IL100265A - Electric jumper switch - Google Patents

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. <IMAGE> [EP0492551A1]

Description

Aim ->bmn Aim Electric jumper switch DE NORA PERMELEC S.p.A.

C. 85100 STATE OF THE ART Electrolyzers such as membrane electrolyzers of the chlor-alkali filter-press type for the electrolysis of sodium chloride are susceptible to damage when disconnect-ing 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 closes 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 curren 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.

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 INVKNTIOB 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 poin 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 th 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 th 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 embodimeiit 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.

Figsj. 8, 9 and 10 schematically illustrate three of I the several alternatives for the internal electrical circuitryl of the jumper switch of the invention directed to avoidl a shift of electrical current in the adjacent cells of the electrolyzers immediately preceding and following Ithe 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 switc 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 cionnected 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 Iraeans 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 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 β to control the flow of electric current to the multiplicity of extension arms 13 and to the contact i 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 t 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 curren 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 hav bee divided in subunits 20, 21 and 22, 23 respectively, to which extension arras 12 and 13 are connected.. Each, subuni which is electrically insulated from the other is provided with switch units (24, 25 and 27, 28 respectively) and resistor I 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 monopola 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 thicknes 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, curreat can be transferred unifo mily from electrolyzers comprising any numbe of individual cell units without causing a shift in electrical current.

As a matter of fact the electrical current i 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 resul 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, or internal bus bars divided into subunits, each one provided with switch and resistor means, 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.

Wit 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 dawn on the workers. The jumper switch also blocks access to and from the bypassed electroj.yzer. 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 causecL 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 without departing from the spirit or scope thereof and it should be understood that the invention is intended to be limited only as defined in the appended claims .

Claims (5)

- 15 - 100265/2 CLAIMS:

1. A jumper switch means for electrically bypassing a monopolar electrolyzer out of a plurality of monopolar electrolyzers connected in series to an electrical power source, which electrolyzers consist of individual electrolysis cells each having anodic and cathodic contact points, said jumper switch means comprising an internal circuitry and a multiplicity of extension arms for connection to the electrolyzers immediately preceding and following the electrolyzer to be bypassed, characterized in that said jumper switch means is positioned above said plurality of electrolyzers, said multiplicity of extension arms comprises first extension i arms suitable for connection to the anodic contact point of each individual cell of ,the electrolyzer immediately preceding the electrolyzer to be bypassed, second 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 first and second extension i arms being joined to said internal circuitry to provide bypassing of the electrolyzer without a shift of electric current in the adjacent cells of the electrolyzers immediately preceding and following the electrolyzer to be bypassed!. i

2. j The jumper switch means of Claim 1, wherein said connections between the extension arms and the anodic and cathodic contact points are of the friction type.

3. The jumper switch means of Claim 1, wherein the extension arms are flexible.

4. The jumper switch means of Claim 1, wherein the extension arms are rigid. \ I

5. The jumper switch means of Claim 2, wherein said friction-type connections are spring-loaded pincers.