Supercritical carbon dioxide pipeline commissioning process system and commissioning method

Abstract

The present application relates to a kind of supercritical carbon dioxide pipeline commissioning process system and commissioning method, it is related to the technical field of petrochemical equipment, for solving the problem that supercritical carbon dioxide pipeline commissioning is not easy to control the stable transition of carbon dioxide phase state.The supercritical carbon dioxide pipeline commissioning process system includes: first station inlet pipeline assembly;Trunk booster pump, set on first station inlet pipeline assembly;Trunk pipeline, with the output end of first station inlet pipeline assembly communication;End station inlet pipeline, with the output end of trunk pipeline communication;Nitrogen injection and back pressure establishment device, with first station inlet pipeline assembly communication;Carbon dioxide replacement pressure increasing device, with the input end of first station inlet pipeline assembly communication;Carbon dioxide back pressure establishment device, with carbon dioxide replacement pressure increasing device and upstream pipeline communication.In the present application, by stabilizing trunk pipeline pressure, to ensure that no phase change occurs during liquid phase carbon dioxide replacement process.

Description

Technical Field

[0001] This invention relates to the field of petrochemical equipment technology, and in particular to a supercritical carbon dioxide pipeline commissioning process system and commissioning method. Background Technology

[0002] my country's carbon dioxide emission sources and utilization / storage sites are geographically constrained, necessitating spatial transshipment. Considering the safety, stability, and economic feasibility of existing transportation methods, pipeline transport is the optimal way to achieve large-scale carbon dioxide transportation. A significant challenge arising from this is the safe commissioning of supercritical carbon dioxide pipelines. Before commissioning, carbon dioxide pipelines operate at low pressure and ambient temperature. If liquid carbon dioxide directly enters the pipeline, it will vaporize significantly, absorbing heat and causing low temperatures, leading to dry ice formation and pipeline blockage. Therefore, the key to commissioning supercritical carbon dioxide pipelines lies in controlling the smooth transition of the carbon dioxide phases. Improper operation during commissioning can lead to risks such as dry ice blockage, low-temperature brittle fracture of the pipe, water hammer overpressure, and slugging. However, in existing supercritical carbon dioxide pipeline technologies, controlling the smooth transition of the carbon dioxide phases during commissioning is not easy. Summary of the Invention

[0003] This invention provides a supercritical carbon dioxide pipeline commissioning process system and commissioning method to solve the problem of difficulty in controlling the smooth transition of carbon dioxide phase state during supercritical carbon dioxide pipeline commissioning.

[0004] This invention provides a supercritical carbon dioxide pipeline commissioning process system, comprising: a first-station inlet pipeline assembly; a mainline booster pump installed on the first-station inlet pipeline assembly; a mainline pipeline connected to the output end of the first-station inlet pipeline assembly; a final-station inlet pipeline connected to the output end of the mainline pipeline; a nitrogen injection and back pressure building device connected to the first-station inlet pipeline assembly for building back pressure in the downstream pipeline of the mainline booster pump; a carbon dioxide displacement and pressurization device connected to the input end of the first-station inlet pipeline assembly for increasing the pressure of carbon dioxide in the upstream pipeline of the mainline booster pump and displacing nitrogen in the downstream pipeline; and a carbon dioxide back pressure building device connected to the carbon dioxide displacement and pressurization device and the upstream pipeline for building back pressure in the upstream pipeline of the mainline booster pump.

[0005] In one embodiment, the first-station inlet pipeline assembly includes: a first-station inlet pipeline having an output end and an input end, with a mainline booster pump disposed on the first-station inlet pipeline; a pre-pump valve control assembly disposed on the first-station inlet pipeline and located upstream of the mainline booster pump; a post-pump valve control assembly disposed on the first-station inlet pipeline and located downstream of the mainline booster pump; and a heat exchanger assembly disposed on the first-station inlet pipeline and located downstream of the post-pump valve control assembly.

[0006] In one embodiment, the pre-pump valve control assembly includes: a first-station inlet shut-off valve disposed on the first-station inlet pipeline and closer to the input end relative to the mainline booster pump; and a pre-pump shut-off valve disposed on the first-station inlet pipeline and located between the first-station inlet shut-off valve and the mainline booster pump.

[0007] In one embodiment, the post-pump valve control assembly includes a post-pump check valve, a post-pump shut-off valve, and a post-pump regulating valve, which are sequentially installed on the post-pump inlet pipeline along the flow direction of the fluid in the inlet pipeline of the first station.

[0008] In one embodiment, the heat exchanger assembly includes a pre-heat exchanger shut-off valve, a main heat exchanger, and a post-heat exchanger shut-off valve, which are sequentially arranged on the inlet pipeline of the first station along the flow direction of the fluid in the pipeline.

[0009] In one embodiment, a first venting assembly is also included, which is connected to the pipeline of the first station inlet pipe located between the pump downstream valve control assembly and the heat exchanger assembly.

[0010] In one embodiment, the nitrogen injection and back pressure establishment device includes: a liquid nitrogen vehicle for storing liquid nitrogen; a vaporizer connected to the liquid nitrogen vehicle; and a nitrogen injection pipeline, one end of which is connected to the vaporizer and the other end of which is connected to the inlet pipeline of the first station.

[0011] In one embodiment, the carbon dioxide replacement pressurization device includes: a liquid carbon dioxide storage tank having a gas output end and a liquid output end; a connecting pipe having one end connected to the liquid output end and the other end connected to the input end of the first station inlet pipe; and a low-pressure pump pre-shutdown valve, a low-pressure carbon dioxide booster pump, and a low-pressure pump post-shutdown valve, which are sequentially arranged on the connecting pipe along the flow direction of the fluid in the connecting pipe.

[0012] In one embodiment, the carbon dioxide back pressure building device includes: a gas phase carbon dioxide injection line, one end of which is connected to a gas output end and the other end of which is connected to an upstream pipeline of a main booster pump; and a gas phase line shut-off valve, which is installed on the gas phase carbon dioxide injection line.

