A purging device and method for an LNG pipeline

Abstract

The application provides a purging device and method for LNG pipeline, which comprises a purging pipeline connected between an isolation valve and a blind plate in an inlet pipeline of a high-pressure pump, a main pipeline connected to the purging pipeline in sequence, a pilot valve, a pressure detection assembly, a nitrogen injection assembly, a vent valve, a vaporizer, and a first regulating valve connected to a BOG pipeline, and a bypass pipeline connected in parallel to the main pipeline, wherein a second regulating valve is arranged on the bypass pipeline. In this embodiment, when the gas pressure of the main pipeline exceeds a first preset threshold, the pipeline enters a discharge state, and the first regulating valve is opened; when the gas pressure of the main pipeline is lower than a second preset threshold, the pipeline enters a pressure regulating state, and the second regulating valve is opened; and the gas pressure is increased through the nitrogen injection assembly to enter the discharge state; finally, the pipeline enters a detection state, and the first regulating valve and the second regulating valve are closed; and the methane volume content of the gas is detected through the vent valve. In this way, the purging and replacement of LNG can be realized, and the safety is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of LNG pipeline purging, in particular to a purging device and method for LNG pipeline. BACKGROUND

[0002] When performing preventive maintenance on a high-pressure pump, the high-pressure pump inlet pipeline and pump cylinder need to be replaced and qualified, and then a blind plate is inserted into the high-pressure pump inlet pipeline. Due to the internal leakage of the high-pressure pump inlet hand valve, when the blind plate is extracted again after the high-pressure pump is maintained, the high-pressure pump inlet hand valve and the blind plate are filled with LNG liquid.

[0003] In order to make the blind plate extraction operation process safe, the LNG in the pipeline section needs to be replaced and cleaned. At the same time, because the LNG pipeline only has one drain valve available, the following two methods are used for purging: one is to connect a metal armored pipe at the drain valve, and discharge the LNG liquid into the exhaust pipeline. Because there is back pressure in the exhaust pipeline, this method cannot completely discharge the LNG liquid, thereby causing safety risks in the blind plate extraction operation process. The other method is to connect a metal armored pipe at the drain valve, and discharge the LNG liquid into the BOG pipeline. This method will cause a large displacement of LNG into the BOG pipeline, and also has the risk of equipment damage caused by LNG liquid entering the BOG compressor. SUMMARY

[0004] The summary section is used to introduce the concepts in a brief form, which will be described in detail in the following detailed description section. The summary section of the present disclosure is not intended to identify key or essential features of the claimed technical solutions, nor is it intended to limit the scope of the claimed technical solutions.

[0005] Some embodiments of the present application provide a purging device and method for LNG pipeline to solve the technical problems mentioned in the background section.

[0006] In a first aspect, some embodiments of the present application provide a purging device for LNG pipeline, which comprises a purging pipeline connected between an isolation valve and a blind plate in a high-pressure pump inlet pipeline, and a drain valve, a pressure detection assembly, a nitrogen injection assembly, a vent valve, a gasifier, and a first regulating valve connected to a BOG pipeline in sequence in a main pipeline of the purging pipeline, wherein

[0007] When the gas pressure of the main pipeline exceeds a first preset threshold, the main pipeline enters a discharge state, and the first regulating valve is opened to discharge the gasified gas to the BOG pipeline;

[0008] The purging pipeline further comprises a bypass pipeline connected in parallel with the main pipeline, and a second regulating valve is arranged on the bypass pipeline;

[0009] The gas pressure of the main pipeline is lower than a second preset threshold value, enters a pressure adjustment state, the second adjustment valve is opened, and the pipeline pressure is increased by the nitrogen injection assembly to enter a discharge state;

[0010] After a preset number of discharges, a detection state is entered, the first adjustment valve and the second adjustment valve are closed, and the methane volume content of the gas is detected by the vent valve.

[0011] In a second aspect, some embodiments of the present application provide a method for purging an LNG pipeline, the method comprising:

[0012] Detecting whether the purging device leaks by the nitrogen injection assembly;

[0013] Detecting the dew point by the vent valve until the dew point is lower than a preset temperature value;

[0014] Opening the guide valve, and in response to the gas pressure in the main pipeline exceeding a first preset threshold value, entering a discharge state;

[0015] In response to the gas pressure being lower than a second preset threshold value, entering a pressure adjustment state, increasing the purging pipeline pressure by the bypass pipeline and the nitrogen injection assembly to enter a discharge state;

[0016] After a preset number of discharges, a detection state is entered, and the methane volume content of the gas in the purging pipeline is detected by the vent valve.

