WO2015131248A1

WO2015131248A1 - Compact differential pressure flow meters

Info

Publication number: WO2015131248A1
Application number: PCT/AU2015/050089
Authority: WO
Inventors: Geoff SOKOLL
Original assignee: Mezurx Pty Ltd
Priority date: 2014-03-07
Filing date: 2015-03-05
Publication date: 2015-09-11

Abstract

A differential pressure (DP) flow meter, comprising a pipe elbow having a bend, an inlet portion upstream of the bend, and an outlet portion downstream of the bend, wherein at least one partial flow obstruction device is arranged inside the pipe elbow proximate to the bend, and wherein the at least one partial flow obstruction device and the bend are mutually arranged to collectively produce differential pressure in fluid flowing through the pipe elbow.

Description

COMPACT DIFFERENTIAL PRESSURE FLOW METERS

Field

[0001 ] The present invention relates to differential pressure (DP) flow meters. Background

[0002] DP flow meters are used to measure fluid flow in pipelines in industrial processes such as oil and gas production. DP flow meters generally comprise a differential pressure producing element, such as a wedge element or an elbow bend, in a pipe length having a circular cross-section. The fluid flow rate is proportional to the square root of the resulting differential pressure at the upstream and downstream sides of the wedge element, or the inner and outer apexes of the elbow bend.

[0003] Conventional wedge and elbow DP flow meters have various disadvantages. Figure 1 illustrates a conventional wedge DP flow meter (or "wedge meter") 10 comprising a wedge element 12 protruding into fluid flow through a straight pipe 14. Pressure sensors 16, 18 are provided at the upstream and downstream sides of the wedge element 12. The wedge meter 10 further comprises upstream and downstream straight pipe lengths 20, 22 on the upstream and downstream sides of the wedge element 12.

[0004] Conventional wedge meters 10 require the fluid density to be known in order to calculate volumetric flow rate. Either the fluid density is measured before the wedge meter is used (and the fluid density is then assumed to be constant), or for cases where the fluid density may vary, a device to constantly measure fluid density simultaneously is required. The present applicant's WO 2012/061873 addresses this disadvantage by using a Coriolis meter to measure the density of fluid passing through a wedge meter.

[0005] In addition, conventional wedge meters 10 typically require long lengths of straight unrestricted pipe on the upstream and downstream sides of the wedge to ensure that fluid flow across the wedge is uniform. The minimum straight pipe length on the upstream side of the wedge depends on the pipe diameter, and the fitting at the end of the straight run. The minimum upstream pipe length is typically 10 pipe diameters (10D). The minimum length of the downstream straight pipe run also depends on the pipe diameter, and is typically 5 pipe diameters (5D). The long upstream and downstream pipe lengths required by conventional wedge meters are disadvantageous in oil and gas installations where physical space is limited.

[0006] Figure 2 illustrates a conventional elbow DP flow meter (or "elbow meter") 30 comprising an elbow bend 32 in a pipe elbow 34 having a circular cross-section. Pressure sensors 36, 38 are provided in the radially inner and outer walls 40, 42 of the elbow bend 32. This type of DP flow meter operates on the principle that as fluid flows around the elbow bend 32, centrifugal action produces a higher pressure on the outer wall 42 of the elbow bend 32 compared to the inner wall 40 of the elbow bend 32. Elbow meters 30 produce very little loss of pressure (which is advantageous when overall system pressure loss is of concern), however the small pressure differentials require extremely sensitive pressure sensors 36, 38 and hence limit the accuracy of the fluid flow measurements.

[0007] In this context, there is a need for compact DP flow meters that address or at least partially ameliorate the disadvantages of conventional wedge and elbow meters.

Summary

[0008] According to the present invention, there is provided a DP flow meter, comprising a pipe elbow having a bend, an inlet portion upstream of the bend, and an outlet portion downstream of the bend, wherein at least one partial flow obstruction device is arranged inside the pipe elbow proximate to the bend, and wherein the at least one partial flow obstruction device and the bend are mutually arranged to collectively produce differential pressure in fluid flowing through the pipe elbow.

