A system and method for safe release of dense phase carbon dioxide pipeline

Abstract

The present invention discloses a system and method for safe discharge of a dense phase carbon dioxide pipeline, wherein the safe discharge system comprises a dense phase carbon dioxide pipeline transportation and cutoff system, a valve chamber bypass system, a two-stage discharge system and a pipeline temperature and pressure detection system, wherein the two-stage discharge system is used for graded pressure discharge of dense phase carbon dioxide, and an interstage heat exchange system is provided in the two-stage discharge system, wherein the interstage heat exchange system is used for temperature regulation of the medium after the discharge of the previous stage. The present invention is based on the operation process characteristics of the dense phase carbon dioxide pipeline, combined with the conventional oil product pipeline maintenance and discharge scheme, and takes into account the characteristics of low temperature solidification of dense phase carbon dioxide. By providing units such as a two-stage discharge system, an interstage heat exchange system, a trunk temperature detection system and a control system, the risk of dry ice formation in the dense phase carbon dioxide pipeline venting system is effectively avoided, and the material safety of the trunk discharge pipeline is effectively guaranteed, thereby realizing safe discharge of the dense phase carbon dioxide pipeline.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon dioxide release, and in particular relates to a system and method for safe release of dense phase carbon dioxide pipeline. Background Art

[0002] With the growing demand for energy conservation, emission reduction and environmental protection in the energy and chemical industry and the improvement of carbon dioxide oil recovery technology, long-distance transportation of carbon dioxide through pipelines has become an important way to promote and achieve efficient capture, storage and utilization of carbon dioxide. The critical temperature of carbon dioxide is about 31.1°C and the critical pressure is about 7.38MPa.g. When transporting carbon dioxide by pipeline over long distances, a dense phase transportation mode with a pressure higher than the critical pressure is usually adopted to improve the economy of transportation. In addition, carbon dioxide has the characteristic of solidification at low temperatures. The triple point of pure carbon dioxide is -56.6°C and 0.518MPa.g, which is a significant feature of carbon dioxide that is different from conventional hydrocarbon media.

[0003] Similar to conventional hydrocarbon pipelines, CO2 pipelines need to be equipped with shutoff valve chambers along the way and provide a release function before pipeline maintenance to ensure efficient maintenance of pipe sections with safety hazards and reduce the overall medium discharge volume. For conventional hydrocarbons, when the pipeline is released, it is necessary to consider the low temperature problem caused by the vaporization of the medium after the release, and ensure the safety of the venting process by selecting appropriate materials. In contrast, for dense phase carbon dioxide pipelines, when it is directly pressure-released and the venting medium is discharged to the atmosphere, the adiabatic expansion process of the dense phase medium may cause the medium temperature after the release to be close to -90°C. In addition, there is a venting back pressure in the venting pipeline, which can easily cause the temperature and pressure of the venting medium to enter the solid phase formation area, causing the risk of "dry ice" formation, resulting in blockage of the venting pipeline or pipe fittings, affecting normal venting operations, and even causing safety hazards. Therefore, reasonable measures should be taken for the dense phase carbon dioxide pipeline venting system to avoid safety problems caused by "dry ice".

[0004] At present, there are many reports on the process technology of carbon dioxide pipeline transportation in relevant literature, which mainly focus on issues such as pipeline route selection, transportation phase control, and pipeline material selection. There is some concern about the problem of dry ice caused by low temperature in the aforementioned venting process, but there are few reports on research results on solutions, and there are no configuration requirements for safe venting systems. Summary of the invention

[0005] The purpose of the present invention is to: in order to address the above-mentioned problems, further promote the development of dense-phase carbon dioxide pipeline transportation technology, ensure operational safety, provide a more economical and reasonable way to safely release carbon dioxide, and avoid the problem of dry ice-induced flow channel blockage caused by the low temperature of the medium during the release process, so as to promote the development and progress of industry technology and a dense-phase carbon dioxide pipeline safe release system and method.

[0006] The main technical idea of ​​the present invention is based on the operating process characteristics of the dense phase carbon dioxide pipeline, combined with the conventional oil pipeline maintenance and discharge scheme, considering the characteristics of the low temperature solidification (forming "dry ice") of dense phase carbon dioxide, by setting up a two-stage discharge system, an interstage heat exchange system, a trunk temperature detection system and a control system, etc., which not only effectively avoids the risk of dry ice formation in the dense phase carbon dioxide pipeline venting system, but also effectively ensures the material safety of the trunk discharge pipeline, and realizes the safe discharge of the dense phase carbon dioxide pipeline. Furthermore, by setting up a movable module, the efficient reuse of the carbon dioxide discharge device in multiple trunk valve chambers can be realized, reducing the construction cost.