[0013] This invention also provides a commissioning method using the above-mentioned supercritical carbon dioxide pipeline commissioning process system, which includes the following steps:

[0014] Step 1: Activate the nitrogen injection and back pressure establishment device to purge the pipeline with a slight positive pressure and seal the pressure.

[0015] Step 2: Activate the carbon dioxide back pressure building device to establish back pressure in the low-pressure section before the pump.

[0016] Step 3: Activate the nitrogen purging and back pressure building device to establish back pressure in the high-pressure section after the pump and the main pipeline.

[0017] Step 4: Turn on the carbon dioxide replacement and pressurization device to replace and pressurize the carbon dioxide in the low-pressure section before the pump.

[0018] Step 5: Keep the carbon dioxide replacement pressurization device running and turn on the main line booster pump to replace the nitrogen in the high-pressure section after the pump, the main line pipeline, and the terminal station inlet pipeline.

[0019] Compared with existing technologies, the advantages of this invention are as follows: Nitrogen replacement is performed using a nitrogen injection and back pressure establishment device, primarily removing residual water and air, and sealing the pipeline with a slight positive pressure to prevent corrosion. A carbon dioxide back pressure establishment device is used to establish back pressure in the low-pressure section before the pump, preventing vaporization and dry ice blockage when cryogenic liquid carbon dioxide enters. Back pressure is also established in the high-pressure section after the pump and the main pipeline using the nitrogen injection and back pressure establishment device. This ensures that high-purity nitrogen will not damage the environment after pipeline drying and replacement. A carbon dioxide replacement pressurization device is used to ensure that no phase change occurs during the liquid carbon dioxide replacement process in the pipeline, i.e., by stabilizing the pressure in the main pipeline, a phase change is prevented during the liquid carbon dioxide replacement process. This achieves a smooth transition of the carbon dioxide phase, thereby ensuring the smooth commissioning of the supercritical carbon dioxide pipeline. Attached Figure Description

[0020] The invention will now be described in more detail with reference to embodiments and the accompanying drawings.

[0021] Figure 1 This is a schematic diagram of the structural composition of the supercritical carbon dioxide pipeline commissioning process system in Embodiment 1 of the present invention;

[0022] Figure 2 This is a flowchart of the production method in Embodiment 2 of the present invention;

[0023] Figure 3 This is a state diagram of the supercritical carbon dioxide pipeline commissioning process system in step one of Embodiment 2 of the present invention;

[0024] Figure 4 This is a state diagram of the supercritical carbon dioxide pipeline commissioning process system in step two of Embodiment 2 of the present invention;

[0025] Figure 5 This is a state diagram of the supercritical carbon dioxide pipeline commissioning process system in step three of Embodiment 2 of the present invention;

[0026] Figure 6 This is a state diagram of the supercritical carbon dioxide pipeline commissioning process system in step four of Embodiment 2 of the present invention;

[0027] Figure 7 This is a state diagram of the supercritical carbon dioxide pipeline commissioning process system in step five of Embodiment 2 of the present invention;

[0028] Figure 8 This is a flowchart of the back pressure establishment method in Embodiment 3 of the present invention.

[0029] Figure label:

[0030] 11. First station inlet pipeline; 12. Pre-pump valve control assembly; 121. First station inlet shut-off valve; 122. Pre-pump shut-off valve; 13. Post-pump valve control assembly; 131. Post-pump check valve; 132. Post-pump shut-off valve; 133. Post-pump regulating valve; 14. Heat exchanger assembly; 141. Pre-heat exchanger shut-off valve; 142. Main line heat exchanger; 143. Post-heat exchanger shut-off valve; 20. Main line booster pump; 30. Main line pipeline; 40. Terminal station inlet pipeline; 50. 51. Nitrogen injection and back pressure establishment device; 52. Nitrogen injection pipeline; 53. Nitrogen injection valve before the first pump; 60. Nitrogen injection valve in the pigging area; 61. Carbon dioxide replacement and pressurization device; 62. Liquid carbon dioxide storage tank; 63. Connecting pipeline; 64. Low-pressure pump inlet shut-off valve; 65. Low-pressure carbon dioxide booster pump; 70. Low-pressure pump outlet shut-off valve; 71. Carbon dioxide back pressure establishment device; 72. Gas phase carbon dioxide injection pipeline; 83. Gas phase line shut-off valve; 94. First release... Empty assembly; 81. Pump post-pump throttling valve; 82. Pump post-pump vent valve; 90. First station inlet bypass; 100. Launching bypass ball valve; 110. Launching bypass shut-off valve; 120. Launching cylinder; 130. Launching cylinder outlet ball valve; 140. Second vent assembly; 1401. Launching cylinder vent valve; 1402. Launching cylinder throttling valve; 150. Third vent assembly; 1501. End-station vent valve; 1502. End-station throttling valve; 160. Inspection Measuring instruments and devices; 1601, Pressure gauge after cryogenic liquid phase booster pump; 1602, Pressure gauge after main line booster pump; 1603, Temperature gauge before heat exchanger; 1604, Temperature gauge after heat exchanger; 1605, Pressure gauge for launching cylinder; 1606, Small range pressure gauge; 1607, Ball passing indicator; 1608, Main line pressure gauge; 1609, Pipeline wall temperature detector; 1610, Ground temperature detector; 170, First station outgoing shut-off valve; 180, Main line ball valve. Detailed Implementation

[0031] The invention will now be further described with reference to the accompanying drawings.

