Purging device for LNG (Liquefied Natural Gas) pipeline

Abstract

The utility model provides a purging device for an LNG (liquefied natural gas) pipeline, which comprises a purging pipeline connected between an isolation valve and a blind plate in an inlet pipeline of a high-pressure pump, and a drain valve, a pressure detection component, a nitrogen injection component, an emptying valve, a gasifier and a first regulating valve connected with a BOG (boil-off gas) pipeline which are sequentially connected to a main pipeline of the purging pipeline, the purging pipeline further comprises a bypass pipeline connected with the main pipeline in parallel, and a second adjusting valve is arranged on the bypass pipeline. In the implementation mode, when the gas pressure of the main pipeline exceeds the first preset threshold value, the main pipeline enters a discharging state, and the first adjusting valve is opened; if the gas pressure of the main pipeline is lower than a second preset threshold value, entering a pressure adjusting state, opening a second adjusting valve, and increasing the gas pressure through a nitrogen injection assembly so as to enter a discharging state; finally, entering a detection state, and closing the first regulating valve and the second regulating valve; and the volume content of methane in the gas is detected through the emptying valve. In this way, purging and replacement of LNG can be achieved, and safety is improved.

Description

Technical Field

[0001] The utility model relates to the technical field of LNG pipeline purging, in particular to a LNG pipeline purging device. Background Art

[0002] When performing preventive maintenance on the high-pressure pump, it is necessary to replace the high-pressure pump inlet pipe and pump barrel and then insert a blind plate on the high-pressure pump inlet pipe. Due to internal leakage of the high-pressure pump inlet manual valve, when the blind plate is pulled out again after the high-pressure pump is overhauled, the space between the high-pressure pump inlet manual valve and the blind plate is filled with LNG liquid.

[0003] In order to ensure the safety of the blind plate extraction process, the LNG in the pipe section needs to be purged and replaced. At the same time, because there is only one drain valve available for the LNG pipeline, there are two purging methods used in the past: one is to connect a metal armored pipe at the drain valve to discharge the LNG liquid into the drain line. Due to the back pressure in the drain line, this method cannot completely discharge the LNG liquid, resulting in safety risks in the blind plate extraction process; the other is to connect a metal armored pipe at the drain valve to discharge the LNG liquid into the BOG pipeline. This method will cause a large amount of LNG to enter the BOG pipeline, causing large displacement, and there is also a risk of LNG liquid entering the BOG compressor and causing equipment damage. Utility Model Content

[0004] The content of this utility model is used to introduce the concepts in a brief form, which will be described in detail in the detailed implementation section below. The content of this disclosure is not intended to identify the key features or essential features of the technical solution claimed for protection, nor is it intended to limit the scope of the technical solution claimed for protection.

[0005] Some embodiments of the present utility model provide a purging device for an LNG pipeline to solve the technical problems mentioned in the above background technology section.

[0006] Some embodiments of the utility model provide a purging device for an LNG pipeline, the purging device comprising a purging pipeline connected to an isolation valve and a blind plate in an inlet pipeline of a high-pressure pump, and a guide valve, a pressure detection component, a nitrogen injection component, a vent valve, a vaporizer, and a first regulating valve connected to a BOG pipeline in sequence to a main pipeline of the purging pipeline, wherein:

[0007] The gas pressure of the main pipeline exceeds a first preset threshold value and enters a discharge state, and the first regulating valve opens to discharge the gasified gas into the BOG pipeline;

[0008] The purge pipeline further includes a bypass pipeline connected in parallel with the main pipeline, and a second regulating valve is provided on the bypass pipeline;

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

[0010] In response to a preset number of discharges, a detection state is entered, 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.

[0011] The above embodiments of the utility model have the following beneficial effects: through the LNG pipeline purging device and method of the present invention, firstly, the LNG between the isolation valve and the blind plate in the inlet pipeline of the high-pressure pump can be purged and replaced to be qualified, thereby ensuring the safety of the blind plate extraction operation. In addition, the risk of displacement of LNG entering the BOG pipeline and damage to the BOG compressor can be avoided.

[0012] Specifically, the reason for the poor LNG (Liquefied Natural Gas) purge replacement effect is that there is back pressure in the exhaust pipeline to which LNG is discharged. Based on this, a purge device for an LNG pipeline in some embodiments of the present invention vaporizes LNG through a vaporizer to generate steam, thereby gradually increasing the gas pressure in the purge pipeline. It can be discharged into the BOG (Boil Off Gas) pipeline under pressure. Since a first regulating valve is provided, the gas can be discharged into the BOG pipeline only when the gas pressure exceeds a first preset threshold and the gas enters a discharge state. In this way, the pressure of the gas discharge can be controlled so that the gas can be smoothly discharged into the BOG pipeline.

