U.S. patent number 3,766,044 [Application Number 05/157,469] was granted by the patent office on 1973-10-16 for electrolytic cell system including upper and lower reacting chambers.
This patent grant is currently assigned to Chemeck Engineering Ltd.. Invention is credited to Gothe O. Westerlund.
United States Patent |
3,766,044 |
Westerlund |
October 16, 1973 |
ELECTROLYTIC CELL SYSTEM INCLUDING UPPER AND LOWER REACTING
CHAMBERS
Abstract
An electrolytic cell assembly and system is provided which
includes two or more modular units, each being provided for
throughflow of electrolyte and includes a plurality of parallel
alternately spaced anodes and cathodes, with the anodes and
cathodes occupying less than the entire cross-sectional area of
each unit. The end plates of each of the modular units are
respectively an anode end plate and a cathode end plate. The
electrodes project, preferably at right angles, from the end
plates, but in staggered spaced-apart relation, so that each anode
electrode (with the exception of the end ones) can be disposed
between a pair of adjacent cathode electrodes and vice versa. The
end plates are provided with either anode electrodes or cathode
electrodes projecting, preferably at right angles, from one face.
Between adjacent modular units are intermediate plates which, in
one variant, are imperforate and act as combined anode and cathode
holding and current transmitting plates. The intermediate plates
are provided both with anode electrodes projecting from one face
and cathode electrodes projecting from the other face. In another
variant, the intermediate plates are porous to permit the
throughflow of electrolyte and products of electrolysis from one
modular unit to the neighboring one. The system includes means
attached to each unit to bring cell products to a common upper
reacting chamber, means connecting the upper reacting chamber to a
common lower reacting chamber, and means connected between the
lower reacting chamber and the units for introducing contents of
the lower reacting chamber into each unit.
Inventors: |
Westerlund; Gothe O.
(Vancouver, British Columbia, CA) |
Assignee: |
Chemeck Engineering Ltd.
(Vancouver, British Columbia, CA)
|
Family
ID: |
4087093 |
Appl.
No.: |
05/157,469 |
Filed: |
June 28, 1971 |
Foreign Application Priority Data
Current U.S.
Class: |
204/236; 204/270;
204/268 |
Current CPC
Class: |
C25B
9/70 (20210101); C25B 9/19 (20210101) |
Current International
Class: |
C25B
9/06 (20060101); C25B 9/18 (20060101); B01k
003/00 () |
Field of
Search: |
;204/82,95,256,258,268,270,275 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Mack; John H.
Assistant Examiner: Solomon; W. I.
Claims
I claim:
1. An electrolysis assembly comprising in combination: A) a pair of
multi-unit cell systems, each comprised of at least two units
disposed horizontally in lateral end-to-end relationship, each such
unit comprising:
a. an open-ended main chamber including inlet means for the flow of
electrolyte to, and between adjacent, parallel, alternately spaced
anodes and cathodes and outlet means constructed and arranged to
withdraw electrolyte along with gaseous products of electrolysis
entrained and/or occluded therein from the chamber, said chamber
being electrically isolated from said anodes and cathodes;
b. an anode end plate disposed at, and sealing one open end of said
chamber, the anode end plate being provided with a plurality of
spaced-apart anodes projecting from one face thereof into said
chamber;
c. a cathode end plate disposed at, and sealing the other open end
of said chamber, the cathode end plate being provided with a
plurality of spaced-apart cathodes projecting from one face thereof
into said main chamber in staggered alternate relationship to the
anodes also projecting into said chamber;
said anodes and cathodes occupying less than the entire
cross-sectional area of the chamber thereby to provide at least one
non-electrolysis zone within said unit, thereby to enable internal
liquor circulation resulting from gases evolved on the electrode
surfaces to interchange electrolyte between the electrodes and to
provide substantially homogeneous conditions in the chamber; the
plate between two adjacent such units being a common intermediate
cathode-anode holding and current transmitting plate disposed at,
and sealing the adjacent open ends of said two adjacent such units,
and being provided with a plurality of spaced-apart cathodes
projecting from one face thereof into one such unit in staggered
alternate relationship to the anodes also projecting into said unit
from the other end thereof and a plurality of spaced-apart anodes
projecting from the other face thereof into the other such unit in
staggered alternate relationship to the cathodes also projecting
into said unit from the other end thereof;
B. a common upper reacting chamber having a liquor inlet connected
to said cell system, a brine inlet and a gas outlet;
C. a common lower reacting chamber having a liquor inlet, a liquor
outlet connected to said cell systems to feed said systems and a
finished product outlet; and
D. a common conduit interconnecting the upper reacting chamber and
the lower reacting chamber, said conduit being located between the
pair of cell systems and being provided with heat exchanger
means;
the circulation between cell systems, upper reacting chamber and
lower reacting chamber being by means of gas lift, each unit in the
cell systems including an effluent liquor riser pipe leading to a
portion of the upper reacting chamber and a liquor infeed riser
leading from a lower portion of the lower reacting chamber.
