Constant current calibration device and method for high temperature and high pressure supercritical CO2 flowmeter using PVTt method

Abstract

The present invention relates to a constant current calibration device and method for a high-temperature and high-pressure supercritical CO2 flowmeter using a PVTt method, wherein the constant current calibration device comprises a carbon dioxide normal temperature liquid storage tank, an inlet compression pump, a temperature-adjustable standard gas storage tank, a pressure-stabilizing and reducing valve, a constant current boosting pump, a heater, a filter, a second pressure gauge, a second thermometer, a flowmeter to be tested, a desuperheater, a third thermometer, and a flow regulating valve, which are connected end to end in sequence. The present invention decomposes the pressurization and temperature-raising process of obtaining a supercritical carbon dioxide fluid, and obtains a supercritical carbon dioxide working fluid that meets the calibration requirements of the flowmeter to be tested through a combined structure of a pre-placed temperature-adjustable standard gas storage tank + a pressure-stabilizing and reducing valve through a pressure-compensating and temperature-raising method. The present invention realizes carbon dioxide flow calibration by applying the PVTt method to a temperature-adjustable standard gas storage tank, ensures that carbon dioxide is in a supercritical state through a temperature regulating module on the temperature-adjustable standard gas storage tank, and improves the carbon dioxide output quality of the gas storage tank to increase the calibration duration.

Description

Technical Field

[0001] The present invention relates to the technical field of flowmeter constant current calibration devices and methods, and in particular to a high-temperature and high-pressure supercritical CO2 flowmeter constant current calibration device and method using a PVTt method. Background Art

[0002] The supercritical carbon dioxide Brayton cycle power generation system is considered to be one of the most promising advanced power cycles. Boilers using supercritical carbon dioxide cycles have the advantages of strong flexibility and thermal-electric decoupling, and their position in power systems dominated by renewable energy generation is becoming increasingly important.

[0003] Accurate measurement of the working fluid flow rate of the heating surface is essential for the promotion and application of supercritical carbon dioxide boilers, but there is no high-temperature and high-pressure supercritical carbon dioxide fluid precision flowmeter with a temperature not less than 400℃ and a pressure not less than 20MPa at home and abroad, and there is also a lack of flowmeter calibration devices and methods that can operate under this condition. The original value transfer is the most accurate flowmeter calibration method. Among them, the most common weighing calibration method is suitable for non-closed systems, such as calibrating liquid flowmeters under normal temperature and pressure conditions. For carbon dioxide flowmeters that need to be calibrated in a closed system, the connection between the gas storage device and the system will affect the weighing results; and the critical temperature of carbon dioxide is only 31.2℃, which can easily exist in a gaseous / supercritical state, and is suitable for the PVTt method commonly used for gas flowmeter calibration and also original value transfer. However, the general PVTt method is to transfer gas to the standard gas tank through a compression pump after the flow meter to be tested. Under the condition of low gas temperature and pressure, the compression pump has low technical requirements and the process is easy to implement. However, for the supercritical carbon dioxide cycle power generation system, especially the high temperature and high pressure conditions of the supercritical carbon dioxide working fluid in the heating surface of the supercritical carbon dioxide boiler, the working conditions of the compression pump are poor, which will affect the calibration accuracy. Therefore, it is urgent to develop and design a flow meter calibration device and method for high temperature and high pressure supercritical carbon dioxide fluid using the PVTt method. Summary of the invention

[0004] In order to solve the technical problem that the prior art cannot accurately measure the flow rate of the working medium on the heated surface, the present invention decomposes the pressurization and temperature increase process of obtaining the supercritical carbon dioxide fluid, and obtains the supercritical carbon dioxide working medium that meets the calibration requirements of the flow meter to be tested through the combined structure of the pre-adjustable temperature standard gas storage tank + the pressure regulating valve by the pressure compensation and temperature increase method. Based on this, the present invention provides a constant flow calibration device and method for a high-temperature and high-pressure supercritical CO2 flowmeter using the PVTt method. The specific technical solutions are as follows:

