US3175150A

US3175150A - Apparatus for detecting short circuits in electrolytic cells having liquid mercury cathodes

Info

Publication number: US3175150A
Application number: US295557A
Authority: US
Inventors: Druylants Paul
Original assignee: Solvay SA
Current assignee: Solvay SA
Priority date: 1962-07-24
Filing date: 1963-07-16
Publication date: 1965-03-23
Anticipated expiration: 1982-03-23
Also published as: NL107564C; BE635200A; NL281336A; ES288160A1; CH398511A; GB1066445A

Description

March 23, 1965 P. DRUYLANTS FOR DETECTING SHORT 3,175,150 CIRCUITS IN ELECTRQLYTIC CELLS HAVING LIQUID MERCURY CATHODES APPARATUS Filed July 16, 1963 INVENTOR PA UL DRUYLAN 7Z5 =ou m m muzmmmmmm 7 m m m m m M5053 552m 2 nv Jr X\/ h mats #52 3375 m0 I Q I Id! 29543 f maom a? u 0 J JJMU nfibofiufim ATFORNE Y5 United States atent ()5 ice 3,175,150 Patented Mar. 23, 1965 2 Claims. (c1. 324-29 The present invention relates to an apparatus for detecting short circuits in electrochemical reaction cells for the electrolysis of aqueous solutions of alkali metal halides.

In such cells the short circuit obviously results from an accidental contact between the anode assembly and the mercury cathode. This contact may be due to the presence of impurities on the surface of the mercury, for example, of coarse mercury or of particles of graphite; or to poor regulation of the distance between the anode and the cathode. The breakage of an anode can also produce such a short circuit.

Short circuits occurring in a cell with a liquid cathode are generally from one of three sources;

(a) They can be due to small contact regions which are local or which move more or less rapidly with the dew of mercury, and which contact regions cause poor current distribution and diminution of the yield of the cell by bypassing some of the current intended for electrolysis.

(b) They can be due to a localized larger contact region of a certain size which causes inconveniences like those under (a), but more aggravated since it bypasses a substantial portion of the current of a single anode and can in time cause heating and burning of the latter;

(0) They can be due to a low resistance and local contact region of small extent. In such a case besides the results under (a) the passage of a very strong current is permitted through the area of contact, resulting in local heating of the bottom of the cell, causing it to Warp and eventually to leak.

It is obviously of primary importance to be able to detect the occurrence of a short circuit in order to ensure the economy and safety of electrolytic cells with mercury cathodes.

If a voltmeter is connected across the bases of two consecutive cells of a series, any of the short circuits mentioned above will be indicated by a swinging of the needle. The amplitude of such swinging is, however, weak and very irregulatr so that it cannot be depended on to indicate the seriousness of the short circuit. Hence a small short circuit of no practical importance can cause a pronounced swinging of the needle while a short circuit that causes burning of an anode or piercing of a bottom, may be hardly noticeable.

There are in commercial use very sensitive contact voltmeters which require only a slight impulse to release an alarm. Such voltmeters may have contacts controlled by the needle of the volrneter that can be adjusted manually in such a manner that during normal service they are as close as possible to the needle of the voltmeter, ready to detect feeble pulsations of the needle. To increase the sensitivity of detection, the voltmeters are con nected to the centers of the cells with reference to their lengths so as to occupy middle positions relative to all the anodes. Notwithstanding its advantages, such a system offers a serious inconvenience. First of all, the position to be given to the contacts in order that they may remain as close as possible to the needle is a function of the amperage in the cells and of the temperature of the brine, for a given adjustment of the distance between the anode and the cathode. When operating in this manner, the safety of the system depends on the man in charge of the installation because it is he who, by more or less frequent manual intervention, according to the operating conditions, must adjust the positions of the contacts. Finally, the spreading of the scale is small because oscillations must be detected which are at the most only equal to 0.1 v. on a scale of 5 v.

It is thus an object of the present invention to provide a new and improved short circuit indicator for electrolylsis cells of the character described.

