Electrolytic cell

Electrolytic cell for the production of alkali metal or alkaline earth metal chlorate from the corresponding chlorides, which cell is constructed from a plurality of cells (10) connected in series, whereby all electrodes (11, 19) except the terminal electrodes (19) are bipolar and designed with a vertical base plate (14), having one side functioning as anode in one cell unit (10) and the other side functioning as cathode in an adjacent cell unit (10) and whereby the exterior sides of the terminal electrodes (19) have electrical connections for the cell row while the sides turned inwards and both sides of the base plates (14) on the other electrodes (11) have a number of vertical electrode plates (17, 18), fitted essentially at right angles to the base plates (14), and whereby the base plates are positioned in such a manner that the electrode plates (17, 18) of adjacent base plates (14) are interleaved between each other, without direct electrical contact between themselves, forming an electrode package of electrode plates. A housing (1) encloses the cell row so that spaces for electrolyte flow are formed below, at the sides of and above the electrode packages, whereby the space above these is larger than the others and forms a flow space in which the essential part of the disproportionation reaction of the chlorate can take place.

TECHNICAL FIELD 
The present invention relates to an electrolytic cell construction and more 
particularly to an electrolytic cell construction for the production of 
alkali metal or alkaline earth metal chlorate by electrolysis of alkali 
metal or alkaline earth metal chloride. 
BACKGROUND OF THE INVENTION 
Bipolar electrode constructions are used to an ever increasing extent in 
order to obtain compact, efficient and economical electrolysis units and 
by bipolar electrode constructions are understood such electrodes which 
have one face functioning as an anode in one cell unit and the other face 
functioning as a cathode in an adjacent cell unit. By positioning a number 
of such units in a row, a battery of cells connected in series is 
obtained, which only requires current supply connections at the end 
electrodes but no special electrical connections between each cell unit. 
An especially advantageous electrode construction for these purposes, when 
a large electrode surface is desired, consists of a base plate provided 
with electrode plates fixed essentially at right angles to the base plate. 
This type of construction gives, besides a large electrode surface, a low 
voltage drop per running meter of the cell box which reduces risks of 
current leakage and short-circuit, both in the cell and outside it. The 
base plate can be provided with electrodes on one side only (unipolar 
embodiment) while means for current supply are provided on the other side. 
This arrangement does not only give the advantage that the base plates can 
form one wall of the cell, but also means that the base plates are 
available for a very simple connection to the current supply connections. 
The base plates can also be provided with electrode plates on both sides 
(bipolar embodiment) and the electrode plates on one side will then form 
cathodes while those on the other side will form anodes. By positioning a 
number of such electrode units in a row, with the electrode plates of 
adjacent electrodes between each other, a battery of cells connected in 
series will be obtained, after adding side walls, bottom and cover, and in 
this only the terminal electrode units have to be of the unipolar type and 
be provided with means for current supply on one side of the base plates 
instead of with electrode plates. This arrangement gives a very simple 
design of the cell row and also eliminates requirements on special current 
connections between the cells. 
When employing the principles for bipolar electrodes at electrolytic 
production of chlorate, certain problems specific to this process will, 
however, arise. The chlorate production comprises a number of sub-steps 
and the sequence of reactions is probably a first formation of hydroxyl 
ions at the cathode during hydrogen generation and of elementary chlorine 
at the cathode, whereafter the hydroxyl ions and chlorine react to 
hypochlorite ions, which finally are disproportionated to chlorate and 
chloride. A number of requisites have to be fulfilled if this course of 
reaction is to take place at optimum conditions. The electrolyte flow past 
the electrode surfaces must be rather high and the production of 
hypochlorite at each circulation of the electrolyte past the electrodes 
must be moderate in order to avoid side reactions and other negative 
effects. The electrolyte circulation must further permit an efficient 
removal of formed hydrogen gas, and formed chlorine gas must be 
efficiently absorbed and retained in the electrolyte during the entire 
course of reaction. The electrolyte must be given a sufficient residence 
time after the electrolysis to give a complete reaction, particularly for 
the disproportionation of hypochlorite to chlorate. These conditions are 
seldom fulfilled in known bipolar electrode constructions of the above 
discussed type, as these generally are designed to be as compact as 
possible and to give the highest possible current density which often has 
resulted in an optimum relation between the volume and the residence time, 
but not in a carefully considered circulation flow of the electrolyte. 
