Methanol pipeline maintenance and replacement system and method

Abstract

The invention discloses a methanol pipeline maintenance and replacement system and method. The system comprises a pipeline conveying system, a movable pipe cleaning system, an efficient displacement system and a residual medium safety treatment system. According to the invention, effective recovery, emptying and safety treatment are carried out on the pipe storage medium of the methanol pipeline under the maintenance working condition, it is guaranteed that no toxic gas directly enters the atmosphere in the recovery and release process, and the purposes of efficient recovery and safe emptying of methanol are achieved.

Description

Technical Field

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

[0002] To solve the problems of hydrogen energy storage and transportation and improve the value of the hydrogen energy industry, a technical route of wind power hydrogen production and methanol synthesis has emerged, which puts forward strong requirements for methanol storage and transportation technology. Methanol can be used as a hydrogen carrier for efficient storage and transportation, and can be used for hydrogen conversion or direct utilization to achieve energy conversion or industrial applications. Methanol transportation through pipelines is an effective means to achieve planned medium- and long-distance transportation.

[0003] Due to the certain toxicity, corrosiveness and flammability of methanol, the process of methanol pipeline transportation faces risks such as combustion of the medium and diffusion of toxicity after leakage. In the pipeline transportation of conventional hydrocarbons, periodic in-pipeline detection is a key means to effectively diagnose the internal state of the pipeline, and external maintenance also needs to be carried out regularly; when abnormal conditions occur in the pipeline body, maintenance and replacement of the target pipe section are required, that is, the pipeline is shut down and the medium in this section of the pipeline is emptied to provide a maintenance space.

[0004] Due to the characteristics of methanol such as toxicity, flammability, no phase change during pressure reduction, and slow vaporization, when discharging methanol pipelines, issues such as rapid emptying of the internal medium of the pipeline, safe treatment of the residual medium, and efficient replacement of the pipeline need to be considered; at the same time, pipeline shutdown will have a greater impact on medium transportation, which poses technical requirements for efficient discharge. There is a lack of solutions to the above problems in the existing publicly disclosed technologies. Summary of the Invention

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

[0006] The purpose of the present invention is achieved by the following technical solutions:

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

[0008] A pipeline transportation system, the pipeline transportation system includes upstream station pipelines, main pipelines and downstream station pipelines from upstream to downstream. Cut-off valves are respectively provided on the upstream station pipelines and downstream station pipelines to provide a main pipeline transportation channel for the methanol pipeline to connect the upstream supply side and the downstream consumption side. The pipeline transportation system also includes bypasses and bypass cut-off valves provided on each pipeline to provide a medium flow channel for pipeline maintenance and pigging, cooperate with the connection of a movable pigging system, and provide medium recovery and displacement in the main pipeline;

[0009] Pigging system, the pigging system includes a pig launcher pipeline arranged upstream and a pig receiver pipeline arranged downstream, and is used to provide medium recovery and displacement in the main pipeline when the main pipeline needs to be overhauled;

[0010] Displacement system, the displacement system includes a gas displacement pipeline and a nitrogen supply system, and is used to perform pressure-driven displacement of methanol in the main pipeline with natural gas before pipeline overhaul, and further displace the natural gas in the main pipeline after displacement with nitrogen;

[0011] Residual medium safety treatment system, the residual medium safety treatment system is arranged on the downstream pipeline bypass and is used to safely treat the residual natural gas-methanol mixture in the pipeline after main pipeline displacement.

[0012] Furthermore, the pipeline transportation system includes an upstream main pipeline shut-off valve arranged in the upstream station pipeline and a downstream main pipeline shut-off valve arranged 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, and the downstream bypass is provided with a downstream bypass shut-off valve. The outlet of the pig launcher pipeline is connected to the main pipeline through an upstream pigging shut-off valve. Between the main pipeline and the inlet of the pig receiver pipeline, a series of downstream pigging first shut-off valve and downstream pigging second shut-off valve are arranged in sequence. A pig receiver pipeline bypass regulating valve is also connected in parallel at both ends of the downstream pigging second shut-off valve.

