Simulation experiment system for dissolving nitrogen in propane and experiment method thereof

Abstract

The invention relates to the technical field of energy storage, and provides a simulation experiment system for dissolving nitrogen in propane and an experiment method of the simulation experiment system. The cold accumulation assembly comprises a cold accumulation part and a control part, the cold accumulation part is arranged in the simulation storage tank and is filled with a cold accumulation agent, and the control part is arranged on the cold accumulation part and is used for controlling the flow of the cold accumulation agent; the nitrogen filling device is connected with an inlet of the simulation storage tank and used for filling nitrogen into the simulation storage tank and keeping the simulation storage tank in a constant-pressure state, and the nitrogen filling device is provided with a corresponding pressure monitoring assembly; the data monitoring system is connected with the temperature monitoring assembly and the pressure monitoring assembly and used for monitoring temperature information and pressure information of the simulation storage tank. The diffusion and dissolution process of nitrogen in liquid propane under actual working conditions can be simulated, the solubility of nitrogen in liquid propane under low temperature and normal pressure can be predicted, and important data support is provided for cold storage process design of a liquid air energy storage system.

Description

Technical Field

[0001] The invention relates to the technical field of energy storage, and in particular to a simulation experimental system and an experimental method for nitrogen dissolving in propane. Background Art

[0002] With the rapid development of renewable energy, the instability, randomness and volatility of power generation have posed a challenge to the safe and stable operation of the power grid. In order to solve this problem, a variety of energy storage technologies have been developed to achieve the purpose of peak load reduction and valley load filling.

[0003] Among them, liquid air energy storage technology has attracted attention due to its high efficiency and limited geographical restrictions. The liquid air energy storage system stores electrical energy in the form of low-temperature, low-pressure, high-density liquid air, rationally absorbs off-peak electricity and various forms of waste heat resources from the power grid, and stably outputs various forms of energy such as cold, heat, electricity, and industrial gas when needed. In the process of energy storage, air is compressed, liquefied, and stored, and liquid propane is used as a cold storage medium to liquefy the air.

[0004] During use, in order to prevent the internal components of the cold storage tank from being oxidized, corroded, polymerized, degraded, and forming explosive mixtures due to the presence of oxygen, it is necessary to fill the space above the liquid propane level in the cold storage tank with nitrogen. However, the solubility of nitrogen in liquid propane changes with temperature. When nitrogen is dissolved in liquid propane, the pressure in the tank changes, which can easily affect system performance and even bring safety hazards.

[0005] To this end, the relevant technology directly measures the dissolution of nitrogen in liquid propane at different temperatures and pressures through a test bench. However, this method measures the solubility of nitrogen in liquid propane, but actually measures the solubility of a two-phase system formed after nitrogen is uniformly mixed in liquid propane, which leads to deviations between experimental data and actual applications. Summary of the invention

[0006] The present invention provides a simulation experimental system for the dissolution of nitrogen in propane, which is used to solve the above-mentioned technical defects in the prior art, realizes the simulation of the nitrogen dissolution process under low temperature and constant atmospheric pressure, and can predict the solubility of nitrogen in liquid propane under low temperature and constant atmospheric pressure, thereby providing important data support for the cold storage process design of the liquid air energy storage system, and helping to improve the design efficiency and safety of the liquid air energy storage system.

[0007] The invention also provides a simulation experimental method for dissolving nitrogen in propane.

[0008] The invention provides a simulation experiment system for nitrogen dissolving in propane, comprising a simulation storage tank, a cold storage component, a nitrogen filling device and a data monitoring system.

[0009] The interior of the simulated storage tank is suitable for filling liquid propane, a gas phase space for filling nitrogen is formed above the liquid level of the liquid propane in the simulated storage tank, and a temperature monitoring component is provided inside the simulated storage tank; The cold storage component includes a cold storage component and a control component, wherein the cold storage component is arranged inside the simulated storage tank, the cold storage component is filled with a cold storage agent, and the control component is arranged in the cold storage component and is used to control the flow rate of the cold storage agent to maintain the temperature of the liquid propane in the simulated storage tank and the nitrogen in the gas phase space; A nitrogen filling device is connected to the inlet of the simulated storage tank, and is used to fill nitrogen into the simulated storage tank and keep the simulated storage tank in a constant pressure state. The nitrogen filling device is provided with a corresponding pressure monitoring component; The data monitoring system is connected to the temperature monitoring component and the pressure monitoring component respectively, and is used to monitor the temperature information and pressure information of the simulated storage tank, and display the temperature information and the pressure information in real time.

[0010] According to the simulation experimental system of nitrogen dissolution in propane provided by the present invention, the nitrogen filling device comprises a buffer bottle, a nitrogen reservoir and a nitrogen bottle connected in sequence, and the buffer bottle is connected to the inlet of the simulation storage tank; A first valve is provided on the connecting pipeline between the nitrogen bottle and the nitrogen reservoir, a second valve is provided on the connecting pipeline between the nitrogen reservoir and the buffer bottle, and a third valve is provided on the connecting pipeline between the buffer bottle and the inlet of the simulation tank.

[0011] According to the simulation experimental system for nitrogen dissolution in propane provided by the present invention, the cold storage component includes a cold storage body, the cold storage body is spirally arranged along the height direction of the simulated storage tank, the upper end of the cold storage body is provided with a liquid outlet pipe, the lower end of the cold storage body is provided with a liquid inlet pipe, the liquid inlet pipe and the liquid outlet pipe both pass through the simulated storage tank and extend out of the simulated storage tank, and the control component is arranged on the liquid inlet pipe, and is used to control the flow rate of the coolant in the liquid inlet pipe.

