Multi-phase carbon dioxide pipeline shutdown and restart test system and method

Abstract

The invention provides a multiphase carbon dioxide pipeline shutdown and restart test system and method. The multiphase carbon dioxide pipeline shutdown and restart test system comprises injection equipment, main pipeline equipment, pressure reduction and temperature control equipment and restart filling equipment. And the main pipeline equipment comprises a main pipeline as well as an exhaust valve, a mass density meter and a main line stop valve which are sequentially arranged at the tail end of the main pipeline. The pressure-reducing temperature control equipment comprises a pressure-reducing pipeline, and a pressure-reducing valve, a cooler and an inlet stop valve which are arranged on the pressure-reducing pipeline. The restarting filling equipment comprises a restarting pipeline, a bypass pipeline, a vertical low-temperature storage tank, an outlet stop valve, a low-temperature high-pressure plunger pump, a one-way valve, a stop valve before heating, a heater, a stop valve after heating, a mass flow meter and a flow meter stop valve, the carbon dioxide temperature pressure, phase state and liquid holdup collaborative change rule can be explored, basic data are provided for drawing a carbon dioxide phase state migration path, operation guidance is provided for pipeline transportation stopping and restarting, and the pipeline transportation stopping and restarting risks are reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of carbon dioxide transmission experiments, and in particular relates to a multi-phase carbon dioxide pipeline shutdown and restart test system and method. Background Art

[0002] At present, CCUS (carbon capture, utilization and storage) technology is highly valued. The CCUS industry chain consists of multiple links such as carbon dioxide capture, compression, transportation, utilization or storage, which requires high integration and coordinated development of all links. Carbon dioxide transportation is one of the important links in the CCUS industry chain, so it will inevitably rely on the construction of long-distance carbon dioxide pipelines and their supporting infrastructure.

[0003] There are more than 50 independent CO2 pipelines in operation internationally, with a total length of nearly 10,000 kilometers. Domestic CO2 pipeline technology has developed slowly, and CO2 transportation is mainly carried out by road in cryogenic tanks. In 2023, the first long-distance, high-pressure, dense-phase CO2 pipeline will be put into operation in China. The pipeline trunk line will be 109 km long, the pipe diameter will be DN300, the design pressure will be 12 MPa, and the design output will be 1.7 million tons / year.

[0004] At present, carbon dioxide pipelines mostly draw on the design and transportation experience of natural gas pipelines. There is no unified carbon dioxide pipeline transportation industry standard. Some foreign standards only propose work rules and technical requirements for pipeline carbon dioxide transportation. The content is mainly qualitative general description without process and technical details.

[0005] In terms of the mode of transportation, CO2 pipeline transportation can be divided into gaseous transportation, liquid transportation, dense phase transportation and supercritical transportation. Among them, (1) Gaseous transportation: During the transportation process, CO2 remains in the gas phase in the pipeline, and the transportation pressure is increased by compression of the compressor. Whether the pipeline is equipped with an insulation layer needs to be determined through thermal calculation. (2) Liquid transportation: During the transportation process, CO2 remains in the liquid phase in the pipeline, and the transportation pressure is increased by pumping to overcome the friction resistance and terrain height difference along the way. Whether the pipeline is equipped with an insulation layer needs to be determined through thermal calculation. (3) Dense phase transportation: When the pressure of CO2 is higher than the critical point pressure of 7.38MPa, and the temperature is higher than the triple point temperature of -56℃ and lower than the critical point temperature of 31.4℃, CO2 is in a dense phase state, and CO2 remains in a dense phase state in the pipeline during transportation. (4) Supercritical transportation: During the transportation process, CO2 remains in a supercritical state in the pipeline (temperature and pressure are both higher than the critical value), and the transportation pressure is increased by compression of the compressor.

[0006] After the existing crude oil pipeline is shut down, the oil temperature inside the pipeline gradually decreases. At a certain temperature, the crude oil turns into a non-Newtonian fluid with thixotropy and yield stress. If the shutdown time is long, the pressure required to restart the pipeline will exceed the maximum allowable working pressure of the pipeline. The existing crude oil pipeline shutdown and restart judgment criteria are based on "minimum restart pressure limit exceeded" and "flow recovery difficulty". During the shutdown process of the wet natural gas pipeline, the medium in the pipeline exchanges heat with the surrounding environment. If the shutdown time is too long, hydrates may form, which may block the pipeline and make restarting difficult in severe cases. The safe shutdown time of the pipeline can be determined by comparing the hydrate formation conditions (pressure, temperature) with the pressure and temperature parameters in the pipeline after the shutdown. Unlike the shutdown and restart conditions of crude oil and natural gas pipelines, the phase state of carbon dioxide is determined by two parameters: temperature and pressure.

[0007] For CO2 pipelines, we should not only pay attention to the temperature changes along the pipeline during the shutdown and restart process, but also pay attention to the phase changes of CO2 under the synergistic effect of pressure and temperature. At present, there is no scientific definition for the safe shutdown time of supercritical CO2 pipelines. During the long-distance CO2 pipeline transportation process, impurities, temperature and pressure, terrain, operation and other factors will induce CO2 temperature and pressure fluctuations. When approaching the critical point, the fluid vaporizes, bubbles in the pipe are constantly generated and destroyed, forming impact slug flow, and the pressure in the pipe suddenly changes, causing water hammer and pipeline vibration.

[0008] During the shutdown process of the CO2 pipeline, from the perspective of operational safety, the gasification of the fluid should be avoided, that is, the pipeline restart operation should be completed before gasification. For the shutdown process of the CO2 pipeline, existing research has not provided: (1) the coordinated change law of pressure, temperature, density, and phase state of the CO2 pipeline during the shutdown process; (2) the migration path line of CO2 across phases during the shutdown process; (3) the pressure and temperature prediction formula for the initial gasification of CO2; (4) the liquid holdup change prediction formula after CO2 gasification; (5) the maximum allowable pipeline shutdown time. Since it is impossible to predict the temperature, pressure and phase change law during the pipeline shutdown process, it is impossible to judge the safe operation status of the pipeline. On-site operators cannot grasp the risks and hidden dangers of the pipeline shutdown process, and have no basis for operation when performing pipeline shutdown operations.

[0009] As for the restart process of the CO2 pipeline, existing research has not provided: (1) the safety plan for restarting the pipeline after the fluid in the pipeline has been gasified; (2) the corresponding relationship between the liquid holdup (gasification rate) of the CO2 fluid and the risk of pipeline restart, that is, whether the higher the gasification degree, the greater the risk of pipeline restart. The restart risk after the pipeline has been gasified is unclear; (3) the timing of pipeline restart, that is, the latest allowed restart time; (4) the composition, calculation formula and pressure wave transmission law of pipeline restart pressure. It is impossible to determine whether the restart pressure is higher than the pipeline design pressure, and the restart operation may cause the risk of pipeline overpressure rupture and leakage; (5) When the pipeline is restarted, the newly injected liquid phase CO2 will squeeze the existing gas-liquid mixed phase CO2 in the pipe. It is unclear about the corresponding relationship between the fluid temperature in the pipe, the pressure rise rate and the mass flow rate of the newly injected liquid phase CO2, the transformation law of gas-liquid mixed phase CO2 to liquid phase CO2, the transformation law of liquid phase CO2 to dense phase CO2, and the transformation law of dense phase CO2 to supercritical phase CO2.

[0010] Since it is impossible to predict the temperature, pressure and phase change rules during the pipeline restart process, it is impossible to determine the safe operation status of the pipeline. On-site operators cannot grasp the risks and hidden dangers of the pipeline restart process, and there is a high safety risk when performing pipeline restart operations. Summary of the invention

[0011] The main purpose of the present invention is to provide a multiphase carbon dioxide pipeline shutdown and restart test system and method, aiming to solve the technical problem of high risk of carbon dioxide pipeline shutdown and restart operation in the prior art.

[0012] In order to achieve the above object, the present invention provides a multiphase carbon dioxide pipeline shutdown and restart test system, the multiphase carbon dioxide pipeline shutdown and restart test system comprising:

[0013] The injection device comprises two filling branches arranged in parallel, and the two filling branches are used to connect to the carbon dioxide transport tank truck;

[0014] The main pipeline equipment comprises a main pipeline and an exhaust valve, a mass density meter and a trunk stop valve which are sequentially arranged at the end of the main pipeline, the ends of the two filling branches converge at the head end of the main pipeline, a plurality of temperature and pressure measuring components are arranged at a first interval on the main pipeline, the temperature and pressure measuring components are used to detect the high-frequency pressure of carbon dioxide, the low-frequency pressure of carbon dioxide, the temperature of carbon dioxide and the temperature of the pipeline wall in the main pipeline, a plurality of transparent phase observation windows are arranged at a second interval on the main pipeline, and a heating belt for heating the main pipeline is wrapped outside the main pipeline;

[0015] The pressure reducing and temperature controlling device comprises a pressure reducing pipeline and a pressure reducing valve, a cooler and an inlet stop valve arranged on the pressure reducing pipeline, wherein the head end of the pressure reducing pipeline is connected to the end of the main pipeline;

[0016] The restart filling equipment comprises a restart pipe, a bypass pipe and a vertical low-temperature storage tank, an outlet stop valve, a low-temperature high-pressure plunger pump, a one-way valve, a pre-heating stop valve, a heater, a post-heating stop valve, a mass flow meter and a flow meter stop valve arranged on the restart pipe. The bypass pipe is provided with a bypass stop valve, one end of the bypass pipe is connected to the pipeline between the pre-heating stop valve and the one-way valve, and the other end of the bypass pipe is connected to the pipeline between the post-heating stop valve and the mass flow meter. The head end of the restart pipe is connected to the end of the pressure reducing pipe, and the end of the restart pipe is connected to the restart interface on the main pipe, and the restart interface is arranged close to the injection equipment.

[0017] In an embodiment of the present invention, the multiphase carbon dioxide pipeline shutdown and restart test system further includes a bursting disc arranged on the main pipeline, and the bursting disc is externally connected to a bursting pipe.