[0005] A constant flow calibration device for a high-temperature and high-pressure supercritical CO2 flowmeter using a PVTt method comprises a carbon dioxide normal temperature liquid storage tank, an inlet compression pump, a temperature-adjustable standard gas storage tank, a pressure-stabilizing and pressure-reducing valve, a constant flow booster pump, a heater, a filter, a flowmeter to be tested, a temperature reducer and a flow regulating valve, wherein the inlet compression pump is installed between the normal temperature liquid storage tank and the temperature-adjustable standard gas storage tank, an inlet valve and an outlet valve are installed at the inlet and outlet of the temperature-adjustable standard gas storage tank, respectively, a first thermometer, a first pressure gauge and a temperature regulating module are installed on the temperature-adjustable standard gas storage tank, respectively, the outlet valve is connected to the flowmeter to be tested, the pressure-stabilizing and pressure-reducing valve, the constant flow booster pump, the heater, the filter, a second pressure gauge and a second thermometer are sequentially arranged between the outlet valve and the inlet of the flowmeter to be tested, the outlet of the flowmeter to be tested is connected to the normal temperature liquid storage tank, and the temperature reducer, the third thermometer and the flow regulating valve are sequentially arranged between the outlet of the flowmeter to be tested and the normal temperature liquid storage tank.

[0006] The first thermometer and the first pressure gauge are used to measure the temperature and pressure in the temperature-adjustable standard gas storage tank, respectively. Under normal working conditions, the output pressure of the pressure-stabilizing and pressure-reducing valve is slightly lower than the working condition required by the flow meter to be tested, leaving a margin for the pressure increase of the working fluid after being heated by the heater, and the insufficient pressure is supplemented by the constant-current booster pump; the measurement signals of the second pressure gauge and the second thermometer are respectively transmitted to the control chip, which is used to adjust the working power of the constant-current booster pump and the heater, so that the temperature, pressure and flow conditions required for constant-current calibration can be achieved before the working fluid flows through the flow meter to be tested.

[0007] The present invention can maintain the carbon dioxide working medium in the temperature-adjustable standard gas storage tank in a supercritical state and keep it within a temperature range where the density varies greatly with the pressure by means of a temperature regulating module arranged on the temperature-adjustable standard gas storage tank. The quality of the output carbon dioxide of the temperature-adjustable standard gas storage tank can be improved while the calibration time can be increased, and the carbon dioxide flow calibration can be realized by using the PVTt method.

[0008] The present invention can make the output pressure of the adjustable temperature standard gas tank relatively stable and slightly lower than the set working pressure of the supercritical carbon dioxide working medium through the pre-adjustable temperature standard gas tank and the combined structure of the pressure-stabilizing and pressure-reducing valve, and further through the fine adjustment of the constant current booster pump, the pressure before the flow meter to be tested and the supercritical carbon dioxide flow through the flow meter to be tested can be kept stable. After the working medium flows out of the adjustable temperature standard gas tank and flows through the constant current booster pump, the working medium is heated by the heater, the temperature of the supercritical carbon dioxide working medium passing through the constant current booster pump is reduced, the temperature tolerance requirement of the constant current booster pump is reduced, and the heating power of the heater is adjusted by the control chip receiving the measurement signal of the second thermometer, and the power of the constant current booster pump is fine-tuned by the control chip receiving the measurement signal of the second pressure gauge, so that the supercritical carbon dioxide working medium can flow through the flow meter to be tested at a constant flow rate under stable temperature and pressure conditions, thereby further simplifying the flow calibration calculation and improving the calibration accuracy.

[0009] Furthermore, a heat-insulating material is wrapped on a pipeline connecting the heater, the filter, the second pressure gauge, the second thermometer and the flow meter to be tested.

[0010] In addition to wrapping the pipeline between the heater and the flow meter to be tested with heat insulation material to reduce heat loss, the present invention can also achieve the technical effect of further reducing heat loss by shortening the length of the pipeline between the heater and the flow meter to be tested.

[0011] Furthermore, the rated pressure resistance of the temperature-adjustable standard gas storage tank is 30 MPa.

[0012] Furthermore, the inlet compression pump is used to pressurize the carbon dioxide in the carbon dioxide room-temperature liquid storage tank and then enter the temperature-adjustable standard gas storage tank through the inlet valve.

