U.S. patent application number 14/430052 was filed with the patent office on 2015-08-20 for underwater water treatment unit and method for cleaning said unit.
The applicant listed for this patent is SAIPEM S.A, TOTAL SA, VEOLIA EAU-COMPAGNIE GENERALE DES EAUX, VWS WESTGARTH LTD.. Invention is credited to Stephane Anres, Didier Bigeonneau, Wayne Evans, Raymond Hallot, David Lothian, Pierre Pedenaud, Luc Riviere.
Application Number | 20150231533 14/430052 |
Document ID | / |
Family ID | 47425036 |
Filed Date | 2015-08-20 |
United States Patent
Application |
20150231533 |
Kind Code |
A1 |
Riviere; Luc ; et
al. |
August 20, 2015 |
UNDERWATER WATER TREATMENT UNIT AND METHOD FOR CLEANING SAID
UNIT
Abstract
The invention concerns an underwater water treatment unit which
has specific cleaning means which are suitable for cleaning
filtration membranes in the unconventional conditions associated
with use at great or very great depths, as well as a method for
cleaning the membrane of the underwater water treatment unit.
Inventors: |
Riviere; Luc; (Idron,
FR) ; Pedenaud; Pierre; (Lescar, FR) ;
Bigeonneau; Didier; (Montbrun-lauragais, FR) ; Anres;
Stephane; (Saint Cyr L'ecole, FR) ; Hallot;
Raymond; (Voisins Le Bretonneux, FR) ; Evans;
Wayne; (Moor, GB) ; Lothian; David;
(Ardrossan, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TOTAL SA
SAIPEM S.A
VEOLIA EAU-COMPAGNIE GENERALE DES EAUX
VWS WESTGARTH LTD. |
Courbevoie
Montigny Le Bretonneux
Paris
East Kilbride |
|
FR
FR
FR
GB |
|
|
Family ID: |
47425036 |
Appl. No.: |
14/430052 |
Filed: |
September 19, 2013 |
PCT Filed: |
September 19, 2013 |
PCT NO: |
PCT/FR2013/052167 |
371 Date: |
March 20, 2015 |
Current U.S.
Class: |
210/797 ;
210/191 |
Current CPC
Class: |
C02F 2209/02 20130101;
C02F 2303/16 20130101; C02F 2103/08 20130101; C02F 2307/00
20130101; C02F 1/442 20130101; C02F 2303/20 20130101; C02F 2103/10
20130101; B01D 2321/08 20130101; B01D 29/66 20130101; B01D 61/147
20130101; B01D 61/027 20130101; B01D 2311/103 20130101; C02F 1/444
20130101; C02F 2101/101 20130101; B01D 65/02 20130101; C02F
2103/365 20130101; C02F 1/001 20130101; B01D 61/58 20130101 |
International
Class: |
B01D 29/66 20060101
B01D029/66; C02F 1/00 20060101 C02F001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 20, 2012 |
FR |
12 58853 |
Claims
1. An underwater water treatment unit suitable for injection into a
hydrocarbon field, said unit including: means for supplying the
underwater unit with power; an underwater water treatment system
which includes at least one filtration membrane, a water intake
which is suitable to bring a flow of water drawn from the
environment of the system into the underwater unit, a pipe
connecting said water intake and said filtration membrane, a
discharge pipe for treated water and at least one supply pump which
is suitable for carrying out the water filtration; a hydraulic
cleaning circuit for cleaning said membrane, said circuit forming a
loop between the inlet and the outlet of said membrane, and having
a discharge pipe; at least two water storage tanks, each water tank
being connected to the cleaning circuit; at least one tank for
storing a cleaning product selected from among an acid and a base,
the cleaning product tank being connected to the cleaning circuit;
at least one cleaning pump which is suitable for setting the
liquids in the cleaning circuit into motion; said filtration
membrane being provided with at least one heating means, and at
least one of the water tanks being provided with at least one means
for heating the tank.
2. The underwater unit as claimed in claim 1, wherein the
filtration membrane is a microfiltration membrane, an
ultrafiltration membrane, a nanofiltration membrane or a reverse
osmosis membrane.
3. The underwater unit as claimed in claim 2, wherein the water
treatment system includes a nanofiltration membrane and an
ultrafiltration membrane which is situated upstream of said
nanofiltration membrane, the hydraulic cleaning circuit forming: a
loop between the inlet and the outlet of the nanofiltration
membrane or a loop between the inlet and the outlet of the
ultrafiltration membrane, or two loops between the inlet and the
outlet of the nanofiltration membrane on the one hand and between
the inlet and the outlet of the ultrafiltration membrane on the
other hand, valves being situated in the loops in order to allow
the membrane desired for cleaning to be selected.
4. The underwater unit as claimed in claim 1, characterized in that
said unit includes at least two storage tanks for the cleaning
product, at least one of the tanks being a storage tank for an acid
and at least one of the tanks being a storage tank for a base, the
acid and base tanks being connected to the cleaning circuit.
5. The underwater unit as claimed in claim 1, wherein said unit
includes at least three water storage tanks, at least two of the
water tanks being provided with at least one means for heating the
tank.
6. The underwater unit as claimed in claim 1, wherein the supply
pump and the cleaning pump are mounted on the same shaft.
7. The underwater unit as claimed in claim 1, wherein said unit
further includes a discharge pipe which allows the contents of the
hydraulic cleaning circuit to be discharged into the water storage
tank or tanks.
8. A method for cleaning the filtration membrane of an underwater
unit including means for supplying the underwater unit with power:
an underwater water treatment system which includes at least one
filtration membrane, a water intake which is suitable to bring a
flow of water drawn from the environment of the system into the
underwater unit, a pipe connecting said water intake and said
filtration membrane, a discharge pipe for treated water and at
least one supply pump which is suitable for carrying out the water
filtration; a hydraulic cleaning circuit for cleaning said
membrane, said circuit forming a loop between the inlet and the
outlet of said membrane, and having a discharge pipe; at least two
water storage tanks, each water tank being connected to the
cleaning circuit; at least one tank for storing a cleaning product
selected from among an acid and a base, the cleaning product tank
being connected to the cleaning circuit; at least one cleaning pump
which is suitable for setting the liquids in the cleaning circuit
into motion; said filtration membrane being provided with at least
one heating means, and at least one of the water tanks being
provided with at least one means for heating the tank, said method
including the steps consisting in: a) cutting off the inlet of
water into said filtration membrane; b) injecting water contained
in one of the water storage tanks into the hydraulic cleaning
circuit, and making said water circulate in a loop in the hydraulic
cleaning circuit using the cleaning pump; c) heating the filtration
membrane up to a temperature of between 15.degree. C. and
40.degree. C. inclusive using the heating means; d) injecting a
cleaning product contained in at least one storage tank into the
hydraulic cleaning circuit; e) discharging the contents of the
hydraulic cleaning circuit via the discharge pipe; f) injecting
water contained in one of the water storage tanks into the
hydraulic cleaning circuit again, and making said water circulate
in a loop in the hydraulic cleaning circuit; and g) discharging the
contents of the hydraulic cleaning circuit via the discharge pipe
again.
9. The method for cleaning as claimed in claim 8, wherein the
cleaning product injected into the hydraulic cleaning circuit
during step d) is an acid.
10. The method for cleaning as claimed in claim 8, wherein said
method includes, between step f) and step g), the steps: d')
injecting a cleaning product that is different from the product
injected during step d) into the hydraulic cleaning circuit, said
product being contained in at least one storage tank; e')
discharging the contents of the hydraulic cleaning circuit via the
discharge pipe; and f') injecting water contained in one of the
water storage tanks into the hydraulic cleaning circuit again, and
making said water circulate in a loop in the hydraulic cleaning
circuit.
