Method for operating a flow measuring point of a medium having at least one liquid phase

Abstract

The invention relates to a method for operating a flow measurement point for a medium having at least one liquid phase, the flow measurement point comprising a Coriolis measuring device for measuring the mass flow rate and the density of the medium flowing through a pipe and a differential pressure measuring device for sensing the differential pressure between a flow region arranged upstream of the Coriolis measuring device and a flow region arranged downstream of the Coriolis measuring device; wherein the flow measurement based on the differential pressure measurement values is corrected by means of measurement values acquired using the Coriolis measuring device.

Description

Technical Field

[0001] The present invention relates to a method for operating a flow measurement point, the flow measurement point including a Coriolis measuring device and a differential pressure measuring device. Background Technology

[0002] Coriolis measuring devices, used to measure the flow rate or density of liquid media flowing through pipes, suffer from reduced accuracy in flow measurement under certain conditions, such as very low flow rates or air bubbles in the medium. In such cases, detecting the pressure drop across the medium using a differential pressure measuring device and using the measured value of the differential pressure for flow measurement has proven advantageous; see, for example, DE102005046319A1. However, in applications where the medium composition fluctuates over relatively short periods, flow measurement using differential pressure is also susceptible to destructive uncertainties.

[0003] Therefore, the purpose of this invention can be viewed as achieving or improving flow measurement under difficult conditions. Summary of the Invention

[0004] This objective is achieved by the method according to the invention.

[0005] In the method according to the invention for operating a flow measurement point of a medium having at least one liquid phase,

[0006] The flow measurement point includes:

[0007] A Coriolis measuring device for measuring the mass flow rate and density of a medium flowing through a pipe, wherein the Coriolis measuring device has at least one measuring tube, which in each case has an inlet and an outlet;

[0008] The differential pressure measuring device is configured to detect the pressure difference between a flow region upstream of a flow obstacle, particularly a Coriolis measuring device, and a flow region downstream of that flow obstacle.

[0009] The method includes the following steps:

[0010] The condition of the medium is checked using Coriolis measuring equipment;

[0011] - When a pure liquid medium is detected

[0012] The first density of the medium is measured using a Coriolis measuring device and the measured value of the first density is stored.

[0013] The first mass flow rate was measured using a Coriolis measuring device;

[0014] The first viscosity of the medium is determined based on the first density, pressure difference, and first mass flow rate, and the measured value of the first viscosity is stored.

[0015] - When gaseous fractions are detected in the medium

[0016] The first Reynolds number of the medium is determined by means of the following terms.

[0017] -First viscosity;

[0018] - When gaseous fractions are detected, the first density and / or second density of the medium are measured using a Coriolis measuring device;

[0019] - When gaseous fractions are detected, the second mass flow rate is measured using a Coriolis measuring device.

[0020] The third mass flow rate is determined based on the pressure difference and the first Reynolds number.

[0021] In this way, mass flow rate measurements can be corrected based on differential pressure measurements, resulting in sufficiently accurate measurements even under challenging conditions.

[0022] For example, when crude oil is extracted from an oil field, the state of the medium can fluctuate rapidly. Gases dissolved in the medium under high pressure can form bubbles during decompression, thus affecting variables of the medium such as density or viscosity.

[0023] For the start of this method, when a gaseous medium is initially present, a person skilled in the art can specify, for example, initial values ​​for the measurements of a first density and a first viscosity, which he obtains, for example, by estimation, experience, or physical calculation. He can also make the flow measurement point wait at the start of the method until the first presence of a pure liquid medium.

[0024] When determining the first Reynolds number using the first viscosity, first density, second density, or second mass flow rate, the corresponding measured value is used. The same applies to the determination of other measured variables.

[0025] In one embodiment, when a gaseous fraction is detected, the following iterative method steps are performed:

[0026] The second Reynolds number is determined using the following terms:

[0027] -Third mass flow rate;

[0028] -First viscosity:

[0029] -First density and / or second density,

[0030] Store the measured value of the second Reynolds number.

[0031] The third mass flow rate is determined based on the pressure difference and the second Reynolds number, and the measured value of the third mass flow rate is stored.

[0032] This iteration can further improve measurement accuracy.

[0033] In one embodiment, the iteration is terminated once the difference between the consecutive measurements of the third mass flow rate or the second Reynolds number falls below a limit value.