[0032] Example 1

[0033] like Figure 1As shown, the present invention provides a supercritical carbon dioxide pipeline commissioning process system, which includes a first-station inlet pipeline assembly, a main line booster pump 20, a main line pipeline 30, a last-station inlet pipeline 40, a nitrogen injection and back pressure building device 50, a carbon dioxide replacement and pressurization device 60, and a carbon dioxide back pressure building device 70. The main line booster pump 20 is installed on the first station inlet pipeline assembly; the main line pipeline 30 is connected to the output end of the first station inlet pipeline assembly; the terminal station inlet pipeline 40 is connected to the output end of the main line pipeline 30; the nitrogen injection and back pressure building device 50 is connected to the first station inlet pipeline assembly and is used to build back pressure in the downstream pipeline of the main line booster pump 20; the carbon dioxide replacement and pressurization device 60 is connected to the input end of the first station inlet pipeline assembly and is used to increase the pressure of carbon dioxide in the upstream pipeline of the main line booster pump 20 and replace the nitrogen in the downstream pipeline; the carbon dioxide back pressure building device 70 is connected to the carbon dioxide replacement and pressurization device 60 and the upstream pipeline and is used to build back pressure in the upstream pipeline of the main line booster pump 20.

[0034] It should be noted that when a supercritical carbon dioxide pipeline is put into operation, the pipeline is initially under low pressure and ambient temperature. If liquid carbon dioxide enters the pipeline directly, it will vaporize in large quantities, absorbing heat and causing low temperatures, eventually forming dry ice that blocks the pipeline. Therefore, back pressure needs to be established in the pipeline to ensure a smooth transition of the carbon dioxide phase during the commissioning process.

[0035] In the above setup, nitrogen purging is performed using a nitrogen injection and back pressure building device 50 during the nitrogen purging stage. This primarily removes residual water and air and creates a slight positive pressure seal in the pipeline to prevent corrosion. During the back pressure building stage, a carbon dioxide back pressure building device 70 is used to build back pressure in the low-pressure section upstream of the pump (the pipeline upstream of the main booster pump 20). When cryogenic liquid carbon dioxide enters, it will not vaporize, thus preventing problems such as dry ice freezing and blockage.

[0036] It should be noted that the operating pressure of the high-pressure section after the pump (the pipeline downstream of the main booster pump 20) and the main pipeline 30 is above the critical pressure of carbon dioxide. If carbon dioxide is used to establish back pressure, it will liquefy after being pressurized to a certain level due to the influence of pipeline temperature and ambient temperature. For example, it will liquefy at 4.0 MPa at 5℃ and cannot directly enter the pipeline. However, if the back pressure value is not higher than the bubble point pressure of carbon dioxide at the highest ground temperature or ambient temperature along the pipeline, the subsequent liquid carbon dioxide will still undergo a phase change when it enters the pipeline, which can easily cause risks such as dry ice freezing blockage, low-temperature brittle fracture of the pipe, and slug blockage.

[0037] In the above setup, the nitrogen injection and back pressure establishment device 50 establishes back pressure for the high-pressure section after the pump and the main pipeline. The back pressure value should be determined based on the carbon dioxide bubble point pressure at the highest ground temperature or ambient temperature along the supercritical carbon dioxide pipeline during commissioning, with a margin of 0.5 MPa. Nitrogen is widely available and easily obtained; using the nitrogen injection and back pressure establishment device 50 to establish back pressure ensures that high-purity nitrogen will not damage the environment after pipeline drying and replacement. During the liquid-phase carbon dioxide replacement pressurization stage, the carbon dioxide replacement pressurization device 60 ensures that no phase change occurs during the liquid-phase carbon dioxide replacement process.

[0038] In this invention, a nitrogen injection and back pressure establishment device is used for nitrogen purging, primarily to remove residual water and air, and to seal the pipeline under slight positive pressure to prevent corrosion. A carbon dioxide back pressure establishment device is used to establish back pressure in the low-pressure section before the pump, preventing vaporization and dry ice blockage when cryogenic liquid carbon dioxide enters. The nitrogen injection and back pressure establishment device also establishes back pressure in the high-pressure section after the pump and the main pipeline. This ensures that high-purity nitrogen will not damage the environment after the pipeline has been dried and purged. A carbon dioxide purging pressurization device is used to ensure that no phase change occurs during the liquid carbon dioxide purging process in the pipeline, i.e., by stabilizing the pressure in the main pipeline. This achieves a smooth transition of the carbon dioxide phase, thereby ensuring the smooth commissioning of the supercritical carbon dioxide pipeline.

[0039] Specifically, such as Figure 1 As shown, in one embodiment, the first-station inlet pipeline assembly includes a first-station inlet pipeline 11, a pre-pump valve control assembly 12, a post-pump valve control assembly 13, and a heat exchanger assembly 14. The first-station inlet pipeline 11 has an output end and an input end, and the mainline booster pump 20 is mounted on the first-station inlet pipeline 11. The pre-pump valve control assembly 12 is mounted on the first-station inlet pipeline 11 and located upstream of the mainline booster pump 20. The post-pump valve control assembly 13 is mounted on the first-station inlet pipeline 11 and located downstream of the mainline booster pump 20. The heat exchanger assembly 14 is mounted on the first-station inlet pipeline 11 and located downstream of the post-pump valve control assembly 13.

[0040] Specifically, such as Figure 1 As shown, in one embodiment, the pre-pump valve control assembly 12 includes a first-station inlet shut-off valve 121 and a pre-pump shut-off valve 122. The first-station inlet shut-off valve 121 is disposed on the first-station inlet pipeline 11 and is closer to the input end relative to the main line booster pump 20; the pre-pump shut-off valve 122 is disposed on the first-station inlet pipeline 11 and is located between the first-station inlet shut-off valve 121 and the main line booster pump 20.

[0041] Specifically, such as Figure 1As shown, in one embodiment, the post-pump valve control assembly 13 includes a post-pump check valve 131, a post-pump shut-off valve 132, and a post-pump regulating valve 133. Along the flow direction of the fluid in the first station inlet pipeline 11, the post-pump check valve 131, the post-pump shut-off valve 132, and the post-pump regulating valve 133 are sequentially arranged on the first station inlet pipeline 11.

[0042] Specifically, such as Figure 1 As shown, in one embodiment, the heat exchanger assembly 14 includes a pre-heat exchanger shut-off valve 141, a main line heat exchanger 142, and a post-heat exchanger shut-off valve 143. Along the flow direction of the fluid in the first station inlet pipeline 11, the pre-heat exchanger shut-off valve 141, the main line heat exchanger 142, and the post-heat exchanger shut-off valve 143 are sequentially arranged on the first station inlet pipeline 11.