[0007] The technical solution adopted by the present invention is: a dense phase carbon dioxide pipeline safety release system, characterized by: comprising a dense phase carbon dioxide pipeline transportation and cutoff system, a valve chamber bypass system, a two-stage release system and a pipeline temperature and pressure detection system;

[0008] The dense phase carbon dioxide pipeline transportation and cut-off system comprises an upstream trunk line, a trunk line cut-off valve and a downstream trunk line connected in sequence, wherein the upstream trunk line and the downstream trunk line are used to connect the upstream and downstream pipelines and form a dense phase carbon dioxide transportation channel, and the trunk line cut-off valve is used to control the connection or cut-off between the upstream trunk line and the downstream trunk line;

[0009] The valve chamber bypass system includes a valve chamber bypass and a bypass shutoff valve group arranged on the valve chamber bypass. The pipeline of the valve chamber bypass is connected from the upstream trunk of the trunk shutoff valve and connected from the downstream trunk of the trunk shutoff valve to form a trunk bypass. The valve chamber bypass system is used to provide maintenance and venting bypass for the upstream trunk and the downstream trunk after the trunk is shut off, and to provide a connecting bypass when the upstream trunk or the downstream trunk is ready to be restarted;

[0010] The two-stage discharge system is used for performing staged pressure relief on dense phase carbon dioxide. An inter-stage heat exchange system is provided in the two-stage discharge system, and the inter-stage heat exchange system is used for regulating the temperature of the medium after the previous stage of discharge.

[0011] The dense phase carbon dioxide pipeline safe discharge system described in the present invention comprises a bypass cut-off valve group arranged on the valve chamber bypass, which comprises a bypass front section cut-off valve and a bypass rear section cut-off valve, and the bypass front section cut-off valve and the bypass rear section cut-off valve are used to control the discharge channels of the upstream trunk line and the downstream trunk line respectively.

[0012] In the dense phase carbon dioxide pipeline safe release system described in the present invention, the bypass pipeline between the upstream trunk line and the bypass front section shut-off valve is the bypass front section pipeline, the bypass pipeline between the bypass front section shut-off valve and the bypass rear section shut-off valve is the bypass middle section pipeline, and the bypass pipeline between the bypass rear section shut-off valve and the downstream trunk line is the bypass rear section pipeline.

[0013] The dense phase carbon dioxide pipeline safety discharge system of the present invention, wherein the two-stage discharge system comprises a primary discharge valve, a secondary discharge valve, a venting liquid separator and a venting riser, the inlet end of the primary discharge valve is connected to the bypass middle section pipeline through a discharge branch pipeline, the outlet end of the primary discharge valve is connected to the inlet end of the secondary discharge valve through a primary discharge pipeline, the outlet end of the secondary discharge valve is connected to the venting riser through a secondary discharge pipeline, the interstage heat exchange system is arranged on the primary discharge pipeline between the primary discharge valve and the secondary discharge valve, and the venting liquid separator is arranged on the secondary discharge pipeline between the secondary discharge valve and the venting riser.

[0014] The dense phase carbon dioxide pipeline safe discharge system described in the present invention, wherein the interstage heat exchange system includes an inlet pipe, a heating vaporizer and an outlet pipe, wherein the heating vaporizer is used to perform medium and environmental heat exchange on the low-temperature carbon dioxide after the first-stage discharge, the inlet pipe is connected to the front section of the first-stage discharge pipe, and the outlet pipe is connected to the rear section of the downstream first-stage discharge pipe.

[0015] In the dense phase carbon dioxide pipeline safe release system described in the present invention, the heating vaporizer selects an air-temperature vaporizer or an electrically heated water bath vaporizer according to environmental conditions, that is, if the temperature of the operating environment is higher than 0°C, the heating vaporizer adopts an air-temperature vaporizer, and if the temperature of the operating environment is lower than 0°C, the heating vaporizer adopts an electrically heated water bath vaporizer.

[0016] The dense phase carbon dioxide pipeline safe release system of the present invention is provided with a gas injection valve between the bypass front section cut-off valve and the primary release valve.

[0017] The dense phase carbon dioxide pipeline safe discharge system described in the present invention, wherein the pipeline temperature and pressure detection system comprises a bypass front section temperature transmitter and a bypass front section pressure transmitter arranged on the bypass front section pipeline, a bypass rear section temperature transmitter and a bypass rear section pressure transmitter arranged on the bypass rear section pipeline, and a discharge branch pressure transmitter arranged on the discharge branch pipeline, a first-level discharge branch pressure transmitter and a first-level discharge branch temperature transmitter arranged on the first-level discharge pipeline front section pipeline, and a second-level discharge branch temperature transmitter arranged on the second-level discharge pipeline rear section pipeline. The pipeline temperature and pressure detection system is used for real-time monitoring of the working temperature status of pipelines and equipment, and uploading data.

[0018] The dense phase carbon dioxide pipeline safe release system of the present invention, wherein the two-stage release system and the inter-stage heat exchange system are skid-mounted.

