Nitrogen-based low-temperature discharging hose performance testing method

Abstract

The invention discloses a low-temperature discharging hose performance testing method based on nitrogen, and belongs to the related field of liquid carbon dioxide low-temperature discharging hose performance testing. Firstly, liquid nitrogen is heated and vaporized; through cooperative work of the PLC and the electronic pressure regulating valve, the temperature of the output nitrogen is stabilized at the preset target temperature. Secondly, nitrogen pressurization is carried out; vaporized low-temperature nitrogen is conveyed into the low-temperature discharging hose through the gas booster pump and pressurized, and the constant pressure is kept through the adjusting valve. And finally, carrying out experimental loading. Liquid nitrogen is used for replacing LCO2 to serve as an experimental medium, the experimental medium can be in a stable gas state under the target working conditions of-56 DEG C and 0-3.5 MPa, and the problem of pipeline blockage caused by phase change of an original medium is solved; liquid nitrogen vaporization and PID temperature control are carried out, and the medium temperature is accurately controlled within the required working condition of-56 + / -1 DEG C; the pressure can be independently adjusted under the condition that the temperature in the low-temperature discharging hose is kept constant, and high-precision temperature control and pressure control in the whole testing process are achieved.

Description

Technical Field

[0001] This invention belongs to the field of performance testing of cryogenic unloading hoses for liquid carbon dioxide (LCO2), and relates to a cryogenic loading test method that uses liquid nitrogen vaporization and heating as nitrogen gas as an alternative medium. In particular, it relates to a method for heating and vaporizing liquid nitrogen into nitrogen gas, which is suitable for laboratory simulation of comprehensive mechanical performance testing of cryogenic unloading hoses in cryogenic environments. Background Technology

[0002] With the increasing severity of global climate change and greenhouse gas emissions, carbon capture and storage (CCUS) technology has become one of the important means to reduce the concentration of carbon dioxide in the atmosphere. As a core component for LCO2 transport in the marine environment, cryogenic unloading hoses need to undergo a series of mechanical performance tests under low temperature and high pressure environments to ensure service requirements. Currently, the performance testing schemes for cryogenic unloading hoses are mainly divided into two types:

[0003] (1) Use LCO2 directly as the experimental medium

[0004] The drawback of this approach is that when using LCO2 as a cryogenic medium in experiments, its freezing point varies significantly with pressure (the freezing point of CO2 is -78℃ under standard atmospheric pressure; and -53℃ under 3.5MPa pressure). Therefore, for cryogenic experiments under high pressure, pressure fluctuations can easily cause CO2 to undergo a phase change, forming solid carbon dioxide, which can lead to pipeline blockage and seriously affect the continuity and safety of the experiment.

[0005] (2) Use liquid nitrogen instead of LCO2 as the experimental medium.

[0006] This approach utilizes the stable physical properties of liquid nitrogen to avoid safety issues arising from phase transitions. However, liquid nitrogen has a boiling point of -196°C, far below the actual service temperature of cryogenic unloading hoses. Therefore, this approach leads to overly stringent testing, severely affecting the accuracy of experimental results and potentially causing irreversible damage to the cryogenic unloading hose during testing.

[0007] In summary, there is an urgent need for a novel testing method that can accurately simulate the service temperature range of LCO2, avoid the blockage risk caused by the LCO2 phase transition, and prevent "overcooling damage" to the material. This invention addresses this need by proposing a nitrogen-based cryogenic unloading hose performance testing method. Summary of the Invention

[0008] The purpose of this invention is to address the difficulties in temperature and pressure control when using LCO2 as a medium in performance testing of cryogenic unloading hoses, and the problem of distorted results caused by using liquid nitrogen instead of LCO2 as the experimental medium. This invention provides a method based on the vaporization of liquid nitrogen into nitrogen gas as the experimental medium, thereby achieving precise temperature and pressure control during the testing process.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A nitrogen-based cryogenic unloading hose performance testing method includes liquid nitrogen heating and vaporization, nitrogen pressurization, and experimental loading. The specific steps are as follows:

[0011] The first step is to heat and vaporize the liquid nitrogen;

[0012] Liquid nitrogen stored in a liquid nitrogen tank is transported to a vaporizer via a pipeline, where it absorbs heat and transforms into nitrogen gas. A PLC controller, in conjunction with an electronic pressure regulating valve, adjusts the liquid nitrogen tank outlet flow rate to achieve temperature control. A temperature sensor is installed on the vaporizer outlet pipeline to monitor the temperature of the nitrogen gas output from the vaporizer in real time and feeds this information back to the PLC controller. The PLC controller then dynamically adjusts the electronic pressure regulating valve using a PID algorithm to stabilize the output nitrogen temperature at the preset target temperature.