[0043] Specifically, such as Figure 1 As shown, in one embodiment, a first venting assembly 80 is also included, which is connected to the pipeline of the first station inlet pipe 11 located between the pump downstream valve control assembly 13 and the heat exchanger assembly 14.

[0044] Specifically, such as Figure 1 As shown, in one embodiment, the nitrogen injection and back pressure establishment device 50 includes a liquid nitrogen truck, a vaporizer, and a nitrogen injection pipeline 51. The liquid nitrogen truck is used to store liquid nitrogen; the vaporizer is connected to the liquid nitrogen truck; one end of the nitrogen injection pipeline 51 is connected to the vaporizer, and the other end is connected to the first station inlet pipeline 11.

[0045] Specifically, such as Figure 1 As shown, in one embodiment, the carbon dioxide replacement pressurization device 60 includes a liquid carbon dioxide storage tank 61 and a connecting pipe 62. The liquid carbon dioxide storage tank 61 has a gas output end and a liquid output end; one end of the connecting pipe 62 is connected to the liquid output end, and the other end is connected to the input end of the first station inlet pipe 11; a low-pressure pump pre-shutdown valve 63, a low-pressure carbon dioxide booster pump 64, and a low-pressure pump post-shutdown valve 65 are sequentially arranged on the connecting pipe 62 along the flow direction of the fluid within the connecting pipe 62.

[0046] Specifically, such as Figure 1 As shown, in one embodiment, the carbon dioxide back pressure building device 70 includes a gas phase carbon dioxide injection line 71 and a gas phase line shut-off valve 72. One end of the gas phase carbon dioxide injection line 71 is connected to the gas output end, and the other end is connected to the upstream pipeline of the main line booster pump 20; the gas phase line shut-off valve 72 is disposed on the gas phase carbon dioxide injection line 71.

[0047] Specifically, such as Figure 1As shown, in one embodiment, it also includes a first-station inlet bypass 90, one end of which is connected to the pipeline section of the first-station inlet pipe 11 located downstream of the heat exchanger assembly 14, and the other end of which is connected to the output end of the first-station inlet pipe 11. Along the flow direction of the fluid in the first-station inlet bypass 90, a ball launch bypass ball valve 100, a ball launch bypass shut-off valve 110, a ball launch tube 120, and a ball launch tube outlet ball valve 130 are sequentially arranged.

[0048] Specifically, such as Figure 1 As shown, in one embodiment, a second venting assembly 140 is also included, which is connected to the ball-launching tube 120.

[0049] Specifically, such as Figure 1 As shown, in one embodiment, a third venting assembly 150 is also included, which is connected to the terminal station inlet pipe 40.

[0050] Specifically, such as Figure 1 As shown, in one embodiment, a first-station outgoing shut-off valve 170 is provided downstream of the ball valve 130 at the outlet of the launching tube. A mainline ball valve 180 is provided downstream of the shut-off valve 143 after the heat exchanger.

[0051] It should be noted that the second vent assembly 140, the third vent assembly 150, and the first vent assembly have the same structure. They all include a vent line and a throttling valve and a vent valve installed on the vent line.

[0052] It should be noted that the supercritical carbon dioxide pipeline commissioning process system of the present invention specifically includes a nitrogen injection and back pressure building device 50, a carbon dioxide back pressure building device 70, a carbon dioxide replacement and pressurization device 60, a venting device (including a first venting component 80, a second venting component 140 and a third venting component 150) and a detection instrument device.

[0053] The nitrogen injection and back pressure establishment device 50 is installed at the first station. Its upstream is connected to the liquid nitrogen truck and vaporizer through the nitrogen injection pipeline 51, and its downstream is connected to the nitrogen injection valve 52 in front of the pump and the nitrogen injection valve 53 in the cleaning area through the nitrogen injection pipeline 51. The nitrogen injection and back pressure establishment device 50 is used to replace the air in the pipeline and establish back pressure in the high-pressure section after the pump and the main pipeline.

[0054] The carbon dioxide back pressure building device 70 is set at the first station. Its upstream is connected to the top steam line of the liquid carbon dioxide storage tank 61 via the gas phase carbon dioxide injection pipeline 71 and the gas phase line cut-off valve 72. Its downstream is connected to the nitrogen injection valve (3) in front of the pump at the first station via the gas phase carbon dioxide injection pipeline 71. The carbon dioxide back pressure building device 70 is used to replace the nitrogen in the low-pressure section pipeline in front of the pump and build back pressure.

[0055] The carbon dioxide replacement pressurization device 60 is installed at the first station. Its upstream is connected to the liquid phase carbon dioxide storage tank 61, and its downstream is connected to the first station inlet pipeline 11 after being pressurized by the low-pressure carbon dioxide booster pump 64. The carbon dioxide replacement pressurization device 60 is used to fill the pipeline with liquid phase carbon dioxide to replace nitrogen until the entire line is liquid phase carbon dioxide, and then continue to pressurize to the operating pressure.

[0056] The venting device is installed at the first station and all stations along the route. It releases nitrogen and mixed gas through the venting pipeline to replace liquid carbon dioxide and nitrogen. The pressure and phase stability of liquid carbon dioxide during the replacement pressurization process are controlled by adjusting the valve opening.

[0057] The detection instruments are installed at the first station and all stations along the route to monitor changes in parameters within the pipeline and enable timely operation control.

[0058] Specifically, the venting device includes a pump-after-pump throttling valve 81, a pump-after-pump venting valve 82, a launch tube venting valve 1401, a launch tube throttling valve 1402, a terminal venting valve 1501, and a terminal throttling valve 1502.

