Supercritical CO2 pipeline emptying system and method based on bilateral release

Abstract

The invention discloses a supercritical CO2 pipeline emptying system and method based on double-side release, and the system comprises a valve chamber cut-off system, a valve chamber emptying system, a medium introduction and heating system, and a low-point temporary temperature detection system. The valve chambers on the two sides are used for rapid release in the early stage of release, CO2 stored in an upstream or downstream trunk line pipe is introduced from one side in the middle and later stage of release for pressure regulation and heating to promote vaporization of accumulated liquid, and a low-point temperature detection system is arranged, so that the release rate of a cut-off pipeline is effectively increased; and the problem of extremely low temperature caused by liquid-phase accumulated liquid vaporization possibly occurring in the low-point area of the cut-off pipeline is solved. By means of the method, efficient and safe operation of planned emptying of the supercritical CO2 pipeline can be achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon dioxide pipeline transportation, and in particular relates to a supercritical CO2 pipeline venting system and method based on double-side discharge. Background Art

[0002] Compared with conventional natural gas pipelines, supercritical CO2 pipelines have significant characteristics such as high unit volume density and phase change during the release of the medium in the pipe volume. This puts forward specific requirements for the control of the release time and the control of temperature changes caused by the vaporization of the medium during the release process.

[0003] For example, when the supercritical CO2 medium is released between two shut-off valves in a planned manner, its release rate is not only affected by the medium pressure, but also related to the medium phase state. Supercritical CO2 will experience three typical phases during the release process, including supercritical phase (dense phase), gas-liquid two-phase and gas phase.

[0004] During the phase transition, the medium in the pipeline will experience a considerable temperature drop to varying degrees. During the discharge process, affected by the ups and downs of the pipeline, the incompletely vaporized CO2 will tend to gather at the low point of the pipeline due to the influence of density, causing the pipe section near the low point of the pipeline to experience a more severe temperature drop. This may cause a monitoring blind spot in the distributed temperature detection and cause misjudgment of the temperature control during the discharge. In addition, due to the high pipeline pressure and more medium stored in the pipeline, the discharge time of supercritical CO2 will be much longer than that of conventional natural gas pipelines. The existing technology lacks corresponding solutions to solve the above problems. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a supercritical CO2 pipeline venting system and method based on double-sided discharge, which greatly improves the safe discharge rate, increases the operating temperature of the trunk pipeline during the discharge process, and realizes efficient and safe operation of planned venting of the supercritical CO2 pipeline.

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

[0007] A supercritical CO2 pipeline venting system based on double-sided discharge, the system is arranged on the CO2 pipeline trunk line, and the system comprises:

[0008] A valve chamber cutoff system, the valve chamber cutoff system comprising a first valve chamber cutoff subsystem arranged upstream of the trunk line and a second valve chamber cutoff subsystem arranged downstream of the trunk line, the valve chamber cutoff system is used to cut off the pipeline trunk line, the first valve chamber cutoff subsystem and the second valve chamber cutoff subsystem comprise a bypass pipeline interface, the bypass pipeline interface is used to connect the valve chamber venting system and the medium introduction and heating system;

[0009] A valve chamber venting system, the valve chamber venting system comprising a first valve chamber venting subsystem connected to the first valve chamber cut-off subsystem and a second valve chamber venting subsystem connected to the second valve chamber cut-off subsystem, for regulating the pressure and releasing the supercritical CO2 in the pipeline after the pipeline stops transporting;

[0010] A medium introduction and heating system, wherein the medium introduction and heating system is used to adjust the temperature of the liquid medium accumulated in the cut-off pipeline by injecting a high-temperature medium into the cut-off pipeline;

[0011] A temporary low-point temperature detection system is provided at a maximum liquid accumulation position in the pipeline determined according to a discharge simulation.

[0012] Furthermore, the first valve chamber cut-off subsystem and the second valve chamber cut-off subsystem both include a cut-off valve arranged on the main line, a main line bypass connected in parallel with the main line, and a bypass regulating valve. The two ends of the main line bypass are respectively connected to the pipeline main line at the two ends of the cut-off valve. The bypass regulating valve divides the main line bypass into a first main line bypass and a second main line bypass. The first main line bypass is connected to the main line pipeline where the input end of the cut-off valve is located, and the second main line bypass is connected to the main line pipeline where the output end of the cut-off valve is located. The first main line bypass and the second main line bypass are respectively provided with bypass cut-off valves, and temperature monitoring equipment and pressure monitoring equipment are also provided between the bypass cut-off valve and the pipeline main line.