[0013] Specifically, the vaporizer adopts a tubular heat exchange structure with 3-8 coils installed internally. Liquid nitrogen naturally vaporizes within the coils due to ambient heat, achieving a temperature range of -80℃ to -40℃ with an accuracy of ±1℃. The electronic pressure regulating valve adjusts its opening in real-time according to PLC controller commands, controlling the flow rate of liquid nitrogen into the vaporizer within the range of 0.5-5 L / min. By acquiring temperature sensor data in real-time, a PID algorithm calculates the deviation value and outputs a control signal to the electronic pressure regulating valve, achieving closed-loop temperature control.

[0014] Furthermore, the transmission pipeline is made of stainless steel and wrapped with a polyurethane insulation layer to reduce heat loss during liquid nitrogen transportation; the temperature sensor has a measurement accuracy of ±0.15℃ and a response time of ≤5s. The measuring point of the temperature sensor should be less than 0.1m away from the low-pressure gas inlet of the gas booster pump to ensure the representativeness of the monitoring data.

[0015] The second step is to pressurize with nitrogen;

[0016] The vaporized cryogenic nitrogen is fed into a gas booster pump through a transmission pipeline. Compressed air drives the gas booster pump to deliver the cryogenic nitrogen into the cryogenic unloading hose and pressurize it to reach the target pressure required for the experiment. The output pressure is controlled by a regulating valve, which maintains a constant pressure during the experiment.

[0017] Specifically, the gas booster pump adopts the principle of air-driven gas boosting, using compressed air to drive a large-area piston, which in turn pushes a small-area piston to compress and boost the cryogenic nitrogen gas. The area ratio of the large to small pistons can be controlled between 9:1 and 16:1, and can be adjusted according to operating conditions. The output pressure range of the gas booster pump is 0.5MPa-10MPa. When the internal pressure of the cryogenic unloading hose reaches the set value, the regulating valve is locked to achieve a pressure-maintaining function.

[0018] Furthermore, the gas booster pump is equipped with a low-pressure gas switch, a drive gas switch, a pressure release switch, and a regulating valve at its upper end. The low-pressure gas switch controls the nitrogen input, with an inlet pressure range of 0.1MPa-0.5MPa. The drive gas switch controls the compressed air source and can withstand pressures of 0.1MPa-0.8MPa. The pressure release switch controls the pressure release port. The regulating valve is used to set the output pressure of the gas booster pump, with an accuracy of ±1MPa. It can be set to automatically replenish pressure when the internal pressure of the cryogenic unloading hose drops by 0.1MPa-1MPa.

[0019] Furthermore, the gas transmission hose is made of low-temperature and high-pressure resistant rubber hose, with an outer insulation sleeve to slow down the temperature rise of nitrogen during the transmission process;

[0020] Furthermore, a safety valve is installed at the upper end of the liquid nitrogen tank. The safety valve is set to a pressure of 1.5 times the experimental target pressure. When the pressure exceeds the limit, it will automatically release pressure to ensure experimental safety.

[0021] The third step is to perform experimental loading;

[0022] After pressurized cryogenic nitrogen is delivered to the cryogenic unloading hose through a gas transmission hose, the cryogenic unloading hose is subjected to tensile, bending, or torsional loads by an actuator to simulate the mechanical environment under actual in-situ working conditions.

[0023] The beneficial effects of this invention are as follows:

[0024] (1) Since the present invention uses liquid nitrogen instead of LCO2 as the experimental medium, it can remain in a stable gaseous state under the target working conditions of -56℃ and 0-3.5MPa, which solves the problem of pipeline blockage caused by the phase change of the original medium and ensures the continuity and safety of the experiment.