[0012] According to the simulation experimental system for dissolving nitrogen in propane provided by the present invention, the control component includes a fourth valve and a controller, the fourth valve is arranged on the liquid inlet pipe, and the controller is electrically connected to the fourth valve, and is used to control the opening of the fourth valve according to the preset temperature value and the detected temperature value in the simulation storage tank.

[0013] According to the simulation experimental system for nitrogen dissolving in propane provided by the present invention, the outer side of the simulation storage tank is provided with multiple layers of thermal insulation layers; the outlet of the simulation storage tank is connected to an outlet pipeline, and the outlet pipeline is provided with a fifth valve.

[0014] The present invention also provides a simulation experimental method for dissolving nitrogen in propane, based on any one of the simulation experimental systems for dissolving nitrogen in propane, comprising the following steps: Determining that the simulated storage tank meets the experimental requirements, filling the simulated storage tank with liquid propane, and weighing the mass of the liquid propane; According to a plurality of preset temperature values ​​and corresponding detected temperature values, the flow rate of the coolant in the cool storage component is controlled to perform step-by-step cooling of the liquid propane in the simulated storage tank and the nitrogen in the gas phase space; and the temperature information and pressure information of the simulated storage tank are acquired in real time, and based on the temperature information and the pressure information, the solubility of nitrogen in the liquid propane is determined.

[0015] According to the simulation experimental method for dissolving nitrogen in propane provided by the present invention, the step of determining that the simulated storage tank meets the experimental requirements includes: Performing leak detection on the simulated storage tank; If the simulated storage tank has no leakage, vacuum extraction is performed on the simulated storage tank; if the simulated storage tank has leakage, the corresponding leakage position is processed.

[0016] According to the simulation experimental method for dissolving nitrogen in propane provided by the present invention, the flow rate of the refrigerant in the refrigerant storage component is controlled according to a plurality of preset temperature values ​​and corresponding detected temperature values, and the liquid propane in the simulated storage tank and the nitrogen in the gas phase space are cooled in a stepwise manner, including: Determining that the pressure in the simulated storage tank is less than a preset pressure, controlling the nitrogen filling device to fill nitrogen into the simulated storage tank so that the simulated storage tank is maintained in a constant pressure state; When it is determined that the pressure of the simulated storage tank does not change for a preset period of time, the flow rate of the coolant in the cool storage component is controlled to perform step-by-step cooling of the liquid propane in the simulated storage tank and the nitrogen in the gas phase space.

[0017] According to the simulation experimental method for dissolving nitrogen in propane provided by the present invention, the controlling the nitrogen filling device to fill nitrogen into the simulation storage tank so that the simulation storage tank is kept in a constant pressure state comprises: Controlling the third valve between the simulation storage tank and the buffer bottle to open, and making the third valve in a normally open state; The second valve between the buffer bottle and the nitrogen reservoir is controlled to open multiple times, and the opening degree of the second valve is smaller than the opening degree of the third valve.

[0018] According to the simulation experimental method for nitrogen dissolution in propane provided by the present invention, the maximum value of the preset temperature value is lower than the boiling point temperature of propane under normal pressure, and the minimum value of the preset temperature value is the lower limit of the temperature of the propane cold storage medium.

[0019] The simulation experiment system of nitrogen dissolving in propane provided by the present invention is provided with a temperature detection component and a cold storage component in a simulation tank filled with a certain amount of liquid propane, so that the interior of the cold storage component is filled with a cold storage agent to maintain the temperature in the simulation tank, and a nitrogen filling device is connected to the inlet of the simulation tank to keep the simulation tank in a constant pressure state, and a pressure monitoring component is provided in the nitrogen filling device. The temperature information and the corresponding pressure information in the simulation tank are monitored by a data monitoring system, and data fitting is performed to obtain a prediction formula for the diffusion solubility of nitrogen in liquid propane under low temperature and normal pressure. The simulation experiment system can simulate the diffusion and dissolution process of nitrogen in liquid propane under actual working conditions (i.e., low temperature and constant atmospheric pressure), realizes the simulation of the nitrogen dissolution process under low temperature and constant atmospheric pressure, and can predict the solubility of nitrogen in liquid propane under low temperature and normal pressure, providing important data support for the cold storage process design of the liquid air energy storage system, which is helpful to improve the design efficiency and safety of the liquid air energy storage system. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 It is a schematic diagram of a simulation experimental system for nitrogen dissolution in propane provided in an embodiment of the present invention.

[0022] Figure 2 It is a structural block diagram of a simulation experimental system for nitrogen dissolution in propane provided in an embodiment of the present invention.

[0023] Figure 3 It is a flow chart of a simulation experimental method for dissolving nitrogen in propane provided in an embodiment of the present invention.

[0024] Figure 4 It is a detailed flow chart of a simulation experimental method for dissolving nitrogen in propane provided in an embodiment of the present invention.

[0025] Reference numerals: 1. First valve; 2. Second valve; 3. Third valve; 4. Fourth valve; 5. Fifth valve; 6. Simulated storage tank; 7. Insulation layer; 8. Gas phase space; 9. Liquid propane; 10. Buffer bottle; 11. Nitrogen reservoir; 12. Nitrogen bottle; 13. Controller; 14. Temperature sensor; 15. Second pressure sensor; 16. First pressure sensor; 17. Data detection system. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] In the description of the embodiments of the present application, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific circumstances.

