Jumper switch means and method of electrically bypassing an electrolyzer

Abstract: The invention relates to an electric jumper switch means for electric current bypass of at least one electrolyzer (2) consisting of individual electrolysis cells, out of a plurality of monopolar electrolyzers (1, 2, 3) connected in series to an electrical power source characterized in that said jumper switch means comprises a multiplicity of first extension arms (12) suitable for connection to the anodic contact point (11) of each individual cell of the electrolyzer (1) preceding the electrolyzer (2) to be bypassed, a multiplicity of second extension arms (13) suitable for connection to the cathodic contact point (14) of each individual cell of the electrolyzer (3) immediately following the electrolyzer (2) to be bypassed and at least a connection means for connecting said first to said second arms (12, 13) to provide a uniform reduction of the current flow in the individual cells of the electrolyzer (2) to be bypassed without a shift of electrical current in the adjacent cells of the electrolyzers (1,2) immediately preceding and following the electrolyzer (2) to be bypassed.

Description: Electrolyzers such as membrane electrolyzers of the chlor-alkali filter-press type for the electrolysis of sodium chloride are susceptible to damage when disconnecting one electrolyzer from a series of electrolyzers in a circuit. One type of damage affects the electrocatalytically active coating on the cathode surface of the electrolyzer to be bypassed and it is caused by reverse current flow; damage will also occur if excessive current passes through individual cells of the electrolyzers adjacent to the electrolyzer to be bypassed as a consequence of shifting the current flow to those cells closest to the bypass switch connection. A number of solutions to these problems have been proposed such as in U.S. Patents No. 4,561,949 and No. 4,589,966 which both describe short circuit devices that permit partial or total flow of electric current to be bypassed around an electrolyzer. Both patents provide a method to redirect the current around the electrolyzer to be disconnected without creating a reverse current flow to the bypassed electrolyzer. However, neither patent provides a means for uniform flow of current from a plurality of cells of a preceding adjacent electrolyzer to a plurality of cells in a following adjacent electrolyzer. Another example of a short-circuit device that permits by-pasing electric current around and electrolyer connected in series with other electrolysers can be found in DE-A-2,834,570. OBJECTS OF THE INVENTION It is an object of the invention to provide an apparatus for shutting down an electrolyzer in a plurality of electrolyzers connected in series to an electrical power source, especially monopolar electrolytic electrolyzers for the electrolysis of aqueous solutions, which apparatus is capable to prevent the shift in current through individual cells of the electrolyzers adjacent to the electrolyzer to be bypassed and to prevent damage to electrolyzers by avoiding reverse current flow. It is a further object of the present invention to provide for an improved method for by-passing an electrolyzer in an multiplicity of electrolyzers by using the jumper switch means of the invention. These and other objects and advantages of the invention will become obvious from the following detailed description. THE INVENTION The novel electrical jumper switch means of the invention for electric current bypass of at least one electrolyzer consisting of individual electrolysis cells, out of a plurality of monopolar electrolyzers connected in series to an electrical power source characterized in that said jumper switch means comprises a multiplicity of extension arms suitable for connection to the anodic contact point of each individual cell of the electrolyzer preceding the electrolyzer to be bypassed and a multiplicity of extension arms suitable for connection to the cathodic contact point of each individual cell of the electrolyzer immediately following the electrolyzer to be bypassed, said jumper switch means comprising a resistor means to provide a uniform reduction of the current flow in the individual cells of the electrolyzer to be bypassed without a shift in electrical current in the adjacent cells of the electrolyzers immediately preceding and following the electrolyzer to be bypassed. Referring now to the drawings: Figs. 1 and 2 illustrate a conventional short circuit switch of the prior art and the current flow therethrough. Figs. 3, 4 and 5 schematically illustrate one embodiment of the invention consisting of an overhead jumper switch means in a top, front (section X-X) and side view respectively. Fig. 6 is a pictorial view of the embodiment of figs. 3, 4 and 5. Fig. 7 s a pictorial view of a second embodiment of the invention of a jumper switch means located beneath the electrolyzers. Figs. 8, 9 and 10 schematically illustrate three of the several alternatives for the internal electrical circuitry of the jumper switch of the invention directed to avoid a shift of electrical current in the adjacent cells of the electrolyzers immediately preceding and following the electrolyzer to be bypassed. In Figs. 1 and 2, the conventional short circuit