WO2015091452A1

WO2015091452A1 - Probe for measuring conductivity at high pressure and high temperature

Info

Publication number: WO2015091452A1
Application number: PCT/EP2014/077917
Authority: WO
Inventors: Jean-Christophe NUGUET
Original assignee: Areva
Priority date: 2013-12-20
Filing date: 2014-12-16
Publication date: 2015-06-25
Also published as: FR3015689B1; FR3015689A1

Abstract

This probe for measuring the conductivity of a fluid, comprising: an envelope (20) delimiting internally a measurement chamber (44), the envelope (20) exhibiting a first front aperture (42) surrounded by a first flange (22); a first electrode (24) engaged in the measurement chamber (44) through the first front aperture (42); a second flange (26) integral with the first electrode (24), the second flange (26) being arranged opposite the first flange (22) and exhibiting a second front aperture (56) in coincidence with the first front aperture (42); a second electrode (28) engaged in the measurement chamber (44) through the first front aperture (42) and the second front aperture (56). A third flange (30) integral with the second electrode (28) is arranged opposite the second flange (26), and a rigid fixing (32) holds the first, second and third flanges (22, 26, 30) to one another.

Description

Probe for measuring high-temperature and high-temperature conductivity

The present invention relates to a probe for measuring the conductivity at high pressure and high temperature, comprising:

an envelope internally delimiting a measurement chamber, the envelope having a first front opening surrounded by a first flange;

a first electrode engaged in the measurement chamber through the first front opening;

a second flange integral with the first electrode, the second flange being arranged vis-à-vis the first flange and having a second front opening coinciding with the first front opening;

a second electrode engaged in the measurement chamber through the first front opening and the second front opening.

This probe is intended to measure the conductivity, or the resistivity, of a solution between two electrodes. An alternating voltage, the frequency of which varies according to the conductivity of the medium, is applied to the electrodes. This results in the formation of a current between the two electrodes which is a function of the conductivity of the solution. Calibration is performed using standard solutions that allow conductivity values to be matched with current measurements. The measuring probe is equipped with a temperature sensor that compensates the conductivity as a function of temperature.

Such a probe is typically intended to be implanted in a circuit carrying a heat transfer fluid requiring a continuous or point measurement of the physicochemical characteristics of the fluid.

The measurement of the conductivity of a volume of fluid is performed by various techniques, the general principle of which is to contact two electrodes by means of a volume of fluid to be analyzed. Classically, the various probes are classified by their general mechanical characteristics, that is to say the mechanical capabilities of a probe to be able to withstand the environment including mechanical stresses due to high pressures, thermal stresses favoring creep and corrosion of the electrodes or the combination of several aggressor effects that may affect the sealing system, the electrical insulators or the technique of connecting the supply and discharge circuits of fluids that can be heat-transferable.

Under certain conditions of extreme use, especially for nuclear installations, the range of conventional conductivity probes does not support the severe operating conditions exceeding temperatures of 150 ° C and pressures above several tens of bars.

To meet these constraints, many solutions have been designed in particular assemblies implementing various sealing techniques, thermal and electrical insulators supporting operating conditions or electrodes of particular annular, lamellar and cylindrical shape more or less adapted circulating a fluid in a measuring chamber.

JPS63243743 discloses a probe developed to meet the measurement operating conditions of a fluid having a high temperature and pressure, designed a first tubular electrode and a second solid electrode, both concentric, arranged in a resistant chamber at high pressures.

However, the first electrode is attached to the second electrode by an intermediate piece, a cap, creating a degradable arrangement for extreme conditions of temperature and pressure.

An object of the invention is to obtain a probe capable of conducting conductivity measurements continuously or occasionally, in an extreme environment where the conditions reach a temperature of 350 ° C. and a pressure of 150 bars.

For this purpose, the subject of the invention is a probe of the aforementioned type, in which the probe further comprises a third flange secured to the second electrode and arranged opposite the second flange, and a rigid attachment of the first second and third flanges to each other.