Other problems are caused by the corrosive environment in the cell. This 
environment is dependent partly on the composition of the electrolyte and 
partly on the high temperatures which are normally kept in order to 
achieve a high reaction rate. Corrosion problems lead to a limited service 
life for essentially all parts of the cell and necessitates a regular 
servicing of the cell. The cell should consequently be easy to dismount 
and it should be easy to replace and to clean its parts. As the electrodes 
themselves in cells with bipolar electrodes form partition walls problems 
of sealing these against the walls of the cell box will also arise, both 
with respect to electrolyte leakage and current leakage between the cells, 
and the sealings must be made with arrangements which are safe from the 
corrosion aspect and which do not make it much more difficult to 
disassemble the cell. 
Known constructions do only to a limited extent possess the mentioned 
properties. Bipolar systems have thus been designed either with external 
reaction vessels and forced circulation, or they have had a complicated 
internal construction which has not been very suitable with respect to 
corrosion and maintenance. 
THE INVENTION GENERALLY 
The primary object of the present invention is to provide an improved and 
simplified cell construction, for electrolytical chlorate production, of 
the kind that comprises bipolar electrodes, a construction which is 
especially improved with respect to electrolyte circulation, corrosion 
resistance at higher temperatures and accessability for repairs and 
servicing. 
This object is accomplished by a cell designed according to the claims. 
The cell of the invention is thus of the kind which is built up from a 
plurality of cells connected in series, whereby all the electrodes except 
the terminal ones are bipolar and provided with a vertical base plate, one 
side of which functions as an anode in one cell unit and the other side 
functions as a cathode in an adjacent cell unit. The exterior sides of the 
terminal electrodes are equipped with electrical connections for the cell 
row while the sides turned inwards and the two sides of the other base 
plates have a number of vertical electrode plates, fitted essentially at 
right angles to the base plates, and the base plates are positioned in 
such a manner that the electrode plates of adjacent base plates are 
interleaved between each other, without direct electrical contact between 
themselves, forming an electrode package of electrode plates. With this 
arrangement, which is known per se, a high current density can be applied 
to each cell and at the same time a large flow area for vertical flow of 
electrolyte past the electrodes is obtained, which is essential in order 
to obtain the above mentioned rapid circulation. 
According to the invention the cell row is enclosed in a housing of such 
dimensions that a space is formed between the bottom of the housing and 
the lower edges of the electrode plates, a space is formed between the 
vertical sides of the housing which are parallel to the electrode plates 
and the nearest electrode plates and a space is formed between the upper 
sides of the electrode plates and the top of the housing. The last 
mentioned space is larger than those below and at the sides of the 
electrode plates, and form an extra flow and reaction space for the 
electrolyte. Further intermediate partitions are arranged between the cell 
unit in form of extensions of the base plates downwards, towards the sides 
and upwards limiting a space for each cell unit. It is preferred that 
vertical walls which direct the flow are arranged parallel to the 
electrode plates, the walls extending from the upper side of the outermost 
electrode plates in the cell unit up in the space above the cell package. 
By this arrangement a flow channel for the electrolyte circulating in the 
cell is formed. The electrolyte flows past the electrode plates, is 
enriched with hydrogen gas, rises upwards between the side walls and the 
flow directing walls, when such walls are present above the electrode 
package, turns at the top of the channel where hydrogen gas is 
concentrated, flows downwards along the walls of the housing and finally 
turns at the bottom and anew flows up between the electrode plates. The 
flow is essentially stable during the entire circulation and substantially 
free from back-mixing which gives a maximum reaction rate for the chlorate 
formation. A substantial height of liquid is obtained above the electrode 
plates which gives a great lifting effect and circulation rate and a good 
absorption of chlorine gas and at the same time a sufficient residence 
time for the electrolyte during the circulation is obtained. The width of 
the circulation channels and the position of the electrode plates give a 
low flow resistance. The enclosed electrolyte volume leads to a stable and 
easily controlled operation with only minor variations of the operation 
parameters. 