11. The method for cleaning as claimed in claim 10, wherein the
cleaning product injected into the hydraulic cleaning circuit
during step d) is a base and the cleaning product injected into the
hydraulic cleaning circuit during step d') is an acid.
12. The method for cleaning as claimed in claim 8, wherein said
method subsequently includes the steps: h) resuming the water
treatment in the water treatment system of the unit; and i)
replacing the water which has been used during steps b) and f), by
injecting water obtained leaving the treatment system into the
water storage tanks.
13. The method for cleaning as claimed in claim 8, wherein the
water injected into the hydraulic cleaning circuit during step f),
is heated to a temperature of between 15.degree. C. and 40.degree.
C. inclusive thanks to the means for heating the water storage
tanks or tanks.
14. The method for cleaning as claimed in claim 8, wherein the
underwater water treatment unit is placed underwater, at a minimum
depth of 500 meters.
15. The method for cleaning as claimed in claim 8, wherein the
contents of the hydraulic cleaning circuit is discharged into the
water storage tanks or tanks which has or have been drained
following step b).
16. The method for cleaning as claimed in claim 12, wherein the
method includes the step of replacing the water which has been used
during step f' injecting water obtained in leaving the treatment
system in the water storage tanks.
17. The method for cleaning as claimed in claim 13, wherein the
water injected into the hydraulic cleaning circuit during step f'
is heated to a temperature of between 15.degree. and 40.degree. C.
inclusive thanks to the means for heating the water storage tanks
or tanks.
Description
RELATED APPLICATIONS
[0001] The present application is a National Phase entry of PCT
Application No. PCT/FR2013/052167, filed Sep. 19, 2013, which
claims priority from FR Patent Application No. 12 58853, filed Sep.
20, 2012, said applications being hereby incorporated by reference
herein in their entirety.
TECHNICAL SCOPE OF THE INVENTION
[0002] The present invention is to be found in the field of
underwater applications, in particular within the oil and gas
sector. More specifically, the invention concerns an underwater
water treatment unit which has specific cleaning means, as well as
a method for cleaning the membrane of the underwater water
treatment unit.
BACKGROUND OF THE INVENTION
[0003] The injection of water into hydrocarbon fields is a
well-known technique in the oil and gas sector. It is an operation
which consists in injecting water, commonly known as injection
water, into an oil and gas well, on the one hand to recover the
hydrocarbons and on the other hand to avoid the wells collapsing,
which can come about due to the drop in pressure as a result of the
hydrocarbons being extracted.
[0004] The origin of the injection water generally depends on its
availability and on the constraints around the site of the
hydrocarbon extraction. For example, in the case of offshore
extraction, using water drawn from the sea is known. Treatment
steps, however, are generally essential in order to obtain from the
seawater water which has the quality sufficient to enable it to be
reintroduced into the underground formation. The injection water is
always obtained by means of a filtration step, aiming to reduce or
even eliminate suspended matter, and by means of a deoxygenation
step. Often a supplementary treatment in the form of
desulphurization is used if the contents of the underground
formation are such that reduction in the sulfate ions is
necessary.
[0005] The injection water can also be aquifer water, river or lake
water, and possibly domestic or industrial wastewater. Here too,
treatment steps can be necessary to obtain water which has a
quality which is compatible with injection into the underground
formation.
[0006] When the injection water is seawater, the presence of
sulfates in the water is typically a problem if the underground
formation contains barium, calcium or strontium ions. Indeed, the
sulfate ions form mineral deposits (scaling) with the barium,
calcium or strontium ions and these are disadvantageous to good
hydrocarbon extraction. Furthermore, the presence of sulphates can
be the cause of the generation by bacteria of hydrogen sulfide
(H.sub.2S), a toxic and corrosive gas, which can cause piping that
is used for recovering hydrocarbons to corrode. The elimination of
the sulfates from the water before it is injected into the
underground formation is therefore often necessary.
[0007] A conventional method enabling the elimination of sulphates
from the water consists in a nanofiltration membrane method which
retains the multivalent ions and allows the monovalent ions to
pass. Another conventional method enabling water desalination
consists in a reverse osmosis method. Such methods are described,
for example, in patent applications WO 2006/134367 and WO
2007/138327.
[0008] Generally, the water treatment units are placed close to the
hydrocarbon field. In the case of underwater fields, said units are
conventionally installed on the surface, on the offshore platform
for extracting hydrocarbons or on attached floating platforms,
currently called FPSO units (acronym of "Floating Production,
Storage and Offloading" according to Anglo-Saxon terminology,
signifying a floating unit for production, storage and
offloading).
[0009] One of the major problems associated with installing water
treatment units on the surface is the space required. Said units
take up space. Yet the management of space on the offshore
platforms is tricky as space is limited and many of the
installations are essential. There is therefore a need for water
treatment units which require minimum space on offshore
platforms.
[0010] One solution to this problem has already been proposed in
the prior art. It consists in replacing the existing treatment
units by underwater units which are capable of operating
underwater. In particular, international patent application WO
2009/122134 describes an underwater seawater treatment unit. The
fact of putting the unit underwater also has an advantage in terms
of power: the system placed in an underwater environment profits
from hydrostatic pressure which is approximately proportional to
the depth at which it is situated. U.S. Pat. No. 7,600,567 and
patent application GB 2 451 008 also describe an underwater water
treatment unit which is able to be placed underwater at a depth of
between 250 and 700 meters inclusive.
[0011] Now currently, discoveries of large size hydrocarbon fields
are made increasingly rarely in shallow and moderately deep waters,
that is to say at depths of up to 500 meters. With the aim of
ensuring renewal of reserves, it is necessary to develop new fields
which are located at great depths (that is to say at a depth of
between 500 and 1,500 meters inclusive) and at ultra-great depths
(that is to say deeper than 1,500 meters).
[0012] In shallow and moderately deep waters, temperature and
salinity conditions as well as aquatic fauna are not radically
different to conditions on the surface. By contrast, at great
depths and ultra-great depths, the water temperature is
approximately between 3.degree. C. and 5.degree. C. and the water
viscosity increases with the depth. Furthermore, pressure increases
by 10 MPa every 1000 meters. Thus, the environmental conditions to
which the underwater water treatment units are subjected are quite
specific.
[0013] In addition, the true underwater environment cannot be
defined solely by conditions of pressure and temperature. It is a
complex environment, with variable chemical compositions, above all
including micro-organisms that are specific to great depths and to
the ultra-great depths.
[0014] Said micro-organisms tend to hang onto and build up on
certain surfaces, and more particularly to clog up all underwater
devices rapidly. Said phenomenon of clogging up which is biological
in origin is currently designated by the Anglo-Saxon term of
biofouling. It is a question of the degradation or deterioration of
a surface or of an object left in an aquatic environment, as
typically in the sea, by the growth of living organisms such as
bacteria, protozoa, algae and crustaceans.
[0015] When they are placed at great depths or at ultra-great
depths, the underwater water treatment units, and in particular the
filtration membranes that they contain, are therefore subject to
very specific environmental conditions.
[0016] Means which are intended to reduce, or even suppress, the
clogging of the filters are known by the expert. For example,
patent application WO 2012/049618 describes a water treatment
method which enables the risks of the membrane filters clogging up
to be reduced thanks to a treatment of the retentate prior to its
recycling. According to another example, patent U.S. Pat. No.