[0017] The above-mentioned embodiments of the present application have the following beneficial effects: by the purging device and method for an LNG pipeline, first, the LNG between the isolation valve and the blind plate in the high-pressure pump inlet pipeline can be replaced to ensure the safety of the blind plate extraction operation. In addition, the risk of LNG entering the BOG pipeline and displacement and BOG compressor damage can be avoided.

[0018] Specifically, the reason why the LNG purging replacement effect is poor is that the LNG discharged to the exhaust pipeline has back pressure. Based on this, the purging device for an LNG pipeline of some embodiments of the present application gasifies the LNG by the gasifier to generate steam, and then gradually increases the gas pressure in the purging pipeline. It can be discharged to the BOG pipeline under the action of pressure. Because the first adjustment valve is provided, when the gas pressure exceeds the first preset threshold value, it enters the discharge state and the gas is discharged to the BOG pipeline. In this way, the pressure of the gas discharge can be controlled, so that the gas can be smoothly discharged to the BOG pipeline.

[0019] Further, when the LNG gradually decreases, the gas pressure also decreases, which will cause the gas pressure to be difficult to be discharged to the BOG pipeline smoothly. At the same time, the methane volume content in the gas in the purge pipeline may exceed the standard, which will also cause risks to the blind plate extraction operation. Therefore, in order to solve the above problems, the purge device further comprises a second regulating valve arranged to the bypass pipeline and a nitrogen injection assembly arranged to the main pipeline. When the pressure of the main pipeline is lower than the second preset threshold value, the first regulating valve is in a closed state, at this time, the second regulating valve is opened, so that the gas is not discharged, but returned to the main pipeline from the bypass pipeline, enters into a pressure regulating state, so that the gas pressure gradually increases, and then discharged when the gas pressure exceeds the first preset threshold value.

[0020] When the LNG is completely gasified, no new steam is generated, and the steam cannot make the gas pressure exceed the first preset threshold value even if it returns to the main pipeline from the bypass pipeline. In order to completely purge the steam, the nitrogen injection assembly arranged in the purge device can inject nitrogen into the main pipeline, thereby increasing the gas pressure in the purge pipeline, so that the gas in the purge pipeline can be more completely purged.

[0021] It should be noted that opening the second regulating valve indicates that the gas pressure is at a low value, thereby obtaining the degree of gasification of the LNG, and nitrogen can be supplemented in time for purging and replacement.

[0022] Specifically, if the second regulating valve and the bypass pipeline are not arranged, only the gas pressure exceeding the first preset threshold value can be determined by opening the first regulating valve, the change of the gas pressure cannot be obtained, and the gasification progress of the LNG cannot be grasped. Therefore, nitrogen cannot be supplemented in time to increase the gas pressure. If the nitrogen is supplemented too early, excessive nitrogen will enter the BOG pipeline, which will cause the heat value of the natural gas for external transmission to fluctuate, which is not conducive to the stable operation of the downstream gas power plant. If the nitrogen is supplemented too late, the working efficiency of the purge device will be reduced.

[0023] Therefore, by arranging the second regulating valve and the bypass pipeline, it can be obtained when the gas pressure is lower than the low value, i.e., the second preset threshold value. The change of the gas pressure indicates that the gas pressure generated by the gasified steam cannot exceed the first preset threshold value to enter the discharge state. At this time, the bypass pipeline can transmit the steam to the main pipeline to gradually increase the gas pressure. In this way, the injection of nitrogen can be reduced, thereby avoiding the heat value fluctuation of the natural gas for external transmission in the BOG pipeline. Finally, the second regulating valve is still in an open state, indicating that the LNG has been completely gasified, and the nitrogen is supplemented again at this time, which not only reduces the injection of nitrogen but also ensures the working efficiency of the device.

[0024] Finally, the LNG is gasified into steam by the gasifier, which can avoid displacement of the BOG pipeline and damage of the BOG compressor, improve the reliability of the device and reduce the maintenance cost while ensuring the purging effect. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the specific embodiments or the prior art, the following will briefly introduce the drawings needed to be used in the specific embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0026] Figure 1 Structure diagram of an embodiment of a purging device for LNG pipeline according to the present application;

[0027] Figure 2 Flow chart of some embodiments of a purging method for LNG pipeline according to the present application.