Description
BACKGROUND OF THE INVENTION
This invention relates to a modular electrolytic cell unit which is
assembled as a multi-unit electrolytic cell assembly to provide a
compact system for high production. It also relates to the complete
electrolysis system which may be provided therefrom.
Monopolar electrolytic cells provided with metal anodes and metal
cathodes for the production of alakali metal chlorates from alkali
metal chlorides are now extremely well known. However, plants
employing monopolar cells normally find it necessary to employ high
amperage, about 20,000 to 150,000 amps, and low voltage which
usually is expensive in capital cost for both power substation
cost, bus bar cost and power losses by the current transmission
losses. It is therefore manifest that it is desirable to provide an
electric cell and system in which the voltage and amperage are
optimized to provide high production for optimum capital cost.
SUMMARY OF THE INVENTION
a. Aims of the Invention
An object of one aspect of this invention is to provide a modular
electrolytic cell assembly provided with metal electrodes in which
the conventional bus bar connections between cell units may be
eliminated.
An object of another aspect of this invention is to provide such an
assembly which offers high production output by the use of multiple
such modular units.
An object of yet another aspect of this invention is the provision
of such modular units in the assembly which are electrically
connected in series so that the assembly will have a voltage equal
to a unit voltage times number of such modular units.
An object of yet another aspect of this invention is the provision
of such a system which makes it practical to employ a rectifier
power substation which is economically optimized by designing for a
desirable voltage: current ratio.
An object of yet another aspect of this invention is to provide
such modular units assembled in such a way as to minimize the floor
area compared to conventional units of such throughput.
An object of still another aspect of this invention is to provide
such modular units assembled in such a way as to minimize valving
and piping requirements and to simplify control.
An object of a still further aspect of this invention is to provide
such modular units assembled in such a way as to provide improved
circulation of liquid due to gas lift and density differential.
b. Brief Description of Aspects of the Invention
By the present invention, in its broad aspects, a modular
electrolytic cell unit is provided which includes two or more
modular units, each being a double open-ended, preferably
cylindrical, chamber. In one variant of the invention, each such
chamber is provided with circumferential inlet and outlet means for
throughflow of electrolyte in a direction of flow parallel to, and
between, adjacent, parallel alternately spaced anodes and cathodes.