[0013] Furthermore, when LNG gradually decreases, the gas pressure also becomes lower, which will make it difficult to discharge the gas pressure smoothly to the BOG pipeline. At the same time, the methane volume content of the gas in the purge pipeline may exceed the standard, which will also pose a risk to the blind plate extraction operation. Therefore, in order to solve the above problems, the purge device also includes a second regulating valve arranged in the bypass pipeline and a nitrogen injection assembly arranged in the main pipeline. When the pressure of the main pipeline is lower than the second preset threshold, 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, and returns to the main pipeline from the bypass pipeline, entering the pressure regulation state, so that the gas pressure gradually increases, and then the gas is discharged after the pressure exceeds the first preset threshold.

[0014] As the LNG is completely gasified, no new steam is generated, and even if the steam returns to the main pipeline through the bypass pipeline, the gas pressure cannot exceed the first preset threshold. In order to completely purge the steam, the nitrogen injection assembly provided 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 purged more thoroughly.

[0015] It should be noted that opening the second regulating valve indicates that the gas pressure is at a low value, thereby being able to obtain the degree of gasification of LNG and to replenish nitrogen in time for purging and replacement.

[0016] Specifically, if the second regulating valve and bypass pipeline are not provided, the opening of the first regulating valve can only determine that the gas pressure exceeds the first preset threshold, and the change in gas pressure cannot be obtained, and the progress of LNG gasification cannot be grasped. This results in the inability to replenish nitrogen in time to increase the gas pressure. If nitrogen is replenished too early, excessive nitrogen will enter the BOG pipeline, causing fluctuations in the calorific value of the exported natural gas, which is not conducive to the stable operation of the downstream gas-fired power plant. If nitrogen is replenished too late, the working efficiency of the purge device will be reduced.

[0017] Therefore, by setting a second regulating valve and a bypass pipe, it is possible to obtain when the gas pressure is lower than the low value, that is, the second preset threshold value. The change in the gas pressure indicates that the gas pressure that can be generated by the vaporized steam cannot exceed the first preset threshold value to enter the discharge state. At this time, the bypass pipe 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 transported 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 vaporized. At this time, adding nitrogen not only reduces the injection of nitrogen but also ensures the working efficiency of the device.

[0018] Finally, by gasifying LNG into steam through the vaporizer, displacement of the BOG pipeline and damage to the BOG compressor can be avoided. While ensuring the purge effect, the reliability of the device is improved and the maintenance cost is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the specific implementation methods of the utility model or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 The utility model is a schematic structural diagram of an embodiment of a purging device for an LNG pipeline.

[0021] Description of reference numerals:

[0022] 11: High-pressure pump inlet pipeline; 12: Isolation valve; 13: Blind plate; 2: Purge pipeline; 21: Main pipeline; 22: Bypass pipeline; 3: Drain 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: Vaporizer; 8: First regulating valve; 9: Second regulating valve; 10: BOG pipeline. DETAILED DESCRIPTION

[0023] The technical solution of the utility model will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0024] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present invention.

[0025] In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present utility model, "multiple" means two or more, unless otherwise clearly and specifically defined. In addition, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present utility model can be understood according to specific circumstances.

[0026] The present disclosure will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0027] First see Figure 1 , Figure 1 FIG. 1 is a schematic diagram of the structure of an embodiment of a purging device for an LNG pipeline according to the utility model. Figure 1 As shown, the high-pressure pump inlet pipeline 11 generally includes an isolation valve 12 and a blind plate 13. The purge device is connected between the isolation valve 12 and the blind plate 13 to purge and replace the LNG between the isolation valve 12 and the blind plate 13 to ensure safety during the extraction operation of the blind plate 13.

[0028] The purge device includes a purge pipeline 2. The purge pipeline 2 includes a main pipeline 21, which is connected between the isolation valve 12 and the blind plate 13. A shower valve 3, a pressure detection component 4, a nitrogen injection component 5, a vent valve 6, a vaporizer 7 and a first regulating valve 8 are sequentially arranged in the direction of the main pipeline 21 away from the high-pressure pump inlet pipeline 11.

