Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD AND APPARATUS FOR THE ON-SITE GENERATION OF A
GAS
FIELD OF THE INVENTION
This invention relates to a method and an apparatus for the on-site generation
of a
gas, particularly, but not exclusively, chlorine gas.
BACKGROUND TO THE INVENTION
There are numerous advantages of having a facility for the on-site generation
of
chlorine gas. Chlorine gas is considered to be a hazardous substance and
strict
controls govern its storage and transport. In addition and because of its
hazardous
status, it is expensive to transport pressurised vessels containing liquid
chlorine.
This increases the costs of production facilities using the gas.
There is also a market, for on-site generators of relatively small volumes of
chlorine
gas, in facilities that use small quantities of chlorine gas. These facilities
include
water purification and sewage treatment plants and cooling towers where water
used
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in these towers is chlorinated. To avoid having to store large quantities of
liquid
chlorine or chlorine in a solid granulated or pelletized form, these
facilities could
make use of an on-site and on demand apparatus for generating chlorine.
Chlorine
gas and sodium hypochlorite are also used as a disinfectant.
In addition, relatively small chlorine gas generators can be used in rural
communities
to purity and render potable water drawn from small dams and rivers.
In addition to chlorine generation apparatuses there is also a market for
apparatuses
which generate other gasses on an on-demand and on-site basis. Such gasses
would include the halogen bromine which is used as an agricultural soil
sterilizing
agent and which is particularly effective in combating nematode infestations
of the
soil.
Apparatuses which generate chlorine gas by means of electrolysis are well
known.
These apparatuses generate chlorine gas from the anode of an electrolytic cell
through which a solution of sodium chloride is passed. At the cathode hydrogen
gas
and sodium hydroxide are produced.
Many of the above-mentioned apparata are suitable for and have been used for
the
on-site generation of chlorine gas. One example is disclosed in United States
Patent
No. 4,308,123. In this example an electrolytic cell having an anode and a
cathode
separated from one another by a chemically resistant ion exchange membrane
permeable only to positively charged ions is used. The anode chamber is
charged
with an acidic sodium chloride solution while the cathode chamber is charged
with a
basic aqueous solution. When an electric current is passed through the chamber
chlorine gas is produced at the anode and hydrogen and sodium hydroxide are
produced at the cathode. Chlorine and sodium hydroxide generated may be
combined to form sodium hypochlorite.
The above-described apparatus has a disadvantage in that anolyte and catholyte
feed tanks or reservoirs as well as anolyte and catholyte surge tanks are
necessary.
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These tanks represent a potential hazard particularly in a semi-industrial
environment
where strict safety controls may not be diligently enforced.
Furthermore, many known gas generators require pumps to circulate the
electrolyte
solutions. These pumps require a source of energy and, often sophisticated,
control
systems. In addition they also need regular maintenance which, in remote
areas, is a
disadvantage particularly given the potentially hazardous nature of the gases
produced.
OBJECT OF THE INVENTION
It is an object of the present invention to provide a method and an apparatus
for the
on-site generation of gasses, particularly chlorine which at least partly
alleviates the
above-mentioned disadvantages.
SUMMARY OF THE INVENTION
In accordance with an aspect of the invention there is provided a method for
the on-
site generation of a gas said method comprising the steps of:
a) forming a dissociatable electrolyte solution which, in use,
dissociates into positively charged and negatively charged ions at
least one of which is an ion of a gaseous element;
b) heating the electrolyte solution upstream of at least one eiectrolytic
cell and thereby causing it to circulate and re-circulate through
conduits and through the or each electrolytic cell by means of a
thermosyphon effect;
c) liberating, from the solution, at one electrode of the or each
electrolytic cell, a gas;
d) passing the liberated gas and electrolyte solution through at least
one gas separator to separate the gas from the electrolyte solution
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prior to re-circulating the electrolyte solution through the
electrolysis cell; and,
e) at no time storing the electrolyte in a reservoir.
In accordance with another aspect of the present invention, there is provided
a method
for the on-site generation of a gas comprising the steps of:
a) forming a dissociatable electrolyte solution which, in use,
dissociates into positively charged and negatively charged ions at
least one of which is an ion of a gaseous element;
b) heating the electrolyte solution near a lower ingress of at least one
electrolytic cell and thereby causing it to circulate and re-circulate
through conduits and through the or each electrolytic cell by means
of a thermosyphon effect;
c) liberating, from the solution, at one electrode of the or each
electrolytic cell, a gas;
d) passing the liberated gas and electrolyte solution through at least
one gas separator to separate the gas from the electrolyte solution
prior to re-circulating the electrolyte solution through the electrolysis
cell; and,
e) at no time storing the electrolyte solution in a reservoir.