[0034] The limit value is, for example, 5% of the average of the measurements that form the difference, especially 2%, preferably 1%, or the limit value is, for example, 5% of one of the measurements that form the difference, especially 2%, preferably 1%.

[0035] In one embodiment, the state of the medium is checked by means of a Coriolis measuring device, wherein the attenuation of vibration and / or fluctuation of resonant frequency of at least one measuring tube of the Coriolis measuring device is used during the check.

[0036] In one embodiment, when measuring density, the resonant frequency of at least one measuring tube of a Coriolis measuring device is used.

[0037] In one embodiment, when a gaseous fraction is detected, a physical mathematical model is used to correct the density measurement.

[0038] The model takes into account the effect of air bubbles on the measurement of medium density.

[0039] In the measuring tube of a Coriolis measuring device, air bubbles in the medium, particularly depending on their diameter, move perpendicularly to the inner wall of the measuring tube in a direction parallel to the tube's movement, thus affecting the measured values ​​of density and viscosity. This model takes into account relative motion; therefore, it is possible to correct for the destructive effects of air bubbles. More information on this can be found, for example, in H. Zhu, Application of Coriolis Mass Flowmeters in Bubbly and Particulate, Shaker, ISBN 978-3-8322-8216-5, 2009.

[0040] In one embodiment, when a gaseous fraction is detected, a second density of the medium is measured using a Coriolis measuring device.

[0041] The volume ratio of the gaseous fraction to the liquid fraction is determined based on a first density and a second density.

[0042] The differential pressure measurement value is corrected using this ratio.

[0043] Then the mass flow rate can be accurately determined with the help of this correction.

[0044] In one embodiment, the differential pressure measuring device has a first pressure sensor and a second pressure sensor, wherein the first pressure sensor is arranged upstream of the flow obstacle, and wherein the second pressure sensor is arranged downstream of the flow obstacle.

[0045] And / or the differential pressure measuring device has a differential pressure sensor that detects the pressure difference between the upstream side and the downstream side of the flow obstruction.

[0046] The differential pressure measuring device can be part of the flow meter or a separate measuring device that transmits the measured value of the differential pressure to the flow meter.

[0047] In one embodiment, the electronic measurement / control circuitry of the Coriolis measuring device provides and outputs measurements of the mass flow rate.

[0048] Specifically, when a pure liquid medium is detected, the output is the measured value of the first mass flow rate detected by the Coriolis measuring device.

[0049] Furthermore, when a gaseous fraction is detected in the medium, a measurement of the third mass flow rate, detected by means of pressure difference, is output.

[0050] In one embodiment, the effect of static pressure difference on the measured value of pressure difference is corrected.

[0051] In one embodiment, if the absolute value of the pressure difference is below a limit value, the mass flow rate determined by the pressure difference is set to zero, where the limit value is, for example, 20 mbar, especially 10 mbar, and preferably 5 mbar. Attached Figure Description

[0052] The invention will now be described with reference to exemplary embodiments.

[0053] Figure 1 The illustration shows an exemplary flow measurement point equipped with a Coriolis measuring device and a differential pressure measuring device;

[0054] Figure 2 An exemplary Coriolis measuring device is illustrated;

[0055] Figure 3 The sequence of the method according to the present invention is illustrated. Detailed Implementation

[0056] Figure 1An exemplary flow measurement point 1 is illustrated, which includes a medium conduction conduit 2 and a Coriolis measuring device 10 disposed within the conduit for detecting the mass flow rate and density of the medium flowing through the conduit. Furthermore, the flow measurement point has a differential pressure measuring device configured to detect the pressure difference between a flow region 3.1 disposed upstream of the Coriolis measuring device and a flow region 3.2 disposed downstream of the Coriolis measuring device. Alternatively, it is also possible to measure the pressure difference across another flow obstruction.

[0057] As shown here, the differential pressure measuring device can have a first pressure sensor 21.1 upstream of the Coriolis measuring device and a second pressure sensor 21.2 downstream of the Coriolis measuring device. The difference between the measured values ​​of the pressure sensors is used as a measure of the differential pressure across the Coriolis measuring device. Alternatively or additionally, as shown here, the differential pressure measuring device can have a differential pressure sensor 22 inserted into a bypass channel and sealingly dividing the bypass channel into a first section and a second section; for example, the differential pressure can be detected by the deflection of the diaphragm of the differential pressure sensor 22.

