Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
11~39(~.9
The present invention relates to the production of
sodium chlorate, and, in particular, to chlorate cell con-
structions and multiple cell plants.
Sodium chlorate is a valuable industrial chemical and
5 is produced by the electrolysis of aqueous sodium chloride
solutions. Various cell constructions and configurations are
known for effecting the electrolysis.
The present invention provides sodium chlorate forming
procedures and cell constructions which are particularly advan-
10 tageous when compared with conventional operations.
In one aspect of the present invention, there is pro-
vided a method for the production of sodium chlorate, which
comprises: feeding sodium chloride solution to be electrolyzed
in parallel from a single feed source to a plurality of sodium
15 chlorate-producing zones; removing sodium chlorate solution in
parallel from the plurality of sodium chlorate-producing zone
to form a single sodium chlorate stream; each of the sodium
chlorate-producing zones comprising a single reaction zone to
which the sodium chloride solution to be electrolyzed is fed
20 and from which the sodium chlorate solution is removed, and a
plurality of diaphragmless electrolysis zones each connected
to the single reaction zone for flow of liquor rich in sodium
chloride for electrolysis from the reaction zone into the
respective electrolysis zone and for flow of electrolyzed liquor
25 lean in sodium chloride from the respective electrolysis zone
into the reaction zone; establishing the single feed source of
sodium chloride solution by adding fresh sodium chloride solu-
tion to part of the single sodium chlorate stream, adjusting
the pH of the resulting mixed solution to a value required for
30 electrolysis and subjecting the pH adjusted mixed solution to
i9~9
heat exchange to provide the single feed source with the
required temperature, and recovering the remainder of the
single sodium chlorate stream as the product of the method.
In another aspect of the present invention, there
is provided an electrolysis plant for the production of
sodium chlorate solution, comprising: a plurality of electro-
lysis units; each of the electrolysis units comprising a
reaction tank; first liquid inlet means for feeding sodium
chloride solution to be electrolyzed to the tank; first
liquid outlet means for removing sodium chlorate product solu-
tion from the tank; and a plurality of individual electrolysis
cells, each cell having a plurality of anode and cathode
electrodes located therein in interleaved manner to define
upwardly-directed parallel electrolysis channels therebetween
extending between a lower inlet communicating with the reac-
tion tank through second liquid outlet means therein and an
upper outlet communicating-with the reaction tank through
second liquid inlet means therein; the plurality of electroly-
sis cells being connected in electrical series with each other
by flexible electrical connectors but otherwise not being
:~ physically connected to one another; feed conduit means con-
nected in parallel to the first liquid inlet means of each of
the reaction tanks; product conduit means connected in parallel
to the first liquid outlet means of each of the reaction tanks;
and mixing tank means having first liquid inlet means connected
to the product conduit means, second liquid inlet means con-
nected to a source of fresh sodium chloride solutian, third
liquid inlet means connected to a source of hydrochloric acid,
first liquid outlet means for removal of product sodium
~9~t19
chlorate solution therefrom, and second liquid outlet means
connected to the feed conduit means through heat exchanger
means.
The invention also includes an electrolysis unit
for the plant which comprises an electrolysis unit for the
production of sodium chlorate by electrolysis of sodium
chloride solution, comprising: a reaction tank; first liquid
inlet means for feeding sodium chloride solution to be elec-
trolyzed to the tank; first liquid outlet means for removing
sodium chlorate product solution from the tank; and a plural-
ity of individual electrolysis cells, each cell having a
plurality of anode and cathode electrodes located therein in
interleaved manner to define upwardly-directed parallel elec-
trolysis channels therebetween extending between a lower inlet
: 15 communicating with the reaction tank through second liquid
outlet means therein and an upper outlet communicating with
the reaction tank through second liquid inlet means therein;
the plurality of electrolysis cells being connected in elec-
trical series with each other by flexible electrical connec-
tors but otherwise not being physically connected to one
another.
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;
Figure 2 is an exploded perspective view of a single
chlorate cell provided in accordance with one embodiment of
the invention;
Figure 3 is a close up perspective view of an elec-
19
3A
trode 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
10 conn~ctions from one cell unit to the reaction tank.
Referring first to Figure 1, there is illustrated
therein a multicell unit sodium chlorate plant 10. The chlor-
ate plant 10 consists of a plurality of individual sodium
` chlorate-producing units 12 connected in parallel flow relation-
; 15 ship with 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 con-
veniently 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
25 other to permit liquor for electrolysis to be forwarded from
the tank 14 to each
~9~19
cell 16 and electrolyzed 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.
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
in the sodium chlorate solution outlet line 20 to
monitor the temperature of the solution, so that changes
in flow rate to the reactor tank 14 may be made
accordingly.
The sodium chlorate solution lines 20 combine
- 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 10 by line 26. Sodium
chloride solution make up is fed to the mixing tank 24
by line 28 and hydrochloric acid required to acidify the
solution to the required 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 t~e
sodium chloride solution in feed line 28.
