Hydrogen-rich natural gas sound velocity measurement and verification method based on external clamping type ultrasonic flowmeter

Abstract

The invention provides a hydrogen-rich natural gas sound velocity measurement and verification method based on an external clamping type ultrasonic flowmeter, and a hydrogen-rich natural gas mixture sound velocity measurement device with adjustable components is used in the method. The method comprises the following steps of building the component-adjustable hydrogen-rich natural gas mixture sound velocity measurement device, representing the external clamping type ultrasonic flowmeter, calibrating the external clamping type ultrasonic flowmeter, measuring the sound velocity of hydrogen-rich natural gas, calculating the uncertainty of sound velocity measurement and correcting a standard model. According to the method, a self-made sound velocity measuring device based on an external clamping type ultrasonic flowmeter is included, the device can keep temperature, pressure and other thermodynamic conditions stable and controllable in the whole measuring process, and therefore it is guaranteed that accurate sound velocity characteristics are obtained, and then a prediction model of the characteristics of the current gaseous natural gas and similar mixtures is corrected; a contribution is made to the accuracy of a thermodynamic property calculation program in a field flow instrument, and the ultrasonic flowmeter installed on a pipeline for conveying pure hydrogen or mixed hydrogen is calibrated in the future.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrasonic gas flow measurement and detection, and particularly relates to a method for measuring and correcting the sound speed of hydrogen-rich natural gas based on an external clamp ultrasonic flowmeter. Background Art

[0002] Increasing the hydrogen content in natural gas to reduce carbon emissions is an important way to achieve energy transformation in the gas field. However, while the hydrogen content in the natural gas pipeline network increases, the heterogeneity of the thermodynamic properties of the hydrogen-rich mixture will also become greater and greater. Moreover, the relevant mixtures have never been used in large quantities before, and their specific properties and flow rates have not been accurately measured and calculated.

[0003] Currently, the AGA-8 and AGA-10 thermodynamic models are widely adopted internationally as the calculation standards for the properties of gaseous natural gas and its mixtures. This standard uses standard natural gas and nitrogen as reference fluids to establish a thermodynamic property calculation model, and calculates the properties and flow rates of gaseous natural gas and its mixtures with different media. However, the hydrogen content limit in the model is within 10 mol%, which means that the model cannot accurately predict the properties and flow rates of hydrogen-rich natural gas exceeding this limit value. Considering that the thermodynamic properties of hydrogen-rich mixtures have an important impact on gas flow measurement and gas trade settlement, and it is very likely that the hydrogen content in future natural gas will exceed 10 mol%. Under such conditions, it is necessary to find a method to accurately measure the thermodynamic properties of high-hydrogen-content mixtures to verify or correct the existing prediction models and the relevant calculation models inside the flowmeter, so as to achieve accurate measurement of the flow rate of hydrogen-rich mixtures.

[0004] In the process of obtaining the thermodynamic properties of hydrogen-rich mixtures, the sound speed of the mixture is the most critical parameter to be measured, because it is one of the most useful characteristic parameters required to achieve an accurate equation of state and the calculation of density, pressure, and specific heat, and is also closely related to the measured value of the mixture flow rate. However, due to the low density and high diffusivity of hydrogen, current traditional flow measurement tools, including orifice flowmeters and turbine flowmeters, often have problems such as inaccurate flow readings and low measurement efficiency when applied to hydrogen-rich mixtures. Therefore, it is necessary to use an advanced ultrasonic flowmeter for non-invasive flow measurement, which urgently requires a specific device and method compatible with hydrogen to measure the sound speed in hydrogen-rich gas mixtures. Summary of the Invention

[0005] In view of the problems that existing traditional flow measurement tools such as orifice plate flow meters and turbine flow meters often have inaccurate flow readings and low measurement efficiency when applied to hydrogen-rich mixtures, it is necessary to use an advanced ultrasonic flow meter for non-invasive flow measurement. This poses an urgent technical problem of measuring the speed of sound in hydrogen-rich gas mixtures using specific equipment and methods compatible with hydrogen. The present invention provides a method for measuring and correcting the speed of sound in hydrogen-rich natural gas based on an external clamp-on ultrasonic flow meter.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A method for measuring and correcting the speed of sound in hydrogen-rich natural gas based on an external clamp-on ultrasonic flow meter. In this method, a device for measuring the speed of sound in a hydrogen-rich natural gas mixture with adjustable components is used. The device includes a vacuum chamber and a gas distribution unit. The gas distribution unit includes a gas mixer and an on-line chromatograph analyzer internally connected to the gas mixer. The outlet of the gas mixer is connected to an inlet pipe extending into the vacuum chamber. In the vacuum chamber, there are relatively arranged a first flange and a second flange. In a plurality of fixing holes around the first flange and the second flange, support rods are connected by bolts. The outer ends of the support rods are fixedly connected to the inner wall of the vacuum chamber. On the relative inner sides of the first flange and the second flange, a pressure pipe is fixed. The inner wall of the pressure pipe is provided with a thermometer, a pressure gauge, and two heat exchangers arranged relatively. The outer wall of the pressure pipe is provided with a fixed guide rail. The transducer of the external clamp-on ultrasonic flow meter for measuring the speed of sound in the gas is closely attached to the outer wall of the pressure pipe by the fixed guide rail. The inner end of the inlet pipe extending into the vacuum chamber is hermetically connected to the outer end of the central hole of the first flange. The inlet of the pressure pipe is hermetically connected to the inner end of the central hole of the first flange. The outlet of the pressure pipe is hermetically connected to the inner end of the central hole of the second flange. The outer end of the central hole of the second flange is hermetically connected to an outlet pipe extending outside the vacuum chamber. On both sides of the outlet pipe, there are cold / hot fluid inlet pipes and cold / hot fluid outlet pipes extending into the vacuum chamber. The inner ends of the cold / hot fluid inlet pipes and the cold / hot fluid outlet pipes communicate with each other outside the first flange. The outer ends of the cold / hot fluid inlet pipes and the cold / hot fluid outlet pipes are connected to existing external cold / hot baths.

