Note: Descriptions are shown in the official language in which they were submitted.
CHLORATE CELL BOX STRUCTURE
The present invention relates to cell boxes useful
for the production of sodium chlorate.
This application is a division of copending Canadian
5 application Serial No. 321,399 filed February 13, 1979.
Sodium chlorate is a valuable industrial chemical
and is produced by the electrolysis of aqueous sodium chloride
solutions. Various cell constructions and configurations are
known for effecting the electrolysis.
In accordance with the present invention, there is
provided a cell box for the electrolysis of sodium chloride
solution to form sodium chlorate, comprising: a cathode
backing plate constructed of mild steel and constituting one
side wall of the cell box; an anode backing plate constructed
15 of titanium and located parallel to said cathode backing
plate, the anode backing plate constituting a second side
wall of the cell box; a plurality of parallel, thin cathode
electrode sheets constructed of mild steel and welded in
respective parallel grooves formed in the cathode backing
20 plate, the plurality of cathode sheets extending from the
cathode backing plate towards the anode backing plate; a
plurality of parallel, thin anode electrode sheets construc-
ted of titanium a~d having an electroconductive surface
thereon and welded in respective paxallel grooves formed in
25 the anode backing plate, the plurality of anode sheets
extending from the anode backing plate towards the cathode
backing plate in interleaved relationship with the cathode
sheets to define a plurality of electrolysis channels
therebetween; frame means constructed of mild steel and
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surrounding the outer periphery of the plurality of cathode
sheets to enclose the same within the box, the frame means
having portions welded to the cathode backing plate and
other portions connected to the anode backing plate in elec-
trically-insulating relationship therewith; inlet means con-
structed of mild steel and welded to yet other portions of
the frame means and to the cathode ~acking plate, the inlet
means being located at one end of and in uninterrupted flow
relationship with the plurality of electrolysis channels; and
outlet means constructed of mild steel and welded to addition-
al portions of the frame means and the cathode backing plate,
the inlet means being located at the other end of and in
uninterrupted flow relationship with the plurality o
electrolysis channels.
The invention is described further, by way of illus-
tration, with reference to the accompanying drawings, wherein:
Figure 1 is a schematic flow sheet of a multiple
cell unit sodium chlorate producing plant provided in accor-
dance with the parent application;
Figure 2 is an exploded perspective view of a
single chlorate cell box provided in accordance with one
embodiment of the invention;
Figure 3 is a close up perspective view of an
electrode plate spacer element used in the chlorate cell of
Figure 2 and the assembly thereof with an electrode plate;
Figure 4 is a sectional view of the chlorate cell
taken on line 4-4 of Figure 2;
Figure 5 is a sectional view taken on line 5-5 of
Figure 4;
Figure 6 is a sectional view taken on line 6-6 of
Figure 5; and
Figure 7 is an elevational view illustrating piping
connections from one cell unit to the reaction tank of the
plant of Eigure 1.
Referring first to Figure 1, there is illustra-
ted therein a multicell unit sodium chlorate plant 10.
The chlorate plant 10 consists of a plur~lity of
individual sodium chlorate-producing units 12 connected
in parallel flow relationship w-th each other. Two of
the chlorate-producing units 12 are illustrated-although
more usually are used, depending on the production
capacity desired, with each unit 12 conveniently being
sized to produce, for example, about 1200 tons per year
of sodium chlorate.
Each chlorate unit 12 includes a reactor tank
14 containing a body of liquor in which chlorate-forming
reactions occur from the products of the electrolysis.
A plurality of diaphragm-less electrolysis cells 16 is~
connected to the tank 14 in parallel liquor flow
relationship with respect to each other to permit liquor
for electrolysis to be forwarded from the tank 14 to each
cell 16 and electroly~ed liquor from each cell 16 to
recycle to the tank 14.
Each reactor tank 14 has an inlet pipe 18 for
feeding thereto brine solution for electrolysis and an
outlet pipe 20 for removal of sodium chlorate solution
therefrom. A vent 22 for gaseous products of the
electrolysis is provided for the reactor tank 14.
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The flow rate of brine solution to each
reactor tank 14 may be individually controlled by a
manual valve 23 in accordance with the desired reactor
tank liquor temperature. A sensor 25 may be provided
5 in the sodium chlorate solution outlet line 20 to
monitor the temperature of the solution, so that changes
in flow rate to the reactor t:ank 14 may be made
accordingly.