[0025] (2) The present invention uses liquid nitrogen vaporization and PID temperature control to precisely control the medium temperature within the required working condition of -56±1°C, which not only meets the requirements of low temperature environment, but also avoids the distortion of experimental results due to excessively low temperature.

[0026] (3) The present invention adopts an integrated vaporization-pressurization experimental method, which can independently adjust the pressure while keeping the internal temperature of the low-temperature unloading hose constant, thus achieving high-precision temperature and pressure control throughout the test process. Attached Figure Description

[0027] Figure 1 A schematic diagram of the overall equipment for implementing the method of the present invention;

[0028] Figure 2 A front view of the apparatus for implementing the liquid nitrogen heating and vaporization step in the method of the present invention;

[0029] Figure 3 A top view of the apparatus for implementing the liquid nitrogen heating and vaporization step in the method of the present invention;

[0030] Figure 4 A front view of the apparatus for implementing the nitrogen pressurization step in the method of the present invention;

[0031] Figure 5 A top view of the apparatus for implementing the nitrogen pressurization step in the method of the present invention;

[0032] Figure 6 This is a flowchart of the present invention;

[0033] In the diagram: 1. Liquid nitrogen tank, 2. Vaporizer, 3. Safety valve, 4. Filling port, 5. Transmission steel pipe, 6. Steel pipe adapter, 7. PLC controller, 8. Electronic pressure regulating valve, 9. Temperature sensor, 10. Connection line, 11. Gas booster pump, 12. Low-pressure gas inlet, 13. Drive gas inlet, 14. Pressure relief port, 15. Boost gas outlet, 16. Gas transmission hose, 17. Low-pressure gas switch, 18. Drive gas switch, 19. Pressure release switch, 20. Regulating valve, 21. Actuator tripod, 22. Actuator, 23. Cryogenic unloading hose, 24. Flange. Detailed Implementation

[0034] The present invention will be further described below with reference to specific embodiments.

[0035] Figure 1 The overall implementation environment of the method of the present invention is illustrated schematically. Figure 2 , 3 The apparatus for implementing the liquid nitrogen vaporization step is shown, including a liquid nitrogen tank 1, a vaporizer 2, and a PLC controller 7. The liquid nitrogen tank 1 is a double-walled vacuum-insulated Dewar flask with an effective volume of 300L and a working pressure of 0.2-1.5MPa. A safety valve 3 and a filling port 4 are installed at the upper end of the liquid nitrogen tank 1, and liquid nitrogen is transported to the vaporizer 2 via a transmission steel pipe 5. The transmission steel pipe 5 is a stainless steel pipe with an inner diameter of 20mm, wrapped with 30mm thick polyurethane insulation material. The vaporizer 2 adopts a multi-stage coil structure with 6 coil stages, a single-stage coil length of 4m, and an inner diameter of 10mm. It can raise the temperature range to -80℃ to -40℃ with an accuracy of ±1℃. Inside the vaporizer 2, the liquid nitrogen absorbs ambient heat and vaporizes to the target temperature through the multi-stage coils, and is then transported to a gas booster pump 11 via another transmission steel pipe 5.

[0036] The PLC controller 7 is connected to the outlet pipe of liquid nitrogen tank 1 and the outlet pipe of vaporizer 2 via connection lines 10. The electronic pressure regulating valve 8 is installed on the connection line 10 between the PLC controller 7 and the outlet pipe of the liquid nitrogen tank. The electronic pressure regulating valve 8 is driven by an electric actuator, with a response time ≤2s and a flow rate adjustment range of 0.5-5L / min. The temperature sensor 9 is installed on another connection line 10 between the PLC controller 7 and the outlet pipe of the vaporizer, forming a closed-loop monitoring and control circuit. The temperature sensor 9 is a Pt100 platinum resistance thermometer with a measurement accuracy of ±0.15°C and a response time ≤5s. It can feed back temperature data to the PLC controller 7 in real time. The PLC controller 7 has a built-in PID control algorithm module with a sampling period of 1s. It calculates the control quantity based on the temperature deviation and outputs it to the electronic pressure regulating valve 8 to achieve dynamic adjustment of the liquid nitrogen flow rate and ensure that the nitrogen temperature is accurately and stably maintained within the range of -56°C ±1°C.

