JP4727236B2 - Electromagnetic flow meter for molten metal - Google Patents

Description

  The present invention relates to an electromagnetic flowmeter that measures the flow rate of molten metal by measuring an electromotive force generated in the molten metal that moves in the duct by electromagnetic induction, and in particular, forms a magnetic circuit that passes magnetic flux in the duct. The present invention relates to an electromagnetic flowmeter for molten metal in which an inner core is inserted.

  In order to measure the flow rate of the molten metal in the fast breeder reactor using metal or the pipe for extinction treatment, it is conceivable to use an electromagnetic flow meter. The configuration of a conventional electromagnetic flow meter used for such a purpose is shown in FIGS. Molten metal moves in the cylindrical duct 1. A pair of magnetic poles 6 and 6 are opposed to each other in a direction orthogonal to the central axis of the duct 1 across the duct 1, and the molten metal moving in the duct 1 between the magnetic poles 6 and 6 is defined as the direction of movement. Magnetic flux is formed so as to cut in the orthogonal direction. Further, a pair of electrodes 2 and 2 are arranged facing each other in a direction orthogonal to the direction in which the central axis of the duct 1 and the magnetic poles 6 and 6 face each other. The electrodes 2 and 2 are connected to a voltmeter 7 for measuring a voltage generated in the molten metal moving in the duct 1.

  In such an electromagnetic flowmeter for molten metal, when the molten metal flows through the duct 1 so as to cut the magnetic flux formed between the magnetic poles 6 and 6, the direction of the magnetic flux and the molten metal are obeyed according to the so-called Fleming's right hand rule. An electromotive force is generated in the molten metal in a direction perpendicular to the direction in which the metal flows. The direction of the voltage of the electromotive force is the direction in which the electrodes 2 and 2 face each other, and the voltage value is theoretically proportional to the flow rate of the molten metal. Therefore, by outputting this voltage through the electrodes 2 and 2 and measuring it with the voltmeter 7, the flow rate of the molten metal can be measured. The product of the cross-sectional area of the duct 1 where the magnetic flux formed between the magnetic poles 6 and 6 crosses and the flow velocity of the molten metal is the flow rate of the molten metal.

Such a molten metal electromagnetic flowmeter is used, for example, in the field of fast breeder reactors for measuring the flow rate of liquid metal sodium, and for neutron science, it is used for measuring the flow rate of molten Pb-Bi.
In such a conventional electromagnetic flow meter, non-magnetic austenitic stainless steel having good oxidation resistance and corrosion resistance has been used for the duct 1 for the purpose of preventing corrosion by molten metal.

Since the molten metal passing through the molten metal channel contains a large amount of oxygen during refining in the atmosphere, the oxygen in the molten metal must be removed by H ₂ gas bubbling or vacuum degassing. Otherwise, an oxide film is formed on the duct surface when the molten metal is filled into the duct. Therefore, when the molten metal is filled in the duct, it is necessary to always perform this deoxygenation gas treatment.

However, even if such deoxidation treatment of the molten metal is performed, the molten metal is filled in the duct, and the oxide film on the inner surface of the duct of this nonmagnetic austenitic stainless steel is removed, the molten metal When oxygen is filled, a slight amount of oxygen contained in the high-temperature gas atmosphere of non-oxidizing gas Ar or N ₂ is taken in. As a result, a Cr oxide film is formed on the inner surface of the duct and the surface of the member inserted in the duct, and the molten metal and wettability are impaired. For this reason, the electromotive force generated in the molten metal decreases or becomes unstable, and accurate flow rate measurement cannot be performed.

  As described above, in the electromagnetic flow meter, an increase in contact resistance accompanying a decrease in wettability between the duct or electrode and the molten metal causes a decrease in voltage output, resulting in a decrease in output of the electromagnetic flow meter. When calculating the output E (mV) measured through the electrodes 2 and 2 in consideration of the contact resistance, it is expressed by the following equation (1).