[0008] The method includes the following steps:

[0009] S1. Construction of a device for measuring the speed of sound in a hydrogen-rich natural gas mixture with adjustable components;

[0010] S2. Characterization of the external clamp-on ultrasonic flow meter: According to the pipe parameters of the fluid flow and the fluid properties, through experiments, determine the installation method of the transducer of the external clamp-on ultrasonic flow meter as diagonal installation or reflection installation, and the specific installation spacing of the transducer to maximize the quality of the sound signal received by the transducer and obtain a high signal-to-noise ratio.

[0011] S3. External clamp-on ultrasonic flowmeter calibration: Under controlled laboratory conditions with a pressure of 0 MPa ≤ p ≤ 12 MPa and a temperature of -10 °C ≤ T ≤ 65 °C, the experimental value of the sound velocity c obtained by the external clamp-on ultrasonic flowmeter in a reference fluid with a known sound velocity r,exp is compared with the reference value of the sound velocity c r,ref and the sound velocity measurement deviation D between the experimental value of the sound velocity and the reference value of the sound velocity at each measurement point is calculated through the equation to make the deviation lower than the preset threshold, and the calibration equation c c = c r,exp [a - b×(T + 273)] is obtained through deviation fitting, where c c is the sound velocity after calibration correction, a and b are deviation fitting coefficients, and the uncertainty u(c r,ref ) introduced by the reference fluid is calculated as follows:

[0012]

[0013] where u(p) and u(T) are the uncertainty of pressure measurement and the uncertainty of temperature measurement respectively, and are the sensitivity coefficients of the sound velocity with respect to pressure and temperature respectively, and R is the uncertainty introduced by measurement repeatability;

[0014] S4. Sound velocity measurement of hydrogen-rich natural gas: Use the external clamp-on ultrasonic flowmeter characterized in step S2 and calibrated in step S3 to measure the sound velocity in hydrogen-rich natural gas. The hydrogen-rich natural gas mixture is prepared by the gravimetric method, and the component uncertainty of the natural gas mixed with hydrogen is ≤ 0.1%. During measurement, the temperature and pressure of the device are constant, the fluid is stationary, and the sound velocity measurement value is calibrated and corrected through the calibration equation obtained in step S3;

[0015] S5. Calculation of sound velocity measurement uncertainty: The relative expanded uncertainty u(c c ) of the sound velocity measurement of the hydrogen-rich natural gas mixture includes the uncertainty of the mixture components and the uncertainties generated by measurement repeatability, temperature, pressure, and the calibration equation, and is specifically calculated by the following formula:

[0016]

[0017] where, and are the uncertainties introduced by temperature and pressure measurements respectively, u(x) is the uncertainty introduced by the mixture components, u cal is the uncertainty generated by the calibration equation, and R is the uncertainty introduced by measurement repeatability;

[0018] Obtain the measurement range interval of the actual sound speed by calculating the measurement uncertainty of the sound speed and the sound speed measurement value corrected by calibration equation in step S4.

[0019] S6. Standard model correction: Compare the sound speed measurement value of the hydrogen-rich natural gas mixture corrected by the calibration equation in step S4 and the measurement uncertainty of the sound speed obtained in step S5 with the expected value of the sound speed calculated by the thermodynamic models provided by AGA-8 and AGA-10 and the uncertainty range respectively, plot the deviation curve between the actual value of the sound speed measurement and the expected value of the sound speed calculated by the model, and correct the embedded thermodynamic calculation model of the gas flowmeter using the deviation curve.

[0020] Furthermore, a pressure and flow regulating valve is provided in the gas distribution unit outside the vacuum chamber.

[0021] Furthermore, a Teflon gasket is sleeved in the central holes of the first flange and the second flange, and the inlet pipe and the outlet pipe are hermetically connected to the outer ends of the central holes of the flanges through the Teflon gasket.

[0022] Furthermore, the pressure pipe is made of stainless steel, and the inner diameter of the pressure pipe is 50mm, 100mm or 150mm.

[0023] Furthermore, a coupling agent is coated on the outer wall of the pressure pipe, and the transducer of the clamp-on gas ultrasonic flowmeter is coupled to the outer wall of the pressure pipe through the coupling agent.

