Natural gas hydrogen-doped or pure hydrogen verification and calibration loop

Abstract

The utility model discloses a natural gas hydrogen-doped or pure hydrogen verification and calibration loop. The loop comprises a gas supplementing and exhausting device, a filtering device, a circulating fan, a heat exchanger, a temperature control system, a bypass adjusting device, a working-grade standard device, a detected device, a transmission turbine device and a verification control system which are sequentially connected according to a gas flowing sequence to form the loop, the air supply and exhaust device is mounted at an air inlet of the loop, and a pressure regulating valve is arranged in the air supply and exhaust device; a detected flowmeter is arranged at the detected device; the verification control system is installed in a control room. The loop can be used for detecting or calibrating a detected flow meter for measuring natural gas hydrogen-doped or pure hydrogen gas, can reduce the dependence of a detection station on an upstream gas source, is not influenced by the pressure and flow of the natural gas hydrogen-doped or pure hydrogen gas conveyed downstream, can expand the detection capability of the natural gas hydrogen-doped or pure hydrogen flow metering detection station, and can be used for detecting or calibrating the natural gas hydrogen-doped or pure hydrogen flow metering detection station. And a flow value traceability system is perfected.

Description

Technical Field

[0001] This utility model relates to the field of natural gas and hydrogen verification and calibration technology, specifically to a natural gas blending or pure hydrogen verification and calibration loop. Background Technology

[0002] Hydrogen has advantages such as being clean, efficient, widely available, and renewable, making it a widely used and safe fuel that has gradually become a key focus of energy development for major economies worldwide. However, hydrogen storage and transportation costs are high. Blending hydrogen into existing natural gas pipeline networks can reduce carbon dioxide emissions, lower hydrogen storage and transportation costs, and enable low-cost, large-scale, long-distance hydrogen transportation.

[0003] Flow meters for natural gas blended with or pure hydrogen used in trade measurement must be sent to authorized calibration institutions for actual flow verification. Currently, there are no specialized calibration institutions in China for natural gas blended with or pure hydrogen flow meters. Existing natural gas blended with hydrogen flow meters are generally sent to natural gas calibration stations for verification. However, natural gas blended with or pure hydrogen does not fully comply with the calculation standards for natural gas. Therefore, the uncertainty and indication error of the data after flow meter calibration are relatively large, affecting the final trade settlement and easily leading to significant disagreements between upstream and downstream parties regarding the measurement results.

[0004] Traditional natural gas calibration stations use gas from upstream gas transmission stations for calibration, which is easily affected by upstream and downstream operating conditions. For example, if the incoming gas pressure is low while the flow meter requires high pressure, or if the incoming gas flow rate is small and does not reach the calibration flow rate of the flow meter, the calibration requirements cannot be met.

[0005] The working-grade standard flow meters used in the calibration process need to be disassembled and sent for inspection periodically. However, there are many working-grade standard flow meters, and they are large in diameter, size and weight, which makes them inconvenient to disassemble and transport. Traceability is also troublesome. Periodic disassembly and inspection would be very cumbersome and difficult and would pose transportation safety risks. Utility Model Content

[0006] The purpose of this invention is to provide a calibration loop for natural gas blending with hydrogen or pure hydrogen, which solves the problem of calibration and verification of flow meters used for natural gas blending with hydrogen or pure hydrogen gas trade measurement.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A calibration loop for natural gas blending with hydrogen or pure hydrogen includes a gas supply and exhaust device, a filter device, a circulating fan, a heat exchanger, a temperature control system, a bypass regulating device, a working-level standard device, a device under test, a transmission turbine device, and a calibration control system, which are connected in sequence according to the gas flow order to form the loop. The gas supply and exhaust device is installed at the gas inlet of the loop and has a built-in pressure regulating valve. A flow meter under test is installed at the device under test. The calibration control system is installed in a control room.

[0009] Preferably, the filtration device includes a filter, a pressure transmitter, a temperature transmitter, a differential pressure transmitter, a pressure gauge, and a thermometer.

[0010] Preferably, the bypass regulating device includes a flow regulating valve, a mass flow meter, a temperature transmitter, and a pressure transmitter.

[0011] Preferably, the working-level standard device includes at least two standard pipelines connected in parallel. The standard pipelines are connected in series with an electric forced sealing ball valve, a pressure gauge, a verification mass flow meter and a working-level standard flow meter in the gas flow direction from inlet to outlet. A rectifier is connected to both ends of the verification mass flow meter.