[0013] Furthermore, the pig launcher pipeline includes a movable pig launcher, the movable pig launcher is equipped with a pig launcher balance valve, and a branch pipe containing a pig launcher displacement valve is also connected to the pipeline between the pig launcher outlet and the upstream pigging shut-off valve;

[0014] The pig receiver pipeline includes a movable pig receiver, the movable pig receiver is equipped with a pig receiver displacement valve, and the pig receiver is connected to the downstream bypass shut-off valve through a pigging regulating valve.

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

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

[0017] Furthermore, the residual medium safety treatment system includes a treatment system shut-off valve. One end of the treatment system shut-off valve is connected to the downstream bypass, and the other end is connected to one end of a vent and liquid separation tank. The other end of the vent and liquid separation tank is connected to a vent flare.

[0018] Further, the system further includes a data observation system, which includes pressure monitoring devices and temperature monitoring devices provided in the pipelines of the upstream station, pressure monitoring devices and temperature monitoring devices provided in the pipelines of the downstream station, and a pigging pipeline flow transmitter provided at the inlet of the pig receiver.

[0019] On the other hand, the present invention also provides a method for overhaul and replacement of a methanol pipeline, which is implemented based on the overhaul and replacement system described above. The method includes:

[0020] Step A: During normal transportation, methanol enters the main pipeline after being pressurized by the upstream station yard and is transported to the downstream station yard in a liquid phase. Before the pipeline is to be overhauled, the shut-off valves of the pipelines in the upstream station and the downstream station are closed, and the operating pressures of the pipelines in the upstream station and the downstream station are continuously observed.

[0021] Step B: After the pipeline stops transporting, connect the pigging system and the displacement system to the pipeline transportation system. Place a pig in the pig launcher pipeline, and start the nitrogen supply system to continuously replace the air in the pig launcher pipeline with nitrogen until the oxygen content in the air-nitrogen mixed medium is lower than a preset percentage. Stop injecting nitrogen and introduce methanol from the upstream station yard to displace nitrogen, and then close the pig launcher pipeline.

[0022] Similarly, replace the air in the pig receiver pipeline with nitrogen until the oxygen content in the air-nitrogen mixed medium is lower than a preset percentage.

[0023] Utilize the methanol in the pipelines of the upstream station yard and the downstream station yard to increase the pressure of the pig launcher pipeline and the pig receiver pipeline through a bypass, so that the pressure at the highest point along the pipeline during the subsequent displacement process is not lower than a preset pressure threshold.

[0024] Step C: Start the pigging system and the displacement system to perform the displacement of the methanol medium in the main pipeline. During the displacement process, monitor the inlet pressure of the pig receiver pipeline, control the fluid velocity within a preset velocity range, and introduce the displaced medium in the main pipeline into the residual medium safety treatment system.

[0025] Step D: Reduce the pressure of the medium in the main pipeline to atmospheric pressure, displace the methanol in the main pipeline with natural gas, stop displacing the methanol with natural gas when the methanol concentration is lower than a preset methanol concentration percentage, and displace the natural gas in the pipeline with nitrogen until the methane concentration is lower than a preset methane concentration percentage, and then end the displacement of natural gas with nitrogen.

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

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

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

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

[0030] (1) In view of the chemical value, toxicity, phase change characteristics, etc. of methanol medium, the present invention reasonably considers the problem of medium discharge in methanol pipelines before maintenance, and proposes a complete set of safety recovery and treatment measures. By setting a reserved movable pigging system, an efficient displacement system, and a residual medium safety treatment system, the system is optimized and simplified during the normal operation of the methanol pipeline, and before maintenance, the efficient collection of methanol medium in the pipeline and the safe treatment of residual medium are realized by temporarily adding a movable pigging system, an efficient displacement system, and a residual medium safety treatment system, which has both safety and economy. Further, in view of the problem of high-point vaporization of methanol during pipeline transportation and the possible "broken flow closure water hammer" caused thereby, it is overcome by the coupling method of actively increasing the high-point displacement pressure and controlling the displacement speed. In view of the toxicity problem of methanol, by setting a multi-stage replacement scheme, the direct emptying of methanol gas is avoided.

