Enlarged pipe for microwave flow measurement

Abstract

This invention relates to a conduit for flow measurement, including a measuring antenna configured to measure predetermined characteristics of a fluid within the conduit. The conduit includes an input end and an output end having predetermined dimensions. The conduit includes a first cross-section extending in a first direction beyond the predetermined input and output dimensions, and a second cross-section perpendicular to the first direction, the dimension B of which is smaller than the dimension A in the first direction.

Description

Technical Field

[0001] This invention relates to an enlarged conduit for flow measurement. Since a standard venturi tube is a limitation on the pipe diameter, this can be called a reverse venturi tube, used to guide the flow of the fluid to be measured. The conduit portion includes a measuring probe for monitoring the contents and flow conditions, particularly for microwave-based dielectric constant measurements. Background Technology

[0002] Microwave-based multiphase flow meters (MPFMs) need to be able to measure the dielectric constant when oil is in continuous flow or when the gas volume fraction (GVF) is high, so that the losses are low enough that the dielectric constant can be measured using a cavity resonator, and when the losses are high, a transmission method must be used. This has been discussed in many publications, such as EP2845000B1, EP2954319B1, EP3308160B1, and EP3286561B1. The measurement system must also be able to measure the salinity of the aqueous phase to compensate for the effects of salinity variations. In addition, density and flow velocity need to be measured so that the composition and flow velocity can be calculated. Density can be measured using a gamma density meter, etc., which will not be elaborated here, as this invention is mainly related to the measurement of the dielectric constant of the liquid in a multiphase flow, specifically the salinity and water content (WC).

[0003] EP3308160B1 proposes a solution involving three antennas, which are used both for differential transmission of composition and salinity measurements and for exciting a resonator. A specific solution involves supporting a conical or cylindrical insert at the center of the pipe, in which case fluid is guided through the gap between the insert and the pipe.

[0004] The structures described in the aforementioned publications include inserts that generate differential pressure and can also be used for velocity measurement. One problem with these solutions is that they are invasive, adding obstruction to fluid flow. Therefore, the present invention relates to a non-invasive design with the same basic concept, combining a resonator sensor with differential transmission for composition and salinity measurement.

[0005] EP1451562B1 mentions an alternative to the invasive solution, showing the pipe section constituting the inverted Venturi solution, where the pipe diameter is increased while providing the resonator and pressure differential. A similar solution related to full-wave transverse resonance is also discussed in US10175075. However, this circularly symmetrical resonator has a fundamental problem associated with the first approach, therefore the resonant mode is generally preferred, as described below. There are two reasons for preferring the first mode: one is that the resonant frequency needs to be lower than the cutoff frequency in the pipe 2 to be included in the resonator. If a higher mode is used, the section to be expanded needs to be further enlarged to achieve this, which unnecessarily reduces the flow velocity and may lead to unnecessary flow instability. Another reason is that for higher modes, the distance between the frequency and other peaks is smaller, increasing the risk of not being able to identify the correct peak under high dynamic conditions. A solution with this problem is described in US5455516. The resonator in this publication is not an inverted Venturi but has a fairly large cross-section in one dimension, which will separate the resonant frequencies in that direction, but the difference between the modes is too small for practical measurements. Summary of the Invention

[0006] The invention is further defined in the appended independent claims.

[0007] A novel design combining resonators and differential transmission measurements is achieved in a non-invasive manner. It also offers flexibility in antenna placement and tube size, as the antenna can be mounted within a planar tube wall in a preferred embodiment without any curvature adaptation or other issues. Furthermore, it eliminates the need for filling with dielectric tubes or composite materials, as required by some previously proposed non-invasive designs. Attached Figure Description

[0008] The invention will now be discussed in more detail with reference to the accompanying drawings, and the invention will be illustrated by way of examples.

[0009] Figure 1 This demonstrates the damaged resonance peak value measured in an inverted venturi tube using known techniques.

[0010] Figure 2 A preferred embodiment of the invention is described, which has two opposing flat surfaces, resulting in clear resonance.

[0011] Figures 3a-3c Different alternative cross sections according to the present invention are illustrated.

[0012] Figure 4 This explains the frequency response of the design. Figure 2 and 3a As shown, it has a flat top and bottom. Detailed Implementation

[0013] As mentioned above, the inverse venturi solution is well-known, for example from EP1451562B1 and US10175075, but the problem with the basic cylindrical geometry is that the lowest waveguide mode (TE11) forming the resonance is not circularly symmetrical and has no predefined orientation. This means that two orthogonal modes can exist. They are independent but have the same resonant frequency. Inhomogeneities in the flow can cause the independent resonant frequencies to shift and lead to them interfering with each other, resulting in a damaged combined resonant peak, such as... Figure 1 The split resonance peak is shown. Even when simulated using an empty sensor in HFSS (High Frequency Structure Simulator, a simulation program based on the finite element method), the peak is shown to split in the middle.