[0013] Furthermore, the filter is used to separate the corrosion layer of the pipeline material that is peeled off under the corrosion effect of the high-temperature and high-pressure supercritical carbon dioxide working medium, so as to protect the flow meter to be inspected.

[0014] Furthermore, the desuperheater is used to reduce the temperature of the working medium.

[0015] Furthermore, the third thermometer is used to monitor the working fluid temperature so that the working fluid temperature is not lower than the freezing point of carbon dioxide under the pressure condition to be tested, so as to prevent the high-pressure carbon dioxide from forming dry ice to block the pipeline.

[0016] Furthermore, the temperature-adjustable standard gas storage tank is used to calculate the mass of the outflowing carbon dioxide using the PVTt method according to the changes in the values ​​of the first thermometer and the first pressure gauge before and after calibration, combined with the volume of the temperature-adjustable standard gas storage tank.

[0017] Furthermore, the temperature regulating module is used to place the supercritical carbon dioxide in a temperature range where the density varies greatly with the pressure, so as to increase the mass of carbon dioxide that can be exported by the temperature-adjustable standard gas storage tank.

[0018] A constant current calibration method for a high temperature and high pressure supercritical CO2 flowmeter using the PVTt method, wherein the constant current calibration method is implemented by a constant current calibration device for a high temperature and high pressure supercritical CO2 flowmeter using the PVTt method according to any one of the above preferred schemes, and comprises the following steps:

[0019] Close the inlet valve of the temperature-adjustable standard gas storage tank, open the outlet valve, the pressure-stabilizing and reducing valve and the flow regulating valve of the temperature-adjustable standard gas storage tank, and connect an external vacuum pump to the flow regulating valve to extract the air in the constant-current calibration device until the second pressure indication drops to 0 or remains unchanged, and then close the flow regulating valve;

[0020] Open the inlet valve and the inlet compression pump of the temperature-adjustable standard gas storage tank, open the flow regulating valve after the second pressure indication number is higher than the atmospheric pressure, measure the oxygen content in the purge gas until it is lower than the detection limit of the oxygen analyzer, close the flow regulating valve and the outlet valve of the temperature-adjustable standard gas storage tank in sequence, adjust the pressure-stabilizing and reducing valve to the lowest outlet pressure position, and at this time, the inlet compression pump starts to supply gas to the temperature-adjustable standard gas storage tank;

[0021] Turn on the temperature regulating module, and after the second pressure indication reaches 30Mpa, first fully open the outlet valve of the temperature-adjustable standard gas storage tank, then adjust the pressure-stabilizing and pressure-reducing valve until the second pressure indication is slightly lower than the required working pressure, and at the same time slowly open and adjust the flow regulating valve so that the indication of the flow meter to be tested is close to the required calibrated flow value. At the same time, gradually tighten the inlet valve of the temperature-adjustable standard gas storage tank so that the value of the first pressure gauge is maintained at around 30MPa; turn on the constant-flow booster pump, heater and desuperheater, and fine-tune the inlet valve of the temperature-adjustable standard gas storage tank, the pressure-stabilizing and pressure-reducing valve and the flow regulating valve until the system is stable and balanced and the first pressure gauge, the second pressure gauge, the second thermometer, the flow meter to be tested and the third thermometer all display the required indications;

[0022] Close the inlet valve of the temperature-adjustable standard gas storage tank, confirm that the system is still running stably, record the first thermometer and the first pressure indication and start timing, confirm that the indication of the flow meter to be tested remains unchanged during the timing process, close the outlet valve of the temperature-adjustable standard gas storage tank and stop timing when the first pressure indication is close to the required working pressure, then turn off the heater, the desuperheater, the constant-flow booster pump and the flow regulating valve in turn, and record the first thermometer and the first pressure indication;

[0023] The corresponding gas density in the standard gas storage tank is calculated based on the numerical values ​​of the first thermometer and the first pressure gauge at the timing start and end points. Combined with the volume of the adjustable temperature standard gas storage tank and the calibration timing, the accurate flow rate of supercritical carbon dioxide within the timing range is obtained, thereby calibrating the flow meter to be tested. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the overall structure of a preferred embodiment of the present invention.