[0013] Further, the bypass pipeline interface includes a first bypass pipeline interface provided between the bypass shutoff valve of the first trunk bypass and the bypass regulating valve, a second bypass pipeline interface provided between the bypass regulating valve and the bypass shutoff valve of the second trunk bypass, and a third bypass pipeline interface provided between the second bypass pipeline interface and the bypass shutoff valve of the second trunk bypass;

[0014] The medium introduction and heating system is connected to the valve chamber cutoff system through a first bypass pipeline interface and a second bypass pipeline interface;

[0015] The valve chamber venting system is communicated with the valve chamber shutoff system via a third bypass pipeline interface.

[0016] Furthermore, the medium introduction and heating system includes a drainage regulating valve, a vaporizer and a heater connected in series in sequence, the input end of the drainage regulating valve is connected to the first bypass pipe interface through a branch inlet shut-off valve, and the output end of the heater is connected to the second bypass pipe interface through a branch outlet regulating valve.

[0017] Furthermore, the valve chamber venting system includes a venting regulating valve and a bypass venting regulating valve in parallel, the input ends of the venting regulating valve and the bypass venting regulating valve are connected to the third bypass pipeline interface through a venting shut-off valve, and the output ends of the venting regulating valve and the bypass venting regulating valve are connected in series with a heat exchanger and a venting riser in sequence.

[0018] Furthermore, the low-point temporary temperature detection system includes a first shut-off valve of the main branch and a second shut-off valve of the main branch connected in series in sequence, the input end of the first shut-off valve of the main branch is connected to the maximum liquid accumulation position of the pipeline main line, and the output end of the second shut-off valve of the main branch is also provided with a connection port for connecting a temperature transmitter.

[0019] On the other hand, the present invention also provides a supercritical CO2 pipeline venting method based on double-sided discharge, the method is implemented based on any of the above-mentioned venting systems, and the method includes:

[0020] During normal transportation, the valve room cut-off system and the low-point temporary temperature detection system are not connected to the pipeline trunk line. The maximum liquid accumulation position of the cut-off pipeline during the venting process is determined as the setting position of the low-point temporary temperature detection system;

[0021] Before the planned maintenance of the pipeline, reduce the pipeline flow, monitor the temperature and pressure at various points along the pipeline, maintain the difference between the pipeline pressure and the saturated vapor pressure of the medium at the corresponding lowest temperature as the preset pressure value, reduce the medium inventory in the pipeline during the planned release by reducing the medium density, open the valve chamber to cut off the system to stop the pipeline;

[0022] Connect the pipeline trunk line and the valve chamber cut-off system, vent the trunk line pipeline from the supercritical state to the gas-liquid two-phase state according to the maximum allowable venting volume of the first valve chamber cut-off subsystem and the second valve chamber cut-off subsystem, continuously monitor the temperature and pressure of each preset point, reduce the discharge volume of the valve chamber venting system when the temperature is lower than the preset temperature threshold, and stop venting the valve chamber venting system when the pressure is lower than the preset threshold;

[0023] Select the valve chamber cut-off subsystem to access the medium introduction and heating system, close the valve chamber venting subsystem corresponding to the valve chamber cut-off subsystem where the medium introduction and heating system is located, keep the other valve chamber venting subsystem in a connected state, open the medium introduction and heating system, maintain the consistency of the amount of CO2 introduced and discharged upstream and downstream of the trunk line, and make the amount of CO2 introduced reach the preset temperature and enter the pipeline trunk line. When the temperature of the low-point temperature transmitter continues to rise to the preset temperature, close the entrance of the medium introduction and heating system, and use the valve chamber venting subsystem without a medium introduction and heating system to vent the medium in the pipeline trunk line.

[0024] Furthermore, the medium introduction and heating system is connected to a valve chamber cutoff subsystem closer to the maximum liquid accumulation position, and the valve chamber venting system is opened.

[0025] Furthermore, the method further comprises:

[0026] During the venting process, the medium temperature at the lowest point in the pipeline is continuously monitored. When the temperature is lower than the preset threshold, the medium introduction and heating system is turned on again until all the medium in the pipeline trunk is discharged.

