Note: Descriptions are shown in the official language in which they were submitted.
CA 02181249 2005-05-20
1
UNIT FOR TREATING WATER BY OZONATION, AND
CORRESPONDING OZONISED WATER PRODUCTION APPARATUS
This invention relates to treatments of water by ozonization and more
particularly
the development of a principle of a unit for the treatment of water by
ozonization
including an installation for the production of ozonized fluid.
The use of ozone, particularly in water treatment processes, as a bactericidal
and
virulicidal agent has been known for a long time. This compound is also used
in water
purification systems during combined ozonization-coagulation, ozonization-
flotation,
ozonization-adsorption treatment stages on filtering media (with the
possibility of
biological action on the filter) without forgetting more classic applications
such as the
removal of iron and manganese or the removal of colour, of tastes and odours
from
treated waters. Finally it is known that ozone has an oxidising action on a
certain number
of micro-pollutants (phenols, certain detergents,...) (see B. Langlais,
"Nouveau
d~veloppement de 1'ozonation en eau potable et technologie appropritse",
L'eau;
1' industrie, les nuisance, n° 109, April 1987, pp. 28 to 30).
So as to encourage contact of gaseous ozone with the treated effluent, it is
usual
to use mixers of various types. These mixers can comprise injection systems
such as
porous devices, pressure reducing diffusers, emulsifiers (still called filter
pumps or
hydro-injectors), by static mixers or by dynamic mixers (for example an
agitator or a
motor driven turbine).
These known mixers are generally situated upstream of contact tanks
(contactors)
designed in such a way that the oxidising gas is kept in contact with the flow
of liquid to
be treated for a predetermined period of time.
By way of an example, French patent FR 2662616 describes an installation
including, for example, in succession, a transfer device for adding an
oxidising gas such
as ozone to the liquid to be treated, a module for the forced dissolution of
ozone in the
liquid and a contactor module. The forced dissolution module described in this
document
comprises a tank including a first central chamber forming a shaft for the
exhaustion of
the gases, arid a second annular recirculation, chamber coaxial with the
exhaust shaft.
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The two chambers are separated by an internal wall and there is communication
between
them at their upper and lower parts so that recirculation of l:he treatment
medium is
permitted by cyclically passing from one to the other.
These different types of devices have a certain number of disadvantages. Hence
in
order to ensure a minimum contact necessary time for all of the liquid to be
treated, a high
mean passage time must be maintained in the reactors. 'This requires
structures which are
over-sized, costly and take up a lot of space. Furthermore, they generally do
not allow
good homogeneity in the distribution of oxidising gas in the treated medium.
The objective of this invention is to provide an installation that allows an
ozonized
treatment fluid to be supplied that enables optimisation of the contact of the
ozone with a
liquid to be treated such as water.
Another objective of the invention is to propose such an installation with
high
output.
Yet another objective of the invention is to provide: a water treatment unit
equipped with such an installation requiring a reduced volume and optimised
for civil
engmeermg.
Another objective of the invention is to provide such a unit allowing the
treatment
of the water to be maximised and homogenised, particularly with the purpose of
allowing
its disinfection and the flotation of the organic materials that it contains
with the help of
the ozonized fluid formed.
Yet another objective of the invention is to provide such a unit with a
minimised
passage time in the reactors for the liquid to be treated whilst keeping to
the minimum
contact times.
A particular objective of the invention is to allow the release into the
treated water
of micro-bubbles of ozone having a size between about 20 microns arid 200
microns
thanks to the introduction, into the treated medium of a fluid being in the
form of
ozonized white water.
It should be remembered that the term "white water" is used in the technology
to
designate a mixture of water and nascent air obtained by the depressurising of
a
pressurised fluid made up of a mixture of air and water in equilibrium with a
determined
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pressure. The white colour of the water thus obtained refers to the colour
that the mixture
takes at the moment the air is depressurised.