[0025] Figure 2 Schematic diagram of the curve showing how carbon dioxide density changes with temperature and pressure.

[0026] Description of reference numerals:

[0027] 1-inlet compression pump; 2-inlet valve; 3-first thermometer; 4-first pressure gauge; 5-temperature-adjustable standard gas storage tank; 6-outlet valve; 7-pressure-stabilizing and reducing valve; 8-constant-flow booster pump; 9-heater; 10-filter; 11-second pressure gauge; 12-second thermometer; 13-flow meter to be tested; 14-desuperheater; 15-third thermometer; 16-flow regulating valve; 17-temperature regulating module. DETAILED DESCRIPTION

[0028] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0029] In the description of the present invention, it should be noted that the terminology nouns in the various embodiments, such as words indicating directions such as "upper", "lower", "front", and "back", are only for simplifying the description of the positional relationship based on the drawings in the specification, and do not mean that the referred elements and devices must be operated according to the specific directions and defined operations and methods and structures in the specification. Such directional nouns do not constitute limitations to the present invention.

[0030] like Figure 1 As shown, in order to solve the technical problem that the prior art cannot accurately measure the working fluid flow rate of the heated surface, the present invention decomposes the pressurization and heating process of obtaining the supercritical carbon dioxide fluid, and obtains the supercritical carbon dioxide working fluid that meets the calibration requirements of the flow meter 13 to be tested through the combined structure of the pre-adjustable temperature standard gas storage tank 5 + the pressure-stabilizing and reducing valve 7 by the pressure-compensating and heating method. Based on this, the present invention provides a constant-current calibration device and method for a high-temperature and high-pressure supercritical CO2 flowmeter using the PVTt method, and the specific technical solutions are as follows:

[0031] The constant flow calibration device of high temperature and high pressure supercritical CO2 flowmeter using PVTt method comprises a carbon dioxide room temperature liquid storage tank, an inlet compression pump 1, a temperature-adjustable standard gas storage tank 5, a pressure-stabilizing and reducing valve 7, a constant flow booster pump 8, a heater 9, a filter 10, a flowmeter to be inspected 13, a desuperheater 14 and a flow regulating valve 16, wherein the inlet compression pump 1 is installed between the room temperature liquid storage tank and the temperature-adjustable standard gas storage tank 5, the inlet valve 2 and the outlet valve 6 are installed at the inlet and outlet of the temperature-adjustable standard gas storage tank 5, and the temperature-adjustable standard gas storage tank 5 is respectively provided with a first temperature valve 2 and an outlet valve 6. The outlet valve 6 is connected to the flow meter 13 to be tested, and the pressure-stabilizing and reducing valve 7, the constant-current booster pump 8, the heater 9, the filter 10, the second pressure gauge 11 and the second thermometer 12 are arranged in sequence between the outlet valve 6 and the inlet of the flow meter 13 to be tested, the outlet of the flow meter 13 to be tested is connected to the normal-temperature liquid storage tank, and the desuperheater 14, the third thermometer 15 and the flow regulating valve 16 are arranged in sequence between the outlet of the flow meter 13 to be tested and the normal-temperature liquid storage tank.

[0032] The first thermometer 3 and the first pressure gauge 4 are used to measure the temperature and pressure in the temperature-adjustable standard gas storage tank 5. The output pressure of the pressure-stabilizing and pressure-reducing valve 7 is slightly lower than the working condition required by the flow meter 13 to be tested under normal working conditions, leaving a margin for the pressure increase of the working medium after being heated by the heater 9, and the insufficient pressure is supplemented by the constant-current booster pump 8; the measurement signals of the second pressure gauge 11 and the second thermometer 12 are respectively transmitted to the control chip, which is used to adjust the working power of the constant-current booster pump 8 and the heater 9, so that the temperature, pressure and flow conditions required for constant-current calibration can be achieved before the working medium flows through the flow meter 13 to be tested.

