A system and method for purging and replacing a pump barrel and outlet piping of an LNG low pressure pump

Abstract

This invention provides a purging and replacement system and method for an LNG low-pressure pump barrel and outlet pipeline, relating to the field of LNG pipeline purging and replacement technology. The system includes: a low-pressure pump, comprising a pump barrel with a bottom valve at the bottom; an outlet pipeline connected at both ends to the pump barrel and a discharge pipeline, with an outlet shut-off valve installed on the outlet pipeline; a blind flange detachably mounted on the outlet pipeline at a pipeline flange downstream of the outlet shut-off valve; a monitoring assembly including a metal hose and a local pressure gauge mounted on the metal hose, one end of the metal hose connected to a pipeline drain valve between the outlet shut-off valve and the blind flange, and the other end connected to the discharge pipeline; and a nitrogen injection unit connected to the pump barrel and outlet pipeline via a nitrogen quick-connect fitting for injecting nitrogen into the system for purging and replacement. This method utilizes this system to determine the LNG discharge status within the pump barrel by observing changes in the local pressure gauge pointer. This invention saves nitrogen consumption and improves purging efficiency through segmented purging.

Description

Technical Field

[0001] This invention relates to the field of LNG pipeline purging and replacement technology, and in particular to a purging and replacement system and method for an LNG low-pressure pump barrel and outlet pipeline. Background Technology

[0002] Before performing preventive maintenance on the low-pressure pump, it is necessary to drain the LNG from the pump barrel and outlet pipeline, purge and replace the BOG (Boil-Off Gas) to ensure it is up to standard, and install a blind flange on the outlet pipeline. The purging methods previously used include: ① lifting the low-pressure pump and closing the bottom valve of the pump barrel; ② using nitrogen to drain the LNG from the pump barrel and outlet pipeline; ③ replacing the natural gas in the pump barrel and outlet pipeline with nitrogen; ④ installing a blind flange at the outlet of the low-pressure pump after the replacement is up to standard.

[0003] The above purging method has the following shortcomings: 1. It is difficult to determine whether the LNG in the low-pressure pump barrel has been completely discharged; 2. Incomplete LNG discharge from the pump cylinder requires multiple purgings to achieve satisfactory replacement, resulting in high workload for personnel and large nitrogen consumption.

[0004] Therefore, there is an urgent need for a purging and replacement system and method for the LNG low-pressure pump barrel and outlet pipeline to solve the above-mentioned technical problems. Summary of the Invention

[0005] The purpose of this invention is to provide a purging and replacement system and method for the pump cylinder and outlet pipeline of an LNG low-pressure pump, to solve the technical problems in the prior art, such as the difficulty in determining whether the LNG in the pump cylinder has been completely discharged, the need for multiple purgings to achieve qualified replacement due to incomplete LNG discharge, high labor intensity for personnel, and large nitrogen consumption. The various technical effects of the preferred technical solutions provided by this invention are detailed below.

[0006] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a purging and replacement system for an LNG low-pressure pump barrel and outlet pipeline, comprising: A low-pressure pump, including a pump barrel, wherein a bottom valve is provided at the bottom of the pump barrel; An outlet pipe is connected at both ends to the pump cylinder and the discharge pipe, respectively, and an outlet shut-off valve is installed on the outlet pipe; A blind flange is detachably installed on the outlet pipe at the pipe flange downstream of the outlet shut-off valve. The monitoring component includes a metal hose and a local pressure gauge mounted on the metal hose, one end of the metal hose being connected to a drain valve between the outlet shut-off valve and the blind plate, and the other end being connected to the discharge pipeline; The nitrogen injection unit is connected to the pump cylinder and the outlet pipe via a nitrogen quick connector and is used to inject nitrogen into the system for purging and replacement.

[0007] Furthermore, the nitrogen injection unit includes a nitrogen pipeline, and a ball valve and a check valve disposed on the nitrogen pipeline, wherein the check valve is located between the ball valve and the nitrogen quick connector.

[0008] Furthermore, the discharge pipeline includes a TSV valve and a TSV valve bypass ball valve, and the outlet end of the TSV valve is provided with a TSV valve outlet drain valve, and the other end of the metal hose is connected to the TSV valve outlet drain valve.

[0009] Furthermore, the system also includes a return pipeline, on which an FV valve and an FV valve bypass valve connected in parallel are installed. One end of the return pipeline is connected to the outlet pipeline, and the other end is connected to the LNG storage tank.

[0010] Furthermore, a pressure gauge and a temperature gauge are also installed on the outlet pipe to monitor the pressure and temperature inside the outlet pipe.