[0019] A method for safe release of dense phase carbon dioxide pipeline, characterized by comprising the following steps:

[0020] Step 1: a dense phase carbon dioxide pipeline safety release system is set up on the pipeline trunk line for transporting dense phase carbon dioxide, wherein the dense phase carbon dioxide pipeline safety release system includes a dense phase carbon dioxide pipeline transportation and cutoff system, a valve chamber bypass system, a two-stage release system, an inter-stage heat exchange system, and a pipeline temperature and pressure detection system;

[0021] Step 2: When the upstream trunk line needs to be shut down for maintenance, close the starting point external transmission pump of the pipeline transmission system, the trunk line shut-off valve of this station, the trunk line shut-off valve of the upstream adjacent valve room and the downstream terminal shut-off valve. When a movable two-stage discharge system and interstage heat exchange system are used, after the maintenance and shutdown, the two-stage discharge system and the interstage heat exchange system are transported to the valve room by skids and connected to the valve room bypass system;

[0022] Step 3: Keep the bypass front-end block valve, bypass rear-end block valve, primary relief valve and secondary relief valve closed, inject nitrogen into the pipe section between the bypass front-end block valve and the primary relief valve, the pressure is the same as the main pipeline shut-off pressure, and inject nitrogen into the pipe section between the primary relief valve and the secondary relief valve, and control the pressure at 2-2.2MPa.g;

[0023] Step 4: Configure the vaporizer type according to the ambient temperature. If the temperature of the working environment is higher than 0°C, select an air-temperature vaporizer to ensure that the medium temperature after heating is higher than -5°C; if the ambient temperature is lower than 0°C, select an electric heating water bath vaporizer to ensure that the medium temperature after heating is higher than -5°C;

[0024] Step 5: First, open the bypass cut-off valve group and the first-stage pressure relief valve, start the heating vaporizer, and slowly open the second-stage relief valve. After the discharge medium is vaporized, it is discharged into the atmosphere from the venting riser;

[0025] Specifically, the pressure in the first-level discharge pipeline is controlled to be stable at 2-2.2MPa.g, the outlet medium temperature of the heating vaporizer is controlled to be higher than -5°C, and the medium temperature in the trunk pipeline is controlled to be higher than -20°C. When the upstream trunk pressure drops to 2MPa.g, the pressure in the first-level discharge pipeline is controlled to be stable at 1-1.2MPa.g, and the outlet medium temperature of the heating vaporizer is controlled to be higher than -5°C, and the medium temperature in the trunk pipeline is controlled to be higher than -20°C. When the upstream trunk pressure drops to 1MPa.g, the discharge valve is fully opened, and the subsequent discharge operation is completed using the second-level discharge valve;

[0026] Step 6: When the main pipeline pressure drops to 0.1MPa.g, dry air is injected from the upstream shut-off valve chamber to replace the remaining carbon dioxide in the pipeline and discharged from the venting system of the valve chamber of this station.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] Based on the operation process characteristics of the dense phase carbon dioxide pipeline, combined with the conventional oil pipeline maintenance and discharge scheme, the present invention takes into account the characteristics of the low temperature solidification of dense phase carbon dioxide, and sets up a two-stage discharge system, an interstage heat exchange system, a trunk temperature detection system and a control system. The system not only effectively avoids the risk of dry ice formation in the dense phase carbon dioxide pipeline venting system, but also effectively ensures the material safety of the trunk discharge pipeline, and realizes the safe discharge of the dense phase carbon dioxide pipeline. Furthermore, by setting up a movable module, efficient reuse of the carbon dioxide discharge device is realized.

[0029] The specific manifestations are:

[0030] (1) Scientific setting

[0031] This system focuses on the maintenance and discharge needs of dense-phase carbon dioxide pipelines, focusing on the large temperature drop after dense-phase carbon dioxide is depressurized, and the problem of "dry ice" formation. Since temperature changes have little effect on adiabatic discharge when dense-phase carbon dioxide is in a dense phase state, conventional heating and discharge cannot effectively increase the temperature after discharge. Therefore, based on the setting concept of conventional hydrocarbon pipeline venting systems, the number of discharge stages is increased, and the method of graded pressure relief combined with inter-stage heat exchange is used to fully utilize the external environment to heat the carbon dioxide (gas phase + liquid phase) after the first-stage pressure relief, ensuring that the medium temperature after the second-stage pressure relief is always higher than the dry ice formation temperature, thereby ensuring safe discharge.

[0032] (2) Economical

[0033] This system prefabricates the valve chamber discharge system in a skid-mounted form, which can realize the reuse of multiple venting systems similar to the valve chamber, reflecting its economy. At the same time, the form of the vaporizer is selected according to the ambient temperature, and the air-temperature vaporizer is preferably selected to basically achieve energy-free carbon dioxide heat exchange. In addition, by using the two-stage discharge combined with inter-stage heat exchange mode proposed by this system, the use of low-temperature carbon steel can meet the problem of dense phase carbon dioxide venting, avoiding the concept of using stainless steel venting system settings in conventional settings.

[0034] (3) Promoting technological development

[0035] Considering that the development of dense phase carbon dioxide pipelines in my country is still in its infancy, the present invention will contribute to the further development of the safe handling technology for medium release in dense phase carbon dioxide pipelines, and will also contribute to the promotion of the concept of movable release systems in valve chambers of special medium pipeline transportation projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The present invention will be described by way of specific embodiments with reference to the accompanying drawings, in which

[0037] Figure 1 It is a system schematic diagram of the present invention.

