EP1769104A2

EP1769104A2 - Electric circuit of an electrolyzer with bipolar electrodes and electrolysis installation with bipolar electrodes

Info

Publication number: EP1769104A2
Application number: EP05752677A
Authority: EP
Inventors: Joachim Lange
Original assignee: Solvay SA
Current assignee: Solvay SA
Priority date: 2004-06-10
Filing date: 2005-06-08
Publication date: 2007-04-04
Also published as: FR2871479A1; EA200700005A1; AR052970A1; WO2005121410A2; CA2568833A1; JP2008501864A; BRPI0511955A; WO2005121410A3; US20070205110A1; CN101048534A; EA011603B1; FR2871479B1

Abstract

Electric circuit of an electrolyzer with substantially vertical bipolar electrodes, comprising at least one busbar (9, 10) that is placed below and/or above the electrolyzer (3) . Electrolysis installation comprising such a circuit and at least one electrolyzer (3) with vertical bipolar electrodes.

Description

Electric circuit of an electrolyzer with bipolar electrodes and electrolysis installation with bipolar electrodes

The invention relates to electrolyzers with bipolar electrodes, and especially to the electric power supply of such electrolyzers. The invention especially relates to an electric circuit for supplying rectified electric power to an electrolyzer with bipolar electrodes. Electrolyzers with bipolar electrodes, supplied with DC power, are commonly used in the electrochemical industry. Such electrolyzers are commonly used to electrolyze aqueous solutions of sodium chloride, in order to produce chlorine, aqueous sodium hydroxide solutions or aqueous solutions of sodium chlorate. Considering the high current densities employed in electrolyzers with bipolar electrodes, rectified AC power is generally substituted for DC power. Rectified AC power normally presents pulses of which the frequency and amplitude depend on the rectifier used. Accordingly, the electromagnetic field produced by the rectified AC power is likely to generate induced currents which may be relatively strong in certain industrial applications, particularly with bipolar electrolyzers for the continuous production of chlorine and of aqueous sodium hydroxide solutions. It is also well known that under extreme conditions, high electromagnetic fields can have detrimental effects on the human organism, especially those produced by rectified AC power, because of the induced currents that they are liable to generate. It is consequently important to take measures to protect the personnel in the neighbourhood of the industrial installations or to reduce the strength of the electromagnetic fields. Standards have moreover been set in this sense, requiring the limitation of the strength of electromagnetic fields in industrial premises. Among these standards, European standard 89/391/EEC is particularly stringent. It is an object of the invention to provide an electric circuit of novel design, to supply high strength electric current to an industrial electrolyzer with bipolar electrodes. It is a particular object of the invention to provide an electric circuit with which the electromagnetic field in the neighbourhood of the electrolyzer is reduced to a sufficiently low value to meet the abovementioned European standard. It is even more particularly an object of the invention to reduce the strength of the magnetic field on walkways installed along the side walls of electrolyzers with bipolar electrodes. In consequence, the invention relates to an electric circuit of an electrolyzer with bipolar electrodes, comprising at least one electric current line that is placed outside the electrolyzer, characterized in that the electric current line comprises at least one busbar which is placed below andor above the electrolyzer. The invention relates more specifically to electrolyzers with substantially vertical bipolar electrodes. Such electrolyzers are well known in the art, where they are widely used for the electrolysis of aqueous solutions of metal halides, particularly sodium chloride. These electrolyzers are generally formed from a succession of metal frames each comprising a bipolar electrode, these frames being juxtaposed as in a filter press (Moderne Chlor-alkali technology, Volume 3, SCI, 1986, chapter 13 "Operating experience gained with the bipolar Hoechst-Uhde membrane cell" ; Modern Chlor-alkali Technology, Volume 4, SCI, 1990, chapter 20 'Ηoechst-Uhde single element membrane electrolyzer : concept-experiences-applications"). The frames usually have a square or rectangular profile, so tha when they are juxtaposed, as in a filter press, they form an upper wall, a lower or bottom wall, and two side walls of the electrolyzer. The electrolyzer is normally supplied with DC power or, more generally, with rectified AC power. The DC or rectified AC power flows from a terminal of the DC source or of the rectifier, through the bipolar electrodes, and then returns to the other terminal of the DC source or the rectifier, via an electric current line located outside the electrolyzer. According to the invention, the said return electric current line comprises at least one busbar that is placed below or above the electrolyzer. The choice of placing the busbar below or above the electrolyzer is dictated by considerations related to the construction of the electrolyzer and the method of assembling the bipolar electrodes. As a variant, the abovementioned electric current line may comprise a busbar placed below the electrolyzer and another busbar placed above the electrolyzer. According to another variant, the electrolyzer may also comprise a plurality of busbars below the electrolyzer and/or a plurality of busbars above the electrolyzer. In practice, for considerations related to the assembly and maintenance of the electrolyzer, it is generally preferable for the abovementioned electric current line not to comprise a busbar above the electrolyzer. It has been found, all other things remaining equal, that the electric circuit according to the invention significantly reduces the electromagnetic field in the neighbourhood of the electrolyzer with bipolar electrodes, chiefly along its side walls, especially on walkways that are normally installed along the side walls and are used by the operating and maintenance personnel. In the discussion below, the expression "in the neighbourhood of the electrolyzer" means the space along the side walls of the electrolyzer, where the walkways