[0059] Specifically, the detection instrument device 160 includes a pressure gauge 1601 after the cryogenic liquid phase booster pump, a pressure gauge 1602 after the main line booster pump, a temperature gauge 1603 before the heat exchanger, a temperature gauge 1604 after the heat exchanger, a pressure gauge 1605 for the launching cylinder, a small-range pressure gauge 1606, a ball-passing indicator 1607, a main line pressure gauge 1608, a pipe wall temperature detector 1609, and a ground temperature detector 1610.

[0060] Example 2

[0061] like Figure 2 As shown, the present invention provides a commissioning method, which adopts the supercritical carbon dioxide pipeline commissioning process system described above.

[0062] It includes the following steps:

[0063] Step 1: Activate the nitrogen injection and back pressure establishment device to purge the pipeline with a slight positive pressure and seal the pressure.

[0064] Step 2: Activate the carbon dioxide back pressure building device to establish back pressure in the low-pressure section before the pump.

[0065] Step 3: Activate the nitrogen injection and back pressure establishment device to establish back pressure in the high-pressure section after the pump and the main pipeline.

[0066] Step 4: Activate the carbon dioxide replacement and pressurization device to replace and pressurize the carbon dioxide in the low-pressure section before the pump.

[0067] Step 5: Keep the carbon dioxide replacement pressurization device running and turn on the main line booster pump to replace the nitrogen in the high-pressure section after the pump, the main line pipeline, and the terminal station inlet pipeline.

[0068] Specifically, in one embodiment, the more specific steps are as follows:

[0069] Step 1: Ensure all balancing valve assemblies along the pipeline remain open (balancing valve assemblies are a common design feature in long-distance pipeline stations; they refer to bypass valve assemblies for valves within the station or main line. Ball valves larger than a certain nominal diameter that need to open under full differential pressure are typically equipped with balancing valve assemblies. During commissioning and replacement, these balancing valve assemblies are kept open to replace gas in the bypass pipeline; they are not shown in the diagram). Keep the venting pipeline valves closed. Activate the nitrogen replacement and back pressure establishment device. Liquid nitrogen is supplied by a liquid nitrogen truck. The liquid nitrogen passes through a vaporizer and vaporizes into gaseous nitrogen. Nitrogen is then introduced into the entire pipeline through the nitrogen injection pipeline, connecting the nitrogen injection valve 52 before the first station pump and the nitrogen injection valve 53 in the pigging area, replacing the air in the pipeline. Nitrogen replacement uses a full-line nitrogen injection method. During the replacement process, no isolation ball is used between the nitrogen and air; nitrogen directly pushes the air out of the pipeline. Open the venting valve and throttling valve at the end station (included in the third venting assembly) to release the air in the pipeline. By adjusting the opening of the vent valve at the terminal station, the pressure of the main pipeline is maintained between 0.05MPa and 0.3MPa, and the gas replacement rate in the pipeline is between 1.6 and 3.2 m / s. The replacement of gas in the valve chambers along the pipeline utilizes nitrogen from the main pipeline and is carried out simultaneously with the replacement of gas in the main pipeline. Once the gas dew point at each station and valve chamber monitoring point along the pipeline is no higher than -45℃ and the oxygen content is ≤2%, the terminal vent valve and throttling valve are closed. Nitrogen is then continued to be introduced until the pressure in the pipeline reaches 0.05MPa-0.07MPa. The nitrogen injection and back pressure building devices are then closed, and the nitrogen in the pipeline is sealed at 0.05MPa (slight positive pressure).

[0070] As shown in the attached figure. Figure 3 As shown, valves 121, 63, 65, 72, 81, 82, 1402, and 1401 are closed. Valve 122 is open, as are valves 52, 53, 131, 132, 133, 141, 143, 100, 110, 130, 170, 180, 1501, and 1502. (Valves indicated by the bold black line are open; those not indicated are closed.)

[0071] Step 2: Close the booster pump outlet shut-off valve. Activate the carbon dioxide back pressure building device, open the vapor phase line shut-off valve and nitrogen injection valve, and introduce carbon dioxide vapor from the top of the liquid phase carbon dioxide storage tank into the low-pressure pipeline before the pump through the vapor phase carbon dioxide injection pipeline. When the pressure reading on the downstream pressure gauge reaches the pressure of the liquid phase carbon dioxide storage tank, open the downstream vent valve and throttling valve to displace the nitrogen in the pipeline. When the carbon dioxide content at the vent is detected to reach 95% and shows an increase for three consecutive times, sequentially close the downstream vent valve, throttling valve, vapor phase line shut-off valve, and the nitrogen injection valve before the first pump.

[0072] As shown in the attached figure. Figure 4 As shown, valves 53, 63, 65, and 121 are closed; valves 132, 133, 141, 143, 100, 110, 180, 1401, 1402, 130, 170, 1501, and 1502 are closed. Valves 72, 52, 122, 131, 81, and 82 are open. (Valves indicated by the bold black line are open; those not indicated are closed.)

[0073] Step 3: Ensure all balancing valve groups along the pipeline remain open and venting pipeline valves remain closed. Activate the nitrogen injection and back pressure establishment device, using a liquid nitrogen truck to supply liquid nitrogen. The liquid nitrogen passes through a vaporizer, vaporizing into gaseous nitrogen gas, which is then introduced into the high-pressure and main pipeline downstream of the pump via the nitrogen injection pipeline connected to the nitrogen injection valve before the first station pump. Control the pressure rise rate within the pipeline to no more than 1 MPa / h using valves inside the liquid nitrogen truck. Monitor pressure changes within the pipeline using pressure sensors installed at stations and valve chambers along the pipeline. When the pressure reaches 30% of the required back pressure value, shut off the nitrogen purging and back pressure establishment device, allowing the main pipeline pressure to stabilize for 24 hours. Repeat the above steps until the pipeline pressure reaches 60% of the required back pressure value, then shut off the nitrogen injection and back pressure establishment device, allowing the main pipeline pressure to stabilize for 24 hours. Continue repeating the above steps until the pressure along the entire pipeline reaches the required back pressure value, then shut off the nitrogen injection and back pressure establishment device.

