Device for detecting fluoride ions in nitric medium

Abstract

A device for detecting fluoride ions in a nitric acid solution, comprising: – a detection probe (1) including: a zirconium measuring element (6) and a zirconium reference element (7); – measuring conductors (11, 12, 13, 14); – an electrical resistance measuring circuit connected to said measuring conductors (11, 12, 13, 14), and adapted to measure the relative electrical resistance of a portion of the measuring element (6) with respect to a portion of the reference element (7); – a detection circuit adapted to correlate an increase in said relative resistance with the presence of fluoride ions in the nitric acid solution. Figure for the abstract: Fig. 2

Description

Title of the invention: Device for detecting fluoride ions in a nitric medium Technical field

[0001] The invention relates to the field of detection of chemical elements and more particularly relates to the detection of the chemical element fluorine (F) in free form, i.e. in the form of fluoride ions. PRIOR ART

[0002] It is known to detect the presence of the fluorine element within a solution, in particular by means of reactive tubes, with spectroscopic means, or even with chromatographic means.

[0003] Current processes and devices are expensive to implement and generally require destructive sampling in the solution. Their implementation is generally tedious and they are difficult to integrate into a continuous industrial process.

[0004] Furthermore, these methods and devices are generally limited to the detection of the fluorine element as a whole, whether present in complex or free form, and are not capable of distinguishing fluoride ions from the fluorine element present in complex form (for example when it is bound to a metal cation, or when it is bound to a proton to form hydrofluoric acid). Statement of the invention

[0005] The invention aims to improve the detection devices of the prior art.

[0006] To this end, the invention relates to a device for detecting fluoride ions in a nitric medium comprising: - a detection probe comprising: a zirconium measuring element having a wall delimiting a closed internal space, this measuring element being intended to be immersed in the nitric medium to be inspected; a zirconium reference element, arranged in the internal space of the measuring element and electrically connected by a first end to the measuring element; - measuring conductors electrically connected to the measuring element and to the reference element, and adapted to measure the electrical resistance of a portion of the measuring element and a portion of the reference element; - an electrical resistance measuring circuit connected to said measuring conductors, and adapted to measure the relative electrical resistance of said portion of the measuring element, with respect to said portion of the reference element; - a detection circuit adapted to correlate an increase in said relative resistance with the presence of fluoride ions in the nitric medium.

[0007] The invention precisely allows the detection of only fluoride ions within the nitric medium.

[0008] The device according to the invention can be installed online, on a continuous process, to allow continuous monitoring and almost real-time detection of the presence of fluoride ions in the nitric medium inspected, without requiring sampling or intervening on the nitric medium.

[0009] The device according to the invention can provide highly precise information, without necessarily resorting to expensive resources.

[0010] The invention can be implemented for example in industries producing nitric acid, or any process using nitric acid, manufacturing structures intended to receive nitric acid (such as acid storage tanks, or for the treatment of used nuclear fuel), in the field of manufacturing chemical monitoring and control instruments, or laboratory chemistry.

[0011] The device according to the invention may include the following additional characteristics, alone or in combination:

[0012] - said measuring conductors comprise: a first electrical measuring conductor electrically connected to the measuring element at a first measuring point and a second measuring conductor electrically connected to the measuring element at a second measuring point located at a predetermined distance from the first measuring point; a first reference measuring conductor electrically connected to the reference element at a first reference measuring point and a second reference measuring conductor electrically connected to the reference element at a second reference measuring point located at a predetermined distance from the first reference measuring point;

[0013] - the device further comprises a first electrically powered supply conductor connected to the measuring element, and a second supply conductor electrically connected to a second end of the reference element;

[0014] - said conductors are of the same material as the measuring element;

[0015] - the detection probe comprises a body on which the measuring element is sealed tically attached, said conductors being connected at the output of this body to external wiring;

[0016] - said body is of the same material as the measuring element;

[0017] - the measuring element has a tubular shape, and the reference element has an oblong shape extending longitudinally into the measuring element, the reference element being electrically connected to the measuring element at one end of the measuring element on one end of the measuring element;

[0018] - the measuring element is formed of a tube closed by a cap on which the element reference is electrically connected;

[0019] - the detection probe comprises an electrically insulating material in contact with the internal faces of the measuring element and in contact with the reference element, this electrically insulating material having a thermal conductivity greater than 1.15 W / mk;

[0020] - said conductors are welded onto the measuring element by vacuum welding;

[0021] - the electrical resistance measuring circuit is suitable for a resistance measurement “4-wire” type;

[0022] - the reference element comes from the same metallurgical casting as the element of measure. PRESENTATION OF FIGURES

[0023] Other characteristics and advantages of the invention will emerge from the non-limiting description which follows, with reference to the appended drawings in which:

[0024] - [Fig.l] schematically illustrates a fluoride ion detection device in nitric medium according to the invention;

[0025] - [Fig.2] illustrates in perspective the detection probe of the device of [Fig.l];

[0026] - [Fig.3] is a sectional view of the detection probe;

[0027] - [Fig.4] illustrates an example of relative resistance measurement with the probe of detection.