[0028] In the embodiments of the present application, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0029] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the embodiments of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0030] During the cold storage process of the liquid phase cold storage medium, the inert protective gas (such as nitrogen) inside the cold storage tank will dissolve into the liquid propane. Since the solubility of nitrogen in propane is related to temperature, a large amount of nitrogen will dissolve during the cooling process of the liquid propane circulation, and will precipitate during the heating process, which will cause the pressure inside the cold storage tank to deviate from the design pressure, which will not only affect the cold storage performance, but also easily cause the safety risk of overpressure in the tank.

[0031] The related art directly measures the dissolution of nitrogen in liquid propane at different temperatures and pressures through a test bench. However, this method measures the solubility of nitrogen in liquid propane, rather than the nitrogen gradually dissolving in liquid propane through the liquid surface during the cold storage of liquid propane to simulate the actual application process. In this way, nitrogen exists in the form of dissolved diffusion with a concentration gradient in liquid propane, which leads to a deviation between the experimental data and the actual application. To this end, an embodiment of the present invention provides a simulation experimental system for the dissolution of nitrogen in propane.

[0032] Figure 1 It is a schematic diagram of a simulation experimental system for nitrogen dissolution in propane provided in an embodiment of the present invention.

[0033] See also Figure 1 The embodiment of the present invention provides a simulation experimental system for dissolving nitrogen in propane, including a simulation storage tank 6, a nitrogen filling device and a data monitoring system.

[0034] A certain amount of liquid propane 9 can be poured into the simulated storage tank 6. A gas phase space 8 is formed in the simulated storage tank 6 and above the liquid surface of the liquid propane 9. Nitrogen is poured into the gas phase space 8. An inlet and an outlet are provided on the simulated storage tank 6. A temperature detection component is provided inside the simulated storage tank 6. The temperature detection component can be a plurality of temperature sensors 14. The temperature sensors 14 are arranged at intervals along the height direction (longitudinal direction) of the simulated storage tank 6 to detect the longitudinally distributed temperature in the simulated storage tank 6, that is, the temperature detection area extends from the bottom to the top of the simulated storage tank 6. Therefore, the temperatures of the liquid propane 9 and the nitrogen in the gas phase space 8 can be detected by the corresponding temperature sensors 14, and the temperatures of the liquid propane 9 and the nitrogen in the gas phase space 8 are both the average values ​​of the corresponding temperature values.

[0035] The outer shell of the simulated storage tank 6 is wrapped with multiple layers of heat-insulating materials to form a heat-insulating layer 7, and the heat-insulating materials are used to keep the simulated storage tank 6 warm to limit the leakage of cold energy.

[0036] The cold storage component includes a cold storage part and a control part. The cold storage part is arranged inside the simulated storage tank 6. The cold storage component is filled with a cold storage agent to maintain the temperature of the liquid propane 9 in the simulated storage tank 6 and the nitrogen in the gas phase space 8, that is, to maintain the temperature of the nitrogen-propane two-phase system. The control part is arranged in the cold storage part to control the flow of the cold storage agent, thereby adjusting the temperature of the liquid propane 9 in the simulated storage tank 6 and the nitrogen in the gas phase space 8.

[0037] The nitrogen filling device is connected to the inlet and is used to fill nitrogen into the simulated storage tank 6 and keep the simulated storage tank 6 at a constant pressure. The nitrogen filling device is provided with a corresponding pressure monitoring component.

[0038] The data monitoring system is used to monitor the pressure information and temperature information in the simulated storage tank 6 in real time, and display the monitored pressure information and temperature information in real time through the screen to form a curve of pressure and temperature changes over time.

[0039] It can be understood that the simulation experiment system of nitrogen dissolving in propane provided in the embodiment of the present invention is provided with a temperature detection component and a cold storage component in the simulation tank 6 filled with a certain amount of liquid propane, so that the cold storage component is filled with a cold storage agent to maintain the temperature in the simulation tank 6, and a nitrogen filling device is connected to the inlet of the simulation tank 6 to keep the simulation tank 6 in a constant pressure state, and a pressure monitoring component is provided in the nitrogen filling device. The temperature information and the corresponding pressure information in the simulation tank 6 are monitored by the data monitoring system, and data fitting is performed to obtain a prediction formula for the diffusion solubility of nitrogen in liquid propane under low temperature and normal pressure. The simulation experiment system can simulate the diffusion and dissolution process of nitrogen in liquid propane 9 under actual working conditions (i.e., low temperature and constant atmospheric pressure), realizes the simulation of the nitrogen dissolution process under low temperature and constant atmospheric pressure, and can predict the solubility of nitrogen in liquid propane 9 under low temperature and normal pressure, providing important data support for the cold storage process design of the liquid air energy storage system, which is helpful to improve the design efficiency and safety of the liquid air energy storage system.

[0040] Continue reading Figure 1 In some embodiments of the present invention, the nitrogen filling device includes a buffer bottle 10, a nitrogen reservoir 11 and a nitrogen bottle 12, the nitrogen bottle 12 is connected to the nitrogen reservoir 11, the nitrogen reservoir 11 is connected to the buffer bottle 10, and the buffer bottle 10 is connected to the inlet. Among them, a first valve 1 is provided on the connecting pipeline between the nitrogen bottle 12 and the nitrogen reservoir 11, and a second valve 2 is provided on the connecting pipeline between the nitrogen reservoir 11 and the buffer bottle 10. The first valve 1 and the second valve 2 are used to control the opening and closing of the corresponding connecting pipelines, thereby controlling the inflow and discharge of nitrogen gas.