[0033] The present invention uses a temperature regulating module 17 provided on the temperature-adjustable standard gas storage tank 5 to enable the carbon dioxide working medium in the temperature-adjustable standard gas storage tank 5 to always be maintained in a supercritical state and kept within a temperature range where the density varies greatly with the pressure. While improving the quality of the output carbon dioxide of the temperature-adjustable standard gas storage tank 5, the calibration time can be increased, and the PVTt method can be used to realize the carbon dioxide flow calibration.

[0034] The present invention can make the output pressure of the adjustable temperature standard gas tank 5 relatively stable and slightly lower than the set working pressure of the supercritical carbon dioxide working medium through the pre-adjustable temperature standard gas tank 5 and the pressure-stabilizing and reducing valve 7, and further through the fine adjustment of the constant current booster pump 8, the pressure before the flow meter 13 to be tested and the supercritical carbon dioxide flow rate through the flow meter 13 to be tested can be kept stable. After the working medium flows out of the adjustable temperature standard gas tank 5 and flows through the constant current booster pump 8, the working medium is heated by the heater 9, the temperature of the supercritical carbon dioxide working medium passing through the constant current booster pump 8 is reduced, and the temperature tolerance requirement of the constant current booster pump 8 is reduced, and the control chip receiving the measurement signal of the second thermometer 12 is used to adjust the heating power of the heater 9, and the control chip receiving the measurement signal of the second pressure gauge 11 is used to fine-tune the power of the constant current booster pump 8, so that the supercritical carbon dioxide working medium can flow through the flow meter 13 to be tested at a constant flow rate under stable temperature and pressure conditions, thereby further simplifying the flow calibration calculation and improving the calibration accuracy.

[0035] Alternatively, if Figure 1 As shown, the pipeline connecting the heater 9, the filter 10, the second pressure gauge 11, the second thermometer 12 and the flow meter to be tested 13 is wrapped with a heat-insulating material.

[0036] In addition to wrapping the pipe between the heater 9 and the flow meter 13 to be tested with insulation material to reduce heat loss, the present invention can also achieve the technical effect of further reducing heat loss by shortening the length of the pipe between the heater 9 and the flow meter 13 to be tested.

[0037] Alternatively, if Figure 1 As shown, the rated pressure of the adjustable temperature standard gas storage tank 5 is 30 MPa.

[0038] Alternatively, if Figure 1 As shown, the inlet compression pump 1 is used to pressurize the carbon dioxide in the carbon dioxide room temperature liquid storage tank and then enter the temperature-adjustable standard gas storage tank 5 through the inlet valve 2.

[0039] Alternatively, if Figure 1 As shown, the filter 10 is used to separate the corrosion layer of the pipeline material that is peeled off under the corrosion effect of the high-temperature and high-pressure supercritical carbon dioxide working medium, so as to protect the flow meter 13 to be tested.

[0040] Alternatively, if Figure 1 As shown, the desuperheater 14 is used to reduce the temperature of the working medium.

[0041] Alternatively, if Figure 1 As shown, the third thermometer 15 is used to monitor the working fluid temperature so that the working fluid temperature is not lower than the freezing point of carbon dioxide under the pressure condition to be tested, so as to prevent the high-pressure carbon dioxide from forming dry ice to block the pipeline.

[0042] Alternatively, if Figure 1 As shown, the temperature-adjustable standard gas storage tank 5 is used to calculate the outflow carbon dioxide mass by using the PVTt method according to the value changes of the first thermometer 3 and the first pressure gauge 4 before and after calibration, combined with the volume of the temperature-adjustable standard gas storage tank 5.

[0043] Alternatively, if Figure 1 As shown, the temperature adjustment module 17 is used to keep the supercritical carbon dioxide in a temperature range where the density varies greatly with the pressure, so as to increase the output quality of the carbon dioxide of the temperature-adjustable standard gas storage tank 5 .