[0011] Furthermore, the metal hose is a metal-armored hose.

[0012] Furthermore, the range of the local pressure gauge is 0-0.5 bar.

[0013] Secondly, the present invention provides a purging and replacement method for the pump barrel and outlet pipeline of an LNG low-pressure pump, utilizing the aforementioned purging and replacement system for the LNG low-pressure pump barrel and outlet pipeline, comprising the following steps: S1: The low-pressure pump outlet pipeline is purged and replaced by nitrogen injection unit until the methane concentration in the exhaust gas is lower than the predetermined safety threshold multiple times in a row. S2: Install a blind flange at the pipe flange downstream of the outlet shut-off valve to physically isolate the outlet pipe from the pump cylinder; S3: The pump cylinder is drained and purged by the nitrogen injection unit. During this process, the discharge status of LNG in the pump cylinder is determined by the change of the pointer of the local pressure gauge on the monitoring component. S4: Continue purging the pump barrel until the methane concentration in the exhaust gas is below the predetermined safety threshold multiple times in a row.

[0014] Furthermore, in step S3, determining the LNG discharge status in the pump cylinder specifically means that when the pointer of the local pressure gauge changes from periodic oscillation to continuous oscillation, it indicates that the LNG in the pump cylinder has been basically discharged.

[0015] Furthermore, the predetermined safety threshold is 1%vol.

[0016] The purging and replacement system for the LNG low-pressure pump barrel and outlet pipeline provided by this invention features an outlet pipeline with both ends connected to the pump barrel of the low-pressure pump and the discharge pipeline, respectively. An outlet shut-off valve is installed on the outlet pipeline, and a blind flange is detachably installed on the outlet pipeline at the pipeline flange downstream of the outlet shut-off valve. The cooperation between the outlet shut-off valve and the blind flange enables physical isolation between the outlet pipeline and the pump barrel, facilitating segmented purging during the purging and replacement process. The monitoring components include a flexible metal hose and a local pressure gauge mounted on the hose. One end of the flexible metal hose is connected to a drain valve between the outlet shut-off valve and the blind flange, and the other end is connected to the discharge pipeline. The fluctuation of the local pressure gauge pointer provides a clear and visual basis for determining whether LNG has been completely discharged, avoiding the problem of nitrogen waste caused by blind purging.

[0017] The purging and replacement method for the LNG low-pressure pump barrel and outlet pipeline provided by this invention involves first independently purging and replacing the low-pressure pump outlet pipeline, and then installing a blind flange for physical isolation after passing the test; followed by draining and purging the low-pressure pump barrel. During the purging process of the pump barrel, the pointer fluctuation of the local pressure gauge connected between the pump barrel and the discharge pipeline is monitored to determine whether the liquid LNG in the pump barrel has been completely drained, thereby precisely controlling the purging process. This method adjusts the traditional method of purging the pump barrel and outlet pipeline together to segmented purging, avoiding the impact of unqualified pump barrel purging on the purging effect of the outlet pipeline. The purging time is reduced by 2 / 3 compared to previous methods, nitrogen consumption is reduced by 2 / 3, and the LNG discharge status in the pump barrel can be quickly determined by the added local pressure gauge, avoiding prolonged purging and nitrogen waste caused by incomplete BOG discharge from the pump barrel. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of an embodiment of the purging and replacement system for the LNG low-pressure pump barrel and outlet pipeline of the present invention.

[0020] In the diagram: 1. Ball valve; 2. Check valve; 3. Low-pressure pump; 4. Foot valve; 5. Outlet shut-off valve; 6. Blind flange; 7. Nitrogen quick connector; 8. FV valve; 9. FV valve bypass valve; 10. Outlet pipeline; 11. Nitrogen pipeline; 12. Local pressure gauge; 13. Pipeline drain valve; 14. Metal hose; 15. TSV valve outlet drain valve; 16. XV valve; 17. TSV valve; 18. XV valve bypass ball valve; 19. TSV valve bypass ball valve; 20. Pressure gauge; 21. Thermometer. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0022] In the description of this invention, it should be understood that the terms "center," "side," "length," "width," "height," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and "side," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0023] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0024] Figure 1 This is a structural schematic diagram of this embodiment, as shown below. Figure 1 As shown, this embodiment provides a purging and replacement system for an LNG low-pressure pump barrel and outlet pipeline, including a low-pressure pump 3, an outlet pipeline 10, a blind flange 6, a monitoring component, and a nitrogen injection unit.