[0037] Figure 4 , 5 The apparatus for implementing the nitrogen pressurization step is shown, including a gas booster pump 11. The gas booster pump 11 employs a differential boosting structure with a piston area ratio of 9:1. The large piston has a diameter of 150 mm, the small piston has a diameter of 50 mm, the boosted gas volume per cycle is 0.5 L, the cycle frequency is 20 times / minute, and the maximum output pressure is 10 MPa. The gas booster pump 11 has a low-pressure gas switch 17, a drive gas switch 18, a pressure release switch 19, and a regulating valve 20 at its upper end, and a low-pressure gas inlet 12, a drive gas inlet 13, a boosted gas outlet 15, and a pressure release port 14 on its side. The low-pressure gas inlet 12 is connected to the outlet pipeline of the vaporizer 2 via a transmission steel pipe 5 and is controlled by a low-pressure gas switch 17. The inlet pressure range is 0.1-0.5 MPa. The driving gas inlet 13 is connected to an external compressed air source via another transmission steel pipe 5. It can withstand a pressure of 0.1-0.8 MPa and a flow rate ≥50 L / min. It is controlled by a driving gas switch 18. The booster gas outlet 15 is used to output pressurized cryogenic nitrogen. The outlet pressure is controlled by a regulating valve 20 and is delivered to the cryogenic unloading hose 23 via a cryogenic high-pressure gas transmission hose 16. The regulating valve 20 is a precision back pressure regulating valve. The target pressure can be set with an accuracy of ±0.1 MPa. When the outlet pressure reaches the set value, the valve core automatically closes to achieve automatic pressure maintenance. When the set pressure drops by more than 0.2 MPa, it automatically opens to replenish pressure. The pressure release port 14 is used to safely release the remaining high-pressure gas inside the gas booster pump 11 after the experiment. It is controlled by a pressure release switch 19.

[0038] The apparatus for implementing the experimental loading step includes a tripod 21, an actuator 22, a cryogenic unloading hose 23, and a flange 24. The tripod 21 serves as the fixed end of the cryogenic unloading hose 23, and the actuator 22 is used to apply the load. It can adjust the axial position and the model of the flange 24 to adapt to the performance testing of cryogenic unloading hoses 23 of different sizes.

[0039] The specific implementation process of this method is illustrated by taking the tensile test of the cryogenic unloading hose as an example:

[0040] Before the experiment, all equipment was connected according to the technical plan, the airtightness of the pipeline connections was checked, and an airtightness test was conducted on the system. Considering the heat loss of the pipeline system during transmission, pre-loading was required before the formal experiment. The specific method was as follows: the output temperature of vaporizer 2 was set to -60°C. After the system stabilized, the actual internal temperature of the cryogenic unloading hose 23 was measured. If the measured temperature was -56°C, the temperature decay was 4°C. Based on this, the target output temperature of vaporizer 2 should be set to -60°C.

[0041] After completing the above preparations, conduct the experiment according to the following steps:

[0042] (1) Nitrogen vaporization heating steps: Open the safety valve 3 of liquid nitrogen tank 1, start the PLC controller 7, close the pressure release switch 19, open the low-pressure gas switch 17 and the drive gas switch 18, initially set the regulating valve 20 to the closed state, and connect the power supply and signal lines of the electronic pressure regulating valve 8 and the temperature sensor 9. Set the target temperature to -60°C on the PLC controller 7 (determined based on the pre-test results), set the PID control parameters, and start the temperature control program. During the liquid nitrogen vaporization process, the PLC controller 7 collects the measurement data of the temperature sensor 9 in real time and displays the current temperature, set temperature, opening degree of the electronic pressure regulating valve 8, and other parameters on the display screen. If the temperature monitored by temperature sensor 9 is higher than the target value (e.g., -58°C), it indicates that the liquid nitrogen output flow in liquid nitrogen tank 1 is insufficient, causing the vaporizer 2 to overheat the liquid nitrogen. In this case, PLC controller 7 will automatically drive electronic pressure regulating valve 8 to increase its opening after calculating using the PID algorithm. If the temperature monitored by temperature sensor 9 is lower than the target value (e.g., -62°C), it indicates that the liquid nitrogen output flow in liquid nitrogen tank 1 is too large, causing insufficient vaporization of liquid nitrogen in vaporizer 2. In this case, PLC controller 7 will drive electronic pressure regulating valve 8 to decrease its opening. Through this dynamic adjustment, precise temperature control is achieved.