[0024] Furthermore, in steps S2 and S3, the clamp-on ultrasonic flowmeter is calibrated under the conditions of 3 pressure points of 1MPa, 2MPa, and 3MPa and 3 temperature points of 10°C, 20°C, and 30°C, and the sound speed measurement device of the hydrogen-rich natural gas mixture with adjustable components is selected as the experimental device, and the reference fluid selected in step S3 is nitrogen or helium.

[0025] Furthermore, the preset threshold of the sound speed measurement deviation in step S3 is 0.2%.

[0026] Furthermore, the hydrogen-rich natural gas mixture prepared by the gravimetric method in step S4 has a hydrogen proportion of 80% and a standard natural gas proportion of 20%, and the uncertainty of the standard natural gas components is 0.05%.

[0027] Furthermore, the uncertainty u(x), u cal and R are calculated respectively by the following formulas:

[0028]

[0029] where u(x ref) is the component uncertainty of natural gas mixed with hydrogen, is the sensitivity coefficient for synthesizing the speed of sound with respect to uncertainty, u(c hh ) is the uncertainty of the speed of sound of natural gas mixed with hydrogen, res mean is the average residual between the expected value of the speed of sound calculated by the speed of sound and thermodynamic model after calibration correction through the calibration equation, k is the coverage factor, n is the number of sample repeated measurements, c i is the measured value of the speed of sound in the i-th test, is the average value of the measured speed of sound in the i-th test.

[0030] Compared with the prior art, the method for measuring and correcting the speed of sound of hydrogen-rich natural gas based on an external clamp-on ultrasonic flowmeter provided by the present invention includes a self-made speed of sound measurement device. The device is based on an external clamp-on ultrasonic flowmeter, overcoming the problems that traditional flow measurement tools such as orifice flowmeters and turbine flowmeters often have inaccurate flow readings and low measurement efficiency when applied to hydrogen-rich mixtures. The device can keep thermodynamic conditions such as temperature and pressure stable and controllable throughout the measurement process, covering the entire range of 0 MPa ≤ p ≤ 12 MPa and -10 °C ≤ T ≤ 65 °C, thereby ensuring accurate speed of sound characteristics of natural gas mixtures with high hydrogen content under different working conditions from a metrological perspective, and further verifying or correcting the prediction models of current gaseous natural gas and similar mixture characteristics, contributing to the accuracy of the internal thermodynamic characteristic calculation program of on-site flow meters, and calibrating ultrasonic flow meters installed on pipelines transporting pure hydrogen or hydrogen mixtures in the future, providing an important reference for the trade settlement of high-hydrogen-content gases in the future. Description of the Drawings

[0031] Figure 1 is a schematic structural diagram of a device for measuring the speed of sound of a hydrogen-rich natural gas mixture with adjustable components provided by the present invention.

[0032] Figure 2 is Figure 1 a schematic structural diagram of the first flange and the second flange in

[0033] Figure 3 is a schematic flow diagram of a method for measuring and correcting the speed of sound of hydrogen-rich natural gas based on an external clamp-on ultrasonic flowmeter provided by the present invention.

[0034] Figure 4 is a schematic diagram of the principle of measuring the speed of sound by an external clamp-on ultrasonic flowmeter with transducers arranged diagonally provided by the present invention.

[0035] Figure 5 is a schematic diagram of the speed of sound deviation of helium measured by an external clamp-on ultrasonic flowmeter provided by the present invention.

[0036] Figure 6It is a schematic diagram of the measured and corrected sound speed of a hydrogen and natural gas mixture provided by the present invention.

[0037] Figure 7 It is a schematic diagram of the deviation curve between the actual measured sound speed of hydrogen-rich natural gas provided by the present invention and the expected sound speed provided by the AGA model.

[0038] In the figure, 1 is a vacuum chamber; 2 is a gas mixer; 3 is an inlet pipe; 4 is a first flange; 41 is a fixing hole; 42 is a central hole; 5 is a second flange; 6 is a support rod; 7 is a pressure pipe; 8 is a heat exchanger; 9 is a fixing guide rail; 10 is an external clamp type gas ultrasonic flowmeter; 11 is an outlet pipe; 12 is a cold / hot fluid inlet pipe; 13 is a cold / hot fluid outlet pipe; 14 is a pressure and flow regulating valve; 15 is a coupling. Detailed implementation manners

[0039] In order to make the technical means, creative features, achieved purposes and functions of the present invention easy to understand, the present invention will be further described below with reference to specific drawings.