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

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

[0033] Description of the Drawings: 1 - Pipeline in the upstream station, 2 - Upstream main line shut-off valve, 3 - Main line pipeline, 4 - Downstream main line shut-off valve, 5 - Pipeline in the downstream station, 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 - First downstream pigging shut-off valve, 14 - Second downstream pigging shut-off valve, 15 - Bypass regulating valve, 21 - Movable pig launcher, 22 - Pig launcher balance valve, 23 - Pig launcher replacement valve, 24 - Movable pig receiver, 25 - Pig receiver 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 - Drain and separator tank, 43 - Flare stack. Detailed Implementation Modes

[0034] The following specific examples illustrate the implementation modes of the present invention. Those skilled in the art can easily understand the 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 implementation modes. Various 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, without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0035] All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0036] Due to the characteristics of methanol such as toxicity, flammability, pressure reduction without phase change, and slow vaporization, when discharging the methanol pipeline, issues such as rapid emptying of the internal medium of the pipeline, safe treatment of the residual medium, and efficient replacement of the pipeline need to be considered; at the same time, pipeline shutdown will have a greater impact on the medium transportation, which poses technical requirements for efficient discharge. There is a lack of solutions to the above problems in the existing publicly disclosed technologies.

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

[0038] Embodiment 1

[0039] Refer to Figure 1 As Figure 1The figure shows a schematic diagram of the methanol pipeline maintenance and replacement system in this embodiment. The system includes the upstream station pipeline 1, the upstream trunk line shut-off valve 2, the trunk line pipeline 3, the downstream trunk line shut-off valve 4, the downstream station pipeline 5, the upstream trunk line pressure transmitter 6, the upstream trunk line temperature transmitter 7, the downstream trunk line pressure transmitter 8, the downstream trunk line temperature transmitter 9, the upstream bypass regulating valve 10, the downstream bypass shut-off valve 11, the upstream pigging shut-off valve 12, the first downstream pigging shut-off valve 13, the second downstream pigging shut-off valve 14, the bypass regulating valve 15, the movable pig launcher 21, the pig launcher balance valve 22, the pig launcher replacement valve 23, the movable pig receiver 24, the pig receiver replacement valve 25, the pigging regulating valve 26, the pigging pipeline flow transmitter 27, the CNG storage tank 31, the CNG regulating valve 32, the CNG heat exchanger 33, the natural gas replacement shut-off valve 34, the nitrogen supply system 35, the nitrogen replacement shut-off valve 36, the treatment system shut-off valve 41, the vent and liquid separation tank 42, the vent flare 43, etc.

[0040] The upstream station pipeline 1, the upstream trunk line shut-off valve 2, the trunk line pipeline 3, the downstream trunk line shut-off valve 4, the downstream station pipeline 5, the upstream trunk line pressure transmitter 6, the upstream trunk line temperature transmitter 7, the downstream trunk line pressure transmitter 8, the downstream trunk line temperature transmitter 9, the upstream bypass regulating valve 10, the downstream bypass shut-off valve 11, the upstream pigging shut-off valve 12, the first downstream pigging shut-off valve 13, the second downstream pigging shut-off valve 14, the bypass regulating valve 15, etc. constitute the pipeline transportation system, which is used to provide a trunk line 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 shut-off valve 11, the upstream pigging shut-off valve 12, the first downstream pigging shut-off valve 13, the second downstream pigging shut-off valve 14, the bypass regulating valve 15, etc. provide a medium flow path for pipeline maintenance and pigging, and cooperate with the movable pigging system to provide the functions of medium recovery and displacement in the trunk line.

