface b is used to connect the liquid phase port of the LNG tank truck, the liquid outlet interface c is used to connect the liquid phase port of the LNG storage tank on the LNG station, and the gas outlet interface d is used to connect the gas phase port of the LNG storage tank.

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

[0055] The liquid inlet interface b is connected to the liquid inlet of the gas-liquid separation buffer tank 1 through the liquid inlet pipeline B. The second control valve 3 is installed on the liquid inlet pipeline 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 a liquid outlet pipeline C. A liquid phase flow meter 4 and a third control valve 5 are sequentially arranged 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 an outlet pipeline D. The outlet pipeline D is provided with a fourth control valve 6, a gas phase flow meter 7 and a fifth control valve 8 in 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 flowmeter 4 detects that the gas phase ratio in the LNG flowing through the liquid phase flowmeter 4 is lower than the 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, and the LNG flowing into the gas phase port of the LNG storage tank is measured through the gas phase flowmeter 7.

[0060] The high-precision unloading metering device for LNG stations of the embodiment of the present application is configured to respectively connect the liquid phase port and the gas phase port of the LNG storage tank of the LNG station by setting a liquid outlet pipeline C and a gas outlet pipeline D, and to set a liquid phase flowmeter 4 and a third control valve 5 on the liquid outlet pipeline C, and to set a gas phase flowmeter 7, a fourth control valve 6 and a fifth control valve 8 on the gas storage pipeline. In the initial stage of unloading, due to the low gas content in the LNG, the third control valve 5 is opened and controlled, and the fourth control valve 6 and / or the fifth control valve 8 are closed, and the liquid phase flowmeter 4 is used for metering. When the liquid phase flowmeter 4 detects that the gas phase ratio in the LNG flowing through the liquid phase flowmeter 4 is lower than the preset BOG gas ratio threshold, the third control valve 5 is closed and controlled, 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 by the liquid phase flowmeter 4, thereby avoiding the problem of inaccurate unloading metering caused by poor metering accuracy of the liquid phase flowmeter 4 when the gas content is high, and effectively improving the metering accuracy of the LNG unloading amount of the LNG station.

[0061] Specifically, the liquid phase flowmeter 4 and the gas phase flowmeter 7 in this example are both mass flowmeters.

[0062] In one embodiment, a liquid level meter 9 is provided on the gas-liquid separation buffer tank 1 , and the liquid level meter 9 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 of the LNG station further includes a first pressure detection module 10 and a second pressure detection module 11, wherein:

[0064] The first pressure detection module 10 is arranged on the return air pipeline A and close to the return air interface a. The first pressure detection module 10 is used to detect the pressure of the LNG tank truck;

[0065] The second pressure detection module 11 is disposed on the gas outlet pipeline D and close to 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, the first pressure detection module 10 and the second pressure detection module 11 are both pressure transmitters.

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

[0068] By providing the supercharger 13 and the supercharging pipeline E, the LNG tank truck can be pressurized when the pressure of the LNG tank truck is low, thereby preventing the unloading flow from being low when the pressure of the tank truck is low and affecting the metering accuracy of the liquid phase flowmeter 4.

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

[0070] By setting up a precooling pipeline, the pipeline and the gas-liquid separation buffer tank 1 are precooled before unloading, so as to avoid the pipeline and the gas-liquid separation buffer tank 1 from being too high in temperature during the unloading process, which may cause LNG to vaporize and form BOG, thereby reducing the gas content in the LNG during the unloading process and further improving the metering accuracy of the liquid flow meter 4 during the unloading process.

[0071] In one embodiment, the high-precision unloading metering device of the LNG station further includes a controller 16, the first control valve 2, the third control valve 5, the fourth control valve 6, the fifth control valve 8, the seventh control valve 14 and the eighth control valve 15 are electrically controlled valves, the second control valve 3 and the sixth control valve 12 are manual valves, the first control valve 2, the third control valve 5, the fourth control valve 6, the fifth control valve 8, the seventh control valve 14, the eighth control valve 15 and the supercharger 13 are respectively connected to the signal output end of the controller 16, and the liquid phase flow meter 4, the gas phase flow meter 7, the liquid level meter 9, the first pressure detection module 10 and the second pressure detection module 11 are respectively connected to the signal input end 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 according to the detection data of the liquid phase flow meter 4, the gas phase flow meter 7, the liquid level meter 9, the first pressure detection module 10 and the second pressure detection module 11 during the unloading process, the automation degree of the device is improved.