[0040] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "longitudinal", "radial", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention. In the description of the present invention, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0041] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "installation", "connection", "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, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0042] Please refer to Figure 1 and Figure 2As shown in the figure, the present invention provides a method for measuring and correcting the sound speed of hydrogen-rich natural gas based on an external clamp type ultrasonic flowmeter. In this method, a device for measuring the sound speed of a hydrogen-rich natural gas mixture with adjustable components is used. The device includes a vacuum chamber 1 and a gas distribution unit. The gas distribution unit includes a gas mixer 2 and an on-line chromatograph analyzer (not shown in the figure) that is internally connected to the gas mixer. The specific structures and working principles of the gas mixer 2 and the on-line chromatograph analyzer are well-known prior arts to those skilled in the art, and thus will not be described in detail here. The outlet of the gas mixer 2 is connected to an inlet pipe 3 that extends into the vacuum chamber 1. In the vacuum chamber 1, a first flange 4 and a second flange 5 are arranged oppositely. A support rod 6 is connected by bolts in a plurality of fixing holes 41 around the first flange 4 and the second flange 5. The outer end of the support rod 6 is fixedly connected to the inner wall of the vacuum chamber 1. Pressure pipes 7 are fixedly arranged on the opposite inner sides of the first flange 4 and the second flange 5. A thermometer T, a pressure gauge P, and two heat exchangers 8 arranged oppositely are provided on the inner wall of the pressure pipe 7. The thermometer T and the pressure gauge P are used to measure the temperature and pressure of the hydrogen-rich natural gas mixture in the pressure pipe 7, and the measurement uncertainties are ±0.02 °C and ±0.025 MPa. The two heat exchangers 8 can be arranged on the front inner wall and the rear inner wall of the pressure pipe 7, and it should be noted that they are staggered from the external clamp type gas ultrasonic flowmeter 10 arranged on the outer wall of the pressure pipe 7 (the external clamp type gas ultrasonic flowmeter 10 can be arranged on the left / right outer wall of the pressure pipe 7). The two heat exchangers 8 are used for precise control of the temperature of the mixed gas, and specifically, an existing non-contact heat exchanger can be used to achieve this. A fixed guide rail 9 is provided on the outer wall of the pressure pipe 7. The transducer of the external clamp type gas ultrasonic flowmeter 10 for measuring the sound speed of the gas is closely attached to the outer wall of the pressure pipe 7 by the fixed guide rail 9. The external clamp type gas ultrasonic flowmeter 10 uses an ultrasonic Lamb wave transducer and is used to measure the sound speed of the mixed gas flowing through the pressure pipe 7. The inner end of the inlet pipe 3 extending into the vacuum chamber 1 is hermetically connected to the outer end of the central hole of the first flange 4. The inlet of the pressure pipe 7 is hermetically connected to the inner end of the central hole 42 of the first flange 4. The outlet of the pressure pipe 7 is hermetically connected to the inner end of the central hole 42 of the second flange 5. The outer end of the central hole 42 of the second flange 5 is hermetically connected to an outlet pipe 11 that extends outside the vacuum chamber 1. Cold / hot fluid inlet pipes 12 and cold / hot fluid outlet pipes 13 that extend into the vacuum chamber 1 are provided on both sides of the outlet pipe. The inner ends of the cold / hot fluid inlet pipes 12 and the cold / hot fluid outlet pipes 13 communicate with each other outside the first flange 4. The outer ends of the cold / hot fluid inlet pipes 12 and the cold / hot fluid outlet pipes 13 are connected to an existing external cold / hot bath. In this device, since the foregoing various hardware components are all mature hardware, it is very easy for those of ordinary skill in the art to assemble and connect them.

[0043] When the device for measuring the sound speed of a hydrogen-rich natural gas mixture with adjustable components provided by the present invention is in operation, first, the proportion of the components of the hydrogen-rich natural gas mixture is adjusted in the gas mixer by existing methods such as ultrasonic atomization or vortex stirring. At the same time, the mixing deviation is corrected through feedback control by an on-line chromatographic analyzer, so as to continuously output a hydrogen-rich natural gas mixture with controllable composition. Then, the hydrogen-rich natural gas mixture mixed in the gas mixer is injected into the pressure pipeline through the central hole of the first flange after passing through the inlet pipeline. The temperature and pressure are adjusted to appropriate working conditions to fill the hydrogen-rich natural gas mixture in the pressure pipeline. The sound speed of the hydrogen-rich natural gas mixture in the pressure pipeline is measured by an external clamp type gas ultrasonic flowmeter. During the measurement process, the gas can be kept flowing or the pipeline can be closed to make the gas static. After the measurement is completed, the gas is discharged from the outlet pipeline. During the measurement, two independently operating heat exchangers perform precise temperature control of the mixed gas, and the temperature stability can be better than ±0.1°C. At the same time, a thermometer and a pressure gauge measure the temperature and pressure of the hydrogen-rich natural gas mixture in the pressure pipeline. The temperature in the vacuum chamber is controlled by the cold / hot fluid in the cold / hot fluid inlet and outlet pipelines. This device is based on an external clamp type ultrasonic flowmeter and can be used to measure the sound speed in a hydrogen-rich natural gas mixture, overcoming the problems that often occur in existing traditional flow measurement methods including orifice flowmeters and turbine flowmeters, such as inaccurate flow readings and low measurement efficiency when applied to hydrogen-rich mixtures. During the whole measurement process, stable and controllable thermodynamic conditions, especially temperature and pressure, are maintained, that is, the sound speed characteristics measurement with stable and controllable thermodynamic conditions such as process temperature and pressure is realized, so as to effectively obtain the accurate sound speed characteristics of a natural gas mixture with adjustable components and high hydrogen content under different working conditions, verify or correct the existing calculation models of gaseous natural gas and similar mixture characteristics, realize the timely correction and accurate calculation of the flow measurement of hydrogen-rich natural gas, and provide an important reference for gas flow metering and gas trade settlement.