[0044] A constant current calibration method for a high temperature and high pressure supercritical CO2 flowmeter using the PVTt method, wherein the constant current calibration method is implemented by a constant current calibration device for a high temperature and high pressure supercritical CO2 flowmeter using the PVTt method in any one of the above preferred embodiments, such as Figure 1 As shown, the following steps are included:

[0045] Close the inlet valve 2 of the temperature-adjustable standard gas storage tank 5, open the outlet valve 6, the pressure-stabilizing and reducing valve 7 and the flow regulating valve 16 of the temperature-adjustable standard gas storage tank 5, the flow regulating valve 16 is externally connected to a vacuum pump to extract the air in the constant-current calibration device until the reading of the second pressure gauge 11 drops to 0 or remains unchanged, and then close the flow regulating valve 16;

[0046] Open the inlet valve 2 and the inlet compression pump 1 of the temperature-adjustable standard gas storage tank 5, open the flow regulating valve 16 after the reading of the second pressure gauge 11 is higher than the atmospheric pressure, measure the oxygen content in the purge gas until it is lower than the detection limit of the oxygen analyzer, and then close the flow regulating valve 16 and the outlet valve 6 of the temperature-adjustable standard gas storage tank 5 in turn, adjust the pressure-stabilizing and reducing valve 7 to the lowest outlet pressure position, and then the inlet compression pump 1 starts to supply gas to the temperature-adjustable standard gas storage tank 5;

[0047] Open the temperature regulating module 17, and after the reading of the second pressure gauge 11 reaches 30Mpa, first fully open the outlet valve 6 of the temperature-adjustable standard gas storage tank 5, and then adjust the pressure-stabilizing and reducing valve 7 until the reading of the second pressure gauge 11 is slightly lower than the required working pressure, and at the same time slowly open and adjust the flow regulating valve 16 to make the reading of the flow meter 13 to be tested close to the required calibrated flow value. At the same time, gradually tighten the inlet valve 2 of the temperature-adjustable standard gas storage tank 5 to maintain the value of the first pressure gauge 4 at around 30MPa; open the constant-flow booster pump 8, the heater 9 and the desuperheater 14, and fine-tune the inlet valve 2 of the temperature-adjustable standard gas storage tank 5, the pressure-stabilizing and reducing valve 7 and the flow regulating valve 16 until the system is stable and balanced and the first pressure gauge 4, the second pressure gauge 11, the second thermometer 12, the flow meter 13 to be tested and the third thermometer 15 all display the required readings;

[0048] Close the inlet valve 2 of the temperature-adjustable standard gas storage tank 5, and after confirming that the system is still running stably, record the readings of the first thermometer 3 and the first pressure gauge 4 and start timing, confirm that the reading of the flow meter to be tested 13 remains unchanged during the timing process, and when the reading of the first pressure gauge 4 is close to the required working pressure, close the outlet valve 6 of the temperature-adjustable standard gas storage tank 5 and stop timing, then turn off the heater 9, the desuperheater 14, the constant flow booster pump 8 and the flow regulating valve 16 in sequence, and record the readings of the first thermometer 3 and the first pressure gauge 4;

[0049] The gas density in the corresponding temperature-adjustable standard gas storage tank 5 is calculated based on the numerical values ​​of the first thermometer 3 and the first pressure gauge 4 at the timing start and end points. Combined with the volume of the temperature-adjustable standard gas storage tank 5 and the calibration timing, the accurate flow rate of supercritical carbon dioxide within the timing range is obtained, thereby calibrating the flow meter 13 to be tested.

[0050] The PVTt method used in the present invention is to calibrate the flow meter 13 to be tested by comparing the flow time cumulative value of the flow meter 13 to be tested with the output gas volume of the temperature-adjustable standard gas tank 5; the corresponding density can be obtained according to the gas temperature and pressure in the temperature-adjustable standard gas tank 5 at the beginning and end of the test, and the output gas volume of the temperature-adjustable standard gas tank 5 can be obtained by combining the accurately measured volume of the temperature-adjustable standard gas tank 5. Figure 2 As shown, there is a temperature range (about 100-200°C in the figure) between the critical temperature of carbon dioxide 31.2°C and 650°C, where the density of supercritical carbon dioxide changes greatly with pressure. When in this temperature range, as the pressure decreases, the mass change of the supercritical carbon dioxide working fluid in the adjustable temperature standard gas storage tank 5 will be greater. Therefore, a temperature regulating module 17 is configured on the adjustable temperature standard gas storage tank 5 to control the supercritical carbon dioxide to be under temperature conditions with higher gas storage quality.