[0027] The beneficial effects of the present invention are:

[0028] (1) Based on the basic physical properties of supercritical CO2, the phase change law and the characteristics of planned emptying of the fluctuating pipeline, the present invention aims at the characteristics of large pipe capacity between the shut-off valves of the supercritical CO2 pipeline (at least 8 km in length), high medium inventory and unbalanced liquid accumulation in the fluctuating pipeline. From the perspectives of efficient discharge, promoting the vaporization of accumulated liquid and safe operation, the present invention respectively sets up a valve chamber shut-off system, a valve chamber emptying system, an upstream and downstream medium introduction and heating system and a low point temporary temperature detection system. Compared with conventional means, the safe discharge rate can be greatly improved, the operating temperature of the trunk pipeline during the discharge process can be increased, and the efficient and safe operation of the planned emptying of the supercritical CO2 pipeline can be realized. Thus, efficient, economical and safe planned emptying of the supercritical CO2 pipeline can be realized.

[0029] (2) The present invention innovatively adopts the solution of introducing the medium stored in the upstream (or downstream) trunk pipe, avoiding the number of openings in the non-shutoff valve area of ​​the pipeline, reducing the probability of pipeline leakage and the burden of operation and maintenance; at the same time, the use of double-sided discharge can effectively share the discharge load of a single valve chamber, reduce the impact range of medium diffusion after discharge, and greatly eliminate the low temperature problem caused by the pressure reduction of the medium in the pipe during the discharge process, providing support for the rapid resumption of production of the pipeline. More importantly, by identifying the low-point accumulation and the low temperature problem caused by it, the discharge idea is innovated, which essentially ensures the safety of materials.

[0030] (3) The valve chamber venting system and the medium introduction and heating system of the present invention are detachably connected to the valve chamber cut-off system, which greatly reduces the investment in setting up a fixed discharge system and upstream and downstream medium introduction and heating systems. The present invention proposes a mode of reducing the operating pressure of the pipeline before a planned shutdown, thereby reducing the discharge volume of the planned emptying of the pipeline and supporting rapid resumption of production to a certain extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a structural block diagram of a supercritical CO2 pipeline venting system based on double-side discharge according to an embodiment of the present invention. DETAILED DESCRIPTION

[0032] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0033] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making any creative work shall fall within the scope of protection of the present invention.

[0034] During the phase transition, the medium in the pipeline will experience a considerable temperature drop to varying degrees. During the discharge process, affected by the ups and downs of the pipeline, the incompletely vaporized CO2 will tend to gather at the low point of the pipeline due to the influence of density, causing the pipe section near the low point of the pipeline to experience a more severe temperature drop. This may cause a monitoring blind spot in the distributed temperature detection and cause misjudgment of the temperature control during the discharge. In addition, due to the high pipeline pressure and more medium stored in the pipeline, the discharge time of supercritical CO2 will be much longer than that of conventional natural gas pipelines. The existing technology lacks corresponding solutions to solve the above problems.

[0035] In order to solve the above technical problems, the following embodiments of the supercritical CO2 pipeline venting system and method based on double-sided discharge of the present invention are proposed.

[0036] Example 1

[0037] This embodiment is based on the basic physical properties of supercritical CO2, the law of phase change and the characteristics of planned pipeline emptying. In view of the characteristics of large pipe capacity between the shut-off valves of the supercritical CO2 pipeline (at least 8 km of pipe length), high medium inventory, and unbalanced liquid accumulation in the undulating pipeline, from the perspectives of safe diffusion, efficient emptying, and safe operation, a valve chamber shutoff system, a valve chamber emptying system, an upstream and downstream medium introduction and heating system, a low point temporary temperature detection system, etc. are respectively set to achieve efficient and safe operation of planned emptying of the supercritical CO2 pipeline. Among them, the valve room cut-off system is set in the pipeline valve room, mainly including the main line cut-off valve, bypass pipeline, bypass instrument, which is used to cut off the pipeline when the pipeline is planned to stop transmission, and support segmented discharge; the valve room venting system includes the venting valve and movable venting system set in the valve room, which support planned venting; the upstream and downstream medium introduction and heating system includes the bypass regulating valve and movable water bath vaporizer set in the valve room, which are used to take high-pressure CO2 from the upstream and downstream pipelines of the cut-off pipeline and heat it, continuously purge the cut-off pipeline, realize the medium temperature compensation of the cut-off pipeline, and promote the liquid phase gasification of the cut-off pipeline in the low-point gas-liquid two-phase state; the low-point temporary temperature detection system includes a valve well temporarily set for the low-point pipe section with serious liquid accumulation, so as to install a temperature transmitter before the planned discharge, which is used to monitor the medium temperature of the pipeline low point in real time in the middle and late stages of the planned discharge. In this way, efficient, economical and safe planned venting of supercritical CO2 pipelines is achieved.