According to a particularly preferred embodiment the partition walls or the 
base plates are mutually connected with special connecting means, separate 
from the housing, and the partition walls are designed to have essentially 
the same shape as the cross section of the housing and have sealings along 
the edges in contact with the housing. This means that the housing can be 
designed without special means for fixing and with a smooth inner side 
which facilitates renovation and repairs. The electrodes can be lifted out 
of the housing as a unit or be disassembled on the spot. Few parts of a 
simple design diminish the corrosion problems. If the housing, as well as 
other parts parallel to the electrode plates, are made from plastic 
material while the partition walls are made from titanium, a construction 
which is very resistant to corrosion and safe with respect both to 
internal and external short-circuits and current leakage is obtained. 
DETAILED DESCRIPTION OF THE INVENTION 
Known materials for chlorate cells can be used in the bipolar electrodes. 
It is, however, preferred that the base plate comprises a titanium plate 
which advantageously can be joined to another plate on the side which 
functions as a cathode. This other plate can be an iron plate and can be 
joined to the titanium plate by means of explosive joining or other 
methods for intimate joining. For base plates with several layers of this 
kind, the titanium plate is preferably shaped in such a manner that the 
partition walls can be connected and sealed thereto and this is most 
simply done by making the titanium plate extend somewhat beyond the iron 
plate around the circumference of the base plate. Electrode plates are 
fixed to the base plate at essentially right angles thereto and they are 
suitably fixed by means of welding and soldering. The height and the 
length of the electrode plates can very e.g. between 0.1 and 1 meter, but 
are preferably between 0.2 and 0.5 m. The material of the electrode plates 
can on the cathode side be iron and on the anode side be noble oxide or 
titanium covered with such. The electrode plates on the anode side and the 
cathode side respectively are suitably somewhat displaced with respect to 
each other in order that a straight cell row is obtained when several 
electrodes are assembled and the cathode electrode plates are positioned 
between the anode electrode plates. In normal cases there is one more 
anode plate than the number of cathode plates, so that the electrode 
package after assembly will be terminated by anode plates on both sides 
for the protection of the nearest cathode plates. Electrode plates of 
different polarities should not be in touch with each other so that 
electrical contact is established, but should be kept separated and 
preferably have a well defined and, between the different parts of 
electrode, constant distance from each other. The thickness of the 
electrode plates can be between 0.5 and 10 mm and is preferably between 
1.5 and 4 mm. The free gap between the assembled electrode plates is 
preferably also within these range limits, but does not have to be the 
same as the thickness of the electrode plates. Spacers can be arranged 
between the electrode plates but should not occupy more than a fraction of 
the space between the electrode plates in order that the vertical flow of 
the electrolyte should not be hindered. The number of cells connected in 
series is suitably between 3 and 15 for one row and preferably between 6 
and 12. A number of 8 cells has been found to give a manageable cell row 
unit. The terminal electrodes have of course, as has been mentioned above, 
only electrode plates on the sides turned inwards to the cell while 
current supply means advantageously can be arranged on the outer surface. 
The base plates, which suitably are un-perforated, form at least a part of 
the walls between the cells connected in series. After the electrodes have 
been assembled in the above discussed manner, an electrode package is thus 
formed from the electrode plates. The vertical sides of the package are 
made up from the outermost electrode plates and from the base plates and 
the horizontal sides are formed form the upper and lower edges of the 
electrode plates. The last mentioned edges do consequently not form 
impermeable surfaces but permit vertical flow of the electrolyte. An 
electrode row constructed in this manner is not self-supporting but for 
formation of a continuous unit and for maintaining dimensional accuracy 
between the electrodes special connecting means are necessary. 
A cell housing, containing the electrolyte, is arranged around the 
electrodes connected in series in the electrode package. This housing 
shall not enclose the electrode packages tightly, but shall leave 
sufficient space around the electrode packages so that a controlled 
circulation flow can be obtained. The plane of the circulation flow is 
parallel to the base plate of the electrodes. The housing is common to the 
entire row of cells connected in series. The electrode packages can then 
be placed at one of the long sides of the housing so that the upwards flow 
of the electrolyte takes place on this side and the downwards flow on the 
opposite long side, but it is preferred that the cell package is placed in 
a central position in the housing, in order that the flow upwards be 
central while the flow downwards takes place along both the long sides. In 
order to get the most satisfactory circulation flow, the area for flow 
upwards should approximately correspond to that for the flow downwards, 
which means that the total free distance from the cell package to the two 
long sides should be between 0.75 and 1.25 times the horizontal width of 
the cell package at right angles to the long sides, and the total distance 
is preferably between 0.8 and 1.15 times the width of the cell package. 