[0041] Specifically, in the shown system, the upstream station pipeline 1, the upstream main pipeline shut-off valve 2, the main pipeline 3, the downstream main pipeline shut-off valve 4, and the downstream station pipeline 5 are all made of carbon steel, which are used to provide a flow channel for the normal transportation of methanol. The upstream main pipeline shut-off valve 2 and the downstream main pipeline shut-off valve 4 have emergency shut-off functions; the upstream main pipeline pressure transmitter 6 and the upstream main pipeline temperature transmitter 7 are arranged downstream of the upstream main pipeline shut-off valve 2, which are used to detect the starting pressure and temperature parameters of the main pipeline 3 in real time, and are also used for detecting the point parameters in this area during subsequent pigging and replacement processes; the downstream main pipeline pressure transmitter 8 and the downstream main pipeline temperature transmitter 9 are arranged upstream of the downstream main pipeline shut-off valve 4, which are used to detect the ending pressure and temperature parameters of the main pipeline 3 in real time, and are also used for detecting the point parameters in this area during subsequent pigging and replacement processes; the upstream bypass regulating valve 10 is arranged on the bypass upstream of the upstream main pipeline shut-off valve 2, with one end connected to a branch pipe and the other end connected by a blind flange. It is normally closed and is a manual regulating valve. It is opened before the displacement of the medium in the main pipeline 3, and is used to provide methanol for displacing nitrogen to the movable pig launcher 21 from the upstream station pipeline 1; the downstream bypass shut-off valve 11 is arranged on the branch pipe downstream of the downstream main pipeline shut-off valve 4, and the other end is a blind flange. It is normally closed and is a manual carbon steel ball valve. It is used to open during the displacement of the main pipeline 3 to provide a channel for the methanol in the main pipeline 3 to flow into the downstream station pipeline 5; the upstream pigging shut-off valve 12 is arranged on the pigging branch of the upstream station yard, with one end connected by a blind flange, which is used to connect the movable pigging system. It is normally closed and is a manual ball valve; the downstream first pigging shut-off valve 13 and the downstream second pigging shut-off valve 14 are arranged in sequence on the pigging branch of the downstream station yard. They are normally closed and are manual ball valves; the branches 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 are directly connected to the main pipeline 3, which is used to provide a path for the pig ball to pass through; the bypass regulating valve 15 is arranged on the bypass of the downstream second pigging shut-off valve 14. It is normally closed and is a manual regulating valve. One side is blocked by a blind flange and is replaced when connecting the movable pig receiver 24. It is used to provide pressurized methanol from the main pipeline 3 to the pig receiver 24 to establish back pressure for the pig receiver 24.

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

[0043] The movable pig launcher 21, the pig launcher balance valve 22, the pig launcher replacement valve 23, the movable pig receiver 24, the pig receiver replacement valve 25, the pigging regulating valve 26, the pigging pipeline flow transmitter 27, etc. constitute a movable pigging system, which is used to provide operations for recovering and displacing the medium in the main pipeline when the main pipeline needs to be repaired, and reasonably control the operating pressure according to the characteristics of the pipeline undulation to avoid the problem of medium vaporization inside the pipeline.

[0044] Specifically, in the shown system, the movable pig launcher 21 is a movable pig launcher skid made of carbon steel, which is used to provide the function of launching a pig; the pig launcher balance valve 22 is arranged on the connecting branch line between the large barrel and the small barrel of the movable pig launcher 21. It is normally closed and is a manual ball valve made of carbon steel. It is only temporarily opened before the movable pig launcher 21 is ready to launch, and is used to connect the large barrel and the small barrel to provide the functions of displacement and pressure boosting; the pig launcher displacement valve 23 is arranged on the branch line downstream (adjacent) of the movable pig launcher 21. It is normally closed and is a manual ball valve made of carbon steel. It is only temporarily opened before the movable pig launcher 21 is ready to launch, and is used for the displacement function; the movable pig receiver 24 is a movable pig launcher skid made of carbon steel, which is used to provide the function of receiving a pig and serves as the flow path of the displaced methanol in the main pipeline; the receiver displacement valve 25 is arranged on the branch pipe at the tail of the large barrel of the movable pig receiver 24. It is normally closed and is a manual ball valve made of carbon steel, and is used to provide the nitrogen displacement function for the air inside the movable pig receiver 24; the pigging regulating valve 26 is arranged on the branch pipe at the tail of the large barrel of the movable pig receiver 24. It is normally closed and is an electric regulating valve made of carbon steel, and is used to cooperate with the CNG regulating valve 32 to adjust the medium pressure, medium flow rate, etc. in the main pipeline 3 during the process of displacing methanol; the pigging pipeline flow transmitter 27 is arranged upstream of the movable pig receiver 24 and is used to detect the medium flow rate during the displacement and replacement processes and convert it into the medium flow velocity.