[0044] As a specific embodiment, please refer to Figure 1 As shown, a pressure flow and regulating valve 14 is provided in the gas distribution unit outside the vacuum chamber 1. Thus, the pressure and flow of the hydrogen-rich natural gas mixture with adjustable components continuously output by the gas mixer 2 can be adjusted through the pressure and flow regulating valve 14 of the existing technology, so as to continuously output a hydrogen-rich natural gas mixture with controllable composition, adjustable pressure and flow.

[0045] As a specific embodiment, a Teflon gasket (not shown in the figure) is sleeved in the central holes 42 of the first flange 4 and the second flange 5. The inlet pipeline 3 and the outlet pipeline 12 are hermetically connected to the outer ends of the central holes 42 of the flange through the Teflon gasket. Thus, while allowing the hydrogen-rich natural gas mixture to flow through, the structural integrity of the flange and the pressure tightness can be maintained when the pressure pipeline 7 is pressurized.

[0046] As a specific embodiment, the pressure pipeline 7 is a pipeline made of stainless steel and is used as a pressure vessel. The nominal inner diameter can be freely selected. Specifically, the inner diameter of the pressure pipeline 7 can be 50 mm, 100 mm, 150 mm, etc., and the pipeline can withstand a gas with a pressure of 10 MPa.

[0047] As a specific embodiment, please refer to Figure 1 As shown, a coupling agent 15 is coated on the outer wall of the pressure pipeline 7, and the transducer of the external clamp type gas ultrasonic flowmeter 10 is coupled to the outer wall of the pressure pipeline 7 through the coupling agent 15, thereby reducing the influence of noise and vibration on the measurement result.

[0048] Please refer to Figure 1 As shown, the method for measuring and correcting the sound velocity of hydrogen-rich natural gas based on an external clamp type ultrasonic flowmeter includes the following steps:

[0049] S1. Build a sound velocity measurement device for a hydrogen-rich natural gas mixture with adjustable components. The built measurement device is as Figure 1 shown. Specifically, a FLUXUS G601 external clamp type gas ultrasonic flowmeter (component 10) is selected for sound velocity measurement, and the transducers of the external clamp type ultrasonic flowmeter are arranged diagonally; the measurement principle is as Figure 4 shown. The sound velocity is calculated by the upstream and downstream times of ultrasonic propagation measured. The calculation formula is as follows:

[0050]

[0051] Among them, c f is the fluid sound velocity, L is the ultrasonic propagation path length, t1 is the time for ultrasonic wave to propagate countercurrently inside the fluid, and t2 is the time for ultrasonic wave to propagate downstream inside the fluid. The measurement is carried out when the fluid pipeline is filled with static fluid, that is, the flow rate is 0. At this time, the ultrasonic propagation time is the same in both directions, that is, t1 = t2, and the medium sound velocity at a given temperature and pressure can be simply and accurately obtained.

[0052] S2. Characterization of the external clamp type ultrasonic flowmeter: According to the pipeline parameters of the fluid flow and the fluid properties, determine the installation method of the transducer of the external clamp type ultrasonic flowmeter as diagonal installation or reflection installation through experiments, as well as the specific installation spacing of the transducers, so as to maximize the quality of the sound signal received by the transducers and obtain a high signal-to-noise ratio.

[0053] S3. Calibration of the external clamp type ultrasonic flowmeter: Before measuring the sound velocity of the hydrogen-rich mixture, calibrate the external clamp type ultrasonic flowmeter from a metrological perspective, that is, under controlled laboratory conditions where the pressure is 0 MPa ≤ p ≤ 12 MPa and the temperature is -10 °C ≤ T ≤ 65 °C, the experimental value c r,exp of the sound velocity obtained by the external clamp type ultrasonic flowmeter in a reference fluid (such as nitrogen or helium) with a known sound velocity is compared with the reference value c of the sound velocityr,ref Compare through the equation Calculate the sound velocity measurement deviation D between the experimental value of the sound velocity at each measurement point and the reference value of the sound velocity, make the deviation lower than the preset threshold, and obtain the calibration equation c through deviation fitting c = c r,exp [a - b×(T + 273)], where c c is the sound velocity after calibration correction, a and b are deviation fitting coefficients, and at the same time calculate the uncertainty u(c r,ref ) introduced by the reference fluid as follows:

[0054]

[0055] where, u(p) and u(T) are the pressure measurement uncertainty and temperature measurement uncertainty respectively, and are the sensitivity coefficients of the sound velocity with respect to pressure and temperature respectively, and R is the uncertainty introduced by measurement repeatability.