The downcoming electrolyte flow turns at the bottom of the housing and 
flows horizontally in towards and below the cell package through which it 
then anew percolates vertically. The distance between the lower edge of 
the cell package and the bottom of the housing should also, for this 
reason, be so great that it corresponds to the flow area for the downwards 
flowing electrolyte. For a central positioning of the cell package the 
distance to the bottom should thus be between 0.2 and 0.8 times the width 
of the cell package and preferably between 0.3 and 0.6 times this width. 
If the cell package is positioned at the side of the cell housing, the 
distance to the bottom should be between 0.3 and 1.0 and preferably 
between 0.4 and 0.8 times the horizontal width of the cell package. The 
housing should be designed in such a manner that there is a greater space 
for vertical electrolyte flow above the cell packages than the space below 
the cell package. The purpose of this space is to produce the driving 
force in the circulation flow by taking advantage of the hydrogen gas 
lift, and if a powerful circulation is to be achieved the space must not 
be given a too small height. Another purpose of this space is to give, 
together with other circulation spaces, a sufficient residence time for 
the electrolyte for a sufficient conversion of hypochlorite to chlorate 
before the electrolyte anew passes in between the electrodes. An important 
object of the cell construction of the invention is to give the 
electrolyte most of the required residence time for conversion, and 
preferably substantially the entire residence time, within the housing, in 
order to avoid additional external reaction vessels to the greatest 
extent. The volume of the housing must then not be too small but neither 
so big that it gives rise to constructional problems. A suitable 
electrolyte level above the electrode packages is thus between 5 and 15 
times the height of the electrode packages and preferably between 7 and 13 
times this height. It is advantageous, from several points of view, that 
the entire housing is filled with electrolyte so that no larger gas 
volumes are formed. This means that electrolyte containing finely 
dispersed hydrogen gas is led from the housing and to a gas separation 
step, apart from the volume of the housing. The outlet for the electrolyte 
can advantageously be arranged at the top of the housing. The height of 
the cell box in absolute dimensions will thus suitably be between 2 and 5 
m or preferably between 3 and 4 m. The housing should be divided into a 
bottom part and a cover part, which can be separated from each other, but 
which during operation are tightly connected with each other, e.g. by 
horizontal flanges following around the vessel. The dividing line is 
suitably somewhat above the cell package in the bottom part to give a good 
accessability to this when the cover is removed. 
The selection of material for the housing as well as for the electrodes is 
of great importance with respect to corrosion resistance and thereby to 
the possibilities of keeping high electrolyte temperatures which reduces 
the necessary reaction volume. The material of the housing is suitably a 
body with an interior corrosion resistant coating. The body can be of 
metal, but it is preferred that it is made from synthetic material as this 
reduces corrosion problems and risks of short-circuits and gives a lighter 
construction. Among synthetic materials glass fibre reinforced polyester, 
optionally containing embedded metal reinforcements is preferred. The 
inner side should be coated with a corrosion resistant material which can 
be metallic, e.g. made of titanium, but in that case electric insulation 
is required between each step. A synthetic material which has a good 
resistance to the electrolyte is thus to prefer. Suitable such materials 
are plastics containing fluor, such as polytetrafluoroethylene, 
polyfluoroethylenpropylene and polyvinylidene fluoride. It has 
particularly been found that such plastic coated on fabric works well and 
the fabric has then been made from fibres of synthetic materials, 
particularly glass fibres. The coating, as well as repairs, are 
facilitated and the durability is increased if the inner sides of the 
vessel, both its bottom and cover, are made essentially smooth without 
particular fixing means or other devices for partition walls, which is 
possible if the partition walls are arranged in the manner described 
below. 