One end plate of the modular unit is an anode end plate and the
opposite end plate is a cathode end plate. The anode end plate is
disposed at, and seals, one open end, the anode end plate being
provided with a plurality of spaced-apart anodes projecting from
one face thereof into the chamber. Similarly, the cathode end plate
is disposed at, and seals, the other open end, the cathode end
plate being provided with a plurality of spaced-apart cathodes
projecting from one face thereof into the chamber in staggered
alternate relationship to the anode electrodes which also project
into the same chamber. In this variant of the invention, if two or
more such modular units are provided in lateral, side-by-side
relationship, each two adjacent such units are provided with a
common intermediate cathode-anode holding and current transmitting
plate disposed at, and sealing, the adjacent open ends of two
adjacent such cells. Such common plate is provided with a plurality
of spaced-apart cathodes projecting from one face thereof into the
main chamber in staggered alternate relationship to the anodes also
projecting into the main chamber, and a plurality of spaced-apart
anodes projecting from the other face thereof into the main chamber
in staggered alternate relationship to the cathodes also projecting
into the main chamber.
In another variant of the invention, two or more such modular units
are provided in vertically stacked relationship. The lowermost of
the units is provided with inlet means, e.g. circumferential inlet
means for an introduction of electrolyte. The uppermost of the
units is provided with outlet means, e.g. radial outlet means for
the removal of electrolyte and both dissolved and gaseous products
of electrolysis. One end plate of the modular units is an anode end
plate and the other end plate is a cathode end plate. The anode end
plate is disposed at, and seals, one open end, the anode end plate
being provided with a plurality of spaced-apart anodes projecting
from one face thereof into the chamber. Similarly, the cathode end
plate is disposed at, and seals, the other open end, the cathode
end plate being provided with a plurality of spaced-apart cathodes
projecting from one face thereof into the chamber in staggered
alternate relationship to the anode electrodes which also project
into the same chamber. Each two adjacent such units are provided
with a common intermediate cathode-anode holding and current
transmitting plate disposed at, and sealing, the adjacent open ends
of two adjacent such cells. Such common plate is provided with a
plurality of spaced-apart cathodes projecting from one face thereof
into the main chamber in staggered alternate relationship to the
anodes also projecting into the main chamber, and a plurality of
spaced-apart anodes projecting from the other face thereof into the
main chamber in staggered alternate relationship to the cathodes
also projecting into the main chamber. The sealing provided is
between the cell units and the exterior of the cell units. The
adjacent cell units are interconnected by providing communicating
apertures in the common holding plates. The current leakage is
controlled by the cross-sectional area and length of the
apertures.
By another aspect of each of these variants of this invention, the
main open-ended chamber is cylindrical. Each open end is thus
provided with an angular flange and each end plate is secured to
the open end by means engaging the angular flange, the means being
clamped between a retaining ring and the end plate being secured to
the open end, a gasket being disposed between the open end and the
end plate. When more than two such units are used, each
intermediate plate is disposed between adjacent modular units and
simultaneously clamp the adjacent units together by spaced-apart
means engaging the annular flanges, the means being clamped between
a pair of spaced-apart retaining rings and the intermediate plate
being secured to the open ends of the adjacent modular units, a
gasket being disposed between each open end and the intermediate
plate.
The invention also provides in another of its variants, the
provision of any of the variants of electrolytic cell units
described above in combination with a common upper reacting
chamber, having liquor inlet means from the cells, a brine inlet
and gas outlet, and a lower reacting chamber having a liquor outlet
means to the cell, and finished product outlet. The cell assemblies
direct effluent to the upper reacting chamber by gas lift and
receive inlet from the lower reacting chamber. The two chambers are
interconnected by a common connecting conduit, preferably through a
heat exchanger. The reacting chambers are provided with sufficient
conduit piping to minimize current leakage.