[0038] Markings in the figure: 1 is the upstream trunk line, 2 is the trunk shut-off valve, 3 is the downstream trunk line, 4 is the bypass front section temperature transmitter, 5 is the bypass front section pressure transmitter, 6 is the bypass rear section temperature transmitter, 7 is the bypass rear section pressure transmitter, 8 is the bypass front section shut-off valve, 9 is the bypass rear section shut-off valve, 10 is the gas injection valve, 11 is the bypass front section pipeline, 12 is the bypass middle section pipeline, 13 is the bypass rear section pipeline, 21 is the discharge branch pipeline, 22 is the first-level discharge pipeline, 23 is the second-level discharge pipeline, 24 is the first-level discharge valve, 25 is the second-level discharge valve, 26 is the heating vaporizer, 27 is the venting separator tank, 28 is the venting riser, 29 is the discharge branch pressure transmitter, 30 is the first-level discharge branch pressure transmitter, 31 is the first-level discharge branch temperature transmitter, and 32 is the second-level discharge branch temperature transmitter. DETAILED DESCRIPTION

[0039] All features disclosed in this specification, or steps in all methods or processes disclosed, except mutually exclusive features and / or steps, can be combined in any manner.

[0040] Any feature disclosed in this specification (including any additional claims and abstract), unless otherwise stated, may be replaced by other equivalent or alternative features having similar purposes. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0041] like Figure 1 As shown, a dense phase carbon dioxide pipeline safe release system includes a dense phase carbon dioxide pipeline transportation and cutoff system, a valve chamber bypass system, a two-stage release system and a pipeline temperature and pressure detection system.

[0042] Specifically, the dense phase carbon dioxide pipeline transportation and cutoff system includes an upstream trunk line 1, a trunk line cutoff valve 2 and a downstream trunk line 3 connected in sequence, wherein the upstream trunk line 1 and the downstream trunk line 3 are used to connect the upstream and downstream pipelines and form a dense phase carbon dioxide transportation channel, and the trunk line cutoff valve 2 is used to control the connection or cutoff between the upstream trunk line 1 and the downstream trunk line 3. In this embodiment, the upstream trunk line 1 is buried, and the pipeline material is carbon steel; the trunk line cutoff valve 2 is a full-diameter cutoff valve with an automatic cutoff function, which is made of carbon steel and is buried; the downstream trunk line 3 is buried, and the pipeline material is carbon steel, and an opening is provided on the upstream and downstream pipelines near the trunk line cutoff valve 2 to connect the valve chamber bypass pipeline.

[0043] Specifically, the valve chamber bypass system includes a valve chamber bypass and a bypass shut-off valve group arranged on the valve chamber bypass. The pipeline of the valve chamber bypass is connected by the upstream trunk line 1 of the trunk shut-off valve 2, and is connected by the downstream trunk line 3 of the trunk shut-off valve 2 to form a trunk bypass, which serves to connect the upstream trunk line and the downstream trunk line. The valve chamber bypass system is used to provide a maintenance and venting bypass for the upstream trunk line 1 and the downstream trunk line 3 after the trunk line is shut off, and to provide a connecting bypass when the upstream trunk line 1 or the downstream trunk line 2 is ready to restart.

[0044] The bypass cut-off valve group arranged on the bypass of the valve chamber is composed of a bypass front section cut-off valve 8 and a bypass rear section cut-off valve 9. The bypass front section cut-off valve and the bypass rear section cut-off valve are manual ball valves, which are normally closed and made of carbon steel. The size is consistent with the valve chamber bypass pipeline, and is used to connect the upstream trunk line, the valve chamber bypass, the downstream trunk line and the venting system; the bypass pipeline between the upstream trunk line 1 and the bypass front section cut-off valve 8 is the bypass front section pipeline 11. The bypass front section cut-off valve 8 and the bypass The bypass pipeline between the rear-section shut-off valve 9 is the bypass middle-section pipeline 12, and the bypass pipeline between the bypass rear-section shut-off valve 9 and the downstream trunk line 3 is the bypass rear-section pipeline 13. The bypass front-section pipeline, the bypass middle-section pipeline and the bypass rear-section pipeline are all made of carbon steel, with a pipe diameter preferably of DN100, and are installed in the open air. The design pressure is consistent with that of the trunk pipeline. The bypass front-section shut-off valve 8 and the bypass rear-section shut-off valve 9 are used to control the discharge channels of the upstream trunk line 1 and the downstream trunk line 3, respectively.