According to one aspect of the present invention in a preferred embodiment thereof, there is first provided a plurality of electrolysis cells not necessarily of similar nature but usually of the same type. These cells are connected in series with successive anode to cathode connections, and the anode of the first cell is connected to a source of positive voltage potential whereas the cathode of the last cell is connected to corresponding negative voltage potential. There is a voltmeter associated with each cell in the following manner: each voltmeter is provided with two coils capable of producing opposite flux and correspondingly oppositely directed torques for the meter needle. One coil, called the measuring coil, is connected across the anode and cathode path of the as sociated cell. The other voltmeter coil which can also be called reference coil, is connected across a resistance element. All resistance elements so provided pertain to a resistor which is divided into such resistance elements by adjustable taps. Accordingly, the voltages respectively applied to reference coils pertaining to voltmeters associated with two cells having a common anode-cathode connection are altered in opposite directions. There may be provided switches to shunt the reference coil of a voltmeter, the associated cell of which has been removed from circuit for any reason.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that the invention, the objects, and features of the invention and further objects, features and advantages thereof will be better understood from the following description taken in connection with the accompanying drawing in which:

There is shown a circuit network diagram constituting a preferred embodiment of the invention and provided with suitable liquids.

Turning now to the detailed description of the drawing in the figure thereof, there are shown three electrolytic cells (3,, C and C connected in series and in between the terminals of a suitable direct current voltage source. The anodes and cathodes of these cells are shown diagrammatically only and comprise solid anodes A A A and mercury cathodes K K K Anode A of cell (3;, is connected to the plus pole of the voltage source Whereas cathode K of cell C is connected to the minus pole of the voltage source. For completing the series circuit connection there are the following anode to cathode connections: A, to K A to K In the drawing, as shown by legends on cell C the mercury cathode is at the bottom with the upper surface indicated by the line below anode A and thereon is the aqueous solution being treated with its upper surface indicated by the line above anode A The anode is the heavy line beneath the surface of the aqueous solution and above the surface of the body of mercury forming the cathode.

V V and V represent voltmeters respectively associated with cells C to C Each such voltmeter has two coils b and b capable of producing opposite flux and correspondingly oppositely directed torques for the voltmeter needle. In case the equal flux is produced by each coil, the voltmeter indicates zero.

Coil of voltmeter V is connected across cell C i.e., between cathode K and anode A thereof. in a similar manner, coils b of voltmeters V and V are connected across electrolysis cells C and C respectively.

S S and S are switches for short circuiting of reference coils b of the voltmeter. Switches S to S are individually closed whenever the corresponding cell is removed from the circuit.

Safety fuses are represented by F and they are appropriately connected in the circuit network.

As. will become more apparent below, coils b are the actual measuring coils, Whereas coils b serve as reference coils. Thus, the iluX produced by coil represents a measuring flux indicative of the voltage drop in the cell to which such coil b is connected. Coils correspondingly produce a reference flux as follows: The reference circuit network primarily comprises a resistor R made up of similar resistance elements or sections R R R which are connected in series. Potentiometers shunted across small portions of adjoining resistance elements provide for suitable adjustable taps to subdivide resistor R into these variable resistance elements primarily comprising these sections R R R it is apparent, that upon adjusting of any tap the voltage drawn from one section is altered in opposite direction to that drawn from the adjoining section.

it can be seen specifically from the drawing, that coils b of voltmeters V V V are respectively connected across resistors R R R but using the taps of the potentiometers between R R and R -R for completion of the reference network. Resistor R as a whole is connected between cathode K and anode A i.e., the reference resistor is connected across all of the electrolysis cells and, at the same time across the direct current source.

Use is thus being made of contact voltmeters which are equipped with two coils Whose flux oppose each other in that the coils produce oppositely directed torques effective at the needle as stated above. The coils are arranged in such a manner as to compare the voltage drop in each cell of the series of cells with the voltage drop in a respective section of a reference resistor network connected to the ends of the series of cells. The sum of the voltage drops in the reference resistor is always equal to the sum of the voltage drops in the cells, so that after adjustment of each section of the reference resistor, the needle of each voltmeter occupies the zero position, and any deviation of the voltmeter needle from this position indicates and detects immediately a short circuit in the corresponding cell.

Contact voltmeters of this kind are easily produced and, because of the two coils, serve to measure a difference of potential. The scale of such a voltmeter covers a total range of 1.5 v., so that it is possible to measure very small changes of potential.