It has already been suggested in the state of the technology to use white
water for
the back blowing of membranes used in the context of micro-filtration or ultra-
filtration of
water. Hence, French patent application No. 9109803 describes a back blowing
method
that includes a step consisting of causing a mixture of water and air under
pressure to
pass through the membrane as a flow contrary to the direction of filtration
placing the
supply chamber under a sudden negative pressure with respect to the permeate
recovery
chamber. The pressure reduction, particularly inside the pores of the membrane
enables it
to be back blown.
Hence the invention has an objective of allowing the production of an ozonized
white water formed during the reduction of pressure of a mi~aure of ozone and
air at
equilibrium with a predetermined pressure. It should be noted that when such a
mixture
has not been used, ozone involves handling conditions which are significantly
more
restricting than when air is used.
A particular objective of the invention is to suggest an iinteresting
application of
such a fluid consisting of using it in the context of the treatment of a water
to be purified
in order to allow the flotation of organic materials that are contained in it.
These different objectives as well as others that will appear in the
following, are
achieved thanks to the invention which relates to a unit for the treatment of
water by
ozonization characterised in that it includes on the one hand at least one
installation for the
production of ozonized white water and, on the other hand at least one
contactor in such a
way that the mixture of water to be treated and the white water is made in
said contactor,
said installation and said contactor being constituted by separate: reactors
connected via a
duct and in that said installation for the production of ozonized white water
includes
means for dissolution under pressure of ozone in a carriers liquid, said means
of
dissolution being made up of a pressurisation vessel having an inlet for said
carrier
liquid, an inlet for ozone, an outlet under pressure of the fluid product and
means of
ensuring the regulation of the pressure inside said vessel and the continuous
leakage of
the gasses that did not dissolve in said carrier liquid, the contactor
comprising pressure
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reduction means for ozonized white water provided by the pressurised output of
said
production installation of ozonized white water, said pressure reduction means
being
provided upstream said contactor. It should be noted that in certain
embodiments, the
ozone inlet and the carrier liquid inlet to the pressurisation vessel can be
merged,
particularly when the pressurisation vessel includes a static mixer.
This pressurisation vessel will advantageously be selected from the group made
up of the ejector columns, the ejector columns and static mixer., the bubble
columns, the
bubble columns using the air lift phenomenon and the mechanically agitated
bubble
columns.
Such an installation allows an ozonized fluid to be supplied which, when its
pressure is reduced, can give bubbles of ozone gas with an extremely small
diameter
which allows a very large contact surface between the ozone and the treated
fluid. The
increase in interface between the ozone and the fluid, compared) with classic
ozonization
techniques, allows the effectiveness of this compound to be increased in a
significant
fashion and allows a notable reduction in the contact time necessary for its
use. In
practice, such an installation can supply an ozonized white water whose graded
micro-
bubbles have a size particularly between 20 and 200 micrometres.
Preferably, said means allowing regulation of the pressure in said vessel
includes
a discharger. Such a device allows a particular pressure to be maintained in
the
pressurisation vessel by the use of a continuous leakage of the gasses which
have not
dissolved in the carrier liquid. The maintenance of this pressure thereby
allows the
optimisation of the dissolution of ozone in this liquid up to its saturation
while avoiding
the accumulation of undissolved ozone inside the pressurisation vessel. It
should
however be noted that elements other than a discharger can also be used as
pressure
regulation means, for example a pressure reducer or a motorised valve
controlled by a
pressure measurement.
Equally preferably, said pressurisation vessel has a carrier liquid diffuser
in its
upper part and a gaseous ozone diffuser in its lower part, said carrier liquid
and ozone
passing through said pressurisation vessel in counter current and the fluid
product outlet
being provided in the lower part of said pressurisation vessel. T'he carrier
liquid diffuser
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can particularly comprise a sprinkler unit while the gaseous ozone diffuser
can comprise a
porous device or a diffusion device that ensures homogeneous distribution of
the gas
over the cross section of the vessel.
Advantageously, said pressurisation vessel includes a packing material that
5 encourages the transfer of the gaseous ozone into said carrier liquid. Such
a packing
material can particularly be in the form of rings in bulk such as Pall type
rings. Such
rings have openings which reduce the resistance to gaseous Flow and permit a
much
reduced pressure drop for the liquid passing through the pressurisation
vessel. The
material transfer is improved by better access to the inside of the rings.