[0014] Reference Figure 2 This invention relates to an improvement of pipe 1, which constitutes an improved reverse venturi tube with a cross-section larger than that of the inlet and outlet ends 2b of pipe 1. The term "cross-section" in this invention is used to refer to a dimension perpendicular to the pipe and the flow direction.

[0015] The pipe 1 is located between two pipes 2, which guide fluid flow through a transition zone 2a of predetermined length, replacing the circular cross-section known in the prior art. The cross-section of the illustrated embodiment is a combination of a circular cross-section portion and a linear cross-section portion, resulting in two opposing planes 3 and two opposing curved surfaces 4, the latter having a larger spacing than the former. This has several advantages, such as:

[0016] - Quadrature resonances are separated in frequency, so each peak is clear.

[0017] Three or more antennas 5 used for measuring transmission and resonance can be located on plane 3, and the exact same configuration can be used for multiple pipe diameters. Any desired configuration can be used, such as delta, axial, or transverse linear.

[0018] - Surface-sensitive cavity resonator sensors, as described in EP2104837, can be easily integrated onto one of the planes.

[0019] - This design has no theoretical flow rate limit.

[0020] - There are no dielectric tubes, sleeves, inserts or fillers inside the cavity.

[0021] Figure 2 The frequency response produced by the design shown exhibits two distinct and clear peaks, 12 and 13, as... Figure 4 As shown, it also displays Figure 1 The split peak response 11 of the medium cylindrical design is shown in dashed line for reference.

[0022] More specifically, Figure 2 The designed frequency response has a flat top 3 and bottom, with a distinct first resonance peak, sufficiently distant from the next peak to avoid peak-to-peak confusion under highly dynamic flow conditions. This distance can be varied by changing the aspect ratio of the design. As disclosed in EP3286561B1, these two resonance peaks can be used to measure flow characteristics.

[0023] As Figures 3a-3c shown, other shapes of pipe cross-sections can be considered, such as having an elliptical ( Figure 3c ) or rectangular cross-section ( Figure 3b ), or the surface suitable for receiving antenna 5 has a standard curvature suitable for the selected antenna, while the curvature in the vertical direction is different. The main aspect is that the two peaks are clearly separated and the direction of the resonant field relative to the cross-section is defined.

[0024] According to the present invention, the cross-sectional area of pipe 1 is preferably larger than the cross-sectional area of the rest of pipe 2 so as not to intrude into the fluid flow, but a solution with a constant area along the pipe and the pipe can also be considered if no pressure change in the flow is required.

[0025] By way of illustration, reference Figure 3b shows a pipe defining a rectangular waveguide with dimensions AxB, where A > B, A is the distance between the first two opposite faces 4, and B is the distance between the last two opposite faces 3. For the first mode, where A corresponds to half wavelength, the next mode is where A corresponds to a full wavelength. The orthogonal mode has a cut-off frequency where B corresponds to half wavelength. If A = 2B, the next two modes will have the same cut-off frequency, which is twice that of the first mode. Thus, waveguides generally have this ratio and an octave is obtained when only one mode can exist. According to the present invention, an intermediate solution is preferred, where B < A < 2B, to obtain resonant modes reflected by the opposite faces, each mode providing a different standing wave. A longer distance, A > 2B, will result in long resonators with resonances too close. Therefore, the dimensions should be chosen so as to obtain a reasonable separation between the resonant modes.

[0026] Therefore, the concept of multiphase flow measurement (MPFM) is based on measuring the water content (WC) and salinity locally at the wall of the liquid under high-loss conditions using a probe or antenna 5, rather than attempting to measure the effective dielectric constant of the entire flow, as it is severely affected by different flow states. However, if required, additional receiving antennas can be installed on the opposite walls. Tests with surface-sensitive salinity sensors have shown that expanding the pipe will cause the liquid to flow closer to the wall, facilitating the measurement of salinity and local WC.

[0027] Two additional antennas 6 located in the flow direction can be used for cross-correlation, as Figure 2As shown. If they are located on opposite walls, the measured velocity represents the average velocity of the entire flow. If they are located on the same wall, the measured velocity represents the velocity closer to the wall, but the received signal is stronger.

[0028] As described in EP3308160B1, it is possible to select Figure 2 The position of the main antenna is determined so that the transmission measurement antenna is positioned in at least one higher resonant mode in the venturi tube to reduce resonance interference while performing transmission measurements under moderate loss conditions.