[0045] Specifically, the two-stage discharge system is used to vent the upstream trunk line or downstream trunk line that needs to be repaired, and to perform graded pressure relief on the dense phase carbon dioxide. An interstage heat exchange system is provided between at least two adjacent pressure reliefs in the two-stage discharge system. The interstage heat exchange system is used to adjust the temperature of the medium after the previous stage of discharge, appropriately increase the temperature of carbon dioxide, avoid the generation of dry ice after the subsequent secondary discharge, and further reduce the requirements for pipeline material selection. The two-stage discharge system and the interstage heat exchange system adopt a skid-mounted mode. In this embodiment, a two-stage discharge method is adopted, and the interstage heat exchange system is arranged between the two stages of discharge, that is, after the first stage of pressure relief, external heat input is provided to appropriately increase the temperature of the medium, and then enter the second stage of pressure relief, so as to avoid the formation of dry ice in the medium during the pressure relief process.

[0046] The two-stage discharge system includes a primary discharge valve 24, a secondary discharge valve 25, a discharge separator 27 and a discharge riser 28. The inlet end of the primary discharge valve 24 is connected to the bypass middle section pipeline 12 through a discharge branch pipeline 21, and the outlet end of the primary discharge valve 24 is connected to the inlet end of the secondary discharge valve 25 through a primary discharge pipeline 22. The primary discharge valve is used to perform primary discharge and depressurize the dense phase medium into gas-liquid two-phase. An injection valve 10 is provided between the bypass front section shut-off valve 8 and the primary discharge valve 24. The injection valve is a manual ball valve made of carbon steel, with a size of DN50, equipped with a short joint, normally closed, and used to inject gas into the pipeline during discharge to adjust the pressure. The outlet end of the secondary relief valve 25 is connected to the venting riser 28 through the secondary relief pipeline 23. The secondary relief valve plays the role of secondary relief, reducing the pressure of the discharge medium to the back pressure of the downstream venting pipeline. The inter-stage heat exchange system is arranged on the primary discharge pipeline 22 between the primary relief valve 24 and the secondary relief valve 25. The venting liquid separator 27 is arranged on the secondary discharge pipeline 23 between the secondary relief valve 25 and the venting riser 28. The venting liquid separator is used to buffer the discharge medium and temporarily separate, store and re-vaporize the liquid phase that may be entrained therein. The venting riser is used to safely discharge the carbon dioxide that has been depressurized to normal pressure (or slightly positive pressure) into the atmosphere.

[0047] In this embodiment, the discharge branch pipeline is made of carbon steel, and the design pressure is consistent with the bypass middle pipeline. It is used to provide a channel connected to the first-level discharge valve when the main pipeline is discharged. The first-level discharge pipeline is made of carbon steel, with a design pressure of 3MPa.g, which is used to provide a carbon dioxide flow channel after the first-level discharge; the first-level discharge pipeline is divided into a front section and a rear section, which connects the inter-stage heat exchange system. The secondary discharge pipeline is made of low-temperature carbon steel, with a minimum design temperature of -45°C and a design pressure of 1.2MPa.g. It is used to provide a carbon dioxide flow channel after the secondary discharge. The middle is connected to the emptying separator tank, and the end is connected to the emptying riser. The first-level discharge valve is an electric regulating valve made of carbon steel, which is normally closed and controlled by a logic control system. The opening is adjusted after feedback. The second-level discharge valve is an electric regulating valve made of low-temperature carbon steel, which is normally closed and controlled by a logic control system. The opening is adjusted after feedback. The primary relief valve and the secondary relief valve work together to control the amount of carbon dioxide released to meet the temperature control requirements of the upstream trunk or downstream trunk, the temperature control requirements of the primary relief pipeline, and the temperature control requirements of the secondary relief pipeline. The venting liquid separation tank is made of low-temperature carbon steel, a horizontal separator, and an electric heating system is set up to receive the liquid phase medium that may be carried in the discharge medium and provide re-vaporization treatment. The venting riser is made of low-temperature carbon steel, with a height of not less than 20m, and the terminal medium Mach number is not less than 0.3.

[0048] The inter-stage heat exchange system includes an inlet pipe, a heating vaporizer 26 and an outlet pipe, both of which are made of low-temperature carbon steel. The heating vaporizer 26 is used to exchange heat between the medium and the environment for the low-temperature carbon dioxide after the first-stage discharge. The inlet pipe is connected to the front section of the first-stage discharge pipe 22, and the outlet pipe is connected to the rear section of the downstream first-stage discharge pipe 22. The heating vaporizer 26 selects an air-temperature vaporizer or an electrically heated water bath vaporizer according to environmental conditions. That is, if the temperature of the operating environment is higher than 0°C, the heating vaporizer 26 adopts an air-temperature vaporizer, and if the temperature of the operating environment is lower than 0°C, the heating vaporizer 26 adopts an electrically heated water bath vaporizer, thereby ensuring moderate heating without the need for complete vaporization of the medium.

[0049] In this embodiment,

[0050] Specifically, the pipeline temperature and pressure detection system includes a bypass front-end temperature transmitter 4 and a bypass front-end pressure transmitter 5 arranged on the bypass front-end pipeline 11, a bypass rear-end temperature transmitter 6 and a bypass rear-end pressure transmitter 7 arranged on the bypass rear-end pipeline 13, and a discharge branch pressure transmitter 29 arranged on the discharge branch pipeline 21, a first-level discharge branch pressure transmitter 30 and a first-level discharge branch temperature transmitter 31 arranged on the front part of the first-level discharge pipeline 22, and a second-level discharge branch temperature transmitter 32 arranged on the rear part of the first-level discharge pipeline 22. The pipeline temperature and pressure detection system is used to monitor the working status of pipelines and equipment in real time and upload data.