7,600,567, cited previously, describes backwashing the filtration
membranes. According to one embodiment, gas can be added to the
wash water. Said embodiment is not suitable for the case where the
units which contain the filtration membranes are situated at great
depths. Another embodiment consists in adding a biocide and/or an
anti-fouling agent to the wash water. Said chemical products are
for the most part organic molecules. After the wash phase, they are
discharged into the environment and are therefore susceptible to
causing ecological problems, especially when the filtration
membranes are situated at great depths or at ultra-great depths
where the biological environment is still not well understood.
[0017] It would therefore be advantageous to reduce the use of said
conventional cleaning means in the very specific environmental
conditions to which the units situated at great depths or
ultra-great depths are subject.
[0018] Furthermore, in the case of seawater treatment units with a
view to using the water as injection water in an oil well, said
units preferably have to remain operational for several months, or
even several years without any intervention whatsoever.
Furthermore, it is preferable for the unit to be as sturdy as
possible so as to reduce the number of essential maintenance
operations.
[0019] It is therefore necessary to have a treatment unit which is
suitable for said very specific environmental conditions at great
depths and at ultra-great depths.
[0020] Furthermore, conventional means for cleaning filtration
membranes are described in the scientific publications by Davis et
al. ("Membranes solve North Sea waterflood sulfate problems" Oil
& Gas Journal, Nov. 25, 1996) and by O'Donnell ("Membrane
technology works on North Sea platform" Oil & Gas Journal, Dec.
2, 1996), and in the patents and patent applications U.S. Pat. No.
3,827,976, U.S. Pat. No. 5,403,479 and US 2012/0090641. Said
documents do not provide a solution to the specific problem posed
here by the environmental conditions.
[0021] It is within this context that the inventors have discovered
an alternative solution, which is advantageous from an ecological
point of view, enabling the filtration membranes to be washed using
acid and/or alkaline solutions in underwater conditions. Gentle on
the environment, and used in very diluted solutions, the acid
and/or alkaline solutions can possibly be discharged into the
environment after use. However, the invention also provides means
which enable the discharge of said solutions into the environment
to be avoided.
SUMMARY OF THE INVENTION
[0022] Said objectives, among others, are resolved by the present
invention, the object of which is an underwater water treatment
unit which is suitable for injection into a hydrocarbon field, said
unit including: [0023] means for supplying the underwater unit with
power; [0024] an underwater water treatment system which includes
at least one filtration membrane, a water intake which is suitable
to bring a flow of water drawn from the environment of the system
into the underwater unit, a pipe connecting said water intake and
said filtration membrane, a discharge pipe for treated water and at
least one supply pump which is suitable for filtering the water;
[0025] a hydraulic circuit for cleaning said membrane, forming a
loop between the inlet and the outlet of said membrane, and having
a discharge pipe; [0026] at least two water storage tanks, each
water tank being connected to the cleaning circuit; [0027] at least
one tank for storing a cleaning product selected from among an acid
and a base, the cleaning product tank being connected to the
cleaning circuit; [0028] at least one cleaning pump which is
suitable for setting the liquids in the cleaning circuit into
motion; said filtration membrane being provided with at least one
heating means, and at least one of the water tanks being provided
with at least one means for heating the tank.
[0029] A further object of the invention is a method for cleaning
the filtration membrane of an underwater unit such as defined
previously, said method including the steps consisting in: [0030]
a) cutting off the inlet of water into said filtration membrane;
[0031] b) injecting water contained in one of the water storage
tanks into the hydraulic cleaning circuit, and making said water
circulate in a loop in the hydraulic cleaning circuit using the
cleaning pump; [0032] c) heating the filtration membrane up to a
temperature of between 15.degree. C. and 40.degree. C. inclusive
using the heating means; [0033] d) injecting a cleaning product
contained in at least one storage tank into the hydraulic cleaning
circuit; [0034] e) discharging the contents of the hydraulic
cleaning circuit via the discharge pipe; [0035] f) injecting water
contained in one of the water storage tanks into the hydraulic
cleaning circuit again, and making said water circulate in a loop
in the hydraulic cleaning circuit; [0036] g) discharging the
contents of the hydraulic cleaning circuit via the discharge pipe
again.
BRIEF DESCRIPTION OF THE FIGURES
[0037] FIG. 1 is a schematic representation of an embodiment of the
underwater water treatment unit according to the invention.
[0038] FIG. 2 is a schematic representation of an embodiment of the
means for cleaning a unit according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0039] In the present application, the expression "between . . .
and . . . inclusive" must be understood as including the limit
values.
[0040] The underwater unit according to the invention is designed
for treating water in such a way that said water is able to be
injected into a hydrocarbon field. The water which is treated is
preferably seawater and the water obtained is injection water.
[0041] In order to perform the water treatment, the underwater unit
according to the invention first of all includes a means for
supplying the underwater unit with power and an underwater water
treatment system. Said water treatment system comprises at least
one filtration membrane, a water intake which is suitable to bring
a flow of water drawn from the environment of the system into the
underwater unit, a pipe connecting said water intake and said
filtration membrane, a discharge pipe for treated water and at
least one supply pump which is suitable for filtering the
water.
[0042] The filtration membranes are devices that are well known to
the expert which enable different components of a liquid flow to be
separated. The nature of the separation is determined in part by
the dimension of the pores in the membranes.
[0043] According to the IUPAC classification: [0044] a
microfiltration membrane has macropores the diameter of which is in
excess of 50 nm, [0045] an ultrafiltration membrane has mesopores
the diameter of which is between 2 nm and 50 nm inclusive, [0046] a
nanofiltration membrane has micropores the diameter of which is
less than 2 nm.
[0047] On the other hand, osmosis membranes are specific membranes
which are well known to the expert. An osmosis membrane is a
semi-permeable membrane which only allows solvent (in general
water) to pass and not other substances in solution.
[0048] The filtration membrane of the present invention can be a
microfiltration membrane, an ultrafiltration membrane, a
nanofiltration membrane, or even a reverse osmosis membrane. In
addition, according to a more advantageous embodiment, the
filtration membrane in the present invention is a membrane for
desulfation. The term "membrane for desulfation" refers in the
present invention to a membrane which enables sulfate ions to be
separated from water. It is a particularly advantageous embodiment
for the oil industry as said membranes enable the elimination of
sulfates in the seawater which is intended to be re-injected into
the underground formations which contain hydrocarbons.
[0049] Among the nanofiltration membranes for the desulfation of
seawater, the membranes SR90 of DOW Filmtec and the NANO-SW of
Hydranautics can be cited, among others.
[0050] The underwater water treatment system can include several
filtration membranes, arranged in series and/or in parallel, which
are identical or different. According to a preferred embodiment,
the underwater water treatment system includes a nanofiltration
membrane and an ultrafiltration membrane, said ultrafiltration
membrane being situated upstream of said nanofiltration membrane.
The underwater water treatment system can therefore include, in
order with respect to the normal flowing of the water flow in the
system: [0051] a water inlet; [0052] a pipe connecting said water
inlet and an ultrafiltration membrane; [0053] said ultrafiltration
membrane; [0054] a pipe connecting said ultrafiltration membrane
and a nanofiltration membrane; [0055] said nanofiltration membrane;
then [0056] on the one hand, a discharge pipe downstream of said
nanofiltration membrane; and on the other hand, a discharge pipe
for the retentate of the nanofiltration membrane.
[0057] According to another embodiment, the underwater water
treatment system includes a microfiltration membrane and/or an
ultrafiltration membrane.
[0058] Furthermore, the underwater water treatment system can
include other filters which can be selected, for example, from
among a sieve and a pre-filter. A sieve is a grid having a mesh
that is more or less fine or a surface that is perforated with
holes. The job of a sieve is generally to separate different sized
solid particles from a liquid flow, the size of the particles
separated depending on the size of the mesh or the holes in the
filter. The term "pre-filter" designates a filter that is likely to
stop relatively large-sized solid particles, that is to in excess
of 100 micrometers. The pre-filter enables coarse filtering.