[0041] The nitrogen cylinder 12 is used to store high-pressure and high-purity nitrogen, and is used to fill the nitrogen reservoir 11 with sufficient nitrogen before the experiment begins, so as to facilitate the subsequent experiments.

[0042] The nitrogen reservoir 11 is used to inject a sufficient amount of nitrogen from the nitrogen bottle 12 before the experiment begins. This part of nitrogen is replenished in small quantities to the downstream buffer bottle 10 and the gas phase space 8 of the simulation tank 6 multiple times during the experiment to maintain a constant pressure in the simulation tank 6. The constant pressure is about 0.1 MPa, ensuring that the dissolution process of nitrogen in liquid propane 9 is monitored in the temperature range of 96K to 227K under constant pressure.

[0043] The buffer bottle 10 is connected between the simulation storage tank 6 and the nitrogen reservoir 11 to play a buffering role.

[0044] When the nitrogen filling device provided in the embodiment of the present invention is working, the nitrogen bottle 12 provides high-pressure and high-purity nitrogen, which is delivered to the simulated storage tank 6 through the nitrogen reservoir 11 and the buffer bottle 10. Since the simulated storage tank 6 contains liquid propane 9, the flow rate of the coolant is controlled by the control component of the cool storage component, thereby adjusting the temperature in the simulated storage tank 6 to simulate the actual working conditions in the cool storage tank.

[0045] In addition, the nitrogen filling device can also be an integral structure, in which a plurality of sealable accommodating cavities are arranged, and the plurality of accommodating cavities respectively assume the respective functions of the buffer bottle 10, the nitrogen reservoir 11 and the nitrogen bottle 12.

[0046] Figure 2 It is a structural block diagram of a simulation experimental system for nitrogen dissolution in propane provided in an embodiment of the present invention.

[0047] See also Figure 2 The pressure monitoring assembly includes a plurality of pressure sensors, such as a first pressure sensor 16 and a second pressure sensor 15. The first pressure sensor 16 is installed inside the nitrogen reservoir 11 to detect the pressure P1 inside the nitrogen reservoir 11. The second pressure sensor 15 is installed inside the buffer bottle 10 to detect the pressure P2 inside the buffer bottle 10. Since the buffer bottle 10 is connected to the gas phase space 8 of the simulated storage tank 6, the pressure P2 detected by the second pressure sensor 15 is also the pressure of the simulated storage tank 6.

[0048] It is equivalent to that the data monitoring system is electrically connected to the temperature sensor 14 of the simulated storage tank 6, and the data monitoring system is also electrically connected to the first pressure sensor 16 of the nitrogen reservoir 11 and the second pressure sensor 15 of the buffer bottle 10. The data monitoring system detects the temperature information Tn of the simulated storage tank 6 in real time through the temperature sensor 14, detects the pressure in the buffer bottle 10 and the simulated storage tank 6 through the second pressure sensor 15, and monitors the pressure in the nitrogen reservoir 11 through the first pressure sensor 16.

[0049] Continue reading Figure 1 In some embodiments of the present invention, the cold storage assembly includes a cold storage body, which is located inside the simulated storage tank 6 and is spirally arranged along the height direction of the simulated storage tank 6. A liquid outlet pipe is provided on the cold storage body, and a liquid inlet pipe is provided at the lower end of the cold storage body. Both the liquid inlet pipe and the liquid outlet pipe penetrate the simulated storage tank 6 and extend out of the simulated storage tank 6. A control component is provided on the liquid inlet pipe to control the flow rate of the refrigerant in the liquid inlet pipe.

[0050] This is equivalent to the coolant entering from the lower port of the cool storage body and exiting from the upper port of the cool storage body, which can reduce the resistance of the cool storage body caused by the bending and turning of the connecting pipelines and improve the heat exchange efficiency.

[0051] Among them, the cold storage body is a pure copper coil, which is filled with a cold storage agent such as liquid nitrogen. The liquid nitrogen flows through the copper tube located in the simulated storage tank 6 and exchanges heat with the liquid propane and nitrogen inside the simulated storage tank 6 to control the temperature of the liquid propane and nitrogen.

[0052] Continue reading Figure 1 In some embodiments of the present invention, the control component includes a fourth valve 4 and a controller 13. The fourth valve 4 is used to control the flow of the injection pipeline. The controller 13 is used to control the switching frequency of the fourth valve 4 to change the liquid nitrogen flow rate, thereby achieving the reduction and increase of the test temperature.

[0053] The valve can be an electric valve, the opening of the electric valve can be controlled, and the states of the electric valve include open, closed, half open and half closed, which can control the flow of liquid nitrogen in the injection pipeline. The controller 13 can be a PID proportional-integral-differential controller 13, which controls the switching frequency of the electric valve by changing the input signal value. The simulation experiment system uses the electric valve and the PID controller 13 to accurately control the temperature of the simulation tank 6, which can improve the accuracy and reliability of the experimental data.

[0054] Specifically, the control parameters of the electric valve will be set in the controller 13, mainly including M5, P, t, Clt, dF, etc., and a preset temperature value is set in the controller 13. When there is a difference between the detected temperature value and the preset temperature value, the controller 13 controls the electric valve to produce an action, and the magnitude of the electric valve action is positively correlated with the magnitude of the difference. When the difference between the detected temperature value and the preset temperature value is small, the opening of the electric valve is small and gradually tends to be stable, and finally the purpose of controlling the liquid nitrogen flow rate is achieved.

