RU2589354C2 - Multiphase flow meter - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention relates to x-ray multi-phase flow meter. Flow meter comprises a first detector to measure volume flow rate of multiphase fluid medium inside the section of pipe and second detector for determination of absorption of x-ray or gamma radiation fluid inside section of pipe at least two different wavelengths. According to invention, wall (18) section of pipe comprises circular undercut (20) located upstream first and second detector, which enables to destroy sticking to wall of liquid film downstream of undercuts.

EFFECT: improved determination of phase composition.

7 cl, 3 dwg

Description

The invention relates to a multiphase flow meter, according to the restrictive part of paragraph 1 of the claims.

To determine the exact mass flow rate of multiphase fluids, such as mixtures of oil, water and gas in pipelines, it is necessary to determine both the volumetric flow and the phase composition of the fluid. The volumetric flow can be determined using conventional flow detectors, for example, by recording the pressure drop in the venturi.

To measure the phase composition, it is known to use X-ray absorption using the fact that the gas and liquid phases usually have different absorption coefficients. Therefore, by measuring the absorption of x-ray or gamma radiation at least at two different wavelengths, the ratio of the individual phases can be determined. An example of a flow meter based on this technology is known from US 6,265,713 B1.

One of the problems that make accurate flow measurement difficult is the flow properties of multiphase mixtures inside pipes. In particular, the liquid phase tends to form a film along the pipe wall, which moves at a speed different from the speed of the main stream. The presence of such a liquid film may make it difficult to determine the phase ratio and thereby lead to an incorrect flow measurement.

Therefore, the object of the invention is the creation of a multiphase flow meter, according to the restrictive part of paragraph 1 of the claims, which provides improved measurement accuracy.

The problem is solved using a flow meter, according to paragraph 1 of the claims.

The multiphase X-ray flow meter according to the invention comprises first detection means for measuring the volumetric flow rate of the multiphase fluid inside the pipe section and second detection means for determining the absorption of X-ray radiation by the fluid inside the pipe section at least at two different wavelengths.

To prevent the formation of a liquid film, the wall of the pipe section contains a circumferential undercut located downstream of the first and second detector means. Liquid films formed upstream of the pipe section can be scraped off the wall at the undercut, so that the liquid phase is again connected to the main fluid stream in the area of the pipe used for measurement, which reduces the inaccuracies caused by the incorrect determination of the phase ratio within the stream.

The dead zone of the fluid created by the undercut helps to prevent the formation of a liquid film again on a large part of the pipe, so that a film-free state in the entire measurement zone can be ensured.

In one preferred embodiment of the invention, the undercut forms a sharp-angled edge, with the first part of the pipe wall being upstream of the undercut. The presence of such a sharp edge facilitates tearing of the film and the formation of liquid droplets that can be carried away by the main fluid stream.

In addition, preferably, the second part of the pipe wall is formed upstream of the first part of the pipe wall, which is inclined outward from the center of the pipe in the opposite direction to the flow direction. In other words, the pipe narrows downstream before undercutting, directing and concentrating the liquid film to the edge and contributing to the destruction of the film.

In another embodiment, the second portion of the pipe wall is substantially parallel to the portion of the undercut wall extending directly from the edge. This geometry helps to destroy the film and provides a sufficiently long film-free part of the pipe for the correct measurement of the phase ratio.

In an alternative embodiment of the invention, the first part of the pipe wall is inclined outward from the center of the pipe at an angle smaller than the second part of the pipe wall. Drops formed from the film at the edge of the first part of the pipe wall in the flow direction are thereby directed to the center of the pipe, slowing down the attachment of the drops again to the pipe wall, which leads to an increase in the length of the pipe part suitable for measuring flow.

The following is an explanation of the invention and its embodiments with reference to the accompanying drawings, which depict:

FIG. 1 is a pipe used in one embodiment of a flowmeter according to the invention in an isometric view;

FIG. 2 - pipe wall edge bounding the measuring part of the pipe, according to FIG. 1, on an enlarged scale;

FIG. 3 is a cross-sectional view of the edge of a pipe wall according to FIG. 2;

FIG. 4 is a cross section of the edge of the pipe wall with a different geometry.