[0059] The flow of water enters the underwater water treatment
system via a water inlet. A water inlet is a conventional system
which includes an opening enabling a flow of water to enter the
system. The water inlet can possibly be provided with a strainer
screen which holds back large diameter solid elements, thus
avoiding the filtration system quickly becoming blocked by large
elements.
[0060] The location of the water inlet determines the quality of
the water entering the underwater water treatment system. In an
advantageous manner, the water inlet can be mobile, for example by
means of a telescopic system which enables the site of the water
inlet to be varied without modifying the location of the underwater
water treatment unit itself. In particular, a telescopic system or
a rewinding means can allow the level of the water inlet to be
moved, referenced with respect to the bottom of the water or to the
surface.
[0061] In the underwater water treatment system of the present
invention, the filtration membrane can be placed in a specific
module which includes two chambers, a first chamber upstream of the
filtration membrane and a second chamber downstream of the
filtration membrane, the filtration membrane forming a partition
between the two chambers. The first chamber upstream is provided
with at least one pipe which enables the inlet of the water flow.
The second chamber downstream is provided with at least one
discharge pipe. The first chamber upstream is possibly also equally
provided with a second discharge pipe. The dimensioning of the
chambers upstream and downstream can be made by the expert, in
particular in terms of the type of filter and the nature of the
speed of the flow to be filtered.
[0062] Conventionally, the flow of water can be brought into the
first chamber of the filter by a supply pipe. The portion of the
flow which crosses the filter and reaches the second chamber,
downstream of the filter, is commonly called the filtrate. The
portion of the flow which is retained by the filter is commonly
called the retentate. According to the type of filter, the
retentate can be solid, liquid or a mixture of the two.
[0063] In order to make the water circulate across the filter, the
underwater water treatment system according to the invention
includes at least one pump which is suitable for filtering water.
Said pump can be situated on the pipe which connects the water
inlet and the filter. The pump can be controlled by an electronic
system. Said electronic system can be controlled by a pre-recorded
program which does not require the intervention of an operator. As
an alternative to this, it can be controlled by an operator,
preferably located on the surface, and the information exchanged
between the operator and the electronic system can be transmitted
via cable or online (for example, over the air, notably wirelessly
or acoustically in the water).
[0064] The job of the discharge pipe downstream of the filter is to
discharge the filtrate from the system. Said filtrate constitutes
treated water which is suitable to be used as injection water in a
hydrocarbon field. The filtrate discharge pipe is therefore
preferably connected to a well for extracting hydrocarbons.
[0065] The underwater water treatment system according to the
invention can possibly include a discharge pipe for the filter
retentate. Not recovering the retentate is preferred and it is
therefore preferably released directly into the environment, close
to the underwater water treatment system.
[0066] In order to be able to realize the different steps of
treatment, and in particular to be able to operate the supply pump
which is suitable for filtering water, the underwater water
treatment system, and more generally the underwater water treatment
unit assembly needs a source of energy. This is why the underwater
water treatment unit includes a means for supplying said underwater
unit with power.
[0067] According to a first embodiment, the underwater water
treatment unit is supplied with power from the surface via an
umbilical. An umbilical is a well-known device in the area of
underwater oil production. The umbilical can conduct an electric
current. It can therefore supply the underwater water treatment
unit with electricity from the surface. In particular, the
umbilical can connect the underwater water treatment unit to a
floating control unit, typically a boat or a floating platform, for
example in line with the submerged underwater water treatment unit,
or in a satellite field a few kilometers from the surface unit. The
same umbilical can ensure several functions at once. Typically, the
same umbilical can serve as a pathway for supplying the underwater
water treatment unit with power and for transmitting
instructions.
[0068] According to a second embodiment, the underwater water
treatment unit is electrically autonomous and is supplied with
power thanks to a battery located within the underwater water
treatment unit. The presence of batteries is not preferred on
account of their volume and weight. However, the advantage of said
embodiment is to make the underwater water treatment unit
autonomous and easily movable.
[0069] The underwater water treatment unit can preferably be in a
compact form, with the possible exception of the water inlet and
the discharge pipe which can extend beyond the structure. The
dimensions of said structure can be between 8 m (length).times.5 m
(width).times.5 m (height) and 20 m (length).times.10 m
(width).times.15 m (height) inclusive. The total weight of the unit
out of the water is between 100 tons and 800 tons inclusive.
[0070] The underwater water treatment unit is intended to be placed
underwater at a depth of at least 500 meters, notably of at least
800 meters. The depth of the underwater water treatment unit is in
a preferred manner between 800 meters and 3000 meters inclusive, in
a more preferred manner between 1000 meters and 3000 meters
inclusive, and in an even more preferred manner between 1500 meters
and 3000 meters inclusive.
[0071] In a preferred manner, the underwater water treatment unit
is placed in the sea, and the flow of water drawn from the
environment is a flow of seawater.
[0072] The underwater water treatment unit is subject to an outside
pressure which, in a preferred manner, is between 80 and 300 bar
inclusive, said pressure naturally being a function of the depth at
which the underwater water treatment unit is positioned. The
temperature existing at the site where the underwater water
treatment unit is positioned is also a function of the depth at
which the underwater water treatment unit is situated, but also
more generally of the geographic location where the underwater
water treatment unit is placed. For example, if the underwater
water treatment unit is positioned at a depth of 3000 meters in the
Gulf of Guinea, the temperature of the water will be approximately
4.degree. C. If the underwater water treatment unit is positioned
at a depth of 500 meters, notably at 800 meters, in the Arctic
Ocean, the temperature of the water will be approximately
-2.degree. C. In a general manner, the underwater water treatment
unit is subject to an outside temperature of between 20.degree. C.
and -2.degree. C. inclusive, preferably between 14 .degree. C. and
-2.degree. C. inclusive.
[0073] It is well known that underwater the service life and the
filtration capacity of the filtration membranes can be greatly
reduced by the phenomenon of biofouling which causes the filters to
clog up. However, the conventional means for cleaning filtration
membranes have been shown to be unsuitable for the very specific
environmental conditions to which an underwater water treatment
unit which is situated at great depths or at ultra-great depths is
subject.
[0074] Cleaning in situ enables the frequency of acting on the
filtration membranes (either to replace them or to clean them) to
be reduced.
[0075] This is why the underwater water treatment unit according to
the present invention further includes specific cleaning means.
[0076] The underwater water treatment unit includes: [0077] a
hydraulic circuit for cleaning said membrane, forming a loop
between the inlet and the outlet of said membrane, and having a
discharge pipe; [0078] at least two water storage tanks, each water
tank being connected to the cleaning circuit; [0079] at least one
tank for storing a cleaning product selected from among an acid and
a base, the cleaning product tank being connected to the cleaning
circuit; [0080] at least one cleaning pump which is suitable for
setting the liquids in the cleaning circuit into motion.
[0081] Furthermore, the filtration membrane of the underwater water
treatment system is provided with at least one heating means, and
at least one of the water tanks is provided with at least one means
for heating the tank.
[0082] The hydraulic cleaning circuit according to the invention,
with the aid of the appropriate pipes, forms a closed circuit of
which the filtration membrane is part. The hydraulic cleaning
system circuit includes a discharge pipe which can be controlled by
a valve. As long as said discharge valve is kept closed, a liquid
flow can be circulated in the hydraulic cleaning circuit, and it
flows following said loop in a continuous manner, continually
crossing the filtration membrane. The opening of the discharge
valve enables the loop to be broken and the liquid flow to be
discharged out of the hydraulic cleaning circuit, for example when
the cleaning is completed.
