A methanol pipeline repair replacement system and method

Abstract

The application discloses a methanol pipeline overhaul replacement system and method, which comprises a pipeline conveying system, a movable pigging system, a high-efficiency displacement system and a residual medium safe treatment system. The application can effectively recover, empty and safely treat the medium in the methanol pipeline under the overhaul condition, ensure that no toxic and harmful gas directly enters the atmosphere during the recovery and discharge process, and achieve the purpose of high-efficiency recovery and safe discharge of methanol.

Description

Technical Field

[0001] The present invention belongs to the technical field, and in particular relates to a methanol pipeline maintenance and replacement system and method. Background Art

[0002] To address hydrogen storage and transportation challenges and enhance the value of the hydrogen energy industry, the technology for producing methanol from wind power has emerged, creating a strong demand for methanol storage and transportation technology. Methanol can be used as a hydrogen carrier for efficient storage and transportation, and can be converted into hydrogen or directly utilized for energy conversion or industrial applications. Transporting methanol via pipelines is an effective means of achieving planned medium- and long-distance transportation.

[0003] Because methanol is toxic, corrosive, and flammable, methanol pipeline transportation carries risks such as combustion and toxic spread after leakage. In conventional hydrocarbon pipeline transportation, periodic in-line inspections are key to effectively diagnosing the pipeline's internal condition, and external maintenance also requires regular performance. When an abnormality occurs in the pipeline itself, the target section must be maintained and replaced. This means shutting down the pipeline and clearing the medium within that section to provide space for inspection.

[0004] Due to methanol's toxicity, flammability, lack of phase change during pressure reduction, and slow vaporization, venting methanol pipelines requires considerations such as rapid internal medium drainage, safe disposal of residual medium, and efficient pipeline replacement. Furthermore, pipeline shutdowns significantly impact medium transport, necessitating efficient venting. Existing publicly available technologies lack solutions to these challenges. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a methanol pipeline maintenance and replacement system and method, which can efficiently, economically and safely implement the medium discharge and treatment of the methanol pipeline under the shutdown maintenance condition.

[0006] The object of the present invention is achieved through the following technical solutions:

[0007] A methanol pipeline maintenance and replacement system, the system comprising:

[0008] A pipeline transportation system, comprising an upstream station pipeline, a trunk pipeline, and a downstream station pipeline from upstream to downstream. The upstream station pipeline and the downstream station pipeline are respectively provided with a shut-off valve for providing a trunk transportation channel for the methanol pipeline to connect the upstream supply side and the downstream consumption side. The pipeline transportation system also includes a bypass and a bypass shut-off valve provided in each pipeline for providing a medium flow channel for pipeline maintenance and pigging, and is cooperatively connected to a movable pigging system to provide medium recovery and displacement in the trunk line;

[0009] A pigging system, comprising a ball launching tube pipeline located upstream and a ball collecting tube pipeline located downstream, for recovering and displacing the medium in the trunk line when the trunk line needs maintenance;

[0010] A displacement system, comprising a gas displacement pipeline and a nitrogen supply system, for displacing methanol in the trunk pipeline with natural gas under pressure before pipeline maintenance, and further displacing the natural gas in the trunk pipeline after the displacement with nitrogen;

[0011] The residual medium safety treatment system is arranged in the downstream pipeline bypass and is used to safely treat the natural gas-methanol mixture remaining in the pipeline after the main line is displaced.

[0012] Furthermore, the pipeline transportation system includes a trunk upstream shut-off valve provided in the pipeline in the upstream station and a trunk downstream shut-off valve provided in the pipeline in the downstream station. The bypass includes an upstream bypass and a downstream bypass. The upstream bypass is provided with an upstream bypass regulating valve, and the downstream bypass is provided with a downstream bypass shut-off valve. The outlet of the ball launching tube pipeline is connected to the trunk pipeline through the upstream cleaning shut-off valve. A downstream cleaning first shut-off valve and a downstream cleaning second shut-off valve are sequentially provided in series between the trunk pipeline and the inlet of the ball receiving tube pipeline. A ball receiving tube pipeline bypass regulating valve is also connected in parallel at both ends of the downstream cleaning second shut-off valve.

[0013] Furthermore, the ball launching tube pipeline includes a movable ball launching tube, the movable ball launching tube is equipped with a ball launching tube balancing valve, and the pipeline between the ball launching tube outlet and the upstream pigging cut-off valve is further connected to a branch including a ball launching tube replacement valve;

[0014] The ball collecting drum pipeline includes a movable ball collecting drum, which is equipped with a ball collecting drum replacement valve. The ball collecting drum is connected to the downstream bypass shut-off valve through a pig regulating valve.