[0056] As a specific embodiment, select helium as the reference fluid, and calibrate the clamp-on ultrasonic flowmeter under the conditions of 3 pressure points of 1 MPa, 2 MPa, and 3 MPa and 3 temperature points of 10 °C, 20 °C, and 30 °C, and select Figure 1 The sound velocity measurement device of the hydrogen-rich natural gas mixture with adjustable components shown is used as the experimental device. First, output pure helium through the gas mixer 2, inject it into the stainless steel pipe 7 through the inlet pipe 3, and control the pressure and temperature in the pipe to be stable. Then, according to the fluid pipe structure and fluid properties, it is experimentally determined that the transducers of the clamp-on ultrasonic flowmeter adopt Figure 4 The diagonal installation layout shown, the installation distance between the transducers is 20 mm, and at this time the signal-to-noise ratio is 28 and the signal quality is high. Then compare the experimental value c of the sound velocity obtained in helium r,exp with the reference value c of the sound velocity r,ref (calculated by the Helmholtz equation of state), and calculate the deviation between the experimental value of the sound velocity and the reference value of the sound velocity through the equation as shown in Figure 5 . These deviations are basically lower than 0.2% (preset threshold), indicating that there is good consistency between the measured experimental sound velocity and the reference sound velocity. According to the measurement results, the calibration equation of the clamp-on ultrasonic flowmeter has little correlation with pressure and is mainly affected by temperature. Obtain the calibration equation c c = c r,exp [1.005 - 2.032×10 -5 (T + 273)], that is, when helium is selected as the reference fluid, the deviation fitting coefficient a = 1.005, and the coefficient b = 2.032×10 -5. Further calculation gives the relative expanded uncertainty u(c r,ref ) introduced by the reference fluid helium sound speed measurement as 0.076%.

[0057] S4. Sound speed measurement of hydrogen-rich natural gas: Use an external clamp-on ultrasonic flowmeter characterized in step S2 and calibrated in step S3 to measure the sound speed in hydrogen-rich natural gas. The hydrogen-rich natural gas mixture is prepared by the gravimetric method, and the component uncertainty of the natural gas mixed with hydrogen is ≤0.1%. During the measurement, the device temperature and pressure are constant, the fluid is stationary, and the measured sound speed value is calibrated and corrected by the calibration equation obtained in step S3.

[0058] As a specific embodiment, in the hydrogen-rich natural gas mixture prepared by the gravimetric method in step S4, hydrogen accounts for 80% and standard natural gas accounts for 20%. The component uncertainty of the standard natural gas is 0.05%. The mixture is output through the gas mixer 2 and injected into the stainless steel pipe 7 through the inlet pipe 3. Sound speed measurements are carried out at three pressure points of 1 MPa, 2 MPa, and 3 MPa and three temperature points of 10 °C, 20 °C, and 30 °C. During the measurement, use an external clamp-on ultrasonic flowmeter calibrated in step S3, maintain the diagonal installation arrangement of the transducers, keep the device temperature and pressure constant during the measurement, and the fluid is stationary. The measured sound speed value is calibrated and corrected by the calibration equation c c = c exp [1.005 - 2.032×10 -5 (T + 273)], as shown specifically in Figure 6 .

[0059] S5. Calculation of sound speed measurement uncertainty: The relative expanded uncertainty u(c c ) of the hydrogen-rich natural gas mixture sound speed measurement includes the mixture component uncertainty and the uncertainties caused by measurement repeatability, temperature, pressure, and calibration equation, and is specifically calculated by the following formula:

[0060]

[0061] where, and are the uncertainties introduced by temperature and pressure measurements respectively, u(x) is the uncertainty introduced by the mixture components, u cal is the uncertainty caused by the calibration equation, and R is the uncertainty introduced by measurement repeatability;

[0062] Obtain the measurement range interval of the actual sound speed through the calculated sound speed measurement uncertainty and the sound speed measurement value calibrated and corrected by the calibration equation in step S4. Specifically, the measurement range interval of the actual sound speed can be expressed as [corrected sound speed measurement value - sound speed measurement uncertainty, corrected sound speed measurement value + sound speed measurement uncertainty].

[0063] Furthermore, in step S5, the uncertainty u(x), u cal and R are calculated respectively by the following formulas:

[0064]

[0065] wherein, u(x ref ) is the component uncertainty of natural gas mixed with hydrogen; is the sensitivity coefficient for synthesizing the speed of sound with respect to the uncertainty; u(c hh ) is the speed of sound uncertainty of natural gas mixed with hydrogen; res mean is the average value of the residuals between the speed of sound expected value calculated by the speed of sound after calibration and correction through the calibration equation and the thermodynamic model; k is the coverage factor, taking k = 2 (corresponding to a confidence probability of about 95% under the normal distribution); n is the number of sample repeated measurements; c i is the speed of sound value measured in the i-th test; is the average value of the speed of sound measured in the i-th test. Among them, the uncertainties of u(x ref ) and u(c hh ) can be calculated with reference to the formula of the uncertainty u(c r,ref ) introduced by the reference fluid in step S3.

[0066] As a specific embodiment, during the measurement, several uncertainties of the hydrogen-rich natural gas mixture are synthesized through the equation in step S5, and u(c c ) = 0.096% is calculated.