  Where B = density of magnetic flux passing through the duct (Gauss), v = average velocity (cm / s) of fluid flowing through the duct, d = inner diameter of the duct (cm), K1 = magnetic pole terminal coefficient = f (magnetic pole length = L / duct outer diameter), K2 = duct short circuit coefficient, K3 = magnetic flux reduction coefficient due to magnet temperature = f (magnet temperature), K4 = duct thermal expansion compensation coefficient = 1 + γ · ΔT (γ = linear thermal expansion coefficient of pipe material) ΔT = difference between the use temperature of the tube wall and normal temperature (20 ° C.).

In Equation 1, the magnetic pole terminal coefficient K1 is uniquely determined if the size of the magnet used is known, and the magnetic flux reduction coefficient K3 and the duct thermal expansion compensation coefficient K4 are determined if the magnet temperature and the duct temperature are determined. These are also determined uniquely. On the other hand, the duct short circuit coefficient K2 is expressed by the following formula 2. Here, D = outer diameter of the duct (cm), τ = contact resistance (Ω-cm ² ), ρf = specific resistance of the tube wall (Ω-cm), and ρw = specific resistance of the fluid (Ω-cm).

  The duct short circuit coefficient K2 includes a term including the contact resistance τ, and it can be seen that the increase in the contact resistance τ decreases the duct short circuit coefficient K2 and decreases the output E. The duct short-circuit coefficient K2 decreases as the contact resistance τ increases. Conversely, when the contact resistance τ decreases, the duct short-circuit coefficient K2 increases. Is determined by the electrical resistance of the fluid and the material of the duct.

  The above is the case of an electromagnetic flowmeter having a structure in which nothing is arranged in the duct 1 in order to simplify the theory. Actually, in order to arrange an inner core for passing magnetism between the magnetic poles 6 and 6, and further to make the piping system compact, it is generally performed to make a double pipe with a double duct. . In this case, the inner core is covered with a protective member such as ceramic in order to prevent oxidation of the inner core. The inner core is disposed outside or inside the internal duct.

However, when the inner core disposed in the duct is in contact with the protective member and the internal duct, the wall thickness of the internal duct is increased by the amount of the core and the protective member in the above formula 2. As a result, the numerical value corresponding to d / D in Equation 2 increases. As a result, the duct short-circuit coefficient K2 is reduced by that amount, and the output E expressed by Equation 1 is lowered. Further, if the contact state between the core and the protective member or the core and the internal duct is unstable, the duct short circuit coefficient K2 varies, and there is a problem that the output E represented by the equation 1 varies.
JP 2003-75215 A JP 2003-75217 A JP-A-2-213723

  In view of the problem in the electromagnetic flowmeter for molten metal in which the inner core is disposed in the conventional duct, the present invention provides an interior of the molten metal that is measured between the electrodes as the apparent wall thickness of the duct and other members increases. It is an object of the present invention to provide an electromagnetic flowmeter for molten metal that can suppress a decrease in electromotive force and can stabilize an electromotive force measured between electrodes.

  In the present invention, in order to achieve the above object, the inner core 21 disposed inside the duct 11 and the protective member 24 covering the inner core 21 are insulated by the insulating layer 22. Further, in the multi-pipe structure in which the duct 11 is an external duct and one or more internal ducts 18 are provided therein, an insulating layer 23 is also provided between the internal core 21 and the internal duct 18.

That is, the electromagnetic flowmeter for molten metal according to the present invention is provided with a cylindrical duct 11 that moves the molten metal, and a pair of magnetic poles 16 that are arranged to face each other with the duct 11 interposed therebetween, and form a magnetic flux in the duct 11. 16 and a pair of electrodes 12 and 12 that output a voltage generated in the molten metal that moves in the duct 11 in a direction that cuts the magnetic flux, facing each other with the duct 11 interposed therebetween. Further, an inner core 21 through which the magnetic flux between the magnetic poles 16, 16 passes through a single duct 11, and a protective member 24 that blocks the inner core 21 from a molten metal flow path 19 formed by the duct 11. insert the door, the insulating layer 22 is formed between these inner core 21 and the protective member 24.

  Thus, since the inner core 21 and the protective member 24 are electrically insulated by the insulating layer 22 by forming the insulating layer 22 between the inner core 21 and the protective member 24 covering it, the protective member The apparent thickness of 24 does not increase. Thereby, the duct short circuit coefficient K2 mentioned above does not become small, and the output E does not fall.