[0029] The above-mentioned drain valve 3 is used to control the discharge of LNG between the isolation valve 12 and the blind plate 13. The pressure detection component 4 is used to detect the pressure information of the purge pipeline 2. The pressure detection component 4 may include a connected pressure gauge root valve 41 and a pressure gauge 42, and the pressure gauge root valve 41 is connected to the main pipeline 21. The above-mentioned nitrogen injection component 5 is used to inject nitrogen into the purge pipeline 2, and the nitrogen injection component 5 may include a connected check valve 51 and a nitrogen quick connector 52. The check valve 51 is connected to the main pipeline 21, and the nitrogen quick connector 52 is connected to the nitrogen source. During the process of injecting nitrogen, the nitrogen source is opened, and nitrogen enters the main pipeline 21 through the nitrogen quick connector 52. The above-mentioned vent valve 6 is used to open after the purge is completed to detect the volume content of methane in the discharged gas. The above-mentioned vaporizer 7 is used to gasify the LNG in the purge pipeline 2 into steam. The above-mentioned first regulating valve 8 is also connected to the BOG pipeline 10.

[0030] The purge pipeline 2 further includes a bypass pipeline 22, which is connected in parallel with the main pipeline 21. Both ends of the bypass pipeline 22 can be connected to the outlet end of the nitrogen injection assembly 5 and the outlet end of the gasifier 7. A second regulating valve 9 is provided on the bypass pipeline 22.

[0031] Embodiment 1

[0032] The first regulating valve 8 and the second regulating valve 9 may be electrically controlled valves. The pressure gauge 42 may have a data transmission function. The pressure gauge 42 and the first regulating valve 8 and the second regulating valve 9 are interlocked and controlled. Specifically, the purge system may further include a controller, which may be a PLC (Programmable Logic Controller). The controller may be connected to the valves of the first regulating valve 8, the second regulating valve 9, the vaporizer 7, the pressure gauge 42, and the nitrogen source, and may 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. The following is an explanation of the working process of the purge device.

[0033] First, the shower valve 3 is closed, and the nitrogen source is opened to inject nitrogen into the purge pipe 2 until the pressure in the purge pipe 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.

[0034] Next, use a spray bottle to check whether there are leaks at the connection ends of the blow-off device, such as the flange connection. If there are leaks, they can be repaired by tightening bolts, replacing gaskets, etc.

[0035] Then, the vent valve 6 is opened to detect the dew point until the dew point is lower than -40°C. In this way, it is possible to prevent the valve or equipment from being blocked by ice after the water vapor freezes. Specifically, the nitrogen source can be provided in the form of vaporized liquid nitrogen, and the dew point of the nitrogen can be lower than -40°C, for example, -90°C to -60°C.

[0036] Next, after opening the shower valve 3, as the vaporizer 7 vaporizes the inflowing LNG, the gas pressure in the main pipeline 21 gradually increases. When the pressure gauge 42 detects that the gas pressure exceeds the 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 enter the discharge state. When the pressure gauge 42 detects 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 those skilled in the art based on actual conditions or repeated experiments. As an example, the first preset threshold can be 4 bar.

[0037] Next, as the LNG gradually decreases, the gas pressure also becomes lower. When the pressure gauge 42 detects that the gas pressure is lower than the second threshold, it is even more impossible to reach the first preset threshold. Therefore, 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, and returns to the main pipeline 21 through the bypass pipeline 22, and enters the pressure regulation state, so that the gas gradually accumulates and the gas pressure gradually increases. Then, the gas is discharged after the gas pressure exceeds the first preset threshold. As an example, the second preset threshold can be determined by a technician in this field according to actual conditions or repeated experiments. As an example, the first preset threshold can be 2bar.

[0038] Finally, after the LNG is completely gasified, no new steam is generated. Therefore, even if the steam returns to the main pipeline 21 through the bypass pipeline 22, the gas pressure cannot exceed the first preset threshold. In order to discharge the gas completely, when the controller detects that the opening time of the second regulating valve 9 exceeds the preset time, the controller can open the valve of the nitrogen source connected to it, so that the nitrogen injection component 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 collected by the pressure gauge 42 exceeds the first preset threshold, the controller can open the first regulating valve 8, so that the nitrogen and steam are discharged together, so that the gas purge replacement in the purge pipeline 2 is more thorough. It should be noted that the above-mentioned preset time can be determined by technicians in this field according to actual conditions or repeated experiments.