The spaces which are arranged to make the circulation flow of the 
electrolyte around the electrode package possible, means that special 
partition walls must be arranged on a level with the base plates of the 
electrodes and extend from these, out towards the housing, beneath and at 
the side and up above the electrode packages. The partition walls are 
necessary in order to prevent a too large mixing of the electrolyte 
between the cells and to prevent current leakage. They are also necessary 
to maintain the controlled circulation flow so that a stable and 
substantially tubular flow is obtained. The requirement on effecient 
sealing is at its greatest near the electrodes, where even minor current 
leakages can cause important efficiency losses. The problems decrease with 
the distance from the electrodes owing to the increasing resistance in the 
electrolyte. Although it is possible to enlarge the base plate of the 
electrodes so that it will form a partition wall outside the part which is 
covered with electrode plates, this method is not suitable for economical 
reasons and from a practical point of view. The cell is thus, according to 
the invention, preferably equipped with separate partition walls which 
fill substantially all of the cross-section of the housing which is 
parallel to the base plate, at least at the bottom and the greater part of 
the height of the housing. It is not necessary that the partition walls 
reach right up to the top of the housing, but a free mixing space for the 
electrolyte immediately beneath the upper surface of the cover can be 
allowed without risks of current leakages. The partition wall is provided 
with a notch in its lower part to give a tight fitting of the base plate 
of the electrode. It is suitable to divide the partition wall in a lower 
part, having a design substantially corresponding to the cross-section of 
the lower part of the housing, and an upper part, having a design 
substantially corresponding to the cross-section of the cover of the 
housing. If the partition wall is divided in this manner the dividing line 
suitably goes through the notch for the base plate so that the electrode 
can be inserted or taken out when the upper part of the partition wall has 
been removed. The lower part of the partition wall should be of such 
dimensions that it can carry the load of the bipolar electrode inserted 
therein as well as the load of the upper part of the partition wall. It is 
then suitable to provide the lower edge of the partition wall with a 
footing or something similar to give a lenient finish towards the covering 
of the housing and it is preferred to provide also the side-edges of the 
partition wall with such finishes. In order that the base plate will be 
able to carry a load it must be possible to insert it in the notch of the 
partition wall in a stable manner. A suitable way to get a connection 
between these parts which is easily demounted is to provide the base plate 
or preferably the vertical sides of the partition wall in the notch with 
U-shaped finishes so that the base plate of the bipolar electrode can be 
inserted from above downwards to the bottom. The upper horizontal edge of 
the base plate, or preferably the corresponding edge or edges on the upper 
partition wall can in a similar manner be provided with a U-shaped finish 
so that the upper part of the partition wall can be placed on the lower 
part and on the base plate, fixing the upper wall in position with respect 
to these parts. The partition walls can be made from a material which is 
resistant to the electrolyte and non-conductive, e.g. from a plastic 
material. As the partition walls are parallel to the base plates and at 
right angles to the potential drop in the row of cell compartments 
connected in series they get an iso-potential position and can thus also 
be made from metal, which is preferred, at least for the lower partition 
wall. A preferred metal is titanium which has both good strength 
proprerties and good corrosion resistance. 
As there is no contact between the electrode plates of adjacent bipolar 
electrodes, other than through optional spacers between them, a 
self-supporting electrode row is not obtained from merely electrodes and 
partition walls but the distance between the different partition walls and 
electrodes must first be fixed by other means. Such means are suitably 
arranged between the partition walls instead of between the electrodes. 
One way of fixing the partition walls in a mutual relation and with a 
well-defined and stable distance and with good parallelism between the 
base plates and thereby between the electrode plates is to arrange rods 
along the cell row and to fix these to each partition wall. A plurality of 
such rods should then be arranged and fixed to each partition wall. The 
rods are fixed in such a manner that the relative distance between the 
partition walls is fixed, e.g. by means of spacers on the rods. The rods 
are suitably made from a non-metallic material such as from one of the 
above mentioned synthetic materials, e.g. polytetrafluoroethylene. It is 
most important, and often sufficient, that the lower part of the partition 
walls are provided with this kind of means for fixing as these parts, as 
has been said above, carry the greatest load and furthermore defines the 
electrode distances. With such means the electrodes and the partition 
walls form a continuous and separate unit which can be totally 
self-supporting. Such a unit can be placed in the housing without special 
fixing means in this and function there without additional sealing means. 