[0018] In an embodiment of the present invention, the multiphase carbon dioxide pipeline shutdown and restart test system further includes a controller and a weighing scale for weighing the carbon dioxide transport tank truck, and the filling branch includes:

[0019] A filling hose, one end of which is connected to the connection port of the carbon dioxide transport tank truck;

[0020] A rigid injection pipe, the other end of the filling hose is connected to one end of the rigid injection pipe, the other end of the rigid injection pipe is connected to the main pipeline, the rigid injection pipe is provided with an injection valve, the injection valve is electrically connected to the controller, and the controller is configured as follows:

[0021] According to the weighing information of the weighing scale, the injection valve is closed.

[0022] In an embodiment of the present invention, the heating belt is wrapped with a heat-insulating layer and a fire-blocking layer, and the heating belt includes a heating wire, an insulating layer and a protective cover which are nested in sequence from the inside to the outside.

[0023] In an embodiment of the present invention, the temperature and pressure measurement assembly includes a pressure parameter sensor, a pipe top temperature sensor, a pipe bottom temperature sensor and a pipe wall temperature sensor arranged at circumferential intervals along the main pipeline, the pressure parameter sensor is used to detect the high-frequency pressure of carbon dioxide and the low-frequency pressure of carbon dioxide, and the pressure parameter sensor, the pipe top temperature sensor, the pipe bottom temperature sensor and the pipe wall temperature sensor are all plug-connected to the main pipeline.

[0024] In an embodiment of the present invention, the filling branch extends along a first direction, the main pipeline includes a transverse first pipe section, a transverse last pipe section and an intermediate pipe section, the transverse first pipe section and the transverse last pipe section both extend along the first direction, and the transverse first pipe section and the transverse last pipe section are arranged relatively to each other along a second direction, the transverse first pipe section is connected to the injection equipment, and the transverse last pipe section is connected to the pressure reducing pipeline.

[0025] In an embodiment of the present invention, the middle pipe section includes two vertical sections and a bent section connected between the two vertical sections, and the bent section protrudes toward a direction close to the pressure reducing pipe.

[0026] The present invention further provides a multiphase carbon dioxide pipeline shutdown test method, which is applied to the multiphase carbon dioxide pipeline shutdown and restart test system as described above, wherein the two filling branches are respectively a gas phase filling branch and a liquid phase filling branch, and the multiphase carbon dioxide pipeline shutdown test method comprises:

[0027] Open the exhaust valve, close the trunk stop valve and the flow meter stop valve, and fill the main pipeline with gaseous carbon dioxide through the gas phase filling branch;

[0028] After the first preset filling time, close the exhaust valve;

[0029] When it is determined that the multiphase carbon dioxide pipeline stop and restart test system has no gas leakage, continue to fill the main pipeline with gaseous carbon dioxide until the pressure in the main pipeline is the same as the pressure of the carbon dioxide transport tank truck;

[0030] Filling the main pipeline with gaseous carbon dioxide and liquid carbon dioxide through the gaseous carbon dioxide filling branch and the liquid carbon dioxide filling branch, while opening the exhaust valve until a preset filling weight of liquid carbon dioxide is filled, closing the exhaust valve and stopping the carbon dioxide filling of the gaseous carbon dioxide filling branch and the liquid carbon dioxide filling branch;

[0031] Starting the heating belt to heat the carbon dioxide in the main pipeline until the pressure of the carbon dioxide in the main pipeline reaches a desired pressure and the temperature of the carbon dioxide reaches a desired temperature;

[0032] The heating belt is turned off, and the mixture is left to stand for a second preset time to simulate cooling of the carbon dioxide in the main pipeline. The temperature and pressure parameters in the main pipeline are detected and recorded by the temperature and pressure measurement component, and the liquid holdup of the carbon dioxide in the main pipeline is collected through the phase observation window.

[0033] The present invention further provides a multiphase carbon dioxide pipeline restart test method, which is applied to the multiphase carbon dioxide pipeline shutdown and restart test system as described above, and the multiphase carbon dioxide pipeline restart test method comprises:

[0034] Determine the carbon dioxide phase state at the start-up time and the carbon dioxide phase state after the start-up is completed required for the restart experiment;

[0035] At the start-up time, the carbon dioxide phase is a gas-liquid mixed phase or a gas phase. After the start-up is completed, the carbon dioxide phase is required to be supercritical carbon dioxide. Liquid carbon dioxide, dense carbon dioxide and supercritical carbon dioxide are sequentially filled into the main pipeline through the pressure reducing and temperature controlling device and the restart filling device;

[0036] At the start-up time, the carbon dioxide phase is a gas-liquid mixed phase or a gas phase. After the start-up is completed, the carbon dioxide phase is required to be a dense phase carbon dioxide. Liquid phase carbon dioxide and dense phase carbon dioxide are sequentially filled into the main pipeline through the pressure reducing and temperature controlling device and the restart filling device;

[0037] At the start-up time, the carbon dioxide phase is a gas-liquid mixed phase or a gas phase. After the start-up is completed, the carbon dioxide phase is required to be liquid carbon dioxide. Liquid carbon dioxide is filled into the main pipeline through the pressure reducing and temperature controlling equipment and the restart filling equipment.

[0038] In an embodiment of the present invention, at the start-up time, the carbon dioxide phase is a gas-liquid mixed phase or a gas phase, and after the start-up is completed, the carbon dioxide phase is required to be supercritical carbon dioxide, and the filling of liquid carbon dioxide, dense phase carbon dioxide and supercritical carbon dioxide into the main pipeline in sequence through the pressure reducing temperature control device and the restart filling device includes:

[0039] When confirming that the current parameters of the carbon dioxide in the main pipeline are the same as the parameters required at the restart time, the carbon dioxide is filled into the low-temperature and high-pressure plunger pump through the vertical low-temperature storage tank until the low-temperature and high-pressure plunger pump is filled;

[0040] Open the bypass stop valve and the flowmeter stop valve, close the pre-heating stop valve and the trunk stop valve, pressurize the liquid phase carbon dioxide flowing out of the vertical cryogenic storage tank to a required pressure through the cryogenic and high-pressure plunger pump, and inject it into the main pipeline over the heater until the carbon dioxide in the main pipeline is transformed into dense phase carbon dioxide;

[0041] Open the pre-heating stop valve and the post-heating stop valve, close the bypass stop valve, start the heater, control the outlet temperature of the heater to the required temperature of supercritical carbon dioxide, and the supercritical carbon dioxide entering the main pipeline from the heater pushes the dense carbon dioxide to move downstream;

[0042] Determine that the fluid pressure in the main pipeline reaches the supercritical restart pressure, open the main line stop valve, start the pressure reducing valve and the cooler, open the inlet stop valve, and allow the carbon dioxide in the main pipeline to flow through the pressure reducing valve and the cooler and then enter the vertical cryogenic storage tank until the carbon dioxide flowing out of the main line stop valve is in a supercritical state.

[0043] Through the above technical solution, the multiphase carbon dioxide pipeline shutdown and restart test system provided by the embodiment of the present invention has the following beneficial effects:

[0044] The multiphase carbon dioxide pipeline shutdown and restart test system can carry out multiphase carbon dioxide pipeline shutdown tests, and can carry out restart tests of carbon dioxide pipelines in different phases from shutdown to supercritical phase, dense phase or liquid phase, with a wide range of applications. Sufficient liquid carbon dioxide required for the test is injected into the main pipeline, and the carbon dioxide fluid in the main pipeline is heated by a heating belt to increase the temperature and pressure to reach the liquid phase, dense phase and supercritical phase. The main pipeline can carry out multiphase carbon dioxide shutdown tests, and the pressure, temperature and phase of carbon dioxide in the pipeline before shutdown can be adjusted according to the test needs. During the shutdown process, the fluid in the pipe exchanges heat through the insulation layer and the atmosphere through heat conduction, and naturally cools down to simulate the shutdown process. Detect and record the low-frequency pressure, top fluid temperature, bottom fluid temperature, and wall temperature of each temperature and pressure measurement component along the main pipeline before, during, and after the fluid gasification process of the shutdown process. Observe the fluid phase through the phase observation windows at the starting point, midpoint, and end point, and calculate the liquid holdup. This can explore the coordinated changes in carbon dioxide temperature, pressure, phase, and liquid holdup, provide basic data for drawing the carbon dioxide phase migration path, and provide basic data for deriving the functional relationship between temperature, pressure, and density before carbon dioxide gasification, the pressure and temperature prediction formula at the initial gasification moment, and the liquid holdup change prediction formula after gasification. It can quantitatively describe the temperature, pressure, phase, and liquid holdup before and after gasification during the shutdown process.

[0045] The phase migration path of different phases of carbon dioxide pipelines after stopping to different phases and restarting to different phases can be obtained by experiment. The transformation law of gas-liquid miscible phase / gas phase carbon dioxide to liquid phase carbon dioxide, the transformation law of liquid phase carbon dioxide to dense phase carbon dioxide, and the transformation law of dense phase carbon dioxide to supercritical phase carbon dioxide can be obtained. The risk of restarting after the pipeline is stopped to gas-liquid miscible phase (liquid holdup 0.9, 0.7, 0.5, 0.3) can be evaluated. The corresponding relationship between the temperature and pressure rise rate of the fluid in the pipe and the mass flow rate of the newly injected liquid phase carbon dioxide can be clarified, and a safe restart operation plan can be given in combination with the variable parameter control of the pump flow. The post-pump pressure (restart pressure) data can be obtained by experiment, and the restart pressure composition can be analyzed. By analogy with the crude oil pipeline, an attempt can be made to give a restart pressure calculation formula. It is helpful to predict the temperature, pressure and phase changes during the pipeline shutdown and restart process, and judge the safe operation status of the pipeline. It can provide operational guidance for pipeline shutdown and restart, and reduce the risk of pipeline shutdown and restart.