Further, an internal duct 18 for inserting the inner core 21 from the inner molten metal flow path 20 is inserted into the duct 11 to form a plurality of molten metal passages in the duct 11. As an alternative, an insulating layer 23 is also formed between the inner core 21 and the inner duct 18. In this case as well, the internal core 21 and the internal duct 18 are electrically insulated by the insulating layer 23, so that the apparent thickness of the internal duct 18 does not increase.

As the insulating layer 23, a solid insulating material may be inserted between the inner core 21 and the protective member 24 covering the inner core 21 or between the inner core 21 and the inner duct 18. The insulating layers 22 and 23 that can also serve as a heat insulating layer are preferable. Specifically, the insulating layers 22 and 23 are made to be voids, and air, more preferably, an inert gas such as N ₂ gas or Ar gas is filled therein.

  The cylindrical duct 11 is provided with a pair of electrodes 12 and 12 facing the direction perpendicular to the magnetic flux by 90 ° inside, but in addition to the electrodes 12 and 12, It is preferable to provide two or more pairs of electrodes 12a, 12b, 12c, and 12d that are symmetrically installed at the same angle. The flow rate of the molten metal in the duct 11 is measured from the average value of the electromotive force E, which is the output detected by the plurality of pairs of electrodes 12a, 12b, 12c, and 12d. Thereby, as will be described later, even if the flow of the molten metal in the duct 11 is biased or the magnetic field is spatially biased, the flow rate of the molten metal flowing through the duct 11 can be measured more accurately. I can do it.

  As described above, in the electromagnetic flowmeter for molten metal according to the present invention, the apparent thickness of the protective member 24 and the internal duct 18 is not increased, and the above-described duct short circuit coefficient K2 is not decreased. The output E detected between them does not decrease. Further, since the inner core 21 and the protective member 24 or the inner core 21 and the inner duct 18 are always insulated and there is no change in the electrical contact state, the output detected between the electrodes 12 and 12. E does not fluctuate. By using the average value of a plurality of pairs of electrodes arranged symmetrically on both sides of the electrode 12, fluctuations in the output E can be suppressed even when the flow of molten metal is uneven and the magnetic field is spatially uneven.

In the present invention, the insulating layers 22 and 23 are provided between the inner core 21 disposed inside the duct 11 and the protective member 24 covering the inner core 21 and between the inner core 21 and the inner duct 18 to achieve the object. To do.
Hereinafter, examples of the present invention will be described in detail with specific examples with reference to the drawings.

The configuration of an electromagnetic flow meter for molten metal according to an embodiment of the present invention is shown in FIGS. Molten metal is flowed through the cylindrical duct 11, and the flow rate is the product of the flow velocity and the flow path cross-sectional area of the duct 11.
A pair of magnetic poles 16, 16 are opposed in a direction orthogonal to the central axis of the duct 1 across the duct 11, and are orthogonal to the direction of the molten metal flowing through the duct 11 between the magnetic poles 16, 16. A magnetic flux is formed so as to cut in the direction of the movement.

  Furthermore, a pair of electrodes 12 and 12 are disposed so as to face each other in a direction orthogonal to the direction in which the central axis of the duct 11 and the magnetic poles 16 and 16 face each other, and the distal ends of these electrodes 12 and 12 are the outer periphery of the duct 11. It is connected and fixed to the surface by means such as welding. A voltmeter 17 for measuring an electromotive force generated in the molten metal moving in the duct 11 is connected to the electrodes 12 and 12.

  A metal coating is applied to the inner peripheral surface of the duct 11 in order to improve wettability with molten metal such as molten Na or Pb-Bi. For example, a noble metal such as Rh or Ir is applied as a metal coating. As shown in FIG. 2, this metal coating is the entire circumference near the position where the electrodes 12, 12 and the magnetic poles 16, 16 on the inner peripheral surface of the duct 11 face each other, and the electrodes 12, 12 and the magnetic poles 16, 16 It is applied over a range of a certain length in the axial direction of the duct 11 around the position where 16 is opposed.