Preferably, the combination includes a pair of such modular unit
systems, each cell in each system including: an effluent liquor
riser pipe leading to an upper portion of the upper reacting
chamber; a liquor infeed riser leading from a lower portion of the
lower reacting chamber; and including a common connecting conduit
situated between the pair of modular unit systems, the conduit
being provided with heat exchanger means.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an idealized side elevational view of a plurality of
modular units of an aspect of this invention, assembled to provide
a electrolytic cell assembly as a horizontal unit;
FIG. 2 is an idealized central vertical section of the electrolytic
cell assembly of FIG. 1;
FIG. 3 is a side elevational view, rotated through 90.degree. of
the anode and cathode plates of the embodiment shown in FIG. 2;
FIG. 4 is a section along the line IV--IV of FIG. 3;
FIG. 5 is an idealized central longitudinal vertical sectional view
of a plurality of modular units of another variant of this
invention, assembled to provide an electrolytic cell assembly as a
vertical tower;
FIG. 6 is an idealized side elevational view of a complete
electrolysis system embodying the electrolytic cell assembly of
FIG. 1; and
FIG. 7 is an idealized cross-sectional view along the line VII--VII
of the electrolysis system of FIG. 6.
DESCRIPTION OF PREFERRED EMBODIMENTS
a. Description of FIGS. 1 and 2
Turning now to FIGS. 1 and 2, it is seen that the multi-unit
electrolytic cell system 10 includes a plurality, in this case 4,
modular cell units 11. Structurally, each modular cell unit
includes a cylindrical tube 12, open at each end 13, 14 and
provided with aligned circumferential liquor inlet cylindrical
nozzle 15 and liquor effluent cylindrical nozzle 16. The
circumferential lip adjacent opening 13 is provided with an angular
and annular flange 17, while the circumferential lip adjacent
opening 14 is provided with an angular and annular flange 18. An
end plate 19, in this case a cathode end plate, is secured to the
tube 12 at open end 13 by means of annular retaining flange 20,
which has an angular surface mating angular surface of flange 17,
and retaining ring 21, all being held together with suitable
tension, and with liquor-tight and electrically non-conductive
gasket 22 disposed at the open end 13, by means of bolt and nut
combinations 23, passing through aligned apertures in retaining
ring 21 and cathode end plate 19 respectively. An anode end plate
is of the same structure as cathode end plate 19 and may be secured
at open end 13 in a similar manner.
A combined cathode-anode intermediate plate 24 is provided between
adjacent modular units 11, and the means holding the plate 24 to
the adjacent units 11 also holds adjacent units 11 together. Thus,
gasket 25 is placed at open end 14, an annular retaining flange 26
is placed in mating relation to flange 18, and retaining ring 27 is
placed against annular retaining flange 26. Gasket 22, annular
retaining flange 21, and retaining ring 23 are placed at open end
13 of the adjacent tube 12 of modular unit 11. Then the
sub-assembly is assembled by means of nut and bolt combinations 28
passing through aligned apertures in retaining rings 23, 27 and
intermediate plate 24.
The main body or tube 12 of the modular electrolytic cell 11 is
preferably formed of glass for several reasons, namely, that it is
(i) chemically resistant: (ii) transparent; and (iii) electrically
resistant. One alternative to using glass tube 12 is to use steel,
but in this case, the tube 12 should be electrically connected to
the cathodes for protection against corrosion. It is, of course,
absolutely essential that tube 12 be electrically isolated from the
anodes, e.g. by gaskets and spacers. Another alternative is to make
the tubes of titanium, which is chemically resistant to the liquor
and does not require cathodic protection. To avoid the need for
cathodic protection, the voltage potential is controlled to under 6
volts for current flow from the container. As shown, it is
preferred to have a multi-unit assembly 10 comprising many units,
e.g., one plant is designed for 12 units in one assembly.
b. Description of FIGS. 2, 3 and 4
Turning now to FIGS. 2, 3 and 4, it is seen that the intermediate
plate is provided with a plurality of anode plates 29 on one face
30 thereof and a plurality of cathode plates 31 on the opposite
face 32 thereof. Plate 24 may be a composite plate, e.g. one side
steel to provide face 32 for the cathode electrodes 31, the other
side titanium with noble metal of the platinum group or its oxides
coating to provide face 30 for the anode electrodes 29. Such
composite plates are commercially available, e.g. from Du Pont,
under the Trade Mark DETACLAD.