used by the operating and maintenance personnel of the electrolyzer are normally installed. In the electric circuit according to the invention, the material of the busbar is not a critical factor for the definition of the invention. It is generally made from copper, aluminium or aluminium alloy. In the electric circuit according to the invention, the profile of the cross section of the busbar is not a critical factor for the definition of the invention. It may, for example, be square, rectangular, circular or polygonal. In a first and particular embodiment of the electric circuit according to the invention, the busbar has a rectangular profile and is oriented so that its large sides are substantially horizontal. It has been observed, all other things remaining equal, that the selection of a rectangular section busbar, placed horizontally below and/or above the electrolyzer, minimises the strength of the electromagnetic field in the neighbourhood of the electrolyzer. I has also been observed that the decrease in the electromagnetic field in the neighbourhood of the electrolyzer is greater if the ratio of the thickness to the width of the busbar is smaller. In practice, it is consequently preferable to use a metal flat for the busbar. As a variant, a plurality of metal flats can be used, placed side by side below and/or above the electrolyzer. It has further been observed, all other things remaining equal, that the ' strength of the electromagnetic field in the neighbourhood of the electrolyzer decreases as the busbar is brought closer to the wall of the electrolyzer. In consequence, in a second embodiment of the electric circuit according to the invention, the busbar is placed immediately next to a wall of the electrolyzer. In this embodiment of the invention, the said wall of the electrolyzer is the lower or bottom wall of the electrolyzer or its upper wall, depending on whether the busbar is positioned below or above the electrolyzer. In this embodiment of the invention, the expression "immediately next to the wall of the electrolyzer" means that the distance between this wall and the busbar is not more than five times (preferably three times) the thickness of the busbar. Preferably, this distance does not exceed the thickness of the busbar. In a preferred variant of the abovementioned second embodiment of the invention, the busbar is attached to the said wall of the electrolyzer. In this preferred variant of the invention, the busbar is advantageously a metal flat of which one of the large sides is attached to the said wall, separated from the wall only by the thickness of the necessary electrical insulation. The metal flat may be attached to a portion of the surface of the said wall. It is preferable for the metal flat to be attached to substantially the entire surface of the said wall. In a third particular embodiment of the invention, the abovementioned electric line further comprises two additional busbars, that are placed respectively immediately next to two side walls of the electrolyzer. In this embodiment of the invention, the expression "immediately next to" is identical to the definition of this expression given in the second embodiment discussed above. All other things remaining equal, the presence of the additional busbars reduces the strength of the electromagnetic field in the neighbourhood of the electrolyzer. In this third embodiment according to the invention, the additional busbars may have any shape compatible with the construction of the electrolyzer. They may, for example, have a square, rectangular, polygonal, oval or circular profile. The additional busbars may also have the same profile or different profiles and they may have the same dimensions or different dimensions. In practice, however, it is preferable that the additional busbars have the same profile and the same dimensions. It is also preferable for the additional busbars to have a rectangular profile and that they be attached by their large side respectively to the two side walls of the electrolyzer. In the third embodiment of the invention described above, the respective dimensions of the additional busbars and those of the or each busbar that is placed below and/or above the electrolyzer are determined according to the way in which the electric current is to be distributed to all these busbars. In practice, it is recommended that the strength of the electric current in the busbar positioned below and/or above the electrolyzer differ by no more than 30% (preferably no more than 20%) from the strength of the electric current in each of the additional busbars. It is preferable for the strength of the electric current to be substantially identical in the busbar that is positioned below and/or above the electrolyzer and in each of the additional busbars. In a fourth embodiment of the invention, which is especially advantageous, the return electric current line of the electric circuit is positioned so as to generate an electromagnetic field that is substantially symmetrical about the median vertical plane of the electrolyzer. In this embodiment, the aim (to generate an electromagnetic field that is substantially symmetrical about the median vertical plane of the electrolyzer) is achieved by adequately dimensioning and positioning the or each busbar. The choice of the optimal dimensions and the optimal position is determined by a person skilled in the art, particularly according to the shape and dimensions of the electrolyzer. In practice, this result can generally be achieved by placing the busbar or the busbars symmetrically about the median vertical plane of the electrolyzer. The electric circuit according to the invention significantly reduces the electromagnetic field in the neighbourhood of the electrolyzer with bipolar electrodes. In consequence, the invention further relates to the use of the electric circuit according to the invention, to reduce the electromagnetic field in the neighbourhood of the electrolyzer. The electric circuit according to the invention applies specially to electrolyzers for the continuous electrolysis of water or of aqueous solutions such as aqueous solutions of alkali metal halides, especially of sodium chloride. In consequence, in a preferred embodiment of the invention, the electrolyzer comprises a line for the continuous intake of an aqueous electrolyte and a line for the continuous