[0045] The CNG storage tank 31, CNG regulating valve 32, CNG heat exchanger 33, natural gas displacement cut-off valve 34, nitrogen supply system 35, nitrogen displacement cut-off valve 36, etc. form an efficient displacement system, which is used to carry out pressure-driven displacement of methanol in the main pipeline with natural gas before pipeline maintenance, and further use nitrogen to displace the natural gas in the main pipeline after displacement.

[0046] Specifically, in the shown system, the CNG storage tank 31 is a complete set of compressed natural gas supply storage tank for providing compressed natural gas for displacement and purging; the CNG regulating valve 32 is an electrically controlled regulating valve for regulating the flow rate and pressure of compressed natural gas, preferably made of low-temperature carbon steel; the CNG heat exchanger 33 is arranged downstream of the natural gas pressure regulating valve 32 for regulating the temperature of the pressure-regulated natural gas, including an air-cooled heat exchanger and an electric heater. Preferably, the outlet temperature after regulation by the air-cooled heat exchanger is greater than 0°C, and the outlet temperature after regulation by the electric heater is greater than 40°C, which are respectively used for displacement and purging; the natural gas cut-off valve 34 is arranged downstream of the CNG heat exchanger 33, a manual ball valve for connecting / closing the natural gas supply channel; the nitrogen supply system 35 is a small skid-mounted system, including a nitrogen storage tank, a nitrogen regulating valve, a nitrogen small boosting system, etc., for providing pressurized nitrogen for purging and displacing the downstream system; the nitrogen displacement cut-off valve 36 is arranged downstream of the nitrogen supply system 35, a manual ball valve for connecting / closing the nitrogen supply channel; as an implementation manner, both the CNG heat exchanger 33 and the nitrogen supply system 35 are equipped with temperature transmitters for real-time detection of the temperature after heat exchange. As an implementation manner, the high-efficiency displacement system is designed as a skid for easy movement, relocation and reuse.

[0047] The residual medium safety treatment system is composed of a treatment system cut-off valve 41, a venting and liquid separation tank 42, a venting flare 43, etc., for safely treating the residual natural gas-methanol mixture in the pipeline after trunk line displacement, including safely burning the natural gas-methanol gas and separating and recovering the liquid-phase methanol after gas-liquid separation.

[0048] Specifically, in the shown system, the treatment system cut-off valve 41 is arranged on the bypass downstream of the pigging regulating valve 26, normally closed, a manual ball valve made of carbon steel, and is only opened during the replacement stage of the trunk line pipeline 3 to provide a flow path for the replaced natural gas-methanol mixed medium and nitrogen-natural gas mixed gas; the venting and liquid separation tank 42 is a horizontal carbon steel storage tank with an atmospheric pressure design, arranged downstream of the treatment system cut-off valve 41 for physically separating the natural gas-methanol mixed medium by gravity, collecting the liquid-phase methanol displaced by natural gas, and transporting the separated natural gas to the venting flare 43; the venting flare 43 is arranged downstream of the venting and liquid separation tank 42 for safely igniting and burning the displaced natural gas-methanol mixed gas and at the same time serving as the venting channel for the subsequent natural gas-nitrogen mixed gas; as an implementation manner, a mixed gas sampling port is arranged downstream of the venting and liquid separation tank 42 for detecting the component content of the mixed gas to support the displacement and replacement operations. As an implementation manner, the residual medium safety treatment system is designed as a skid for easy movement, relocation and reuse.

[0049] Under normal operating conditions, liquid phase is generally used for methanol transportation in this embodiment. Given that the bubble point temperature of methanol is relatively high, when the pressure of the medium stored in the pipeline is relieved before pipeline maintenance, methanol cannot be effectively vaporized. Therefore, an active displacement method needs to be adopted to recover methanol. At the same time, due to the high economic efficiency of methanol, a movable pigging system is considered to provide an isolating pigging ball to displace methanol under pressure, so as to improve the recovery rate. In addition, since methanol has certain toxicity and flammability, natural gas purging is carried out on the medium stored in the pipeline (containing a certain amount of residual methanol) after displacement. The mixed gas of natural gas and methanol enters the flare for combustion to achieve the purpose of safe treatment.