[0009] The DP flow meter may further comprise two pressure sensors, one of which is arranged in an inner surface of the inlet portion upstream of, and proximate to, the partial flow obstruction device, and the other of which is arranged in an inner surface of the outlet portion downstream of, and proximate to, the partial flow obstruction device.

[0010] The inlet portion may comprise a horizontal straight pipe length, and the outlet portion may be a U-shaped pipe length having vertically upwards and downwards pipe sections, wherein two pressure sensors are vertically spaced apart in one or both of the vertically upwards and downwards pipe sections so that in use fluid density is measureable using hydrostatic pressure.

[001 1 ] The at least one partial flow obstruction device may be located downstream or upstream of, and proximate to, the bend.

[0012] The at least one partial flow obstruction device may be located proximate to an inner or outer apex of the bend.

[0013] The bend may comprise radially inner and outer internal surfaces, wherein the at least one partial flow obstruction device is located at, or proximate to, the inner or outer internal surfaces.

[0014] The at least one partial flow obstruction device may comprise one or more of a wedge element, an inclined plate, an orifice plate, a pipe constriction, and combinations thereof.

[0015] The pipe elbow may be formed by bending a straight pipe length having a wedge element therein through 90 degrees to form the bend so that the wedge element collapsibly folds onto itself to form an inclined plate located at, or proximate to, the bend.

[0016] The inlet portion and the outlet portion may be disposed at an angle of less than 180° to each other. For example, the inlet portion and the outlet portion may be disposed at an angle of 90° to each other.

[0017] The inlet portion and the outlet portion may be disposed in a common plane, or in different planes to each other. [0018] The present invention also provides a method, comprising forming a pipe elbow by bending a straight pipe length having a wedge element therein through 90 degrees to form a bend in the straight pipe length so that the wedge element collapsibly folds onto itself to form an inclined plate located at, or proximate to, the bend.

[0019] The present invention also provides a method, comprising measuring fluid flow in a pipeline using the DP flow meter described above.

[0020] The method may further comprise simultaneously measuring fluid flow and fluid density in the pipeline using the DP flow meter described above.

Brief Description of Drawings

[0021 ] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which:

Figure 1 is a cross-section view of a conventional wedge meter;

Figure 2 is a cross-section view of a conventional elbow meter;

Figure 3 is a cross-section view of a DP flow meter according to an example embodiment;

Figure 4 is a cross-section view of a conventional wedge meter in a straight pipe length with arrows indicating bending and folding through 90 degrees to form the DP flow meter of Figure 3; and

Figure 5 is a view of the DP flow meter with integral fluid density measurement according to another example embodiment.

Detailed Description

[0022] Referring to Figure 3, a DP flow meter according to an example embodiment may comprise a pipe elbow 50 having an inlet portion 52, a bend 54 and an outlet portion 56. The bend 54 may have radially inner and outer walls 58, 60 with respective inner and outer apexes. At least one partial flow obstruction device 62 may be arranged internally at the inner wall 58 of the bend 54 so that in use the at least one partial flow obstruction device 62 and the bend 54 are mutually arranged to collectively produce differential pressure in fluid flowing through the pipe elbow 50.

[0023] The at least one partial flow obstruction device 62 may comprise one or more of a wedge element, an inclined plate, an orifice plate, a pipe constriction, and combinations thereof. For the sake of clarity and ease of understanding at least one partial flow obstruction device 62 is illustrated by way of example only in the drawings as a single inclined plate 62. It will be appreciated that in alternative examples multiple partial flow obstruction devices 62 may be located downstream and/or upstream of, and proximate to, the bend 54 depending on pipe geometry and fluid flow considerations.