[0028] Explanation of reference signs:

[0029] 11: high-pressure pump inlet pipeline; 12: isolation valve; 13: blind plate; 2: purging pipeline; 21: main pipeline; 22: bypass pipeline; 3: control valve; 4: pressure detection assembly; 41: pressure gauge root valve; 42: pressure gauge; 5: nitrogen injection assembly; 51: check valve; 52: nitrogen quick connector; 6: vent valve; 7: gasifier; 8: first regulating valve; 9: second regulating valve; 10: BOG pipeline. DETAILED DESCRIPTION

[0030] The technical solutions of the present application will be described below in conjunction with embodiments. Obviously, the described embodiments are some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0031] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application.

[0032] Furthermore, the terms "first", "second", etc. are used only for the purpose of description and do not connote or imply relative importance or a number of indicated technical features. Thus, features with "first", "second", etc. can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically defined. In addition, the terms "mounting", "connecting", "connection" should be interpreted broadly, for example, it can be fixed connection, or detachable connection, or integral connection; it can be mechanical connection, or electrical connection; it can be direct connection, or indirect connection through an intermediate medium, or internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0033] The present disclosure will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0034] First, refer to Figure 1 , Figure 1 is a structural schematic view of an embodiment of a purging device for LNG pipeline of the present application. As shown in Figure 1 , the high-pressure pump inlet pipeline 11 generally comprises an isolation valve 12 and a blind plate 13. The purging device is connected between the isolation valve 12 and the blind plate 13, for purging and replacing LNG between the isolation valve 12 and the blind plate 13, to ensure safety during the blind plate 13 extraction operation.

[0035] The purging device comprises a purging pipeline 2. The purging pipeline 2 comprises a main pipeline 21, and the main pipeline 21 is connected between the isolation valve 12 and the blind plate 13. In the direction away from the high-pressure pump inlet pipeline 11, the main pipeline 21 is sequentially provided with a pilot valve 3, a pressure detection assembly 4, a nitrogen injection assembly 5, a vent valve 6, a vaporizer 7, and a first regulating valve 8.

[0036] The purge valve 3 is used to control the discharge of LNG between the isolation valve 12 and the blind plate 13. The pressure detection assembly 4 is used to detect the pressure information of the purge pipeline 2. The pressure detection assembly 4 can include a pressure gauge root valve 41 connected with the main pipeline 21 and a pressure gauge 42. The nitrogen injection assembly 5 is used to inject nitrogen into the purge pipeline 2, which can include a check valve 51 connected with the main pipeline 21 and a nitrogen quick connector 52 connected with a nitrogen source. During the injection of nitrogen, the nitrogen source is opened, and the nitrogen enters the main pipeline 21 through the nitrogen quick connector 52. The vent valve 6 is used to open after the purge is completed to detect the volume content of methane in the discharged gas. The vaporizer 7 is used to vaporize the LNG in the purge pipeline 2 into steam. The first regulating valve 8 is also connected with the BOG pipeline 10.

[0037] The purge pipeline 2 further includes a bypass pipeline 22 connected in parallel with the main pipeline 21. The bypass pipeline 22 can be connected at both ends to the outlet end of the nitrogen injection assembly 5 and the outlet end of the vaporizer 7. The second regulating valve 9 is arranged on the bypass pipeline 22.

[0038] Embodiment one

[0039] The first regulating valve 8 and the second regulating valve 9 can be electrically controlled valves. The pressure gauge 42 can have a data transmission function. The pressure gauge 42 and the first regulating valve 8 and the second regulating valve 9 are interlocked. Specifically, the purge system can further include a controller, which can be a PLC (Programmable Logic Controller). The controller can be in communication with the first regulating valve 8, the second regulating valve 9, the vaporizer 7, the pressure gauge 42, and the valve of the nitrogen source, and can control the opening and closing of the first regulating valve 8 and the second regulating valve 9 according to the pressure information transmitted by the pressure gauge 42. Next, the working process of the purge device will be described.