The sodium chlorate solution lines 20 combine
10 to form a single product solution in line 21 which is
fed to a single common mixing tank 24 for the plant.
Sodium chlorate solution is removed from the tank 24
as the product of the plant lO by line 26. Sodium
chloride solution make up is fed to the mixing tank 24
15 by line 28 and hydrochloric acid required to acidify the
solution to the requir~d pH for electrolysis, for
example, about 6.8, is fed to the mixing tank by line 30.
Any sodium dichromate catalyst for the electrolysis
reaction desired to be added may be included in the
20 sodium chloride solution in feed line 28.
A vent line 31 may be provided for the mixing
tank 24 for the removal of any residual entrained gases
entering the mixing tank with the sodium chlorate
solution in line 21.
The mixing tank 24 is separated internally into
two chambers by a baffle 32 which extends upwardly
therewithin to below the liquid level. The sod um
chlorate solution in line 21 discharges to one chamber
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below the liquid level therein and the product removal
line 26 communicates therewith while the sodium chloride
solution and hydrochloric acicL feed lines 28 and 30
discharge to the other chamber balow the liquid level
5 therein. In this way, contamination of the product
chlorate stream 26 by the added materials is avoided
while mixing of the added material with chlorate
solution overflowing the baffle 32 is permitted.
The sodium chlorate solution enriched with
10 added sodium chloride and acidified with hydrochloric
acid ~referred to herein as "brine solution"~, is
removed from the second chamber of the mixing tank 24
by line 34 and is passed through a heat exchanger 36
of any convenient construction. The brine solution
15 then is fed in parallel to the plurality of units 12
by the respective feed lines 18.
The heat`exchanger 36 cools the recirculating
li~uor in line 34 to the desired feed temperature, for
example, about 40C, while the heat generated in the
20 cells 16 is removed as sensible heat in the overflow
product lines 20. As indicated above, the temperature
of this liquor may be controlled to a desired value, for
example, in the range of about 60 to about 90C, by
suitable valved control of tha brine flow to the cell
25 units 12.
The cells 16 are electrically connected to each
other by flexible electrical connectors 38 which permits
relative movement of the cells 16, so that any desired
relative location may be achieved.
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Each cell 16 is provided with a valved drain
line 40 and an individual flow controL valve 42 which
allows individual ones or all the cells to be cut off
from liquid flow and to be drained for servicing.
The sodium chlorate plant 10, therefore,
utilizes a single brine make up, acidi~ication and heat
exchange for a multiple number of sodium chlorate-
producing units 1~ operating in parallel relationship
to each other, the number of such units 12 depending
on their individual capacity and the overall production
capacity of the plant 10. The mixing tank 24 and heat
exchanger 36 are sized to meet the overall capacity of
the plant 10.
The arrangement of cell units 12 and the
lS construction thereof as illustrated in Fisure 1 has
considerable benefits. Thus, each individual unit 12
produces a product stream of the desired chlorate
concentration as a result of the action of the plurality
o cells 16 acting in parallel. The product stream in
each line 20 does not require further elec~rolysis prior
to removal from the system. Each unit 12, therefore, is
self-contained and hence individual operating problems
may be isolated and remedied wi~hout interrupting
operation of the other units.
2~ By providing a single brine make up, acidifica-
tion and heat exchange for the sodium chlorate plant 10,
capital equipment costs associated with these items are
minimized and uniformity of operating conditions through-
out the plant 10 is achieved in simple manner.
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By providing a plurality of cells 16 in
parallel relationship with a single reaction tank 14 in
each unit 12, the effect of individual variations in
operating characteristics of the cells on product
quality is minimized and lesser equipment costs are
5 realized than is the case if each cell 16 has its own
reaction tank 14.
Flexible electrical connectors provided
between the individual cells 16 permit considerable
variation in the relative positioning of the cells 16
10 with respect to each other and avoids any difficulties
associated with connecting the cells in fixed relation-
ship in a bank.
The sodium chlorate producing plant 10 just des-
cri~ed and tAe sodium chlorate producing process effected
therein constitute the subject matter defined in the claims
of the parent application.