  One or more internal ducts 18 are inserted into the duct 11. In the illustrated example, one internal duct 18 is coaxially disposed in the external duct 11 so that the central axes coincide. A portion between the inner duct 18 and the outer duct 11 is an outer flow path 19 through which molten metal flows, and a portion inside the inner duct 18 is an inner flow path 20 through which molten metal also flows.

  An inner core 21 is disposed on the outer peripheral side of the inner duct 18 at a position where the outer duct 11 is sandwiched between the pair of magnetic poles 16 and 16 and the electrodes 12 and 12. The inner core 21 is a cylindrical magnetic member having a larger diameter than the inner duct 18. A screw is formed on the outer periphery of one end side of the internal duct 18. Such a screw is not formed on the other end side of the inner core 21.

  Further, as shown in FIG. 2, two support fittings 25 and 25 ′ are fixed to the outer periphery of the internal duct 18 at intervals with a means such as welding, and the end surfaces of the pair of support fittings 25 and 25 ′ are inside. It faces the longitudinal direction of the duct 18. The support fittings 25 and 25 ′ have a hollow conical shape, and are fixed by welding through an internal duct 18 through a hollow hole formed along the central axis of the conical shape. Circumferential grooves 26 and 26 ′ are formed on the opposing end surfaces of the pair of support brackets 25 and 25 ′. Of these, on the outer peripheral surface side of the groove 26 of one support bracket 25 shown on the right side of FIG. The female thread is cut.

  A screw at one end of the inner core 21 is screwed into a circumferential groove 26 having a female screw of one support fitting 25 fixed to the outer periphery of the inner duct 18. Further, the other end side of the inner core 21 is fitted in a circumferential groove 26 ′ of the other support fitting 25 ′ fixed to the outer periphery of the inner duct 18. A margin is provided in the longitudinal direction of the internal duct 18 between the circumferential groove 26 ′ of the support fitting 25 ′ and the end of the internal core 21, and the end of the support fitting 25 ′ and the internal core 21 is provided. The part is movable in the longitudinal direction of the internal duct 18. This is to prevent the occurrence of thermal stress caused by the difference in the expansion coefficient when the materials of the protection member 24, the support fittings 25, 25 'and the internal duct 18 are different.

  A cylindrical protective member 24 is fitted into the outer peripheral portion of the pair of support fittings 25, 25 '. Both end portions of the protective member 24 are closely fixed to the outer periphery of the support fittings 25 and 25 ′, so that the protection member 24, the support fittings 25 and 25 ′, and the internal duct 18 surround the inner core 21. . Thereby, the space in which the inner core 21 is accommodated is completely partitioned from the outer passage 19 and the inner passage 20.

A space is formed between the inner peripheral side and the outer peripheral side of the inner core 21, that is, between the inner core 21 and the protective member 24 and between the inner core 21 and the inner duct 18, and these spaces are the insulating layers 22, 23, respectively. It has become. In these void-like insulating layers 22 and 23, air may be sealed, but in order to prevent oxidation of the inner surface of the protective member 24, the support fittings 25 and 25 ′ and the internal duct 18, It is preferable that an inert gas such as N ₂ gas or Ar gas is sealed in the gap. The insulating layers 22 and 23 are preferably voids filled with an inert gas, but a heat-resistant solid insulating member may be inserted instead.

  In such an electromagnetic flowmeter for molten metal, when the molten metal flows through the duct 11 so as to cut the magnetic flux formed between the magnetic poles 16 and 16, the direction of the magnetic flux and the molten metal are in accordance with the so-called Fleming's right hand rule. An electromotive force is generated in the molten metal in a direction perpendicular to the direction in which the metal flows. The direction of the voltage due to the electromotive force is the direction in which the electrodes 12 are opposed to each other, and the voltage value is theoretically proportional to the flow rate of the molten metal. For this reason, the flow rate of the molten metal can be measured by outputting this voltage from the electrodes 12 and 12 through the duct 11 and measuring the voltage with the voltmeter 17. As already described, the product of the cross-sectional area of the duct 11 where the magnetic flux formed between the magnetic poles 16 and 16 crosses and the flow velocity of the molten metal is the flow rate of the molten metal, whereby the flow rate of the molten metal is measured. The