[0040] After the purge valve 3 is opened, as the vaporizer 7 vaporizes the LNG flowing in, the gas pressure in the main pipeline 21 gradually rises. When the pressure gauge 42 collects that the gas pressure exceeds a first preset threshold, the controller controls the first regulating valve 8 to open, so that the gas can be smoothly discharged into the BOG pipeline under the action of pressure, and enters the discharge state. When the pressure gauge 42 collects that the gas pressure is lower than the first preset threshold, the controller controls the first regulating valve 8 to close. As an example, the first preset threshold can be determined by a person skilled in the art according to actual conditions or repeated experiments. As an example, the first preset threshold can be 4 bar.

[0041] Next, as the LNG gradually decreases, the gas pressure also gradually decreases. When the pressure gauge 42 detects that the gas pressure is lower than the second threshold, the first preset threshold cannot be reached, and thus the controller controls the first regulating valve 8 to close and the second regulating valve 9 to open, so that the gas is not discharged but returned to the main pipeline 21 through the bypass pipeline 22, enters the pressure regulating state, and gradually accumulates, so that the gas pressure gradually increases, and then is discharged when the gas pressure exceeds the first preset threshold. As an example, the second preset threshold can be determined by a person skilled in the art according to actual conditions or repeated experiments. As an example, the first preset threshold can be 2 bar.

[0042] Finally, after the LNG is completely gasified, no new steam is generated, and thus even if the steam is returned to the main pipeline 21 through the bypass pipeline 22, the gas pressure cannot exceed the first preset threshold. In order to completely discharge the gas, when the controller detects that the second regulating valve 9 is opened for more than a preset time, the controller can open the valve of the nitrogen source connected in communication therewith, so that the nitrogen injection assembly 5 can inject nitrogen into the main pipeline 21, thereby increasing the gas pressure in the purge pipeline 2. In this way, when the pressure value detected by the pressure gauge 42 exceeds the first preset threshold, the controller can open the first regulating valve 8, so that the nitrogen and the steam are discharged together, so that the gas in the purge pipeline 2 is more completely replaced. It should be noted that the preset time can be determined by a person skilled in the art according to actual conditions or repeated experiments.

[0043] By setting the second regulating valve and the bypass pipeline, it can be determined when the gas pressure is lower than the low value, i.e., the second preset threshold. The change of the gas pressure indicates that the gas pressure generated by the gasified steam cannot exceed the first preset threshold to enter the discharge state. At this time, the bypass pipeline can transmit the steam to the main pipeline to gradually increase the gas pressure. In this way, the injection of nitrogen can be reduced, thereby avoiding fluctuations in the calorific value of the natural gas in and out of the BOG pipeline. Finally, the second regulating valve is still in the open state, indicating that the LNG has been completely gasified, and at this time, the additional nitrogen not only reduces the injection of nitrogen but also ensures the working efficiency of the device.

[0044] After discharging a preset number of times by injecting nitrogen, a detection state can be entered to detect the methane volume content of the mixed gas in the purge pipeline 2. The controller can control the nitrogen injection assembly 5 to control the pressure in the purge pipeline 2 to be between the first preset threshold and the second preset threshold, so that the first regulating valve 8 and the second regulating valve 9 are both closed. The operator can open the vent valve 6 to take multiple samples to complete the detection of the methane volume content of the mixed gas.

[0045] Example Two

[0046] The first regulating valve 8 and the second regulating valve 9 can also be self-acting regulating valves. The first regulating valve 8 can be configured to open when the gas pressure exceeds a first preset threshold, and the second regulating valve 9 can be configured to open when the gas pressure is lower than a second preset threshold. In this way, the pressure gauge 42 can not have a data transmission function. The controller also does not need to receive the pressure information collected by the pressure gauge 42, and then actively control the first regulating valve 8 and the second regulating valve 9. In this way, the procurement cost of the pressure gauge 42 is reduced, and the information collection, data processing, and control signal process of the controller are simplified, and the use intensity of the controller is reduced.

[0047] Embodiment three

[0048] Further, when the first regulating valve 8 and the second regulating valve 9 are self-acting regulating valves, the controller can also be omitted and manually operated by the staff. Specifically, in the discharge state, when the gas pressure exceeds the first preset threshold, the first regulating valve 8 automatically opens. In the pressure regulating state, the gas pressure is lower than the second preset threshold, the first regulating valve 8 is closed, and the second regulating valve 9 is opened, so as to increase the gas pressure through the bypass pipeline 22. When the LNG is completely gasified, the steam cannot make the gas pressure exceed the first preset threshold even if it returns to the main pipeline 21 through the bypass pipeline 22. Therefore, the staff can observe the value change of the pressure gauge 42, and when the pressure gauge 42 does not reach the first preset threshold for a preset period of time, it indicates that the LNG is completely gasified. Alternatively, the staff can also observe whether there is frost at the inlet of the gasifier 7, and if not, it indicates that the LNG is completely gasified.