[0028] Elements similar and common to the various embodiments have the same reference numbers in the figures. DETAILED DESCRIPTION

[0029] [Fig.l] schematically illustrates a device for detecting fluoride ions in a nitric medium according to the invention.

[0030] The detection device comprises a detection probe 1 intended to come into contact with the nitric medium as well as an electronic measurement module 2 comprising the components necessary for the operation of the detection device. The module 2 is connected to the detection probe 1 by one or more cables 3, and comprises the interfaces adapted to the device and in particular for consulting or exporting the data and the alerts produced, directly or by means of additional computer means. The module 2 comprises an electrical resistance measurement circuit 25, and a detection circuit 26. The circuits 25, 26 can be constituted by any known electronic and / or computer means, with the appropriate programming, and possibly by an external computer with an appropriate communication interface.

[0031] The nitric medium 4 is here shown diagrammatically inside a portion of a container (circulation conduit, tank, etc.) which is delimited by a wall 5.

[0032] The detection probe 1 comprises a measuring element 6 which is an envelope closed adapted to come into contact with the nitric medium 4, with a wall delimiting a closed internal space, and sealed to this medium. The detection probe 1 is, in this exemplary embodiment, adapted to be mounted in a sealed manner on the wall 5 so that the measuring element 6 is in contact with the nitric medium 4.

[0033] The nitric medium 4 can be any solution comprising at least part of nitric acid.

[0034] [Fig.2] is a perspective view of the detection probe 1, with the measuring element 6 seen in transparency so as to make its internal components visible.

[0035] [Fig.3] also represents the detection probe 1, here in a sectional view.

[0036] The measuring element 6 is formed from a zirconium metal wall.

[0037] With reference to Figures 2 and 3, the measuring element 6 contains a reference element 7. The reference element 7 is made of the same material as the measuring element 6. The reference element 7 has an oblong shape extending longitudinally in the measuring element (6). The reference element can be constituted by any oblong shape: wire, blade or strip, cylinder, etc. In the present example, this oblong shape is a blade.

[0038] The reference element 7 is made of the same material and preferably from the same metallurgical casting as the measuring element 6, therefore made of zirconium.

[0039] In the present example, the measuring element 6 consists of a tube 8 hermetically closed at its end by a plug 9. The detection probe 1 comprises a body 10 and the measuring element 6 is hermetically sleeved on this body 10, for example by welding.

[0040] The reference element 7 is arranged inside the measuring element 6 and is electrically connected to the measuring element 6. In the present example, the reference element 7 is electrically connected to the measuring element 6 at the plug 9, by one of the ends of the reference element 7. In this example, the reference element 7 also extends over the entire length of the measuring element 6.

[0041] The measuring element 6 thus has a tubular shape, and the blade which constitutes in this example the reference element 7 extends longitudinally in the measuring element 6, the reference element 7 being electrically connected to the measuring element 6 at one end of said blade on one end of the tubular shape of the measuring element 6.

[0042] The electrical connection between the reference element 7 and the measuring element 6 can be made by any means which does not affect the sealing of the assembly, such as welding, gluing, etc.

[0043] An electrically insulating and thermally conductive material 24 is cast inside the measuring element 6 and holds the reference element 7 in place, in the electrical insulation of the measuring element 6 but by thermally coupling it.

[0044] The device further comprises measuring conductors 11, 12, 13, 14 adapted to the measurement: - the electrical resistance of a portion of the measuring element 6; and - the electrical resistance, taken as reference, of a portion of the reference element 7.

[0045] Thus, the device here comprises a first measuring conductor 11 electrically connected to the measuring element 6 at a first measuring point 15, as well as a second measuring conductor 12 electrically connected to the measuring element 6 at a second measuring point 16. These measuring points 15, 16 are located on the internal face of the measuring element 6.

[0046] Similarly, the device here comprises a first reference measuring conductor 13 electrically connected to the reference element 7 at a first reference measuring point 17, as well as a second reference measuring conductor 14 electrically connected to the reference element 7 at a second reference measuring point 18.