removal of an aqueous electrolyte. The invention applies in particular to electrolyzers for the production of sodium chlorate by the electrolysis of aqueous solutions of sodium chloride. The invention applies especially to electrolyzers for the production of chlorine and of aqueous sodium hydroxide solutions, by the electrolysis of aqueous solutions of sodium chloride, these electrolyzers comprising membranes that are selectively permeable to cations, and which are inserted between the bipolar electrodes. The electric circuit according to the invention applies to any electrolysis installation incorporating at least one electrolyzer with vertical bipolar electrodes. In consequence, the invention further relates to an electrolysis installation comprising at least one electrolyzer with bipolar electrodes, connected to an electric circuit according to the invention. The installation according to the invention may comprise a single electrolyzer or a plurality of electrolyzers connected in electrical series. The invention relates in particular to the use of this installation for the production of chlorine and of aqueous sodium hydroxide solutions. Particular features and details of the invention will appear from the following description of the figures appended hereto, which show a number of particular embodiments of the invention. Figure 1 shows an overall plan view of an electrolysis installation prior to the invention. Figure 2 shows a schematic longitudinal elevation view of a particular embodiment of the electrolysis installation according to the invention. Figure 3 shows a vertical cross section on the plane ni-LU of Figure 2. Figure 4 is a view similar to that of Figure 3, of another embodiment of the installation according to the invention. Figure 5 is a preferred variant of the installation in Figure 4. In these figures, the same reference numerals designate identical elements. The electrolysis installation shown in Figure 1 is prior to the invention and does not conform to it. It comprises three electrolyzers 1, 2 and 3 designed for the production of chlorine, hydrogen and sodium hydroxide by the electrolysis of an aqueous solution of sodium chloride. The electrolyzers 1, 2 and 3 are of the vertical bipolar electrode type. They are formed by the juxtaposition of vertical rectangular frames 4, each containing a vertical bipolar electrode (not shown). The frames 4 are juxtaposed as in a filter press. Membranes that are selectively permeable to cations are inserted between the frames 4 to form alternating anode and cathode chambers. The anode chambers of the electrolyzers 1, 2 and 3 communicate with a line (not shown) for the continuous intake of an aqueous solution of sodium chloride. They also communicate with a manifold (not shown) for the continuous removal of chlorine. The cathode chambers of the electrolyzers 1, 2 and 3 communicate with two manifolds (not shown) that serve respectively for the continuous extraction of hydrogen, on the one hand, and of an aqueous sodium hydroxide solutions, on the other. The electrolyzers 1 , 2 and 3 are coupled in electrical series with a rectifier 5 of an AC power source, via an electric circuit comprising, on the one hand, busbars 6 inserted between the electrolyzers 1, 2 and 3 and, on the other, a return electric current line 7, placed outside the electrolyzers 1, 2 and 3. The electric circuit further comprises a bipolar switch 8. In the electrolysis installation in Figure 1, the return electric current line 7 consists of a long busbar running along a longitudinal side wall of the electrolyzers 1, 2 and 3. In the electrolysis installation shown in Figure 1, each of the three electrolyzers 1, 2, and 3 may, for example, comprise 30 to 40 elementary electrolysis cells and the electric power supply comprises, for example, a 520 V DC rectifier, capable of delivering a current of between 8 and 20 kA. Depending on the surface area of the electrodes, this may result in an anodic current density of 2.5 to 6 kA/m² of anode area. However, these numerical values are purely indicative and do not limit the scope of the invention and the claims that follow. When the bipolar switch is closed, rectified electric current flows successively in the electrolyzers 1, 2, and 3, through the bipolar electrodes and in the return line 7. This electric current generates an electromagnetic field in the environment of the installation. The installation shown in Figures 2 and 3 conforms to the invention. In these figures, only the electrolyzer 3 has been shown. In the installation in Figures 2 and 3, the return electric current line 7 comprises two busbars 9 and 10 that are placed below the bottom wall 11 of the electrolyzer 3. The busbars 9 and 10 are prismatic bars of a metal that is a good electrical conductor (preferably copper or aluminium). These busbars are placed symmetrically on each side of the median vertical plane X-X of the electrolyzer. The busbars 9 and 10 are further placed in the neighbourhood of the bottom wall 11 of the electrolyzer 3, The layout of the busbars 9 and 10 in the way shown in Figure 3 has the effect of reducing the strength of the electromagnetic field on the walkways 12 running along the side walls 13 of the electrolyzer 3 and which are intended for the electrolyzer maintenance personnel. All other things remaining equal, it has been found that the strength of the electromagnetic field on the walkways 12 is reduced more if the busbars 9 and 10 are closer to the mid-plane X-X and to the bottom wall 11. It has also been observed that the strength of the electromagnetic field on the walkways 12 is reduced by decreasing the ratio of the thickness to the width of the busbars 9 and 10. It is accordingly preferable to use flats or horizontal strips for the busbars 9 and 10. In the embodiment shown in Figure 4, the return electric current line 7 comprises a metal flat or strip 14 that is attached to the bottom wall 11 of the electrolyzer and that substantially covers this entire wall. In the installation in Figure 5, the electric current line 7 comprises a metal flat 14 that is applied against the bottom wall 11 of the electrolyzer 3 and two additional busbars 15 and 16 positioned respectively along the two side walls 13 of the electrolyzer 3. The two additional busbars 15 and 16 are advantageously metal flats or strips that are attached to the side walls 13.

