BRPI0607386A2 - electrical circuit to reduce electromagnetic fields in the vicinity of an electrolyser, and method for reducing electromagnetic fields in the vicinity of the electrical circuit of an electrolyser - Google Patents

Abstract

ELECTRICAL CIRCUIT TO REDUCE ELECTROMAGNETIC FIELDS NEAR AN ELECTROLISER, AND METHOD FOR REDUCING ELECTROMAGNETIC FIELDS NEAR AN ELECTROLISER CIRCUIT. An electrical circuit for reducing the electromagnetic fields in the vicinity of an electrolyser is described, comprising a primary circuit supplying the electrolyser and a secondary electrical circuit arranged in the vicinity of the primary circuit, for a current to pass in the opposite direction to that in the main circuit. in order to compensate for the electric fields generated by it.

Description

"ELECTRICAL CIRCUIT TO REDUCE ELECTRIC CAMPOSE IN THE NEAR OF A ELECTROLISER, AND METHOD TO REDUCE ELECTRIC CAMPOSE IN THE SURROUNDINGS"

The invention relates to electrolysers, especially for electrical supply of such electrolysers.

The invention more particularly relates to a circuit for supplying a rectified electrical current to a bipolar electrolyte electrolyzer.

Electrolysers, in particular with bipolar electrodes, supplied with direct current are commonly used in the electrochemical industry. Such electrolysers are commonly used for aqueous sodium chloride electrolyte solutions for the purpose of chlorine production, aqueous sodium hydroxide solutions or aqueous sodium chloride solutions.

In view of the high current densities employed in bipolar electrolyte electrolysers, a rectified alternating current is generally used in place of direct current. The alternating current usually has phases whose frequencies and amplitudes depend on the rectifier being used.

It is further known that high electromagnetic fields, especially those produced by a rectified alternating current, can have detrimental consequences on the human body under extreme conditions, because of the induced currents that they have the risk of generating the body. It is therefore important to take measures to protect the personnel in the vicinity of industrial facilities or to reduce the intensity of the magnetic fields there. Standards have also been published in this respect, requiring that the intensity of electromagnetic fields in industrial enterprises be reduced. Among these standards, the European standard89 / 391 / EEC is particularly strict.

It is an object of the invention to provide an unprecedented design electrical circuit to supply an industrial electrolyser with a strong electric current.

It is a particular object of the invention to provide a circuit with which the electromagnetic field in the vicinity of the electrolyser is reduced sufficiently low to meet the above-mentioned European standard.

It is more particularly an object of the invention to reduce the intensity of the electromagnetic field in the walkways disposed along the side walls of the electrolysers with bipolar electrodes.

The invention, therefore, relates to an electrical circuit for reducing electromagnetic fields in the vicinity of an electrolyser, the electrical circuit comprising a primary electrical circuit itself comprising the electrolyser and an electrical line comprising at least one bus to return the current that the electrolyser passes, and a secondary electrical circuit arranged at least partially in the vicinity of the primary circuit, for a current passing in the opposite direction to that of the main circuit in order to compensate for the electromagnetic field generated by the primary circuit.

According to the invention, a secondary electrical circuit is arranged in the vicinity of the primary circuit. The passage of current in the opposite direction in the secondary circuit is to cause a magnetic field that at least partially nullifies that created by the passage of the primary current. The secondary circuit must therefore be capable of carrying a current of sufficient intensity to obtain the desired compensation. In order to obtain good field compensation, the secondary circuit must be arranged as close as possible in the vicinity of the primary circuit. It is recommended that a part of the secondary circuit should be attached to the electrolyser and another part should preferably be attached to the busbar or busbars, in order to obtain optimum field compensation, taking into account the structural demands that may make it necessary to separate the two circuits in certain positions. In order to optimize compensation, certain segments of the secondary circuit are generally distributed over a plurality of parallel connected conductors. It is possible to supply the secondary circuit using the primary circuit supply by means of a control resistor. However, it is recommended that at least the part of the secondary circuit that is disposed in the vicinity of the return line should be supplied separately. A separate supply also has the advantage that the secondary current frequency can be adapted to preferentially eliminate certain particularly problematic frequencies from the magnetic field produced by the electrolyser. In general, it is recommended that the part of the secondary circuit that is disposed in the vicinity of the bus, or buses, should carry a higher current (preferably at least 5 times higher) than the one that passes through the attached part on the electrolyser, the reason for the current being a function of the distance between the bus and the electrolyser.