[0047] The electrical connection between the measuring conductors 11, 12, 13, 14 at the measuring points 15, 16, 17, 18 is made by any known and suitable means such as welding.

[0048] The first and second measuring points 15, 16 of the measuring element 6, on the one hand, and the first and second reference measuring points 17, 18 of the reference element 7, on the other hand, are respectively spaced apart by a predetermined distance, defining a portion of the measuring element 6 and of the reference element 7 on which the corresponding electrical resistance will be measured.

[0049] The measurement of the electrical resistance between each pair of measuring points 15, 16; 17, 18 can be carried out by any known means. In the present example, this measurement of electrical resistance is carried out by a so-called “4-wire” measurement.

[0050] For this implementation, the device comprises a first power supply conductor 20 which is electrically connected to the base of the measuring element 6, on its internal face, at a first power supply point 22. The first power supply point 22 is located in this case at the contact between the first power supply conductor 20 and the internal face of the measuring element 6. Alternatively, the first power supply conductor 20 can be electrically connected to the body 10, preferably near the junction between the body 10 and the measuring element 6 (the first power supply point 22 then being located at the junction between the body 10 and the measuring element 6). This variant allows a simplification of the manufacturing method of the device.

[0051] The device also comprises a second supply conductor 21 which is electrically connected to the reference element 7 at a second feed point 23. The second feed point 23 is located on an end of the reference element 7 which is opposite the end by which the reference element is electrically connected to the measuring element 6. Thus, the feed conductors allow a current to pass in series through the measuring element 6 and the reference element 7.

[0052] The measuring conductors 11, 12, 13, 14 and the power supply conductors 20, 21 are connected to the output of the body 10 to an external wiring (shown schematically by the cable 3 in [Fig.l]) necessary for the connection with the module 2. The conductors 11, 12, 13, 14, 20, 21 are sheathed for example by a suitable electrically insulating polymer.

[0053] [Fig.4] schematically illustrates the 4-wire resistance measurement applied to both the measuring element 6 and the reference element 7. In [Fig.4], the resistor 19 schematically represents the resistance to be measured of the portion of the measuring element 6 or of the reference element 7 located between the two measuring points 15, 16 or 17, 18.

[0054] In a known manner for a 4-wire resistance measurement, a current source (contained in the module 2, in the resistance measuring circuit 25) causes a constant current to flow between the two supply points 22, 23. This current passes through the measuring element 6 and the reference element 7. The voltage between the two measuring points 15, 16 on the one hand, and 17, 18 on the other hand is then measured precisely (using voltage measuring means contained in the module 2, in the resistance measuring circuit 25) to deduce the value of the resistance 19 by Ohm's law. A precise measurement of the electrical resistance of the portion of the measuring element 6 and of the portion of the reference element 7 in question is thus carried out continuously, so as to detect minimal variations in resistance.

[0055] The module 2, thanks to the measuring circuit 25, also carries out a relative measurement of the resistance of said portion of the measuring element 6 with respect to the resistance of said portion of the reference element 7. In other words, the measuring circuit 25 determines the variation in electrical resistance of the portion of the measuring element 6 which goes beyond the variation in the electrical resistance of the portion of the reference element 7. This relative measurement can be carried out by an individual measurement of the resistance of said portion of the measuring element 6, and of said portion of the reference element 7, and the ratio of these voltages is determined by the module 2, possibly with computer means connected to the module 2 by a suitable interface.To obtain this relative resistance, the value of the electrical resistance relative to the reference element 7 can be continuously subtracted from the value of the electrical resistance relative to the measuring element 6.

[0056] The measurement of this relative electrical resistance makes it possible to quantify the value of the electrical resistance (of said portion of the measuring element) independently dependent on the temperature. The insulating material 24 being thermally conductive, the measuring element 6 and the reference element 7 are subjected to substantially the same temperature, and the variations in electrical resistance relating to changes in temperature will be seen by both the measuring element 6 and the reference element 7. These variations in electrical resistance due to temperature will therefore not be taken into account in the measurement of said relative electrical resistance, the latter therefore only varying under the influence of the interactions of the measuring element 6 with the nitric medium 4.

[0057] When the detection device is in operation, the measuring element 6 is immersed in the nitric medium 4 and the fluoride ions which would be present in the nitric medium react with the material constituting the measuring element 6. Thus, the presence of fluoride ions in the nitric medium 4 causes a reduction in the thickness of the measuring element 6, which is in contact with the nitric medium 4, and has no effect on the reference element 7, which is protected inside the measuring element 6.