The electrodes may be welded to the holding plate or connected. As
clearly seen in FIG. 2, the anode and cathode electrodes 29, 31
respectively are offset to fit precisely in between each other when
assembled to an adjacent unit. The interelectrode space varies
between 2 and 10 mm. The end plates 19 are, of course, either an
anode or a cathode, but would have the same construction features
as the intermediate electrode assembly.
c. Description of FIG. 5
Another variant of the invention is shown schematically in FIG. 5.
The multi-unit electrolytic cell system 110 is a vertical tower of
plurality, in this case nine, cells or compartments 111. The number
of such compartments may, however, be as few as two, or as many as
50. Each shell of the cell or compartment 111 is a cylindrical tube
112 formed, for example, of plastics material, e.g. polyvinyl
chloride, polystyrene, etc. or glass.
Structurally, then, each modular cell unit or compartment 111
includes a cylindrical tube 112, open at each end 113, 114. The
circumferential lip adjacent opening 113 is provided with an
angular and annular flange 117, while the circumferential lip
adjacent opening 114 is provided with an angular and annular flange
118. An end plate 119, in this case a cathode end plate, is secured
to the tube 112 at open end 113 by means of annular retaining
flange 120, which has an angular surface mating angular surface of
flange 117, and retaining ring 121, all being held together with
suitable tension, and with liquor-tight and electrically
non-conductive gasket 122 disposed at the open end 113, by means of
bolt and nut combinations 123, passing through aligned apertures in
retaining ring 121 and cathode end plate 119 respectively. The
anode end plate 1191 is similar in structure to the cathode end
plate 191 and may be secured to open end 113 in a similar
fashion.
A combined cathode-anode intermediate plate 124 is provided between
adjacent modular units 111, and the means holding the plate 124 to
the adjacent units 111 also holds adjacent units 111 together.
Thus, gasket 125 is placed at open end 114, an annular retaining
flange 126 is placed in mating relation to flange 118, and
retaining ring 127 is placed against annular retaining flange 126.
Gasket 122, annular retaining flange 121, and retaining ring 123
are placed at open end 113 of the adjacent tube 112 of modular unit
111. Then the sub-assembly is assembled by means of nut and bolt
combinations 128 passing through aligned apertures in retaining
rings 123, 127 and intermediate plate 124.
As described hereinbefore with reference to FIGS. 1 - 4, the main
body or tube 112 of the modular electrolytic cell 111 is preferably
formed of glass for several reasons, namely, that it is (i)
chemically resistant; (ii) transparent; and (iii) electrically
resistant. One alternative to using glass tube 112 is to use steel,
but in this case, the tube 112 should be electrically connected to
the cathodes for protection against corrosion. It is, of course,
absolutely essential that tube 112 be electrically isolated from
the anodes, e.g. by gaskets and spacers. Another alternative is to
make the tubes of titanium, which is chemically resistant to the
liquor and does not require cathodic protection. To avoid the need
for cathodic protection, the voltage potential is controlled to
under 6 volts for current flow from the container. As shown, it is
preferred to have a multi-unit assembly 110 comprising many units,
e.g., one plant is designed for 12 units in one assembly.
The intermediate plate 124 is provided with a plurality of anode
plates 129 on one face thereof and a plurality of cathode plates
131 on the opposite face thereof. Plate 124 may be a composite
plate, e.g. one side steel to provide the face for the cathode
electrodes 131, the other side titanium with noble metal of the
platinum group or its oxides coating to provide the face for the
anode electrodes 129. Such composite plates are commercially
available, e.g. from Du Pont, under the Trade Mark DETACLAD.
The electrodes may be welded to the holding plate or connected. The
anode and cathode electrodes 129, 131 respectively are offset to
fit precisely in between each other when assembled to an adjacent
unit. The interelectrode space 134 varies between 2 and 10 mm. The
end plates 119 are, of course, either an anode or a cathode, but
would have the same construction features as the intermediate
electrode assembly.