[0046] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The accompanying drawings are used to provide an understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention, but do not constitute a limitation of the present invention. In the accompanying drawings:

[0048] Figure 1 It is a structural schematic diagram of a multiphase carbon dioxide pipeline shutdown and restart test system according to one embodiment of the present invention;

[0049] Figure 2 It is a schematic structural diagram of a restart filling device of a multiphase carbon dioxide pipeline shutdown and restart test system according to an embodiment of the present invention;

[0050] Figure 3 1 is a schematic diagram of the structure of a temperature and pressure measurement component of a multiphase carbon dioxide pipeline shutdown and restart test system according to an embodiment of the present invention.

[0051] Description of Reference Numerals

[0052] Label Name Label Name

[0053] 1 Charging branch 3 Pressure reduction and temperature control equipment

[0054] 101 Filling hose 301 Pressure relief pipe

[0055] 102 Rigid injection pipe 302 Pressure reducing valve

[0056] 103 injection valve 303 cooler

[0057] 2 Main pipeline equipment 304 inlet stop valve

[0058] 201 Main pipeline 4 Restart filling equipment

[0059] 2011 Transverse first section 401 Restart pipeline

[0060] 2012 Horizontal end pipe section 402 Bypass pipe

[0061] 2013 Vertical Section 403 Vertical Cryogenic Storage Tank

[0062] 2014 Bend Section 404 Outlet Stop Valve

[0063] 202 Exhaust valve 405 Low temperature high pressure plunger pump

[0064] 203 Mass density meter 406 Check valve

[0065] 204 Main line stop valve 407 Pre-heating stop valve

[0066] 205 Temperature and pressure measurement component 408 Heater

[0067] 2051 Pressure parameter sensor 409 Heated stop valve

[0068] 2052 Tube Top Temperature Sensor 410 Mass Flow Meter

[0069] 2053 pipe bottom temperature sensor 411 flow meter stop valve

[0070] 2054 Pipe wall temperature sensor 412 Bypass stop valve

[0071] 206 Phase observation window TT Temperature sensor

[0072] 207 Heating belt PT pressure sensor

[0073] 208 rupture disc DETAILED DESCRIPTION

[0074] The specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0075] The multiphase carbon dioxide pipeline shutdown and restart test system according to the present invention will be described below with reference to the accompanying drawings.

[0076] like Figures 1 to 3As shown, in an embodiment of the present invention, a multiphase carbon dioxide pipeline shutdown and restart test system includes an injection device, a main pipeline device 2, a pressure reduction and temperature control device 3 and a restart filling device 4, the injection device includes two filling branches 1 arranged in parallel, and the two filling branches 1 are used to connect the carbon dioxide transport tank truck; the main pipeline device 2 includes a main pipeline 201 and an exhaust valve 202, a mass density meter 203 and a trunk stop valve 204 sequentially arranged at the end of the main pipeline 201, the ends of the two filling branches 1 converge at the head end of the main pipeline 201, a plurality of temperature and pressure measurement components 205 are arranged at a first interval on the main pipeline 201, and the temperature and pressure measurement components 205 are used to detect the high-frequency pressure of carbon dioxide, the low-frequency pressure of carbon dioxide, the temperature of carbon dioxide and the wall temperature of the pipeline in the main pipeline 201, a plurality of transparent phase observation windows 206 are arranged at a second interval on the main pipeline 201, and the main pipeline 201 is wrapped with a heating belt 207 for heating the main pipeline 201; the pressure reduction and temperature control device 3 includes a pressure reduction pipeline 301 and The pressure reducing valve 302, the cooler 303, and the inlet stop valve 304 are arranged on the pressure reducing pipeline 301, and the head end of the pressure reducing pipeline 301 is connected to the end of the main pipeline 201; the restart filling equipment 4 includes the restart pipeline 401, the bypass pipeline 402 and the vertical low-temperature storage tank 403, the outlet stop valve 404, the low-temperature high-pressure plunger pump 405, the one-way valve 406, the pre-heating stop valve 407, the heater 408, the post-heating stop valve 409, and the mass flow meter 410. and a flowmeter stop valve 411, a bypass stop valve 412 is arranged on the bypass pipe 402, one end of the bypass pipe 402 is connected to the pipeline between the stop valve 407 and the one-way valve 406 before heating, the other end of the bypass pipe 402 is connected to the pipeline between the stop valve 409 and the mass flowmeter 410 after heating, the head end of the restart pipe 401 is connected to the end of the pressure reducing pipe 301, the end of the restart pipe 401 is connected to the restart interface on the main pipe 201, and the restart interface is arranged close to the injection equipment.

[0077] The multiphase carbon dioxide pipeline shutdown and restart test system can carry out multiphase carbon dioxide pipeline shutdown and multiphase carbon dioxide pipeline restart tests, and has a wide range of applications. Sufficient liquid carbon dioxide required by the test is injected into the main pipeline 201, and the carbon dioxide fluid in the main pipeline 201 is heated by the heating belt 207 to increase the temperature and pressure to reach the liquid phase, dense phase, and supercritical phase. The main pipeline 201 can carry out a multiphase carbon dioxide shutdown test, and the pressure, temperature, and phase of the carbon dioxide in the pipeline before the shutdown can be adjusted according to the test needs. During the shutdown process, the fluid in the pipe exchanges heat through the insulation layer and the atmosphere, and the temperature is naturally reduced. The shutdown process is simulated, and the low-frequency pressure, pipe top fluid temperature, pipe bottom fluid temperature, and pipe wall temperature of each temperature and pressure measurement component 205 along the main pipeline 201 before, during, and after the gasification of the fluid during the shutdown process are detected and recorded. The fluid phase state is observed through the starting point, midpoint, and end point phase state observation window 206, and the liquid holdup is calculated. The coordinated change law of carbon dioxide temperature, pressure, phase state, and liquid holdup can be explored to provide basic data for drawing the carbon dioxide phase state migration path, and to derive the functional relationship between temperature, pressure, and density before carbon dioxide gasification, the pressure and temperature prediction formula at the initial gasification time, and the liquid holdup change prediction formula after gasification. It can quantitatively describe the temperature, pressure, phase state, and liquid holdup before and after gasification during the shutdown process, provide operational guidance for pipeline shutdown and restart, and reduce the risk of pipeline shutdown and restart.

[0078] It is also possible to conduct restart tests of CO2 pipelines in different phases after shutting down to supercritical phase, dense phase or liquid phase. Including:

[0079] (1) Before the shutdown, the carbon dioxide in the pipeline is in a supercritical state.

[0080] ① Test and stop transmission until the supercritical phase and then restart filling

[0081] ② Test and stop the transmission until the dense phase and then start filling

[0082] ③Stop the test until the liquid phase is reached and then restart filling

[0083] ④ Stop the test until the gas-liquid mixture is reached (including different liquid holdup ratios) and then start filling

[0084] (2) Before the transmission is stopped, the carbon dioxide in the pipeline is in a dense phase.

[0085] ①Stop the test until the transmission reaches the dense phase and then start filling

[0086] ②Stop the test until the liquid phase and then restart filling

[0087] ③ Stop the test until the gas-liquid mixture is reached (including different liquid holdup ratios) and then start filling

[0088] (3) Before the transmission is stopped, the carbon dioxide in the pipeline is in liquid phase.

[0089] ①Stop the test and start filling after the pump reaches the liquid phase

[0090] ② Stop the test until the gas-liquid mixture is mixed (including different liquid holdup ratios) and then start filling

[0091] In terms of restart filling test, the vertical cryogenic storage tank 403 can store liquid carbon dioxide at -20℃ and 2MPa, and the fluid pressure can be increased by the cryogenic and high-pressure plunger pump 405, and the fluid temperature can be increased by the heater 408 behind the pump. Through the combined working mode of the cryogenic and high-pressure plunger pump 405 and the heater 408, supercritical phase, dense phase, liquid phase or gas phase carbon dioxide can be filled into the main pipeline 201 according to the test requirements, meeting the requirements of multi-phase carbon dioxide gas source injection, and having high adaptability.

[0092] It should be noted that the temperature and pressure measurement component 205 can detect the high-frequency pressure of carbon dioxide in the pipeline (to study the decompression wave at the moment of decompression), the low-frequency pressure of carbon dioxide in the pipeline (to study the pressure change over time during the entire decompression process), the temperature of carbon dioxide in the pipeline, and the temperature of the pipeline wall. During the test measurement process, considering the changes of the above parameters at different positions of the pipeline axis, in order to facilitate the system to measure the above parameter changes, the temperature and pressure measurement components 205 are arranged on the main pipeline 201 at intervals (such as 10m) to arrange the sensors.

[0093] Four sensor joints are set along the pipeline annular direction to install the pressure parameter sensor 2051, the pipe top temperature sensor 2052, the pipe bottom temperature sensor 2053 and the pipe wall temperature sensor 2054. The temperature sensor can be an armored thermocouple or a patch thermocouple. It can measure the pipeline pressure, the fluid temperature at the bottom and top of the pipeline, and the pipe wall temperature. The high-frequency pressure and the low-frequency pressure share a sensor joint, which can be replaced as needed. In order to improve the scalability of sensor installation, the sensors installed in the main pipeline 201 all adopt a unified connection type, that is, the M20×1.5 external thread connection type. Therefore, an M20×1.5 internal thread joint needs to be set on the wall of the main pipeline 201, and the sensor joint is integrated with the pipe wall through insert welding. The liquid holdup rate at a certain position of the pipeline can be calculated by visual inspection and manual measurement of the phase observation window 206.

[0094] When the exhaust valve 202 is open, the main pipeline 201 can be connected to the atmosphere. In the process of inputting gaseous carbon dioxide into the main pipeline 201 for gas washing, by opening the exhaust valve 202, other gases in the main pipeline 201 can be discharged out of the pipe. In the process of injecting liquid carbon dioxide into the main pipeline 201, by opening the exhaust valve 202, the injection rate of liquid carbon dioxide can be accelerated. The mass density meter 203 measures the density value of carbon dioxide, and the phase of carbon dioxide can be determined by the density value. The density of each phase of carbon dioxide is as follows: supercritical state: 200-600kg / m 3, dense phase: 600~1200kg / m 3 , liquid phase: 600~1200kg / m 3 , gas phase: 1~200kg / m 3 During the charging and pressure holding stage of starting the low temperature and high pressure plunger pump 405 to pump liquid carbon dioxide into the main pipeline 201, the main line stop valve 204 is always in a closed state. When the mass density meter 203 determines that the phase of carbon dioxide is the phase required by the test, the main line stop valve 204 is opened.