[0012] Preferably, the device under test includes at least two parallel test pipelines, which are connected in series in the direction of gas flow from inlet to outlet: a first test station, a second test station, an expansion joint, and a pressure gauge. A rectifier is connected to both ends of the first test station, and a flow meter is placed at the first and second test stations.

[0013] Preferably, the transmission turbine device includes a bypass pipeline and at least one transmission turbine pipeline, the bypass pipeline and the transmission turbine pipeline are connected in parallel, and a pressure gauge and two transmission turbine flow meters are connected in series in the transmission turbine pipeline, with a rectifier connected in front of each transmission turbine flow meter.

[0014] Preferably, the verification and control system includes a metrological verification system workstation and a process control system workstation; the process control system workstation includes the calibration and control of gas medium flow rate, valve switching, fan control system, and temperature control system.

[0015] This invention enables the verification or calibration of flow meters used to measure natural gas mixed with hydrogen or pure hydrogen. It reduces the dependence of verification stations on upstream gas sources and is unaffected by the pressure and flow rate of downstream natural gas mixed with hydrogen or pure hydrogen. This expands the verification capabilities of natural gas mixed with hydrogen or pure hydrogen flow metering verification stations and further improves the flow value traceability system.

[0016] Compared to existing calibration devices in the field of natural gas and hydrogen calibration technology, the loop design reduces the dependence of calibration stations on upstream gas sources and is not affected by the pressure and flow rate of downstream natural gas mixed with hydrogen or pure hydrogen. This can expand the calibration capabilities of natural gas mixed with hydrogen or pure hydrogen flow metering calibration stations and further improve the flow value traceability system.

[0017] Working-grade standard flow meters do not require disassembly for testing. Instead, smaller-diameter transfer turbine flow meters can be sent to authorized calibration institutions for higher-precision standard device traceability. Transfer turbine flow meters are easier to disassemble, assemble, and transport. The traceable transfer turbine flow meters can be used to transfer the measurement values ​​of working-grade standard flow meters, saving labor and economic costs. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the overall process of this utility model;

[0019] Figure 2 This is a topology diagram of the calibration and control system of this utility model;

[0020] Figure 3 This is a schematic diagram of the overall structure of this utility model;

[0021] In the diagram: 1. Gas supply and exhaust device; 2. Filter device; 3. Circulating fan; 4. Heat exchanger; 5. Temperature control system; 6. Bypass regulating device; 7. Working-grade standard device; 8. Device under test; 9. Transfer turbine device; 10. Verification control system; 11. Printer; 12. Switch; 13. Process control system PLC controller; 14. Electric forced sealing ball valve; 15. Pressure transmitter; 16. Temperature transmitter; 17. Combustible gas detector; 18. Mass spectrometer; 20. Differential pressure transmitter; 30. Fan circulation control system; 60. Flow regulating valve; 70. Verification mass flow meter; 71. Working-grade standard flow meter; 80. Flow meter under test; 90. Transfer turbine flow meter; 101. Process control system workstation; 102. Database server; 103. Metrological verification system workstation; 115. Metrological verification system data acquisition controller. 120. Metering-compensated pressure transmitter; 121. Metering-compensated temperature transmitter; 180. Analytical instruments. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings:

[0023] like Figures 1-3 The natural gas blending or pure hydrogen calibration loop shown includes a gas replenishment and exhaust device 1, a filter device 2, a circulating fan 3, a heat exchanger 4, a temperature control system 5, a bypass regulating device 6, a working-level standard device 7, a device under test 8, a transmission turbine device 9, and a calibration control system 10, forming a loop.

[0024] The air supply and exhaust device 1 is installed at the air inlet of the ring channel. The filter device 2, circulating fan 3, heat exchanger 4, temperature control system 5, bypass regulating device 6, working level standard device 7, tested device 8, and transmission turbine device 9 are connected in sequence according to the gas flow order.

[0025] The calibration control system 10 is installed in the control room to collect instrument signals from the loop for metrological calibration and process control.