It is also recommended that the part of the circuit that is arranged between the rectifiers and the electrolysis installations should be configured in order to obtain good field compensation. Therefore care must be taken that the power supply and return conductors are in close proximity to each other. To this end, it is recommended that these conductors should be branched into a plurality of elements connected in parallel so that these conductors can be intertwined with one another, for example with stacked alternating layers of the elements of each conductor.

The invention applies to any type of electrolyser, such as monopolar or bipolar mercury electrolysers, diaphragm or membrane. However, it applies more specifically to electrolysers with substantially vertical bipolar electrodes. Such electrolysers are well known in engineering, where they are widely used to electrolyte aqueous metal halide solutions, particularly sodium chloride. These electrodes are usually formed by a succession of metal structures, each comprising a bipolar electrode, these structures being juxtaposed in the form of a filter press (Modern Chlor-alkalitechnology, volume 3, SCI, 1986 chapter 13 "Operating experience gainedwith the bipolar"). Hoechst-Yhde membrane cell "; Modern Chlor-alkalitechnology, volume 4, SCI, 1990, chapter 20" Hoeschst-Uhde single elementmembrane electrolyser: concept-experiences-applications "). The structures conventionally have a square or rectangular profile so that when they are juxtaposed in the form of a filter press they form an upper wall, a bottom or base wall and two side walls of the electrolyser. The electrolyser is usually supplied with direct current or, more generally, rectified alternating current. The rectified direct current flows from one terminal of the direct current source or rectifier through the electrodes and then returns to the other terminal of the direct current source or rectifier via an electrical current line that is disposed outside the electrolyser.

The electrical circuit according to the invention is advantageously supplied with rectified alternating current. Three-phase alternating current rectification provides a current whose oscillations have a base frequency six times greater than the fundamental frequency of the three-phase current (eg 6 times 50 Hz) and a full spectrum of harmonics.

In a recommended embodiment of the invention, the circuit comprises a supply using at least two rectifiers in order to distribute currents whose waveforms are phase shifted relative to each other. The electrolysis electrical circuit is advantageously supplied with three phase alternating current.

The use of at least two phase shifted rectifiers according to this embodiment makes it possible to increase the frequency of the rectified current oscillations supplying the electrolyzer or electrolyzers. Given the intensity and particular arrangement of the currents involved in electrolysers, the circuit according to the invention makes it possible to substantially reduce the electromagnetic fields emitted in the vicinity of the installation.

In an advantageous variant of this embodiment, the circuit comprises two rectifiers whose phase shift is between 290 and 31 °, preferably close to 30 °. In this variant, a current is obtained whose waveforms have a base frequency 12 times higher than the base frequency of the unrectified three-phase current.

In another advantageous variant of this embodiment of the circuit, the circuit further comprises at least one dewatering coil that couples the outputs of at least two rectifiers. The drain coil is for establishing an anti-parallel reactance between the rectifier outputs. The coil is advantageously formed by mounting plates and steel strips to limit heating losses. The rectifier outputs go in opposite directions, so that a resulting disturbance present in one of the outputs induces by the reactance an inverse disturbance in the current from the other output. When the two outputs are overlapped by the parallel connection, a less disturbed total current is thus obtained.

In a preferred embodiment of the electrical circuit according to the invention, the return electric line comprises at least one busbar arranged below or above the electrolyser. The choice of arranging the busbar below or above the electrolyser is governed by considerations regarding the construction of the electrolyser and the mounting mode of the bipolar plates. As a variant, the above-mentioned electric current line may comprise a bus arranged below the electrolyser and another bus arranged above the electrolyser.

In another embodiment, the electrolyser may also comprise a plurality of buses below the electrolyser and / or a plurality of buses above the electrolyser. In practice, for considerations relating to the assembly and maintenance of the electrolyser, it is generally preferable that the above-mentioned power line does not comprise a busbar above the electrolyser.

All other things being equal, it has been observed that the electrical circuit according to the invention substantially reduces the electromagnetic field in the vicinity of the electrolyzer with bipolar electrodes, especially along its sidewalls, especially on the walkways that are normally present along these sidewalls. are typically used by operating and maintenance personnel.

In the electrical circuit according to the invention, the bushing material is not critical to the definition of the invention. It is usually made of copper, aluminum or aluminum alloy.