[0083] According to a preferred embodiment, the underwater water
treatment system includes a nanofiltration membrane, and an
ultrafiltration membrane, said ultrafiltration membrane being
situated upstream of said nanofiltration membrane. In this case,
the hydraulic cleaning circuit according to the invention can
advantageously form: [0084] a loop between the inlet and the outlet
of the nanofiltration membrane, or [0085] a loop between the inlet
and the outlet of the ultrafiltration membrane, or [0086] two loops
between the inlet and the outlet of the nanofiltration membrane on
the one hand and between the inlet and the outlet of the
ultrafiltration membrane on the other hand, valves being situated
in the loops in order to allow the membrane desired for cleaning to
be selected.
[0087] The choice of the number of loops in the hydraulic cleaning
circuit can depend on the need for cleaning the underwater water
treatment unit. Said need can vary in terms of the type of
filtration membranes used, but also in terms of the aquatic
environment of the underwater water treatment unit, for example the
water quality, its temperature, its pressure, its chemical
composition and the micro-organisms that it contains.
[0088] In a preferred manner, when the underwater water treatment
system includes a nanofiltration membrane and an ultrafiltration
membrane, the hydraulic cleaning circuit preferably forms two loops
between the inlet and the outlet of the nanofiltration membrane on
the one hand and between the inlet and the outlet of the
ultrafiltration membrane on the other hand, valves being situated
in the loops in order to select the membrane which requires
cleaning
[0089] The means for cleaning the underwater water treatment unit
according to the invention include a certain number of storage
tanks At least two storage tanks are intended for storing water. At
least one storage tank is intended for storing a cleaning product
which is selected from among an acid and a base.
[0090] The tanks are suitable for fulfilling their storage function
in an aquatic environment, at the temperature and at the pressure
to which the underwater water treatment unit is subject. The
dimensioning of the tanks can be calculated by the expert in terms
of the quantity of water and of cleaning product necessary for
cleaning the filtration membrane for the desired amount of time. In
a preferred manner, the tanks are dimensioned in such a manner that
the underwater unit is autonomous for at least six months. As the
space required is not a limiting constraint within the framework of
an underwater water treatment unit, sturdy equipment is preferred,
requiring the least possible maintenance.
[0091] In a specific embodiment, the storage tank or tanks are
flexible, as a result of which they collapse or flatten when the
liquid is withdrawn when the tank is drained.
[0092] In another specific embodiment, the flexible storage tank or
tanks are surrounded by a rigid shell enabling them to tolerate low
overpressures and enabling the water to circulate within the rigid
structure when the tank collapses.
[0093] Each tank is connected to the cleaning circuit. In a
preferred manner, a valve is arranged at the outlet of each tank so
as to be able to control the opening and closing of the each
tank.
[0094] The acid which can be used as a cleaning product can be an
organic or mineral acid. It can be chosen from among the
conventional compounds known to the expert. It can be selected, in
particular, from the group consisting of citric acid and
hydrochloric acid. The acids are suitable for dissolving the
mineral deposits.
[0095] The base that can be used as a cleaning product can be an
organic or mineral base, in a preferred manner a mineral base. It
can be chosen among the conventional compounds known to the expert.
It can be chosen in particular from among caustic soda or a
detergent having an exclusive chemical formula. The bases are
specially developed to eliminate organic colonization or microbial
residues. The cleaning products are preferably in the form of
concentrated aqueous solutions, the concentration can be between 1%
and 4% inclusive.
[0096] According to a preferred embodiment, the underwater unit
includes at least two storage tanks for the cleaning product, at
least one of the tanks being a storage tank for an acid and at
least one of the tanks being a storage tank for a base, the acid
and base tanks being connected to the cleaning circuit.
[0097] In a general manner, the underwater water treatment unit is
subject to specific pressure and temperature conditions as a result
of its submersion. Especially, the underwater water treatment unit
is subject to an outside temperature of between 20.degree. C. and
-2.degree. C. inclusive, in a preferred manner between 14 .degree.
C. and -2.degree. C. inclusive. The inventors have noted that, in
these conditions, the means for cleaning have had to be
suitable.
[0098] This is why the underwater water treatment unit further
includes means for heating. The filtration membrane of the
underwater water treatment unit is provided with at least one
heating means, and at least one of the water tanks is provided with
at least one means for heating the tank.
[0099] Said means for heating advantageously enable the filtration
membrane to be cleaned at a temperature that is higher than the
outside temperature. The heating means can be placed in an
appropriate manner close to the filtration membrane in order to
heat the filtration membrane and close to or in the water tank in
order to heat the water contained therein.
[0100] The heating means can be supplied with power by the means
for supplying the underwater unit with power.
[0101] Heating can be effected, for example, at one location of the
circulation loop and the hot liquid can be continuously circulated
across the filtration membrane.
[0102] As an alternative to this, the heating means are such that
they enable the water surrounding the filtration membrane to be
heated rather than heating the circulation loop directly.
[0103] According to a preferred embodiment, the underwater water
treatment unit includes at least three water storage tanks, at
least two of the water tanks being provided with at least one means
for heating the tank.
[0104] The underwater water treatment unit further includes at
least one cleaning pump suitable for setting the liquids in the
cleaning circuit into motion. Said cleaning pump can be supplied
with power by the means for supplying the underwater unit with
power. In a preferred manner, the cleaning pump is placed in the
hydraulic cleaning circuit.
[0105] In an advantageous manner, the supply pump and the cleaning
pump can be mounted on the same shaft. Said embodiment enables the
sturdiness of the underwater unit according to the invention to be
increased. This represents an important advantage as the
maintenance of the unit, when it is submerged at a great depth or
an ultra-great depth, is complicated and costly.
[0106] The underwater water treatment unit according to the
invention can therefore be used to treat a flow of water drawn from
the aquatic environment of the unit, and to treat it in such a
manner that it is usable as injection water. In normal mode, the
method of treating water using the underwater unit according to the
invention includes the steps consisting in: [0107] introducing a
flow of water into the underwater water treatment unit via the
water inlet; [0108] introducing said flow in the underwater water
treatment system up to the filtration membrane; [0109] obtaining a
filtrate downstream of said filtration membrane; and [0110]
injecting said filtrate at least in part into a hydrocarbon
field.
[0111] The underwater water treatment unit can be placed underwater
at a depth of at least 500 meters. Furthermore, the hydrocarbon
field into which the treated water is injected is preferably an
offshore field.
[0112] The filtration membrane can be cleaned from time to time in
order to maintain its filtration capacity and to prevent it
clogging up.
[0113] An object of the present invention is a method for cleaning
the membrane of an underwater unit such as defined previously, said
method including the steps consisting in: [0114] a) cutting off the
inlet of water into the filtration membrane; [0115] b) injecting
water contained in one of the water tanks into the hydraulic
cleaning circuit, and making said water circulate in a loop in the
hydraulic cleaning circuit using the cleaning pump; [0116] c)
heating the membrane up to a temperature of between 15.degree. C.
and 40.degree. C. inclusive using the heating means; [0117] d)
injecting a cleaning product contained in at least one storage tank
into the hydraulic cleaning circuit; [0118] e) discharging the
contents of the hydraulic cleaning circuit via the discharge pipe;
[0119] f) injecting water contained in one of the water tanks into
the hydraulic cleaning circuit again, and making said water
circulate in a loop in the hydraulic cleaning circuit; [0120] g)
discharging the contents of the hydraulic cleaning circuit via the
discharge pipe again.
[0121] Step a) consists in cutting off the inlet of water into the
filtration membrane. If it is desirable, however, not to cut off
the production of water treated for injection, it is possible to
provide several filtration membranes and/or several water treatment
systems, arranged in parallel in the same underwater unit.