[0055] This is equivalent to using the temperature value measured in the simulated storage tank 6 obtained by the data monitoring system as an input signal of the controller 13 of the electric valve, and setting a preset temperature value in the controller 13. By calculating the difference between the detected temperature value and the preset temperature value, the electric valve is controlled to adjust the opening to achieve control of the liquid nitrogen flow rate, thereby achieving temperature control in the simulated storage tank 6.

[0056] The simulation experimental system for nitrogen dissolution in propane provided in the embodiment of the present invention is intended to establish an experimental platform for testing the diffusion solubility of nitrogen in liquid propane, so as to obtain the actual diffusion solubility of nitrogen in liquid propane under normal pressure and low temperature conditions, thereby filling the data gap of the diffusion solubility of nitrogen in liquid propane under normal pressure and low temperature conditions, and providing a scientific basis for the design and optimization of liquid air energy storage systems.

[0057] In the process of step-by-step cooling, nitrogen will gradually dissolve in liquid propane, thereby changing the amount and pressure of nitrogen in the simulated storage tank 6. Therefore, after obtaining the temperature and pressure data of the simulated storage tank 6 through the data monitoring system, the solubility of nitrogen in liquid propane is calculated by the ideal gas state equation. The simulation experiment system has good stability and repeatability, which can ensure the reliability of experimental results, facilitate experimental data processing and analysis, and can obtain a prediction model for the diffusion solubility of nitrogen in liquid propane through data fitting.

[0058] Figure 3 It is a flow chart of a simulation experimental method for dissolving nitrogen in propane provided in an embodiment of the present invention. Figure 4 It is a detailed flow chart of a simulation experimental method for dissolving nitrogen in propane provided in an embodiment of the present invention.

[0059] See also Figure 3 and Figure 4 The embodiment of the present invention provides a simulation experimental method for dissolving nitrogen in propane, comprising the following steps: Step S100: Determine whether the simulated storage tank 6 meets the experimental requirements, fill the simulated storage tank 6 with liquid propane, and weigh the mass of the liquid propane.

[0060] It is understandable that determining whether the simulated storage tank 6 meets the experimental requirements is equivalent to pre-processing the simulated storage tank 6, the purpose of which is to ensure good experimental results and high accuracy. The pre-processing mainly refers to the leak detection of the entire container in the simulated experimental system of nitrogen dissolving in propane, vacuuming the container, and filling it with liquid propane and nitrogen.

[0061] The leak detection of the entire container is mainly carried out by two methods: pressure holding leak detection and vacuum leak detection.

[0062] For leak detection by holding pressure method, nitrogen with an absolute pressure of about 2 bar can be filled into each container of the simulation experiment system through the nitrogen bottle 12, and then soapy water is applied to the interfaces of each connecting pipeline of the simulation experiment system, valve interfaces, welding seams and other parts prone to gas leakage. If bubbles continue to appear in a certain part after applying soapy water, or the bubbles continue to grow, it means that there is a gas leak here. If no bubbles continue to appear or the bubbles grow, it means that the holding pressure method has not been detected.

[0063] In addition to soapy water, helium can also be used for pressure holding leak detection. Fill the simulation experiment system with about 2 bar of helium through a helium cylinder, and then use a helium detection probe to detect the interfaces of various connecting pipes, valve interfaces, welding seams and other parts that are prone to gas leakage. If a gas leak occurs in a certain part, the helium concentration at that part will exceed the helium concentration in the air (about 10-7). At this time, the helium concentration detector connected to the helium detection probe will alarm, indicating that there is a helium leak here.

[0064] For vacuum leak detection, you need to use a helium concentration detector / vacuum pumping machine to connect the simulation experiment system, and first turn on the vacuum pump to evacuate the simulation experiment system to a vacuum degree of about 10-3 to 10-4Pa, then use a helium bag to fill some helium, and use the bag nozzle to spray a small amount of helium to the interfaces of each connecting pipeline, valve interface, welding seam and other parts prone to gas leakage. If there is a leak in a certain part, the helium will be sucked into the simulation experiment system by the vacuum negative pressure inside the simulation experiment system, and the helium concentration detector will be detected and an alarm will be sounded. The parts where gas leaks occur need to be processed. Leaks at the valve interface or the connecting pipeline interface require tightening the valve and the connecting pipeline interface, and then re-leakage detection until there is no leakage. For leaks in the weld, it is necessary to re-weld and re-leakage detection.

[0065] After the leak detection is completed, the entire simulation experiment system is evacuated using a vacuum pump. During the vacuuming process, all the valves connected inside the simulation experiment system are opened, and the first valve 1 on the nitrogen reservoir 11 side is connected to the vacuum pump. The vacuuming process first uses a mechanical pump to evacuate the vacuum degree to 10Pa or less and maintain it for about ten minutes.

[0066] Then, turn on the molecular pump and ionized silicon to perform high-precision vacuuming and vacuum degree detection. At this time, the vacuuming process needs to continue until the ionized silicon reading is at the 10-4Pa level, and the vacuum degree is considered qualified. After vacuuming, disconnect the first valve 1 and the vacuum pump, connect the first valve 1 to the nitrogen bottle 12, and close the second valve 2 connected between the nitrogen reservoir 11 and the buffer bottle 10, and then fill the nitrogen reservoir 11 with about 3-4MPa of nitrogen from the nitrogen bottle 12.