[0015] Furthermore, the gas replacement pipeline includes a natural gas storage tank, a natural gas regulating valve, a natural gas heat exchanger and a natural gas replacement shut-off valve connected in sequence, and the other end of the natural gas replacement shut-off valve is connected to the upstream bypass;

[0016] The nitrogen supply system is connected to the upstream bypass through a nitrogen replacement shut-off valve.

[0017] Furthermore, the residual medium safety treatment system includes a treatment system shutoff valve, one end of the treatment system shutoff valve is connected to the downstream bypass, and the other end is connected to one end of the venting separator tank, and the other end of the venting separator tank is connected to the venting torch.

[0018] Furthermore, the system also includes a data observation system, which includes pressure monitoring equipment and temperature monitoring equipment installed in the pipeline of the upstream station, pressure monitoring equipment and temperature monitoring equipment installed in the pipeline of the downstream station, and a pipe cleaning pipeline flow transmitter installed at the inlet of the ball collecting cylinder.

[0019] On the other hand, the present invention also provides a methanol pipeline maintenance and replacement method, which is implemented based on any of the aforementioned maintenance and replacement systems, and includes:

[0020] Step A: During normal transportation, methanol enters the trunk pipeline after being pressurized by the upstream station and is transported to the downstream station in the liquid phase. Before the pipeline is inspected and repaired, the shut-off valves of the upstream and downstream station pipelines are closed, and the operating pressures of the upstream and downstream station pipelines are continuously monitored;

[0021] Step B: After the pipeline is shut down, connect the pigging system and displacement system to the pipeline transportation system, place a pigging ball in the launch tube pipeline, start the nitrogen supply system to continuously replace the air in the launch tube pipeline with nitrogen until the oxygen content in the air-nitrogen mixture is lower than the preset percentage, stop nitrogen injection, and introduce methanol from the upstream station to displace nitrogen, and then close the launch tube pipeline;

[0022] Similarly, nitrogen is replaced in the ball collecting tube pipeline until the oxygen content in the air-nitrogen mixed medium is lower than the preset percentage;

[0023] Utilize the methanol in the pipelines of the upstream and downstream stations to increase the pressure of the ball launcher and ball receiver pipelines through the bypass, so that the pressure at the highest point along the pipeline during the subsequent displacement process does not fall below the preset pressure threshold;

[0024] Step C: Start the pigging system and displacement system to displace the methanol medium in the trunk pipeline. During the displacement process, monitor the inlet pressure of the ball collecting drum pipeline, control the fluid velocity within the preset velocity range, and introduce the displaced medium in the trunk pipeline into the residual medium safety treatment system;

[0025] Step D: Reduce the medium pressure in the trunk pipeline to normal pressure, and displace the methanol in the trunk pipeline with natural gas. When the methanol concentration is lower than the preset methanol concentration percentage, stop displacing the methanol with natural gas, and displace the natural gas in the pipeline with nitrogen until the methane concentration is lower than the preset methane concentration percentage. End the nitrogen displacing natural gas.

[0026] Furthermore, the preset percentage of oxygen content is 1%, the preset percentage of methanol concentration is 1%, and the preset percentage of methane concentration is 1%.

[0027] Furthermore, the preset pressure threshold is 0.6 MPa.

[0028] Furthermore, the preset speed range is 2 m / s.

[0029] The beneficial effects of the present invention are:

[0030] (1) The present invention takes into account the chemical value, toxicity, phase change characteristics and other characteristics of methanol medium, and rationally considers the medium discharge problem of methanol pipeline before maintenance, and proposes a complete set of safe recovery and treatment measures. By setting up a reserved movable cleaning system, an efficient displacement system, and a residual medium safety treatment system, the system optimization and simplification during normal operation of the methanol pipeline are guaranteed, and by temporarily adding a movable cleaning system, an efficient displacement system, and a residual medium safety treatment system before maintenance is required, the efficient collection of methanol medium in the pipeline and the safe treatment of residual medium are achieved, which is both safe and economical. Furthermore, in order to solve the problem of high-point vaporization of methanol during pipeline transportation and the "interruption and bridging water hammer" that may be caused by it, it is overcome by actively increasing the high-point displacement pressure and controlling the displacement speed. In order to solve the problem of methanol toxicity, a multi-stage replacement scheme is set up to avoid direct discharge of methanol gas.