It is seen that the lowermost unit of the plurality of stacked
units 111 includes a circumferential liquor inlet nozzle 115, and
the uppermost unit of plurality of stacked units 111 includes an
axial product outlet 116, carrying liquor and evolved gas which is
entrained and/or occluded within the liquor.
It is also seen that the holding plates 124 are provided with
perforations 130 thereby to channel the reactant liquor and the
products of the reaction from the bottommost unit to the uppermost
unit. The arrows 132 show the flow of the reactant liquor and the
product through the plate 124 or an insert in the plate 124.
It will be observed that there is a non-electrolytic space 133.
Assuming the electrodes 129, 130 do not seal tightly to the
container 112, i.e. communicate with side sections and that there
is a significant pressure drop for flow through the openings 130 in
the holding plate 124, there will be a significant internal
circulation between the side sections or non-electrolytic spaces
133 and the space 134 between electrodes.
It is seen that the assembly in FIG. 5 is basically the same as the
assembly of FIGS. 1 and 2 earlier described. However, it will be
noted that the flow through the assembly is longitudinally
therethrough. Preferably all of the liquor to the assembly is fed
to the lowest unit in the assembly through inlet nozzle 115 and
liquor and gas are channelled from one unit to the other,
preferably by openings 130 in the electrode holding plates 124 and
finally discharged to a reactor from the top unit through outlet
nozzle 116. The current leakage is controlled by cross-sectional
area of the openings 130 in the plate 124 and the thickness of
electrode holding plate 124. While not shown, the apertures 130 may
be provided with hollow cylindrical inserts for annealing the
effluent liquor and product gases. Then, the current leakage would
be governed by the cross-sectional area of the hollow cylindrical
inserts and the length of such inserts.
The main advantages of such vertical assembly compared to the
horizontal assembly include the following, namely: (1) the floor
area requirement is drastically reduced; (2) one inlet for the
liquor and one outlet for the product for each assembly is
possible, thus minimizing valving and piping requirements and
simplifying control; and (3) the assembly works essentially as a
column containing a product of significantly lower density then the
liquor feed; thus, the gas lift as well as the density differential
cooperate in improving the circulation of liquor through the
assembly.
It is also noted that the electrodes 129, 131 do not normally cover
the entire cross-sectional area of the cell container. Thus, the
design incorporates internal circulation. This is an especially
important feature of the design when the assembly is erected
vertically, since the internal liquor circulation resulting from
the gas evolution on the electrode surface provides for interchange
of electrolyte between the electrodes and standardizes conditions
in the cell chambers.
While not shown in detail, the vertical assembly design may be
designed to make the column size sufficiently large to provide
mainly by means of non-electrolytic spaces 133 in the compartment
the total desirable electrolyte volume and retention time for
chemical reactions to chlorate. In this case, no external
recirculation would be required. This is very desirable in some
aspects since it minimizes piping requirements and provides cascade
arrangement between compartments, or cells, under favourable
conditions. Thus, electrolyte (brine) enters at the lowest
compartment and finished product leaves at the top compartment, the
retention time being provided in each and every compartment. This
construction provides the conditions for conversion of hypochlorite
to chlorate in each compartment. Temperature control could be
maintained by, for example, installing a cooling coil in he
compartments or jacketing the columns. On the other hand, with the
variant of FIGS. 1 and 2, a separate cell assembly may be installed
indoors and the reactors outdoors.
The electrode assembly may be fitted inside a larbe tube (e.g. a
glass column) rather than dividing the column into sections. The
electrode holding plates would then be placed between sections.