[0074] As shown in the attached figure. Figure 5 As shown, valves 52, 63, 65, 72, 121, 122, 131, 132, 81, 82, 1401, and 1402 remain closed. Valves 53, 133, 141, 143, 100, 110, 130, 170, 180, 1501, and 1502 are open. (Valves indicated by the bold black line are open; those not indicated are closed.)

[0075] Step 4: Confirm that the valve before the main line booster pump is open and the outlet shut-off valve of the booster pump is closed. Start the carbon dioxide replacement and pressurization device, open the shut-off valve before and after the liquid phase line pump, and start the low-pressure carbon dioxide booster pump. The liquid carbon dioxide in the liquid phase carbon dioxide storage tank, after being pressurized by the low-pressure carbon dioxide booster pump, is delivered to the first station inlet pipeline, passing sequentially through the first station inlet shut-off valve and the pump inlet shut-off valve, thus replacing and pressurizing the low-pressure pipeline before the pump. When the pressure gauge reading after the cryogenic liquid phase carbon dioxide booster pump reaches the rated pressure before the main line booster pump, open the pump outlet vent valve and the throttling valve to replace the gaseous carbon dioxide in the pipe. When white mist-like carbon dioxide dry ice particles are observed leaking out, and the medium temperature is below -20℃, sequentially close the throttling valve and the pump outlet vent valve, and shut down the carbon dioxide replacement and pressurization device.

[0076] As shown in the attached figure. Figure 6 As shown, valves 52, 53, 72, 132, 133, 141, 143, 100, 110, 1402, 1401, 130, 170, 180, 1501, and 1502 are closed. Valves 63, 65, 121, 122, 131, 81, and 82 are open. (Valves indicated by the bold black line are open; those not indicated are closed.)

[0077] Step 5: Confirm that the valve before the main line booster pump is open and the outlet shut-off valve of the main line booster pump is closed. Turn on the carbon dioxide replacement pressurization device, open the shut-off valve before and after the low-pressure pump, and start the low-pressure carbon dioxide booster pump. Open the outlet shut-off valve of the main line booster pump to 5-10%, then start the main line booster pump. When the pressure gauge reading after the main line booster pump reaches the back pressure value of the main line pipeline, open the outlet shut-off valve of the main line booster pump to 100%. Stabilize the liquid phase carbon dioxide replacement pressure at the back pressure value of the main line pipeline by adjusting the opening of the regulating valve after the pump. Ensure that the shut-off valve before and after the heat exchanger is open. Close the main line ball valve, and sequentially open the ball launcher bypass ball valve, ball launcher bypass shut-off valve, and ball launcher outlet ball valve. Use a ball-passing detector to check the isolation ball's departure from the station. Open the vent valve and throttling shut-off valve at the end of the pipeline to release the replaced nitrogen and mixed gas in the pipeline. By controlling the opening of the vent valve to match the discharge rate with the booster pump's displacement, the pressure in the main pipeline is stabilized, ensuring no phase change occurs during the liquid-phase carbon dioxide replacement process. Replacement is complete when the carbon dioxide concentration at the terminal station reaches 95% and three consecutive monitoring tests show no decrease in carbon dioxide content.

[0078] As shown in the attached figure. Figure 7As shown, valves 52, 53, 72, 81, 82, 1401, and 1402 are closed. Valves 63, 65, 121, 122, 131, 132, 133, 141, 143, 180, 100, 110, 130, 170, 1502, and 1501 are open. (Valves indicated by the bold black line are open; those not indicated are closed.)

[0079] When establishing back pressure in the high-pressure section after the pump and the main pipeline, the nitrogen back pressure value should be determined based on the carbon dioxide bubble point pressure at the highest ground temperature or ambient temperature along the supercritical carbon dioxide pipeline when it is put into operation, and should be at least 0.5 MPa higher than the bubble point pressure.

[0080] Working principle of the invention:

[0081] When supercritical carbon dioxide pipelines are put into operation, the pipelines are initially in a low-pressure, ambient-temperature state. If liquid carbon dioxide directly enters the pipeline, it will vaporize significantly, absorbing heat and causing low temperatures, leading to dry ice formation and pipeline blockage. Back pressure needs to be established in the pipeline to ensure a smooth transition of the carbon dioxide phase during commissioning. During the nitrogen purging stage, residual water and air are primarily removed, and the pipeline is sealed under slight positive pressure to prevent corrosion. During the back pressure establishment stage, the low-pressure section before the pump uses saturated carbon dioxide vapor from the top of the liquid carbon dioxide storage tank to establish back pressure, bringing the pressure and temperature to the same level as the liquid carbon dioxide storage tank. When the low-temperature liquid carbon dioxide enters, it will not vaporize, preventing dry ice blockage. The high-pressure section after the pump and the main pipeline operate at pressures above the critical pressure of carbon dioxide. If carbon dioxide is used to establish back pressure, the carbon dioxide concentration will be affected by pipeline temperature and ambient temperature. When compressed to a certain level, carbon dioxide will liquefy (e.g., it will liquefy at 4.0 MPa at 5℃) and cannot directly enter the pipeline. However, if the back pressure value is not higher than the bubble point pressure of carbon dioxide at the highest ground temperature or ambient temperature along the pipeline, the subsequent liquid carbon dioxide will still undergo a phase change when it enters the pipeline, which can easily cause risks such as dry ice freezing blockage, low-temperature brittle fracture of the pipe, and slugging. Therefore, nitrogen is used to establish back pressure in the high-pressure section after the pump and the main pipeline. The back pressure value should be determined based on the bubble point pressure of carbon dioxide at the lowest ground temperature or ambient temperature along the pipeline when the supercritical carbon dioxide pipeline is put into operation, with a margin of 0.5 MPa. Nitrogen is widely available and easy to obtain. Using liquid nitrogen trucks to inject back pressure ensures that high-purity nitrogen will not damage the environment after the pipeline has been dried and replaced. During the liquid-phase carbon dioxide replacement pressurization stage, the opening of the vent valve at the end of the pipeline is adjusted to control the release rate of the replaced nitrogen and mixed gas in the pipeline to be consistent with the displacement of the booster pump, thereby stabilizing the pressure of the main pipeline and ensuring that no phase change occurs during the liquid-phase carbon dioxide replacement process. During the liquid-phase carbon dioxide replacement of nitrogen stage, an isolation ball is launched by the first station launch tube to reduce the mixing of liquid-phase carbon dioxide and nitrogen, which greatly reduces the length of the carbon dioxide-nitrogen mixed gas section.