In the electrical circuit according to the invention, the cross-sectional profile of the busbar is not critical to the definition of the invention. It may be, for example, square, rectangular, circular or polygonal.

In a first particular embodiment of the electrical circuit according to the invention, the busbar has a rectangular profile and is oriented so that its large faces are substantially horizontal. All other things being equal, it was observed that the selection of a rectangular section busbar arranged horizontally below and / or above the electrolyser minimizes the size of the electromagnetic field at the vicinity of the electrolyser. It was also observed that the reduction of the electromagnetic field in the vicinity of the electrolyser is also greater when the ratio between bus thickness and width is small. In practice, it is therefore preferable to use a metal sheet for the bus. As a variant, a plurality of sheet metal arranged sideways below and / or above the electrolyser may be used.

All other things being equal, it was further observed that the size of the electromagnetic field in the vicinity of the electrolyte decreases when the bus is placed close to the electrolyser wall.

In a second embodiment of the electric circuit according to the invention, the bus is therefore arranged in close proximity to an electrolyser wall. In this embodiment of the invention, the electrolyser wall is the bottom or base wall of the electrolyser, or its upper wall, depending on whether the busbar is located below or above the electrolyser. In this embodiment of the invention, the term "immediate proximity to the electrolyser wall" means that the distance between this wall and the busbar is at most five times (preferably three times) the busbar thickness. Preferably, stistance does not exceed busbar thickness.

In a preferred embodiment of the second embodiment of the invention, the busbar is attached to said electrolyser sidewall. In this preferred alternative embodiment of the invention, the cover is advantageously a metal plate from which one of the large faces is attached to said side wall, with only the required electrical insulating thickness separating the bus from the wall. The metal plate may be attached to a portion of the surface area of said wall. It is preferable for the sheet metal to be attached substantially to the entire surface area of said wall.

In a third particular embodiment of the invention, the aforesaid power line further comprises two additional buses which are respectively arranged in close proximity to the two side walls of the electrolyser. In this embodiment of the invention, the term "in immediate proximity" corresponds to the definition given for this expression in the second embodiment explained above.

All other things being equal, the presence of the additional buses reduces the size of the electromagnetic field at the vicinity of the electrolyser.

In this third embodiment according to the invention, the additional buses may have any shape compatible with the construction of the electrolyser. They may have, for example, a square, rectangular, polygonal, oval or circular profile. Additional buses may additionally have the same or different profiles, and they may have the same or different dimensions. In practice, however, it is preferable that additional buses have the same profile and dimensions.

In addition it is preferable that the additional busbars have a rectangular profile, and that they are respectively attached by means of their large faces on the two sidewalls of the electrolyser.

In the third embodiment of the aforementioned invention, the respective dimensions of the additional busbars and those of any busbar arranged below and / or above the electrolyser are determined by the manner in which the electric current is to be distributed between these busbars.

In a fourth embodiment of the invention, which is especially advantageous, the return current line of the electrical circuit is positioned so as to generate an electromagnetic field that is substantially symmetrical with respect to the median vertical plane of the electrolyser. The purpose of this modality (generating an electromagnetic field that is substantially symmetrical with respect to the electrolyser's vertical median plane) is achieved by sizing and positioning properly on any busbar. The choice of ideal dimensions and ideal position is determined by those skilled in the art, in particular depending on the shape and dimensions of the electrolyser. In practice, this result can generally be obtained by arranging the bus, or buses, symmetrically in relation to the electrolyser's vertical median plane.

The electrical circuit according to the invention substantially reduces the electromagnetic field in the vicinity of the electrolyser with bipolar electrodes.

Accordingly, the invention also relates to a method for reducing electromagnetic fields in the vicinity of the electrical circuit of an electrolyser comprising a primary electrical circuit, the electrolyser itself and an electrical line comprising at least one bus to return the current that the electrolyser passes, according to the present invention. which an electric current passes through a secondary electrical circuit arranged in the vicinity of the primary circuit in the opposite direction to that of the primary circuit.

In a preferred embodiment of the method according to the invention, the primary circuit comprises a supply that uses two rectifiers to distribute currents whose waveforms are phase shifted relative to one another.

In an advantageous version of this embodiment, the primary circuit further comprises a drain coil that couples the outputs of the two rectifiers.