[0051] Among them, the bypass front section temperature transmitter and the bypass rear section temperature transmitter are mainly used to monitor the medium temperature in the trunk pipeline during the discharge process to ensure that the medium temperature is higher than the minimum allowable use temperature (-20℃) of the trunk pipeline material; the discharge branch pressure transmitter is set in the discharge branch pipeline to indicate the internal leakage of the bypass front section cut-off valve and the bypass rear section cut-off valve under normal pipeline operation, and also to indicate the stamping pressure before the discharge of the discharge branch pipeline. The primary discharge branch temperature transmitter is installed on a discharge pipeline upstream of the interstage heat exchange system, and is used to detect the minimum medium temperature of the primary discharge pipeline in real time. When the temperature is lower than -15℃, it will alarm and send a low temperature signal. The primary discharge branch pressure transmitter is installed on a discharge pipeline upstream of the interstage heat exchange system, and is used to detect the maximum pressure of the primary discharge pipeline in real time. The secondary discharge branch temperature transmitter is installed downstream of the secondary discharge valve, and is used to detect the minimum medium temperature of the secondary discharge pipeline in real time. When the temperature is lower than -40℃, it will alarm and send a low temperature signal.

[0052] Among them, the collected data of pressure transmitters and temperature transmitters in various parts of the system are uploaded to the logic control system to adjust the opening of the control valve, heat the carburetor load, and ensure system safety.

[0053] The working principle and working process of the present invention are:

[0054] (1) When a certain section of the dense phase carbon dioxide pipeline needs to be shut down for maintenance, the upstream block valve and the downstream block valve of the trunk line of the section are closed. In this embodiment, the upstream trunk line needs to be shut down for maintenance, and the adjacent trunk line block valve needs to be closed.

[0055] (2) During the main line discharge, there is a problem of the dense phase carbon dioxide in the main line being depressurized and cooled, and low temperatures in the discharge system may cause the carbon dioxide to form dry ice. Therefore, it is necessary to set up the safety discharge system described in the present invention to ensure the safety of the discharge process.

[0056] (3) The system is equipped with a secondary regulating valve and an interstage heat exchange system of the discharge system to replace the conventional primary discharge. The purpose is to control the medium pressure at around 2MPa.g after the primary pressure reduction, forming a gas-liquid two-phase, and the temperature after discharge is around -10℃; the interstage heat exchange system can provide sufficient heat supplement for the two-phase carbon dioxide (the interstage heat exchange system can use an air-temperature vaporizer or an electrically heated water bath vaporizer and a combination thereof) to increase the medium temperature so that after the secondary discharge, the medium temperature is controlled above -45℃. The above setting not only avoids the formation of dry ice in the medium, but also optimizes the material of the secondary discharge system from stainless steel (dense phase carbon dioxide is directly discharged to normal pressure, and the temperature is reduced to -90℃) to low-temperature carbon steel. Furthermore, during conventional primary discharge, heating the dense phase carbon dioxide to be discharged cannot improve the medium temperature after pressure relief. Therefore, secondary discharge is considered, and the temperature of the interstage two-phase medium is increased to meet the temperature requirements after discharge.

[0057] (4) In this system, multiple temperature monitoring instruments are installed to focus on tracking the main pipeline temperature during the main discharge process and the medium temperature in the secondary discharge system. In the event of excessive temperature drop, timely feedback is given to the discharge valve to control the discharge speed and ensure the safety of the main pipeline and the discharge system.

[0058] (5) Furthermore, the secondary discharge system and the interstage heat exchange system can be skid-mounted and transported to the corresponding valve room before planned maintenance, which can reduce the overall construction investment of the dense phase carbon dioxide pipeline.

[0059] A method for safely releasing dense phase carbon dioxide from a pipeline comprises the following steps:

[0060] Step 1: a dense phase carbon dioxide pipeline safety release system is set up on the pipeline trunk line for transporting dense phase carbon dioxide, wherein the dense phase carbon dioxide pipeline safety release system includes a dense phase carbon dioxide pipeline transportation and cutoff system, a valve chamber bypass system, a two-stage release system, an inter-stage heat exchange system, and a pipeline temperature and pressure detection system;

[0061] Step 2: When the upstream trunk line needs to be shut down for maintenance, close the starting point external transmission pump of the pipeline transmission system, the trunk line shut-off valve of this station, the trunk line shut-off valve of the upstream adjacent valve room and the downstream terminal shut-off valve. When a movable two-stage discharge system and interstage heat exchange system are used, after the maintenance and shutdown, the two-stage discharge system and the interstage heat exchange system are transported to the valve room by skids and connected to the valve room bypass system;