[0039] By setting a second regulating valve and a bypass pipe, it is possible to obtain when the gas pressure is lower than the low value, that is, the second preset threshold. The change in the gas pressure indicates that the gas pressure generated by the vaporized steam cannot exceed the first preset threshold to enter the discharge state. At this time, the bypass pipe can transfer 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 transported inside and outside the BOG pipeline. Finally, the second regulating valve is still in the open state, indicating that the LNG has been completely vaporized. At this time, adding nitrogen not only reduces the injection of nitrogen but also ensures the working efficiency of the device.

[0040] After the preset number of discharges by injecting nitrogen, the 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 component 5 to control the pressure in the purge pipeline 2 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 both closed. The staff can open the vent valve 6 for multiple sampling to complete the methane volume content detection of the mixed gas.

[0041] Embodiment 2

[0042] The first regulating valve 8 and the second regulating valve 9 may also be self-operated regulating valves. The first regulating valve 8 may be configured to open when the gas pressure exceeds a first preset threshold, and the second regulating valve 9 may be configured to open when the gas pressure is lower than a second preset threshold. In this way, the pressure gauge 42 may not have the function of transmitting data. The controller 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 process of information collection, data processing, and control signals of the controller is simplified, thereby reducing the use intensity of the controller.

[0043] Embodiment 3

[0044] Furthermore, when the first regulating valve 8 and the second regulating valve 9 are self-operated regulating valves, the controller can 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 opens automatically. In the pressure regulation state, the gas pressure is lower than the second preset threshold, the first regulating valve 8 is closed, the second regulating valve 9 is opened, and the gas pressure is increased through the bypass pipe 22. When the LNG is completely vaporized, even if the steam returns to the main pipe 21 through the bypass pipe 22, the gas pressure cannot exceed the first preset threshold. Therefore, the staff can observe the value change of the pressure gauge 42. 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 vaporized. Or the staff can also observe whether there is frost at the inlet of the vaporizer 7. If not, it indicates that the LNG is completely vaporized.

[0045] 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 value, thereby allowing the gas to be discharged. In this way, after the LNG is completely gasified, the gas in the purge pipeline 2 can be purged and replaced to meet the requirements.

[0046] Finally, the staff turns on 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 for multiple sampling to complete the methane volume content detection of the mixed gas.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the utility model, rather than to limit it. Although the utility model has been described in detail with reference to the aforementioned embodiments, ordinary technicians in this field should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solution deviate from the scope of the technical solution of the embodiments of the utility model.

Claims

1. A purging device for an LNG pipeline, characterized in that: It includes a purge pipeline connected to the isolation valve and the blind plate in the inlet pipeline of the high-pressure pump, and a shower valve, a pressure detection component, a nitrogen injection component, a vent valve, a vaporizer, and a first regulating valve connected to the BOG pipeline. The gas pressure of the main pipeline exceeds a first preset threshold value and enters a discharge state, and the first regulating valve opens to discharge the gasified gas into the BOG pipeline; The purge pipeline further includes a bypass pipeline connected in parallel with the main pipeline, and a second regulating valve is provided on the bypass pipeline; The gas pressure of the main pipeline is lower than a second preset threshold value, entering a pressure regulation state, the second regulating valve is opened, and the gas pressure is increased through the nitrogen injection assembly to enter a discharge state; In response to a preset number of discharges, a detection state is entered, 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.

2. The LNG pipeline purging device according to claim 1, characterized in that: The pressure detection assembly includes a pressure gauge root valve and a pressure gauge connected to each other, and the pressure gauge root valve is connected to the purge pipeline.

3. The purging device for an LNG pipeline according to claim 1, characterized in that: The nitrogen injection assembly comprises a check valve and a nitrogen quick connector which are connected to each other. The check valve is connected to the purge pipeline, and the nitrogen quick connector is connected to a nitrogen source.

4. The LNG pipeline purging device 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 LNG pipeline purging device according to claim 1, characterized in that: The bypass pipe is connected to an outlet end of the nitrogen injection assembly and an outlet end of the gasifier.

7. The LNG pipeline purging device according to claim 1, characterized in that: The purge device also includes a controller, which is communicatively connected with the pressure detection component, the nitrogen injection component, the gasifier, the first regulating valve and the second regulating valve.

8. The purging device for an LNG pipeline according to claim 7, characterized in that: The controller is a PLC.

9. The purging device for an LNG pipeline according to claim 7, characterized in that: The first regulating valve is an electrically controlled valve.

10. The purging device for an LNG pipeline according to claim 7, characterized in that: The second regulating valve is an electrically controlled valve.

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