The electrical circuit according to the invention applies especially to electrolysers for continuous electrolysis of water or aqueous solutions, such as aqueous solutions of an alkali metal halide, especially sodium chloride. In a preferred embodiment of the invention, the electrolyzer therefore comprises a conduit for the continuous admission of an aqueous electrolyte and a conduit for the continuous discharge of an aqueous electrolyte.

In particular, the invention applies to electrolysers to manufacture sodium chlorate by electrolysis of aqueous sodium chloride solutions. The invention applies especially well to chlorine electrolysers and aqueous sodium hydroxide solutions by electrolysis of aqueous sodium chloride solutions, such electrolysers comprising selectively cationic permeable membranes, which are disposed between the electrodesbipolar.

The electrical circuit according to the invention applies to any electrolysis plant incorporating at least one electrolyser with vertical bipolar electrodes.

Accordingly, the invention also relates to an electrolysis plant comprising at least one bipolar electrolyte electrolyser, which is connected to an electrical circuit according to the invention. The installation according to the invention may comprise a single electrolyser, or a plurality of electrolysers that are connected to electrical or parallel series.

The invention relates in particular to the use of this facility to produce chlorine and aqueous sodium hydroxide solutions.

Features and details of the invention will become apparent during the following description of the accompanying figures, which represent some particular embodiments of the invention.

Figure 1 shows in plan view the general layout of an electrolysis plant according to a particular embodiment of the invention;

Figure 2 is a schematic longitudinal elevational view of another particular embodiment of the electrolysis plant according to the invention;

Fig. 3 is a vertical cross-sectional view in the plane III-III of Fig. 2;

Fig. 4 is a view, similar to Fig. 3, of another embodiment of the installation according to the invention;

Figure 5 is a preferred embodiment of the installation of Figure 4;

Figures 6 and 7 are similar to figures 4 and 5, but also represent the secondary circuit.

In these figures, identical elements are denoted by the same reference reference.

The electrolysis installation outlined in figure 1 comprises three electrolysers 1, 2 and 3 designed for the production of chlorine, hydrogen and sodium hydroxide by electrolysis of an aqueous sodium chloride solution. Electrolysers 1, 2 and 3 are vertical bipolar type electrolysers. They are formed by the juxtaposition of vertical rectangular structures 4, each containing a vertical (not shown) bipolar electrode. The structures 4 are juxtaposed as a filter press.Selectively cation-permeable membranes are arranged between structures 4 to alternately delimit anodic and cathodic chambers.The anodic chambers of electrolysers 1, 2 and 3 are in common conduit communication (not shown). ) for continuous admission of an aqueous sodium chloride solution. They are further in communication with a collector (not shown) for continuous chlorine discharge. The cathodic chambers of electrolysers 1, 2 and 3 are in communication with two collectors (not shown) which are respectively used for continuous extraction of hydrogen on the one hand and an aqueous solution of sodium hydroxide on the other hand.

Electrolysers 1, 2 and 3 are coupled in electrical series by means of a drain coil 19 to two rectifiers 5a and 5b by means of an electric circuit comprising, on the one hand, conductor bars 6 disposed between electrolysers 1, 2 and 3 and, on the other hand, a return current line 7 arranged outside the electrolysers 1, 2 and 3. Rectifiers 5a and 5b are supplied with a phase shift of 300 by an alternating current source 18.

In the electrolysis installation shown in Figure 1, each of the three electrolysers 1, 2 and 3 may comprise, for example, from 30 to 40 elemental electrolysis cells, and the electrical supply comprises, for example, a 520 V DC rectifier capable of distribute a current of 8 to 20 kA. Depending on the surface area of the electrodes, this can result in an anode current density of 2.5 to 6 kA / m2 of anode area. These numerical values, however, are indicative only and do not limit the scope of the invention and the subsequent claims.

When the bipolar switch is closed, an electrified current passes successively through the electrolysers 1, 2 and 3 through its bipolar electrodes and to the return line 7. This electric current generates an electromagnetic field in the installation environment.

According to the invention, a secondary circuit comprising segments 17a and 17b is arranged near the electrolysers and the return line.