Claims

C L A I M S

1 - Electric circuit of an electrolyzer with bipolar electrodes, comprising at least one electric current line that is placed outside the electrolyzer, characterized in that the electric current line (7) comprises at least one busbar (9, 10, 14) which is placed below andor above the electrolyzer (3).

2 - Circuit according to Claim 1, characterized in that the busbar (14) is attached to a wall (11) of the electrolyzer (3).

3 - Circuit according to Claim 2, characterized in that the wall is a bottom wall (11) of the electrolyzer. 4 - Circuit according to either of Claims 2 and 3, characterized in that the busbar is a metal flat (14) of which one of the large sides is attached to the wall (11).

5 - Circuit according to either of Claims 3 and 4, characterized in that the busbar (14) is attached substantially to the entire surface of the wall (11). 6 - Circuit according to any of Claims 1 to 5, characterized in that the electricjine (7) further comprises two additional busbars (15, 16) which arg attached respectively to two side walls (13) of the electrolyzer (3). 7 - Circuit according to any of Claims 1 to 6, characterized in that the electric line (7) is positioned so as to generate an electromagnetic field that is substantially symmetrical about the median vertical plane (X-X) of the electrolyzer.

8 - Circuit according to any of Claims 1 to 7, characterized in that the electrolyzer comprises a line for the continuous intake of an aqueous electrolyte and a line for the continuous removal of an aqueous electrolyte. 9 - Circuit according to Claim 8, characterized in that the electrolyzer comprises membranes that are selectively permeable to cations, and which are inserted between the bipolar electrodes.

10 - Use of the electric circuit according to any of Claims 1 to 9, to reduce the electromagnetic field in the neighbourhood of the electrolyzer. 11 - Electrolysis installation comprising at least one electrolyzer (3) with bipolar electrodes, connected to an electric circuit (9, 10, 14, 15, 16) according to any of Claims 1 to 9.

12 - Use of the installation according to the preceding claim, for the production of chlorine and of aqueous sodium hydroxide solutions.