[0062] Step 3: Keep the bypass front-end block valve, bypass rear-end block valve, primary relief valve and secondary relief valve closed, inject nitrogen into the pipe section between the bypass front-end block valve and the primary relief valve, the pressure is the same as the main pipeline shut-off pressure, and inject nitrogen into the pipe section between the primary relief valve and the secondary relief valve, and the pressure is controlled at 2MPa.g;

[0063] Step 4: Configure the vaporizer type according to the ambient temperature. If the temperature of the working environment is higher than 0°C, select an air-temperature vaporizer to ensure that the medium temperature after heating is higher than -5°C; if the ambient temperature is lower than 0°C, select an electric heating water bath vaporizer to ensure that the medium temperature after heating is higher than -5°C;

[0064] Step 5: First, open the bypass cut-off valve group and the first-stage pressure relief valve, start the heating vaporizer, and slowly open the second-stage relief valve. After the discharge medium is vaporized, it is discharged into the atmosphere from the venting riser;

[0065] Specifically, the pressure in the first-stage discharge pipeline is controlled to be stable at 2MPa.g, the outlet medium temperature of the heating vaporizer is controlled to be higher than -5°C, and the medium temperature in the trunk pipeline is controlled to be higher than -20°C. When the upstream trunk pressure drops to 2MPa.g, the pressure in the first-stage discharge pipeline is controlled to be stable at 1MPa.g, and the outlet medium temperature of the heating vaporizer is controlled to be higher than -5°C, and the medium temperature in the trunk pipeline is controlled to be higher than -20°C. When the upstream trunk pressure drops to 1MPa.g, the discharge valve is fully opened, and the subsequent discharge operation is completed using the second-stage discharge valve;

[0066] Step 6: When the main pipeline pressure drops to 0.1MPa.g, dry air is injected from the upstream cut-off valve chamber to replace the remaining carbon dioxide in the pipeline and discharged from the venting system of the valve chamber of this station.

[0067] The present invention is not limited to the above-mentioned specific embodiments, but extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. A dense phase carbon dioxide pipeline safety release system, characterized by: It includes dense phase carbon dioxide pipeline transportation and cut-off system, valve chamber bypass system, two-stage discharge system and pipeline temperature and pressure detection system; The dense phase carbon dioxide pipeline transportation and cut-off system comprises an upstream trunk line (1), a trunk line cut-off valve (2) and a downstream trunk line (3) which are connected in sequence, wherein the upstream trunk line (1) and the downstream trunk line (3) are used to connect the upstream and downstream pipelines and form a dense phase carbon dioxide transportation channel, and the trunk line cut-off valve (2) is used to control the connection or cut-off between the upstream trunk line (1) and the downstream trunk line (3); The valve chamber bypass system comprises a valve chamber bypass and a bypass shutoff valve group arranged on the valve chamber bypass. The pipeline of the valve chamber bypass is connected from the upstream trunk line (1) of the trunk shutoff valve (2) and connected from the downstream trunk line (3) of the trunk shutoff valve (2) to form a trunk bypass. The valve chamber bypass system is used to provide a maintenance and venting bypass for the upstream trunk line (1) and the downstream trunk line (3) after the trunk line is shut off, and to provide a connecting bypass when the upstream trunk line (1) or the downstream trunk line (3) is ready to be restarted. The two-stage discharge system is used to perform staged pressure relief on dense phase carbon dioxide. An inter-stage heat exchange system is provided in the two-stage discharge system, and the inter-stage heat exchange system is used to adjust the temperature of the medium after the previous stage of discharge; The bypass cut-off valve group arranged on the bypass of the valve chamber comprises a bypass front section cut-off valve (8) and a bypass rear section cut-off valve (9), wherein the bypass front section cut-off valve (8) and the bypass rear section cut-off valve (9) are used to control the discharge channels of the upstream trunk line (1) and the downstream trunk line (3) respectively; The bypass pipeline between the upstream trunk line (1) and the bypass front section shutoff valve (8) is the bypass front section pipeline (11), the bypass pipeline between the bypass front section shutoff valve (8) and the bypass rear section shutoff valve (9) is the bypass middle section pipeline (12), and the bypass pipeline between the bypass rear section shutoff valve (9) and the downstream trunk line (3) is the bypass rear section pipeline (13); An air injection valve (10) is provided between the bypass front section cut-off valve (8) and the first-stage relief valve (24); The pipeline temperature and pressure detection system comprises a bypass front section temperature transmitter (4) and a bypass front section pressure transmitter (5) arranged on the bypass front section pipeline (11), a bypass rear section temperature transmitter (6) and a bypass rear section pressure transmitter (7) arranged on the bypass rear section pipeline (13), a discharge branch pressure transmitter (29) arranged on the discharge branch pipeline (21), a first-stage discharge branch pressure transmitter (30) and a first-stage discharge branch temperature transmitter (31) arranged on the front section of the first-stage discharge pipeline (22), and a second-stage discharge branch temperature transmitter (32) arranged on the rear section of the first-stage discharge pipeline (22). The pipeline temperature and pressure detection system is used to monitor the working temperature status of pipelines and equipment in real time and upload data.