[0051] Although the present invention discloses the above preferred embodiments, the present invention is not limited thereto. Those skilled in the art can perform various permutations and combinations of the above preferred embodiments and form a complete technical solution without departing from the spirit and scope of the present invention, and the protection scope of the present invention shall be subject to the scope defined in the claims.

Claims

1. A constant current calibration device for high temperature and high pressure supercritical CO2 flowmeter using the PVTt method, characterized in that: The invention comprises a carbon dioxide normal temperature liquid storage tank, an inlet compression pump (1), a temperature-adjustable standard gas storage tank (5), a pressure-stabilizing and reducing valve (7), a constant-current booster pump (8), a heater (9), a filter (10), a flow meter to be tested (13), a temperature reducer (14) and a flow regulating valve (16), wherein the inlet compression pump (1) is installed between the normal temperature liquid storage tank and the temperature-adjustable standard gas storage tank (5), the inlet and outlet of the temperature-adjustable standard gas storage tank (5) are respectively installed with an inlet valve (2) and an outlet valve (6), and the temperature-adjustable standard gas storage tank (5) is respectively installed with a first thermometer (3), a first pressure gauge (4) and a temperature regulating valve (6). The flow meter (13) is connected to the flow meter to be tested (13), and the pressure-stabilizing and reducing valve (7), the constant-current booster pump (8), the heater (9), the filter (10), the second pressure gauge (11) and the second thermometer (12) are arranged in sequence between the outlet valve (6) and the inlet of the flow meter (13) to be tested, the outlet of the flow meter (13) to be tested is connected to the normal-temperature liquid storage tank, and the desuperheater (14), the third thermometer (15) and the flow regulating valve (16) are arranged in sequence between the outlet of the flow meter (13) to be tested and the normal-temperature liquid storage tank.

2. The constant current calibration device for high temperature and high pressure supercritical CO2 flowmeter using the PVTt method according to claim 1 is characterized in that: The pipeline connecting the heater (9), the filter (10), the second pressure gauge (11), the second thermometer (12) and the flow meter to be tested (13) is wrapped with a heat-insulating material.

3. The constant current calibration device for high temperature and high pressure supercritical CO2 flowmeter using the PVTt method according to claim 1, characterized in that: The rated bearing pressure of the temperature-adjustable standard gas storage tank (5) is 30 MPa.

4. The constant current calibration device for high temperature and high pressure supercritical CO2 flowmeter using the PVTt method according to claim 1, characterized in that: The inlet compression pump (1) is used to pressurize the carbon dioxide in the carbon dioxide room temperature liquid storage tank and then enter the temperature-adjustable standard gas storage tank (5) through the inlet valve (2).

5. The constant current calibration device for high temperature and high pressure supercritical CO2 flowmeter using the PVTt method according to claim 1, characterized in that: The filter (10) is used to separate the corrosion layer of the pipeline material that is peeled off under the corrosion effect of the high-temperature and high-pressure supercritical carbon dioxide working medium, so as to protect the flow meter (13) to be tested.

6. The constant current calibration device for high temperature and high pressure supercritical CO2 flowmeter using the PVTt method according to claim 1, characterized in that: The desuperheater (14) is used to reduce the temperature of the working medium.

7. The constant current calibration device for high temperature and high pressure supercritical CO2 flowmeter using the PVTt method according to claim 1, characterized in that: The third thermometer (15) is used to monitor the working medium temperature so that the working medium temperature is not lower than the freezing point of carbon dioxide under the pressure condition to be tested, so as to prevent the high-pressure carbon dioxide from forming dry ice to block the pipeline.

8. The constant current calibration device for high temperature and high pressure supercritical CO2 flowmeter using the PVTt method according to claim 1, characterized in that: The temperature-adjustable standard gas storage tank (5) is used to calculate the mass of the outflowing carbon dioxide using the PVTt method based on the changes in the values ​​of the first thermometer (3) and the first pressure gauge (4) before and after calibration, combined with the volume of the temperature-adjustable standard gas storage tank (5).