[0058] The differential pressure measuring device can be part of a Coriolis measuring apparatus, as shown here, wherein the measurement signal from a pressure sensor or differential pressure sensor is transmitted to the electronic measurement / control circuitry of the Coriolis measuring apparatus 10; see also Figure 2 The measurement signal is then processed by an electronic measurement / control circuit, which generates and provides a measured value of the differential pressure. Alternatively, the differential pressure measuring device can also be a standalone measuring device and can be configured to transmit the measured value of the differential pressure to a Coriolis measuring device.

[0059] Figure 2 A Coriolis measuring device 1 is shown, which has a measuring pickup 10, an electronic measuring / control circuit 20, and a housing 30 for accommodating the electronic measuring / control circuit.

[0060] The measurement pickup has two measuring tubes 11, each with an inlet 11.1 and an outlet 11.2, held by a support element 16. The measuring tubes are configured to vibrate against each other. The numbering of the measuring tubes shown here is illustrative; the measurement pickup can also have, for example, only one measuring tube or four measuring tubes, particularly arranged in two pairs, where each pair is configured to vibrate against each other. The measurement pickup has an exciter 14 configured to excite the vibration of the measuring tubes. The measurement pickup has two sensors 15 configured to detect the vibration of the measuring tubes. The medium flowing through the measuring tubes characteristically affects the vibration of the measuring tubes, thereby allowing the mass flow rate and / or density and / or viscosity of the medium to be derived from the measurement signals of the sensors.

[0061] For example, Coriolis measuring devices work very well in pure liquid media that may optionally carry a variety of different components, such as oil-water mixtures. In special applications, such as when crude oil is extracted from an oil field, the medium can carry gaseous fractions in the form of bubbles, making flow measurement using Coriolis measuring devices very complex. It is known from the prior art that in such cases, the pressure difference across the Coriolis measuring device is used as a measure of mass flow rate. In this case, when a pure liquid medium is present, the density or viscosity of the medium is determined using a Coriolis measuring device, and when gaseous fractions are present, flow parameters are determined using the pressure difference and density or viscosity.

[0062] However, when gaseous fractions are present, the determination of density or viscosity is often not accurate enough.

[0063] therefore, Figure 3 An exemplary method according to the present invention is described, by means of which high measurement accuracy can be achieved at the flow measurement point, even when gaseous fractions are present in the medium.

[0064] The method comprises the following steps:

[0065] In step 101 of the first method, the state of the medium is checked by means of a Coriolis measuring device;

[0066] -When a pure liquid medium is detected

[0067] The first density of the medium is measured using a Coriolis measuring device and the measured value of the first density is stored in a subsequent method step 102.1;

[0068] In subsequent method step 102.2, the first mass flow rate is measured using a Coriolis measuring device;

[0069] The first viscosity of the medium is determined based on the first density, pressure difference, and first mass flow rate, and the measured value of the first viscosity 102.3 is stored in subsequent method steps;

[0070] - When gaseous fractions are detected in the medium

[0071] In subsequent method step 103.1, the first Reynolds number of the medium is determined by means of the following:

[0072] -First viscosity;

[0073] - When gaseous fractions are detected, the first density and / or second density of the medium are measured using a Coriolis measuring device;

[0074] - When gaseous fractions are detected, the second mass flow rate is measured using a Coriolis measuring device.

[0075] Furthermore, in subsequent method step 103.2, the third mass flow rate is determined based on the pressure difference and the first Reynolds number.

[0076] If gaseous fractions are present in the medium, the actual mass flow rate can be better estimated by using the first Reynolds number and pressure difference to determine the third mass flow rate.

[0077] The Reynolds number of the medium affects the flow profile of the medium in the measuring tube of the Coriolis measuring device. Gaseous fractions in the form of bubbles affect the Reynolds number and therefore the flow profile, and this must therefore be taken into account when determining the third mass flow rate. The relationship between the Reynolds number Re, flow rate v, medium density ρ, and the first viscosity η (dynamic viscosity) is given by the following equation:

[0078]

[0079] Where d is the diameter of the measuring tube.

[0080] It is highly advantageous here if the first viscosity is determined by pressure difference rather than by the Coriolis measuring device according to the invention. Even very small gaseous fractions in the form of small bubbles can have a significant impact on the viscosity measurement of the Coriolis measuring device without detecting the presence of very low gaseous fractions. In this case, mass flow rate measurements by pressure difference would be severely distorted.