According to a preferred embodiment of the invention the space for the 
electrolyte flowing upwards is separated from that flowing downwards by 
arrangement of a flow-tube in the space above the electrode packages. The 
flow-tube is arranged vertically and has an opening at its lower part 
which collects all the electrolyte coming up from the electrode package, 
and brings it up to the desired height in the housing where it is allowed 
to turn and flow downwards. The tube can have many different shapes, it 
can e.g. have a flow-regulating neck at the middle or have special 
gas-separating means at the top. In order to obtain a good circulation 
flow it has, however, been found that it is sufficient that the rising 
flow is separated from the one going downwards by means of a smooth 
flow-controlling wall which is arranged vertically and at right angles to 
the partition walls and which extends between these above the outer edges 
of the electrode package, in such a way that the flow-controlling walls 
together with the partition walls form the tube for the rising liquid. As 
the flow-controlling walls thus extend between the partition walls they 
can also serve as spacers between these and fixing means for them. If the 
flow-controlling walls are provided with fixing means at their vertical 
edges and the partition walls are provided with corresponding fixing means 
vertically above the outer contour of the electrode package and these 
means are joined, a continuous structure is obtained from these walls and 
this structure does not require special fixing means in the cover of the 
housing for obtaining a stable fixing. 
Supply pipes for the electrolyte can be arranged in the form of 
longitudinal pipes in the cell and these pipes can be placed in notches in 
the partition walls. If these notches are at the dividing line between the 
lower and the upper part of the partition walls the pipes can be inserted 
and removed when the upper and lower parts of the partition walls have 
been separated. The pipes are connected to feed pipes outside of the cell 
via inlets in the housing. If the electrolyte between the cell spaces can 
be mixed within the housing, e.g. in a space at the top of the housing as 
described above, it might suffice to supply the electrolyte to some of the 
cell spaces only and a longitudinal pipe is then not necessary but simple 
inlets can be used. At least one opening should be provided in the upper 
part of the housing for conveying the electrolyte to a special 
hydrogen-gas separating step and to the chlorate separating step. 
A construction designed as described above can be dismounted in the 
following manner. The cover is loosened and removed. The unit comprising 
upper partition walls and flow-controlling walls is removed and can if so 
desired be further disassembled somewhere else. Optional supply pipes and 
outlet pipes are removed from their notches. The unit of electrodes and 
lower partition walls is lifted out of the lower part of the housing. The 
individual electrodes can be removed from the notches in the partition 
walls. The individual partition walls are separated by removal of the 
fixing means between them. The electrodes and the lower partition walls 
can alternatively be disassembled while they are still in the bottom part 
of the housing. The cell is assembled in inverted order. 
In order to get a satisfactory circulation flow in a cell of the above 
described type the current concentration should be 10 to 40, preferably 18 
to 35, amperes per liter circulating electrolyte in each potential drop. A 
preferred flow rate of 0.05 to 0.7 m/s in the electrode gap and a 
residence time for the electrolyte of 0.5 to 7 minutes between the 
passages through the electrode gaps can then be obtained. The temperature 
should be kept between 50.degree. and 90.degree. C. and preferably between 
60.degree. and 80.degree. C. in order that the conversion of hypochlorite 
to chlorate will be sufficiently rapid. At the exit from the electrode gap 
the hypochlorite concentration expressed as sodium hypochlorite should be 
between 0.5 and 5 grams/liter and preferably between 1.5 and 3.5 
grams/liter. The chlorate concentration is between 300 and 700 grams per 
liter, calculated as sodium chlorate, and the chloride concentration is 
between 50 and 300 grams per liter, calculated as sodium chloride. The pH 
of the electrolyte is roughly between 5 and 8 but is preferably between 
5.8 and 6.5 and most preferably about 6.1. From the electrolyte a part of 
the flow is in a known manner conveyed from the cell for separation of 
hydrogen gas and chlorate and recirculation to the cell.