The probe according to the invention may comprise one or more of the following characteristics, taken in isolation or in any technically possible combination:

the probe comprises an electrical insulator in the form of a ring between the second flange and the third flange;

- The probe comprises a lid disposed vis-à-vis the third flange and a ring-shaped electrical insulation between the third flange and the cover;

the first, second and third flanges are arranged in respective planes parallel to each other;

the attachment comprises a plurality of fixing members removably fixing the first, second and third flanges to each other;

the probe comprises an electrical insulator in the form of a ring between each fixing member and the second flange and / or between each fixing member and the third flange; the first electrode comprises a tubular wall internally delimiting a central channel, the second electrode comprising a cylindrical rod engaged in the central channel;

the probe comprises an electrical insulator in the form of a sleeve interposed radially between the tubular wall and the rod;

the second electrode comprises a blind passage, bored in the cylindrical rod, the probe comprising a temperature sensor engaged in the blind passage;

the first and second electrodes are made of stainless steel, and in which at least respective surfaces facing the first and second electrodes have a surface coating of a noble metal;

- The surface coating is advantageously carried out by a gold deposit;

- At least respective surfaces vis-à-vis the first and the second electrode have a surface condition having a roughness whose mean arithmetic difference (Ra) is greater than 1;

- The probe comprises fluid supply and discharge connections opening into the measuring chamber, welded to the casing;

the probe comprises seals bearing temperatures greater than 150 ° C, at least between the first flange and the second flange and between the second flange and the third flange;

the probe comprises a sensor for measuring the temperature of the fluid in the measurement chamber, the probe comprising a control unit connected to the first and second electrodes and to the temperature measurement sensor, programmed to calculate the conductivity of the fluid in function; a potential difference between first and second electrodes and as a function of the fluid temperature measured by the measuring sensor.

The invention also relates to a method for measuring the conductivity of a fluid by a measuring probe comprising the following steps:

- Provision of a measurement probe as defined above;

- circulation of a fluid in the measuring probe;

- measurement of the conductivity of the fluid.

The invention will be better understood on reading the description which follows, given solely by way of example, and with reference to the appended drawings, in which:

FIG. 1 is an overall perspective view of the probe for measuring the conductivity at high pressure and high temperature according to the invention, - Figure 2 is a sectional view of the conductivity measuring probe along a median axial plane 11-11 of Figure 1.

In everything that follows, the meaning of "back" to "front" is understood as the direction of flow of the fluid in the supply of the measuring probe. The direction of the backward forward is represented along the central axis X from the bottom of the measuring chamber to the lid.

The direction towards the "outside" is understood as an orientation perpendicular to the central axis X, originating in the central axis X and moving away from it.

The probe 10 illustrated in FIG. 1 is intended for measuring the conductivity of a fluid at high pressure and high temperature.

The term "probe" is understood in the sense of the present invention as a measuring device equipped with a sensor performing a measurement of a physical quantity, in this case the electrical conductivity. A present measuring probe is intended to be integrated in an operating line carrying a heat transfer fluid.

Electrical conductivity is the opposite of resistivity. This measurement is useful in driving an installation and informs the operator of the evolution of the coolant.

For the purposes of the present invention, the term "coolant" fluid is understood to mean a fluid intended to carry heat energy, a fluid that can be compressed so as not to exceed a limit of boiling temperature, in particular a fluid that can be related to one another. to pressurized water, liquid sodium, molten salts.

A measurement probe 10 of the conductivity of a fluid comprises a casing 20 with a first flange 22, a first electrode 24 with a second flange 26, a second electrode 28 with a third flange 30 and a rigid attachment 32 of the first, second and third flanges 22, 26, 30 to each other.

In the example shown in FIG. 2, the probe further comprises a cover 34 and an electrical insulation 36.

The casing 20 comprises a first tubular wall 38 and a bottom 40 closing a rear end 41 of the tubular wall 38, a first front opening 42 leaving a front end of the tubular wall 38 open. The first flange 22 projects radially outwards with respect to the tubular wall 38. The first flange 22 is integral with the front end 43 of the casing 20. The section of the tubular wall 38 has in the example a circular section. Alternatively, the section of the tubular wall 38 may have other shapes including a quadrilateral section.

The tubular wall 38 has a central axis marked X in FIG. The casing 20 internally delimits a measuring chamber 44. The probe 10 comprises fluid supply and fluid evacuation connections 48, opening into the measuring chamber 44, and welded to the casing 20. The connection fluid feed 46 is carried by the bottom portion 40 of the casing 20, preferably at the center coincide with the central axis X. The discharge connection 48 of the fluid is carried by the tubular wall 38 of the casing 20.

The first tubular wall 38 is sized to withstand extreme conditions. For example, for a casing 20 made of stainless steel, the radius of the measuring chamber 44 is between 29 and 31 mm and the thickness of the casing 20 is between 9 and 1 1 mm.