[0038] Reference Figure 1 ,like Figure 1 Shown is a structural block diagram of the supercritical CO2 pipeline venting system based on double-sided discharge in this embodiment.

[0039] The valve chamber shutoff system includes a shutoff valve arranged on the trunk line, which in this embodiment includes a shutoff valve 1 upstream of the trunk line, a shutoff valve 9 downstream of the trunk line, a bypass first shutoff valve 2, a bypass regulating valve 3, a bypass second shutoff valve 4, a bypass first temperature transmitter 5, a bypass first pressure transmitter 6, a bypass second temperature transmitter 7, a bypass second pressure transmitter 8, etc. It is mainly used to cut off the pipeline trunk line before planned maintenance or after pipeline leakage to reduce the pipeline discharge volume; the bypass pipeline interface of the shutoff valve chamber is used to connect the valve chamber venting system, the upstream and downstream medium introduction and heating system, etc., to achieve efficient discharge of the shutoff pipeline by the valve chamber; at the same time, the bypass instrument is used to detect the pressure and temperature of the point; in addition, the bypass regulating valve is used to safely fill the pipeline with medium after maintenance. The valve chamber where the shutoff valve 9 downstream of the trunk line is located is configured in the same manner as the valve chamber where the shutoff valve 1 upstream of the trunk line is located, so it is not described in detail in this embodiment.

[0040] The valve chamber venting system includes a venting shutoff valve 11, a venting regulating valve 12, a bypass venting regulating valve 13, an air bath type heat exchanger 14, a venting riser 15, etc., which are arranged downstream of the valve chamber interface, and are used to regulate the pressure and discharge the supercritical CO2 in the pipeline after the pipeline stops transmission. It should be noted that the downstream of the venting shutoff valve 11 is a blind flange, which is connected to the movable venting system before venting; the movable venting system includes a skid-mounted venting regulating valve 12, a bypass venting regulating valve 13, an air bath type heat exchanger 14, a venting riser 15, etc., and also includes a temperature transmitter and a flow transmitter installed on the pipeline, which are transported by car. A similar interface is also set in the downstream shutoff valve chamber, and its function is consistent with that of the upstream shutoff valve chamber.

[0041] The venting shutoff valve 11 is arranged on the bypass pipeline of the valve chamber. It is a carbon steel manual ball valve. It is opened only when the trunk pipeline is vented. Its downstream end is connected to a blind flange (replaced and connected to the movable venting system during discharge); the venting regulating valve 12, the bypass venting regulating valve 13, the air bath heat exchanger 14, the venting riser 15 and the like constitute the movable venting system; the venting regulating valve 12 and the bypass venting regulating valve 13 are both manually controlled regulating valves made of stainless steel. The venting regulating valve 12 is the regulating valve that is opened first. In the initial stage of discharge (from supercritical state to near 3MPa pressure range); the bypass vent regulating valve 13 cooperates with the vent regulating valve 12 to coordinate and open in the later stage of discharge (1.5MPa to normal pressure range) to coordinate operation and to increase the discharge rate as much as possible under the premise of ensuring that the medium temperature in the trunk line is not lower than -15°C; the air bath heat exchanger 14 is made of stainless steel and uses air as the heat exchange medium to increase the temperature of the discharged CO2; the vent riser 15 is made of carbon steel and is used to lift the released CO2 to a safe discharge height (preferably above 15m).

[0042] The upstream and downstream medium introduction and heating system includes a branch line inlet shutoff valve 21, a branch line outlet regulating valve 22, a drainage regulating valve 23, an air bath type vaporizer 24, a heater 25, etc., which are arranged downstream of the valve chamber interface. They are used to inject high-temperature medium into the cut-off pipeline in the middle and late stages of the cut-off pipeline discharge to adjust the temperature of the liquid phase medium accumulated in the cut-off pipeline, promote its temperature rise and vaporization, overcome the low temperature problem caused by its pressure reduction and vaporization, and improve the discharge efficiency of the cut-off pipeline. Furthermore, the drainage regulating valve 23, the air bath type vaporizer 24, the heater 25, etc. are implemented as a skid and transported by car.