[0026] like Figure 2 As shown, the calibration control system 10 employs two systems: a process control system workstation 101 and a metrological calibration system workstation 103. The core equipment of the process control system workstation 101 is a PLC controller, but a DCS controller can also be used. The electrically powered forced-seal ball valve 14, flow regulating valve 60, differential pressure transmitter 20, pressure transmitter 15, temperature transmitter 16, combustible gas detector 17, mass spectrometer 18, analytical instruments 180, temperature control system 5, and fan circulation control system 30 in the loop are connected to the AI, AO, DI, DO, and RS485 channels of the process control system PLC controller 13 via cables. The analytical instruments 180 include an online methane detector, an online hydrogen detector, and an online oxygen detector. The process control system PLC controller 13 is connected to the switch 12 via a network cable. The switch 12 is connected to the process control system workstation 101 via a network cable. On the screen of the process control system workstation 101, the pressure, temperature and flow of the gas medium in the loop can be regulated and controlled, valves can be switched, status parameters can be collected, monitored and displayed, and automatic verification and other tasks can be completed by interacting with the fan circulation control system 30 and the temperature control system 5.

[0027] The core equipment of the metrology verification system workstation 103 is the data acquisition controller. The flow meter under test 80, the transfer turbine flow meter 90, the working standard flow meter 71, the verification mass flow meter 70, the metrology-compensated pressure transmitter 120, and the metrology-compensated temperature transmitter 121 are connected to the HART, PI, and AI channels of the metrology verification system data acquisition controller 115 via cables. The metrology verification system data acquisition controller 115 is connected to the switch 12 via a network cable. The switch 12 is connected to the database server 102, the metrology verification system workstation 103, and the printer 11 via network cables. Database server 102 is mainly responsible for all data acquisition, processing and database storage related to the calibration of flow meters, temperature transmitters and pressure transmitters. Metrological calibration system workstation 103 can display flow meter flow rate, temperature, pressure, gas composition values ​​and other measured values ​​and fault alarm information in real time. It is responsible for configuring and issuing calibration tasks, selecting pipelines, calculating calibration data, storing calibration data, comparing and viewing inspection data, and generating calibration certificate reports. Printer 11 is used to print calibration certificates.

[0028] The gas replenishment and exhaust device 1 is used to replenish and regulate the pressure of natural gas mixed with hydrogen or pure hydrogen in the loop, or to release pressure by exhausting the gas. A pressure regulating valve is installed in the gas replenishment and exhaust device 1 to ensure that the gas pressure in the loop reaches the predetermined experimental pressure value. Once the gas pressure in the loop reaches the set value, the switch valve connecting the gas replenishment and exhaust device 1 to the loop is closed, stopping the gas replenishment to the loop pipeline. When it is necessary to remove the gas from the loop, the gas can be extracted through the exhaust function.

[0029] The filtration device 2 includes a filter, a pressure transmitter, a temperature transmitter, a differential pressure transmitter 20, a pressure gauge, a thermometer, and a bypass valve. The filtration device 2 relies on the filter to filter impurities in the gas to prevent damage to downstream equipment. The differential pressure transmitter 20 is used to detect the differential pressure across the filter. A large differential pressure indicates that the filter is blocked. In order not to affect normal calibration, the device can be switched to bypass.

[0030] The circulating fan 3 includes a frequency converter control system and at least one externally mounted magnetically coupled fan. The circulating fan 3 is the core equipment, and its functions are: first, to provide power for the circulation of the calibration gas in the loop, compensating for frictional losses in the gas flow within the annular pipe and pressure losses as the fluid passes through various devices; second, to provide a certain calibration flow rate for the loop, allowing for flow rate adjustment; and third, to meet different compression ratios under various pressure and flow conditions. The circulating fan 3 generally uses a high-speed motor, externally mounted and magnetically coupled, but other types of motors that meet the requirements can also be used.

[0031] The frequency converter control system employs HMI visual monitoring to control the speed of the circulating fan 3 to regulate flow, and displays system status, operating data, and fault diagnosis information in real time. The control system includes a touchscreen, PLC controller, and frequency converter, and is equipped with an emergency stop button. The frequency converter control system connects to the motor and sensors of the circulating fan 3, and communicates with the calibration control system 10 via the Modbus protocol.

[0032] Heat exchanger 4 is a shell-and-tube heat exchanger, but other types of heat exchangers can also be used. The function of heat exchanger 4 is to remove the heat generated by the work done on the natural gas mixed with hydrogen or pure hydrogen gas in the loop device due to the pressurization of the circulating fan 3.