While the assembly has been shown vertical, it may be inclined to
various degrees up to and including vertical installation, i.e.,
from 0 to 90.degree. relative to the horizontal.
d. Description of FIGS. 6 and 7
Turning now to FIGS. 6 and 7, it is seen that a pair of
multimonopolar electrolytic cell assembly and system 10 is disposed
between and interconnected to an upper reaction chamber 36 and a
lower reaction chamber 37 to provide an electrolysis system 35.
Each outlet nozzle 15 is connected to an effluent riser pipe 38,
each riser pipe extending upwardly within upper reaction chamber 36
to terminate near the top thereof at outlet 39. Entrained and/or
occluded gases formed during the electrolysis reaction are
permitted to separate from the liquor 40 and to pass upwardly into
a gas chamber 41 provided with a frangible cover 42 (for safety
reasons) and with a gas outlet nozzle 43 leading away from the
electrolysis system. Fresh brine is introduced through cylindrical
inlet nozzle 44 which extends downwardly into the upper reaction
chamber 36 to terminate in a submerged outlet 45.
Degassed liquor in which the reaction to chlorate has been at least
partially completed passes through a common connecting conduit 46
disposed between the pair of multi-unit cell systems 10 and passes
through an annular heat exchanger 47 having cooling water inlet 48
and water effluent 49. If desired, the heat exchanger may be
cooling coils disposed in the lower reaction chamber 37, or any
other suitable means. From the lower reacting chamber, an inlet
riser pipe 50, connected to each inlet nozzle 15 of cell 11
originates at an inlet 51 near the bottom of chamber 37 and brings
liquor 53 from lower reacting chamber 37 to cells 11. Finished
product chlorate is withdrawn from outlet nozzle 54 at the bottom
of chamber 37 and passes via outflow conduit 55 leading to chlorate
storage (not shown).
During the course of the electrolysis, gases produced are in the
liquor in the form of entrained or occluded bubbles. This reduces
the density of the liquor to such an extent that the effluent
liquor is pumped, by gas lift, up effluent riser pipes 38 and is
sucked upwardly through inlet riser pipes 50. The pipe risers 38
and 50 provide sufficient piping to minimize current leakage.
In the example where the cells 11 are used for chlorate
electrolysis, the electrolyte is brine and the electrolytic
products are: hypochlorite, chlorate and hydrogen gas, as well as
by-product oxygen and water vapor.
Since the electrolysis is of sodium chloride brine with no
diaphragm, the effluent, consisting of Cl.sub.2, Na.sup.+, H.sub.2,
OH.sup.-, ClOH, Cl.sup.-, H.sup.+, and OCl.sup.- and in the form
both of liquor and gaseous products, pass from effluent pipe risers
38 to upper reacting chamber 36. The level of the liquor 40 in
upper reacting chamber 36 is shown by level line 52 and is higher
than outlets 39 so that liquor and gaseous products are separated
from one another. The upper portion of the upper reacting chamber
36 consequently acts as a degasifier. Recycle liquor passes down
through upper reacting chamber 36 through common conduit 46 to
lower reacting chamber 37.
The liquor velocity through upper reacting chamber 36 is reduced to
such an extent that optimum separation of the entrained gases takes
place without short-circuiting through the tank, which would result
from too low a liquor velocity. The velocity, on the other hand,
must be sufficient to utilize the entire vessel but not too rapid
to inhibit the expulsion of any further entrained and/or occluded
product gases. The optimum velocity is a function of the apparent
density of the liquid, which, in turn, is dependent on the amount
of entrained gases and the bubble size. It has been found that a
liquor velocity of about 10 ft/min. can separate substantially 100
percent of the entrapped gases.