[0025] The low-pressure pump 3 includes a pump casing with a bottom valve 4 at its bottom. The two ends of the outlet pipe 10 are connected to the pump casing and the discharge pipe, respectively, and an outlet shut-off valve 5 is installed on the outlet pipe 10. A blind flange 6 is detachably installed on the outlet pipe 10 at the pipe flange downstream of the outlet shut-off valve 5. By installing the outlet shut-off valve 5 on the outlet pipe 10 and the blind flange 6 at the pipe flange downstream of the outlet shut-off valve 5, physical isolation between the outlet pipe 10 and the pump casing is achieved, facilitating segmented purging during the purging and replacement process.

[0026] The monitoring component includes a metal hose 14 and a local pressure gauge 12 mounted on the metal hose 14. One end of the metal hose 14 is connected to the drain valve 13 between the outlet shut-off valve 5 and the blind flange 6, and the other end is connected to the discharge pipeline. During operation, the pressure changes inside the pump cylinder can be monitored in real time through the metal hose 14 connected to the drain valve 13 between the outlet shut-off valve 5 and the blind flange 6, and the local pressure gauge 12 is connected to the metal hose 14 to determine the LNG discharge status.

[0027] In this embodiment, the metal hose 14 is a metal-armored hose, which has excellent low-temperature resistance and pressure resistance, enabling it to adapt to the low-temperature operating conditions of the LNG system. It is also less prone to wear and has a long service life, improving the system's reliability and safety. For the low-pressure conditions during the pump purging process, the local pressure gauge in this embodiment has a range of 0-0.5 bar, making it more sensitive to minute pressure changes and able to clearly capture periodic and continuous pointer oscillations, thus improving the accuracy of determining the LNG discharge status.

[0028] The nitrogen injection unit is connected to the pump cylinder and outlet pipe 10 via a nitrogen quick connector 7, and is used to inject nitrogen into the system for purging and replacement. In this embodiment, the nitrogen injection unit includes a nitrogen pipe 11, and a ball valve 1 and a check valve 2 installed on the nitrogen pipe 11. The ball valve 1 controls the flow of nitrogen, improving operational safety and reliability. Simultaneously, placing the check valve 2 between the ball valve 1 and the nitrogen quick connector effectively prevents LNG or BOG from flowing back into the nitrogen pipe 11, further avoiding safety accidents and ensuring safe operation.

[0029] As an optional implementation, the discharge pipeline includes a TSV valve 17 and a TSV valve bypass ball valve 19. A TSV valve outlet drain valve 15 is installed at the outlet end of the TSV valve 17, and the other end of the metal hose 14 is connected to the TSV valve outlet drain valve 15. By connecting the other end of the metal hose 14 to the TSV valve outlet drain valve 15, the existing TSV valve discharge pipeline is used as the discharge channel for the purge gas, eliminating the need for additional discharge pipeline installation. Simultaneously, the TSV valve bypass ball valve 19 facilitates manual control of the discharge process, combining an automatic safety valve with a manually operated valve.

[0030] As an optional implementation, the system also includes a return pipeline, on which an FV valve 8 and an FV valve bypass valve 9 connected in parallel are installed. One end of the return pipeline is connected to the outlet pipeline, and the other end is connected to the LNG storage tank. By installing an FV valve and its parallel FV valve bypass valve on the return pipeline, it can be used for the cooling circulation of the low-pressure pump under normal operating conditions. Before purging operations, the return channel can be cut off by closing the FV valve and its bypass valve to ensure that the purging medium does not enter the storage tank and interfere with other equipment, thereby improving the system's independence and operational flexibility.

[0031] As an optional implementation, a pressure gauge 20 and a temperature gauge 21 are also installed on the outlet pipe 10 to monitor the pressure and temperature within the outlet pipe 10. This provides data support for operators to assess the pipe status and control the purging process, avoiding safety risks caused by excessive pressure or abnormal temperature.

[0032] Optionally, the outlet pipeline 10 is also equipped with an XV valve 16 and an XV valve bypass ball valve 18 connected in parallel with the XV valve 16. The XV valve 16 and the XV valve bypass ball valve 18 are pneumatically operated remote-controlled shut-off valves, which can be quickly opened and closed by accepting remote control signals. Under normal operating conditions, they work in conjunction with TSV valves to control the LNG transport path; under maintenance conditions, before purging and replacement, the XV valve 16 and the XV valve bypass ball valve 18 must be closed to interrupt the low-pressure pump cooling cycle, allowing the pipeline temperature to naturally rise to above 0°C in preparation for subsequent purging.