[0031] (2) Based on the frequency of planned maintenance, the present invention sets up a movable pipe cleaning system, an efficient displacement system, and a residual medium safety treatment system, which reflects the advantage of low cost in terms of engineering investment. In addition, the above-mentioned movable system has no special material requirements and can be replaced by similar devices of pipeline systems for other transport media. In view of the economic efficiency of methanol, an active methanol recovery mode is proposed. Through isolation by a pipe cleaning device, most of the methanol stored in the pipeline can be recovered. In addition, in order to increase the methanol recovery rate and reduce the time for emptying methanol in the pipeline, an efficient displacement system with natural gas pressure displacement is set up. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of a methanol pipeline maintenance and replacement system according to an embodiment of the present invention.

[0033] Illustrations: 1-upstream station pipeline, 2-upstream main line shut-off valve, 3-main line pipeline, 4-downstream main line shut-off valve, 5-downstream station pipeline, 6-upstream main line pressure transmitter, 7-upstream main line temperature transmitter, 8-downstream main line pressure transmitter, 9-downstream main line temperature transmitter, 10-upstream bypass regulating valve, 11-downstream bypass shut-off valve, 12-upstream pigging shut-off valve, 13-downstream pigging first shut-off valve, 14-downstream pigging second shut-off valve, 15-bypass regulating valve, 2 1- Removable ball launching cylinder, 22- Ball launching cylinder balancing valve, 23- Ball launching cylinder replacement valve, 24- Removable ball receiving cylinder, 25- Ball receiving cylinder replacement valve, 26- Pigging regulating valve, 27- Pigging pipeline flow transmitter, 31-CNG (compressed natural gas) storage tank, 32-CNG regulating valve, 33-CNG heat exchanger, 34- Natural gas replacement shut-off valve, 35- Nitrogen supply system, 36- Nitrogen replacement shut-off valve, 41- Treatment system shut-off valve, 42- Venting separator tank, 43- Venting flare. DETAILED DESCRIPTION

[0034] The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. The details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other unless they conflict.

[0035] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work shall fall within the scope of protection of the present invention.

[0036] Due to methanol's toxicity, flammability, lack of phase change during pressure reduction, and slow vaporization, venting methanol pipelines requires considerations such as rapid internal medium drainage, safe disposal of residual medium, and efficient pipeline replacement. Furthermore, pipeline shutdowns significantly impact medium transport, necessitating efficient venting. Existing publicly available technologies lack solutions to these challenges.

[0037] In order to solve the above technical problems, the following embodiments of a methanol pipeline maintenance and replacement system and method of the present invention are proposed.

[0038] Example 1

[0039] Reference Figure 1 ,like Figure 1The figure shows a schematic diagram of the methanol pipeline maintenance and replacement system of this embodiment. The system includes an upstream station pipeline 1, a trunk upstream block valve 2, a trunk pipeline 3, a trunk downstream block valve 4, a downstream station pipeline 5, an upstream trunk pressure transmitter 6, an upstream trunk temperature transmitter 7, a downstream trunk pressure transmitter 8, a downstream trunk temperature transmitter 9, an upstream bypass regulating valve 10, a downstream bypass block valve 11, an upstream pigging block valve 12, a downstream pigging first block valve 13, a downstream pigging second block valve 14, a bypass regulating valve 1 5. Movable ball launching cylinder 21, ball launching cylinder balancing valve 22, ball launching cylinder replacement valve 23, movable ball receiving cylinder 24, ball receiving cylinder replacement valve 25, pigging regulating valve 26, pigging pipeline flow transmitter 27, CNG storage tank 31, CNG regulating valve 32, CNG heat exchanger 33, natural gas replacement shut-off valve 34, nitrogen supply system 35, nitrogen replacement shut-off valve 36, treatment system shut-off valve 41, venting separator tank 42, venting flare 43, etc.

[0040] The upstream station pipeline 1, the trunk upstream block valve 2, the trunk pipeline 3, the trunk downstream block valve 4, the downstream station pipeline 5, the upstream trunk pressure transmitter 6, the upstream trunk temperature transmitter 7, the downstream trunk pressure transmitter 8, the downstream trunk temperature transmitter 9, the upstream bypass regulating valve 10, the downstream bypass block valve 11, the upstream pigging block valve 12, the downstream pigging first block valve 13, the downstream pigging second block valve 14, the bypass regulating valve 15, etc. constitute a pipeline transportation system, which is used to provide a trunk transportation channel for the methanol pipeline to connect the upstream supply side and the downstream consumption side; at the same time, the upstream bypass regulating valve 10, the downstream bypass block valve 11, the upstream pigging block valve 12, the downstream pigging first block valve 13, the downstream pigging second block valve 14, the bypass regulating valve 15, etc. provide a medium flow channel for pipeline maintenance and pigging, and are coordinated with the movable pigging system to provide medium recovery and displacement functions in the trunk line.