Equally advantageously, the installation includes means of regulating the
height of
liquid in said pressurisation vessel.
According to an interesting variant of the invention, said regulation means
include
a control valve provided upstream of said carrier liquid inlet, a level
detector provided in
the lower part of said pressurisation vessel and means for transmitting
measurements
taken by said detector to said control valve. Such transmission means may
comprise a
transmitter.
Preferably, the installation includes, in addition, an ozone generator and
means of
compression and aspiration of the ozone formed in said ozone generator. Such
an ozone
generator can comprise any device which allows the production of ozone from
oxygen in
a carrier gas (gas or other mixture).
Equally preferably, said means of compressing ozone are connected to a flow
tank provided upstream of said compression means, said flow tank allowing the
fluctuations in flow and sudden concentration changes at the ozone generator
outlet to be
smoothed out.
Advantageously, the installation also includes a blow off loop provided
between
said compression means and said flow tank, said loop allowing the removal of
load
downstream of said compression means and the variation of flow within a
desired range.
Such a loop also allows one to avoid start up of the compressor under load.
Preferably, said pressurisation vessel is fitted with means for the
recirculation of a
part of the carrier liquid from the outlet under pressure to the inlet of said
vessel.
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Equally advantageously, said means of pressure reduction are chosen from the
group comprising cavitators and spray nozzles.
According to an interesting variant of the invention, said compression means
are
chosen from the group comprising membrane compressors, dry compressors and
liquid
ring pumps.
Equally according to a variant of the invention, the installation also
includes
means of measuring the dissolved ozone in the fluid under pressure which
leaves said
pressurisation vessel.
The installation comprises advantageously, in addition, means of cooling the
gases before their introduction into the vessel. In a preferred wary, these
means of cooling
the gasses before their introduction into the vessel are made up of an
exchanger supplied
with a heat transfer fluid coming from another exchanger which recovers the
cold
released by the gasificatian of liquid oxygen.
Preferably, said contactor belongs to the group that includes separation
reactors
(particularly and including those with membranes), back blowing reactors
(particularly
filtration membranes), and in particular flotation and/or ozoflotation
reactors. In the case
of a flotation reactor, this can operate at atmospheric pressure and be, for
example fitted
with laminae or bubble traps. It should be noted however that: the contactor
used may
equally well operate under pressure. The pressure prevailing in this unit
must, however
be less than the pressure of the fluid leaving the pressurisation vessel so as
to allow the
formation of the ozonized white water.
Advantageously, said contactor is fitted with a pipeline allowing the
pressurisation vessel to be supplied with the water coming out of said reactor
acting as
carrier liquid. It is thereby possible to use a part of the treated water as
the liquid supplied
to the pressurisation vessel. Preferably, filtration means (not shown) are
provided in said
pipeline.
The treatment unit advantageously includes means of destroying or recycling
residual gaseous ozone coming from said contactor and/or said vessel for the
production
of ozonized white water.
It is of course also possibleto carry out the advanced oxidation methods by
adding
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an additive, particularly hydrogen peroxide H202, a catalyst,, and/or carrying
out the
treatment under UV radiation.
The invention as well as the different advantages that it has, wily be more
easily
understood with the help of the description that will follow of a non-
linutative example of
. implementation of it with reference to the drawing, in which
- Figure 1 shows a unit for the production of white water;
- Figure 2 shows a water treatment installation including the unit for the
production of white water according to Figure 1 ;
- Figures 3A to 3D show different types of pressurisation vessels that may be
used for the invention ;
- Figure 4 shows another embodiment of a water treatment installation
including a
unit for producing white water with an eaector column and static mixer.
With reference to Figure 1, an installation for the production of white water
according to the invention is essentially made up of a pressurisation vessel 1
that permits
the supply of a fluid under pressure and a means 6 of reducing the pressure of
this fluid
under pressure allowing the formation of ozonized white water.