[0082] In addition, since the carbon dioxide gas source is at a low temperature after being liquefied and purified at low temperature, direct external transportation would cause soil frost heave along the route, which is not conducive to environmental protection and safe pipeline operation. Therefore, the temperature of the external carbon dioxide is controlled above 5°C by using a heat exchanger.

[0083] Example 3

[0084] This invention provides a back pressure establishment method applicable to the commissioning process of supercritical carbon dioxide pipelines. It includes the following specific steps (see reference). Figure 8 ):

[0085] Step 1: Connect the nitrogen injection truck to the vaporizer and then to the pipeline at the first station. Purge the pipeline with nitrogen at a slightly positive pressure (0.05-0.07MPa) with a flow rate controlled at 1.6-3.2m / s until the water dew point at each station and valve chamber monitoring point along the line is no higher than -45℃ and the oxygen content is ≤2%. Seal the nitrogen in the pipe with 0.05MPa (slight positive pressure).

[0086] Step 2: Close the outlet shut-off valve of the first station carbon dioxide booster pump, introduce gaseous carbon dioxide vapor from the top of the liquid carbon dioxide storage tank into the low-pressure section before the pump, open the vent valve after the pump to detect the carbon dioxide content. When the carbon dioxide content reaches 95% and the carbon dioxide content increases for three consecutive times, the back pressure is established.

[0087] Step 3: Pressurize the high-pressure section and main pipeline after the pump by injecting nitrogen using a nitrogen injection truck. In the first stage, pressurize the entire line to 30% of the required back pressure value. In the second stage, pressurize to 60% of the required back pressure value. In the third stage, pressurize to 100% of the required back pressure value. Close the nitrogen injection valve between each pressure gradient to stabilize the pressure and check for leaks.

[0088] The back pressure establishment method of this invention, applicable to the commissioning process of supercritical carbon dioxide pipelines, specifically includes the following step one: ensuring all balancing valve groups along the pipeline remain open and the venting pipeline valves remain closed. Liquid nitrogen is supplied by a liquid nitrogen truck, which vaporizes into gaseous nitrogen gas through a vaporizer and is then transported into the pipeline through the nitrogen injection valve at the first station. Nitrogen replacement is performed using a full-line nitrogen injection method, without a separating ball between the nitrogen and air during the replacement process; nitrogen directly pushes the air for replacement. During drying, only the valve at the end is opened, and the valve opening is controlled to maintain a pressure of 0.05MPa-0.3MPa in the pipeline, with a flow velocity of 1.6-3.2m / s. Valve chamber drying utilizes the drying gas from the main pipeline and is carried out simultaneously with the pipeline drying. When the gas dew point at the pipeline outlet reaches -45℃, close the pipeline outlet valve and continue pressurizing to 0.05MPa-0.07MPa. Close the nitrogen injection valve at the first station and seal for 4 hours. Take samples through the pressure gauge interfaces of each station, valve chamber, and equipment along the pipeline for dew point testing. If the test is qualified, open the nitrogen injection valve at the first station and the pipeline outlet valve in sequence to continue filling the pipeline with nitrogen for replacement. First, replace the main pipeline. If the test is qualified, use the nitrogen in the pipeline to replace the stations and valve chambers along the pipeline until the nitrogen ratio at each testing point is above 98%. Replacement is complete. The nitrogen in the pipeline is sealed at 0.05MPa (slight positive pressure).

[0089] Step two is as follows: Close the booster pump outlet shut-off valve, and introduce gaseous carbon dioxide from the inlet valve of the first station. The gas source utilizes the saturated carbon dioxide vapor at the top of the carbon dioxide storage tank, whose temperature and pressure are the same as the liquid carbon dioxide in the tank. When the pressure gauge reading after the pump reaches the pressure of the liquid carbon dioxide storage tank, open the vent valve to purge the nitrogen in the pipe. When the carbon dioxide content at the outlet of the vent valve reaches 95% and the carbon dioxide content increases for three consecutive times without decreasing, close the vent valve and the inlet valve of the first station in sequence. The back pressure of the low-pressure section before the pump is then established.

[0090] Step three is as follows: Ensure all balancing valve groups along the pipeline remain open, and venting pipeline valves remain closed. Liquid nitrogen is supplied via a liquid nitrogen truck. The liquid nitrogen passes through a vaporizer, vaporizing into gaseous nitrogen gas, which is then introduced through the valve in the first station's cleaning area. The nitrogen pressurization rate is controlled to not exceed 1 MPa / h via valves inside the liquid nitrogen truck. Pressure sensors installed at stations and valve chambers along the pipeline monitor pressure changes. When the pressure reaches 30% of the required back pressure, the nitrogen injection valve at the first station is closed, and the pressure is stabilized for 24 hours. Repeat the above steps until the pipeline pressure reaches 60% of the required back pressure, then close the nitrogen injection valve at the first station and stabilize the pressure for 24 hours. Continue repeating the above steps until the pressure along the entire pipeline reaches the required back pressure, completing the establishment of back pressure along the entire pipeline.

[0091] The back pressure establishment method of the present invention is applicable to the commissioning process of supercritical carbon dioxide pipelines. The back pressure establishment process should be carried out by pre-testing the temporary pipeline with nitrogen gas before nitrogen injection. The test pressure is 0.3 MPa and the pressure is stabilized for 10 minutes.