[0067] After the nitrogen filling is completed, the entire simulation experiment system is placed on a weighing scale, and the mass reading of the entire simulation experiment system is recorded at this time. Then the simulation experiment system is connected to the storage bottle of liquid propane, and the fifth valve 5 on the outlet pipeline is opened, the third valve 3 is closed, and liquid propane is continuously filled into the simulation tank 6. At the beginning of the filling, since the simulation tank 6 has not been filled, the fifth valve 5 should discharge gas without liquid. As the liquid level of the liquid propane in the simulation tank 6 continues to rise, more and more liquid propane gradually appears in the outlet pipeline. When the simulation tank 6 is almost full of liquid propane, the outlet pipeline discharges almost all liquid propane, then the fifth valve 5 is closed at this time, and the storage bottle of liquid propane is disconnected. The entire simulation experiment system is placed on a weighing scale, and when the weighing reading is stable, the total mass of the simulation experiment system after filling with liquid propane is read, and the difference between the mass reading of the simulation experiment system when it is not filled with liquid propane is taken as the mass of the filled liquid propane.

[0068] Step S200: According to a plurality of preset temperature values ​​and corresponding detected temperature values, the flow rate of the refrigerant in the refrigerant storage component is controlled to perform step-wise cooling of the liquid propane 9 in the simulated storage tank 6 and the nitrogen in the gas phase space 8. The temperature information and pressure information of the simulated storage tank 6 are obtained in real time, and the solubility of nitrogen in the liquid propane 9 is determined based on the temperature information and pressure information.

[0069] It is understandable that after pretreatment, the liquid propane and nitrogen are cooled in a step-by-step manner. The temperature nodes selected for the step-by-step cooling are 227K, 176K, 139K and 96K. Among them, 227K is about 4 degrees lower than the boiling point of propane at normal pressure to ensure that propane remains in a liquid phase during the entire experiment. 176K and 96K correspond to the upper and lower limits of the propane cold storage temperature range designed in the actual project, and 139K is the middle value between 176K and 96K, and an interpolation test is performed.

[0070] After adjusting the set value (SV) of the fourth valve 4 to the preset temperature value, the fourth valve 4 will perform PID proportional, integral and differential regulation according to the internal parameters set in advance to control the switching frequency of the fourth valve 4, thereby realizing the flow regulation of the refrigerant, so as to stabilize the temperature of the liquid propane 9 in the simulated storage tank 6 and the nitrogen in the gas phase space 8 at around the preset temperature value.

[0071] At the beginning of the experiment, the first preset temperature value was 227K. After the average temperature of the simulated storage tank 6 was lowered and stabilized at 227K by cooling with liquid nitrogen, the nitrogen replenishment operation was carried out to keep the nitrogen pressure in the gas phase space of the simulated storage tank and the buffer bottle at approximately 0.1MPa.

[0072] When performing nitrogen replenishment operation, open the third valve 3 to connect the gas phase space of the simulated storage tank 6 and the buffer bottle 10, and then keep the third valve 3 open, and then slightly open the second valve 2. At this time, the higher-pressure nitrogen in the nitrogen reservoir 11 will flow into the buffer bottle 10, and the pressure of the gas phase space of the buffer bottle 10 and the simulated storage tank 6 will increase.

[0073] Since the purpose of the experiment is to determine the solubility of nitrogen in liquid propane under normal pressure, it is necessary to keep the nitrogen pressure in the gas phase space of the simulated storage tank 6 and the buffer bottle 10 at approximately 0.1 MPa, which can be understood as the preset pressure. Therefore, each time the second valve 2 is opened, the nitrogen pressure in the gas phase space of the simulated storage tank 6 and the buffer bottle 10 is adjusted to approximately 0.105 MPa.

[0074] After replenishing nitrogen to 0.105MPa, close the second valve 2 and allow the nitrogen to stand in contact and dissolve in the liquid propane. During the dissolution process, the gas phase nitrogen will continue to decrease, which will cause the nitrogen pressure in the gas phase space of the simulated storage tank 6 and the buffer bottle 10 to continue to decrease.

[0075] When the nitrogen pressure in the gas phase space of the simulated storage tank 6 and the buffer bottle 10 is less than 0.095 MPa, the second valve 2 is reopened and nitrogen is replenished to about 0.105 MPa. The above process is repeated until the dissolution reaches equilibrium at a temperature of 227K.

[0076] The criterion for determining whether the dissolution has reached equilibrium is that the nitrogen pressure in the gas phase space of the simulated storage tank 6 and the buffer bottle 10 has hardly decreased for 8 consecutive hours.

[0077] After reaching the dissolution equilibrium at 227K, the temperature is continued to be lowered, that is, the preset temperature value of the fourth valve 4 is adjusted to 176K, and the fourth valve 4 is controlled to be opened, so that the temperature of the simulated storage tank 6 begins to drop. After the temperature stabilizes to 176K, the aforementioned nitrogen replenishment operation is repeated until the dissolution of nitrogen in liquid propane reaches equilibrium at 176K.

[0078] Continue to repeat the cycle of cooling - multiple nitrogen replenishment - cooling until the dissolution equilibrium process at 139K and 96K is determined, that is, 96K is the target temperature value, until the target temperature value reaches the dissolution equilibrium, which marks the end of the experimental test process.

[0079] During the experiment, the pressure and temperature data in the nitrogen reservoir 11, buffer bottle 10, and simulated storage tank 6 were recorded in real time through the data monitoring system and mobile phone system, and a solubility prediction formula was fitted to provide a detailed data basis and theoretical basis for improving the efficiency of the liquid air energy storage system.