The solution of carrying out the transfer, in a reactor under pressure, from a
compressed ozonized gas, has been chosen rather than an aspiration of ozonized
gas by a
Venturi type emulsifier which does not allow one to work with gas/liquid
ratios that are
sufficiently high and have acceptable load losses.
Vessel 1 forms an absorption column and, so as to obtain maximum dissolution
of the ozone in the water with the help of this gas-liquid contactor with a
minimum of
loss, a packed column has been chosen that operates under dewatering
conditions. The
water and the gas circulate in counter current and the ozone impoverished gas
is
continuously evacuated from the head of the saturation vessel.
The pressurisation vessel is fitted with an inlet 2 for the liquid destined to
be
saturated with ozone. Such a liquid is advantageously water. The vessel 1 has,
in
addition, in its lower part, a gaseous ozone inlet 3 and an outlet 4 for the
fluid saturated
with ozone under pressure. So as to allow a good distribution of carrier
liquid inside the
vessel l, a distribution device 8 having the form of a sprinkler unit is
installed at the inlet
21 ~~ 1249
2. Furthermore, the homogeneous distribution of the ozone over the whole cross
section
of the vessel is ensured thanks to a porous sintered device 9.
fldvantageously, one can provide for the gases to he cooled prior to their
introduction into the vessel 1. Lowering the temperature of the gases (without
of course
S going lower than the freezing point) allows the size of the bubtdes to be
reduced and the
solubility of the ozone to be raised which improves the transfer efficiency.
The cooling
means can comprise a pressure reducer or an exchanger 101 supplied with a heat
transfer
fluid. In a way that rationalises the energy required to operate the process,
it can be
advantageous to cool the heat transfer fluid by making use of the cold
situated in another
point of the treatment unit. Hence the ozone production chain generally has
means for
repeating oxygen coming out of bottles 10~ (before the storage of the oxygen
in the
vessel 3'/ upstream of the ozone generator 30 - see Figure 2 ) which can be
coupled to an
exchanger 103 used to cool the heat transfer fluid already mentioned.
In a way that encourages and optimises the transfer of gaseous ozone into the
carrier liquid, a part of the interior of the vessel is filled with a packing
material, in bulk,
which, in the context of this embodiment comprises Pall type rungs. It should
be noted in
this regard that other types of bulk packing material could be used and
particularly
Raschig rings or partitioned rings. This packing material is contained at the
top by an
open-work plate 15 encouraging good distribution of the carrier liquid over
the whole
cross section of the vessel and, at the bottom by a support 16 which is also
open-work.
The inside of the pressurisation vessel is hence essentially divided into
three zones ~ an
upper zone in which distribution of the carrier liquid occurs, a middle zone
containing the
packing material and a lower zone in which the distribution of gaseous ozone
occurs and
the ozone saturated fluid is evacuated. The transfer of the ozone: into the
carrier liquid is
thereby carried out in counter current.
It should be noted that the vessel can also be adapted so that the
ozone/liquid
transfer occurs in co-current.
So that a constant pressure is maintained inside the pressurisation vessel, it
is
equipped with a discharges 5 that arranges a continuous leaking; of excess gas
which has
not dissolved in the carrier liquid. Vented gas recovered during operation of
the
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9
discharges S is destroyed thanks to a thermal destructor 35.
The pressurisation vessel 1 is also fitted with a safety valve 17 and a
manometer
18. It should finally be noted that the vessel also has a purge ll9 in its
upper part at the
ozone inlet and a drainage device 20.
With the aim of keeping a constant level of liquid in the vessel 1, the
installation is
provided with regulation means 11. These regulation means are essentially made
up of a
control valve 12 provided on the carrier liquid inlet pipe 2 to the
pressurisation vessel and
means 13 for measuring the level of liquid inside this vessel. These
measurement means
13 include a capacitive sensor able to determine the height of liquid in the
vessel. The
measurements taken by this sensor are transmitted via transmission means 14 to
calculation means 21. These calculation means 21 are able to adjust the
opening of the
control valve 13 necessary to achieve the desired equilibrium.