  In this case, the inner core 21 provided in the duct 11 is surrounded by the protective member 24, the support fittings 25, 25 ′ and the inner duct 18, and is completely cut off from the molten metal passing through the outer passage 19. Therefore, the internal core 21 made of a magnetic material such as iron is prevented from being corroded by being exposed to the molten metal. Further, since the inner core 21 and the protective member 24 and the inner core 21 and the inner duct 18 are electrically insulated by the insulating layers 22 and 23, the apparent thickness of the protective member 24 and the inner duct 18 is increased. Does not grow.

  FIG. 3 shows the use of the double-pipe structure ducts 11 and 18 having the flow rate measuring units 15 and 15 having the inner core as described above, and the molten metal from the molten metal tank 14 through the outer flow path 19 and the inner flow path 20. An example of using this is shown. The flow rate measuring units 15 and 15 have a structure having an inner core 21 sealed with respect to the outer flow path 19 as described with reference to FIGS.

4 and 5 show an embodiment of a single-pipe molten metal path in which no internal duct is inserted into the duct 11. In this case, the support brackets 25, 25 'are basically the same as those of the embodiment described above with reference to FIGS. 1 and 2, except that the support brackets 25, 25' have an empty solid conical shape and no internal duct passes therethrough. . Also in this case, the inner core 21 is surrounded by the support fittings 25, 25 ′ and the cylindrical protective member 24 provided on the outer periphery thereof, and is completely cut off from the molten metal flow path 19 in the duct 11.

Further, a gap is formed between the inner core 21 and the protective member 24, and the insulating layer 22 is formed by this gap, which is basically the same as in the embodiment described above with reference to FIGS. is there. It is preferable that an inert gas such as N ₂ gas or Ar gas is enclosed in the void, and the insulating layer 22 is replaced with a void filled with an inert gas, instead of a heat-resistant solid insulating member. The same may be said of inserting the symbol.

  As described above, in the annular flow type electromagnetic flow meter in which the annular flow path is formed between the cylindrical duct 11 and the internal core 21 disposed therein, the molten metal is formed in each part of the flow path in the duct. The drift is likely to occur due to the difference in the flow velocity. Due to this drift, the electromotive force E which is the output detected between the single electrodes 12 and 12 does not accurately reflect the flow velocity of the molten metal, which may cause errors and variations in measurement. Also, when the magnetic field acting by the magnetic poles 6 and 6 is spatially biased, the measurement may vary.

  Therefore, as a countermeasure, it is preferable to provide a plurality of pairs of electrodes as in the electromagnetic flow meter shown in FIG. 8 and measure the flow rate based on the average value of the electromotive force detected between them. For example, in the electromagnetic flow meter shown in FIG. 8, in addition to the regular electrodes 12 and 12 opposed in the direction orthogonal to the direction in which the magnetic poles 16 and 16 are opposed, The other two pairs of auxiliary electrodes 12a and 12b that face each other in the direction that forms an angle of ± θ are opposed to each other in the direction that forms an angle of ± θ ′ on both sides of the regular electrodes 12 and 12 as a center. Furthermore, two other pairs of auxiliary electrodes 12c and 12d are provided. In addition to the electromotive force measured at the regular electrodes 12 and 12, the electromotive forces measured at these auxiliary electrodes 12a, 12b, 12c and 12d are added as electromotive forces at angles θ and θ ′, respectively. The average flow rate of the entire duct 11 can be obtained. As a result, the influence of the above-described drift current can be canceled, and a more accurate flow rate can be obtained.

  More specifically, the electromotive force measured by the regular electrodes 12 and 12 facing each other in the direction perpendicular to the direction in which the magnetic flux cuts the duct 11 is given by the above-described equation (1). On the other hand, the electromotive force E ′ measured by the electrodes 12a, 12a and the electrodes 12b, 12b facing each other in a direction shifted by an angle ± θ from the direction in which the regular electrodes 12, 12 face each other is the following number. Is given by 3.