The first electrode 24 comprises a second tubular wall 50 delimiting a central channel 52, the central channel 52 having rear and front openings 54, 56 at both ends thereof. The second flange 26 projects radially outwardly with respect to the second tubular wall 50. The second flange 26 surrounds the second front opening 56.

The central channel 52 is coaxial with the central axis X and has a preferably circular section.

The first electrode 24 is made according to applications in stainless steel or platinum. Electrolytic deposition of a noble material or a superposition of materials (gold, nickel + gold, ...) can be performed on the stainless steel electrode to prevent the formation of an insulating oxide layer which could influence the measurement. If the electrode is made of platinum a platinum black deposit can be made to improve the quality of the signal.

A surface coating which covers the first electrode, extends from the rear opening 54 to the second front opening 56, typically over a length of between 50 mm and 60 mm.

Preferably, the inside diameter of the second tubular wall 50 is between 14 and 18 mm and the thickness of the second tubular wall 50 is between 1 and 3 mm.

The second electrode 28 comprises a cylindrical rod 58 which extends from the rear opening 54 to the front opening 56. The second electrode 28 extends along the central axis X. A blind passage 60 is bored in the center of the cylindrical rod 58 and the third flange 30. The third flange 30 has the shape of a disc. The center of the disc is full. The cylindrical rod 58 protrudes along the central axis X from the face of the disk facing rearwardly. The third flange 30 is carried by the front end of the rod 58. The second electrode 28 is made according to applications in stainless steel or platinum. An electrolytic deposit of a noble material or a superposition of materials (gold, nickel + gold, ...) can be performed on the stainless steel electrode, a platinum black deposit can be made on the electrode in platinum.

The specific surface coating that extends from the rear end to the front end of the second electrode 28 is between a length of 40 mm and 60 mm.

Thus, the measuring probe 10 advantageously has respective surfaces vis-à-vis the first and the second electrode 24, 28 having a surface coating produced by electroplating, for example a surface deposit of a precious metal such than gold.

The deposition zones on the first and second electrodes 24, 28 advantageously have a sanded surface state, having a roughness whose mean arithmetic difference (Ra) greater than 1 (μηι).

Preferably, the diameter of the cylindrical rod 58 of the second electrode 28 is between 3 and 8 mm.

Advantageously, the measurement probe 10 comprises a temperature sensor

62, engaged in the blind passage 60. The temperature sensor 62 is depressed at the bottom of the blind passage so that the end of the temperature sensor is in contact with the metal of the second electrode, itself in contact with the solution in this zone. The bottom of the blind passage should be placed close enough to the rear opening 54 at a distance of less than 5 mm.

The rigid attachment 32 of the first, second and third flanges 22, 26 and 30 to each other comprises a set of fasteners 63 passing through a set of bores 64 formed in the various parts held. These fasteners are screws in the example shown. Alternatively, they are tie rods, or any other suitable fastener.

The fastener 32 is preferably made by means of at least 6 screws, providing a balanced angular distribution and preferably arranged on a circle with a radius greater than 90 mm.

The lid 34 is a solid cylindrical plate having a rear surface 65 facing the third flange 30 and a front surface 66. The rear surface 65 has a number of threads 67 equal to the number of bores 64 formed in each of the first, second third flanges 22, 26 and 30.

The lid 34 also has one or more sealed passages for the power supply 68 of the first and second electrodes 24, 28 and for the lines 70 for transferring the conductivity and temperature data to a control unit 72.

The electrical insulation 36 comprises at least two ring-shaped electrical insulators 73, 74, a sleeve-shaped tubular electrical insulator 76 and a set of ring-shaped electrical insulators 78.

The ring-shaped electrical insulators 73, 74 more precisely have circular inner and outer contours, a front plane face and a rear plane face.

Preferably, the diameter of the outer contour of the ring-shaped electrical insulators 73, 74 is concentric with that of the flanges 22, 26, 30 vis-a-vis. The diameter of the inner contour is between 25 and 35 mm.

The tubular electrical insulator 76 is in the form of a tubular sleeve having a through central channel and an outer flange at one end of the sleeve.

Preferably, the inner diameter is equal to that of the outer diameter of the second electrode 28. The outer diameter of the tubular portion is smaller than the inside diameter of the second tubular wall 50 of the first electrode 24. The diameter of the collar of the electrical insulation is greater than the inside diameter of the second tubular wall 50 of the first electrode 24 and remains smaller than the inside diameter of the ring-shaped electrical insulator 73.

The ring-shaped electrical insulators 78 are tubes having an inside diameter slightly greater than the diameter of the screw 32 and have a thickness of between 1 and 3 mm.