[0033] The temperature control system 5 is a single unit, comprising a refrigeration unit, water pump, regulating valve, flow meter, electric heater, cold water tank circulation system, and supporting temperature control system 5. To meet the temperature stability requirements of the gaseous medium flowing within the loop during calibration, a heat exchanger is needed to rapidly and promptly cool the gaseous medium at the loop fan outlet. This is achieved through the temperature control system 5. The quality of the temperature control system 5 directly affects the measurement uncertainty of the loop system and the calibration efficiency of the flow meter, making it the core and challenging aspect of the loop design. The temperature control system 5 communicates with the calibration control system 10 via the Modbus protocol.

[0034] The bypass control device 6 includes a flow regulating valve, a mass flow meter, a temperature transmitter, and a pressure transmitter. In the loop, the flow regulation method is to use a frequency converter connected to the circulating fan 3 for large-flow regulation. However, due to the limitations of the circulating fan 3's flow regulation ratio, a bypass regulation is needed to ensure stable operation at low flow rates. The bypass design is calculated based on 20% of the maximum flow rate of a single circulating fan 3. The bypass pipeline flow is controlled by the bypass flow regulating valve and metered by a mass flow meter to achieve accurate flow regulation of natural gas mixed with hydrogen or pure hydrogen media across the entire range of the loop system. The temperature and pressure transmitters are used to convert the mass flow rate into volumetric flow rate for use in small-flow regulation control.

[0035] The working-grade standard device 7 includes at least two standard pipelines connected in parallel. Each standard pipeline has a manifold connected to its inlet and outlet. The standard pipelines are connected in series in the direction of gas flow from inlet to outlet, including an electrically powered forced-seal ball valve, a pressure gauge, a rectifier, a verification mass flow meter 70, a rectifier, a working-grade standard flow meter 71, and an electrically powered forced-seal ball valve. The verification mass flow meter 70 is a mass flow meter, but other types of flow meters can also be used. The working-grade standard flow meter 71 is a turbine flow meter. A temperature transmitter and a pressure transmitter are installed next to the verification mass flow meter 70 and the working-grade standard flow meter 71, respectively.

[0036] The device under test 8 includes at least two parallel test pipelines; each test pipeline has a manifold connected to its inlet and outlet. Each test pipeline, following the gas flow direction from inlet to outlet, consists of, in series, an electrically powered forced-seal ball valve, a rectifier, a first test platform, a rectifier, a second test platform, an expansion joint, a pressure gauge, and the electrically powered forced-seal ball valve. A flow meter 80 is placed at both the first and second test platforms. Unused platforms are replaced with straight pipe sections of the flow meter 80. A temperature transmitter and a pressure transmitter are installed next to each test platform.

[0037] The transfer turbine unit 9 includes a bypass pipeline and at least one transfer turbine pipeline, which are connected in parallel. The inlet and outlet of both the bypass pipeline and the transfer turbine pipeline are connected to a gas manifold. An electrically operated forced-seal ball valve is installed on the bypass pipeline. Each transfer turbine pipeline, in the direction of gas flow from inlet to outlet, consists of, in series, an electrically operated forced-seal ball valve, a pressure gauge, a rectifier, a transfer turbine flow meter, another rectifier, another transfer turbine flow meter, and another electrically operated forced-seal ball valve. A temperature transmitter and a pressure transmitter are installed next to each of the two transfer turbine flow meters.

[0038] The calibration and control system 10 comprises two parts: a metrological calibration system workstation 103 and a process control system workstation 101. They can share a single system or use two separate systems. The metrological calibration system workstation 103 collects and processes real-time monitoring data such as temperature, pressure, flow rate, and composition during the metrological calibration process; performs flow rate calculations; calibrates the tested flowmeter 80 using a working-grade standard flowmeter 71; calibrates the working-grade standard flowmeter 71 using a transfer turbine flowmeter 90; and displays, outputs, saves, and prints the calibration data. The process control system workstation 101 controls the regulation and flow of the gas medium, switches valves, collects, monitors, and displays status parameters, and interacts with the fan control system and temperature control system 5 to complete automatic calibration tasks.

[0039] like Figure 3 As shown in the diagram, the various devices are connected by pipelines to form a closed loop. Through the gas supply and exhaust device 1, and following the process flow sequence, the loop is slowly and steadily filled with high-pressure natural gas mixed with hydrogen or pure hydrogen gas, except for the device under test 8, to a pressure of 6.3 MPa. The flow meters 80 under test are installed on the first and second test positions according to their diameters, along with their matching temperature and pressure transmitters. Then, the electrically operated forced-seal ball valve at the inlet of the pipeline under test is opened, allowing the high-pressure natural gas mixed with hydrogen or pure hydrogen gas to enter the pipeline until the pressure before and after the valve is balanced.