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

[0073] like Figure 3 As shown, the embodiment of the present application also provides a method for controlling the unloading of the LNG station high-precision unloading metering device described in the above embodiment, and the method may include the following steps:

[0074] S1, when unloading starts, the first control valve and the second control valve are opened to allow the LNG in the LNG tank truck to enter the gas-liquid separation buffer tank through the liquid inlet pipeline, and the gas in the gas-liquid separation buffer tank returns to the LNG tank truck through the gas return pipeline;

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

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

[0077] In this example, at the initial stage of unloading, due to the low gas content in LNG, the third control valve is opened and the fourth control valve and / or the fifth control valve are closed, and measurement is performed by the liquid phase flow meter. When the liquid phase flow meter detects that the gas phase ratio in the LNG flowing through the liquid phase flow meter is lower than the preset BOG gas ratio threshold, the third control valve is closed, and the fourth control valve and the fifth control valve are opened, and the LNG flowing into the gas phase port of the LNG storage tank is measured by the liquid phase flow meter, thereby avoiding the problem of inaccurate unloading measurement caused by poor measurement accuracy of the liquid phase flow meter when the gas content is high, and effectively improving the measurement accuracy of the LNG unloading amount 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 flowmeter accounts for 2% of the sum of the mass of the gas phase and the liquid phase flowing through the liquid phase flowmeter.

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

[0080] S21, when the liquid level meter detects that the liquid level in the gas-liquid separation buffer tank is lower than the preset liquid level lower limit, 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 timing time of the timer reaches the preset buffer time threshold, if the liquid level meter detects that the liquid level in the gas-liquid separation buffer tank is greater than or equal to the preset liquid level lower limit (it means that the LNG in the LNG tank truck has not been unloaded at this time, and there is still LNG flowing from the LNG tank truck to the gas-liquid separation buffer tank), execute S23; if the liquid level meter detects that the liquid level in the gas-liquid separation buffer tank is less than the preset liquid level lower limit (it means that the LNG in the LNG tank truck has been unloaded at this time), execute S24;

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

[0083] S24, close the first control valve and the second control valve, 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 gas phase ratio in the LNG flowing through the liquid phase flow meter is lower than the preset BOG gas ratio threshold, jump to S3.

[0084] In this embodiment, the above process is used to determine whether the LNG in the LNG tank truck has been unloaded. The judgment process is simple and reliable, and different unloading processes are executed according to the judgment results. The liquid phase flow meter or the gas phase flow meter is automatically selected for measurement. When the LNG in the LNG tank truck has been unloaded and the residual liquid in the gas-liquid separation buffer tank is unloaded, the liquid phase flow meter is first used for measurement. When the liquid phase flow meter detects that the gas phase ratio in the LNG flowing through the liquid phase flow meter is lower than the preset BOG gas ratio threshold, it switches to the gas phase flow meter for measurement, thereby effectively improving the measurement accuracy of the LNG unloading amount.

[0085] Specifically, the lower limit value and the upper limit value of the liquid level of the gas-liquid separation buffer tank are set according to the specific model of the gas-liquid separation buffer tank, and the preset buffer time threshold is set according to the specific situation, usually set to 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 phase flow meter detects that the current flow rate is lower than a preset first flow rate threshold, the third control valve is closed to stop the liquid phase flow meter from measuring, wherein the first flow rate threshold is determined according to the rated flow rate of the liquid phase flow meter;

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

[0089] In this embodiment, when the current unloading flow rate is lower than a preset flow rate threshold, the liquid is stopped from being fed into the LNG storage tank and the flow meter is stopped from measuring, thereby effectively preventing the low flow rate from affecting the overall measuring accuracy of the device.

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

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

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

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

[0094] When the unloading flow is low, it is usually because the pressure of the LNG tank truck decreases as the LNG inside the vehicle is unloaded. At this time, the LNG tank truck is pressurized through the supercharger and the booster pipeline to increase the pressure of the LNG tank truck, thereby increasing the unloading flow and improving the measurement accuracy of the liquid phase flowmeter.

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

[0096] In order to avoid the excessive temperature of the pipeline and the gas-liquid separation buffer tank during the unloading process, which will cause LNG to vaporize and form BOG, thereby reducing the gas content in the LNG during the unloading process and further improving the measurement accuracy of the liquid phase flow meter during the unloading process, the pipeline and the gas-liquid separation buffer tank can be pre-cooled before unloading. The specific process is as follows:

[0097] First, fill the gas-liquid separation buffer tank. At this time, the liquid phase flowmeter is still at room temperature, and the liquid phase flowmeter needs to be pre-cooled. The eighth control valve is opened, and the LNG in the gas-liquid separation buffer tank passes through the liquid phase flowmeter and the eighth control valve and returns to the gas-liquid separation buffer tank for pre-cooling. When the liquid phase flowmeter detects that the gas proportion in the LNG flowing through 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 liquid injection into the LNG storage tank of the LNG station, and the liquid phase flowmeter starts metering at the same time.

