A method for measuring the flow of a mixed gas based on an ultrasonic flow meter

Abstract

This invention provides a method for measuring the flow rate of a flowing mixed gas based on an ultrasonic flow meter. This method obtains the concentration values ​​of each component in the mixed gas by measurement and calculation, thereby obtaining the current stationary velocity of the mixed gas based on the concentration values, obtaining the fluid velocity from the difference between the flow velocity and the stationary velocity, and then obtaining the flow rate value. That is, the concentration values ​​of the components in the mixed gas are obtained at the same time as the flow rate of the mixed gas.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic gas flow measurement technology, and in particular to a method for measuring the flow rate of a flowing mixed gas based on an ultrasonic flow meter. Background Technology

[0002] Currently, the flow meters used in natural gas metering and distribution management in China are mainly Roots meters and turbine meters. Both of these are mechanical instruments, which are inherently prone to mechanical defects. For example, they are highly sensitive to natural gas quality, easily jammed, require frequent maintenance, and incur high maintenance costs. Furthermore, as the diameter of natural gas pipelines increases, the size, weight, and price of these mechanical instruments rise significantly. These weaknesses severely restrict the development of natural gas metering and pipeline distribution management towards "precision, stability, intelligence, and efficiency." To overcome the shortcomings of mechanical flow meters, ultrasonic flow meters have emerged in existing technology. However, current ultrasonic flow meters can only measure the flow rate of a gas mixture, but cannot determine the concentration of each component in the mixture. Summary of the Invention

[0003] The purpose of this invention is to overcome the above-mentioned problems in the prior art and provide a method for measuring the flow rate of a flowing mixed gas based on an ultrasonic flow meter. This method for measuring the flow rate of a flowing mixed gas obtains the concentration values ​​of the components in the mixed gas at the same time as measuring the flow rate.

[0004] To achieve the above-mentioned technical objectives and effects, the present invention is implemented through the following technical solution:

[0005] This invention provides a method for measuring the flow rate of a flowing gas mixture based on an ultrasonic flow meter, comprising the following steps:

[0006] Obtain the relaxation absorption amplitude of pure hydrogen and pure methane in a static scenario. , and the corresponding relaxation frequency Then, the relaxation absorption amplitudes of the pure hydrogen and the pure methane under different flow rate scenarios are obtained. 'and the corresponding relaxation frequency The error correlation function is obtained by processing the above data. Correlation function with error ;

[0007] The amplitude of relaxation absorption of the mixed gas N obtained by mixing the hydrogen and the methane at different concentration ratios was obtained. and the corresponding relaxation frequency Establish a database of data samples with different concentrations;

[0008] The transit time t is calculated from the acquired raw data, and thus the ultrasonic propagation velocity of the current gas mixture N is obtained. ;

[0009] In a flowing scenario, the relaxation absorption amplitude of the current mixed gas N is obtained. and the corresponding relaxation frequency The relaxation absorption amplitude and the corresponding relaxation frequency The error correlation function Correlation function with error By performing interpolation to eliminate errors, the true relaxation absorption amplitude of the current mixed gas N is obtained. and the corresponding actual relaxation frequency ;

[0010] The amplitude absorbed by the relaxation and the relaxation frequency The concentration percentage of one gas in the current gas mixture N is calculated, and compared with the data sample database to obtain the concentration value of one gas in the current gas mixture N. ;as well as

[0011] Based on the concentration value of one of the gases in the current mixed gas N The stationary velocity of the current mixed gas N is obtained. Thus, the velocity of the current mixed gas N is obtained. And the flow rate Q of the fluid.

[0012] In one embodiment of the present invention, the error correlation function The method for obtaining it includes the following steps:

[0013] The relaxation absorption amplitude Each is related to the relaxation absorption amplitude. The increment of the relaxation absorption amplitude of the pure hydrogen gas is obtained by performing a difference operation. The relaxation absorption amplitude Each is related to the relaxation absorption amplitude. The increment of the relaxation absorption amplitude of the pure methane is obtained by performing a difference operation. ;

[0014] The relaxation absorption amplitude increment With the relaxation absorption amplitude increment The average value of the relaxation absorption amplitude increment under different flow velocities is obtained by performing a mean operation along the dimension. ;as well as

[0015] For the average value The error correlation function is obtained by performing least squares correlation function fitting. .