[0092] The back pressure establishment method of the present invention is applicable to the commissioning process of supercritical carbon dioxide pipelines. When establishing back pressure in the high-pressure section after the pump and the main pipeline, the nitrogen back pressure value should be determined according to the carbon dioxide bubble point temperature at the lowest ground temperature or ambient temperature along the supercritical carbon dioxide pipeline during commissioning, and should be at least 0.5 MPa higher than the bubble point pressure.

[0093] Although the invention has been described with reference to preferred embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of the invention. In particular, the technical features mentioned in the various embodiments can be combined in any manner as long as there is no structural conflict. The invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A supercritical carbon dioxide pipeline commissioning process system, characterized in that, include: First station inlet pipeline components; as well as A main line booster pump (20) is installed on the inlet pipeline assembly of the first station; The main pipeline (30) is connected to the output end of the first station inlet pipeline assembly; and The terminal station inlet pipe (40) is connected to the output end of the main pipeline (30); A nitrogen injection and back pressure building device (50) is connected to the first station inlet pipeline assembly and is used to build back pressure on the downstream pipeline of the main line booster pump (20); and A carbon dioxide displacement booster device (60), connected to the input end of the first station inlet pipeline assembly, is used to increase the pressure of carbon dioxide in the upstream pipeline of the main line booster pump (20) and displace nitrogen in the downstream pipeline; and A carbon dioxide back pressure building device (70) is connected to the carbon dioxide displacement booster device (60) and the upstream pipeline, and is used to build back pressure on the upstream pipeline of the main line booster pump (20).

2. The supercritical carbon dioxide pipeline commissioning process system according to claim 1, characterized in that, The first station inlet pipeline assembly includes: The first station inlet pipeline (11) has the said output end and the said input end, and the main line booster pump (20) is installed on the first station inlet pipeline (11); and A pre-pump valve control assembly (12) is installed on the inlet pipe (11) of the first station and is located upstream of the main line booster pump (20); and The downstream valve control assembly (13) is installed on the first station inlet pipeline (11) and is located downstream of the main line booster pump (20); The heat exchanger assembly (14) is installed on the first station inlet pipe (11) and is located downstream of the pump downstream valve control assembly (13).

3. The supercritical carbon dioxide pipeline commissioning process system according to claim 2, characterized in that, The pre-pump valve control assembly (12) includes: The first-station inlet shut-off valve (121) is installed on the first-station inlet pipeline (11) and is closer to the input end than the main line booster pump (20); and A pre-pump shut-off valve (122) is installed on the first station inlet pipeline (11) and located between the first station inlet shut-off valve (121) and the main line booster pump (20).

4. The supercritical carbon dioxide pipeline commissioning process system according to claim 2, characterized in that, The downstream valve control assembly (13) includes a downstream check valve (131), a downstream shut-off valve (132), and a downstream regulating valve (133). Along the flow direction of the fluid in the first station inlet pipeline (11), the downstream check valve (131), the downstream shut-off valve (132), and the downstream regulating valve (133) are sequentially arranged on the first station inlet pipeline (11).

5. The supercritical carbon dioxide pipeline commissioning process system according to claim 2, characterized in that, The heat exchanger assembly (14) includes a heat exchanger front shut-off valve (141), a main line heat exchanger (142), and a heat exchanger rear shut-off valve (143). Along the flow direction of the fluid in the first station inlet pipeline (11), the heat exchanger front shut-off valve (141), the main line heat exchanger (142), and the heat exchanger rear shut-off valve (143) are sequentially arranged on the first station inlet pipeline (11).

6. The supercritical carbon dioxide pipeline commissioning process system according to claim 2, characterized in that, It also includes a first venting assembly (80), which is connected to the pipeline of the first station inlet pipe (11) located between the pump downstream valve control assembly (13) and the heat exchanger assembly (14).

7. The supercritical carbon dioxide pipeline commissioning process system according to claim 2, characterized in that, The nitrogen injection and back pressure establishment device (50) includes: Liquid nitrogen truck, used for storing liquid nitrogen; and Vaporizer, connected to the liquid nitrogen vehicle; and The nitrogen injection pipeline (51) has one end connected to the vaporizer and the other end connected to the first station inlet pipeline (11).

8. The supercritical carbon dioxide pipeline commissioning process system according to claim 2, characterized in that, The carbon dioxide replacement pressurization device (60) includes: The liquid carbon dioxide storage tank (61) has a gas outlet and a liquid outlet; and A connecting pipe (62), one end of which is connected to the liquid output end, and the other end of which is connected to the input end of the first station inlet pipe (11); and The low-pressure pump pre-shutdown valve (63), the low-pressure carbon dioxide booster pump (64), and the low-pressure pump post-shutdown valve (65) are sequentially arranged on the connecting pipe (62) along the flow direction of the fluid in the connecting pipe (62).

9. The supercritical carbon dioxide pipeline commissioning process system according to claim 8, characterized in that, The carbon dioxide back pressure building device (70) includes: A gaseous carbon dioxide injection line (71), one end of which is connected to the gas output end, and the other end of which is connected to the upstream pipeline of the main booster pump (20); and A gas phase line shut-off valve (72) is installed on the gas phase carbon dioxide injection line (71).

10. A method for putting a product into production, characterized in that, The commissioning method employs the supercritical carbon dioxide pipeline commissioning process system as described in any one of claims 1 to 9, and includes the following steps: Step 1: Activate the nitrogen injection and back pressure establishment device to purge the pipeline with a slight positive pressure and seal the pressure. Step 2: Activate the carbon dioxide back pressure building device to establish back pressure in the low-pressure section before the main booster pump. Step 3: Activate the nitrogen injection and back pressure establishment device to establish back pressure in the high-pressure section after the main booster pump and in the main pipeline. Step 4: Activate the carbon dioxide replacement and pressurization device to replace and pressurize the carbon dioxide in the low-pressure section before the pump. Step 5: Keep the carbon dioxide replacement pressurization device running and turn on the main line booster pump to replace the nitrogen in the high-pressure section after the pump, the main line pipeline, and the terminal station inlet pipeline.

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