  Similarly, the electromotive force E ″ measured by the electrodes 12c and 12c and the electrodes 12d and 12d facing each other in a direction shifted by an angle ± θ ′ from the direction in which the regular electrodes 12 and 12 face each other is as follows. It is given by Equation 4.

For example, the electromotive force measured by the regular electrodes 12 and 12 is E _0, and four pairs of electrodes 12a and 12a, 12b and 12b, and 12c that face each other by being shifted by angles ± θ and ± θ ′ on both sides. And 12c, 12d, and 12d, and the measured electromotive forces are E ₁ , E ₂ , E ₃ , and E _4. The variation of the electromotive force E caused by the above becomes a leveled value. Thereby, an average flow rate flowing through the annular flow path is obtained, and this average flow rate indicates a more accurate flow rate.

It is a vertical side view which shows the electromagnetic flowmeter for molten metals as one Example of this invention. It is a vertical front view which shows the electromagnetic flowmeter for molten metals as the Example. It is a schematic vertical side view which shows the usage example of molten metal piping provided with the electromagnetic flowmeter for molten metal as the Example. It is a vertical side view which shows the electromagnetic flowmeter for molten metals as another Example of this invention. It is a vertical front view which shows the electromagnetic flowmeter for molten metals as the Example. It is a vertical side view which shows the electromagnetic flowmeter for molten metals as a prior art example of this invention. It is a vertical front view which shows the electromagnetic flowmeter for molten metals as the same prior art example. It is a vertical front view which shows the electromagnetic flowmeter for molten metals as further another Example of this invention.

Explanation of symbols

11 Duct 12 Electrode 16 Magnetic pole 18 Internal duct 19 Outer channel 20 Inner channel 21 Inner core 22 Insulating layer 23 Insulating layer 12a Electrode 12b Electrode 12c Electrode 12d Electrode

Claims (4)

A cylindrical duct (11) for moving the molten metal, and a pair of magnetic poles (16), (16) which are arranged to face each other with the duct (11) interposed therebetween and form a magnetic flux in the duct (11), Molten metal electromagnetic flow rate having a pair of electrodes (12) and (12) that output a voltage generated in the molten metal that is opposed to the duct (11) and moves in the duct (11) in the direction of cutting the magnetic flux. In total, an inner core (21) for passing a magnetic flux between the magnetic poles (16) and (16) is formed in a single duct (11), and the inner core (21) is formed by the duct (11). is the insert and the protective member for blocking the flow path of the molten metal (19) (24), characterized by forming an insulating layer (22) between the protective these inner core (21) member (24) Electromagnetic flowmeter for molten metal. A cylindrical duct (11) for moving the molten metal, and a pair of magnetic poles (16), (16) which are arranged to face each other with the duct (11) interposed therebetween and form a magnetic flux in the duct (11), Molten metal electromagnetic flow rate having a pair of electrodes (12) and (12) that output a voltage generated in the molten metal that is opposed to the duct (11) and moves in the duct (11) in the direction of cutting the magnetic flux. In total, the duct (11) is formed with an inner core (21) through which the magnetic flux between the magnetic poles (16) and (16) passes, and the inner core (21) is formed by the duct (11). A protective member (24) blocking the molten metal flow path (19) and a plurality of passages are formed in the duct (11), and the inner core (21) is connected to the inner molten metal flow path (20). ) and inserting the inner duct (18) for blocking, this Insulating layer between and between the inner core (21) and the internal duct (18) between Luo inner core (21) and the protective member (24) (22), the molten metal, characterized in that the formation of the (23) Electromagnetic flow meter. The electromagnetic flowmeter for molten metal according to claim 1 or 2, wherein the insulating layers (22) and (23) are voids. In addition to a pair of electrodes (12) and (12) disposed opposite to the cylindrical duct (11) in a direction perpendicular to the magnetic flux by 90 °, they are disposed symmetrically at the same angle on both sides. The electromagnetic flowmeter for molten metal according to any one of claims 1 to 3, comprising two or more pairs of electrodes (12a), (12b), (12c), and (12d).

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