[0016] In one embodiment of the present invention, the error correlation function The method for obtaining it includes the following steps:

[0017] The relaxation frequency Each is related to the relaxation absorption amplitude. The relaxation frequency increment of the pure hydrogen gas is obtained by performing a difference operation. The relaxation frequency Each with the relaxation frequency The relaxation frequency increment of the pure methane is obtained by performing a difference operation. ;

[0018] The relaxation frequency increment With the relaxation frequency increment The average value of the relaxation frequency increment under different flow velocities is obtained by performing a mean operation along the dimension. ;as well as

[0019] For the average value The error correlation function is obtained by performing least squares correlation function fitting. .

[0020] In one embodiment of the invention, the stationary velocity The formula can be used to calculate We obtain, where γ is the adiabatic coefficient, R is the molar gas constant, T is the temperature, and M is the molecular weight. H2 M is the molar mass of hydrogen gas. CH4 denoted as , where is the molar mass of methane.

[0021] In one embodiment of the invention, the velocity of the current mixed gas N It can be calculated by formula get.

[0022] In one embodiment of the present invention, the original data is obtained by measuring and collecting data in pipes filled with pure hydrogen and pure methane under different flow rate scenarios using an ultrasonic flow meter.

[0023] In one embodiment of the invention, the ultrasonic propagation speed of the current mixed gas N It can be calculated by formula We obtain that L is the length of the ultrasonic wave propagation path.

[0024] In summary, the present invention provides a method for measuring the flow rate of a flowing mixed gas based on an ultrasonic flow meter. This method obtains the concentration values ​​of each component in the mixed gas by measurement and calculation, thereby obtaining the current stationary velocity of the mixed gas based on the concentration values, obtaining the fluid velocity from the difference between the flow velocity and the stationary velocity, and then obtaining the flow rate value. That is, the concentration values ​​of the components in the mixed gas are obtained at the same time as the flow rate of the mixed gas. Attached Figure Description

[0025] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings:

[0026] Figure 1 This is an overall flowchart of the present invention for measuring the flow rate of a flowing mixed gas;

[0027] Figure 2 This invention obtains the error correlation function. Flowchart;

[0028] Figure 3 This invention obtains the error correlation function. Flowchart;

[0029] Figure 4 This is a graph showing the relationship between the relaxation absorption amplitude A and the relaxation frequency-pressure ratio f / p of the present invention.

[0030] Figure 5 This is a curve plotted based on a data sample library by the present invention, showing the relationship between hydrogen concentration and relaxation absorption amplitude A.

[0031] Figure 6 This is a schematic diagram of the structure of an ultrasonic flow meter in one embodiment of the present invention;

[0032] Figure 7 This is a schematic diagram of the structure of an ultrasonic flow meter in another embodiment of the present invention.

[0033] The labels in the diagram are as follows: 1-First transducer, 2-Second transducer, 3-Reflector, 4-Measuring tube. Detailed Implementation

[0034] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0035] Please see Figure 1 This invention provides a method for measuring the flow rate of a flowing gas mixture based on an ultrasonic flow meter. This method simultaneously measures the flow rate of the gas mixture and obtains the concentration values ​​of the components within the gas mixture. Specifically, the method for measuring the flow rate of a flowing gas mixture includes the following steps S1 to S6:

[0036] S1 obtains the relaxation absorption amplitude of pure hydrogen and pure methane in a static scenario. , and the corresponding relaxation frequency Then, the relaxation absorption amplitudes of the pure hydrogen and the pure methane under different flow rate scenarios are obtained. and the corresponding relaxation frequency The error correlation function is obtained by processing the above data. Correlation function with error Specifically, first, according to the formula... Calculate the relaxation strength of pure hydrogen and pure methane. and Where R is the molar gas constant. To correspond to the vibrational heat capacity inside the gas, C ∞ This represents the heat capacity of the corresponding external degrees of freedom of the gas. Then, according to the formula... The relaxation absorption amplitudes of pure hydrogen and pure methane were calculated. and Where λ is the wavelength of the ultrasound, a is the speed of sound, and f is the frequency of the sound wave. and These represent the relaxation intensity and relaxation frequency of the corresponding gases, respectively. Since different flow velocities affect the relaxation intensity D of the gas, the relaxation absorption amplitudes of pure hydrogen and pure methane under different flow velocities are calculated using the above formula. Then according to such Figure 4 The curve shown obtains the amplitude of relaxation absorption. Corresponding relaxation frequency .