While the installation is being used, it is therefore possible to regulate the
pressure
prevailing inside the pressurisation vessel by taking action, on the one hand
on the
undissolved gases and on the other hand on the quantity of carrier liquid
entering the
vessel. It has been possible to observe that the transfer efficiency increases
with pressure
( with a constant ratio of flow rates Qgas/Qliquid) because of the increase in
solubility of
ozone with pressure.
By way of example, one may provide for the establishment in the vessel of a
pressure of from 2 to 10 bars. The flow rate ratio Qgas/Qliquid can be between
50 and
200% for purposes of information. The tests carried out on a prototype have
shown that a
plateau of dissolved ozone is reached for a ratio between 100 and 150%. The
transfer
efficiency appears to decrease approximately linearly with an increase of the
Qgas/Qliquid
ratio. Fox a constant concentration of ozone, it has been noted that the
better efficiencies
are obtained working at moderate pressure (4 bars) and low gas flow rather
than at higher
pressure (6 bars) and high gas flow.
Figure 2 shows diagrarnatically a unit for the treatment of water according to
the
invention according to a first embodiment with two stages. The: unit includes
mainly an
installation fox producing white water such as that described above with
reference to
Figure 1 and a flotation reactor 50.
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Such a treatment unit allows flotation to be carried out on water arriving at
the
flotation reactor 50 thanks to the white water supplied by the installation
provided for this
purpose. To this purpose, the unit includes means for reducing pressure 6
installed at the
end of the pipeline 7 in the lower part of the flotation unit 50.
S The pipeline 7 is not shown in its entire length but can have a length of
several
metres if needed. Such an arrangement allows the formation of ozonized white
water at a
point remote from the treatment installation, in the case of a distant reactor
50.
The means of reducing pressure 6 comprise in the present example, a cavitator
allowing the conversion of the liquid under pressure leaving the vessel into
ozonized
10 white water. Tests carried out have allowed it to be established that the
creation of
bubbles of small diameter, typically less than 300 micrometres must take place
through
desorption from a medium supersaturated with gas. The micro-bubbles can then
have a
diameter between about 20 and 200 micrometres for a pressure :inside the
vessel of 3 to 6
bars and a pressure roughly equal to atmospheric pressure and the outlet of
the cavitator.
1~ The supply of water to be treated by this flotation unit 50 is ensured by
the
pipeline 54.
The ozone production installation used in the context of the unit shown in
Figure
2 includes, as well as the saturation vessel, an ozone generator 30 which
permits the
production of ozone from oxygen coming from an oxygen. supply 37. The ozone
generator used in the context of this example allows concentrations of ozone
of the order
of 100 to 150 g/Nm~ to be obtained.
The installation includes, in addition, a membrane compressor 31 fitted with a
frequency controller for the flow rate/pressure adjustment. Such a compressor
allows a
discharge pressure of the order of 7 bars.
A reservoir 32 fulfilling a buffering role upstream of the compressor allows
fluctuations in flow to be smoothed out, as well as sudden changes in
concentration that
may arise at the outlet of the ozone generator 30. This reservoir which has a
capacity of
20 litres is equipped with pressure indicators 39 and temperature indicators
40 while a
pressure relief valve set at 1 bar ensures safety. This reservoir 32 is also
fitted with a
drainage valve which, if necessary allows part of the flow to be; by-passed so
as always
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to have a pressure between 0 and 0.1 bar relative pressure upstream of the
compressor
31~
Start up of the compressor must on no account be carried out under load, the
circuit is provided with a blow off loop 33 which permits discharge downstream
of the
compressor. ~1 pressure indicator 42 is provided so as to allow control of the
pressure at
the outflow from this.