[0041] Specifically, in the system shown, the upstream station pipeline 1, the trunk upstream shut-off valve 2, the trunk pipeline 3, the trunk downstream shut-off valve 4, and the downstream station pipeline 5 are all made of carbon steel and are used to provide a flow channel for normal methanol transportation. The trunk upstream shut-off valve 2 and the trunk downstream shut-off valve 4 have an emergency shut-off function; the upstream trunk pressure transmitter 6 and the upstream trunk temperature transmitter 7 are arranged downstream of the trunk upstream shut-off valve 2, and are used to detect the starting pressure and temperature parameters of the trunk pipeline 3 in real time, and are also used in this area during subsequent pipe cleaning and replacement processes. Point parameter detection; the downstream trunk pressure transmitter 8 and the downstream trunk temperature transmitter 9 are arranged upstream of the downstream shut-off valve 4 of the trunk line, and are used to detect the end point pressure and temperature parameters of the trunk pipeline 3 in real time, and are also used for point parameter detection in this area during the subsequent cleaning and replacement process; the upstream bypass regulating valve 10 is arranged on the bypass upstream of the upstream shut-off valve 2 of the trunk line, one end of which is connected to the branch pipe and the other end is connected to the blind flange. It is normally closed and manually adjustable. It is opened before the medium displacement of the trunk pipeline 3, and is used to send gas from the pipeline 1 in the upstream station to the movable The cylinder 21 provides methanol for displacing nitrogen; the downstream bypass shut-off valve 11 is set on the branch pipe downstream of the trunk downstream shut-off valve 4, and the other end is a blind flange, normally closed, manual carbon steel ball valve, which is used to open when the trunk pipeline 3 is displaced, providing a channel for methanol in the trunk pipeline 3 to flow into the downstream station pipeline 5; the upstream pigging shut-off valve 12 is set on the pigging branch of the upstream station, one end of which is connected with a blind flange for connecting to the movable pigging system, normally closed, manual ball valve; the downstream pigging first shut-off valve 13 and the downstream pigging second shut-off valve 14 are set in sequence The pigging branch at the downstream station is normally closed and has a manual ball valve; the branch where the upstream pigging shut-off valve 12, the downstream first pigging shut-off valve 13, and the downstream second pigging shut-off valve 14 are located is directly connected to the main pipeline 3, and is used to provide a path for the pigging ball to pass through; the bypass regulating valve 15 is arranged in the bypass of the downstream second pigging shut-off valve 14, is normally closed, and is a manual regulating valve, one side of which is sealed with a blind flange and is replaced when the movable ball collecting cylinder is connected, and is used to provide pressurized methanol from the main pipeline 3 to the pigging ball collecting cylinder 24, and is used to establish back pressure of the pigging ball collecting cylinder 24.

[0042] It should be noted that the pipeline transportation system in this embodiment can also be applied to a long-distance methanol pipeline system with a trunk shut-off valve.

[0043] The movable ball launching cylinder 21, the ball launching cylinder balancing valve 22, the ball launching cylinder replacement valve 23, the movable ball receiving cylinder 24, the ball receiving cylinder replacement valve 25, the pigging regulating valve 26, the pigging pipeline flow transmitter 27 and the like constitute a movable pigging system, which is used to provide medium recovery and displacement operations in the trunk line when the trunk line needs to be repaired, and reasonably control the operating pressure according to the fluctuation characteristics of the pipeline to avoid the problem of medium vaporization inside the pipeline.