[0095] The vertical cryogenic storage tank 403 of the restart filling device 4 provides liquid carbon dioxide to be injected into the pipeline by the pump during the restart test, and is filled with gas-liquid mixed phase carbon dioxide at a pressure of 2.0 MPa and a temperature of -20°C. The bottom elevation of the vertical cryogenic storage tank 403 is higher than the main pipeline 201 and the cryogenic high-pressure plunger pump 405. A temperature sensor TT and a pressure sensor PT are provided at the inlet of the cryogenic high-pressure plunger pump 405, which can measure the temperature and pressure at the inlet.

[0096] The outlet stop valve 404 is in a closed state before the cryogenic and high-pressure plunger pump 405 is started. The cryogenic and high-pressure plunger pump 405 is used for pressurizing the liquid phase carbon dioxide, and pressurizing the carbon dioxide (pressure 2.0MPa, temperature -20°C) at the inlet of the cryogenic and high-pressure plunger pump 405 to the required pressure of the supercritical state / dense phase / liquid phase. The cryogenic and high-pressure plunger pump 405 can be frequency-controlled, and the speed regulation range is 50%-100% of the rated flow. A pressure sensor PT and a temperature sensor TT are provided at the outlet of the cryogenic and high-pressure plunger pump 405 to measure the pressure and temperature at the outlet of the cryogenic and high-pressure plunger pump 405. The one-way valve 406 can prevent the fluid behind the one-way valve 406 from flowing back into the cryogenic and high-pressure plunger pump 405. The stop valve 407 before heating has a switch function. A temperature sensor TT is provided at the inlet of the heater 408, which can measure the fluid temperature at the inlet of the heater 408. The heater 408 can heat the temperature of the carbon dioxide at the outlet of the low-temperature and high-pressure plunger pump 405 to the temperature required by the supercritical state / dense phase / liquid phase carbon dioxide. A temperature sensor TT is provided at the outlet of the heater 408, which is used to measure the fluid temperature at the outlet of the heater 408. After heating, the stop valve 409 has a switch function. The mass flow meter 410 can determine whether the medium is supercritical state / dense phase / liquid phase carbon dioxide, and is used to detect the mass flow of carbon dioxide filled into the main pipeline 201. The bypass stop valve 412 has a switch function. The flow meter stop valve 411 has a switch function. By increasing the fluid pressure through the low-temperature and high-pressure plunger pump 405 and increasing the fluid temperature through the heater 408, supercritical state / dense phase / liquid phase / gas phase carbon dioxide can be obtained.

[0097] The pressure and temperature requirements for each phase of carbon dioxide are:

[0098] Gas phase: pressure 3.0-6.0MPa, temperature 25-45°C. Liquid phase: pressure 4.5-6.0MPa, temperature -20-5°C.

[0099] Dense phase: pressure 8.1-12.0MPa, temperature -20-20℃.

[0100] Supercritical state: pressure 8.1-12.0MPa, temperature 35-45℃.

[0101] The pressure sensor PT and temperature sensor TT are provided at the front and rear ends of the pressure reducing valve 302 of the pressure reducing and temperature controlling device 3, which can measure the pressure and temperature at the inlet / outlet of the pressure reducing valve 302. The pressure reducing valve 302 reduces the carbon dioxide liquid in the main pipeline 201 system to 2MPa by throttling. The cooler 303 cools the outlet carbon dioxide of the pressure reducing valve 302 to -20°C, ensuring that the temperature of the carbon dioxide fluid entering the vertical low-temperature storage tank 403 is always -20°C during the circulation process. The outlet of the cooler 303 is provided with a temperature sensor TT, which can measure the outlet fluid temperature of the cooler 303. The inlet stop valve 304 is in a closed state before the main stop valve 204 is opened.

[0102] In one embodiment, a multiphase carbon dioxide pipeline shutdown test is performed by a multiphase carbon dioxide pipeline shutdown and restart test system:

[0103] The inspection before gas supply includes checking the on-site power supply situation, data collection working situation, valve opening and closing situation, and heating belt 207 working situation. Once a problem is found, repair it immediately.

[0104] Wash the gas, open the exhaust valve 202 at the end of the main pipeline 201, close the trunk stop valve 204 and the flow meter stop valve 411, open the injection valve 103 on the gas phase filling branch, and start filling the gas phase carbon dioxide into the main pipeline 201.

[0105] Check the air tightness of the system. After filling for a few minutes, close the exhaust valve 202 and check all valves and various threaded connectors for leaks. If there is a leak, exhaust the carbon dioxide in the pipe and repair it after the pressure drops to 0. After the repair, refill the pipe and check if there is still a leak.

[0106] Filling gaseous carbon dioxide, after checking and confirming that there is no leaking point, continue filling gaseous carbon dioxide, and stop filling when the pressure in the main pipeline 201 is equal to the pressure of the carbon dioxide transport tanker;

[0107] Filling liquid carbon dioxide, open the injection valve 103 on the liquid filling branch, and ensure that the injection valve 103 on the gas filling branch is also in an open state, start filling liquid carbon dioxide, and open the exhaust valve 202 at the same time to speed up the filling rate;

[0108] Calculate the mass of carbon dioxide required to fill the main pipeline 201 according to the pressure, temperature and density of the phase (supercritical state / dense phase / liquid phase / gas phase) required by the test and the volume of the main pipeline 201;

[0109] The mass of the filled liquid carbon dioxide is determined by weighing the scale. When the mass of the filled carbon dioxide reaches the mass required for the stop-transmission test, the exhaust valve 202, the injection valve 103 on the gas phase filling branch and the injection valve 103 on the liquid phase filling branch are closed to stop filling.

[0110] Heat up, start the heating belt 207, observe the pressure and temperature in the pipe through the temperature and pressure measuring component 205 and the phase observation window 206, when the pressure reaches the expected pressure but the temperature does not reach the expected temperature, open the exhaust valve 202 to discharge excess carbon dioxide to prevent overpressure in the pipeline;

[0111] When the pressure and temperature in the pipe reach the expected test conditions, turn off the heating belt 207 and let it stand for at least 1 hour to ensure that the pressure and temperature in the pipe are evenly distributed;

[0112] Prepare all the collection equipment, and the temperature and pressure requirements for each phase are: supercritical state (pressure 8.1MPa to 12.0MPa, temperature 35℃ to 45℃), dense phase (pressure 8.1MPa to 12.0MPa, temperature -20℃ to 20℃), liquid phase (pressure 4.5MPa to 6.0MPa, temperature -20℃ to 5℃), and gas phase (pressure 3.0MPa to 6.0MPa, temperature 25℃ to 45℃).

[0113] The shut-down test begins, and the fluid in the pipe cools down naturally, simulating the shut-down process;

[0114] Detect and record the low-frequency pressure, pipe top fluid temperature, pipe bottom fluid temperature, and pipe wall temperature of each temperature and pressure measurement component 205 along the pipeline before and after the fluid is gasified during the stop process, observe the fluid phase state through the starting point, midpoint, and end point phase state observation windows 206, and calculate the liquid holdup;

[0115] After stopping the flow for a period of time, the fluid reaches the expected pressure, temperature and liquid holdup rate of the test, and the test ends.

[0116] Multiphase carbon dioxide pipeline restart filling test method:

[0117] Equipment inspection before restarting the filling test, including checking the on-site power supply, data collection working status, whether the main stop valve 204 is closed, whether the valve in the restart filling equipment 4 is closed, and whether the valve of the pressure reducing and temperature controlling equipment 3 is closed. If any problem is found, repair it immediately;

[0118] Confirm the process parameters of the fluid in the pipe before the restart filling test, confirm that the pipeline shutdown state is the process parameters, phase state and liquid holdup required before the restart filling test, and then conduct the restart filling test. For example, the carbon dioxide fluid is required to be a gas-liquid miscible phase, with a pressure of 6.1MPa, a temperature of 22.7℃ and a liquid holdup of 0.9;

[0119] Fill the cryogenic and high-pressure plunger pump 405, open the outlet stop valve 404, and fill the cryogenic and high-pressure plunger pump 405 with liquid carbon dioxide in the vertical cryogenic storage tank 403;

[0120] Fill the main pipeline 201 with liquid carbon dioxide, keep the trunk stop valve 204 closed, start the low-temperature high-pressure plunger pump 405, open the bypass stop valve 412 and the flow meter stop valve 411, and close the pre-heating stop valve 407;

[0121] The low-temperature high-pressure plunger pump 405 pressurizes the liquid carbon dioxide flowing out of the vertical low-temperature storage tank 403 to the required pressure, and then directly injects it into the main pipeline 201 over the heater 408;

[0122] The newly injected low-temperature liquid carbon dioxide fills and pressurizes the fluid in the pipeline that has been stopped for a period of time, and the pipeline pressure and temperature continue to rise;

[0123] By detecting the temperature and pressure of the fluid through the temperature and pressure measuring components 205 of the pipeline, the phase state of the fluid can be determined; the fluid liquid holdup can be calculated through the phase observation windows 206 at the starting point, midpoint and end point, and the change of the liquid holdup can be determined; the displacement of the low-temperature high-pressure plunger pump 405 can be detected through the mass flow meter 410; the displacement of the low-temperature high-pressure plunger pump 405 can be adjusted through the frequency conversion device of the low-temperature high-pressure plunger pump 405;

[0124] The pressure and temperature sensors TT before and after the equipment can detect the pressure and temperature. During the filling process, the gas phase carbon dioxide completes the transformation into the liquid phase carbon dioxide. When the carbon dioxide fluid pressure is higher than 7.38MPa, the liquid phase carbon dioxide completes the transformation into the dense phase carbon dioxide.