A vent line 31 may be provided for the mixing
~9~19
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 sodium
chlorate solution in line 21 discharges to one chamber
below the liquid level therein and the product removal
line 26 communicates therewith while the sodium chloride
solution and hydrochloric acid feed lines 28 and 30
discharge to the other chamber below the liquid level
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
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
then is fed in parallel to the plurality of units 12
by the respective feed lines 18.
The heat exchanger 36 cools the recirculating
liquor in line 34 to the desired feed temperature, for
example, about 40C, while the heat generated in the
cells 16 is removed as sensible heat in the overflow
product lines 20. As indicated above, the temperature
~9~19
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 the brine flow to the cell
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.
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, acidification and heat
lS exchange for a multiple number of sodium chlorate-
producing units 12 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
construction thereof as illustrated in Figure 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
of cells 16 acting in parallel. The product stream in
each line 20 does not require further electrolysis prior
19
to removal from the system. Each unit 12, therefore, is
self-contained and hence individual operating problems
may be isolated and remedied without interrupting
operation of the other units.
S 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.
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
realized than is the case if each cell 1~ ,.as~ Gwn
reaction tank 14.
Flexible electrical connectors provided
between the individual cells 16 permit considerable
'~ variation in the relative positioning of the cells 16
with respect to each other and avoids any difficulties
associated with connecting the cells in fixed relation-
ship in a bank.
Turning now to Figures 2 to 6, there is illus-
- trated therein the details of construction of a chlorate
cell which represents the preferred construction for
the chlorate cells 16 of Figure 1. A chlorate cell 16
has a generally enclosed box-like structure shown in
e~ploded form in Figure 2 with a lower liquid inlet
~9~9
manifold 50 and an upper liquid outlet manifold 52. The
inlet and outlet 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
cathode end plate are constructed of mild steel. From
the end plate 54 project perpendicularly thereto in
generally vertical alignment a plurality of thin steel
cathode plates 56.
The inlet and outlet manifolds 50 and 52
close the top and bottom of the 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
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
necessary if a corrosion-resistant polymeric material
were 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
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
.
,
-
9 ~ 19
facilitates electrical connections to the cell 16 andminimizes 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
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 the inlet and outlet manifolds
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 interleaved with
the cathode plates 56. The anode end plate 66 is
2Q 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. Thç
titanium 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 6nug
fit relation thereto and the anode plates 68 are welded
therein. The thin anode plates 68 preferably are con-
. ..
10 ~ 9~19
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 cathode plates 56 in the assembled cell box to
define a plurality of parallel vertical flow channels
75 therebetween to permit electrolyte to pass upwardly
through the cell 16 between the electrode plates from the
inlet manifold 50 to the outlet manifold 52. Spacer
elements 76 are provided to maintain the electrode plates
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
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
. ~ ,
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,
25 about 1/16 to about 1/8 inch in thickness.
This arrangement contrasts markedly with
prior systems wherein anode plates are bolted to the end
plate which limits the number of anode plates which
, ' , '
9~19
can be mounted thereon and also increases the thickness
of the cathode plates, typically to about 1/2 inch, to
maintain the desired electrode gap, generally about 1/16
to about 1/8 inch.
An additional advantage of the welded anode
plate construction is that the potentially high voltage
drop between the bolted anode plate and the backing
plate is eliminated.
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
'
~9~19
12
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
82 engaging the outer surfaces of the electrode plate,
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 electrode plate, with the number
depending on the 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
13 ~ 9
provides reliable long-lasting electrode spacing.
The spacer elements 76 constitute the invention of
copending Canadian patent application Serial No. 321,387 filed
February 13, 1979.
An insulating and sealing gasket 90 is provided
around the perimeter of the anode end plate 66 to electric-
ally insulate the same from abutting cathodic frame members
64 in the assembled cell box. The anode plate 66 is mounted
to the frame members 64 by suitably insulated nuts and bolts
92 extending 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 pressure necessary to ensure a fluid tight seal
around the gasket 90. Suitable materials of construction in-
clude melamine for the washers 95 and polypropylene for the
sleeves 93.
Electrical lead connector plates 96 are 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 100 extend horizontally
from the cell box side walls to permit the cell box to be
mounted in upright position in a suitable frame.
14
Turning now to Figure 7, there are shown therein
the pipe connections connecting the cell 16 to the tank 14.
Pipe elements 102 constructed of corrosion resistant but
electrically-conducting material, such as, titanium, are
5 provided in short sections which are electrically insulated
from each other by suitable insulating assemblies 104 to
minimize current leakage along those pipes and corrosion of
the pipes resulting from a potential difference between the
pipes and the liquor flowing therethrough.
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 liquor across the electrode surfaces. Typical
diameter values are about 4 inches for a 35,000-amp cell
as opposed to the prior art values of about 8 to lO inches,
and flow rates are about 10 cm/sec as opposed to the
prior art values of about 40 cm/sec.
It has been found that this comparatively
low liquor flow rate has a negligible effect on oxygen
evolution and efficiency and gas-lift depends on flow
considerations rather than on retention volume. The
much smaller diameter of the pipes results in a capital
cost saving and a decreaded current leakage.
The present invention, therefore, provides a sodium
25 chlorate producing system having certain benefits and a unique
cell unit for use therein. Modifications
"a~ 9
are possible within the scope of the invention.
~ .