[0043] The branch line inlet shutoff valve 21 and the branch line outlet regulating valve 22 are arranged on the bypass pipeline of the valve chamber (respectively arranged upstream and downstream of the bypass regulating valve 3), which are normally closed and made of carbon steel. They are opened only when the venting pipeline needs to introduce high-temperature medium; the drainage regulating valve 23 is an automatic regulating valve made of stainless steel, which is used to regulate the pressure and control the flow of high-pressure CO2; the air bath type vaporizer 24 is made of stainless steel, and uses air as the heat exchange medium to increase the first stage temperature of the pressure-regulated CO2; the heater 25 is made of carbon steel, and uses heat medium (water) as the heat exchange medium to increase the second stage temperature of the pressure-regulated CO2, and the target temperature is preferably set to 70°C. The drainage regulating valve 23, the air bath type vaporizer 24, the heater 25, etc. are implemented as a skid and transported by a car. The introduced and heated medium is continuously sent into the cut-off pipeline, and the liquid phase accumulated in the cut-off pipeline is forced to undergo heat exchange to stimulate its vaporization, thereby avoiding the excessively low temperature of the accumulated liquid phase caused by depressurization and vaporization.

[0044] The low-point temporary temperature detection system is arranged near the maximum liquid accumulation position in the pipeline determined according to the discharge simulation, and includes the first shut-off valve 31 and the second shut-off valve 32 of the trunk branch, and is equipped with a temperature transmitter that can be temporarily connected. It is used to detect the medium temperature at the low point of the pipeline in real time when the pipeline is cut off for discharge, and guide the adjustment of the venting rate.

[0045] The working principle of the supercritical CO2 pipeline venting system based on double-sided discharge provided in this embodiment is as follows:

[0046] (1) Under normal operating conditions, due to the need to maximize the transmission efficiency, CO2 is transported in a supercritical phase. Under this transmission condition, the density of CO2 can reach more than 850kg / m3. Before the planned shutdown of the pipeline, it is proposed to reduce the transmission pressure to reduce the mass of the medium stored in the pipeline, while still ensuring the stability of the transmission phase. Furthermore, in order to improve the accuracy of low-point liquid accumulation and low-point temperature detection, this embodiment proposes the requirement of using the discharge simulation analysis software to simulate the discharge of the cut-off pipeline, so as to determine the pipe section with the most serious liquid accumulation, and provide guidance for selecting the valve chamber for setting the upstream and downstream medium introduction and heating system.

[0047] (2) Since long-distance pipelines are laid along the terrain, there are problems with elevation fluctuations. For conventional natural gas pipelines, after a planned shutdown, the target pipe section (the pipe section between the shut-off valves) is discharged in the pipeline shut-off valve chamber, and the discharge time is generally 6-8 hours. For supercritical CO2 medium, there are problems such as phase change (supercritical phase, gas-liquid two-phase, gas phase) during the discharge process, the phase change causes the medium temperature in the pipeline to decrease, and the gas-liquid two-phase medium separation caused by the terrain fluctuation. In particular, the gas-liquid two-phase separation caused by the terrain fluctuation will cause the medium temperature in the section with lower terrain in the pipeline to be significantly lower than that in the section with higher terrain in the same section of the pipeline. Therefore, it is necessary to consider identifying and controlling the discharge rate. Furthermore, in the front section of the discharge, since the medium pressure in the trunk line is always high, it will not cause the trunk line pipeline temperature to be too low. Therefore, it is possible to consider increasing the discharge rate in the front period of the discharge. Therefore, this embodiment recommends double-sided discharge, which reduces the load of single-sided discharge on the one hand, and discharges on both sides at the same time, which helps to improve the discharge efficiency. To solve the problem of liquid accumulation in pipelines, an upstream and downstream medium introduction and heating system is set up to introduce CO2 from the upstream or downstream trunk line and perform high-temperature heating to exchange heat and vaporize the medium and low-pressure accumulated liquid in the vented pipeline, thereby greatly improving its vaporization rate (compared with natural heat exchange in the environment).

[0048] (3) For the discharge system, this embodiment proposes a mode of using a movable discharge system, the purpose of which is to set up a more flexible movable discharge system, which can minimize the construction investment, and this part of the system can radiate multiple pipe sections at the same time.