As is indicated in the drawing, the voltage drop in each cell C C C as sensed by the measuring coil b of each voltmeter i compared with the voltage drop in that ref erence resistor portion R R R of the resistor R which is connected to the ends of the corresponding reference coil k The reference network including resistor portions R R R, with potentiometers is connected to the ends of the series of cells C C and C in such a manner that the sum of the voltage drops in the portions R R R is at each moment, and regardless of any other operating condition, always equal to the sum of the cell volt ages. For example, if voltmeter V shows zero, and voltmeter V shows +X volts, the voltmeter V must show X volts. Hence by adjusting individually and successively all of the reference resistances, whose sum remains constant, it is possible, by starting from one point, to bring each voltmeter needle to the zero position. This will, in

fact, equalize all of the reference resistor portions in such a manner that the voltmeter-s will all remain permanently in their zero positions during normal operations, not even assuming that each cell carries a similar load. This condition will prevail until the occurrence of a short circuit in any cell. When the latter occurs, the difference due to the voltage impulse in the defective cell will show itself on the extended scale of the voltmeter which controls tha cell and not on the network of voltmeters.

For example, it may be assumed that a short circuit has occurred in cel C which fact is yet unknown to the service personnel. Hence, there is now a direct COIlI1C tion between anode A and cathode K reducing the voltage drop applied to measuring coil [2 of voltmeter V In voltmeter V there will now prevail the reference flux from coil b and the voltmeter will indicate this fact. Since electrolysis is primarily a constant voltage process, the voltage as between cathode A and anode A is now slightly reduced to the voltage drop prevailing across three electrolysis cells plus the voltage drop in the short circuited cell C Cell C will now be removed from the circuit in connecting anode A to cathode K In the reference circuit network complete balance is restored in a similar manner in closing switch S thus removing voltmeter V 2 in effect from the measuring network. The reference voltages across resistances R and R are now causing balance in voltmeters V and V for zero indication.

While only three cells in series are shown, it will be evident that as many cells as desired could be put in series in the practice of the present invention.

The invention is not limited to the embodiments described above but all changes and modifications thereof not constituting departures from the spirit and scope of the invention are intended to be covered by the following claims.

What is claimed is:

1. Apparatus for detecting a short circuit in electrolysis cells having liquid mercury cathodes for the electrolysis of aqueous solutions of alkali metal halide which cells are connected in series circuit connection, the combination comprising: a plurality of voltmeters, one for each cell, each voltmeter having a first coil connected across the anode and cathode of its associated cell, each said voltmeter having a second coil for producing a flux opposite to that of said first coil; and a resistor connected across said series circuit connection of said cells and having a plurality of adjustable taps to divide said resistor into a plurality of series connected resistors, with each such series connected resistor connected across one second coil of one of said voltmeters by means of at least one adjustable tap.

2. In an apparatus for electrolysis of aqueous solutions of alkali metal halides, the combination comprising: a plurality of electrolytic cells connected in series circuit network and to a direct current voltage source, there being a plurality of direct anode-cathode connections of respectively succeeding cells, and there being a first cell and a last cell respectively connected to the direct current voltage source terminals; a voltmeter associated with each cell having a first coil connected to the anode and cathode thereof and having a second coil for producing a flux opposite to that of said first coil; a switch for each voltmeter for bridging the second coil thereof; and a resistor connected across said series circuit network of cells and being divided into a plurality of series resistors by means of adjustable taps, each said series resistor being connected to the second coil of one of said voltmeters,

Jill! each tap adjusting in opposite directions the voltages applied to the said second coils of those voltmeters associated with electrolytic cells having one of said direct anodecathode connections.

No reference cited.

Claims

1. APPARATUS FOR DETECTING A SHORT CIRCUIT IN ELECTROLYSIS CELLS HAVING LIQUID MERCURY CATHODES FOR THE ELECTROLYSIS OF AQUEOUS SOLUTIONS OF ALKALI METAL HALIDE WHICH CELLS ARE CONNECTED IN SERIES CIRCUIT CONNECTION, THE COMBINATION COMPRISING: A PLURALITY OF VOLTMETERS, ONE FOR EACH CELL, EACH VOLTMETER HAVING A FIRST COIL CONNECTED ACROSS THE ANODE AND CATHODE OF ITS ASSOCIATED CELL, EACH SAID VOLTMETER HAVING A SECOND COIL FOR PRODUCING A FLUX OPPOSITE TO THAT OF SAID FIRST COIL; AND A RESISTOR CONNECTED ACROSS SAID SERIES CIRCUIT CONNECTION OF SAID CELLS AND HAVING A PLURALITY OF ADJUSTABLE TAPS TO DIVIDE SAID RESISTOR INTO A PLURALITY OF SERIES CONNECTED RESISTORS, WITH EACH SUCH SERIES CONNECTED RESISTOR CONNECTED ACROSS ON SECOND COIL OF ONE OF SAID VOLTMETERS BY MEANS OF AT LEAST ONE ADJUSTABLE TAP.