[0125] Fill the main pipeline 201 with supercritical carbon dioxide. When the fluid in the pipeline is in a dense phase and the pressure reaches 9 MPa, open the stop valve 407 before heating and the stop valve 409 after heating, close the bypass stop valve 412, start the heater 408, and control the outlet temperature of the heater 408 fluid to the required temperature of supercritical carbon dioxide, such as 40° C. That is, the carbon dioxide fluid at the outlet of the heater 408 is in a supercritical phase, and the supercritical carbon dioxide entering the main pipeline 201 from the outlet of the heater 408 will push the dense phase carbon dioxide in the pipeline to move downstream;

[0126] When the fluid pressure in the pipeline reaches 12MPa, open the main stop valve 204, start the pressure reduction and temperature control equipment 3, put the pressure reducing valve 302 into use, start the cooler 303, open the inlet stop valve 304, and the dense phase carbon dioxide at the end of the main pipeline 201 flows through the pressure reducing valve 302, and the fluid pressure is reduced from 12MPa to 2MPa, and flows through the cooler 303 to reduce the fluid temperature to -20°C. The fluid after pressure reduction and temperature reduction enters the vertical low-temperature storage tank 403, and the fluid circulates. The temperature and pressure of the fluid are detected by the temperature and pressure measurement component 205 at the end of the main pipeline 201, and the fluid density is detected by the mass density meter 203. When it is determined that the phase state of the fluid before the main stop valve 204 is supercritical, it can be determined that the supercritical carbon dioxide after the heater 408 has flowed from the starting point of the pipeline to the end of the pipeline, the pipeline is successfully restarted, and the test is over.

[0127] In one embodiment, the multiphase carbon dioxide pipeline shutdown and restart test system also includes a bursting disc 208 arranged on the main pipeline 201, and the bursting disc 208 is connected to a bursting pipe externally. Once the pressure reaches the bursting pressure, the bursting disc 208 can automatically start to explode. The bursting pressure can be 15MPa, which is lower than the design pressure of the main pipeline 201, and the design pressure of the main pipeline 201 is 16MPa. For safety, a 1m pipe is connected above the bursting disc to vertically discharge to the atmosphere. A DN50 bursting pipe is set in the cross section of the main pipeline 201 for installing a bursting disc with a design bursting pressure of 15MPa. In order to avoid potential damage caused by accidental explosion of the bursting disc, the height of the bursting pipe is set to be about 1m. When the main pipeline 201 is over-pressured, the pressure can be relieved by the rupture of the bursting disc 208. The bursting disc 208 uses a bursting disc 208 that can crack in milliseconds to control the pipeline leakage and opening. It can avoid the situation where the carbon dioxide fluid generates dry ice and blocks the safety valve when flowing through the safety valve with a large pressure difference due to the Joule-Thomson effect, thereby improving the safety of pressure relief.

[0128] Specifically, the multiphase carbon dioxide pipeline shutdown and restart test system also includes a controller and a weighing scale for weighing the carbon dioxide transport tank truck. The filling branch 1 includes a filling hose 101 and a rigid injection pipe 102. The filling hose 101 has one end connected to the connection port of the carbon dioxide transport tank truck; the rigid injection pipe 102, the other end of the filling hose 101 is connected to one end of the rigid injection pipe 102, and the other end of the rigid injection pipe 102 is connected to the main pipeline 201. The rigid injection pipe 102 is provided with an injection valve 103, and the injection valve 103 is electrically connected to the controller. The controller is configured as follows:

[0129] According to the weighing information of the weighing scale, the injection valve 103 is closed.

[0130] The carbon dioxide transport tank truck uses gas-liquid mixed phase carbon dioxide at a pressure of 2.0MPa and a temperature of -20℃ as the medium source. The weighing scale can measure the weight change of the carbon dioxide transport tank truck to calculate the mass of carbon dioxide injected into the main pipeline 201 by the carbon dioxide transport tank truck. The interface of the filling branch 1 is fixed on the carbon dioxide transport tank truck and is used to connect the detachable filling branch 1. The rigid injection pipe 102, which can be a steel pipe, is used as a fixing device to receive the gas / liquid from the filling hose 101. The injection valve 103 is used to control the injection flow of carbon dioxide; during the injection process, gaseous carbon dioxide is first injected to empty and cool the main pipeline 201, and then liquid carbon dioxide is injected. The mass of the injected gas and liquid can be known by the weighing scale. After the injection is completed, the injection valve 103 on the gas phase filling branch and the injection valve 103 on the liquid phase filling branch are closed to stop the gas injection.

[0131] The multiphase carbon dioxide pipeline shutdown and restart test system also includes a temperature control box, a heating belt 207 and an insulation layer. The method of "liquid carbon dioxide injection-heating and increasing temperature and pressure" is used to make the carbon dioxide reach the set initial test pressure and initial test temperature. The temperature of the heating belt 207 is controlled by the temperature control box to increase the temperature of the fluid in the pipe, thereby increasing the pressure to achieve an initial phase of carbon dioxide that meets the conditions. The heating belt 207 is attached to the wall of the pipeline by winding, and the distance between two adjacent circles of the heating belt 207 is about 200mm. The opening and closing and temperature of multiple heating belts 207 are set and controlled by multiple temperature control boxes. The heating belt 207 transfers heat to the outer wall of the pipeline, and then increases the temperature of the fluid in the pipe by heat conduction. Due to the increase in temperature, the thermal motion of the molecules inside the fluid increases, and the heat expands, and the pressure increases accordingly.

[0132] It should be noted that the heating belt 207 is wrapped with a heat-insulating layer and a fire-blocking layer, and the heating belt 207 includes a heating wire, an insulating layer and a protective cover which are nested in sequence from the inside to the outside.

[0133] In one embodiment, the heating belt 207 is composed of a copper core conductor, a polyethylene insulation layer, a plastic protective sleeve, etc., and the power of the heating belt 207 is 20-40W / m. The outside of the heating belt 207 is wrapped by an insulation layer, which is composed of rock wool and fireproof and waterproof glass cloth with a thickness of about 60mm, thereby ensuring that the insulation cotton is waterproof and anti-electric to avoid accidents. The heating belt 207 can heat carbon dioxide to a temperature of 60°C within 4 hours under full load conditions of -20°C and 2MPa. The heating belt 207 has a low cost, a simple structure, and safe operation. .

[0134] Specifically, the temperature and pressure measurement assembly 205 includes a pressure parameter sensor 2051, a pipe top temperature sensor 2052, a pipe bottom temperature sensor 2053 and a pipe wall temperature sensor 2054 which are arranged at circumferential intervals along the main pipeline 201. The pressure parameter sensor 2051 is used to detect the high-frequency pressure of carbon dioxide and the low-frequency pressure of carbon dioxide. The pressure parameter sensor 2051, the pipe top temperature sensor 2052, the pipe bottom temperature sensor 2053 and the pipe wall temperature sensor 2054 are all plugged into the main pipeline 201.

[0135] Specifically, the filling branch 1 extends along the first direction, the main pipeline 201 includes a transverse first pipe section 2011, a transverse last pipe section 2012 and an intermediate pipe section, the transverse first pipe section 2011 and the transverse last pipe section 2012 both extend along the first direction, and the transverse first pipe section 2011 and the transverse last pipe section 2012 are arranged relatively along the second direction, the transverse first pipe section 2011 is connected to the injection equipment, and the transverse last pipe section 2012 is connected to the pressure reducing pipeline 301. In one embodiment, the first direction is the length direction, that is, the left-right direction on the horizontal plane, the second direction is the width direction, that is, the front-back direction on the horizontal plane, and the first direction and the second direction are perpendicular to each other.

[0136] The temperature and pressure measurement components 205 in this embodiment (arranged every 10m) and the main pipeline 201 are arranged to go back and forth at the same horizontal plane height. The main pipeline 201 uses seamless steel pipes, which are composed of long straight pipes, curved pipes, and short straight pipes. The main pipeline 201 is laid overhead by a bracket, the center of the pipeline is 1m-1.5m above the ground, and the bracket spacing is within the range of 8m-10m. The bracket includes a reinforced concrete foundation, anchor bolts (embedded), a pad, a support plate, a rib plate, a lower clamping ring, an upper clamping ring, a clamping plate, bolts and nuts and other structures.

[0137] In one embodiment, the middle pipe section includes two vertical sections 2013 and a bent section 2014 connected between the two vertical sections 2013, and the bent section 2014 protrudes toward the direction close to the pressure reducing pipeline 301. The bent section 2014 is arranged in a U shape, which can improve the compactness of the pipeline of the multi-phase carbon dioxide pipeline shutdown and restart test system.

[0138] The present invention also proposes a multiphase carbon dioxide pipeline shutdown test method, which is applied to the multiphase carbon dioxide pipeline shutdown and restart test system as above, wherein the two filling branches 1 are respectively a gas phase filling branch and a liquid phase filling branch, and the multiphase carbon dioxide pipeline shutdown test method comprises:

[0139] Open the exhaust valve 202, close the trunk stop valve 204 and the flow meter stop valve 411, and fill the main pipeline 201 with gas phase carbon dioxide through the gas phase filling branch;

[0140] After the first preset filling time, the exhaust valve 202 is closed;

[0141] When it is confirmed that there is no gas leakage in the multiphase carbon dioxide pipeline stop and restart test system, continue to fill the main pipeline 201 with gaseous carbon dioxide until the pressure in the main pipeline 201 is the same as the pressure of the carbon dioxide transport tank truck;

[0142] Filling the main pipeline 201 with gaseous carbon dioxide and liquid carbon dioxide through the gaseous carbon dioxide filling branch and the liquid carbon dioxide filling branch, while opening the exhaust valve 202 until the preset filling weight of liquid carbon dioxide is filled, closing the exhaust valve 202 and stopping the carbon dioxide filling of the gaseous carbon dioxide filling branch and the liquid carbon dioxide filling branch;

[0143] The heating belt 207 is started to heat the carbon dioxide in the main pipeline 201 until the pressure of the carbon dioxide in the main pipeline 201 reaches a desired pressure and the temperature of the carbon dioxide reaches a desired temperature;

[0144] The heating belt 207 is turned off, and the carbon dioxide in the main pipeline 201 is left to stand for a second preset time to simulate cooling. The temperature and pressure parameters in the main pipeline 201 are detected and recorded by the temperature and pressure measurement component 205, and the liquid holdup of carbon dioxide in the main pipeline 201 is collected through the phase observation window 206.