There is further provided for facilitating circulation of the electrolyte
solution by
entraining gas bubbles produced in the or each electrolysis cell and
orientating
conduits leading from the or each electrolysis cell to the or each gas
separator
substantially vertically thereby providing a gas lift effect.
The invention also provides for the electrolyte in the solution to be
strengthened, if
necessary, and for any make up water to be saturated by passing it through an
electrolyte salt dissolving tube which is preferably mounted substantially
horizontally,
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and for electrolyte salt in the tube to be replaced with fresh salt,
preferably from a
hopper.
The invention provides further for the electrolyte solution to be a metal
halide,
preferably sodium chloride, alternatively potassium chloride, for the gas
generated at
the anolyte side of the electrolysis cell to be a halogen, preferably
chlorine, and for
hydrogen gas and sodium, alternatively potassium hydroxide to be generated at
the
catholyte side of the electrolysis cell.
There is further provided for the anolyte and catholyte sections of the or
each
electrolytic cell to be separated from one another by an ion selective
membrane,
preferably a perfluoropolymer membrane, which allows the passage of sodium,
alternatively potassium, ions therethrough but which is impermeable to a
halogen,
preferably chlorine, hydrogen gas and hydroxyl ions.
There is further provided for the addition of water, preferably distilled,
alternatively
demineralized, water to the sodium, alternatively potassium hydroxide solution
at
the catholyte side of the electrolyte cell to maintain the pre-determined
concentration of sodium, alternatively potassium, in the catholyte solution.
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There is also provided for the method to include the production of sodium
hypochlorite alternatively potassium hypochlorite by mixing chlorine and
sodium
hydroxide alternatively chlorine and potassium hydroxide, produced by the
method of the invention.
5 According to another aspect of the invention, there is provided an apparatus
for
the on-site generation of a gas comprising at least one electrolytic cell
having an
anolyte section and a catholyte section, at least one section being connected,
by
fluid conduits, to a fluid heater which, in use, heats an electrolyte solution
prior to
its ingress into said section and facilitates circulation of the electrolyte
solution
through the apparatus by means of a thermosyphon effect, the electrolytic
solution being dissociatable into positively charged and negatively charged
ions
at least one of which is an ion of a gaseous element, the heating element in
turn
being connectable by fluid conduits to an electrolyte replenishment means, at
least one gas separator which, in use, separates gas produced in the
electrolytic
cell from electrolyte solution, the apparatus lacking a reservoir for the
storage of
electrolyte solution.
According to a further aspect of the present invention, there is provided an
apparatus for the on-site generation of a gas comprising at least one
electrolytic
cell having an anolyte section and a catholyte section, at least one section
being
connected, by fluid conduits, to a fluid heater which, in use, heats an
electrolyte
solution near a lower ingress into said section and facilitates circulation of
the
electrolyte solution through the apparatus by means of a thermosyphon effect,
the electrolytic solution being dissociatable into positively charged and
negatively
charged ions at least one of which is an ion of a gaseous element, the heating
element in turn being connectable by fluid conduits to an electrolyte
replenishment means, at least one gas separator which, in use, separates gas
produced in the electrolytic cell from electrolyte solution, the apparatus
lacking a
reservoir for the storage of electrolyte solution.
There is further provided for the or each gas separator to be positioned
operatively above the or each electrolysis cell and for conduits linking them
to be
orientated operatively and substantially vertically thereby facilitating
circulation of
the electrolytic solution by means of a gas lift effect.
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There is also provided for the replenishment means to be a substantially
horizontally orientated electrolyte salt dissolving tube through which
electrolyte
solution from the or each gas separator flows prior to flowing through the
heating
element, for the salt dissolving tube to be connected to an electrolyte salt
replenishment hopper which contains a desired salt, and for the salt
dissolving
tube to be connected to a salt separator, preferably a strainer, which is
connected
to the heating element and which, in use, removes particulate salt from the
electrolyte prior to its introduction into the heating element.
The invention provides further for the electrolyte to be a metal halide
solution,
preferably sodium chloride, alternatively potassium chloride, for the gas
generated at
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the anolyte side of the electrolysis cell to be a halogen, preferably
chlorine, and for
hydrogen gas and sodium, alternatively potassium hydroxide to be generated at
the
catholyte side of the electrolysis cell.
There is further provided for the anolyte and catholyte sections of the or
each
electrolytic cell to be separated from one another by an ion selective
membrane,
preferably a perfluoropolymer membrane, which allows the passage of sodium,
alternatively potassium, ions therethrough but which is impermeable to
chlorine and
hydrogen gas.