[0033] This embodiment also provides a purging and replacement method for the LNG low-pressure pump barrel and outlet pipeline, which utilizes the aforementioned purging and replacement system for the LNG low-pressure pump barrel and outlet pipeline, and includes the following steps: S1: The low-pressure pump outlet pipe 10 is purged and replaced by a nitrogen injection unit until the methane concentration in the exhaust gas is lower than a predetermined safety threshold for multiple consecutive times; in this embodiment, the predetermined safety threshold is 1% vol, and "multiple times" means no less than 3 times.

[0034] S2: Install a blind flange 6 at the pipe flange downstream of the outlet shut-off valve 5 to physically isolate the outlet pipe 10 from the pump cylinder.

[0035] S3: The pump cylinder is drained and purged by the nitrogen injection unit. During this process, the discharge status of LNG in the pump cylinder is determined by the change of the pointer of the local pressure gauge 12 on the monitoring component. Specifically, the discharge status of LNG in the pump cylinder is determined when the pointer of the local pressure gauge changes from periodic swing to continuous swing, indicating that the LNG in the pump cylinder has been basically discharged.

[0036] S4: Continue purging the pump barrel until the methane concentration in the exhaust gas falls below a predetermined safety threshold multiple times consecutively. In this embodiment, the predetermined safety threshold is 1% vol.

[0037] Specifically, the purging and replacement method for the LNG low-pressure pump barrel and outlet pipeline includes the following two stages in actual operation: The first stage involves purging the LNG low-pressure pump outlet pipeline, including the following steps: Close the bypass ball valve 18 of the low-pressure pump outlet XV valve to interrupt the low-pressure pump cooling cycle during low-pressure pump maintenance, thereby causing the pipeline temperature to start to rise. When the temperature of the LNG pipeline temperature gauge 21 at the low-pressure pump outlet rises to >0℃, close the low-pressure pump outlet shut-off valve 5, cut off the gas path of FV valve 8 on the return line to ensure that FV valve 8 is closed, and close the FV valve bypass valve 9. Lift the low-pressure pump 3 to close the low-pressure pump bottom valve 4; Nitrogen is injected through nitrogen quick connector 7 to replace the BOG gas in the low-pressure pump outlet pipeline. When the pressure on pipeline pressure gauge 20 reaches 0.1 bar, nitrogen injection is stopped, and the gas is discharged to the storage tank through TSV valve bypass ball valve 19. The purging is repeated, and the methane concentration in the gas is detected at the designated sampling point on the discharge pipeline (such as TSV valve outlet drain valve 15) until three consecutive test results are all below 1% vol (meeting the relevant safety operation requirements).

[0038] After the pressure relief is completed, a blind flange 6 is installed at the pipeline flange downstream of the low-pressure pump outlet shut-off valve 5. The low-pressure pump barrel is effectively isolated from the outlet pipeline, creating conditions for the next stage of separate purging of the pump barrel.

[0039] The second stage involves purging the low-pressure pump barrel, which includes the following steps: A local pressure gauge 12 with a range of 0.5 bar is installed at the LNG pipeline drain valve 13 between the low-pressure pump outlet shut-off valve 5 and the blind plate 6, and is connected to the LNG pipeline drain valve 13 and the TSV valve outlet drain valve 15 through a metal-clad hose. Open the low-pressure pump outlet shut-off valve 5; Open the nitrogen injection ball valve 1 on the low-pressure pump cylinder to inject nitrogen gas to discharge LNG from the low-pressure pump cylinder. Observe the local pressure gauge 12. When its pointer changes from periodic swinging to continuous swinging, it indicates that the LNG in the pump cylinder has been basically discharged. The working principle is as follows: When there is LNG in the pump cylinder, the LNG acts as a sealing "plug" to seal the pump cylinder. After nitrogen gas is injected into the pump cylinder, the pressure gradually increases. When all the LNG in the pump cylinder is discharged into the storage tank through the low-pressure pump bottom valve 4, it is equivalent to the sealing "plug" of the pump cylinder being pulled out. The pump cylinder seal is lost, and the pressure in the pump cylinder drops instantly. The local pressure gauge 12 swings violently. Repeat the above operation, and the local pressure gauge 12 will produce periodic swings. When the pointer of the local pressure gauge 12 swings continuously, it indicates that the LNG in the pump cylinder has been basically discharged.

[0040] Close the nitrogen injection valve, and discharge the residual BOG and nitrogen in the pump cylinder to the storage tank through the connected metal armored pipe via the TSV valve outlet drain valve 15. Repeat the operation multiple times, and test the methane concentration in the gas at the designated sampling point on the discharge pipeline (such as the TSV valve outlet drain valve 15) until the results of three consecutive tests are all below 1%vol (meeting the relevant safety operation requirements).