[0122] Once the membrane has been isolated from the normal water
treatment circuit, in a step b), water contained in one of the
water tanks is injected into the hydraulic cleaning circuit, and
said water is made to circulate in a loop in the hydraulic cleaning
circuit using the cleaning pump.
[0123] In a preferred manner, the water injected during step b)
into the hydraulic circuit is at the same temperature as the
filtration membrane. The filtration membrane is therefore a priori
at the outside ambient temperature as it has been in contact with
the water drawn from the outside environment during the normal
water treatment. The water injected during step b) into the
hydraulic circuit is therefore in a preferred manner at the outside
ambient temperature, which can be between 20.degree. C. and
-2.degree. C. inclusive, in a preferred manner between 14.degree.
C. and -2.degree. C. In a preferred manner, said water can be
treated water which has been obtained by means of the water
treatment method thanks to the underwater unit itself.
[0124] The length of step b) can be determined by the expert in
such a way that the flow of water into the hydraulic cleaning
circuit is constant.
[0125] Step c) of the cleaning method according to the invention
consists therefore in heating the filtration membrane up to a
temperature of between 15.degree. C. and 40.degree. C. inclusive
using the heating means. Said step can be performed by starting up
the heating means which is situated close to the filtration
membrane. As the circulation of the water in the hydraulic cleaning
circuit is maintained, the heating of the filtration membrane also
causes the water circulating in the hydraulic cleaning circuit to
heat. As an alternative to this, said step can be performed by
heating at a location on the circulation loop and by maintaining
circulation of hot liquid across the filtration membrane. In a
preferred manner, step c) is finished when the filtration membrane
and the water circulating in the hydraulic cleaning circuit have
reached a desired stable temperature. The expert can determine the
length of said step c) in terms of, in particular, the initial
temperature of the membrane and of the water, the volume, the flow
of water and the heating power. The desired temperature to be
reached during step c) can be defined in terms of the type of
cleaning product which is injected during the subsequent step
d).
[0126] When step c) is finished, during step d) a cleaning product
which is contained in at least one storage tank is injected into
the hydraulic cleaning circuit. The injection can be controlled by
means of a valve which is situated at the inlet of the storage
tank. The quantity of cleaning product injected can depend of the
type of product, on its concentration in the storage tank and on
the desired cleaning effect.
[0127] The circulation of water in the hydraulic cleaning circuit
is maintained during step c). The cleaning product is diluted or
dispersed in the water. The means for heating the filtration
membrane, in a preferred manner, is kept operating in such a manner
that the temperature remains stable.
[0128] The filtration membrane is therefore crossed by a flow which
contains cleaning product. The circulation of said flow is
maintained in the hydraulic cleaning circuit for a sufficient
amount of time to ensure that the cleaning of the filtration
membrane is effective.
[0129] At the end of said cleaning, the contents of the hydraulic
cleaning circuit are discharged during step e) of the cleaning
method via the discharge pipe. The contents of the hydraulic
cleaning circuit can be discharged directly into the environment
surrounding the underwater water treatment unit, in particular
directly into the sea when the cleaning products used are not toxic
to the flora and fauna present in the environment. As an
alternative to this, when the discharge of the cleaning products
risks becoming an environmental problem, the contents of the
hydraulic cleaning circuit can be discharged into the water tanks
which have been drained following step b). The discharging can be
controlled thanks to a valve which is situated in the discharge
pipe.
[0130] The unit can therefore further include a discharge pipe
which enables the contents of the hydraulic cleaning circuit to be
discharged into the water tank or tanks
[0131] When the entire contents of the hydraulic cleaning circuit
have been discharged, the discharge pipe can be closed again and in
a step f), water contained in one of the water tanks is injected
into the hydraulic cleaning circuit again, and said water is made
to circulate in a loop in the hydraulic cleaning circuit. Said step
f) in an advantageous manner enables the filtration membrane to be
rinsed and to be freed of any possible cleaning product residues.
In a preferred manner, said water which is injected into the
hydraulic cleaning circuit during step f) can be treated water
which has been obtained by means of the method for treating water
thanks to the underwater unit itself. The length of step f) for
rinsing can be determined by an expert so that the rinsing
procedure is effective.
[0132] In a particular embodiment, steps e) and f) are performed
simultaneously.
[0133] At the end of said step f), the contents of the hydraulic
cleaning circuit are once again discharged via the discharge pipe
during step g). In a preferred manner, the contents of the
hydraulic cleaning circuit are discharged directly into the
environment surrounding the underwater water treatment unit, in
particular directly into the sea. The discharging can be controlled
thanks to a valve which is situated in the discharge pipe.
[0134] At the end of step g), the filtration membrane can be
advantageously put back into service. It can be used once again in
the method for treating water. It is possible to re-open the inlet
for water drawn from the environment.
[0135] The cleaning method can be implemented on a one-off basis,
or, in a preferred manner, on a regular basis over time. The
cleaning method according to the invention can be implemented at a
frequency of between once a week and once a year inclusive, in a
more preferred manner between once a month and once every six
months.
[0136] The cleaning method according to the invention is
particularly suitable for cleaning filtration membranes in the
unusual conditions associated with use at great depths or at
ultra-great depths. The objectives of the invention, which are to
obtain efficient cleaning, without however causing damage to the
environment, and without requiring complex and costly maintenance,
are obtained by the method of the present invention which includes,
in particular, a step for heating the filtration membrane.
[0137] Certain filtration membranes, in particular ultrafiltration
membranes, can however be damaged by thermal shock. A thermal shock
can take place when the membrane is heated, during step c) of the
method according to the invention, and/or when the cleaning is
finished and the membrane is put back into service in order to
resume the water treatment in the water treatment system of the
unit.
[0138] To prevent thermal shocks, in a preferred manner the
temperature is increased slowly during step c) of the cleaning
method according to the invention.
[0139] Furthermore, to avoid thermal shocks due to the drop in
temperature, in a preferred manner the water injected into the
hydraulic cleaning circuit during step f) is heated to a
temperature of between 15.degree. C. and 40.degree. C. inclusive
thanks to the heating means of the water storage tank or tanks The
cleaning method can further include a step which consists in
heating the water injected into the hydraulic cleaning circuit in
step f) to a temperature of between 15.degree. C. and 40.degree. C.
inclusive thanks to the means for heating the tank or tanks
containing the water. Said step can be performed by starting up the
heating means which is situated close to or in said tank. In an
advantageous manner, the temperature of the water can be the same
as the temperature of the filtration membrane obtained during step
c). Said heating step can be implemented at the appropriate moment
to ensure that the water is at the desired temperature at the
moment of implementation of step f).
[0140] When said rinsing water circulates in the loop in the
hydraulic cleaning circuit, in a preferred manner the means for
heating the filtration membrane is stopped. In a preferred manner,
the rinsing step can therefore be continued for a length of time
that is sufficient to enable the temperature of the filtration
membrane and of the water which is circulating in the hydraulic
cleaning circuit to drop, until, in a preferred manner, the outside
ambient temperature is obtained. In a preferred manner, cooling is
effected slowly and naturally, by contact with the outside
environment.
[0141] In a preferred manner, the cleaning product injected into
the hydraulic cleaning circuit during step d) is an acid, and in a
more preferred manner, the cleaning product injected into the
hydraulic cleaning circuit during step d) is citric acid. Cleaning
the filtration membrane with acid allows the mineral deposits which
can clog up the membrane to be dissolved. When the cleaning product
injected into the hydraulic cleaning circuit during step d) is an
acid, in a preferred manner the temperature obtained during step c)
is between 20.degree. C. and 40.degree. C. inclusive and in a more
preferred manner is between 25.degree. C. and 35.degree. C.
inclusive.