There is further provided for the addition of water, preferably distilled,
alternatively
demineralized, water to the sodium, alternatively, potassium hydroxide
solution at the
catholyte side of the electrolyte cell to maintain the concentration of
sodium,
alternatively, potassium hydroxide in the catholyte solution.
There is also provided for the apparatus to produce sodium hypochlorite,
alternatively
potassium hypochlorite, by mixing chlorine and sodium hydroxide, alternatively
potassium hydroxide, produced by the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
One embodiment of the invention will be described below by way of example only
and with reference to the accompanying drawings in which:
Figure 1 is a schematic diagram of one embodiment of a method for the on-site
generation of chlorine gas according to the invention;
Figures 2A to C are, respectively, a schematic first side view, a schematic
second
side view and a schematic plan view of an apparatus for the on-site
generation of chlorine gas according to the method of Figure 1; and
Figures 3A to C are, respectively, a front elevation, a plan view and a
sectional part
side view of an array of electrolysis cells used in the apparatus of Figure
2.
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DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS
Referring to Figure 1, a method for the on-site generation of chlorine gas
comprises the
steps of:
a) forming a first dissociatable, sodium chloride or brine, electrolyte
solution (1) which is conveyed, through a conduit (2), to an
anolyte section (3) of an electrolytic cell (7), and a second
dissociatable, basic aqueous, solution (4) which is conveyed,
through a conduit (5) to a catholyte section (6) of an electrolytic
cell (7) which is divided into its sections by a perfluoropolymer
membrane (8) which, while allowing the passage of sodium ions
therethrough, is impermeable to chlorine gas, hydrogen gas and
hydroxyl ions;
b) heating the first dissociatable electrolyte solution (1) prior to
conveying it to the anolyte section (3) of the electrolytic cell (7)
thereby causing it to circulate and re-circulate through the
conduits and through the electrolytic cell (7) by means of a
thermosyphon effect;
c) liberating, from the electrolyte solutions chlorine gas, in the
anolyte section (3) and hydrogen gas, in the catholyte section (6);
d) entraining chlorine and hydrogen gas bubbles in the electrolyte
solutions thereby facilitating circulation of the electrolyte solutions
by means of gas lift, and collecting chlorine gas (9) and hydrogen
gas (10);
e) the method being characterised in that at no time is the electrolyte
solution stored in a reservoir.
In the above-described embodiment, the electrolysis cell (7) has an anode in
its anolyte
section (3) and a cathode in its catholyte section (6). The anode and cathode
are
connected to the positive and negative poles respectively of a direct current
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supply (11) which, in this embodiment, is a direct current power convertor.
The direct
current power convertor (11) receives alternating current (12) from a suitable
alternating current source.
As the salt in the first dissociatable electrolyte solution (1) becomes
depleted it is
refreshed by adding salt from a salt supply hopper (14) to the substantially
horizontally orientated electrolyte salt dissolving tube through which the
first
chlorinated electrolyte solution circulates before being strained, heated and
re-
circulated to the electrolysis cell (7).
As the solution on the anode side becomes volumetrically depleted, it is
compensated by the addition of pure fresh brine (200) into the system. This
pure
fresh brine is made up in item 201 where mains water is passed through a
separate
salt dissolving tube similar to that described in (1) above including a
separate salt
separator/strainer but the saturated solution so formed is then passed through
a
column containing a proprietary type resin which removes heavy metal anion
impurities prior to transferring the purified solution via a conduit (200) to
the anolyte
system (1). The second dissociatable electrolyte solution (4) is refreshed by
the
addition of water from the water supply (13) after it has passed though a
demineralizing unit (15).
In addition to chlorine and hydrogen gas, the method includes producing sodium
hypochlorite in a reactor ((16). Sodium hypochlorite is formed by combining
chlorine
and sodium hydroxide produced in the anolyte and catholyte sections (3 & 6) of
the
electrolysis cell (7) respectively. Once produced the sodium hypochlorite is
stored in
a storage facility (17). Sodium hydroxide produced in the catholyte section
(6) of the
electrolysis cell (7) can also be drawn off and stored in a storage facility
(18).
Referring to Figures 2 A, B and C, an apparatus (20) for the on-site
generation of
chlorine gas comprises at least one electrolysis cell (21) having an anolyte
section
and a catholyte section. At least one section which, in this embodiment, is
the
anolyte section, is connected by a conduit (22) to a fluid heater (23) which,
in use,
heats an electrolyte solution prior to its ingress into said section of the
electrolysis cell
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(21) and facilitates circulation of the electrolyte solution through the
apparatus by
means of a thermosyphon effect.