[0029] As can be seen from the above discussion, this invention solves the fundamental problem related to exciting the lowest resonance in a basic cylindrical cavity without using any cones, fins, or other inserts, while providing additional advantages related to using the same geometric antenna configuration on pipes of several sizes, and allowing for combined use to measure resonance and differential transmission. A major advantage of being able to use the same antenna configuration on pipes of various sizes is that the same model can be used to extract water content and salinity without additional pipe-size-related modifications. This reduces the need for expensive and time-consuming testing and calibration.

[0030] This invention eliminates the need for the use of dielectric materials (pipes, sleeves, or fillers) within the cavity, as these materials can absorb water, become affected by liquids over time, and exhibit temperature dependence that requires compensation. This invention also does not impose any speed limitations.

[0031] In summary, the present invention relates to a conduit for flow measurement, the conduit including a measuring antenna configured to measure predetermined characteristics of a fluid within the conduit. The conduit includes an input end and an output end having predetermined dimensions. The conduit includes a cross-section having a first cross-section in a first direction, the cross-section exceeding the input and output dimensions by a predetermined amount, and a cross-section in a second direction preferably perpendicular to the first direction, the dimension B of which is smaller than the dimension A in the first direction.

[0032] Although the two vertical directions in the resonator are discussed in this invention, providing two different resonance conditions, other solutions can also be considered, in which the shape of the cross section can be selected to obtain more than two resonant frequencies or to adapt to other types of measurements and conditions.

[0033] According to one embodiment, the conduit is formed by two opposing curved pipe walls in a first direction and by two opposing flat pipe walls in a second direction. In the latter case, at least one of the antennas is mounted on the flat pipe wall.

[0034] The antenna is preferably a microwave measurement antenna, configured to measure the resonance and / or transmission characteristics of microwave signals in the pipe.

[0035] The cross-section in the second direction can have dimensions between those of the input and output cross-sections and those in the first direction. Therefore, the pipe portion is larger than the input and output pipes in both directions, but the dimensions are different in the first and second directions.

[0036] Preferably, the first and second sizes are selected to provide a cross-sectional area that is at least the same as, and preferably larger than, the pipe cross-sectional area.

Claims

1. A pipeline for flow measurement, comprising at least one measurement microwave antenna configured to measure a predetermined property of a fluid within the pipeline. The pipeline includes an input end and an output end having a cross-section with a predetermined size. The pipeline forms a microwave resonator. The pipeline has a cross-section in a first direction, the first direction being the direction of the distance between a first group of opposite pipe walls of the pipeline. The cross-section in the first direction has a dimension A in the first direction, and the dimension A extends beyond the input and output dimensions by a predetermined amount. The pipeline has a cross-section in a second direction, the second direction being the direction of the distance between a second group of opposite pipe walls of the pipeline. The second direction has an angle relative to the first direction, and the cross-section in the second direction has a second dimension B in the second direction that is smaller than dimension A. The first and second directions are selected such that B < A < 2B. Resonant modes reflected by opposite cross-section surfaces are obtained, and each cross-section surface provides a different standing wave. in, The at least one measurement microwave antenna is mounted in the surface and configured to measure at least one resonant frequency indicative of the predetermined property of the fluid.

2. The pipe according to claim 1, characterized in that, The first dimension A is selected to correspond to half of the wavelength of the first resonant mode of the microwave signal.

3. The pipeline according to claim 1, characterized in that, The pipeline forms a reverse Venturi tube.

4. The pipeline according to claim 1, characterized in that, In at least one of the directions, the pipeline is formed by two opposite curved pipe walls.

5. The pipeline according to claim 2, characterized in that, In at least one of the directions, the pipeline is formed by two opposite planar pipe walls.

6. The pipeline according to claim 5, characterized in that, At least one of the antennas is mounted on the planar pipe wall.

7. The pipeline according to claim 1, characterized in that, The antenna is a microwave measurement antenna configured to measure the resonant and / or transmission characteristics of microwave signals in the pipeline.

8. The pipeline according to claim 1, characterized in that, The cross-section in the second direction has a dimension between the cross-sections of the input and output and the dimension in the first direction.

9. The pipeline according to claim 1, characterized in that, The angle is 90 degrees.

10. A system for measuring the flow characteristics of a fluid, including a pipe, according to any one of the preceding claims, characterized in that, The at least one measurement microwave antenna includes at least one resonant measurement antenna configured to measure at least one electromagnetic resonance in the pipeline.

11. The system according to claim 9, characterized in that, The at least one measurement microwave antenna includes at least one transmitter and one receiver, and the system is configured to measure the transmission time between the transmitter and the receiver.

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