[0145] In this embodiment, the multiphase carbon dioxide pipeline shutdown test method can carry out a multiphase carbon dioxide pipeline shutdown test, and has a wide range of applications. A sufficient amount of liquid carbon dioxide required by the test is injected into the main pipeline 201, and the carbon dioxide fluid in the main pipeline 201 is heated by the heating belt 207 to increase the temperature and pressure to reach the gas phase, liquid phase, dense phase, and supercritical phase. The main pipeline 201 can carry out a multiphase carbon dioxide shutdown test, and the pressure, temperature, and phase of the carbon dioxide in the pipeline before the shutdown can be adjusted according to the test needs.

[0146] The present invention further provides a multiphase carbon dioxide pipeline restart test method, which is applied to the multiphase carbon dioxide pipeline shutdown and restart test system as described above, and the multiphase carbon dioxide pipeline restart test method comprises:

[0147] Determine the carbon dioxide phase state at the start-up time and the carbon dioxide phase state after the start-up is completed required for the restart experiment;

[0148] At the start-up time, the carbon dioxide phase is a gas-liquid mixed phase or a gas phase. After the start-up is completed, the carbon dioxide phase is required to be supercritical carbon dioxide. Liquid carbon dioxide, dense carbon dioxide and supercritical carbon dioxide are sequentially filled into the main pipeline 201 through the pressure reducing and temperature controlling device 3 and the restart filling device 4.

[0149] At the start-up time, the carbon dioxide phase is a gas-liquid mixed phase or a gas phase. After the start-up is completed, the carbon dioxide phase is required to be a dense phase carbon dioxide. Liquid phase carbon dioxide and dense phase carbon dioxide are sequentially filled into the main pipeline 201 through the pressure reducing temperature control device 3 and the restart filling device 4;

[0150] At the start-up time, the carbon dioxide phase is a gas-liquid mixed phase or a gas phase. After the start-up is completed, the carbon dioxide phase is required to be liquid carbon dioxide. Liquid carbon dioxide is filled into the main pipeline 201 through the pressure reducing temperature control device 3 and the restart filling device 4.

[0151] In this embodiment, the multiphase carbon dioxide pipeline restart test method can carry out a multiphase carbon dioxide pipeline restart test and has a wide range of applications.

[0152] In one embodiment, at the start-up time, the carbon dioxide phase is a gas-liquid mixed phase or a gas phase. After the start-up is completed, the carbon dioxide phase is required to be supercritical carbon dioxide. The liquid phase carbon dioxide, the dense phase carbon dioxide and the supercritical carbon dioxide are sequentially filled into the main pipeline 201 through the pressure reducing temperature control device 3 and the restart filling device 4, including:

[0153] When it is confirmed that the current parameters of the carbon dioxide in the main pipeline 201 are the same as the parameters required at the restart time, the carbon dioxide is filled into the low-temperature and high-pressure plunger pump 405 through the vertical low-temperature storage tank 403 until the low-temperature and high-pressure plunger pump 405 is filled;

[0154] Open the bypass stop valve 412 and the flowmeter stop valve 411, close the pre-heating stop valve 407 and the trunk stop valve 204, pressurize the liquid phase carbon dioxide flowing out of the vertical cryogenic storage tank 403 to the required pressure through the cryogenic high-pressure plunger pump 405, and inject it into the main pipeline 201 over the heater 408 until the carbon dioxide in the main pipeline 201 is completely transformed into dense phase carbon dioxide;

[0155] Open the stop valve 407 before heating and the stop valve 409 after heating, close the bypass stop valve 412, start the heater 408, control the outlet temperature of the heater 408 to the required temperature of the supercritical carbon dioxide, and the supercritical carbon dioxide entering the main pipeline 201 from the heater 408 pushes the dense carbon dioxide to move downstream;

[0156] Determine that the fluid pressure in the main pipeline 201 reaches the supercritical restart pressure, open the trunk stop valve 204, start the pressure reducing valve 302 and the cooler 303, open the inlet stop valve 304, and allow the carbon dioxide in the main pipeline 201 to flow through the pressure reducing valve 302 and the cooler 303 and then enter the vertical low-temperature storage tank 403 until the carbon dioxide flowing out of the trunk stop valve 204 is in a supercritical state.

[0157] Specifically, when it is determined that the multiphase carbon dioxide pipeline is leaking during the shutdown and restart test system, the carbon dioxide filling is stopped and the carbon dioxide in the main pipeline 201 is discharged through the exhaust valve 202 until the carbon dioxide pressure in the main pipeline 201 drops to the exhaust pressure.

[0158] In one embodiment, the length of the main pipeline 201 is 100m, the outer diameter of the pipe is 114.3mm, the wall thickness is 10mm, and the design pressure is 16MPa. The pressure, temperature, and liquid holdup change data of the supercritical carbon dioxide (pressure 12MPa, temperature 40°C) pipeline shutdown process are obtained by using a multiphase carbon dioxide pipeline shutdown and restart test system, and the coordinated change law of carbon dioxide temperature, pressure, phase, and liquid holdup can be obtained. That is, before the pipeline is shut down, the fluid in the main pipeline 201 needs to be in a supercritical state, with a pressure of 12MPa and a temperature of 40°C.

[0159] The atmospheric environment temperature of 2°C can be simulated, and the mass of carbon dioxide that needs to be filled into the test pipeline under this phase is calculated in advance to be 471 kg. A sufficient amount of liquid carbon dioxide is injected into the pipeline using a carbon dioxide transport tank truck, and the pipe wall is heated by the heating belt 207 to raise the temperature and pressure of the carbon dioxide fluid to the required test conditions (pressure 12 MPa, temperature 40°C).

[0160] Close the injection valve 103 and the main stop valve 204 on the filling branch 1, and close the heating belt 207. The fluid in the pipe exchanges heat with the atmosphere through the insulation layer and cools down naturally. The test simulates the stopping process. Use a carbon dioxide transport tanker to inject a sufficient amount of liquid carbon dioxide into the pipeline, preferably 2% more, and heat it with the heating belt 207. When the temperature reaches the test requirements, the pressure may be higher than the test requirements. At this time, open the exhaust valve 202 to discharge part of the liquid carbon dioxide to prevent the pipeline from overpressure. Prevent the injection of less liquid carbon dioxide, which may cause the pressure to meet the test requirements, but the temperature does not meet the test requirements.

[0161] In one embodiment, the supercritical carbon dioxide transmission stop test method is:

[0162] Carry out a pre-gas supply inspection, including on-site power supply conditions, data collection work conditions, valve opening and closing conditions, and heating belt 207 working conditions. Once a problem is found, repair it immediately.

[0163] Wash the air to exhaust the air in the pipe, stop the carbon dioxide transport tanker on the weighing scale, open the exhaust valve 202, close the main line stop valve 204 and the flow meter stop valve 411, and open the injection valve 103 on the gas phase filling branch. Start filling the main pipeline 201 with gas phase carbon dioxide through the carbon dioxide transport tanker.

[0164] Check the air tightness of the system. After filling for a few minutes, close the exhaust valve 202 and check all valves and various threaded connectors for leaks. If there is a leak, exhaust the carbon dioxide in the pipe and repair it after the pressure drops to 0. After the repair, refill the pipe and check if there is still a leak.

[0165] Fill the gaseous carbon dioxide, and after confirming that there is no leakage point, continue filling the gaseous carbon dioxide. When the pressure in the main pipeline 201 is equal to the pressure of the carbon dioxide transport tank truck, stop filling.

[0166] To fill liquid carbon dioxide, open the injection valve 103 on the liquid filling branch, and ensure that the injection valve 103 on the gas filling branch is also in an open state, start filling liquid carbon dioxide, and open the exhaust valve 202 at the same time to speed up the filling rate.

[0167] According to the supercritical pressure and temperature (pressure 12MPa, temperature 40°C) and the volume of the main pipeline 201 required by the test, the supercritical carbon dioxide density and the mass of carbon dioxide (471kg) required to be injected into the main pipeline 201 can be calculated in advance.

[0168] By measuring with a weighing scale, it can be determined whether the mass of liquid carbon dioxide filled in the main pipeline 201 has reached the required mass (471 kg). When the mass of filled carbon dioxide reaches the mass required for the stop test (471 kg), the exhaust valve 202, the injection valve 103 on the gas phase filling branch and the injection valve 103 on the liquid phase filling branch are closed to stop filling.

[0169] Heat up and start the heating belt 207. The test personnel can observe the pressure and temperature in the tube through the temperature and pressure measurement component 205 and the phase observation window 206. When the pressure reaches 12MPa and the temperature does not reach 40°C, open the exhaust valve 202 to discharge excess carbon dioxide fluid to prevent overpressure.

[0170] Let it stand until the pressure in the tube reaches 12 MPa and the temperature reaches 40°C, turn off the heating belt 207, and let it stand for at least 1 hour to ensure that the pressure and temperature in the tube are evenly distributed. During this period, all the collection equipment should be prepared.