The set of electrical insulators 73, 74, 76 and 78 is made of polymer, advantageously in polyimides (Vespel type, meldin ...), or for lower heat transfer fluid temperatures in PEEK or PTFE, or ceramic, advantageously alumina, silicon nitride, or glass (sapphire, quartz, ...).

The tightness of the assembly of the measuring probe 10 is achieved by seals 84, and advantageously by perfluorinated elastomer O-rings supporting temperatures higher than 320 ° C.

The arrangement of the measuring probe 10 according to the invention will now be described.

As illustrated by way of example in FIG. 1, the first, second, third flanges 22, 26 and 30, the cover 34 and the two ring-shaped electrical insulators 73, 74 are coaxial with each other.

The first, second and third flanges 22, 26 and 30 are arranged in respective parallel planes. These planes are perpendicular to the X axis.

The lid 34 is disposed in a plane parallel to the flanges. The first electrode 24 is engaged in the measurement chamber 44 through the first front opening 42.

The second flange 26 secured to the first electrode 24 is opposite and pressed against the first flange 22 of the envelope 20.

The front opening 56 of the central channel 52 is in register with the first front opening 42 of the casing 20, enabling the rod 58 of the second electrode 28 to be inserted therein.

The third flange 30 secured to the second electrode 28 is opposite the second flange 26 of the first electrode 24.

The first ring-shaped electrical insulator 73 and the flange of the tubular electrical insulator 76 extend in a plane perpendicular to the central axis X. They are interposed between the second flange 26 of the first electrode 24 and the third flange 30 of the second electrode 28. The tubular electrical insulator 76 is fitted into the first electrode 24. It is interposed radially between the rod 58 and the tubular wall 50. It electrically isolates the rod 58 from the second tubular wall 50. It provides an additional function for guiding the rod 58 of the second electrode 28. The second ring-shaped electrical insulator 75 is interposed between the third flange 30 and the cover 34.

The screws 63 pass right through the first, second, third flanges 22, 26 and 30 and the ring-shaped electrical insulators 73, 74 to fit into the threaded holes 67 formed in the cover 34. The screws 63 are intended to axially tighten the assembly.

The clamping provides operational prestressing for sealing with the seals 84 disposed between the interfaces of the first and second flanges 22, 26, between the second flange 26 and the ring-shaped electrical insulator 74, between the third flange 30 and the ring-shaped insulator 73 and between the third flange 30 and the cover 34.

The cover 34 also allows the passage of the supply (not shown) of the electrodes 68 and 70 of the signal transfer cables.

A method for measuring the conductivity implemented using the measurement probe 10 according to the invention will now be described.

Initially, the measurement probe 10 is integrated in a pipe containing a heat transfer fluid to be analyzed. The calibration parameters specific to the measuring probe 10 have been entered at the control unit 72 which notably calculates the conductivity. A set of valves (not shown) makes it possible to feed a fluid towards the measurement probe 10 or to deflect it in order to carry out a maintenance operation in particular.

In a configuration where this set of valves allows the supply of the measurement probe 10, the fluid flows to the supply 46 and is introduced into the measurement chamber 44, which it occupies entirely, especially between the first and second chambers. and second electrodes 24, 28.

The first and second electrodes 24, 28 are supplied with current. The voltage between the electrodes is raised periodically or continuously. It is transmitted to the control unit 72 which is programmed to calculate the resistivity of the fluid by calculation. As the parameters for calculating the conductivity of the fluid change with the temperature of the measuring probe 10, the adjustment parameters of the calculation of the conductivity by the control unit 72 are readjusted in real time by the data transmitted by the temperature sensor. 62. Thus the measurement is carried out in real time or punctually. The fluid flowing in the measurement chamber 44 is continuously evacuated by the evacuation 48 which makes it possible to inform in real time of the conductivity of the fluid and to follow its evolution during the operation of an installation.

The measurement probe 10 advantageously carries out measurements of the conductivity and temperature of a fluid present in the measurement chamber 44. The measurement probe 10 integrates, for example, in a circuit for operating a heat transfer fluid.

Because the casing 20 and the electrodes 24, 28 are fixed to each other by first, second and third flanges 22, 26, 30 disposed facing each other and rigidly fixed to one another, then the probe measuring device 10 is adapted to withstand extreme environments, fluids at high temperature and high pressure. Advantageously, the measuring probe 10 withstands pressures greater than 10 bar, at temperatures above 150 ° C.