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

[0099] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0100] Professionals may further appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in the above description according to function. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians may use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0101] The steps of the methods or algorithms described in conjunction with the embodiments disclosed herein may be implemented directly using hardware, software modules executed by a processor, or a combination of the two. The software modules may be placed in a random access memory (RAM), a memory, a read-only memory (ROM), an electrically programmable ROM, an electrically erasable programmable ROM, a register, a hard disk, a removable disk, a 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 implement or use the present application. Various modifications to these embodiments will be 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 the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to 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 an air return interface, a liquid inlet interface, a liquid outlet interface, an air outlet interface, an air return pipeline, a liquid inlet pipeline, a liquid outlet pipeline, an air outlet pipeline and an air-liquid separation buffer tank, wherein the air-liquid separation buffer tank is provided with a top air return port, a liquid inlet port and a bottom medium outlet; The return air interface is used to connect to the gas phase port of the LNG tank truck, the liquid inlet interface is used to connect to the liquid phase port of the LNG tank truck, the liquid outlet interface is used to connect to the liquid phase port of the LNG storage tank on the LNG station, and the gas outlet interface is used to connect to the gas phase port of the LNG storage tank. The air return interface is connected to the top air return port of the gas-liquid separation buffer tank through the air return pipeline, and a first control valve is provided on the air return pipeline. The liquid inlet interface is connected to the liquid inlet of the gas-liquid separation buffer tank through 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 arranged on the liquid outlet pipeline along the medium flow direction. 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 medium flow direction of the gas outlet pipeline is sequentially provided with a fourth control valve, a gas phase flow meter and a fifth control valve. When unloading begins, the third control valve is opened, the fourth control valve and / or the fifth control valve are closed, and the LNG flowing into the liquid phase port of the LNG storage tank is measured by the liquid phase flowmeter; When the liquid phase flowmeter detects that the gas phase ratio in the LNG flowing through the liquid phase flowmeter is lower than the preset BOG gas ratio threshold, the third control valve is closed, and the fourth control valve and the fifth control valve are opened, and the LNG flowing into the gas phase port of the LNG storage tank is measured by the gas phase flowmeter.

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

3. The high-precision unloading metering device for LNG stations according to claim 2 is characterized in that: It also includes a first pressure detection module and a second pressure detection module, wherein: The first pressure detection module is arranged on the return air pipeline and close to the return air interface, and the first pressure detection module is used to detect the pressure of the LNG tank truck; The second pressure detection module is disposed on the gas outlet pipeline and close to the gas outlet interface, and 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 is characterized in that: It also includes a boosting interface and a boosting pipeline, the boosting interface is used to connect the boosting liquid phase port of the LNG tank truck, one end of the boosting pipeline is connected to the boosting interface, the other end of the boosting interface is connected to the return air pipeline, and the other end of the boosting interface is located at the air outlet end of the first control valve, and the sixth control valve, the supercharger and the seventh control valve are sequentially arranged on the boosting pipeline along the medium flow direction.

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

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

7. A method for controlling unloading of a high-precision unloading metering device for an LNG station according to any one of claims 4 to 6, characterized in that: The unloading control method comprises the following steps: S1, when unloading starts, the first control valve and the second control valve are opened to allow the LNG in the LNG tank truck to enter the gas-liquid separation buffer tank through the liquid inlet pipeline, and the gas in the gas-liquid separation buffer tank returns to the LNG tank truck through the gas return pipeline; S2, when the liquid level meter detects that the liquid level in the gas-liquid separation buffer tank is greater than or equal to the preset liquid level upper limit, the first control valve is closed, the second control valve is kept open, and the third control valve is opened to allow the LNG in the gas-liquid separation buffer tank to enter the LNG storage tank through the liquid outlet pipeline. At the same time, the liquid phase flowmeter measures the LNG flowing into the liquid phase port of the LNG storage tank; S3, when the liquid phase flowmeter detects that the gas phase ratio in the LNG flowing through the liquid phase flowmeter is lower than the preset BOG gas ratio threshold, the third control valve is closed, the second control valve is kept open, and the fourth control valve and the fifth control valve are opened to allow the LNG in the gas-liquid separation buffer tank to enter the LNG storage tank through the gas outlet pipeline. At the same time, the gas phase flowmeter 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 of the LNG station according to claim 7 is characterized in that: Between step S2 and step S3, the unloading control method further includes the following steps: S21, when the liquid level meter detects that the liquid level in the gas-liquid separation buffer tank is lower than the preset liquid level lower limit, 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 timing time of the timer reaches the preset buffer time threshold, if the liquid level meter detects that the liquid level in the gas-liquid separation buffer tank is greater than or equal to the preset liquid level lower limit, execute S23; if the liquid level meter detects that the liquid level in the gas-liquid separation buffer tank is less than the preset liquid level lower limit, execute S24; S23, continue to wait until the liquid level meter detects that the liquid level in the gas-liquid separation buffer tank is equal to the preset liquid level upper limit, close the first control valve, keep the second control valve open, and open the third control valve to continue normal unloading; S24, close the first control valve and the second control valve, 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 gas phase ratio in the LNG flowing through the liquid phase flow meter is lower than the preset BOG gas ratio threshold, jump to S3.

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

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

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