switch is intended to bypass electrolyzer 2 by connecting the short circuit switch to bus bars 6 and 7. This apparatus does not prevent the shift of electric current flow (i) towards the apparatus contact points at bus bars 6 and 7. Fig. 2 illustrates the current flow in electrolyzers 1 and 3 just before and after electrolyzer 2 once the switch has been closed. The dashed current lines (i) indicate the increase of current flow of electrolyzers 1 and 3 closest to the switch contact points, as a consequence of the shorter current path in bus bars 6 and 7. Figs. 3, 4 and 5 schematically describe the top, front (section X-X) and side view of a series of monopolar electrolyzers 1, 2 and 3, each containing a plurality of adjacently positioned electrolytic cells 4 and 5 and an overhead jumper switch means 8 directed to bypass electrolyzer 2. The jumper switch means 8 is supported by supporting means 9 and 10 fixed to electrolyzers 1 and 3 and is connected to the anodic contact points 11 of each monopolar cell 4 of the immediately preceding electrolyzer 1 by a multiplicity of extension arms 12. The jumper switch means 8 is also connected to the cathodic contact points 14 of each monopolar cell 5 of the immediately following electrolyzer 3 by a multiplicity of extension arms 13. In order to obtain a low-resistance connection between each couple of extension arms and anodic or cathodic contact points, said extension arms, which may be either rigid or flexible, may be provided in their lower ends with spring-loaded pincers. These last ones are forced to pinch the strip-shaped anodic or cathodic contact points by the weight of the jumper switch means 8 itself. The jumper switch means 8 is also connected to a travelling crane, which allows for positioning the jumper switch means just above the electrolyzer to be by-passed in a series of several electrolyzers of a cell room of an industrial electrolysis plant. Fig. 6 is a pictorial view of the embodiment schematized in figs. 3, 4 and 5. Fig. 7 is an analogous pictorial view of a second embodiment of the invention wherein the jumper switch means 8 is positioned beneath the electrolyzers and is supported by a cart travelling along rails located just below each row of electrolyzers. The remaining components are unchanged as well as the relevant numerals. The electric current is directed from the monopolar cells 4 of the immediately preceding electrolyzer 1 through the contact points 11 and the multiplicity of extension arms 12 to the jumper switch 8. The electric current then flows through resistor means in the jumper switch 8 to control the flow of electric current to the multiplicity of extension arms 13 and to the contact points 14 of the monopolar cells 5 of the immediately following electrolyzer 3. The current is withdrawn progressively in equal portions from the monopolar cells 4 and is fed in equal portions to the monopolar cells 5 : in such a way the problems associated with shifting of the current previously discussed are completely overcome. Figs. 8, 9 and 10 show three possible arrangements for the internal circuitry of the jumper switch means 8 of the invention. More particularly, fig. 8 shows that extension arms 12 and 13 can be connected to bus bars 15 and 16 the cross area of which is by far larger than the one of bus bars connecting the electrolyzers (numerals 6 and 7 in the preceding figures). This generously sized cross area prevents any practically significant shift of current in the adjacent individual cells of the electrolyzers immediately preceding and following the electrolyzer to be bypassed. The jumper switch means 8 is also provided with two switch units 17 and 18 and a resistor means 19: once the extension arms 12 and 13 have been connected to the anodic and cathodic contact points (11 and 14 in figs. 3-7) switch unit 17 is closed and part of the total electric current is bypassed through resistor means 19. The remaining minor part of the electrical current still fed to the electrolyzer to be bypassed allows operating conditions to be established in the electrolyzer so that reverse current is prevented on a subsequent short-circuiting sequence. After a suitable time after closing switch unit 17, switch unit 18 is also closed, allowing the complete by-passing of the electrolyzer without practically important reverse current crossing the electrolyzer itself. An alternative electrical circuitry is illustrated in Fig. 9: in this case the bus bars have been divided in subunits 20, 21 and 22, 23 respectively, to which extension arms 12 and 13 are connected. Each subunit which is electrically insulated from the other is provided with switch units (24, 25 and 27, 28 respectively) and resistor means (26, 29) to be operated as described above for the jumper switch of Fig. 8. Dividing the bus bars in subunits avoids the shift of the electrical current mentioned above, without recurring to the use of massive metal at the cost of some added complexity of the electrical circuitry. Fig. 10 describes the circuitry of Fig. 9 in the extreme case where each couple of anodic and cathodic extension arms 12, 13 is connected to its own switch unit (30, 31) and resistor means (32) in a modular arrangement. When using the parallel arrays of switch units and resistor means described in Figs. 9 