[0049] (4) In order to ensure pipeline safety, this embodiment proposes the requirement of monitoring the medium temperature in the pipeline during the discharge process to prevent the medium temperature in the pipeline from being lower than -15°C; in order to improve the low temperature recognition rate, this embodiment proposes to install a temperature transmitter at the low point of the pipeline.

[0050] Based on the above venting system, this embodiment provides a method for planned venting of a supercritical CO2 pipeline based on double-sided discharge, which specifically includes the following steps:

[0051] Step 1: During normal transportation, keep the upstream shut-off valve 1 and the downstream shut-off valve 9 of the trunk open, and the trunk normally transports supercritical CO2; close the valves of each branch. The valve chamber venting system, the upstream and downstream medium introduction and heating system, and the low-point temporary temperature detection system are not connected to the trunk system. Through the flow simulation software, determine the maximum liquid accumulation position of the cut-off pipeline during the venting process, so as to determine the setting position of the low-point temporary temperature detection system of the pipeline, and at the same time determine the valve chamber position for the upstream and downstream medium introduction and heating system installation (the upstream and downstream medium introduction and heating system should select the valve chamber closer to the maximum liquid accumulation position).

[0052] Step 2: Before the planned maintenance of the pipeline, reduce the pipeline flow, monitor the parameters of the temperature transmitter and pressure transmitter at various locations along the pipeline, keep the pipeline pressure only 0.5MPa higher than the saturated vapor pressure of the medium at the corresponding lowest temperature, and reduce the medium inventory in the pipeline during the planned release by reducing the medium density. Then, slowly close the upstream block valve 1 of the trunk line and the downstream block valve 9 of the trunk line to stop the pipeline.

[0053] Step 3: Connect the valve chamber venting system at both ends of the cut-off pipeline to the venting shutoff valve of the valve chamber cut-off system. Open the venting regulating valve 12, bypass venting regulating valve 13, air bath heat exchanger 14, venting riser 15, etc., and vent the trunk pipeline from supercritical state to gas-liquid two-phase state (the venting pressure range is from initial pressure to around 3MPa) according to the maximum allowable venting volume of the single-side valve chamber (determined by the CO2 diffusion analysis after the release, and the venting volume is monitored by the flow transmitter of the venting system); continuously monitor the indication values ​​of the temperature transmitter and pressure transmitter at each low altitude point. When the temperature of the temperature transmitter is lower than -15°C, immediately adjust the venting regulating valve 12 and bypass venting regulating valve 13 to reduce the venting volume. When the low point pressure is close to 3MPa, close the bypass venting regulating valve 13. In this step, the upstream valve chamber and the downstream valve chamber are vented in coordination, and the values ​​of the valve chamber temperature transmitters and the low point temperature transmitters at the same time need to be monitored.

[0054] Step 4: According to the valve chamber selected in step 1 for installing the upstream and downstream medium introduction and heating system (in this example, the valve chamber where the upstream cut-off valve 1 of the main line is located is selected as the valve chamber for the upstream and downstream medium introduction and heating system, and the valve chamber where the downstream cut-off valve 9 of the main line is located is selected as the valve chamber for subsequent discharge), the upstream and downstream medium introduction and heating system is connected downstream of the branch line inlet cut-off valve 21, and the venting cut-off valve 11 is closed, but the movable venting system of the downstream valve chamber is still kept in a connected state. The branch line inlet cut-off valve 21, branch line outlet regulating valve 22, drainage regulating valve 23, air bath vaporizer 24, heater 25, etc. are opened in order to maintain the consistency of the upstream introduced CO2 amount with the downstream discharged CO2. After multi-stage heating, the upstream introduced CO2 is maintained at about 70°C and enters the cut-off pipeline. When the temperature of the low-point temperature transmitter continues to rise to 20°C, the branch line inlet cut-off valve 21 is temporarily closed, and the medium in the cut-off pipeline is vented using the venting system of the downstream valve chamber. During the venting process, continue to monitor the temperature of the low-point temperature transmitter. When the temperature is lower than -20°C, open the branch line inlet shut-off valve 21 and the heating system again; repeat the operation until all the medium in the cut-off pipeline is discharged.

[0055] In this way, efficient and planned venting of the supercritical CO2 pipeline can be achieved.