[0050] Although methanol has a relatively low saturation pressure at normal temperature, due to possible terrain undulations during long-distance transportation and the use of natural gas for displacing the methanol stored in the pipeline in this embodiment, it is necessary to avoid the problem of flowing vaporization of methanol in the pipeline with terrain undulations. Therefore, the idea of displacing methanol under pressure with natural gas is adopted instead of displacing methanol under normal pressure. The pigging control valve 26 and the CNG control valve 32 are set to work together, and it is required that the pressure at the high point of the methanol pipeline shall not be lower than 0.6 MPa to ensure that methanol does not vaporize during the displacement process.

[0051] In order to safely displace and replace methanol, the ideas of pigging ball isolation displacement, natural gas purging and replacement, gas-liquid separation of natural gas-methanol mixed medium and ignition combustion are adopted. Specifically, using natural gas to push the pigging ball to displace methanol can improve the methanol recovery rate as much as possible. Both methanol and natural gas are flammable, which is convenient for ignition treatment and can avoid methanol evacuation pollution. For the methanol escaping from both sides of the pigging device, taking advantage of the volatility of methanol, the method of continuously purging with high-temperature natural gas is adopted to gradually empty it, and finally nitrogen is used to replace natural gas to provide a safe maintenance environment.

[0052] Embodiment 2

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

[0054] Step 1: During normal transportation, methanol is pressurized by the upstream station and then enters the main pipeline 3, and is transported to the downstream station through liquid phase. Before the pipeline is to be maintained, the upstream main pipeline shut-off valve 2 and the downstream main pipeline shut-off valve 4 are closed in an orderly manner, and the pipeline operating pressure is continuously observed through the upstream main pipeline pressure transmitter 6 and the downstream main pipeline pressure transmitter 8. During this process, the upstream bypass control valve 10, the downstream bypass shut-off valve 11, the upstream pigging shut-off valve 12, the first downstream pigging shut-off valve 13, the second downstream pigging shut-off valve 14, the bypass control valve 15, etc. are all kept in the closed state.

[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 a movable pigging system at the upstream station and the downstream station respectively; connect the movable pig launcher 21, the upstream bypass regulating valve 10 and the upstream pigging block valve 12, and connect the movable pig receiver 24, the downstream bypass block valve 11, the second downstream pigging block valve 14 and the bypass regulating valve 15; connect the launcher replacement valve 23 and the receiver replacement valve 25 to the temporary recovery storage tank or system at the upstream station and the downstream station respectively, for collecting and treating the air, air-nitrogen mixture, and methanol-nitrogen mixture displaced from the pig launcher and the pig receiver; place a pigging ball in the movable pig launcher 21, open the nitrogen supply system 35, the nitrogen replacement block valve 36, the launcher balance valve 22, and the launcher replacement valve 23, and continuously displace the air in the movable pig launcher 21 with nitrogen. The replacement time is preferably 5 minutes. When the oxygen content in the air-nitrogen mixed medium is detected to be less than 1% by sampling, stop the replacement; in order to reduce the gas blockage that may be formed by the nitrogen at the front end of the pigging ball in the main pipeline 3, close the nitrogen replacement block valve 36, open the upstream bypass regulating valve 10, and introduce a part of methanol from the upstream station to displace the nitrogen. The displacement time is 5 minutes; then close the launcher replacement valve 23; similarly, open the receiver replacement valve 25, the pigging regulating valve 26, the treatment system block valve 41, etc., introduce nitrogen from the receiver replacement valve 25, and displace the movable pig receiver 24 with nitrogen. The replacement time is preferably 5 minutes. When the oxygen content in the air-nitrogen mixed medium is detected to be less than 1% by sampling, stop the replacement. Subsequently, open the upstream bypass regulating valve 10 and the downstream bypass block valve 11 respectively, and use the methanol in the pipelines at the upstream station and the downstream station to increase the pressure of the movable pig launcher 21 and the movable pig receiver 24; further, the pressure is increased according to the static water pressure at the highest point along the pipeline being 0.6 MPa, to ensure that the pressure at the highest point along the pipeline is not less than 0.6 MPa during the subsequent displacement process.