[0044] Specifically, in the system shown, the movable ball-launching barrel 21 is a movable ball-launching barrel skid made of carbon steel, which is used to provide a pipe cleaner launching function; the ball-launching barrel balancing valve 22 is arranged on the connecting branch line between the large barrel and the small barrel of the movable ball-launching barrel 21, which is normally closed, a manual ball valve made of carbon steel, and is temporarily opened only before the movable ball-launching barrel 21 is ready to launch the ball, and is used to connect the large barrel and the small barrel, and provide a replacement and boosting function; the ball-launching barrel replacement valve 23 is arranged on the branch line downstream (immediately adjacent) of the movable ball-launching barrel 21, which is normally closed, a carbon steel material, a manual ball valve, and is temporarily opened only before the movable ball-launching barrel 21 is ready to launch the ball, and is used for a replacement function; the movable ball-collecting barrel 24 is a movable ball-launching barrel skid made of carbon steel, and is used to provide a pipe cleaner launching function. The ball collecting cylinder replacement valve 25 is arranged on the branch pipe at the tail end of the movable ball collecting cylinder 24, which is normally closed, made of carbon steel, and is a manual ball valve, used to provide nitrogen replacement function for the air inside the movable ball collecting cylinder 24; the pipe cleaning regulating valve 26 is arranged on the branch pipe at the tail end of the movable ball collecting cylinder 24, which is normally closed, made of carbon steel, and is an electric regulating valve, used to cooperate with the CNG regulating valve 32 to adjust the medium pressure, medium flow, etc. in the trunk pipeline 3 during the process of displacing methanol; the pipe cleaning pipeline flow transmitter 27 is arranged upstream of the movable ball collecting cylinder 24, which is used to detect the medium flow during the displacement and replacement process and convert it into medium flow rate.

[0045] The CNG storage tank 31, CNG regulating valve 32, CNG heat exchanger 33, natural gas replacement shut-off valve 34, nitrogen supply system 35, nitrogen replacement shut-off valve 36, etc. constitute an efficient displacement system, which is used to displace methanol in the trunk pipeline with natural gas under pressure before pipeline maintenance, and further use nitrogen to displace the natural gas in the trunk pipeline after the displacement.

[0046] Specifically, in the system shown, the CNG storage tank 31 is a complete set of compressed natural gas supply tanks, which is used to provide compressed natural gas for displacement and purging; the CNG regulating valve 32 is an electrically controlled regulating valve, which is used to regulate the flow and pressure of compressed natural gas, and is preferably made of low-temperature carbon steel; the CNG heat exchanger 33 is arranged downstream of the natural gas pressure regulating valve 32, and is used to regulate the temperature of the pressure-regulated natural gas, including an air bath heat exchanger and an electric heater. Preferably, the outlet temperature of the air bath heat exchanger after regulation is greater than 0°C, and the outlet temperature of the electric heater after regulation is greater than 40°C, which are used for displacement and purging respectively; The natural gas shutoff valve 34, a manual ball valve, is located downstream of the CNG heat exchanger 33 and is used to connect and close the natural gas supply channel. The nitrogen supply system 35 is a small skid-mounted system that includes a nitrogen storage tank, a nitrogen regulating valve, and a small nitrogen booster system. It provides pressurized nitrogen for displacement and purging in the downstream system. The nitrogen displacement shutoff valve 36, a manual ball valve, is located downstream of the nitrogen supply system 35 and is used to connect and close the nitrogen supply channel. In one embodiment, both the CNG heat exchanger 33 and the nitrogen supply system 35 are equipped with temperature transmitters for real-time temperature monitoring after heat exchange. In one embodiment, the high-efficiency displacement system is designed as a skid for easy relocation and reuse.

[0047] The treatment system shut-off valve 41, venting separator tank 42, venting flare 43 and other components constitute a residual medium safety treatment system, which is used to safely treat the natural gas-methanol mixture remaining in the pipeline after the main line displacement, including safe combustion treatment of the natural gas-methanol gas and gas-liquid separation and recovery of the liquid methanol.

[0048] Specifically, in the illustrated system, a treatment system shutoff valve 41 is located in a bypass downstream of the pigging control valve 26. This normally closed, manual ball valve is constructed of carbon steel and is opened only during the displacement phase of the trunk pipeline 3, providing a flow path for the displaced natural gas-methanol and nitrogen-natural gas mixtures. A venting separator tank 42 is a horizontal carbon steel storage tank designed for atmospheric pressure and located downstream of the treatment system shutoff valve 41. It performs physical gravity separation of the natural gas-methanol mixture, collects the liquid methanol displaced by the natural gas, and transmits the separated natural gas to a venting flare 43. The venting flare 43, located downstream of the venting separator tank 42, safely ignites and burns the displaced natural gas-methanol mixture and serves as a venting channel for subsequent natural gas-nitrogen mixtures. In one embodiment, a mixed gas sampling port is located downstream of the venting separator tank 42 to detect the component content of the mixed gas and support displacement and replacement operations. In one embodiment, the residual medium safety treatment system is designed as a skid for easy relocation and reuse.