[0171] During the initial shutdown process, the fluid in the pipe exchanges heat through the insulation layer and the atmosphere, and cools down naturally, simulating the shutdown process. The low-frequency pressure, pipe top fluid temperature, pipe bottom fluid temperature, and pipe wall temperature of each temperature and pressure measurement component 205 along the main pipeline 201 before, during, and after the gasification of the fluid during the shutdown process are detected and recorded. The fluid phase state is observed through the starting point, midpoint, and end point phase state observation windows 206, and the liquid holdup is calculated. The coordinated change law of carbon dioxide temperature, pressure, phase state, and liquid holdup can be explored to provide basic data for drawing the carbon dioxide phase state migration path, and to derive the functional relationship between temperature, pressure, and density before carbon dioxide gasification, the pressure and temperature prediction formula at the initial gasification moment, and the liquid holdup change prediction formula after gasification. The temperature, pressure, phase state, and liquid holdup before and after gasification of the shutdown process can be quantitatively described, and operational guidance can be provided for pipeline shutdown and restart, reducing the risk of pipeline shutdown and restart. After stopping the flow for a period of time, when the carbon dioxide fluid has been gasified, such as when the pressure is 6.1MPa and the temperature is 22.7℃, the test ends.

[0172] Implementation plan for the supercritical carbon dioxide pipeline filling test after stopping transmission until the gas-liquid mixture is reached:

[0173] Vertical cryogenic storage tank 403, design pressure is 2.5MPa, design temperature is -30℃, volume is 1.2m 3 As the gas source for pipeline restart, liquid carbon dioxide is stored in the vertical cryogenic storage tank 403 at a pressure of 2.0 MPa and a temperature of -20°C.

[0174] Low temperature and high pressure plunger pump 405 is used for pressurizing liquid carbon dioxide. It pressurizes the liquid carbon dioxide (pressure 2.0MPa, temperature -20℃) at the pump inlet to a suitable pressure. The pump inlet design pressure is 2.5MPa, the design temperature is -30℃; the pump outlet design pressure is 12MPa, the design temperature is 20℃; the maximum pump displacement is 0.1kg / s (0.01m / s, 0.31m 3 / h), variable frequency speed regulation, speed regulation range is 50%-100% of rated flow. 0.1kg / s liquid carbon dioxide is pressurized from 2MPa to 12MPa, the calculated power is 1.3kW.

[0175] Heater 408, the minimum inlet temperature is -15℃, the maximum outlet temperature is 45℃, according to 0.1kg / s (0.01m / s), the specific heat capacity of carbon dioxide is 2.3KJ / (kg·℃), and the power is 14kW. Mass flow meter 410, the measuring medium is liquid / dense phase / supercritical carbon dioxide, used to detect the multiphase carbon dioxide flow injected into the main pipeline 201, the design pressure is 16MPa. Pressure reducing valve 302, used to reduce the pressure of 12MPa, 33℃, and mass flow of 0.1kg / s fluid before the valve to 2MPa. According to calculations, due to the throttling temperature drop of pressure reducing valve 302, the calculated temperature after the valve is -18.8℃. Cooler 303, used to further cool the mass flow of 0.1kg / s and -18.8℃ carbon dioxide fluid after the pressure reducing valve 302 to -20℃, and then flow into the vertical low-temperature storage tank 403.

[0176] A restart filling test was carried out after the supercritical carbon dioxide pipeline was shut down to a gas-liquid mixed phase (liquid holdup was 0.9). The phase migration path of the gas-liquid mixed carbon dioxide pipeline restart process with a liquid ratio of 0.9 was obtained through the test. The risk of restarting the pipeline after stopping the pipeline to a gas-liquid mixed phase at different liquid holdups was evaluated, and a safe restart operation plan was given in combination with the flow variable parameter control of the low-temperature and high-pressure plunger pump 405.

[0177] According to the test data of the pressure (restart pressure) after the low-temperature high-pressure plunger pump 405, the restart pressure composition is analyzed, and the restart pressure calculation formula is given by analogy with the crude oil pipeline. The supercritical carbon dioxide pipeline (starting pressure 12MPa, temperature 40℃) has been stopped for a period of time, and the fluid in the pipeline has been gasified. The initial conditions of the restart filling test are 6.1MPa and 22.7℃ of gas-liquid mixed phase fluid pressure at the starting point of the pipeline. At this time, the fluid liquid holdup is 0.9, that is, 10% of the fluid has been gasified.

[0178] During the restart of the filling test process, ensure that the trunk stop valve 204 is always closed, start the low-temperature and high-pressure plunger pump 405, and newly injected low-temperature liquid carbon dioxide is used to fill and pressurize the fluid in the pipeline that has been stopped for a period of time. The pipeline pressure and temperature continue to increase, and the gas phase carbon dioxide completes the conversion to liquid phase carbon dioxide, and the liquid phase carbon dioxide completes the conversion to dense phase carbon dioxide.

[0179] When the pressure at the end of the pipeline reaches 12MPa and the temperature reaches 40℃, it means that the supercritical carbon dioxide at the starting point of the pipeline has flowed to the end of the pipeline, and the pipeline has returned to the transportation state before the shutdown. The pipeline has been successfully restarted and the test is over.

[0180] Test method for restarting and filling supercritical carbon dioxide pipeline after stopping transmission to gas-liquid miscible phase (liquid holdup is 0.9):

[0181] Before restarting the filling test, check the equipment, including the on-site power supply situation, data collection work situation, whether the main stop valve 204 is closed, whether the valve in the restart filling equipment 4 is closed, and whether the valve of the pressure reducing and temperature controlling equipment 3 is closed. If any problem is found, repair it immediately.

[0182] Before the restart filling test, confirm the process parameters of the fluid in the pipe, confirm the process parameters, phase state and liquid holdup required before the pipeline is shut down to the restart filling test, and then conduct the restart filling test. For example, the carbon dioxide fluid is required to be a gas-liquid miscible phase, with a pressure of 6.1MPa, a temperature of 22.7℃ and a liquid holdup of 0.9.

[0183] Fill the cryogenic and high-pressure plunger pump 405 , open the outlet stop valve 404 , and fill the cryogenic and high-pressure plunger pump 405 with the liquid carbon dioxide in the vertical cryogenic storage tank 403 .

[0184] Fill the main pipeline 201 with liquid carbon dioxide, keep the trunk stop valve 204 closed, start the low-temperature and high-pressure plunger pump 405, open the bypass stop valve 412 and the flow meter stop valve 411 at the same time, close the pre-heating stop valve 407, and the low-temperature and high-pressure plunger pump 405 pressurizes the liquid carbon dioxide in the vertical low-temperature storage tank 403 to the required pressure, bypasses the heater 408, and directly injects it into the main pipeline 201.

[0185] During the filling process, the newly injected low-temperature liquid carbon dioxide fills and pressurizes the fluid in the pipeline that has been stopped for a period of time, and the pipeline pressure and temperature continue to rise. Part of the gas phase carbon dioxide reaches the liquefaction pressure and completes the transformation to liquid phase carbon dioxide. When the carbon dioxide fluid pressure is higher than 7.38MPa, the liquid phase carbon dioxide completes the transformation to dense phase carbon dioxide.

[0186] Detect the temperature and pressure of the fluid through the temperature and pressure measurement components 205 of the pipeline to determine the phase state of the fluid;

[0187] The fluid holdup can be calculated through the phase observation window 206 at the starting point, the middle point and the end point, thereby determining the change in the holdup;

[0188] The flow rate injected into the main pipeline 201 can be detected by the mass flow meter 410;

[0189] The displacement of the low-temperature and high-pressure plunger pump 405 can be regulated by the frequency conversion device of the low-temperature and high-pressure plunger pump 405 .

[0190] The pressure and temperature can be detected by the pressure sensor PT and temperature sensor TT before and after the equipment.

[0191] The main pipeline 201 is filled with supercritical carbon dioxide. When the fluid pressure in the pipeline reaches 9MPa and the phase state is dense phase, the stop valve 407 before heating and the stop valve 409 after heating are opened, the bypass stop valve 412 is closed, and the heater 408 is started. The outlet temperature of the fluid of the heater 408 is controlled to be the required temperature of the supercritical state, such as 40°C. That is, the carbon dioxide fluid at the outlet of the heater 408 is in the supercritical phase. The supercritical carbon dioxide entering the main pipeline 201 from the outlet of the heater 408 will push the dense phase carbon dioxide in the pipe to move downstream. Since the main line stop valve 204 is in a closed state, the newly injected fluid has a pressure-holding effect on the existing fluid in the pipe, and the fluid temperature at the end of the main pipeline 201 will continue to rise.

[0192] Open the trunk stop valve 204. When the fluid pressure in the pipeline reaches 12 MPa and the fluid temperature at the end of the main pipeline 201 is 33°C (simulated calculated value), open the trunk stop valve 204.

[0193] The pressure reducing and temperature controlling device 3 is started, the pressure reducing valve 302 is put into use, the cooler 303 is started, and the inlet stop valve 304 is opened.

[0194] The dense phase carbon dioxide at the end of the main pipeline 201 flows through the pressure reducing valve 302, the fluid pressure is reduced from 12MPa to 2MPa, and the fluid temperature is reduced from 33°C to -18.8°C. The fluid then flows through the cooler 303, and the cooler 303 reduces the fluid temperature to -20°C. The depressurized and cooled fluid flows into the vertical cryogenic storage tank 403.

[0195] After the restart filling test is completed, the temperature and pressure of the fluid are detected by the temperature and pressure measuring component 205 at the end of the main pipeline 201, and the fluid density is detected by the mass density meter 203. When it is determined that the fluid phase before the main stop valve 204 is supercritical, it can be known that the supercritical carbon dioxide at the outlet of the heater 408 has flowed from the starting point of the pipeline to the end of the pipeline, and the test is completed.