[0056] Step 3: Perform the displacement of the methanol medium in the main pipeline 3. Specifically, open the natural gas replacement cut-off valve 34, the upstream pigging cut-off valve 12, the upstream pigging first cut-off valve 13, the downstream pigging second cut-off valve 14, the pigging regulating valve 26, the downstream bypass cut-off valve 11, etc., keep the upstream bypass regulating valve 10, the bypass regulating valve 15, the treatment system cut-off valve 41, etc. closed, and open up the displacement path; open the CNG regulating valve 32, introduce the high-pressure compressed natural gas (CNG) into the movable pig launcher 21 after pressure regulation and heat exchange. The temperature of the natural gas after heat exchange is not lower than 0 °C, and the pressure and flow rate of the methanol pipeline are jointly controlled by the CNG regulating valve 32 and the pigging regulating valve 26 to ensure that the pressure at the highest elevation point in the main pipeline 3 is not lower than 0.6 MPa, and the fluid velocity is monitored and converted by the pigging pipeline flow transmitter 27 and controlled within 2 m / s. The methanol displaced by the pigging ball enters the downstream station through the downstream bypass cut-off valve 11; when the pigging ball enters the movable pig receiver 24, close the downstream bypass cut-off valve 11 and open the treatment system cut-off valve 41 to introduce the displaced medium in the main pipeline 3 into the flare 43.

[0057] Step 4: Drain and replace the medium in the main pipeline 3. Specifically, temporarily stop injecting upstream natural gas into the main pipeline 3, increase the opening of the pigging regulating valve 26, and reduce the pressure of the medium in the main pipeline 3 to atmospheric pressure; then continuously supply upstream natural gas, and promote the volatilization of the remaining methanol in the pipeline through continuous natural gas purging; preferably, turn on the electric heating function of the CNG heat exchanger 33 to increase the temperature of the natural gas entering the main pipeline 3 (preferably 40 °C); set a sampling and detection port at the rear end of the drain and separation tank 42, and end the natural gas displacement of methanol when the methanol concentration is less than 1%; then, use nitrogen to displace the natural gas in the pipeline, and end the nitrogen displacement of natural gas when the methane concentration is less than 1%.

[0058] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A methanol pipeline maintenance and replacement system, characterized in that, the system includes: A pipeline transportation system, which includes upstream station pipelines, main pipelines, and downstream station pipelines from upstream to downstream. Cut-off valves are respectively provided on the upstream station pipelines and downstream station pipelines to provide a main pipeline transportation channel for the methanol pipeline to connect the upstream supply side and the downstream consumption side. The pipeline transportation system also includes bypasses and bypass cut-off valves provided on each pipeline to provide a medium flow channel for pipeline maintenance and pigging, cooperate with the connection of a movable pigging system, and provide medium recovery and displacement in the main pipeline; A pigging system, which includes a pig launcher pipeline provided upstream and a pig receiver pipeline provided downstream, and is used to provide medium recovery and displacement in the main pipeline when the main pipeline needs to be maintained; A displacement system, which includes a gas replacement pipeline and a nitrogen supply system, and is used to perform pressure-driven displacement of methanol in the main pipeline with natural gas before pipeline maintenance, and further displace the natural gas in the main pipeline after displacement with nitrogen; A residual medium safety treatment system, which is provided on the downstream pipeline bypass and is used to safely treat the residual natural gas-methanol mixture in the pipeline after main pipeline displacement.

2. The methanol pipeline maintenance and replacement system according to claim 1, characterized in that, The pipeline transportation system includes an upstream main pipeline cut-off valve provided on the upstream station pipeline and a downstream main pipeline cut-off valve provided on 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, and the downstream bypass is provided with a downstream bypass cut-off valve. The outlet of the pig launcher pipeline is connected to the main pipeline through an upstream pigging cut-off valve. Between the main pipeline and the inlet of the pig receiver pipeline, a series of downstream pigging first cut-off valve and downstream pigging second cut-off valve are arranged in sequence. A pig receiver pipeline bypass regulating valve is also connected in parallel at both ends of the downstream pigging second cut-off valve.