Turning now to Figures 2 to 6, there is illustrated
therein the details of construction of a chlorate cell or
cell box which represents the preferred construction for
the chlorate cells 16 of Figure l and constitutes the
subject matter of this invention. A chlorate cell 16
has a generally enclosed box-like structure shown in
exploded form in Figure 2 with a lower liquid inlet
manifold 50 and an upper liquid outlet manifold 52. The
inlet and out:let manifolds 50 and 52, which may be
cathodically protected, are integrally assembled by
welding with an upright rectangular cathode end plate
54~ The inlet and outlet manifolds 50 and 52 and the
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cathode end plate are constructed of mild steel. From
the end plate 54 project perpendicularly thereto in
generally vertical alignment a plurality o thin steel
cathode plates 56.
The inlet and outlet maniolds 50 and 52
close the top and bottom of l:he unit and the cathode
end plate 54 and the two outermost cathode plates 56
enclose three sides of the cell box. The fourth side
of the cell box is occupied by an anode end plate, as
10 described below.
The provision of mild steel inlet and outlet
manifolds enable ready assembly of these items with the
remainder of the cell box by welding, in place of bolts
or other fastening means, which otherwise would be
15 necessary if a corrosion-resistant polymeric material
wexe used as the material of construction.
Similarly the utilization of electrodes to
enclose sides of the cell simplifies construction of the
cell, in that it avoids the necessity to use bolting
20 and sealing gaskets.
The cathode end plate 54 is comprised of an
inner steel sheet 58 explosively bonded to an outer
copper or aluminum sheet 60. This two-part structure
facilitates electrical connections to the cell 16 and
25 minimizes voltage drop along inter-cell connectors~
The steel sheet 58 has a plurality of vertical
slot-like recesses 62 formed therein each receiving the
inner end of one of the thin cathode plates 56 in inter-
ference snug fit relation thereto and the cathode plates
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56 are welded therein.
The two outermost cathode plates 56 which
enclose the sides of the cell 16 are welded to peripheral
frame members 64 to which thle inlet and outlet mani~olds
50 and 52 also are welded. Outer protective and
strengthening plates 65 are welded to the frame members
64 externally of the outermost plates 56.
An upright rectangular anode end plate 66 is
provided parallel to the cathode end plate 54 enclosing
the fourth side of the cell 16. The anode end plate 66
has a plurality of vertically-aligned thin anode plates
68 projecting therefrom parallel to and lnterleaved with
the cathode plates 56. The anode end plate 66 is
comprised of an inner titanium sheet 70 explosively
bonded to an outer copper or aluminum sheet 72 to
facilitate electrical connection to the anode plate and
minimize voltage drop along inter-cell connectors. The
titànium sheet 70 has a plurality of vertical slot-like
recesses 74 formed therein each receiving the inner end
of one of the thin anode plates 68 in interference snug
fit relation thereto and the anode plates 68 are welded
therein. The thin anode plates 68 prefera~ly are con-
structed of titanium with an electrically-conducting
surface thereon, for example, a platinum group metal
or alloy thereto or other electrically-conducting
coating, such as, a platinum group metal oxide.
The thin anode plates 68 interleave with the
thin cathodl_ plates 56 in the assembled cell box to
define a plurality of parallel vertical flow channels
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75 therebetween to permit electrolyte to pass upwardly
through the cell 16 between the electrode plates from the
inlet manifold 50 to the out].et manifold 52. Spacer
elements 76 are provided to maintain the electrode plates
5 56 and 68 in desired spaced relation to each other.
As seen in Figures 2 to 6, the interleaved
electrodes occupy all the space between the side walls of
the cell box and separate the! space into the vertical
flow channels 75, so that the cell box has a very high
10 electrolyzing capacity.
The utilization of the vertical slots or
recesses in the anode and cathode end plates to receive
the electrode plates, the welding therein to assemble
the respective electrode plates with the respective
15 backing plates and the utilization of spacer elements 76
permits maximum cell box space utilization, since the
electrode plates may be made very thin, for example,
aboùt 1/16 to about 1/8 inch in thickness~
This arrangement contrasts markedly with
20 prior systems wherein anode plates are bolted to the end
plate which limits the number of anode plates which
can be mounted thereon and also increases the thicknes~
of the cathode plates, typically to about 1/2 inch, to
maintain the desired electrode gap, generally about 1/16
25 to about 1/8 inch.
An additional advantage of the welded anode
plate constr~ction is that the potentially high voltage
drop between the bolted anode plate and the backing
plate is eliminated.
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The thin cathode plates which may be utilized
in the cell 16 also permit much smaller and lighter
cells for the same capacity to be constructed and the
generally flexible nature of the cathodes permits ready
assembly of the anode plate bundle with the cathode plate
bundle, in contrast to the comparatively inflexible
cathode bundle when thicker cathode plates are used
in the bolted anode construction.