[0081] For example, when inspecting the state of a medium using a Coriolis measuring device, the vibration attenuation and / or resonant frequency fluctuation of at least one measuring tube 11 of the Coriolis measuring device are used. For instance, the viscosity limit value measured by vibration attenuation can be used to distinguish between pure liquid media and media containing air bubbles. The viscosity of a liquid typically has a range of values. Therefore, the presence of air bubbles can be detected when the measured value exceeds this range.

[0082] To improve the accuracy of mass flow rate measurement, the following iterative method steps can be performed when gaseous fractions are detected:

[0083] The second Reynolds number 104.1 is determined using the following terms.

[0084] -Third mass flow rate;

[0085] -First viscosity;

[0086] -First density and / or second density,

[0087] And store the measured value of the second Reynolds number,

[0088] The third mass flow rate, 104.2, is determined based on the pressure difference and the second Reynolds number, and the measured value of the third mass flow rate is stored.

[0089] Repeating these two steps leads to the convergence of the iterative value of the third mass flow rate.

[0090] For example, the iteration can be terminated once the difference between the continuous measurements of the third mass flow rate or the second Reynolds number falls below a limit value, where the limit value is, for example, 5% of the average of the measurements that form the difference, or the average of one of the measurements that form the difference, especially 2%, preferably 1%.

[0091] Alternatively, the iteration can be terminated, for example, when the maximum time period has elapsed, where the maximum time period is defined, for example, by the time interval between two measurements of the mass flow rate.

[0092] To improve measurement accuracy, the influence of static pressure difference on the measured pressure value can be corrected. When the installation of the Coriolis measuring device and the differential pressure measuring device in the pipeline is known, especially when the inclination relative to the horizontal line is known, the static pressure difference can be calculated with the help of the medium density and, for example, the distance of the pressure sensor, and the static pressure difference can be taken into account when determining the measured value of the third mass flow rate.

[0093] If the absolute value of the differential pressure, optionally corrected by static differential pressure, is below a limit value, the mass flow rate determined by means of the differential pressure can be set to zero, where the limit value is, for example, 20 mbar, especially 10 mbar, and preferably 5 mbar. This avoids the possibility of a fixed differential pressure on the order of measurement uncertainty being evaluated as the mass flow rate.

[0094] The electronic measurement / control circuit 12 of the Coriolis measuring device thereby provides and outputs the measured values ​​of mass flow rate, wherein when a pure liquid medium is detected, the measured value of the first mass flow rate detected by means of the Coriolis measuring device is output, and when a gaseous fraction in the medium is detected, the measured value of the third mass flow rate detected by means of differential pressure is output.