Upper reacting chamber 36 and lower reacting chamber 37 combined
are for the purpose of permitting the reaction
2ClOH + ClO.sup.- .fwdarw. ClO.sub.3.sup.- + 2Cl.sup.-
to take place. For any selected temperature, the retention time in
reacting chambers 36, 37 is a function of the concentration of ClOH
and ClO.sup.- present in the liquor which in turn is directly
related to the current density. Thus, it was found that to yield a
current efficiency of greater than 90 percent, with a constant
recirculation of liquor and a pH of approximately 6.5, the current
concentration should be less than 7 amps/ litre at 80.degree.C. or
less than 6 amps/litre at 60.degree.C. The current concentration
(in amps/litre) is the main determining factor in calculating the
reacting chamber volume. The retention time, on the other hand, is
dependent on the rate of the liquor circulation, as well as on the
volume of the reaction vessel.
The liquor entering the upper reacting chamber 36 may have
temperatures ranging from about 45.degree. to 100.degree.C.,
preferably between about 60 and 80.degree.C. FIGS. 6 and 7 show a
heat exchanger 47 which is provided for temperature control. The
reacting chamber parameters are such that there is a sufficiently
long retention time of liquor in reacting chambers 36, 37 to favour
the desirable reaction NaOCl + 2HClO .fwdarw. NaClO.sub.3 +
2HCl.
It is also important to minimize the concentration of the
hypochlorite for if it is too high, it will decompose and anode
electrode coating wear increases. In addition, the pH should be
maintained below 7.5 and preferably between about 5 and 7. At a pH
of 6.8, the optimum reaction of 2 moles of HClO to 1 mole of NaOCl
takes place if no dichromate is present.
Effluent from the lower reacting chamber 37 is conveyed to cells 11
through inlet pipe riser 50 to inlet nozzle 14. Gas is drawn off at
outlet 43 from gas chamber 41. Gases, consisting of H.sub.2,
H.sub.2 O (vapor), O.sub.2, CO.sub.2 and Cl.sub.2 may be vented as
waste through outlet 43 or may be utilized.
If it is desired to utilize the gases from outlet 43 by oxidizing
them, it is noted that the gases have the following ranges of
proportions:
Hydrogen, H.sub.2 86 - 94 % by volume
Water vapor, H.sub.2 O 3 - 10 "
Oxygen, O.sub.2 1 - 4 % by volume
Chlorine, Cl.sub.2 0.1 - 1 "
In combusting the gases the following reactions will take
place:
H.sub.2 + Cl.sub.2 .fwdarw. 2HCl (producing hydrogen chloride)
2H.sub.2 + O.sub.2 .fwdarw. 2H.sub.2 O (producing water vapor)
The hydrogen chloride may be recovered as hydrochloric acid by
scrubbing with water.
It is generally known that the oxygen content of the cell gas
decreases with a lower pH of the electrolyte simultaneously as the
chlorine losses increase. Using a combustion chamber for the
recovery of chlorine losses as hydrochloric acid, the cell may be
operated at a low pH and thus benefit by the resulting improved
current efficiency.
Thus, it should be pointed out that the cell apparatus may be used
employing forced circulation. The process system hereinabove
discussed utilizes the gaseous products as a means to create a lift
in the external pipe riser and thus does not require any means for
forced circulation.
In the above-described assembly containing the cells 11, gases
produced in the cell assemblies 11 rise in the pipe riser and thus
cause recirculation of liquor. Two reactors are preferred, but the
cell assemblies may also be used with a system employing one
reactor only. An external heat exchanger is desirable for easy
maintenance and to achieve a high U-value by the higher velocity
compared to a heat exchanger (or coil) which may be placed inside
the upper reacting chamber 36.
Current flow is from one end of the cell assembly through first
unit anode electrodes 19 via the cell electrolyte space to the
cathode electrodes of the intermediate holding plate 24 and then
into the second unit and so on until the current leaves at the
opposite end of the electrode assembly.
From the foregoing description, one skilled in the art can easily
ascertain the essential characteristics of this invention, and
without departing from the spirit and scope thereof, can make
various changes and modifications of the invention to adapt it to
various usages and conditions. Consequently, such changes and
modifications are properly, equitably and "intended" to be, within
the full range of equivalence of the following claims.
* * * * *