To ensure accurate determination of the mass flow inside the pipeline transporting the mixture of oil, water and gas, a pipe 10 is provided, consisting of a wide section 17 and a narrower section 14 upstream after the wide section in the direction 16 of the fluid flow.

At the boundary between sections 12, 14, pipe wall 18 forms an undercut 20 and a sharp edge 22. A liquid film can form on the walls of section 12. Wall 18, wall 24, edge 22, and undercut 20 are used to separate the liquid film and its destruction. Upon reaching the first edge between the walls 18 and 24 and the edge 22, this liquid film breaks and forms droplets that are carried away within the main fluid stream. Therefore, the pipe wall 18 in a narrow section downstream of edge 22 is substantially free of adhering fluid. This allows you to accurately determine the phase composition of the fluid inside a narrow section using x-ray absorption spectroscopy at two different wavelengths.

In FIG. 3 shows in more detail the geometry of the pipe wall 18 surrounding the edge 22. The part of the pipe wall 18 forming an undercut 20 forms an acute angle β with the first pipe wall part 24 extending parallel to the main axis of the pipe 10. Upstream, the pipe wall part 24 continues with the second part 26 of the pipe wall, which extends approximately parallel to the wall of the undercut 28, which is directly connected to the edge 22, and forms an angle α with the first part 24 of the pipe wall, which is approximately equal to the angle β.

The inclination of the second part 26 of the pipe wall helps to direct the liquid film adhering to the pipe wall toward the center of the pipe 10. After the destruction of the film at the edge 22, the undercut 20 prevents the film from forming again over a considerable length of the narrow section 14.

In FIG. 4 shows an alternative geometry of a portion of the edge of the pipe 10. It is different from that shown in FIG. 3 of the embodiment in that the first part 24 of the pipe wall is not parallel to the main axis of the pipe, but tilted outward relative to the flow direction 16 by an angle γ that is less than the angle α between the first part 24 and the second pipe wall part 26. This gives an additional moment in the direction of the center of the pipe to the droplets formed on the edge 22, due to which the attachment of the indicated drops to the pipe wall is slowed down.

LIST OF POSITIONS

10 pipe

12 wide section

14 Narrow section

16 flow direction

18 pipe wall

20 Undercut

22 Edge

24 Part of the pipe wall

26 Part of the pipe wall

28 Part of the undercut wall.

Claims (7)

1. A multiphase flow meter comprising first detection means for measuring a volumetric flow rate of a multiphase fluid inside a pipe section and second detection means for determining an X-ray or gamma radiation absorption by the fluid inside the pipe section at least at two different wavelengths, characterized in that the wall (18) the pipe section comprises a circumferential undercut (20) located upstream of the first and second detector means. 2. A flowmeter according to claim 1, characterized in that the undercut (20) forms an edge having an acute angle (22) with the first part (24) of the pipe wall downstream of the undercut (20). 3. The flow meter according to any one of paragraphs. 1 or 2, characterized in that the second part (26) of the pipe wall downstream of the first part (24) of the pipe wall is inclined outward from the center of the pipe in a direction opposite to the direction (16) of the flow. 4. A flow meter according to claim 3, characterized in that the first part (24) of the pipe wall is inclined outward from the center of the pipe at an angle smaller than the second part (26) of the pipe wall. 5. A flow meter according to claim 3, characterized in that the second part (26) of the pipe wall is substantially parallel to the part (28) of the undercut wall extending directly from the edge (22). 6. A flowmeter according to claim 5, characterized in that the first part (24) of the pipe wall is inclined outward from the center of the pipe at an angle smaller than the second part (26) of the pipe wall. 6. The flow meter according to claim 1, characterized in that the cross section of the pipe is round.

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