and 10, the switches are to be operated simultaneously (e.g. in Fig. 9: 24 and 27 and then 25 and 28). To properly comprehend the invention, it should be understood that resistivity is the direct current (d.c.) resistance between opposite parallel faces of a portion of the material having a unit lenght and a unit cross section. The resistivity of a material determines the electrical resistance offered by a material and resistance is calculated according to the formula: R =pL/A where R = resistance in micro-ohms p = resistivity in microohms.centimeter L = lenght in cm A = cross sectional area in cm2 Example of resistivity of several metals are as follows: METAL RESISTIVITY (microohm-cm) aluminum 2.655 copper 1.673 cast iron 75 - 98 lead 20.65 magnesium 4.46 nickel 6.84 steel 11 - 45 The voltage drop in a bus bar as identified by numerals 6 and 7 in figures 1, 2, may be calculated for the arrangement of fig. 1, where a conventional short circuit switch is used to bypass electrolyzer 2, and is given by : V = 0,5 R I where R is as defined in equation (1) above I is the total current flowing through the electrolyzers. Assuming a total current of 60.000 Amps, the lenght L equal to 200 cm and the cross sectional area A equal to 100 cm2, the voltage drop V along the bus bar results to be 0,1 Volt. It is for this reason that attaching a short circuit device of the prior art to one end of the bus bar 6 and 7 will cause a shift in current in those cells closest to the jumper switch contact points as illustrated in Fig. 2. In those cases where the prior art taught the use of a switching device attached to bus bars 6 and 7 as in U.S. Patents No. 4,561,949 and No. 4,589,966, the electrolyzers were limited to a few monopolar cells to avoid an excessive shift in current flow. As can be seen, the electrical resistance can be minimized by : (1) decreasing the lenght of the current path; or (2) by increasing the thickness of the bus bars. In both cases, the prior art is limited by practical considerations. Therefore, the prior art will always experience some shift in current. With the jumper switch means of the present invention, current can be transferred uniformily from electrolyzers comprising any number of individual cell units without causing a shift in electrical current. As a matter of fact the electrical current is directly fed from the individual cells of the electrolyzers through the extension arms into the jumper switch means of the invention without travelling across the bus bars which electrically connect the electrolyzers during normal operation. In addition the internal circuitry of the jumper switch means of the invention is designed to allow the portions of the total current which travel along the extension arms to be equal. This result is achieved by using the design alternatives shown in Figs. 8, 9, 10, that is oversized internal bus bars, that is sized in order to give less than 50 mV ohmic drop (assuming a total current of 60,000 Amps), or internal bus bars divided into subunits, each one provided with switch and resistor means, or individual switch and resistor means for each extension arm, this last arrangement allowing, as a further advantage a better control of the heat generated by the electrical current. With conventional jumper switches, the bypassed electrolyzer must be removed by lifting over the jumper switch along aside it which results in unsafe conditions for the workers. The electrolyzer is heavy and is above the workers with the possibility of electrolyte which can be 32% caustic and chlorinated brine in chlor-alkali electrolysis leaking down on the workers. The jumper switch also blocks access to and from the bypassed electrolyzer. By placing the jumper switch of the invention overhead or beneath the bypassed electrolyzer, these problems are avoided and the electrolyzer may be kept at ground level and removed by a conventional fork-lift truck, for example. There is no risk of the electrolyzer dropping on the workers and access to the electrolyzer is open. With the jumper switch means of the invention, there is a saving of up to 40% of copper since the bus bars connecting the electrolyzers can be designed just to transfer current between the electrolyzers and not to minimize the shift of electrical current in the individual cells of the electrolyzers caused by prior art switch means. Also, in view of the fact that the total current is divided into small portions per each extension arms, the voltage drop along the extension arms is negligible and the connection between each extension arm and the relevant anodic or cathodic contact points may be of the friction type (e.g. the spring-loaded pincers mentioned before) rather than the bolted type required by the prior art switch means where the total high current flows therethrough. The prior art bolting is time consuming and requires the workers to be between the operating electrolyzers for a longer period of time which is dangerous. Another advantage of the jumper switch means of the invention is that there is no limit to the number of cells in the electrolyzer to be bypassed. Various modifications of the apparatus and method of the invention may be made and it should be understood that the invention is intended to be limited only as defined in the appended claims.