As may be seen from the detail drawing of
Figure 3, the spacer elements 76 utilized to maintain the
electrode plates in their desired relative prositions
comprise an integrally-formed one-piece member 78
constructed of non-conductive corrosion-resistant
material, such as, polytetrafluoroethylene, the member
78 has a short cylindrical portion 80 dimensioned to
just exceed the thickness of the electrode plate 56
or 68 and two bevel-edged head portions 82 of larger
diameter than the cylindrical portion 80 located one at
each end of the cylindrical portion 80.
The spacer elements 76 are mounted at the
edge of the electrode plate 56 or 68 remote from the end
plates 54 or 66 in any desired number to ensure proper
spacing, by providing an elongate slot 84 extending
inwardly from the electrode plate edge, preferably
perpendicularly thereto, with a vertical dimension
slightly larger than the diameter of the cylindrical
portion 80, sliding the spacer element 76 into the
slot 84, with the flat inner faces of the domed portions
8~ engaging the outer surfaces of the electrode plate,
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and closing off the slot 84 to prevent removal of the
spacer element 76 by turning downwardly and inwardly a
tang 86 formed between a short slot 88 located generally
parallel to slot 84.
A plurality of such spacer elements 76 is
provided for each elec~rode plate, with the number
depending on ths dimensions of the electrode plates.
Usually at least three spacer elements 76 are provided
one near the top of the electrode sheet, another near
the bottom and one approximately in the middle.
Spacer elements have previously been used in
electrolytic cells but have generally involved two
parts which are press-fitted or otherwise joined
together through openings formed in the cell plate.
These two-part spacers have generally been found to be
unsatisfactory in that they tend to come apart during
cell assembly and thereby become ineffective.
The use of the integrally-formed one piece
spacer elements 76 overcomes this prior art problem and
provides reliable long-lasting electrode spacing.
The spacer elements 76 constitute the invention of
copending Canadian patent application Serial No. 321,387
riled February 13, 1979.
An insulating and sealing gasket 9Q is
2S provided around the perimeter of the anode end plats
66 to electrically insulate the same from a~utting
cathodic frame members 64 in the assembled cell box.
The anode plate 66 is mounted to the frame mem~ers 54
by suitably insulated nuts and bolts 92 extending
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through aligned openings 94 in the respective abutting
elements.
The nut and bolt combination 92 utilizes.
sleeves 93 and washers 95 of sufficient strength to
withstand the jointing pressu:re necessary to ensure a
fluid tight seal around the gasket 90. Suitable mater-
ials of construction include melamine for the washers
95 and polypropylene for the sleeves 93.
Electrical lead connector plates 96 are
10~ welded to the outer surface of the cathode end plate
54 while similar electrical lead connector plates 98 are
welded to the outer surface of the anode end plate 66.
The connector plates 96 and 98 are connected to suitable
electrical power leads, not shown.
Cell box mounting plates lOQ extend horizon-
tally from the cell box side walls to permit the cell
box to be mounted in upright position in a suitable
frame.
Turning now to Figure 7, there are shown therein
the pipe connections connecting the cell lb to the tank
14. Pipe elements 102 constructed of corrosion resistant
but electrically-conducting material, s~ch as, titanium,
are provided in short sections which are electrically
insulated from each other by suitable insulating
assemblies 104 to minimize current leakage along those
pipes and co:rrosion of the pipes resulting from a
potential difference between the pipes and the liquor
flowing therethrough.
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The diameters of the inlet and outlet pipes 102
generally are much smaller than the pipes used in other
cell systems of the upwardly flow type so as to result in a
lower flow rate of llquor across the electrode surfaces.
Typical diameter values are about 4 inches for a 35,000-amp
cell as opposed to the prior art, about 8 to 10 inches, and
flow rates are about 10 cm/sec as opposed to the prior art,
about 40 cm/sec.
It has been found that this comparatively low liquor
flow rate has a negligible effect on oxygen evolution and
inefficiency and gas-lift is sized on flow considerations
rather than on retention volume. Th~ much smaller diameter
of the pipes results in a capital cost saving and a decreased
current leakage.
In summary of this disclosure, the present invention,
therefore, provides a unique cell box for use in the elec-
trolytic production of sodium chlorate. Modifications are
possible within the scope of the invention.
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