[0080] The solubility of nitrogen in propane is described in detail below based on the simulated experimental system of nitrogen dissolution in propane provided in an embodiment of the present invention: The solubility is calculated based on the ideal gas state equation to obtain the amount of nitrogen in the gas phase space of each container in the nitrogen filling device, and the solubility of nitrogen in propane is obtained by converting the nitrogen amount.

[0081] Since the simulation experimental system was leak-checked before the experiment, the nitrogen leakage of the simulation experimental system can be ignored, so it can be considered that the amount of nitrogen inside the simulation experimental system is constant.

[0082] The amount of nitrogen filled into the nitrogen reservoir 11 by the nitrogen bottle 12 in the pretreatment before the experiment is the total amount of nitrogen during the experiment. After the experiment starts, the initial total amount of nitrogen can be divided into four parts: the remaining nitrogen amount n in the nitrogen reservoir 11 r , the amount of nitrogen in the buffer bottle 10 is n b , simulate the nitrogen amount n in the gas phase space 8 in the storage tank 6 g , and the amount of nitrogen dissolved in liquid propane n a This relationship can be expressed by formula (1).

[0083] (1).

[0084] At the same time, considering that the gas phase pressure during the experiment is far less than 20 MPa, the above nitrogen amount can be calculated using the ideal gas state equation.

[0085] The ideal gas state equation is expressed as formula (2).

[0086] (2).

[0087] In formula (2), n is the amount of gas (mol), P is the gas pressure (Pa), and V is the volume of the gas phase space (m 3 ), R is the universal gas constant (8.314 J / (mol·K)), and T is the temperature of the gas (K).

[0088] The overall volume of the nitrogen reservoir 11, the buffer bottle 10, the simulated storage tank 6 and the corresponding auxiliary pipelines has been obtained by measurement or calculation at the beginning of the experiment. The volume of each container is shown in Table 1.

[0089] Table 1 Volume of each container

[0090] The volume inside the simulated storage tank 6 is occupied by liquid propane 9 and nitrogen. The mass of the liquid propane 9 has been obtained by weighing during the filling process, and its temperature and pressure can be obtained by testing the temperature sensor and the pressure sensor.

[0091] Furthermore, the temperature of the liquid propane 9 can be obtained by checking the physical property parameters of temperature and pressure to obtain its density, and then the volume Vp of the liquid propane 9 can be obtained by mass conversion. At the same time, the nitrogen volume Vn of the gas phase space 8 can be obtained. The density parameter of propane is obtained by inputting the temperature and pressure values ​​of propane in the HYSYS physical property library.

[0092] Specifically, the volume Vp of the liquid propane 9 and the volume Vn of the nitrogen in the gas phase space 8 are obtained by equations (3) and (4), respectively.

[0093] (3).

[0094] (4).

[0095] Based on the above formula, the nitrogen content of each of the gas phase spaces including the nitrogen reservoir 11, the buffer bottle 10, and the simulated storage tank 6 can be obtained, that is, the remaining nitrogen amount n in the nitrogen reservoir 11 r , the amount of nitrogen in the buffer bottle 10 is n b , simulate the nitrogen amount n in the gas phase space 8 in the storage tank 6 g , and the total amount of nitrogen has been obtained from the initial nitrogen reservoir 11 filling amount .

[0096] Therefore, the total amount of nitrogen in formula (1) can be Subtract the nitrogen content in the gas phase space of each container to calculate the amount of nitrogen dissolved in liquid propane 9 .

[0097] (5).

[0098] After obtaining the amount of nitrogen dissolved in liquid propane 9, the unit molar solubility of nitrogen in liquid propane can be calculated. The same definition as other related studies is maintained here, which is defined as the phase composition fraction in liquid propane, rather than the number of moles of nitrogen dissolved per unit mole of propane, and is calculated by the following formula.

[0099] (6).

[0100] in, is the molar amount of propane, calculated from the mass of propane charged at the beginning of the experiment Divide by its molar mass to convert.

[0101] The simulation experimental system for nitrogen dissolution in propane provided in an embodiment of the present invention records the pressure information and temperature information in the nitrogen reservoir 11, the buffer bottle 10, and the simulation storage tank 6 in real time, and performs data fitting to obtain a prediction formula for the diffusion solubility of nitrogen in liquid propane at low temperature and normal pressure.

[0102] Specifically, according to the MATLAB programming fitting code, the fitting method is nonlinear fitting, and the fitting method is the least squares method, that is, the minimum residual sum is taken as the goal.

[0103] Since the experimental test results are only for the pressure near 0.1MPa and the temperature range of 90K-227K, the data fitting process only fits the temperature, that is, the diffusion solubility of nitrogen in liquid propane at different temperatures under 0.1MPa is fitted.

[0104] The specific fitting results are:

[0105] -30.164684923.

[0106] 52.582333606.

[0107] 74.250536097.

[0108] -27.293050118.

[0109] That is, the new fitting formula obtained is.

[0110] lnx=-30.1648+52.5823 / T+74.2505 P-27.2931.

[0111] Where lnx is the logarithmic solubility of nitrogen in liquid propane, T is the temperature (in K), and P is the pressure (in MPa).

[0112] By using the above new fitting formula and based on the temperature information and pressure information recorded in real time by the simulation experimental system of nitrogen dissolution in propane provided in an embodiment of the present invention, the diffusion solubility of nitrogen in liquid propane can be predicted and compared with the experimental test results.