[0056] This embodiment is based on the basic physical properties of supercritical CO2, the law of phase change and the characteristics of planned emptying of the fluctuating pipeline. In view of the characteristics of large pipe capacity between the shut-off valves of the supercritical CO2 pipeline (at least 8 km of pipe length), high medium inventory and unbalanced liquid accumulation in the fluctuating pipeline, from the perspectives of efficient discharge, promoting vaporization of accumulated liquid and safe operation, a valve chamber shutoff system, a valve chamber emptying system, an upstream and downstream medium introduction and heating system and a low point temporary temperature detection system are respectively set. Compared with conventional means, the safe discharge rate can be greatly improved, the operating temperature of the trunk pipeline during the discharge process can be increased, and efficient and safe operation of the planned emptying of the supercritical CO2 pipeline can be achieved. Therefore, efficient, economical and safe planned emptying of the supercritical CO2 pipeline can be achieved.

[0057] This embodiment innovatively adopts the solution of introducing the medium stored in the upstream (or downstream) trunk pipe, avoiding the number of openings in the non-blocking valve area of ​​the pipeline, reducing the probability of pipeline leakage and the burden of operation and maintenance; at the same time, the use of double-sided discharge can effectively share the discharge load of a single valve chamber, reduce the impact range of medium diffusion after discharge, and greatly eliminate the low temperature problem caused by the pressure reduction of the medium in the pipe during the discharge process, providing support for the rapid resumption of production of the pipeline. More importantly, by identifying the low-point accumulation and the low temperature problem caused by it, the discharge idea is innovated, which essentially ensures the safety of materials.

[0058] In this embodiment, the valve chamber venting system and the medium introduction and heating system are detachably connected to the valve chamber cutoff system, which greatly reduces the investment in setting up a fixed discharge system and upstream and downstream medium introduction and heating systems. This embodiment proposes a mode of reducing the pipeline operating pressure before a planned shutdown, thereby reducing the discharge volume of the planned pipeline venting and supporting rapid resumption of production to a certain extent.

[0059] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A supercritical CO2 pipeline venting system based on double-sided discharge, the system is arranged on the CO2 pipeline trunk line, characterized in that: The system comprises: A valve chamber cutoff system, the valve chamber cutoff system comprising a first valve chamber cutoff subsystem arranged upstream of the trunk line and a second valve chamber cutoff subsystem arranged downstream of the trunk line, the valve chamber cutoff system is used to cut off the pipeline trunk line, the first valve chamber cutoff subsystem and the second valve chamber cutoff subsystem comprise a bypass pipeline interface, the bypass pipeline interface is used to connect the valve chamber venting system and the medium introduction and heating system; A valve chamber venting system, the valve chamber venting system comprising a first valve chamber venting subsystem connected to the first valve chamber cut-off subsystem and a second valve chamber venting subsystem connected to the second valve chamber cut-off subsystem, for regulating the pressure and releasing the supercritical CO2 in the pipeline after the pipeline stops transporting; A medium introduction and heating system, wherein the medium introduction and heating system is used to adjust the temperature of the liquid medium accumulated in the cut-off pipeline by injecting a high-temperature medium into the cut-off pipeline; A temporary low-point temperature detection system is provided at a maximum liquid accumulation position in the pipeline determined according to a discharge simulation.

2. The supercritical CO2 pipeline venting system based on double-sided discharge according to claim 1 is characterized in that: The first valve chamber cut-off subsystem and the second valve chamber cut-off subsystem both include a cut-off valve arranged on the main line, a main line bypass connected in parallel with the main line, and a bypass regulating valve. The two ends of the main line bypass are respectively connected to the pipeline main line at the two ends of the cut-off valve. The bypass regulating valve divides the main line bypass into a first main line bypass and a second main line bypass. The first main line bypass is connected to the main line pipeline where the input end of the cut-off valve is located, and the second main line bypass is connected to the main line pipeline where the output end of the cut-off valve is located. The first main line bypass and the second main line bypass are respectively provided with bypass cut-off valves. Temperature monitoring equipment and pressure monitoring equipment are also provided between the bypass cut-off valve and the pipeline main line.