[0067] S6. Standard model correction: Compare the speed of sound measurement value of the hydrogen-rich natural gas mixture after calibration and correction through the calibration equation in step S4 and the speed of sound measurement uncertainty obtained in step S5 with the speed of sound expected values calculated by the existing AGA-8 and AGA-10 thermodynamic models (calculated through a python programming program according to the AGA report, mixture components, and measurement conditions, the expanded uncertainty of the model's speed of sound is 0.2%, k = 2) and the uncertainty range respectively, and draw the deviation curve between the actual value of the speed of sound measurement and the speed of sound expected value calculated by the model. The deviation curve is as Figure 7As shown, the deviation is within the range of 0.05% to 0.35%, which indicates that under the conditions of higher temperature and lower pressure, the measured value of the sound velocity of the hydrogen-rich mixture using the clamp-on ultrasonic flowmeter is relatively consistent with the expected reference value calculated by the thermodynamic model provided by AGA. When the temperature is lower, it is necessary to use the deviation curve to correct the embedded thermodynamic calculation model of existing flow meters such as gas flow meters by up to 3%, and then correct the thermodynamic characteristic calculation program inside the future on-site flow meter for measuring hydrogen-rich natural gas or calibrate the measurement results.

[0068] Compared with the prior art, the method for measuring and correcting the sound velocity of hydrogen-rich natural gas based on the clamp-on ultrasonic flowmeter provided by the present invention includes a self-made sound velocity measurement device based on the clamp-on ultrasonic flowmeter, which overcomes the problems often encountered in the application of traditional flow measurement tools such as orifice flow meters and turbine flow meters to hydrogen-rich mixtures, such as inaccurate flow readings and low measurement efficiency. During the entire measurement process, the device can maintain stable and controllable thermodynamic conditions such as temperature and pressure, covering the full range between 0 MPa ≤ p ≤ 12 MPa and -10 °C ≤ T ≤ 65 °C, so as to ensure accurate sound velocity characteristics of natural gas mixtures with high hydrogen content under different working conditions from a metrological perspective, and then verify or correct the prediction model of the current gaseous natural gas and similar mixture characteristics, contribute to the accuracy of the thermodynamic characteristic calculation program inside the on-site flow meter, and calibrate the ultrasonic flowmeter installed on the pipeline for transporting pure hydrogen or hydrogen mixtures in the future, providing an important reference for the trade settlement of high-hydrogen-content gases in the future.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for measuring and correcting the sound velocity of hydrogen-rich natural gas based on an external clamp-on ultrasonic flowmeter, characterized in that, A device for measuring the sound speed of a hydrogen-rich natural gas mixture with adjustable components is used in this method. The device includes a vacuum chamber and a gas distribution unit. The gas distribution unit includes a gas mixer and an on-line chromatograph analyzer connected to the inside of the gas mixer. The outlet of the gas mixer is connected to an inlet pipe extending into the vacuum chamber. In the vacuum chamber, there are relatively arranged a first flange and a second flange. Support rods are connected by bolts in a plurality of fixing holes around the first flange and the second flange. The outer ends of the support rods are fixedly connected to the inner wall of the vacuum chamber. On the relative inner sides of the first flange and the second flange, a pressure pipe is fixed. A thermometer, a pressure gauge, and two relatively arranged heat exchangers are provided on the inner wall of the pressure pipe. Fixed guide rails are provided on the outer wall of the pressure pipe. The transducers of the external clamp-on ultrasonic flowmeter for measuring the sound speed of the gas are closely attached to the outer wall of the pressure pipe by the fixed guide rails. The inner end of the inlet pipe extending into the vacuum chamber is hermetically connected to the outer end of the central hole of the first flange. The inlet of the pressure pipe is hermetically connected to the inner end of the central hole of the first flange. The outlet of the pressure pipe is hermetically connected to the inner end of the central hole of the second flange. The outer end of the central hole of the second flange is hermetically connected to an outlet pipe extending outside the vacuum chamber. On both sides of the outlet pipe, there are cold / hot fluid inlet pipes and cold / hot fluid outlet pipes extending into the vacuum chamber. The inner ends of the cold / hot fluid inlet pipes and the cold / hot fluid outlet pipes communicate with each other outside the first flange. The outer ends of the cold / hot fluid inlet pipes and the cold / hot fluid outlet pipes are connected to existing external cold / hot baths; The method includes the following steps: S1. Construction of a device for measuring the sound speed of a hydrogen-rich natural gas mixture with adjustable components; S2. Characterization of the external clamp-on ultrasonic flowmeter: According to the pipeline parameters of the fluid flow and the fluid properties, determine the installation method of the transducers of the external clamp-on ultrasonic flowmeter as diagonal installation or reflection installation, and the specific installation spacing of the transducers through experiments to maximize the quality of the sound signals received by the transducers and obtain a high signal-to-noise ratio; S3. External clamp-on ultrasonic flowmeter calibration: Under controlled laboratory conditions with a pressure of 0 MPa ≤ p ≤ 12 MPa and a temperature of -10 °C ≤ T ≤ 65 °C, the experimental value of the sound velocity c obtained by the external clamp-on ultrasonic flowmeter in a reference fluid with a known sound velocity r,exp is compared with the reference value of the sound velocity c r,ref . The sound velocity measurement deviation D between the experimental value of the sound velocity and the reference value of the sound velocity at each measurement point is calculated through the equation . The deviation is made lower than the preset threshold, and the calibration equation c c = c r,exp [a - b×(T + 273)] is obtained by deviation fitting, where c c is the sound velocity after calibration correction, a and b are deviation fitting coefficients, and the uncertainty u(c r,ref ) introduced by the reference fluid is calculated as follows: where u(p) and u(T) are the pressure measurement uncertainty and the temperature measurement uncertainty, respectively, and are the sensitivity coefficients of the speed of sound with respect to pressure and temperature, respectively, and R is the uncertainty introduced by measurement repeatability; S4. Measurement of the sound speed of hydrogen-rich natural gas: Use the external clamp-on ultrasonic flowmeter characterized in step S2 and calibrated in step S3 to measure the sound speed in hydrogen-rich natural gas. The mixture of hydrogen-rich natural gas is prepared by the gravimetric method. The uncertainty of the components of the natural gas mixed with hydrogen is ≤0.1%. During the measurement, the temperature and pressure of the device are constant, the fluid is stationary, and the measured sound speed value is calibrated and corrected by the calibration equation obtained in step S3; S5. Calculation of the uncertainty in the speed of sound: The relative expanded uncertainty u(c c ) includes the uncertainty in the mixture composition and the uncertainties arising from measurement repeatability, temperature, pressure, and the calibration equation, and is specifically calculated by the following formula: wherein, and are the uncertainties introduced by temperature and pressure measurements respectively, u(x) is the uncertainty introduced by the mixture components, u cal is the uncertainty generated by the calibration equation, and R is the uncertainty introduced by the measurement repeatability; Obtain the measurement range interval of the actual sound speed through the uncertainty of the sound speed measurement calculated and the sound speed measurement value calibrated and corrected by the calibration equation in step S4; S6. Standard model correction: Compare the measured sound speed value of the hydrogen-rich natural gas mixture corrected by the calibration equation in step S4 and the measurement uncertainty of the sound speed obtained in step S5 with the expected sound speed value and the uncertainty range calculated by the thermodynamic models provided by AGA-8 and AGA-10 respectively, plot the deviation curve between the actual measured sound speed value and the expected sound speed value calculated by the model, and use the deviation curve to correct the embedded thermodynamic calculation model of the gas flowmeter.