The electrolyte solution is dissociatable into positively and negatively
charged ions at
least one of which is an ion of a gaseous element. In this embodiment chlorine
gas is
generated and the electrolyte solution in the anolyte section of the apparatus
becomes an acidic sodium chloride solution when chlorine meets with water to
form
hypochlorous acid which dissociates into positively charged sodium and
hydrogen
ions and negatively charged chlorine and hydroxyl ions. The chlorine and
hydrogen
ions combine with like ions to form chlorine and hydrogen gas each of which is
circulated together with the electrolyte solution through gas separators (24 &
25)
which separate the chlorine gas and hydrogen gas respectively from the
electrolyte
solutions. In this embodiment the hydrogen gas is a waste product and is
vented to
atmosphere while the chlorine gas is used or processed further to produce
sodium
hypochlorite by combining chlorine with sodium hydroxide, both of which are
produced by the apparatus.
Each electrolysis cell (21) is divided into an anolyte section and a catholyte
section
by a perfluoropolymer membrane which allows sodium ions to pass therethrough
but
does not allow chlorine, hydrogen or hydroxyl ions to pass through it. This
membrane effectively divides the apparatus as well as the electrolysis cell
into an
anolyte section and a catholyte section.
As electrolyte passes through the anolyte section of the electrolysis cell
(21), chlorine
gas is formed at the anode and becomes entrained in the electrolyte solution
which is
depleted. The entrained gas bubbles facilitate circulation of the electrolyte
and
entrained gas bubbles to a chlorine gas separator (24) by means of a gas lift.
After
passing through the chlorine gas separator (24), the depleted electrolyte
flows
through a conduit (26) and enters a substantially horizontally orientated
electrolyte
salt dissolving tube (27) which is supplied with sodium chloride salt from a
salt
hopper (28) through a chute (29). In the salt dissolving tube (27) the
electrolyte
solution is refreshed. Salt crystals in the electrolyte solution are removed
by passing
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the refreshed electrolyte solution through a salt separator and strainer (30)
from
which it is returned to the fluid heater (23) for the process to be repeated.
As electrolyte passes through the catholyte section of the electrolysis cell
(21),
hydrogen gas is produced at the cathode. The bubbles of hydrogen gas, like the
chlorine gas, become entrained in the electrolyte solution and facilitate
circulation
thereof through a hydrogen gas separator (25). After removal of the hydrogen
and
sodium hydroxide, water which has passed through a demineralisation column
(31) is
added to refresh the catholyte electrolyte solution which passes through the
catholyte
section of the electrolysis cell (21).
The catholyte electrolytic solution is not heated directly as is the anolyte
electrolysis
solution. It is, however, heated in the electrolysis cell (21) as a result of
it being in
contact with the heated anolyte electrolyte solution. It is envisaged that
heating of
the anolyte electrolysis solution prior to its introduction into the
electrolysis cell
improves the efficiency of the gas generation process for the electrolyte is
at its
optimum temperature. Electric current for the anode, cathode and heater is
supplied
by a mains alternating current supply. In the case of the supply to the anode
and
cathode it passes through a direct current convertor (not shown).
Referring to Figures 3 A, B and C, details of a series of electrolysis cells
(40) for use
in the apparatus of Figure 2 are shown. In this embodiment there are two
electrolysis
cells (40) each separated by a perfluoropolymer membrane (41) which is
permeable
to sodium ions but impermeable to chlorine, hydrogen and hydroxyl ions.
Each cell (40) has an anode (42) at which chlorine gas is generated and a
cathode
(43) at which hydrogen gas is generated. The cells (40) are formed by bolting
together a series of plates, two of which are end plates (44) which have
anolyte
electrolyte solution inlets (45) and outlets (46) and catholyte electrolyte
solution inlets
(47) and outlets (48). The inner spacer plates (100) form the counter through
which
anolyte electrolysis solution flows in at a bottom corner of the plate and
consequently
the cell and egresses at the opposite top corner. In a similar fashion, the
catholyte
electrolysis solution ingresses the cell at the opposite bottom corner to the
anolyte
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electrolysis solution, and egresses at the opposite top. The anolyte and
catholyte
thus flow in a countercurrent which, in use, maximises efficiency. The
complete
assembly is bolted together using backing plates (101) and the bolts (102).
It will be appreciated that numerous variations can be made to the above
described
embodiment of the invention without departing from the scope thereof. In
particular,
the embodiments describe a method and an apparatus for the generation of
chlorine
gas and hydrogen gas. The same apparatus can be used for the generation of
bromine gas or, indeed, any gas which can be produced by an electrolytic
reaction.
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