9. The constant current calibration device for high temperature and high pressure supercritical CO2 flowmeter using the PVTt method according to claim 1, characterized in that: The temperature regulating module (17) is used to always maintain the carbon dioxide working medium in the temperature-adjustable standard gas storage tank in a supercritical state, and to keep the supercritical carbon dioxide in a temperature range where the density varies greatly with pressure, so as to increase the mass of carbon dioxide that can be output from the temperature-adjustable standard gas storage tank (5).

10. A constant flow calibration method for a high temperature and high pressure supercritical CO2 flowmeter using the PVTt method, characterized in that: The constant current calibration method is implemented by a constant current calibration device for a high temperature and high pressure supercritical CO2 flowmeter using a PVTt method according to any one of claims 1 to 9, and comprises the following steps: The inlet valve (2) of the temperature-adjustable standard gas storage tank (5) is closed, and the outlet valve (6), the pressure-stabilizing and reducing valve (7) and the flow regulating valve (16) of the temperature-adjustable standard gas storage tank (5) are opened, wherein the flow regulating valve (16) is externally connected to a vacuum pump to extract air from the constant-current calibration device until the reading on the second pressure gauge (11) drops to 0 or remains unchanged, and then the flow regulating valve (16) is closed; Open the inlet valve (2) and the inlet compression pump (1) of the temperature-adjustable standard gas storage tank (5), open the flow regulating valve (16) after the reading of the second pressure gauge (11) is higher than the atmospheric pressure, measure the oxygen content in the purge gas until it is lower than the detection limit of the oxygen analyzer, close the flow regulating valve (16) and the outlet valve (6) of the temperature-adjustable standard gas storage tank (5) in turn, adjust the pressure-stabilizing and reducing valve (7) to the lowest outlet pressure position, and at this time, the inlet compression pump (1) starts to supply gas to the temperature-adjustable standard gas storage tank (5); The temperature regulating module (17) is turned on, and after the reading of the second pressure gauge (11) reaches 30 MPa, the outlet valve (6) of the temperature-adjustable standard gas storage tank (5) is fully opened, and then the pressure-stabilizing and reducing valve (7) is adjusted until the reading of the second pressure gauge (11) is slightly lower than the required working pressure. At the same time, the flow regulating valve (16) is slowly opened and adjusted to make the reading of the flow meter (13) to be tested close to the required calibrated flow value. At the same time, the inlet valve of the temperature-adjustable standard gas storage tank (5) is gradually tightened. The valve (2) is opened to maintain the value of the first pressure gauge (4) at about 30 MPa; the constant-flow booster pump (8), the heater (9) and the desuperheater (14) are turned on, and the inlet valve (2) of the temperature-adjustable standard gas storage tank (5), the pressure-stabilizing and pressure-reducing valve (7) and the flow regulating valve (16) are finely adjusted until the system is in a stable balance and the first pressure gauge (4), the second pressure gauge (11), the second thermometer (12), the flow meter to be tested (13) and the third thermometer (15) all display the required readings; The inlet valve (2) of the temperature-adjustable standard gas storage tank (5) is closed, and after confirming that the system is still running stably, the readings of the first thermometer (3) and the first pressure gauge (4) are recorded and timing is started, and the reading of the flow meter (13) to be tested remains unchanged during the timing process. When the reading of the first pressure gauge (4) is close to the required working pressure, the outlet valve (6) of the temperature-adjustable standard gas storage tank (5) is closed and timing is stopped, and then the heater (9), the desuperheater (14), the constant flow booster pump (8) and the flow regulating valve (16) are closed in sequence, and the readings of the first thermometer (3) and the first pressure gauge (4) are recorded; The gas density in the corresponding standard gas storage tank (5) is calculated based on the numerical values ​​of the first thermometer (3) and the first pressure gauge (4) at the timing start and end points. Combined with the volume of the temperature-adjustable standard gas storage tank (5) and the calibration timing, the accurate flow rate of the supercritical carbon dioxide within the timing range is obtained, thereby calibrating the flow meter (13) to be tested.

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