3. The supercritical CO2 pipeline venting system based on double-sided discharge according to claim 2 is characterized in that: The bypass pipeline interface includes a first bypass pipeline interface provided between the bypass cut-off valve of the first trunk bypass and the bypass regulating valve, a second bypass pipeline interface provided between the bypass regulating valve and the bypass cut-off valve of the second trunk bypass, and a third bypass pipeline interface provided between the second bypass pipeline interface and the bypass cut-off valve of the second trunk bypass; The medium introduction and heating system is connected to the valve chamber cutoff system through a first bypass pipeline interface and a second bypass pipeline interface; The valve chamber venting system is communicated with the valve chamber shutoff system via a third bypass pipeline interface.

4. The supercritical CO2 pipeline venting system based on double-sided discharge according to claim 3 is characterized in that: The medium introduction and heating system includes a drainage regulating valve, a vaporizer and a heater connected in series in sequence. The input end of the drainage regulating valve is connected to the first bypass pipeline interface through a branch line inlet shut-off valve, and the output end of the heater is connected to the second bypass pipeline interface through a branch line outlet regulating valve.

5. The supercritical CO2 pipeline venting system based on double-sided discharge according to claim 3 is characterized in that: The valve chamber venting system includes a venting regulating valve and a bypass venting regulating valve in parallel, the input ends of the venting regulating valve and the bypass venting regulating valve are connected to the third bypass pipeline interface through a venting shut-off valve, and the output ends of the venting regulating valve and the bypass venting regulating valve are connected in series with a heat exchanger and a venting riser in sequence.

6. The supercritical CO2 pipeline venting system based on double-sided discharge according to claim 1 is characterized in that: The low-point temporary temperature detection system includes a first shut-off valve of the main branch and a second shut-off valve of the main branch connected in series in sequence. The input end of the first shut-off valve of the main branch is connected to the maximum liquid accumulation position of the pipeline main line, and the output end of the second shut-off valve of the main branch is also provided with a connection port for connecting a temperature transmitter.

7. The supercritical CO2 pipeline venting system based on double-sided discharge according to claim 1 is characterized in that: The valve chamber venting system and the medium introduction and heating system are detachably connected to the valve chamber shutoff system.

8. A supercritical CO2 pipeline venting method based on double-sided discharge, characterized in that: The method is implemented based on the venting system according to any one of claims 1 to 7, and the method comprises: During normal transportation, the valve room cut-off system and the low-point temporary temperature detection system are not connected to the pipeline trunk line. The maximum liquid accumulation position of the cut-off pipeline during the venting process is determined as the setting position of the low-point temporary temperature detection system; Before the planned maintenance of the pipeline, reduce the pipeline flow, monitor the temperature and pressure at various points along the pipeline, maintain the difference between the pipeline pressure and the saturated vapor pressure of the medium at the corresponding lowest temperature as the preset pressure value, reduce the medium inventory in the pipeline during the planned release by reducing the medium density, open the valve chamber to cut off the system to stop the pipeline; Connect the pipeline trunk line and the valve chamber cut-off system, vent the trunk line pipeline from the supercritical state to the gas-liquid two-phase state according to the maximum allowable venting volume of the first valve chamber cut-off subsystem and the second valve chamber cut-off subsystem, continuously monitor the temperature and pressure of each preset point, reduce the discharge volume of the valve chamber venting system when the temperature is lower than the preset temperature threshold, and stop venting the valve chamber venting system when the pressure is lower than the preset threshold; Select the valve chamber cut-off subsystem to access the medium introduction and heating system, close the valve chamber venting subsystem corresponding to the valve chamber cut-off subsystem where the medium introduction and heating system is located, keep the other valve chamber venting subsystem in a connected state, open the medium introduction and heating system, maintain the consistency of the amount of CO2 introduced and discharged upstream and downstream of the trunk line, and make the amount of CO2 introduced reach the preset temperature and enter the pipeline trunk line. When the temperature of the low-point temperature transmitter continues to rise to the preset temperature, close the entrance of the medium introduction and heating system, and use the valve chamber venting subsystem without a medium introduction and heating system to vent the medium in the pipeline trunk line.

9. The supercritical CO2 pipeline venting method based on double-sided discharge according to claim 8, characterized in that: The medium introduction and heating system is connected to the valve chamber cutoff subsystem closer to the maximum liquid accumulation position, and the valve chamber venting system is opened.

10. The supercritical CO2 pipeline venting method based on double-sided discharge according to claim 8, characterized in that: The method further comprises: During the venting process, the medium temperature at the lowest point in the pipeline is continuously monitored. When the temperature is lower than the preset threshold, the medium introduction and heating system is turned on again until all the medium in the pipeline trunk is discharged.

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