3. The methanol pipeline maintenance and replacement system according to claim 2, characterized in that, The pig launcher pipeline includes a movable pig launcher, and the movable pig launcher is equipped with a pig launcher balance valve. A branch pipe including a pig launcher replacement valve is also connected to the pipeline between the pig launcher outlet and the upstream pigging cut-off valve; The pig receiver pipeline includes a movable pig receiver, and the movable pig receiver is equipped with a pig receiver replacement valve. The pig receiver is connected to the downstream bypass cut-off valve through a pigging regulating valve.

4. The methanol pipeline maintenance and replacement system according to claim 2, 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 cut-off valve connected in sequence. The other end of the natural gas replacement cut-off valve is connected to the upstream bypass; The nitrogen supply system is connected to the upstream bypass through a nitrogen replacement cut-off valve.

5. The methanol pipeline maintenance and replacement system according to claim 1, characterized in that, The residual medium safety treatment system includes a treatment system cut-off valve. One end of the treatment system cut-off valve is connected to the downstream bypass, and the other end is connected to one end of a venting and liquid separation tank. The other end of the venting and liquid separation tank is connected to a venting flare.

6. The methanol pipeline maintenance and replacement system according to claim 1, characterized in that, The system further includes a data observation system, which includes a pressure monitoring device and a temperature monitoring device disposed in the pipeline of the upstream station, a pressure monitoring device and a temperature monitoring device disposed in the pipeline of the downstream station, and a pigging pipeline flow transmitter disposed at the inlet of the pig receiver.

7. A method for overhaul and replacement of a methanol pipeline, characterized in that, the method is implemented based on the overhaul and replacement system according to any one of claims 1-6, and the method includes: Step A: During normal transportation, methanol enters the main pipeline after being pressurized by the upstream station yard and is transported to the downstream station yard in liquid phase. Before the pipeline is to be overhauled, the shut-off valves of the pipelines in the upstream station and the downstream station are closed, and the operating pressures of the pipelines in the upstream station and the downstream station are continuously observed; Step B: After the pipeline stops transporting, connect the pigging system and the displacement system to the pipeline transportation system, place a pig in the pig launcher pipeline, turn on the nitrogen supply system to continuously displace the air in the pig launcher pipeline with nitrogen until the oxygen content in the air-nitrogen mixed medium is lower than the preset percentage, stop injecting nitrogen and introduce methanol from the upstream station yard to displace nitrogen, and then close the pig launcher pipeline; Similarly, displace the pig receiver pipeline with nitrogen 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 station yard and the downstream station yard to increase the pressure of the pig launcher pipeline and the pig receiver pipeline through the bypass, so that the pressure at the highest point along the pipeline during the subsequent displacement process is not lower than the preset pressure threshold; Step C: Turn on the pigging system and the displacement system to perform the displacement of the methanol medium in the main pipeline. During the displacement process, monitor the inlet pressure of the pig receiver pipeline, control the fluid velocity within the preset velocity range, and introduce the displaced medium in the main pipeline into the residual medium safety treatment system; Step D: Reduce the pressure of the medium in the main pipeline to atmospheric pressure, displace the methanol in the main pipeline with natural gas, stop displacing methanol with natural gas when the methanol concentration is lower than the preset methanol concentration percentage, and displace the natural gas in the pipeline with nitrogen until the methane concentration is lower than the preset methane concentration percentage, and then end the nitrogen displacement of natural gas.

8. A method for overhaul and replacement of a methanol pipeline according to claim 7, characterized in that, the preset percentage of the oxygen content is 1%, the preset methanol concentration percentage is 1%, and the preset methane concentration percentage is 1%.

9. A method for overhaul and replacement of a methanol pipeline according to claim 7, characterized in that, the preset pressure threshold is 0.6 MPa.

10. A method for overhaul and replacement of a methanol pipeline according to claim 7, characterized in that, the preset velocity range is 2 m / s.

Images