[0049] Next, the staff can open the nitrogen source and inject nitrogen into the main pipeline 21 until the value of the pressure gauge 42 exceeds the first preset threshold. In this way, the gas can be discharged after the LNG is completely gasified.

[0050] Finally, the staff opens the nitrogen source and continues to inject nitrogen into the main pipeline 21, so that the pressure in the purge pipeline 2 is between the first preset threshold and the second preset threshold, and the first regulating valve 8 and the second regulating valve 9 are both closed. The staff can open the vent valve 6 to take samples multiple times to complete the detection of the methane volume content of the mixed gas.

[0051] The present application also provides a purge method of the purge device of the LNG pipeline, as shown in Figure 2 The purge method can include the following steps:

[0052] Step 101: Detecting whether there is a leak in the purge device by the nitrogen injection assembly.

[0053] In some embodiments, the purge valve 3 is first closed, nitrogen is injected into the purge pipeline 2 by opening the nitrogen source until the pressure in the purge pipeline 2 reaches a preset pressure value. The preset pressure value is between the first preset threshold value and the second preset threshold value, so that the first regulating valve 8 and the second regulating valve 9 are closed.

[0054] Next, the spray pot is used to detect whether each connection end of the dispersion device leaks, such as the flange connection port. If there is a leak, maintenance can be performed by tightening the bolts, replacing the gaskets, etc.

[0055] Step 102: Detect the dew point through the vent valve 6 until the dew point is lower than the preset temperature value.

[0056] In some embodiments, the vent valve 6 is opened to detect the dew point until the dew point is lower than -40°C. In this way, it can be prevented that water vapor icing causes valve or equipment ice blockage. Specifically, the nitrogen source can use the form of vaporization of liquid nitrogen to provide nitrogen, and the dew point of the nitrogen can be lower than -40°C, for example, -90°C to -60°C.

[0057] Step 103: Open the purge valve and enter the discharge state in response to the gas pressure in the main pipeline exceeding the first preset threshold value.

[0058] In some embodiments, when the purge of LNG begins, the purge valve 3 is first opened, so that the LNG enters the main pipeline 21, the vaporizer 7 vaporizes the inflowing LNG, and the gas pressure in the main pipeline 21 gradually increases. When the gas pressure exceeds the first preset threshold value, the first regulating valve 8 is automatically opened, so that the gas can be smoothly discharged into the BOG pipeline under the action of pressure, and enters the discharge state.

[0059] Step 104: Enter the pressure regulating state in response to the gas pressure being lower than the second preset threshold value, and increase the gas pressure through the bypass pipeline and the nitrogen injection assembly to enter the discharge state.

[0060] In some embodiments, as the LNG gradually decreases, the gas pressure of the vaporization also decreases. When the gas pressure is lower than the second threshold value, the first regulating valve 8 is closed, and the second regulating valve 9 is opened, so that the steam is not discharged, but returns to the main pipeline 21 through the bypass pipeline 22, and enters the pressure regulating state. The steam gradually accumulates, and the gas pressure gradually increases. Further, the gas is discharged when the gas pressure exceeds the first preset threshold value.

[0061] Finally, after the LNG is completely gasified, no new steam is generated, so there is no case that the gas pressure exceeds the first preset threshold even if the steam returns to the main pipeline 21 through the bypass pipeline 22. In order to completely discharge the gas, when the opening time of the second regulating valve 9 exceeds the preset time length, or there is no frost at the inlet of the gasifier 7, indicating that the LNG has been completely gasified, the valve of the nitrogen source can be opened, so that the nitrogen injection assembly 5 can inject nitrogen into the main pipeline 21, thereby increasing the gas pressure. In this way, when the gas pressure exceeds the first preset threshold, the first regulating valve 8 is opened, so that nitrogen and steam are discharged together, so that the gas in the purge pipeline 2 is replaced more completely.