[0037] Please see Figure 2 In one embodiment of the present invention, the error correlation function The method for obtaining it includes the following steps S10 to S12:

[0038] S10 will relax the absorption amplitude. Respectively compared with relaxation absorption amplitude The difference operation yields the increment of the relaxation absorption amplitude of pure hydrogen gas. relaxation absorption amplitude Respectively compared with relaxation absorption amplitude The increment of the relaxation absorption amplitude of the pure methane is obtained by performing a difference operation. ;

[0039] S11 relaxation absorption amplitude increment With relaxation absorption amplitude increment The average value of the relaxation absorption amplitude increment under different flow velocities is obtained by performing a mean operation along the dimension. ;as well as

[0040] S12 is the average value By performing least squares correlation function fitting, the error correlation function is obtained. .

[0041] Please see Figure 3 In one embodiment of the present invention, the error correlation function The method for obtaining it includes the following steps S13 to S15:

[0042] S13 will relax frequency Respectively compared with relaxation absorption amplitude The relaxation frequency increment of pure hydrogen gas is obtained by performing a difference operation. relaxation frequency Respectively with relaxation frequency The relaxation frequency increment of pure methane is obtained by performing a difference operation. ;

[0043] S14 relaxation frequency increment With relaxation frequency increment The average value of the relaxation frequency increment under different flow velocities is obtained by performing a mean operation along the dimension. ;as well as

[0044] S15 is the average value The error correlation function is obtained by performing least squares correlation function fitting. .

[0045] Please see Figure 1 S2 obtains the amplitude of relaxation absorption of a mixed gas N obtained from hydrogen and methane at different concentration ratios. and the corresponding relaxation frequency A data sample library with different concentrations was established. Specifically, the hydrogen concentration was varied from 0% to 100%, and the corresponding methane concentration was varied from 100% to 0%. The amplitude of relaxation absorption under different concentration ratios was measured. and the corresponding relaxation frequency This creates a database of data samples based on different concentrations. For example, hydrogen concentration can be plotted on the x-axis as shown in the diagram. Figure 5 The graph shown.

[0046] Please see Figure 1 , Figure 6 and Figure 7 S3 calculates the transit time t from the acquired raw data, thereby obtaining the ultrasonic propagation velocity of the current mixed gas N. Specifically, the raw data is obtained by measuring and collecting data in pipes filled with pure hydrogen and pure methane under different flow rate scenarios using an ultrasonic flow meter. The ultrasonic flow meter includes a measuring tube 4 and a first transducer 1 and a second transducer 2 mounted on the measuring tube 4. The first transducer 1 and the second transducer 2 can be located on one side or both sides of the measuring tube 4. The first transducer 1 emits ultrasonic signals, and the second transducer 2 receives the ultrasonic signals. When the first transducer 1 and the second transducer 2 are located on both sides of the measuring tube 4, a transmitting plate 3 is also provided inside the measuring tube 4 to reflect the ultrasonic signals emitted by the first transducer 1 to the second transducer 2. The ultrasonic signal propagation path length between the first transducer 1 and the second transducer 2 is L. The current ultrasonic propagation velocity of the mixed gas N is... It can be calculated by formula We obtain, where L is the length of the ultrasonic wave propagation path.

[0047] Please see Figure 1 In a flowing scenario, S4 obtains the relaxation absorption amplitude of the current mixed gas N. and the corresponding relaxation frequency The relaxation absorption amplitude and the corresponding relaxation frequency Error correlation function Correlation function with error By performing interpolation to eliminate errors, the true relaxation absorption amplitude of the current gas mixture N is obtained. and the corresponding actual relaxation frequency .

[0048] Please see Figure 1 S5 is the amplitude absorbed by relaxation. and relaxation frequency To calculate the percentage concentration of one gas in the current gas mixture N, compare it with the data sample database to obtain the concentration value of that gas in the current gas mixture N. Specifically, the amplitude of relaxation absorption. and relaxation frequency For reference, in such Figure 1 On the graph shown, read the current amplitude of relaxation absorption. and relaxation frequency lower hydrogen concentration The concentration of methane is 1- .

[0049] Please see Figure 1 S6 is based on the concentration value of one of the gases in the current gas mixture N. Obtain the rest velocity of the current gas mixture N. Thus, the velocity of the current gas mixture N can be obtained. And the fluid flow rate Q. Specifically, the stationary velocity. The formula can be used to calculate We obtain, where γ is the adiabatic coefficient, R is the molar gas constant, T is the temperature, and M is the molecular weight. H2 M is the molar mass of hydrogen gas. CH4 Let N be the molar mass of methane. The current velocity of the N2 mixture. It can be calculated by formula Obtain. If A positive value means that the direction of ultrasound propagation is the same as the direction of gas flow, i.e., it is downstream. A negative value indicates that the direction of ultrasonic propagation is opposite to the direction of gas flow, which is countercurrent. The volumetric flow rate Q is then calculated using the fluid flow rate formula, i.e., Q = t π(h / 2) 2 Where h is the diameter of the measuring tube.