The fasteners 32 and the seals 84 seal the probe 10. The measuring probe 10 is particularly robust and reliable and can endure severe industrial operating conditions for periods corresponding to the scale of the planes. maintenance of a production plant.

The measuring probe 10 also advantageously comprises a flange assembly without moving parts, particularly suitable for mounting and dismounting the measuring probe 10 during the preventive maintenance action.

According to an alternative embodiment not shown, the first and second electrodes do not respectively comprise a tubular wall and a rod, coaxial to each other. For example, the first and second electrodes comprise first and second flat plates, arranged vis-a-vis parallel to one another, inside the measuring chamber. The first and second plates are secured respectively to the second and third flanges. The respective surfaces facing the first and the second electrode have a surface coating of a noble metal.

Claims

1. - A probe for measuring the conductivity of a fluid, comprising:

- an envelope (20) internally defining a measuring chamber (44), the envelope (20) having a first front opening (42) surrounded by a first flange (22);

- a first electrode (24) engaged in the measuring chamber (44) through the first front opening (42);

a second flange (26) secured to the first electrode (24), the second flange (26) being arranged opposite the first flange (22) and having a second front opening (56) coinciding with the first first front opening (42);

- a second electrode (28) engaged in the measuring chamber (44) through the first front opening (42) and the second front opening (56);

characterized in that the probe (10) further comprises a third flange (30) integral with the second electrode (28) and arranged vis-à-vis the second flange (26), and a rigid attachment (32) of first, second and third flanges (22, 26, 30) to each other.

2. - Measuring probe according to claim 1, comprising a ring-shaped electrical insulator (74) between the second flange (26) and the third flange (30).

3. - Measuring probe according to claim 1 or 2, comprising a cover (34) disposed vis-à-vis the third flange and a ring-shaped electrical insulator (73) between the third flange (30) and the lid (34).

4. - Measuring probe according to any one of the preceding claims, wherein the first, second and third flanges (22, 26, 30) are arranged in respective planes parallel to each other.

5. Measuring probe according to any one of the preceding claims, wherein the fastener (32) comprises a plurality of fasteners (63) releasably fixing the first, second and third flanges (22, 26, 30). ) to each other.

6. Measuring probe according to claim 5, comprising a ring-shaped electrical insulator (78) between each fastener (63) and the second flange (26) and / or between each fastener (63) and the third flange (30).

7. Measuring probe according to any one of the preceding claims, wherein the first electrode (24) comprises a tubular wall (50) internally delimiting a central channel (52), the second electrode (28) comprising a cylindrical rod ( 58) engaged in the central channel (52).

8. Measuring probe according to claim 7, comprising a sleeve-shaped electrical insulator (76) interposed radially between the tubular wall (50) and the rod (48).

9. - Measuring probe according to claim 7 or 8, wherein the second electrode (28) comprises a blind passage (60), bored in the cylindrical rod (58), the probe comprising a temperature sensor (62) engaged in the blind passage (60).

10. - Measuring probe according to the preceding claims, wherein the first and the second electrode (24, 28) are made of stainless steel, and wherein at least respective surfaces vis-à-vis the first and the second electrode (24, 28) have a surface coating of a noble metal.

1 1. - Measuring probe according to claim 10, wherein the surface coating is advantageously made by a gold deposit.

12. Measuring probe according to any one of the preceding claims, wherein at least respective surfaces vis-à-vis the first and the second electrode (24, 28) have a surface condition having a roughness of which mean arithmetic difference (Ra) is greater than 1.

13. Measuring probe according to any one of the preceding claims, comprising feed connections (46) and discharge (48) of fluid opening into the measuring chamber (44), welded to the casing (20). ).

14. Measuring probe according to any one of the preceding claims, comprising seals (84) supporting temperatures greater than 150 ° C, at least between the first flange (22) and the second flange (26) and between the second flange (26) and the third flange (30).

15. - Measuring probe according to any one of the preceding claims, comprising a sensor (62) for measuring the temperature of the fluid in the measuring chamber (44), the probe comprising a control unit (72) connected to the first and second electrodes (24, 28) and the temperature measuring sensor, programmed to calculate the conductivity of the fluid as a function of a potential difference between first and second electrodes (24, 28) and as a function of the fluid temperature measured by the measuring sensor (62).

16. - Method for measuring the conductivity of a fluid by a measuring probe (10) comprising the following steps:

- Providing a measurement probe (10) according to any one of the preceding claims;

- circulation of a fluid in the measuring probe (10);

- measurement of the conductivity of the fluid.