Finally, a vessel 36 ensures the safety of the compressor 31 and the ozone
generator 30. This safety vessel 36 is fitted with a capacitive sensor 43
which is triggered
in the presence of water. The purpose of this device is to form a~ non-return
safety device
so as to absolutely prevent any risk that water should go into the ozone
generator which
operates at high voltage The triggering of the sensor 43 brings about the
closing of an
electronically controlled valve 44 situated between the vessel 36 and the
compressor 31,
the shut down of the frequency controller 38 and hence of the compressor and
the shut
down of the ozone generator 30. Such a vessel is, in addition, fitted with a
pressure relief
valve 45 allowing its own safety to be ensured.
The installation for the production of ozonized white 'water used also
includes
means 34 for measuring the ozone dissolved in the fluid under pressure leaving
the
pressurisation vessel.
The circuit supplying water to the pressurisation vessel 1 includes a pipeline
51
coming from the outlet of the flotation reactor .50. In effect, in the context
of this
example, the carrier liquid used by the pressurisation vessel is made up of a
part of the
treated water. To this end, the pipeline 51 is connected onto the outlet pipe
55 of the
flotation unit 50.
The water circuit includes, in addition, a pump 46 and a blow off loop 47e The
pump allows delivery of water at a pressure of 8 bars. To ensure; good
equilibrium of the
fluids in the vessel, it is, in effect permanently necessary that thc:
delivery pressure of the
water should be greater than the pressure prevailing in the pressurisation
vessel.
In an advantageous embodiment, the vessel is provided with means of
recirculating the fluids brought into contact, namely the carrier liquid
and/or the ozonized
gas.
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Hence, it is advantageous to recover the gaseous rejects, which still contain
ozone
and which can then be reused immediately at another point in t:he treatment
chain or re-
routed up stream of the ozone generator 30, successively through a destructor
of residual
ozone 102,, a condenser (with purge) 1022, and desiccation means (for example
over
alumina) 102,, which allows recycling of the oxygenated gas.
The contact time of the carrier liquid with the ozone can for its part, be
increased
by providing a recirculation pipe 60 for a part of the treated flovv into the
vessel, with the
help of a pump 61.
During the operation of the treatment unit shown, the white water production
installation continuously supplies a fluid under pressure made up of water
supersaturated
with ozone. This fluid passes through pipeline 7 to the cavitator 6 installed
at the foot of
the flotation unit 50. The pressure reduction brought about by the cavitator
allows the
continuous release of micro-bubbles of ozone of very small size increasing the
interface
between the treated water and the oxidising gas and thereby optimising the
action of the
latter. The oxidising action of the ozone combined with the movement of the
bubbles
permits excellent flotation of the water present in the flotation unit to be
earned out.
A catalytic destructor 56 is provided to eliminate ozone residues coming from
the
flotation unit. These ozone residues can also be recycled to the ozone
generator as
previously mentioned.
It is appropriate to note that the pressurisation vessel used may comprise a
counter
current packed column as shown in Figures 1 and 2 but may also comprise other
types of
columns.
With reference to Figure 3, the pressurisation vessel used can particularly
comprise a bubble column (A), an ejector column (B), a mechanically agitated
column
(C) or a bubble column using the air lift phenomenon (D).
This pressurisation vessel can also comprise an ejector column 111 including a
static mixer 112 such as that shown in Figure 4.
In accordance to this Figure, the installation according to the invention
includes an
ozone generator 30 working with aspiration means 311 for the formed ozone and
a liquid
jet gas compressor 31. The carrier fluid is pumped by a pump 46.0, the
intimate mixing of
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the gas and this liquid being carried out by a static mixer 112.
The embodiments of the invention described here do not have the object of
reducing the scope of the invention. In particular it could be envisaged to
carry out
modifications to the components making up the installation ;For the production
of the
ozonized white water. It should be noted that the installation for the
production of
ozonized white water according to the invention is particularly appropriate to
supply an
ozoflotation unit such as that described and protected particul~u-ly by French
patent No.
86 08780.
It could also be envisaged that such an installation could be used in a
context other
than that of a flotation unit.
~7Vith the installation for the production of ozonized white water according
to the
invention, concentrations of dissolved ozone greater than 20 mg/1 of liquid
can be attained
and particularly up to, for example 80 g/1 (achieved in a prototype).