[0049] In this embodiment, under normal operating conditions, methanol is generally transported in the liquid phase. Given the high bubble point temperature of methanol, methanol cannot be effectively vaporized when the pipeline medium is depressurized before pipeline maintenance. Therefore, active displacement is required to recover the methanol. At the same time, due to the high economic efficiency of methanol, a movable pigging system is considered to provide isolation pigs to perform pressurized isolation displacement of methanol to improve the recovery rate. In addition, due to the toxicity and flammability of methanol, the pipeline medium (containing a certain amount of residual methanol) after displacement is purged with natural gas, and the mixture of natural gas and methanol enters the torch for combustion, achieving the purpose of safe treatment.

[0050] Although methanol has a low saturation pressure at room temperature, due to the undulating terrain that may occur during long-distance transportation, and natural gas is used to displace the methanol stored in the pipeline in this embodiment, it is necessary to avoid the problem of methanol flowing and vaporizing in the pipeline with undulating terrain. To this end, the idea of ​​natural gas pressure displacement is adopted instead of displacing methanol at normal pressure. The pigging regulating valve 26 and the CNG regulating valve 32 are installed to work together, and the high point pressure of the methanol pipeline is required to be no less than 0.6 MPa to ensure that methanol does not vaporize during the displacement process.

[0051] To safely displace and replace methanol, a strategy of isolated displacement using pigs, natural gas purge replacement, and gas-liquid separation and ignition of a natural gas-methanol mixture was employed. Specifically, using natural gas to propel the pigs to displace methanol maximizes methanol recovery. The flammability of both methanol and natural gas facilitates ignition and avoids methanol discharge contamination. Methanol escaping from both sides of the pig is gradually removed using continuous purges of high-temperature natural gas, leveraging its volatility. Finally, nitrogen is used to replace the natural gas, providing a safe maintenance environment.

[0052] Example 2

[0053] Based on the methanol pipeline maintenance and replacement device provided in the previous embodiment, this embodiment also provides a methanol pipeline maintenance and replacement method, including the following main contents:

[0054] Step 1: During normal transportation, methanol enters the trunk pipeline 3 after being pressurized by the upstream station and is transported to the downstream station through the liquid phase; before the pipeline is inspected and repaired, the trunk upstream block valve 2 and the trunk downstream block valve 4 are closed in order, and the pipeline operating pressure is continuously observed through the upstream trunk pressure transmitter 6 and the downstream trunk pressure transmitter 8; during this process, the upstream bypass regulating valve 10, the downstream bypass block valve 11, the upstream pigging block valve 12, the downstream pigging first block valve 13, the downstream pigging second block valve 14, the bypass regulating valve 15, etc. are all kept closed.

[0055] Step 2: After the pipeline is shut down, install a movable pigging system and an efficient displacement system, and complete the replacement of the pigging system; specifically, install the movable pigging system at the upstream station and the downstream station respectively; connect the movable ball launching cylinder 21, the upstream bypass regulating valve 10 and the upstream pigging shut-off valve 12, connect the movable ball collecting cylinder 24, the downstream bypass shut-off valve 11, the downstream pigging second shut-off valve 14 and the bypass regulating valve 15; connect the ball launching cylinder replacement valve 23 and the ball collecting cylinder replacement valve 25 to the temporary recovery storage tanks or systems of the upstream station and the downstream station respectively, for collecting and processing the air, air-nitrogen mixture and methanol-nitrogen mixture displaced by the ball launching cylinder and the ball collecting cylinder; put the pigging ball in the movable ball launching cylinder 21, open the nitrogen supply system 35, the nitrogen replacement shut-off valve 36, the ball launching cylinder balancing valve 22, the ball launching cylinder balancing valve 23 and the ball collecting cylinder balancing valve 25, and the ball launching cylinder balancing valve 25; The cylinder replacement valve 23 continuously replaces the air in the movable ball-issuing cylinder 21 with nitrogen, and the replacement time is preferably 5 minutes. When the oxygen content in the air-nitrogen mixed medium is sampled and detected to be lower than 1%, the replacement is stopped. In order to reduce the air resistance that may be caused by the nitrogen at the front end of the pig to the trunk pipeline 3, the nitrogen replacement shut-off valve 36 is closed, the upstream bypass regulating valve 10 is opened, and a part of methanol is introduced from the upstream station to displace the nitrogen, and the displacement time is 5 minutes; then the ball-issuing cylinder replacement valve 23 is closed; similarly, the ball-receiving cylinder replacement valve 25, the pig regulating valve 26, the processing system shut-off valve 41, etc. are opened, and nitrogen is introduced from the ball-receiving cylinder replacement valve 25 to replace the movable ball-receiving cylinder 24 with nitrogen, and the replacement time is preferably 5 minutes. When the oxygen content in the air-nitrogen mixed medium is sampled and detected to be lower than 1%, the replacement is stopped. Subsequently, the upstream bypass regulating valve 10 and the downstream bypass shut-off valve 11 are opened respectively, and the methanol in the upstream station and downstream station pipelines is used to increase the pressure of the movable ball launching cylinder 21 and the movable ball receiving cylinder 24; further, the increased pressure is determined according to the hydrostatic pressure of 0.6 MPa at the highest point along the pipeline, to ensure that the pressure at the highest point along the pipeline is not lower than 0.6 MPa during the subsequent displacement process.