[0062] It should be noted that opening the second regulating valve 9 can obtain the degree of gasification of the LNG, and the working frequency of the gasifier 7 can be reduced. If the second regulating valve 9 and the bypass pipeline 22 are not provided, only the first regulating valve 8 and the first preset threshold are used, and the controller cannot obtain the gasification of the LNG, so that the power consumption of the gasifier 7 is higher, and the operating cost is increased.

[0063] Step 105: In response to the discharge preset number of times, enter the detection state, and detect the methane volume content of the gas in the purge pipeline through the vent valve.

[0064] When the nitrogen injection method is used to discharge a preset number of times, the detection state can be entered. The methane volume content of the gas in the purge pipeline 2 is detected. The gas pressure can be controlled between the first preset threshold and the second preset threshold, so that the first regulating valve 8 and the second regulating valve 9 are both closed. The worker can open the vent valve 6 to take multiple samples, and complete the detection of the methane volume content of the gas. The methane volume content can be considered to be qualified when it is less than 0.5%.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A purging device for an LNG pipeline, characterized in that, This includes a purge pipe connected between an isolation valve and a blind flange in the high-pressure pump inlet pipe, and a drain valve, a pressure detection assembly, a nitrogen injection assembly, a vent valve, a vaporizer, and a first regulating valve connected to the BOG pipeline, which are sequentially connected to the main pipe of the purge pipe. The purging pipeline also includes a bypass pipeline connected in parallel with the main pipeline, and a second regulating valve is provided on the bypass pipeline; The purging method of the purging device includes: The nitrogen injection component was used to detect any leaks in the purging device. The dew point is detected by the vent valve until it is lower than a preset temperature value; When the drain valve is opened, in response to the gas pressure in the main pipeline exceeding a first preset threshold, the first regulating valve opens and the second regulating valve closes, entering the discharge state and discharging the vaporized gas into the BOG pipeline; and when the gas pressure is collected to be lower than the first preset threshold, the first regulating valve closes. In response to the gas pressure being lower than a second preset threshold, the first regulating valve closes and the second regulating valve opens, entering a pressure regulation state; the pressure of the purging pipeline is increased through the bypass pipeline and the nitrogen injection assembly to enter a discharge state; After a preset number of emissions, the first regulating valve and the second regulating valve close and enter the detection state, whereby the methane volume content of the gas in the purging pipeline is detected through the vent valve.

2. The purging device for an LNG pipeline according to claim 1, characterized in that, The pressure detection assembly includes a pressure gauge root valve and a pressure gauge connected together, and the pressure gauge root valve is connected to the purging pipe.

3. The purging device for an LNG pipeline according to claim 1, characterized in that, The nitrogen injection assembly includes a check valve and a nitrogen quick connector connected together. The check valve is connected to the purging pipe, and the nitrogen quick connector is connected to a nitrogen source.

4. The purging device for an LNG pipeline according to claim 1, characterized in that, The first regulating valve is a self-operated regulating valve.

5. The purging device for an LNG pipeline according to claim 1, characterized in that, The second regulating valve is a self-operated regulating valve.

6. The purging device for an LNG pipeline according to claim 1, characterized in that, The bypass pipeline is connected to the outlet end of the nitrogen injection assembly and the outlet end of the vaporizer.

7. The purging device for an LNG pipeline according to claim 1, characterized in that, The step of detecting whether the purging device has a leak through the nitrogen injection assembly includes: Close the drain valve; The pressure inside the purging pipe is brought to a preset pressure value by a nitrogen injection component. A spray bottle is used to check for leaks at the connection end of the purging device. The preset pressure value is between the first preset threshold and the second preset threshold.

8. The purging device for an LNG pipeline according to claim 1, characterized in that, In response to the gas pressure being lower than a second preset threshold, the first regulating valve closes, the second regulating valve opens, and the system enters a pressure regulation state. Increasing the gas pressure through the bypass pipe and the nitrogen injection assembly to enter the discharge state includes: In response to the gas pressure being lower than the second preset threshold, a pressure regulation state is entered, and the gas pressure in the purge pipeline is increased through the bypass pipeline; In response to the complete vaporization of the LNG, nitrogen is injected through the nitrogen injection assembly to increase the gas pressure in the purging line.

9. A purging device for an LNG pipeline according to claim 1, characterized in that, The methane volume content being less than 0.5% is considered as qualified for purging and replacement.

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