[0043] (2) Nitrogen pressurization procedure: After the temperature stabilizes, open the driving gas inlet 13 and adjust the pressure regulating valve 20 on the operation panel of the gas booster pump 11 to the experimental target pressure of 3.5 MPa. At this time, the gas booster pump 11 starts to work. Low-temperature nitrogen enters the gas booster pump 11 through the low-pressure gas inlet 12. After being pressurized by compressed air, it is output from the booster gas outlet 15 and continuously pressurized into the low-temperature unloading hose 23 through the gas transmission hose 16. When the pressure in the pipe reaches 3.5 MPa, the pressure regulating valve 20 automatically closes and stops the gas supply. After reaching the target working condition, keep the status of the other valves unchanged and lock the setting value of the pressure regulating valve 20 so that the gas booster pump 11 can maintain the automatic pressure holding function. When the pressure in the pipe drops to 3.4 MPa due to temperature changes or a small leak, the pressure regulating valve 20 automatically opens, the booster pump automatically replenishes gas to 3.5 MPa and then closes again. This process is repeated, and the pressure holding time can reach more than 24 hours. Meanwhile, the temperature at the hose inlet is continuously monitored by a temperature sensor to ensure that the temperature is maintained within the range of -56±1°C.

[0044] (3) Experimental loading procedure: After the temperature and pressure have stabilized, the actuator 22 is activated to apply a tensile load to the cryogenic unloading hose 23. During the loading process, the following parameters are recorded in real time through the data acquisition system: actuator displacement and tensile load, internal pressure and temperature of the cryogenic unloading hose 23. By analyzing the above data, the mechanical properties of the cryogenic unloading hose 23 under the coupled action of low temperature, high pressure and tensile load can be evaluated. After the experiment is completed, the actuator 22 is stopped first, and the cryogenic unloading hose 23 is restored to its original length. Then, the electronic pressure regulating valve 8, the safety valve 3 of the liquid nitrogen tank 1, the low-pressure gas switch 17, and the drive gas switch 18 are closed in sequence to cut off the supply of liquid nitrogen and compressed air. The pressure release switch 19 is slowly opened to discharge the remaining high-pressure gas inside the gas booster pump 11 to the outside through the pressure release port 14. The pressure regulating valve 20 is adjusted to the 0 position and left to stand for 24 hours. After the residual cryogenic nitrogen in the pipe evaporates naturally, the pressure in the pipe is checked to see if it has dropped to normal pressure. The PLC controller 7 and all power supplies are turned off. The cryogenic unloading hose 23 is removed for subsequent appearance inspection, dimensional measurement, and performance evaluation.

[0045] In this embodiment, liquid nitrogen was heated and vaporized to replace LCO2 as the experimental medium. Under the conditions of target temperature -56°C and target pressure 3.5MPa, a continuous and stable low-temperature mechanical loading experiment was achieved for 2 hours. The temperature fluctuation was ≤±1°C and the pressure fluctuation was ≤±0.1MPa. No solidification or poor flow of the medium occurred during the experiment, which verified the effectiveness and reliability of the method of the present invention.

[0046] The embodiments described above are merely examples of implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention.