[0095] List of reference numerals

[0096] 1 Flow measurement point

[0097] 2 pipes

[0098] 3.1 Arranged in the upstream flow area

[0099] 3.2 Arranged in the downstream flow area

[0100] 10 Coriolis measuring equipment

[0101] 11 measuring tubes

[0102] 11.1 Entry

[0103] 11.2 Exports

[0104] 12 Electronic Measurement / Control Circuits

[0105] 13 shell

[0106] 14 exciters

[0107] 15 sensors

[0108] 16 support elements

[0109] 19 electrical connection wires

[0110] 20 Differential Pressure Measurement Device

[0111] 21.1 First pressure sensor

[0112] 21.2 Second pressure sensor

[0113] 22 Differential Pressure Sensor

[0114] 100 methods

[0115] 101 Check the condition of the medium

[0116] 102.1 Measurement of the first density

[0117] 102.2 Measurement of the first mass flow rate

[0118] 102.3 Determine the first viscosity

[0119] 103.1 Determining the First Reynolds Number

[0120] 103.2 Determining the Third Mass Flow Rate

[0121] 104.1 Determining the Second Reynolds Number

[0122] 104.2 Determining the Third Mass Flow Rate

Claims

1. A method (100) for operating a flow measurement point (1) of a medium having at least one liquid phase, the flow measurement point comprising: A Coriolis measuring device (10) for measuring the mass flow rate and density of a medium flowing through a pipe (2), wherein the Coriolis measuring device has at least one measuring tube (11), wherein the at least one measuring tube (11) has an inlet (11.1) and an outlet (11.2) in each case; The differential pressure measuring device (20) is configured to detect the differential pressure between a flow region (3.1) located upstream of the flow obstacle and a flow region (3.2) located downstream of the flow obstacle. The method includes the following steps: The state of the medium is checked using the Coriolis measuring device (101); -When a pure liquid medium is detected The first density of the medium is measured using the Coriolis measuring device and the measured value of the first density is stored (102.1); The first mass flow rate (102.2) was measured using the Coriolis measuring device. The first viscosity of the medium is determined based on the first density, the pressure difference, and the first mass flow rate, and the measured value of the first viscosity (102.3) is stored. -When gaseous fractions are detected in the medium The first Reynolds number (103.1) of the medium is determined by means of the following: -First viscosity; - When the gaseous fraction is detected, the first density and / or second density of the medium are measured by means of the Coriolis measuring device; - When the gaseous fraction is detected, the second mass flow rate is measured using the Coriolis measuring device. The third mass flow rate (103.2) is determined based on the pressure difference and the first Reynolds number.

2. The method according to claim 1, in, The flow obstacle is the Coriolis measuring device.

3. The method according to claim 1, in, When the gaseous fraction is detected, the following iterative method steps are executed: The second Reynolds number (104.1) is determined using the following terms. -The third mass flow rate; -The first viscosity; -The first density and / or the second density, And store the measured value of the second Reynolds number. The third mass flow rate (104.2) is determined based on the pressure difference and the second Reynolds number, and the measured value of the third mass flow rate is stored.

4. The method according to claim 3, in, The iteration is terminated once the difference between consecutive measurements of the third mass flow rate or the second Reynolds number falls below a limit value. Wherein, the limit value is 5% of the average of the measurements that form the difference, or the limit value is 5% of one of the measurements that form the difference.

5. The method according to claim 4, in, The limit value is 2% of the average of the measurements that form the difference.

6. The method according to claim 5, in, The limit value is 1% of the average of the measurements that form the difference.

7. The method according to claim 4, in, The limit value is 2% of one of the measured values ​​that form the difference.

8. The method according to claim 7, in, The limit value is 1% of one of the measured values ​​that form the difference.

9. The method according to any one of claims 1-8, in, The state of the medium is checked by means of the Coriolis measuring device (10), wherein the vibration decay and / or fluctuation of the resonant frequency of at least one measuring tube (11) of the Coriolis measuring device are used during the check.

10. The method according to any one of claims 1-8, in, The resonant frequency of at least one measuring tube (11) of the Coriolis measuring device (10) is used when measuring the density.

11. The method according to claim 10, in, When gaseous fractions are detected, the measurement of the second density is corrected based on a physical mathematical model. The model takes into account the motion of the bubble relative to the wall of the measuring tube in the direction of vibration of the measuring tube.

12. The method according to any one of claims 1-8, in, When gaseous fractions are detected, the second density of the medium is measured using the Coriolis measuring device (10). The volume ratio of the gaseous fraction to the liquid fraction is determined based on the first density and the second density. The differential pressure measurement is corrected by means of the volume ratio.

13. The method according to any one of claims 1-8, in, The differential pressure measuring device (20) has a first pressure sensor (21.1) and a second pressure sensor (21.1), wherein the first pressure sensor is arranged upstream of the flow obstruction, and wherein the second pressure sensor is arranged downstream of the flow obstruction, and / or The differential pressure measuring device includes a differential pressure sensor (22), which detects the pressure difference between the upstream side and the downstream side of the flow obstacle.

14. The method according to any one of claims 1-8, in, The electronic measurement / control circuit (12) of the Coriolis measuring device provides and outputs the measured value of the mass flow rate. When a pure liquid medium is detected, the measured value of the first mass flow rate detected by the Coriolis measuring device is output. Furthermore, when a gaseous fraction is detected in the medium, the measured value of the third mass flow rate, detected by means of the pressure difference, is output. The electronic measurement / control circuit is arranged in the housing (13) of the Coriolis measuring device.

15. The method according to any one of claims 1-8, in, The effect of static pressure difference on the measured value of the pressure difference is corrected.

16. The method according to any one of claims 1-8, in, If the absolute value of the pressure difference is below the limit value, the mass flow rate determined by the pressure difference is set to zero, where the limit value is 20 mbar.

17. The method according to claim 16, in, The limit value is 10 mbar.

18. The method according to claim 17, in, The limit value is 5 mbar.

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