[0058] The presence of fluoride ions in the nitric medium will cause a reduction (even slight) in the zirconium thickness of the measuring element 6, and this presence will be detected by the increase in said relative electrical resistance beyond a predetermined threshold. The detection circuit 26 of the module 2 is adapted (by construction or programming) to correlate an increase in the value of said relative resistance with the presence of fluoride ions in the nitric medium 4. The detection circuit 26 is adapted to detect the presence of fluoride ions in the nitric medium, as a function of an increase in said relative electrical resistance. The detection circuit 26 can be calibrated for example experimentally or by calculation.

[0059] In a particularly advantageous embodiment, the measuring conductors 11, 12, 13, 14, the supply conductors 20, 21, and the body 10 are made of the same material as the measuring element 6 (zirconium). Thus, the entire detection probe 1 can be produced by a welding technique such as high energy density welding processes such as vacuum electron beam or resistance welding, which allow both the assembly of the tube 8 and the plug 9, and the welding of the conductors at the measuring points 15, 16, 17, 18 and at the supply points 22, 23.

[0060] The module 2 can be programmed according to any suitable method, for example to continuously monitor the variation of said relative resistance and thus qualify the evolution of the presence of fluoride ions in the nitric medium 4.

[0061] Variant embodiments of the device may be envisaged, for example the shape and arrangements of the measuring element 6, or the means for measuring the relative resistance which may be different.

Claims

Claims

1. Device for detecting fluoride ions in a nitric medium, characterized in that it comprises: - a detection probe (1) comprising: a measuring element (6) made of zirconium having a wall delimiting a closed internal space, this measuring element (6) being intended to be immersed in the nitric medium (4) to be inspected; a reference element (7) made of zirconium, arranged in the internal space of the measuring element (6) and electrically connected by a first end to the measuring element (6); - measuring conductors (11, 12, 13, 14) electrically connected to the measuring element (6) and to the reference element (7), and adapted to measure the electrical resistance of a portion of the measuring element (6) and of a portion of the reference element (7);- an electrical resistance measuring circuit (25) connected to said measuring conductors (11, 12, 13, 14), and adapted to measure the relative electrical resistance of said portion of the measuring element (6), with respect to said portion of the reference element (7); - a detection circuit (26) adapted to correlate an increase in said relative resistance with the presence of fluoride ions in the nitric medium (4).;

2. Device according to claim 1, characterized in that said measuring conductors (11, 12, 13, 14) comprise: - a first measuring conductor (11) electrically connected to the measuring element (6) at a first measuring point (15) and a second measuring conductor (12) electrically connected to the measuring element (6) at a second measuring point (16) located at a predetermined distance from the first measuring point (15); - a first reference measuring conductor (13) electrically connected to the reference element (7) at a first reference measuring point (17) and a second reference measuring conductor (14) electrically connected to the reference element (7) at a second reference measuring point (18) located at a predetermined distance from the first reference measuring point (17).

3. Device according to one of the preceding claims, characterized in that it further comprises a first supply conductor (20) electrically connected to the measuring element (6), and a second supply conductor (21) electrically connected to a second end of the reference element (7).

4. Device according to one of the preceding claims, characterized in that said conductors are of the same material as the measuring element (6).

5. Device according to one of the preceding claims, characterized in that the detection probe (1) comprises a body (10) on which the measuring element (6) is hermetically attached, said conductors being connected at the output of this body (10) to external wiring (3).

6. Device according to claim 5, characterized in that said body (10) is of the same material as the measuring element (6).

7. Device according to one of the preceding claims, characterized in that the measuring element (6) has a tubular shape, and the reference element (7) has an oblong shape extending longitudinally in the measuring element (6), the reference element (7) being electrically connected to the measuring element (6) at one end of the reference element (7) on one end of the measuring element (6).

8. Device according to one of the preceding claims, characterized in that the measuring element (6) is formed of a tube (8) closed by a plug (9) to which the reference element (7) is electrically connected.

9. Device according to one of the preceding claims, characterized in that the detection probe (1) comprises an electrically insulating material (24) in contact with the internal faces of the measuring element (6) and in contact with the reference element (7), this electrically insulating material (24) having a thermal conductivity greater than 1.15 W / mk

10. Device according to one of the preceding claims, characterized in that said conductors are welded to the measuring element by vacuum welding.

11. Device according to one of the preceding claims, characterized in that the electrical resistance measuring circuit (25) is adapted to a “4-wire” type resistance measurement.

12. Device according to one of the preceding claims, characterized in that the reference element (7) comes from the same metallurgical casting as the measuring element (6).

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