2. The dense phase carbon dioxide pipeline safety release system according to claim 1 is characterized in that: The two-stage discharge system comprises a primary discharge valve (24), a secondary discharge valve (25), a venting separator tank (27) and a venting riser (28); the inlet end of the primary discharge valve (24) is connected to the bypass middle section pipeline (12) through a discharge branch pipeline (21); the outlet end of the primary discharge valve (24) is connected to the inlet end of the secondary discharge valve (25) through a primary discharge pipeline (22); the outlet end of the secondary discharge valve (25) is connected to the venting riser (28) through a secondary discharge pipeline (23); the inter-stage heat exchange system is arranged on the primary discharge pipeline (22) between the primary discharge valve (24) and the secondary discharge valve (25); and the venting separator tank (27) is arranged on the secondary discharge pipeline (23) between the secondary discharge valve (25) and the venting riser (28).

3. The dense phase carbon dioxide pipeline safety release system according to claim 2 is characterized in that: The inter-stage heat exchange system comprises an inlet pipe, a heating vaporizer (26) and an outlet pipe, wherein the heating vaporizer (26) is used to perform medium and environmental heat exchange on the low-temperature carbon dioxide after the first-stage discharge, the inlet pipe is connected to the front section of the first-stage discharge pipe (22), and the outlet pipe is connected to the rear section of the downstream first-stage discharge pipe (22).

4. The dense phase carbon dioxide pipeline safety release system according to claim 3 is characterized in that: The heating vaporizer (26) is selected as an air-temperature vaporizer or an electrically heated water bath vaporizer according to environmental conditions. That is, if the temperature of the working environment is higher than 0°C, the heating vaporizer (26) is an air-temperature vaporizer; if the temperature of the working environment is lower than 0°C, the heating vaporizer (26) is an electrically heated water bath vaporizer.

5. The dense phase carbon dioxide pipeline safety release system according to any one of claims 1 to 4, wherein the dense phase carbon dioxide pipeline safety release system according to claim 1 is adopted, characterized in that: The two-stage discharge system and the inter-stage heat exchange system are skid-mounted.

6. A method for safe release of dense phase carbon dioxide pipeline, characterized in that: The dense phase carbon dioxide pipeline safety release system according to claim 1 comprises the following steps: Step 1: a dense phase carbon dioxide pipeline safety release system is set up on the pipeline trunk line for transporting dense phase carbon dioxide, wherein the dense phase carbon dioxide pipeline safety release system includes a dense phase carbon dioxide pipeline transportation and cutoff system, a valve chamber bypass system, a two-stage release system, an inter-stage heat exchange system, and a pipeline temperature and pressure detection system; Step 2: When the upstream trunk line needs to be shut down for maintenance, close the starting point external transmission pump of the pipeline transmission system, the trunk line shut-off valve of this station, the trunk line shut-off valve of the upstream adjacent valve room and the downstream terminal shut-off valve. When a movable two-stage discharge system and interstage heat exchange system are used, after the maintenance and shutdown, the two-stage discharge system and the interstage heat exchange system are transported to the valve room by skids and connected to the valve room bypass system; Step 3: Keep the bypass front-end block valve, bypass rear-end block valve, primary relief valve and secondary relief valve closed, inject nitrogen into the pipe section between the bypass front-end block valve and the primary relief valve, the pressure is the same as the main pipeline shut-off pressure, and inject nitrogen into the pipe section between the primary relief valve and the secondary relief valve, and control the pressure at 2-2.2MPa.g; Step 4: Configure the vaporizer type according to the ambient temperature. If the temperature of the working environment is higher than 0°C, select an air-temperature vaporizer to ensure that the medium temperature after heating is higher than -5°C; if the ambient temperature is lower than 0°C, select an electric heating water bath vaporizer to ensure that the medium temperature after heating is higher than -5°C; Step 5: First, open the bypass cut-off valve group and the first-stage pressure relief valve, start the heating vaporizer, and slowly open the second-stage relief valve. After the discharge medium is vaporized, it is discharged into the atmosphere from the venting riser; Specifically, the pressure in the first-level discharge pipeline is controlled to be stable at 2-2.2MPa.g, the outlet medium temperature of the heating vaporizer is controlled to be higher than -5°C, and the medium temperature in the trunk pipeline is controlled to be higher than -20°C. When the upstream trunk pressure drops to 2MPa.g, the pressure in the first-level discharge pipeline is controlled to be stable at 1-1.2MPa.g, and the outlet medium temperature of the heating vaporizer is controlled to be higher than -5°C, and the medium temperature in the trunk pipeline is controlled to be higher than -20°C. When the upstream trunk pressure drops to 1MPa.g, the discharge valve is fully opened, and the subsequent discharge operation is completed using the second-level discharge valve; Step 6: When the main pipeline pressure drops to 0.1MPa.g, dry air is injected from the upstream shut-off valve chamber to replace the remaining carbon dioxide in the pipeline and discharged from the venting system of the valve chamber of this station.

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