[0024] In the embodiment illustrated in Figure 3, the at least one partial flow obstruction device 62 is illustrated for the sake of clarity and ease of understanding as being arranged at the inner apex of the inner wall 58. It will be appreciated that other alternative location of the partial flow obstruction device 62 in or about the pipe elbow bend 54 are possible depending on pipe geometry and fluid flow considerations. For example, the at least one partial flow obstruction device 62 may be located downstream or upstream of, and proximate to, the bend 54. Further alternatively, the at least one partial flow obstruction device 62 may be located proximate to an inner or outer apex of the bend 54. Further, the bend 54 may comprise radially inner and outer internal surfaces, and the at least one partial flow obstruction device 62 may be located at, or proximate to, the inner or outer internal surfaces of the bend 54.

[0025] In addition to selectively varying the location of the at least one partial flow obstruction device 62 relative to the bend 54, the relative arrangements of the inlet and outlet portions 52, 56 of the pipe elbow 50 may be selectively varied depending on pipe geometry and fluid flow considerations. For example, the inlet portion 52 and the outlet portion 56 may be disposed at an angle of less than 180° to each other. For example, the inlet portion 52 and the outlet portion 56 may be disposed at an angle of 90° to each other. Further, the inlet portion 52 and the outlet portion 56 may be disposed in a common plane, or in different overlapping or non-overlapping planes to each other.

[0026] The DP flow meter 50 may further comprise two pressure sensors 62, 64, one of which is arranged in an inner wall of the inlet portion 52 upstream of, and proximate to, the inclined plate 62, and the other of which is arranged in an inner wall of the outlet portion 56 downstream of, and proximate to, the inclined plate 62.

[0027] Referring to Figure 4, and for ease of understanding only, the DP flow meter 50 may be formed by bending a conventional wedge meter 10 comprising a straight pipe length 14 with an internal, centrally arranged wedge element 12 through 90 degrees to form the pipe elbow bend 54 so that the wedge element 12 collapsibly folds onto itself to form the inclined plate 62 at the pipe elbow bend 54. Other equivalent fabrication methods or starting materials may also be used to form the DP flow meter 50.

[0028] Referring to Figure 5, in an alternative embodiment of the DP flow meter 50, the inlet portion 52 may be a horizontal straight pipe length, and the outlet portion 56 may be a U-shaped pipe length having vertically upwards and downwards pipe sections 66, 68. Two pressure sensors 70, 72 may be vertically spaced apart in one or both of the vertically upwards and downwards pipe sections 68 so that in use fluid density is measureable using hydrostatic pressure. For example, in the embodiment illustrated in Figure 5, the pressure sensors 70, 72 are vertically spaced apart in the vertically downwards pipe section 68. This embodiment provides integral fluid density measurement so that both fluid flow and fluid density in a pipeline are simultaneously measureable. It will be appreciated that the outlet portion 56 is not limited to a U-shaped pipe length, but may be alternatively implemented in other shapes and configurations of pipe lengths or sections that produce hydrostatic pressure in the fluid downstream of the bend 54.

[0029] Embodiments of the present invention provide compact DP flow meters that may be useful for measuring fluid flow, and optionally simultaneously measuring fluid density, in a pipeline in industrial processes, such as oil and gas production. The embodiments may be regarded as a hybrid of conventional wedge and elbow meters in that an elbow meter with a differential pressure producing plate may be formed from a folded wedge meter. The embodiments may advantageously measure fluid flow by employing the same physical principles as a wedge meter, but using a simple and inexpensive means of integrating fluid density measurement without the use of a more complicated and expensive Coriolis meter, whilst also reducing the overall physical length of the device to address physical space constraints, and reducing fabrication cost.