Claims: A jumper switch means for electrically by-passing a monopolar electrolyzer (2) consisting of individual electrolysis cells (5) having anodic and cathodic contact points, out of a plurality of monopolar electrolyzers (1, 2, 3) connected in series to an electrical power source wherein said jumper switch means comprises a multiplicity of first and second extension arms (12, 13) characterized in that said multiplicity of first extension arms (12) being suitable for connection to said anodic contact point (11) of each individual cell (5) of the electrolyzer (1) preceding the electrolyzer (2) to be by-passed said multiplicity of second extension arms (13) being suitable for connection to said cathodic contact point (14) of each individual cell (5) of the electrolyzer (3) immediately following the electrolyzer (2) to be by-passed and said jumper switch means further comprises at least a connection means for connecting said first to said second arms (12, 13), to provide a uniform reduction of the current flow in the individual cells (5) of the electrolyzer (2) to be by-passed without a shift of electrical current in the adjacent cells (5) of the electrolyzers (1,3) immediately preceding and following the electrolyzer (2) to be by-passed. A jumper switch means as defined in claim 1, wherein said connection means comprises at least a switch and resistor means (17-19, 24-29, 30-32). A jumper switch means as defined in claim 2, wherein said connection means further comprises a first internal bus bar (15) connecting said first extension arms (13), and wherein said switch and resistor means (17-19) is provided in common for all extension arms (12,13). A jumper switch means as defined in claim 2, wherein said connection means further comprises first internal bus bars (20, 21) connecting groups of said first extension arm (12) and second internal bus bars (22, 23) connecting corresponding groups of said second extension arms (13), and wherein separate switch and resistor means (24-29) are provided for each said group of extension arms (12, 13). A jumper switch means as defined in claim 2 wherein each couple of said first and second extension arms (12, 13) is provided with its own switch and resistor means (30-32) in a modular arrangement. A jumper switch means as defined in one of claims 2-5, wherein said switch and resistor means comprises at least two switch units (17, 18; 24, 25; 27, 28; 8, 31) and at least one resistor unit (19; 26; 29; 31), wherein the first switch unit (17; 24; 27; 30) is connected in series to a parallel arrangement of the second switch unit (18; 25; 28; 31) and said resistor unit (19; 26; 29; 31). A jumper switch means as defined in one of claims 1 to 6, wherein the connection between extension arms (12,13) and anodic or cathodic contact points (11, 14) is friction type connection. A jumper switch means as defined in one of claims 1 to 7, wherein the extension arms (12, 13) are rigid. A jumper switch means as defined in one of claims 1 to 7, wherein the extension arms are flexible. A jumper switch means as defined in one of claims 7-9, wherein said friction-type connections are spring loaded pincers. A jumper switch means as defined in one of claims 7-10, wherein the friction-type connections are forced by the weight of said jumper switch means. A method of electrically bypassing an electrolyzer in a plurality of monopolar electrolyzers serially connected to an electrical power source, comprising using the jumper switch means of claims 1 to 11. The method of claim 12 wherein said electric jumper switch means is placed above the bypassed electrolyzer. The method of claim 12 wherein said electric jumper switch means is placed beneath the bypassed electrolyzer.

Inventors: BORRIONE PIERLUIGI ATTILIO VIT, MARZUPIO MAURIZIO, MORRIS GREGORY JEAN ELDON, BORRIONE, PIERLUIGI ATTILIO VITTORIO, MARZUPIO, MAURIZIO, MORRIS, GREGORY JEAN ELDON
Applicants: PERMELEC SPA NORA, DE NORA PERMELEC S.P.A.
Application year: 1991
Main classification: C25B9
IPC codes: H01H33, C25B9