[0040] When the working-grade standard device 7 calibrates the flow meter 80 under test, the calibration control system 10 sets the calibration flow point according to the flow range of the flow meter 80 under test and configures the pipeline combination of the working-grade standard flow meter 71. For example, the calibration flow point of the flow meter 80 under test is 3000m. 3 / h, 1200m 3 / h, 600m 3 / h、80m 3 / h, Figure 3 The standard working unit 7 includes 4 units of DN100 (flow range: 20~400m³). 3 71 standard flow meters (6 units, DN200, flow range: 80~1600m³ / h) are available.3 The working-grade standard flow meter 71 ( / h) can ultimately achieve a flow rate of 20-9600m³ / h. 3 The calibration flow rate range is [value missing]. When the calibration flow rate point is 3000 m³ / h... 3 At a flow rate of 1200 m³ / h, two DN200 standard flow meters 71 are used for calibration. The calibration control system 10 connects the pipelines of the two selected DN200 standard flow meters 71. 3 When the flow rate is 600 m³ / h, one DN200 standard flow meter 71 is used for calibration. The calibration control system 10 shuts off one of the pipelines of the two DN200 standard flow meters 71 to ensure that only one DN200 standard flow meter 71 pipeline is open. 3 At a flow rate of / h, two DN100 standard flow meters 71 are used for calibration. The calibration control system 10 first connects the pipelines of the two selected DN100 standard flow meters 71, and then closes the pipeline of one DN200 standard flow meter 71. The calibration flow point is 80m³ / h. 3 When the flow rate is / h, one DN100 working-class standard flow meter 71 is used for calibration. The calibration control system 10 closes one of the pipelines of the two DN100 working-class standard flow meters 71 to ensure that only one DN100 working-class standard flow meter 71 pipeline is open. During calibration, the flow rate is generally calibrated in descending order. When the working-class standard device 7 calibrates the device under test 8, all electrically powered forced-seal ball valves at the inlet and outlet of the working-class standard flow meter 71 pipeline must be closed, and the electrically powered forced-seal ball valve on the bypass pipeline of the transmission turbine device 9 must be opened.

[0041] During calibration, the flow rate at each calibration point within the loop is adjusted through the interlocking control of the circulating fan 3, the bypass flow regulating valve, and the bypass mass flow meter. Simultaneously, the circulating fan 3, along with the bypass flow regulating valve, performs pressurization at this flow rate, ensuring that the pressure increase of the circulating fan 3 equals the friction loss along the loop at the calibration flow rate. Because the work performed by the circulating fan 3 causes varying degrees of temperature rise in the gas medium within the loop, a heat exchanger 4 connected in series with the circulating fan 3 is used to balance the temperature changes of the medium. A temperature control system 5 is installed to cool the heat exchanger 4. The outlet gas medium temperature of the heat exchanger 4 is interlocked with the cooling water flow rate to control the temperature of the gas medium within the closed process system. Once the pressure, flow rate, and temperature of the loop system stabilize within the calibration requirements, data is collected to complete the calibration or verification of the natural gas blended with hydrogen or pure hydrogen flow rate under specific operating conditions.

[0042] The process for transferring the values ​​of the calibration standard device 7 for the turbine unit 9 is as follows: A. First, ensure that the values ​​of the two DN100 (flow range: 20~400m³) turbine units are transferred. 3 / h) Send the turbine flow meter 90 to an authorized calibration agency for higher precision standard device traceability. Open the bypass electric forced sealing ball valve of the device under test 8, close the electric forced sealing ball valves at the inlet and outlet of all the pipelines of the flow meter 80 under test, open the electric forced sealing ball valves at the inlet and outlet of the turbine flow meter 90, and close the bypass electric forced sealing ball valve of the turbine device 9; B. Use the average value of these two DN100 turbine flow meters 90 as the measurement result, and perform value transfer on the four DN100 working-class standard flow meters 71 of the same diameter in the working-class standard device 7; C. Connect the four DN100 working-class standard flow meters 71 in the working-class standard device 7 in parallel, and use one DN200 (flow range: 80~1600m³) in the working-class standard device 7. 3 / h) The working-class standard flow meter 71 is used to transfer the measurement value; D. This DN200 working-class standard flow meter 71 is then used to transfer the measurement value of the other 5 DN200 working-class standard flow meters 71 in the working-class standard device 7.