[0030] The fluid flow pattern past the inclined plate still behaves in a similar manner to that over the wedge in a conventional wedge meter, hence allowing prediction of the flow rate based on the differential pressure. While embodiments may superficially resemble an elbow meter, the inclusion of the inclined plate, or one or more other types of partial flow obstruction devices, greatly enhances the pressure difference generated by the flow and thus significantly increases the accuracy of the DP flow meter, particularly at low flow rates. Furthermore, the action of the inclined plate and the 90 degree elbow reduce the sensitivity of the flow to upstream disturbances, which allows a reduction in the required length of straight upstream pipe compared to conventional wedge meters.

[0031 ] The embodiment comprising the complete arrangement of a compact folded wedge meter with integrated density measurement combines the folded wedge meter with a series of elbows to form a U shape (possibly upright, or inverted, or other positions in between). The fluid flow subsequently continues up the vertical length of pipe after the first elbow, and then proceeds to turn through 180 degrees and proceed downwards, after which it finally turns another 90 degrees and exists the flow meter. The density of the fluid may be determined by measuring the pressures at two vertically separated locations in a portion of the vertical pipe employing the principles of hydrostatic pressure.

[0032] The above embodiments have been described by way of example only and modifications are possible within the scope of the claims that follow.

Claims

1 . A differential pressure (DP) flow meter, comprising a pipe elbow having a bend, an inlet portion upstream of the bend, and an outlet portion downstream of the bend, wherein at least one partial flow obstruction device is arranged inside the pipe elbow proximate to the bend, and wherein the at least one partial flow obstruction device and the bend are mutually arranged to collectively produce differential pressure in fluid flowing through the pipe elbow.

2. The DP flow meter of claim 1 , further comprising two pressure sensors, one of which is arranged in an inner surface of the inlet portion upstream of, and proximate to, the partial flow obstruction device, and the other of which is arranged in an inner surface the outlet portion downstream of, and proximate to, the partial flow obstruction device.

3. The DP flow meter of claim 1 , wherein the inlet portion comprises a horizontal straight pipe length, and the outlet portion comprises a U-shaped pipe length having vertically upwards and downwards pipe sections, and wherein two pressure sensors are vertically spaced apart in one or both of the vertically upwards and downwards pipe sections so that in use fluid density is measureable using hydrostatic pressure.

4. The DP flow meter of claim 1 , wherein the at least one partial flow obstruction device is located downstream or upstream of, and proximate to, the bend.

5. The DP flow meter of claim 1 , wherein the at least one partial flow obstruction device is located proximate to an inner or outer apex of the bend.

6. The DP flow meter of claim 1 , wherein the bend comprises radially inner and outer internal surfaces, and wherein the at least one partial flow obstruction device is located at, or proximate to, the inner or outer internal surfaces.

7. The DP flow meter of claim 1 , wherein the at least one partial flow obstruction device comprises one or more of a wedge element, an inclined plate, an orifice plate, a pipe constriction, and combinations thereof.

8. The DP flow meter of claim 1 , wherein the pipe elbow is formed by bending a straight pipe length having a wedge element therein through 90 degrees to form the bend so that the wedge element collapsibly folds onto itself to form an inclined plate at, or proximate to, the bend.

9. The DP flow meter of claim 1 , wherein the inlet portion and the outlet portion are disposed at an angle of less than 180° to each other.

10. The DP flow meter of claim 1 , wherein the inlet portion and the outlet portion are disposed at an angle of 90° to each other.

1 1 . The DP flow meter of claim 1 , wherein the inlet portion and the outlet portion are disposed in a common plane, or in different planes to each other.

12. A method, comprising forming a pipe elbow by bending a straight pipe length having a wedge element therein through 90 degrees to form a bend in the straight pipe length so that the wedge element collapsibly folds onto itself to form an inclined plate located at, or proximate to, the bend.

13. A method, comprising measuring fluid flow in a pipeline using the DP flow meter of claim 1 .

14. The method of claim 13, further comprising simultaneously measuring fluid flow and fluid density in the pipeline using the DP flow meter of claim 3.