[0056] Step 3: Displace the methanol medium in the trunk pipeline 3. Specifically, open the natural gas replacement shut-off valve 34, the upstream pigging shut-off valve 12, the downstream pigging first shut-off valve 13, the downstream pigging second shut-off valve 14, the pigging regulating valve 26, the downstream bypass shut-off valve 11, etc., keep the upstream bypass regulating valve 10, the bypass regulating valve 15, the processing system shut-off valve 41, etc. closed, and open the displacement path; open the CNG regulating valve 32, and introduce the high-pressure compressed natural gas (CNG) into the movable ball barrel 21 after pressure regulation and heat exchange. The temperature of the natural gas after heat exchange is not lower than 0°C, and it passes through the CNG The regulating valve 32 and the pig regulating valve 26 coordinate to control the pressure and flow of the methanol pipeline to ensure that the pressure at the highest point in the trunk pipeline 3 is not less than 0.6 MPa, and the fluid velocity is monitored and converted through the pig pipeline flow transmitter 27 to be controlled within 2 m / s. The methanol displaced by the pig ball enters the downstream station through the downstream bypass shut-off valve 11; when the pig ball enters the movable ball collecting cylinder 24, the downstream bypass shut-off valve 11 is closed, and the treatment system shut-off valve 41 is opened to introduce the medium displaced in the trunk pipeline 3 into the venting torch 43.

[0057] Step 4: Empty and replace the medium in the trunk pipeline 3. Specifically, temporarily stop the injection of upstream natural gas into the trunk pipeline 3, increase the opening of the pig regulating valve 26, and reduce the medium pressure in the trunk pipeline 3 to normal pressure; then continue to supply upstream natural gas, and promote the volatilization of residual methanol in the pipeline through continuous purge of natural gas; preferably, turn on the electric heating function of the CNG heat exchanger 33 to increase the temperature of the natural gas entering the trunk pipeline 3 (preferably 40°C); set a sampling detection port at the rear end of the venting separator 42, and when the methanol concentration is less than 1%, stop the natural gas displacement of methanol; then, use nitrogen to displace the natural gas in the pipeline, and when the methane concentration is less than 1%, stop the nitrogen displacement of natural gas.

[0058] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A methanol pipeline maintenance and replacement system, characterized in that: The system comprises: A pipeline transportation system, comprising an upstream station pipeline, a trunk pipeline, and a downstream station pipeline from upstream to downstream. The upstream station pipeline and the downstream station pipeline are respectively provided with a shut-off valve for providing a trunk transportation channel for the methanol pipeline to connect the upstream supply side and the downstream consumption side. The pipeline transportation system also includes a bypass and a bypass shut-off valve provided in each pipeline for providing a medium flow channel for pipeline maintenance and pigging, and is cooperatively connected to a movable pigging system to provide medium recovery and displacement in the trunk line; A pigging system, comprising a ball launching tube pipeline located upstream and a ball collecting tube pipeline located downstream, for recovering and displacing the medium in the trunk line when the trunk line needs maintenance; A displacement system, comprising a gas displacement pipeline and a nitrogen supply system, for displacing methanol in the trunk pipeline with natural gas under pressure before pipeline maintenance, and further displacing the natural gas in the trunk pipeline after the displacement with nitrogen; A residual medium safety treatment system, which is located in the downstream pipeline bypass and is used to safely treat the residual natural gas-methanol mixture in the pipeline after the main line is displaced; The pipeline transportation system includes a trunk upstream shut-off valve provided in the upstream station pipeline and a trunk downstream shut-off valve provided in the downstream station pipeline, the bypass includes an upstream bypass and a downstream bypass, the upstream bypass is provided with an upstream bypass regulating valve, the downstream bypass is provided with a downstream bypass shut-off valve, the outlet of the ball launching tube pipeline is connected to the trunk pipeline through the upstream pigging shut-off valve, a downstream pigging first shut-off valve and a downstream pigging second shut-off valve connected in series are sequentially provided between the trunk pipeline and the inlet of the ball receiving tube pipeline, and a ball receiving tube pipeline bypass regulating valve is further connected in parallel at both ends of the downstream pigging second shut-off valve; The ball launching tube pipeline includes a movable ball launching tube, the movable ball launching tube is equipped with a ball launching tube balancing valve, and the pipeline between the ball launching tube outlet and the upstream pigging cut-off valve is further connected to a branch line including a ball launching tube replacement valve; The ball collecting drum pipeline includes a movable ball collecting drum equipped with a ball collecting drum replacement valve, and the ball collecting drum is connected to the downstream bypass shut-off valve via a pig regulating valve; The system also includes a data observation system, which includes pressure monitoring equipment and temperature monitoring equipment installed in the pipeline of the upstream station, pressure monitoring equipment and temperature monitoring equipment installed in the pipeline of the downstream station, and a pigging pipeline flow transmitter installed at the inlet of the ball collecting drum.