[0196] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0197] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or communication with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be a connection between two elements or an interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0198] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0199] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A multiphase carbon dioxide pipeline shutdown and restart test system, characterized in that: The multiphase carbon dioxide pipeline shutdown and restart test system comprises: The injection device comprises two filling branches (1) arranged in parallel, wherein the two filling branches (1) are used to connect to a carbon dioxide transport tank truck; A main pipeline device (2), comprising a main pipeline (201) and an exhaust valve (202), a mass density meter (203) and a trunk stop valve (204) arranged in sequence at the end of the main pipeline (201); the ends of the two filling branches (1) converge at the head end of the main pipeline (201); a plurality of temperature and pressure measurement components (205) are arranged at first intervals on the main pipeline (201); the temperature and pressure measurement components (205) are used to detect the high-frequency pressure of carbon dioxide, the low-frequency pressure of carbon dioxide, the temperature of carbon dioxide and the temperature of the pipeline wall in the main pipeline (201); a plurality of transparent phase observation windows (206) are arranged at second intervals on the main pipeline (201); and a heating belt (207) for heating the main pipeline (201) is wrapped outside the main pipeline (201); A pressure reducing and temperature controlling device (3), comprising a pressure reducing pipeline (301) and a pressure reducing valve (302), a cooler (303), and an inlet stop valve (304) arranged on the pressure reducing pipeline (301), wherein the head end of the pressure reducing pipeline (301) is connected to the end of the main pipeline (201); The restart filling device (4) comprises a restart pipe (401), a bypass pipe (402), a vertical low-temperature storage tank (403) arranged on the restart pipe (401), an outlet stop valve (404), a low-temperature high-pressure plunger pump (405), a one-way valve (406), a pre-heating stop valve (407), a heater (408), a post-heating stop valve (409), a mass flow meter (410) and a flow meter stop valve (411), wherein the bypass pipe (402) is provided with a bypass stop valve (412), and the One end of the bypass pipe (402) is connected to the pipeline between the pre-heating stop valve (407) and the one-way valve (406), and the other end of the bypass pipe (402) is connected to the pipeline between the post-heating stop valve (409) and the mass flow meter (410). The head end of the restart pipe (401) is connected to the end of the pressure reducing pipe (301), and the end of the restart pipe (401) is connected to the restart interface on the main pipe (201), and the restart interface is arranged close to the injection device.

2. The multiphase carbon dioxide pipeline shutdown and restart test system according to claim 1 is characterized in that: The multiphase carbon dioxide pipeline shutdown and restart test system further comprises a bursting disc (208) arranged on the main pipeline (201), and the bursting disc (208) is externally connected to a bursting pipe.

3. The multiphase carbon dioxide pipeline shutdown and restart test system according to claim 2 is characterized in that: The multiphase carbon dioxide pipeline shutdown and restart test system further comprises a controller and a weighing scale for weighing the carbon dioxide transport tank truck, and the filling branch (1) comprises: A filling hose (101), one end of which is connected to a connection port of the carbon dioxide transport tank truck; A rigid injection pipe (102), the other end of the filling hose (101) is connected to one end of the rigid injection pipe (102), the other end of the rigid injection pipe (102) is connected to the main pipeline (201), the rigid injection pipe (102) is provided with an injection valve (103), the injection valve (103) is electrically connected to the controller, and the controller is configured as follows: According to the weighing information of the weighing scale, the injection valve (103) is closed.

4. The multiphase carbon dioxide pipeline shutdown and restart test system according to claim 1, characterized in that: The heating belt (207) is wrapped with a heat-insulating layer and a fire-blocking layer, and the heating belt (207) comprises a heating wire, an insulating layer and a protective cover which are nested in sequence from the inside to the outside.

5. The multiphase carbon dioxide pipeline shutdown and restart test system according to any one of claims 1 to 4, characterized in that: The temperature and pressure measurement assembly (205) comprises a pressure parameter sensor (2051), a pipe top temperature sensor (2052), a pipe bottom temperature sensor (2053) and a pipe wall temperature sensor (2054) which are arranged at intervals along the circumference of the main pipe (201); the pressure parameter sensor (2051) is used to detect the high-frequency pressure of carbon dioxide and the low-frequency pressure of carbon dioxide; the pressure parameter sensor (2051), the pipe top temperature sensor (2052), the pipe bottom temperature sensor (2053) and the pipe wall temperature sensor (2054) are all plug-connected to the main pipe (201).

6. The multiphase carbon dioxide pipeline shutdown and restart test system according to any one of claims 1 to 4, characterized in that: The filling branch (1) extends along a first direction, and the main pipeline (201) comprises a transverse first pipe section (2011), a transverse last pipe section (2012) and an intermediate pipe section, the transverse first pipe section (2011) and the transverse last pipe section (2012) both extend along the first direction, and the transverse first pipe section (2011) and the transverse last pipe section (2012) are arranged opposite to each other along a second direction, the transverse first pipe section (2011) is connected to the injection device, and the transverse last pipe section (2012) is connected to the pressure reducing pipeline (301).

7. The multiphase carbon dioxide pipeline shutdown and restart test system according to claim 6, characterized in that: The intermediate pipe section comprises two vertical sections (2013) and a bent section (2014) connected between the two vertical sections (2013), and the bent section (2014) protrudes in a direction close to the pressure reducing pipe (301).

8. A multiphase carbon dioxide pipeline shutdown test method, characterized in that: The multiphase carbon dioxide pipeline shutdown test method is applied to the multiphase carbon dioxide pipeline shutdown and restart test system according to any one of claims 1 to 7, wherein the two filling branches (1) are respectively a gas phase filling branch and a liquid phase filling branch, and the multiphase carbon dioxide pipeline shutdown test method comprises: Opening the exhaust valve (202), closing the trunk stop valve (204) and the flow meter stop valve (411), and filling the main pipeline (201) with gaseous carbon dioxide through the gaseous filling branch; After filling for a first preset time, closing the exhaust valve (202); When it is determined that the multiphase carbon dioxide pipeline stop and restart test system has no gas leakage, continue to fill the main pipeline (201) with gaseous carbon dioxide until the pressure in the main pipeline (201) is the same as the pressure of the carbon dioxide transport tank truck; Filling the main pipeline (201) with gaseous carbon dioxide and liquid carbon dioxide through the gaseous carbon dioxide filling branch and the liquid carbon dioxide filling branch, while opening the exhaust valve (202) until a preset filling weight of liquid carbon dioxide is filled, closing the exhaust valve (202) and stopping the carbon dioxide filling of the gaseous carbon dioxide filling branch and the liquid carbon dioxide filling branch; Starting the heating belt (207) so that the heating belt (207) heats the carbon dioxide in the main pipeline (201) until the pressure of the carbon dioxide in the main pipeline (201) reaches a desired pressure and the temperature of the carbon dioxide reaches a desired temperature; The heating belt (207) is turned off, the system is left to stand for a second preset time and the carbon dioxide in the main pipeline (201) is subjected to simulated cooling, the temperature and pressure parameters in the main pipeline (201) are detected and recorded by the temperature and pressure measurement component (205), and the liquid holdup of the carbon dioxide in the main pipeline (201) is collected by the phase observation window (206).

9. A multiphase carbon dioxide pipeline restart test method, characterized in that: The multiphase carbon dioxide pipeline restart test method is applied to the multiphase carbon dioxide pipeline shutdown and restart test system according to any one of claims 1 to 7, and the multiphase carbon dioxide pipeline restart test method comprises: Determine the carbon dioxide phase state at the start-up time and the carbon dioxide phase state after the start-up is completed required for the restart experiment; At the start-up time, the carbon dioxide phase is a gas-liquid mixed phase or a gas phase, and after the start-up is completed, the carbon dioxide phase is required to be supercritical carbon dioxide, and liquid carbon dioxide, dense carbon dioxide and supercritical carbon dioxide are sequentially filled into the main pipeline (201) through the pressure reducing and temperature controlling device (3) and the restart filling device (4); At the start-up time, the carbon dioxide phase is a gas-liquid mixed phase or a gas phase. After the start-up is completed, the carbon dioxide phase is required to be a dense phase carbon dioxide. Liquid phase carbon dioxide and dense phase carbon dioxide are sequentially filled into the main pipeline (201) through the pressure reducing and temperature controlling device (3) and the restart filling device (4); At the start-up time, the carbon dioxide phase is a gas-liquid mixed phase or a gas phase. After the start-up is completed, the carbon dioxide phase is required to be liquid carbon dioxide. Liquid carbon dioxide is filled into the main pipeline (201) through the pressure reducing and temperature controlling device (3) and the restart filling device (4).

10. The multiphase carbon dioxide pipeline restart test method according to claim 9, characterized in that: At the start-up time, the carbon dioxide phase is a gas-liquid mixed phase or a gas phase, and after the start-up is completed, the carbon dioxide phase is required to be supercritical carbon dioxide. The filling of liquid carbon dioxide, dense carbon dioxide and supercritical carbon dioxide into the main pipeline (201) in sequence through the pressure reducing and temperature controlling device (3) and the restart filling device (4) includes: When confirming that the current parameters of the carbon dioxide in the main pipeline (201) are the same as the parameters required at the restarting time, the carbon dioxide is filled into the low-temperature and high-pressure plunger pump (405) through the vertical low-temperature storage tank (403) until the low-temperature and high-pressure plunger pump (405) is filled; The bypass stop valve (412) and the flow meter stop valve (411) are opened, the pre-heating stop valve (407) and the trunk stop valve (204) are closed, and the liquid phase carbon dioxide flowing out of the vertical cryogenic storage tank (403) is pressurized to a required pressure by the cryogenic and high-pressure plunger pump (405), and injected into the main pipeline (201) over the heater (408) until the carbon dioxide in the main pipeline (201) is completely transformed into dense phase carbon dioxide; Open the pre-heating stop valve (407) and the post-heating stop valve (409), close the bypass stop valve (412), start the heater (408), control the outlet temperature of the heater (408) to the required temperature of supercritical carbon dioxide, and the supercritical carbon dioxide entering the main pipeline (201) from the heater (408) pushes the dense carbon dioxide to move downstream; Determine whether the fluid pressure in the main pipeline (201) reaches the supercritical restart pressure, open the main line stop valve (204), start the pressure reducing valve (302) and the cooler (303), open the inlet stop valve (304), and allow the carbon dioxide in the main pipeline (201) to flow through the pressure reducing valve (302) and the cooler (303) and then enter the vertical cryogenic storage tank (403) until the carbon dioxide flowing out of the main line stop valve (204) is in a supercritical state.

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