2. The method for measuring and correcting the sound velocity of hydrogen-rich natural gas based on an external clamp-on ultrasonic flowmeter according to claim 1, wherein The gas distribution unit outside the vacuum chamber is provided with pressure and flow regulating valves.

3. The method for measuring and correcting the sound velocity of hydrogen-rich natural gas based on an external clamp-on ultrasonic flowmeter according to claim 1, wherein, Teflon gaskets are sleeved in the central holes of the first flange and the second flange, and the inlet pipe and the outlet pipe are hermetically connected to the outer ends of the central holes of the flanges through the Teflon gaskets.

4. The method for measuring and correcting the sound velocity of hydrogen-rich natural gas based on an external clamp-on ultrasonic flowmeter according to claim 1, wherein, The pressure pipe is made of stainless steel, and the inner diameter of the pressure pipe is 50mm, 100mm or 150mm.

5. The method for measuring and correcting the sound velocity of hydrogen-rich natural gas based on an external clamp-on ultrasonic flowmeter according to claim 1, wherein The outer wall of the pressure pipe is coated with a coupling agent, and the transducer of the clamp-on gas ultrasonic flowmeter is coupled to the outer wall of the pressure pipe through the coupling agent.

6. The method for measuring and correcting the sound velocity of hydrogen-rich natural gas based on an external clamp-on ultrasonic flowmeter according to claim 1, characterized in that, In steps S2 and S3, the clamp-on ultrasonic flowmeter is calibrated under the conditions of 3 pressure points of 1MPa, 2MPa, and 3MPa and 3 temperature points of 10°C, 20°C, and 30°C, and the sound speed measurement device of the hydrogen-rich natural gas mixture with adjustable components is selected as the experimental device. In step S3, the reference fluid selected is nitrogen or helium.

7. The method for measuring and correcting the sound velocity of hydrogen-rich natural gas based on an external clamp-on ultrasonic flowmeter according to claim 1, wherein The preset threshold of the sound speed measurement deviation in step S3 is 0.2%.

8. The method for measuring and correcting the sound velocity of hydrogen-rich natural gas based on an external clamp-on ultrasonic flowmeter according to claim 1, characterized in that, In step S4, the hydrogen-rich natural gas mixture prepared by the gravimetric method has a hydrogen proportion of 80% and a standard natural gas proportion of 20%, and the uncertainty of the standard natural gas components is 0.05%.

9. The method for measuring and correcting the sound velocity of hydrogen-rich natural gas based on an external clamp-on ultrasonic flowmeter according to claim 1, wherein In the step S5, the uncertainty u(x), u cal and R are calculated respectively by the following formulas: where u(x ref ) is the component uncertainty of natural gas mixed with hydrogen, is the sensitivity coefficient for synthesizing the speed of sound with respect to the uncertainty, u(c hh ) is the uncertainty of the speed of sound of natural gas mixed with hydrogen, res mean is the average residual between the speed of sound after calibration and correction through the calibration equation and the expected value of the speed of sound calculated by the thermodynamic model, k is the coverage factor, n is the number of sample repeated measurements, c i is the measured value of the speed of sound in the i-th test, is the average value of the measured speed of sound in the i-th test.

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