[0142] As an alternative to this, the cleaning product injected
into the hydraulic cleaning circuit during step d) is a base.
Cleaning the filtration membrane with the base enables organic and
microbial matter to be eliminated. When the cleaning product
injected into the hydraulic cleaning circuit during step d) is a
base, in a preferred manner the temperature obtained during step c)
is between 20.degree. C. and 40.degree. C. inclusive, in a more
preferred manner is between 30.degree. C. and 40.degree. C.
inclusive and in a manner even more preferred is between 35.degree.
C. and 40.degree. C. inclusive.
[0143] According to an embodiment of the present invention, the
filtration membrane can be cleaned several times, in a successive
manner, with different cleaning products. The cleaning method
according to the invention can include, between step f) and step
g), the steps consisting in: [0144] d') injecting a cleaning
product that is different from the product injected during step d)
into the hydraulic cleaning circuit, a said product being contained
in at least one storage tank; [0145] e') discharging the contents
of the hydraulic cleaning circuit via the discharge pipe; and
[0146] f') injecting the water contained in one of the water
storage tanks into the hydraulic cleaning circuit again, and making
said water circulate in a loop in the hydraulic cleaning
circuit.
[0147] The steps d') to f') correspond to steps d) a f), with the
difference that the cleaning product injected during step d') is
different to the cleaning product injected during step d). The
steps d') to f') can be as described previously for steps d) to f).
In particular, the water injected into the hydraulic cleaning
circuit during step f') can possibly be heated to a temperature of
between 15.degree. C. and 40.degree. C. inclusive thanks to the
means for heating the tanks or tanks containing the water
[0148] According to a preferred embodiment, including steps a) to
f), then d') to f'), then g), the cleaning product injected into
the hydraulic cleaning circuit during step d) can be a base and the
cleaning product injected into the hydraulic cleaning circuit
during step d') can be an acid. Said embodiment can be advantageous
for cleaning in a more effective manner than cleaning with one
single cleaning product. The cleaning may be carried out more
frequently.
[0149] In a preferred manner, the method for cleaning can
subsequently include, after step g), the steps consisting in:
[0150] h) resuming the water treatment in the water treatment
system of the unit; and [0151] i) replacing the water which has
been used during steps b) and f), and possibly f'), by injecting
water obtained leaving the treatment system into the water storage
tanks
[0152] It is understood that, if the underwater water treatment
system includes several filtration membranes, a cleaning method can
be implemented for each of said membranes, in a preferred manner
each cleaning method being suitable for each membrane. Furthermore,
each cleaning method can be performed at different frequencies.
[0153] One of the advantages of the cleaning method according to
the invention is that it can be completely automated. Each step of
the method can be triggered without direct human intervention, by
electronic systems. This is particularly advantageous insofar as
the underwater water treatment unit is situated in deep water. Any
direct intervention requires either the use of underwater robots or
raising the unit to the surface, which in all cases is a long,
tricky, costly operation. According to one embodiment, the method
can be remote-controlled by an operator, in a preferred manner
located on the surface, and the information exchanged between the
operator and the electronic system can be transmitted via cable
(for example an umbilical) or online (for example, wirelessly).
According to another embodiment, the electronic system can be
controlled by a pre-recorded program which does not require the
intervention of an operator.
[0154] Furthermore, the underwater water treatment unit according
to the invention can include one or several other means intended to
reduce, or even eliminate, the clogging up of the filtration
membrane. Said means can be chosen from among the group constituted
by a recycling circuit which connects the treated water discharge
pipe and the pipe upstream of the filtration membrane, a backwash
circuit, and one or several biocide tanks, at least one of said
tanks being placed so as to enable the injection of biocide into
the pipe connecting the water inlet and the filter, in a preferred
manner close to the water inlet.
[0155] A recycling circuit connecting the treated water discharge
pipe and the pipe upstream of the filtration membrane enables part
of the filtrate recovered at the outlet of the filtration membrane
to be moved to the water flow which is intended to cross said
filtration membrane. The effect of said recycling system is to
dilute the water flow intended to cross the filtration membrane,
which, on the one hand, increases the incoming liquid flow rate,
and, on the other hand, improves the quality of the incoming water
flow, thus facilitating its filtration.
[0156] Backwashing is a method known for cleaning filters. It
consists in making a flow of water circulate in the opposite
direction to the direction of flow of the flow of water across the
filter in normal mode. By doing so, the water circulating against
the current can take with it elements that are more or less coarse
which clog up the filter. A backwashing step can include the
stopping of the normal inlet of the water flow into the filtration
membrane, the inlet of a water flow into the underwater water
treatment system via a second water inlet, the pipe for said flow
up to the face of the filtration membrane is initially on the
downstream side, the recovery of a flow upstream of said filtration
membrane and the discharging of said flow into the environment via
a second discharge pipe. As an alternative to this, when the
underwater water treatment system includes several filtration
membranes in parallel, the backwash step can consist in introducing
the entire water flow coming into the underwater water treatment
system toward just one of the filtration membranes, in recovering
at least part of the filtrate of said filter and in conducting said
filtrate up to the downstream face of a second filtration membrane
situated in parallel with the first via the normal pipe for
discharging the filtrate of said second membrane filtration, then
in recovering said flow upstream of said membrane filtration and
discharging said flow into the environment via a discharge pipe of
the retentate of the second filtration membrane.
[0157] The injection of biocide into the water flow flowing in the
underwater water treatment system according to the invention allows
the phenomenon of biofouling to be reduced. The biocides well known
for said application are, for example, DBNPA (dibromo nitrolo
proprionamide) or isothiazoline.
[0158] In an advantageous manner, the invention allows the
quantities of biocide used for cleaning the membranes in the
methods of the prior art to be reduced, even the use thereof to be
completely eliminated.
[0159] Other characteristics and advantages of the present
invention will proceed from the description of the specific
embodiments shown in the figures.
[0160] FIG. 1 is a schematic representation of an embodiment of the
underwater water treatment unit according to the invention.
[0161] The underwater water treatment unit 1 includes an underwater
water treatment system 2, itself including a filtration membrane 3,
a water inlet 4 suitable for introducing in a flow of water drawn
from the environment, a pipe 5 which connects the water inlet 4 to
the filtration membrane 3, a discharge pipe 6 and a supply pump 7
which is placed on the pipe 5 connecting the water inlet 4 to the
filtration membrane 3.
[0162] The underwater water treatment unit 1 also includes a means
8 for supplying the underwater unit with power, in particular for
supplying the supply pump 7 and the cleaning pump 10.
[0163] Furthermore, the underwater water treatment unit 1 includes
a hydraulic cleaning circuit 9 and a cleaning pump 10 which is
placed in the hydraulic cleaning circuit 9. The hydraulic cleaning
circuit 9 forms a loop which includes the filtration membrane 3.
The hydraulic circuit also includes a discharge pipe 11.
[0164] The underwater water treatment unit 1 also includes two
water storage tanks 12 and 13 and one cleaning product storage tank
14. Each tank is connected to the hydraulic cleaning circuit 9.
[0165] Finally, in the embodiment shown in FIG. 1, only the
filtration membrane 3 and the water storage tank 13 are provided
with heating means 15 and 16.
[0166] FIG. 2 is a schematic representation of an embodiment of the
means for cleaning a unit according to the invention.
[0167] Said figure shows two filtration membranes 20 and 21, the
membrane 20 can be an ultrafiltration membrane and the membrane 21
can be a nanofiltration membrane.