[0050] In summary, the present invention provides a method for measuring the flow rate of a flowing mixed gas based on an ultrasonic flow meter. This method obtains the concentration values ​​of each component in the mixed gas by measurement and calculation, thereby obtaining the current stationary velocity of the mixed gas based on the concentration values, obtaining the fluid velocity from the difference between the flow velocity and the stationary velocity, and then obtaining the flow rate value. That is, the concentration values ​​of the components in the mixed gas are obtained at the same time as the flow rate of the mixed gas.

[0051] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method of measuring the flow of a mixed gas based on an ultrasonic flow meter, characterized by It includes the following steps: Obtain the relaxation absorption amplitude of pure hydrogen and pure methane in a static scenario. , and the corresponding relaxation frequency Then, the relaxation absorption amplitudes of the pure hydrogen and the pure methane under different flow rate scenarios are obtained. 'and the corresponding relaxation frequency The error correlation function is obtained by processing the above data. Correlation function with error ; The amplitude of relaxation absorption of the mixed gas N obtained by mixing the hydrogen and the methane at different concentration ratios was obtained. and the corresponding relaxation frequency Establish a database of data samples with different concentrations; The transit time t is calculated from the acquired raw data, and thus the ultrasonic propagation velocity of the current gas mixture N is obtained. ; In a flowing scenario, the relaxation absorption amplitude of the current mixed gas N is obtained. and the corresponding relaxation frequency The relaxation absorption amplitude and the corresponding relaxation frequency The error correlation function Correlation function with error By performing interpolation to eliminate errors, the true relaxation absorption amplitude of the current mixed gas N is obtained. and the corresponding actual relaxation frequency ; The amplitude absorbed by the relaxation and the relaxation frequency The concentration percentage of one gas in the current gas mixture N is calculated, and compared with the data sample database to obtain the concentration value of one gas in the current gas mixture N. ; as well as Based on the concentration value of one of the gases in the current mixed gas N The stationary velocity of the current mixed gas N is obtained. Thus, the velocity of the current mixed gas N is obtained. And the flow rate Q of the fluid.

2. The method for measuring the flow rate of a flowing gas mixture according to claim 1, characterized in that, The error correlation function The method for obtaining it includes the following steps: The relaxation absorption amplitude Each is related to the relaxation absorption amplitude. The increment of the relaxation absorption amplitude of the pure hydrogen gas is obtained by performing a difference operation. The relaxation absorption amplitude Each is related to the relaxation absorption amplitude. The increment of the relaxation absorption amplitude of the pure methane is obtained by performing a difference operation. ; The relaxation absorption amplitude increment With the relaxation absorption amplitude increment The average value of the relaxation absorption amplitude increment under different flow velocities is obtained by performing a mean operation along the dimension. ;as well as For the average value The error correlation function is obtained by performing least squares correlation function fitting. .

3. The method for measuring the flow rate of a flowing gas mixture according to claim 1, characterized in that, The error correlation function The method for obtaining it includes the following steps: The relaxation frequency Each is related to the relaxation absorption amplitude. The relaxation frequency increment of the pure hydrogen gas is obtained by performing a difference operation. The relaxation frequency Each with the relaxation frequency The relaxation frequency increment of the pure methane is obtained by performing a difference operation. ; The relaxation frequency increment With the relaxation frequency increment The average value of the relaxation frequency increment under different flow velocities is obtained by performing a mean operation along the dimension. ;as well as For the average value The error correlation function is obtained by performing least squares correlation function fitting. .

4. The method for measuring the flow rate of a flowing gas mixture according to claim 1, characterized in that, The static speed From the calculation formula We obtain, where γ is the adiabatic coefficient, R is the molar gas constant, T is the temperature, and M is the molecular weight. H2 M is the molar mass of hydrogen gas. CH4 denoted as , where is the molar mass of methane.

5. The method for measuring the flow rate of a flowing gas mixture according to claim 4, characterized in that, The current velocity of the mixed gas N From the calculation formula get.

6. The method for measuring the flow rate of a flowing gas mixture according to claim 1, characterized in that, The original data is obtained by measuring and collecting data in pipes filled with pure hydrogen and pure methane under different flow rate scenarios using an ultrasonic flow meter.

7. The method for measuring the flow rate of a flowing gas mixture according to claim 1, characterized in that, The ultrasonic propagation speed of the current mixed gas N From the calculation formula We obtain that L is the length of the ultrasonic wave propagation path.

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