Claims

1. A nitrogen-based method for testing the performance of cryogenic unloading hoses, characterized in that, The performance testing method for the cryogenic unloading hose includes liquid nitrogen heating and vaporization, nitrogen pressurization, and experimental loading. The specific steps are as follows: The first step is to heat and vaporize the liquid nitrogen; Liquid nitrogen stored in the liquid nitrogen tank is transported to the vaporizer through a transmission pipeline, where it absorbs heat and transforms into nitrogen gas. The PLC controller works in conjunction with the electronic pressure regulating valve to control the temperature by adjusting the outlet flow of the liquid nitrogen tank. A temperature sensor is installed on the outlet pipeline of the vaporizer to monitor the temperature of the nitrogen gas output from the vaporizer in real time and feed it back to the PLC controller. Then, the electronic pressure regulating valve is dynamically adjusted through a PID algorithm to stabilize the temperature of the output nitrogen gas at the preset target temperature. The second step is to pressurize with nitrogen; The vaporized cryogenic nitrogen is fed into the gas booster pump through the transmission pipeline. The gas booster pump is driven by compressed air to deliver the cryogenic nitrogen into the cryogenic unloading hose and pressurize it to reach the target pressure required for the experiment. The output pressure is controlled by the regulating valve, and its pressure holding function is used to maintain a constant pressure during the experiment. The third step is to perform experimental loading; After pressurized cryogenic nitrogen is delivered to the cryogenic unloading hose through a gas transmission hose, tensile, bending, or torsional loads are applied to the cryogenic unloading hose through an actuator to simulate the mechanical environment under actual in-situ working conditions.

2. The nitrogen-based cryogenic unloading hose performance testing method according to claim 1, characterized in that, In the first step, the vaporizer adopts a tubular heat exchange structure with 3-8 stages of coils inside. When liquid nitrogen flows in the coils, it is naturally vaporized by ambient heat, with a temperature range of -80℃ to -40℃ and an accuracy of ±1℃. The electronic pressure regulating valve adjusts its opening in real time according to the PLC controller instructions, controlling the flow rate of liquid nitrogen into the vaporizer within the range of 0.5-5L / min. By collecting temperature sensor data in real time, the PID algorithm calculates the deviation value and outputs a control signal to the electronic pressure regulating valve to achieve closed-loop temperature control.

3. The nitrogen-based cryogenic unloading hose performance testing method according to claim 1, characterized in that, In the first step, the transmission pipeline is made of stainless steel and wrapped with a polyurethane insulation layer; the temperature sensor has a measurement accuracy of ±0.15℃ and a response time of ≤5s.

4. The nitrogen-based cryogenic unloading hose performance testing method according to claim 1, characterized in that, In the first step, the measuring point of the temperature sensor should be less than 0.1m away from the low-pressure gas inlet of the gas booster pump.

5. The nitrogen-based cryogenic unloading hose performance testing method according to claim 1, characterized in that, In the second step, the gas booster pump adopts the principle of air-driven gas boosting. It uses compressed air to drive a large-area piston, which in turn pushes a small-area piston to compress and boost the cryogenic nitrogen. The area ratio of the large and small pistons is controlled between 9:1 and 16:1, and can be adjusted according to the working conditions. The output pressure range of the gas booster pump is 0.5MPa-10MPa. When the internal pressure of the cryogenic unloading hose reaches the set value, the regulating valve is locked to achieve the pressure holding function.

6. The nitrogen-based cryogenic unloading hose performance testing method according to claim 1, characterized in that, In the second step, the upper end of the gas booster pump is equipped with a low-pressure gas switch, a drive gas switch, a pressure release switch, and a regulating valve; the low-pressure gas switch controls the nitrogen input, with an inlet pressure range of 0.1MPa-0.5MPa; the drive gas switch controls the compressed air source, with a pressure of 0.1MPa-0.8MPa; and the pressure release switch is used to control the pressure release port.

7. The nitrogen-based cryogenic unloading hose performance testing method according to claim 6, characterized in that, The regulating valve is used to set the output pressure of the gas booster pump with an accuracy of ±1MPa.

8. The nitrogen-based cryogenic unloading hose performance testing method according to claim 1, characterized in that, In the second step, the gas booster pump is set to automatically replenish the pressure when the internal pressure of the cryogenic unloading hose drops by 0.1MPa-1MPa.

9. The nitrogen-based cryogenic unloading hose performance testing method according to claim 1, characterized in that, The gas transmission hose is made of low-temperature and high-pressure resistant rubber hose, with an outer insulation sleeve.

10. The nitrogen-based cryogenic unloading hose performance testing method according to claim 1, characterized in that, A safety valve is installed at the top of the liquid nitrogen tank. The safety valve is set to a pressure of 1.5 times the target pressure of the experiment. When the pressure exceeds the limit, it will automatically release pressure to ensure experimental safety.

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