The electrolysis installation shown in Figures 2 and 3 illustrates a particular embodiment of the invention. The secondary circuit is not represented on them. Only the electrolyser 3 has been represented in these figures.In the installation of figures 2 and 3, the return electric line 7 comprises two buses 9 and 10 which are arranged under the lower wall11 of the electrolyser 3. Buses 9 and 10 are prismatic bus bars. A metal that is a good conductor of electricity (preferably copper or aluminum). These bars are symmetrically arranged on either side of the electrolyser vertical median X-X plane. The bars 9 and 10 are further arranged near the bottom wall 11 of the electrolyser 3. The effect of arranging the buses 9 and 10 in the manner outlined in Figure 3 is to reduce the size of the electromagnetic field in the walkways 12 arranged along the sidewalls 13 of the electrolyser 3 and which are for the opersonal operation of the electrolyser.

All other things being equal, it was observed that the intensity of the electromagnetic field in the gangways 12 is proportionally smaller when the bars 9 and 10 are close to the median plane XX and appears inferior 11. It was also observed that the size of the electromagnetic field in the gangways 12 is reduced by decreasing the thickness to width ratio of bars 9 and 10. Therefore, it is preferable to use horizontal horizontal plates for buses 9 and 10.

In the embodiment shown in Figure 4, in which the secondary circuit has not been shown in the same way, the return electric current line 9 comprises a metal plate or strip 14 which is attached to the lower wall 11 of the electrolyser and substantially covers the entire wall.

In the installation of Figure 5, the electric line 7 comprises a metal plate 14 which is applied against the bottom wall 11 of the electrolyser 3, and two additional rails 15 and 16 which are respectively disposed along the two side walls 13 of the electrolyser 3. The two Additional rails 15 and 16 are advantageously bolts or metal strips that are attached to the sidewalls 13.

In the installations of Figures 6 and 7, which are similar to those of Figures 4 and 5, circuit 17a, 17b has been shown. The current passes through the conductors 17b in a direction opposite to the one passing through the plate 14. The same is true for the conductors 17a and the plates 15 and 16.

Claims (14)

1. An electrical circuit for reducing electromagnetic fields in the vicinity of an electrolyser (1, 2, 3), which comprises: - a primary electric circuit itself comprising the electrolyser and an electrical line (7) comprising at least one busbar ( 9, 10, 14) to return the current flowing through the electrolyser, - a secondary electrical circuit (17a, 17b) arranged at least partially in the vicinity of the primary circuit, for a current to pass in the opposite direction to the main circuit to compensate for it. electromagnetic field generated by the primary circuit. Circuit according to Claim 1, characterized in that the busbar (9, 10, 14) is arranged below and / or above the electrolyzer (3). Circuit according to Claim 1, characterized in that the busbar (14) is attached to a wall (11) of the electrolyser (3). Circuit according to the preceding claim, characterized in that the wall is a lower wall (11) of the electrolyser. Circuit according to Claim 3 or 4, characterized in that the busbar is a metal plate (14), one of the largest faces of which is attached to the wall (11). Circuit according to any of the preceding claims, characterized in that the power line (7) further comprises two additional buses (15, 16), which are respectively attached to the two side walls (13) of the electrolyser (3). Circuit according to any one of the preceding claims, characterized in that the electric line (7) is positioned so as to generate an electromagnetic field that is substantially symmetrical with respect to the electrolyser vertical median plane (X-X). Circuit according to any one of the preceding claims, characterized in that the electrolyser comprises a conduit for the continuous intake of an aqueous electrolyte and a conduit for the continuous discharge of an aqueous electrolyte. Circuit according to the preceding claim, characterized in that the electrolyser comprises two selectively cation-permeable membranes disposed between the bipolar electrodes. Circuit according to any one of the preceding claims, characterized in that the primary circuit comprises a supply using two rectifiers (5a, 5b) in order to distribute currents whose waveforms are phase shifted relative to one another. Circuit according to the preceding claim, characterized in that it further comprises a drain coil (19) coupling the outputs of the two rectifiers. A method for reducing the electromagnetic fields in the vicinity of the electrical circuit of an electrolyser (1, 2, 3) comprising a primary electrical circuit, the electrolyser itself, and an electrical line (7) comprising at least one current return bus. passes through the electrolyser, characterized in that an electrical conductivity passes through a secondary electrical circuit (17a, 17b) arranged in the vicinity of the primary circuit, in the opposite direction to that of the primary circuit. A method according to the preceding claim, characterized in that the primary circuit comprises a supply that uses two rectifiers in order to distribute currents whose phase shifted waveforms 300 relative to each other. A method according to the preceding claim, characterized in that the primary circuit further comprises a drain coil (19) coupling the outputs of the two rectifiers.