2. The methanol pipeline maintenance and replacement system according to claim 1, characterized in that: The gas replacement pipeline includes a natural gas storage tank, a natural gas regulating valve, a natural gas heat exchanger and a natural gas replacement shut-off valve connected in sequence, and the other end of the natural gas replacement shut-off valve is connected to the upstream bypass; The nitrogen supply system is connected to the upstream bypass through a nitrogen replacement shut-off valve.

3. The methanol pipeline maintenance and replacement system according to claim 1, characterized in that: The residual medium safety treatment system includes a treatment system shutoff valve, one end of the treatment system shutoff valve is connected to the downstream bypass, and the other end is connected to one end of the venting separator tank, and the other end of the venting separator tank is connected to the venting torch.

4. A methanol pipeline maintenance and replacement method, characterized in that: The method is implemented based on the maintenance and replacement system according to any one of claims 1 to 3, and the method includes: Step A: During normal transportation, methanol enters the trunk pipeline after being pressurized by the upstream station and is transported to the downstream station in the liquid phase. Before the pipeline is inspected and repaired, the shut-off valves of the upstream and downstream station pipelines are closed, and the operating pressures of the upstream and downstream station pipelines are continuously monitored; Step B: After the pipeline is shut down, connect the pigging system and displacement system to the pipeline transportation system, place a pigging ball in the launch tube pipeline, start the nitrogen supply system to continuously replace the air in the launch tube pipeline with nitrogen until the oxygen content in the air-nitrogen mixture is lower than the preset percentage, stop nitrogen injection, and introduce methanol from the upstream station to displace nitrogen, and then close the launch tube pipeline; Similarly, nitrogen is replaced in the ball collecting tube pipeline until the oxygen content in the air-nitrogen mixed medium is lower than the preset percentage; Utilize the methanol in the pipelines of the upstream and downstream stations to increase the pressure of the ball launcher and ball receiver pipelines through the bypass, so that the pressure at the highest point along the pipeline during the subsequent displacement process does not fall below the preset pressure threshold; Step C: Start the pigging system and displacement system to displace the methanol medium in the trunk pipeline. During the displacement process, monitor the inlet pressure of the ball collecting drum pipeline, control the fluid velocity within the preset velocity range, and introduce the displaced medium in the trunk pipeline into the residual medium safety treatment system; Step D: Reduce the medium pressure in the trunk pipeline to normal pressure, and displace the methanol in the trunk pipeline with natural gas. When the methanol concentration is lower than the preset methanol concentration percentage, stop displacing the methanol with natural gas, and displace the natural gas in the pipeline with nitrogen until the methane concentration is lower than the preset methane concentration percentage. End the nitrogen displacing natural gas.

5. A methanol pipeline repair and replacement method according to claim 4, characterized in that: The preset percentage of the oxygen content is 1%, the preset percentage of the methanol concentration is 1%, and the preset percentage of the methane concentration is 1%.

6. A methanol pipeline repair and replacement method according to claim 4, characterized in that: The preset pressure threshold is 0.6 MPa.

7. A methanol pipeline repair and replacement method according to claim 4, characterized in that: The preset speed range is 2 m / s.

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