[0043] The working-grade standard device 7, calibrated by the transmission turbine flow meter 90, exhibits a relative expanded uncertainty better than 0.16% (k=2), repeatability better than 0.05%, and stability better than 0.05% / a, resulting in higher verification accuracy. Domestic natural gas verification stations generally can only verify flow meters with an accuracy of 1.0 class. According to the verification procedures, the relative expanded uncertainty of the working-grade standard device 7 should not exceed one-third of the absolute value of the maximum permissible error of the flow meter 80 under test. Therefore, the working-grade standard device 7, calibrated by the transmission turbine flow meter 90, can perform online actual flow verification of flow meters with an accuracy of 0.5 class.

[0044] The combustible gas detector 17 is used to monitor the environment for leaks of combustible gases such as methane or hydrogen, thereby preventing fires and explosions.

[0045] The calibration control system 10 can automatically configure pipelines, set calibration flow points, calibration times, and calibration time with a single click, automatically connect the process flow, automatically regulate pressure and control flow, automatically switch to standard pipelines, and has safety protection logic (including differential pressure alarm logic for valves before and after the pipeline, overspeed protection logic for standard gauges, low pressure alarm and interlock protection logic for the loop). It automatically judges the stability of fluid temperature, pressure, and flow, automatically starts calibration and automatically analyzes calibration results, automatically performs recalibration when the calibration results are unqualified, automatically restores the initial process after the calibration task is completed, and automatically generates calibration certificates and original data records after the calibration task is completed.

[0046] The above embodiments are merely illustrative of the concept and implementation of this utility model, and are not intended to limit it. Under the concept of this utility model, the technical solutions without substantial changes are still within the scope of protection.

Claims

1. A calibration loop for detecting and calibrating natural gas blended with hydrogen or pure hydrogen, characterized in that: The system includes a gas supply and exhaust device (1), a filter device (2), a circulating fan (3), a heat exchanger (4), a temperature control system (5), a bypass regulating device (6), a working standard device (7), a device under test (8), a transmission turbine device (9), and a calibration control system (10), which are connected in sequence according to the gas flow order to form a loop. The gas supply and exhaust device (1) is installed at the air inlet of the loop and has a built-in pressure regulating valve. The device under test (8) is equipped with a flow meter (80). The calibration control system (10) is installed in the control room.

2. The natural gas blending or pure hydrogen calibration loop according to claim 1, characterized in that: The filtration device (2) includes a filter, a pressure transmitter, a temperature transmitter, a differential pressure transmitter (20), a pressure gauge, and a thermometer.

3. The natural gas blending or pure hydrogen calibration loop according to claim 1, characterized in that: The bypass regulating device (6) includes a flow regulating valve, a mass flow meter, a temperature transmitter, and a pressure transmitter.

4. The natural gas blending or pure hydrogen calibration loop according to claim 1, characterized in that: The working-level standard device (7) includes at least two standard pipelines connected in parallel. The standard pipelines are connected in series with an electric forced sealing ball valve, a pressure gauge, a verification mass flow meter (70) and a working-level standard flow meter (71) in the gas flow direction from inlet to outlet. A rectifier is connected to both ends of the verification mass flow meter.

5. The natural gas blending or pure hydrogen calibration loop according to claim 1, characterized in that: The device under test (8) includes at least two parallel test pipelines. The test pipelines are connected in series in the direction of gas flow from inlet to outlet: first test station, second test station, expansion joint and pressure gauge. A rectifier is connected to both ends of the first test station. A flow meter (80) is placed at the first test station and the second test station.

6. The natural gas blending or pure hydrogen calibration loop according to claim 1, characterized in that: The transmission turbine device (9) includes a bypass pipeline and at least one transmission turbine pipeline. The bypass pipeline and the transmission turbine pipeline are connected in parallel. The transmission turbine pipeline is connected in series with a pressure gauge and two transmission turbine flow meters (90). A rectifier is connected to the front end of each transmission turbine flow meter (90).

7. The natural gas blending or pure hydrogen calibration loop according to claim 1, characterized in that: The calibration control system (10) includes a metrological calibration system workstation (103) and a process control system workstation (101); the process control system workstation (101) includes calibration of gas medium flow rate regulation, valve switching, fan control system and temperature control system.

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