[0113] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A simulation experimental system for dissolving nitrogen in propane, characterized in that: include: A simulated storage tank, the interior of which is suitable for filling with liquid propane, a gas phase space for filling with nitrogen is formed above the liquid level of the liquid propane in the simulated storage tank, and a temperature monitoring component is provided inside the simulated storage tank; A cold storage component, comprising a cold storage component and a control component, wherein the cold storage component is arranged inside the simulated storage tank, the cold storage component is filled with a cold storage agent, and the control component is arranged in the cold storage component and is used to control the flow rate of the cold storage agent to maintain the temperature of the liquid propane in the simulated storage tank and the nitrogen in the gas phase space; A nitrogen filling device connected to the inlet of the simulated storage tank, used to fill nitrogen into the simulated storage tank and keep the simulated storage tank in a constant pressure state, and the nitrogen filling device is provided with a corresponding pressure monitoring component; The data monitoring system is connected to the temperature monitoring component and the pressure monitoring component respectively, and is used to monitor the temperature information and pressure information of the simulated storage tank, and display the temperature information and the pressure information in real time.

2. The simulation experimental system for dissolving nitrogen in propane according to claim 1, characterized in that: The nitrogen filling device comprises a buffer bottle, a nitrogen reservoir and a nitrogen bottle which are connected in sequence, and the buffer bottle is connected to the inlet of the simulated storage tank; A first valve is provided on the connecting pipeline between the nitrogen bottle and the nitrogen reservoir, a second valve is provided on the connecting pipeline between the nitrogen reservoir and the buffer bottle, and a third valve is provided on the connecting pipeline between the buffer bottle and the inlet of the simulation tank.

3. The simulation experimental system for dissolving nitrogen in propane according to claim 1, characterized in that: The cold storage component includes a cold storage body, which is spirally arranged along the height direction of the simulated storage tank. A liquid outlet pipe is provided at the upper end of the cold storage body, and a liquid inlet pipe is provided at the lower end of the cold storage body. Both the liquid inlet pipe and the liquid outlet pipe pass through the simulated storage tank and extend out of the simulated storage tank. The control component is arranged on the liquid inlet pipe to control the flow rate of the cold storage agent in the liquid inlet pipe.

4. The simulation experimental system for dissolving nitrogen in propane according to claim 3, characterized in that: The control component includes a fourth valve and a controller. The fourth valve is arranged on the liquid inlet pipe. The controller is electrically connected to the fourth valve and is used to control the opening of the fourth valve according to the preset temperature value and the detected temperature value in the simulated storage tank.

5. The simulation experimental system for dissolving nitrogen in propane according to any one of claims 1 to 4, characterized in that: The outer side of the simulated storage tank is provided with multiple layers of thermal insulation; An outlet pipeline is connected to the outlet of the simulated storage tank, and a fifth valve is arranged on the outlet pipeline.

6. A simulation experimental method for dissolving nitrogen in propane, based on the simulation experimental system for dissolving nitrogen in propane according to any one of claims 1 to 5, characterized in that: The steps include: Determining that the simulated storage tank meets the experimental requirements, filling the simulated storage tank with liquid propane, and weighing the mass of the liquid propane; According to a plurality of preset temperature values ​​and corresponding detected temperature values, the flow rate of the coolant in the cool storage component is controlled to perform step-by-step cooling of the liquid propane in the simulated storage tank and the nitrogen in the gas phase space; and the temperature information and pressure information of the simulated storage tank are acquired in real time, and based on the temperature information and the pressure information, the solubility of nitrogen in the liquid propane is determined.

7. The simulation experimental method for dissolving nitrogen in propane according to claim 6, characterized in that: Determining that the simulated storage tank meets the experimental requirements includes: Performing leak detection on the simulated storage tank; If the simulated storage tank has no leakage, vacuum extraction is performed on the simulated storage tank; if the simulated storage tank has leakage, the corresponding leakage position is processed.

8. The simulation experimental method for dissolving nitrogen in propane according to claim 6, characterized in that: The method controls the flow rate of the coolant in the cool storage component according to a plurality of preset temperature values ​​and corresponding detected temperature values, and performs step-wise cooling on the liquid propane in the simulated storage tank and the nitrogen in the gas phase space, including: Determining that the pressure in the simulated storage tank is less than a preset pressure, controlling the nitrogen filling device to fill nitrogen into the simulated storage tank so that the simulated storage tank is maintained in a constant pressure state; When it is determined that the pressure of the simulated storage tank does not change for a preset period of time, the flow rate of the coolant in the cool storage component is controlled to perform step-by-step cooling of the liquid propane in the simulated storage tank and the nitrogen in the gas phase space.

9. The simulation experimental method for dissolving nitrogen in propane according to claim 8, characterized in that: The controlling the nitrogen filling device to fill nitrogen into the simulated storage tank so that the simulated storage tank is kept in a constant pressure state comprises: Controlling the third valve between the simulation storage tank and the buffer bottle to open, and making the third valve in a normally open state; The second valve between the buffer bottle and the nitrogen reservoir is controlled to open multiple times, and the opening degree of the second valve is smaller than the opening degree of the third valve.

10. The simulation experimental method for dissolving nitrogen in propane according to claim 8, characterized in that: The maximum value of the preset temperature value is lower than the boiling point temperature of propane under normal pressure, and the minimum value of the preset temperature value is the lower limit of the temperature of the propane cold storage medium.

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