[0041] By adopting the above-mentioned purging and replacement method for the LNG low-pressure pump cylinder and outlet pipeline, the traditional method of purging the pump cylinder and outlet pipeline together is changed to segmented purging. This avoids the purging effect of the outlet pipeline being affected by the unqualified purging of the pump cylinder. The purging time is reduced by 2 / 3 compared with the previous method, and the nitrogen consumption is reduced by 2 / 3. Furthermore, the LNG discharge status in the pump cylinder can be quickly determined by the added local pressure gauge 12, avoiding the long purging time and nitrogen waste caused by the incomplete discharge of BOG in the pump cylinder.

[0042] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A purging and replacement system for the pump barrel and outlet pipeline of an LNG low-pressure pump, characterized in that... ,include: A low-pressure pump, including a pump barrel, wherein a bottom valve is provided at the bottom of the pump barrel; An outlet pipe is connected at both ends to the pump cylinder and the discharge pipe, respectively, and an outlet shut-off valve is installed on the outlet pipe; A blind flange is detachably installed on the outlet pipe at the pipe flange downstream of the outlet shut-off valve. The monitoring component includes a metal hose and a local pressure gauge mounted on the metal hose, one end of the metal hose being connected to a drain valve between the outlet shut-off valve and the blind plate, and the other end being connected to the discharge pipeline; The nitrogen injection unit is connected to the pump cylinder and the outlet pipe via a nitrogen quick connector and is used to inject nitrogen into the system for purging and replacement.

2. The purging and replacement system for the LNG low-pressure pump casing and outlet pipeline according to claim 1, characterized in that: The nitrogen injection unit includes a nitrogen pipeline, and a ball valve and a check valve disposed on the nitrogen pipeline, wherein the check valve is located between the ball valve and the nitrogen quick connector.

3. The purging and replacement system for the LNG low-pressure pump casing and outlet pipeline according to claim 1, characterized in that: The discharge pipeline includes a TSV valve and a TSV valve bypass ball valve. The outlet end of the TSV valve is provided with a TSV valve outlet drain valve, and the other end of the metal hose is connected to the TSV valve outlet drain valve.

4. The purging and replacement system for the LNG low-pressure pump casing and outlet pipeline according to claim 1, characterized in that: The system also includes a return pipeline, which is equipped with an FV valve and an FV valve bypass valve connected in parallel with the FV valve. One end of the return pipeline is connected to the outlet pipeline, and the other end is connected to the LNG storage tank.

5. The purging and replacement system for the LNG low-pressure pump casing and outlet pipeline according to claim 1, characterized in that: The outlet pipe is also equipped with a pressure gauge and a thermometer to monitor the pressure and temperature inside the outlet pipe. And / or, the outlet pipe is equipped with an XV valve and an XV valve bypass ball valve connected in parallel with the XV valve.

6. The purging and replacement system for the LNG low-pressure pump casing and outlet pipeline according to claim 1, characterized in that: The metal hose is a metal-armored hose.

7. The purging and replacement system for the LNG low-pressure pump casing and outlet pipeline according to claim 1, characterized in that: The range of the local pressure gauge is 0-0.5 bar.

8. A purging and replacement method for the pump barrel and outlet pipeline of an LNG low-pressure pump, characterized in that... The purging and replacement system for the LNG low-pressure pump barrel and outlet pipeline according to any one of claims 1-7 includes the following steps: S1: The low-pressure pump outlet pipeline is purged and replaced by nitrogen injection unit until the methane concentration in the exhaust gas is lower than the predetermined safety threshold multiple times in a row. S2: Install a blind flange at the pipe flange downstream of the outlet shut-off valve to physically isolate the outlet pipe from the pump cylinder; S3: The pump cylinder is drained and purged by the nitrogen injection unit. During this process, the discharge status of LNG in the pump cylinder is determined by the change of the pointer of the local pressure gauge on the monitoring component. S4: Continue purging the pump barrel until the methane concentration in the exhaust gas is below the predetermined safety threshold multiple times in a row.

9. The purging and replacement method for the LNG low-pressure pump casing and outlet pipeline according to claim 8, characterized in that... In step S3, determining the LNG discharge status in the pump cylinder specifically means that when the pointer of the local pressure gauge changes from periodic oscillation to continuous oscillation, it indicates that the LNG in the pump cylinder has been basically discharged.

10. The purging and replacement method for the LNG low-pressure pump casing and outlet pipeline according to claim 8, characterized in that, The predetermined safety threshold is 1%vol.

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