DESCRIPTION OF THE DRAWINGS 
As is best shown in FIGS. 1 and 2 the cell housing, with general numeral 1, 
comprises a bottom part 2 and a cover part 3 which parts can be tightly 
joined along their respective flanges 4 and 5. The housing has inlets 6 
for supply pipes for the electrolyte and for current connections 7. The 
housing also has an outlet 8 for electrolyte and hydrogen gas. The housing 
is made from polyester having an inner corrosion resistant coating of 
polyvinylidene fluoride which is about 3 mm thick. Reinforcing profiles 9 
of polyester are arranged on the outer side of the housing, and these may 
optionally contain metal reinforcements. The housing has a height of 3.6 
m, a width of 0.9 m and a length of 3.4 m. The inner portion of the 
housing is divided into 8 cell compartments 10 by arrangement of 
partitions comprising bipolar electrodes 11, lower partition walls 12 and 
upper partition walls 13. The construction of the bipolar electrodes 11 is 
best shown in FIG. 5. The electrodes comprise a base plate 14 of an anode 
plate 15 made from titanium and intimately joined to a cathode plate 16 
made from iron. Anode electrode plates 17 of titanium covered with noble 
metal oxide are welded on to the anode plate and cathode electrode plates 
18 of iron are welded on to the cathode plate 16. The anode electrode 
plates 17 and the cathode electrode plates 18 are somewhat displaced with 
respect to each other. The total active surface of the electrode plates is 
about 10 m.sup.2 and the plates should stand a current of 25 kA. The cell 
potential is about 3 volts. Seven bipolar electrodes are arranged in the 
housing and their base plates 14 are parallel and their anode electrode 
plates and cathode electrode plates are placed between each other for 
formation of the cells connected in series. The cell rows are at each end 
terminated by a unipolar electrode 19 which has electrode plates only on 
the side facing the inner of the housing and which has means for external 
current supply feed on the other side. The bipolar electrodes 11 are 
carried by the lower partition walls 12 and the latter are best shown in 
FIG. 1 and 3. The lower partition wall 12 is made from a plate of 
titanium, about 3 mm thick, and is essentially U-shaped. The outer side 
edges and the bottom edge are provided with footings 20 welded thereto. 
The lower part of the vertical inner edges of the U-shaped partition wall 
12 is provided with U-profiles 21, welded thereon, and intended to grasp 
the vertical edges of the anode plate 15 when the bipolar electrode 11 is 
inserted, from above and downwards, into the central notch of the lower 
partition wall 12. The electrode 11 with then rest on the horizontal edge 
22 of the partition wall 12. The notches in the partition wall 12 are 
somewhat deeper than the height of the base plate of the electrode and a 
part of the notch will thus remain after the insertion of the electrode. 
Four holes 23 have been made in the partition wall 12 and rods 24 are 
brought through these and fixed to the partition walls for keeping the 
latter together at a desired distance and this is best evident from FIG. 
2. The construction of the upper partition wall 13 is shown in FIGS. 1 and 
4. The upper partition wall 13 can be made from thinner material than the 
lower one as it does not have a carrying function and in this embodiment 
it has a thickness of about 2 mm and is likewise made from titanium. Its 
upper edge is essentially straight and ends about 0.4 m from the top of 
the housing. Its lower edge has a shape corresponding to that of the lower 
partition wall, i.e. it has an extension 25 going down into that part of 
the notch in the partition wall 12 which is not occupied by the base 
plate. On the lower part of the extension 25 is welded a U-profile 26 
which is intended to grip the upper horizontal part of the anode plate 15. 
Other parts of the dividing line between the upper partition wall 13 and 
the lower partition wall 12 are filled with packings 27 of synthetic 
material and these have an H-profile and join the partition walls to each 
other. In the partition walls 13 are notches 28 wherein a longitudinal 
pipe 29 can be placed, which pipe can be connected to an outer pipe 30 via 
the inlet 6. Electrolyte can then be fed to each cell compartment via 
inlet pipes 31. The upper partition wall 13 has, as the lower one 12, 
welded footings 20 at its vertical edges in order to spare the inner 
covering of the housing. The partition wall 13 is also provided with 
vertically welded flanges 32 at which the flow-controlling walls 33 can be 
fixed. These flow-controlling walls 33 are made from 
polytetrafluoroethylene and goes from the outer vertical sides of the base 
plate 14 up to a height about 0.9 m below the upper edge of the partition 
walls 13. The outer flow-controlling walls 33 are provided with additional 
parts 34 of synthetic material for protecting the ends of the housing. 
Each cell space in the shown construction holds about 1 m.sup.3 of 
electrolyte. The whole housing is filled with electrolyte at operation and 
a potential is applied between the current connections 7. The hydrogen, 
which has lift, will then make the electrolyte circulate as previously 
described, i.e. up between the flow-controlling walls 33 and down between 
the long sides of the housing and the flow-controlling walls 33. At the 
highest flow point the electrolyte flow turns and a part of it is conveyed 
from the housing via the opening 8. The removed amount corresponds to a 
complete change of electrolyte each hour. The remaining electrolyte flows 
anew in between the electrode gaps in the cell package after having turned 
at the bottom of the housing. 
The invention is not limited to the shown embodiments but can vary within 
the scope of the appended claims.