[0168] The hydraulic cleaning circuit 22 forms two loops, a first
loop including the filtration membrane 20 and the second loop
including the filtration membrane 21. The opening and closing of
the circulating of the liquid in said two loops are controlled by
way of valves 23 and 24. When the filtration membrane 20 needs
cleaning, the valve 23 is opened and the valve 24 is closed.
Conversely, when the filtration membrane 21 needs cleaning, the
valve 24 is opened and the valve 23 is closed.
[0169] Each membrane is provided with a heating means 25 and
26.
[0170] A cleaning pump 27 is placed in the hydraulic cleaning
circuit 22. Furthermore, the hydraulic cleaning circuit 22 includes
a valve 28 which allows the circulation of the flow in the
hydraulic cleaning circuit 22 to be controlled, and a discharge
pipe 29 which has a valve 29'.
[0171] The cleaning means also include three water tanks 30, 31 and
32, and two cleaning product tanks 33 and 34. Each tank is
connected to the hydraulic cleaning circuit 22. The valves 35 and
36 are placed at the inlet of the cleaning product tanks 33 and 34,
in order to be able to control the injection of cleaning product
into the hydraulic cleaning circuit 22. The water storage tanks 30,
31 and 32 are themselves provided with pairs of valves 37a/37b,
38a/38b and 39a/39b. In an advantageous manner, said pairs of
valves allow the injection of water into the hydraulic cleaning
circuit 22 to be controlled, but equally they allow the tanks 30,
31 and 32 to be filled by a flow of water coming from the pipe 40.
In a preferred manner, the water coming in through the pipe 40 is
water obtained leaving the water treatment system. The filling of
the tanks can be controlled by the valve 41 and by the valve
42.
[0172] The water storage tanks 31 and 32 are provided with heating
means 43 and 44.
[0173] By way of example, a method according to the invention for
cleaning the filtration membrane 20 is described below.
[0174] In order to clean the filtration membrane 20, the valve 23
is opened and the valve 24 is closed. The filtration membrane 20 is
isolated from the water treatment system. The valves 28 and 42 are
open whilst the discharge valve 29' is closed. The hydraulic
cleaning circuit 22 thus forms a loop which includes the filtration
membrane 20. Furthermore, the valves 35, 36, 37a/37b, 38a/38b and
39a/39b are closed, as well as the valve 41.
[0175] The water contained in the tank 30 is injected into the
hydraulic cleaning circuit 22 by opening the valve 37b. The water
is at the ambient outside temperature. Said water is made to
circulate in the hydraulic cleaning circuit 22 using the cleaning
pump 27.
[0176] The heating means 25 is switched on. This will enable the
temperature of the filtration membrane 20 and of the water
circulating in the hydraulic cleaning circuit 22 to be increased up
to a temperature of between 15.degree. C. and 40.degree. C.
inclusive.
[0177] When said temperature is reached, a cleaning product
contained in the storage tank 33 is injected into the hydraulic
cleaning circuit 22, by opening the valve 35.
[0178] When the membrane has been sufficiently cleaned, the
contents of the hydraulic cleaning circuit 22 are discharged via
the discharge pipe 29 by opening the valve 29'. Once the
discharging step is finished, the valve 29' is re-closed.
[0179] Water contained in the tank 31 is then injected into the
hydraulic cleaning circuit again by opening the valve 38b. The
water contained in the tank 31 is at the temperature of the
filtration membrane 20, that is to say at a temperature of between
15.degree. C. and 40.degree. C. inclusive. Said temperature has
been obtained by heating the tank using the heating means 43. Said
water is always made to circulate in the hydraulic cleaning circuit
22 using the cleaning pump 27.
[0180] When the rinsing of the filtration membrane 20 is completed,
the contents of the hydraulic cleaning circuit 22 are once again
discharged via the discharge pipe 29 by opening the valve 29'. Once
the discharging step is finished, the valve 29' is re-closed.
[0181] Once, therefore, the cleaning process has been completed,
the treatment of the water in the water treatment system can be
resumed using the filtration membrane 20. Furthermore, it is
possible to replace the water which has been used by injecting
water obtained leaving the treatment system into the water storage
tanks 30 and 31 via the pipe 40. To do this, the valves 37a, 38a
and 41 are opened and the valves 37b, 38b and 42 are kept
closed.
[0182] By way of example, a second method according to the
invention for cleaning the filtration membrane 21 is described
below.
[0183] In order to clean the filtration membrane 21, the valve 24
is opened and the valve 23 is closed. The filtration membrane 21 is
isolated from the water treatment system. The valves 28 and 42 are
open whilst the discharge valve 29' is closed. The hydraulic
cleaning circuit 22 thus forms a loop which includes the filtration
membrane 21. Furthermore, the valves 35, 36, 37a/37b, 38a/38b and
39a/39b are closed, as well as the valve 41.
[0184] The water contained in the tank 30 is injected into the
hydraulic cleaning circuit 22 by opening the valve 37b. The water
is at the ambient outside temperature. Said water is made to
circulate in the hydraulic cleaning circuit 22 using the cleaning
pump 27.
[0185] The heating means 26 is switched on. This will enable the
temperature of the filtration membrane 21 and of the water
circulating in the hydraulic cleaning circuit 22 to be increased up
to a temperature of between 15.degree. C. and 40.degree. C.
inclusive.
[0186] When said temperature is achieved, a cleaning product
contained in the storage tanks 34 is injected into the hydraulic
cleaning circuit 22 by opening the valve 36.
[0187] When the cleaning of the membrane is completed, the contents
of the hydraulic cleaning circuit 22 are discharged via the
discharge pipe 29 by opening the valve 29'. Once the discharging
step is finished, the valve 29' is re-closed.
[0188] Water contained in the tank 31 is then once again injected
into the hydraulic cleaning circuit by opening the valve 38b. The
water contained in the tank 31 is at a temperature of the
filtration membrane 21, that is to say between 15.degree. C. and
40.degree. C. Said temperature has been obtained by heating the
tank 31 using the heating means 43. Said water is always made to
circulate in the hydraulic cleaning circuit 22 using the cleaning
pump 27.
[0189] When the rinsing of the filtration membrane 21 is completed,
this time the cleaning product contained in the storage tank 33 is
injected into the hydraulic cleaning circuit 22 by opening the
valve 35.
[0190] When the cleaning of the membrane is completed, the contents
of the hydraulic cleaning circuit 22 are discharged via the
discharge pipe 29 by opening the valve 29'. Once the discharging
step is finished, the valve 29' is re-closed.
[0191] Water contained in the tank 32 is then once again injected
into the hydraulic cleaning circuit by opening the valve 39b. The
water contained in the tank 32 is at a temperature of the
filtration membrane 21, that is to say between 15.degree. C. and
40.degree. C. Said temperature has been obtained by heating the
tank using the heating means 44. Said water is always made to
circulate in the hydraulic cleaning circuit 22 using the cleaning
pump 27.
[0192] When the rinsing of the filtration membrane 21 is completed,
the contents of the hydraulic cleaning circuit 22 are once again
discharged via the discharge pipe 29 by opening the valve 29'. Once
the discharging step is finished, the valve 29' is re-closed. Once,
therefore, the cleaning process has been completed, the treatment
of the water in the water treatment system can be resumed using the
filtration membrane 21. Furthermore, the water which has been used
is replaced by injecting water obtained leaving the treatment
system into the water storage tanks 30, 31 and 32 via the pipe 40.
To do this, the valves 37a, 38a, 39a and 41 are opened and the
valves 37b, 38b, 39b and 42 are kept closed.
[0193] The embodiments above are intended to be illustrative and
not limiting. Additional embodiments may be within the claims.
Although the present invention has been described with reference to
particular embodiments, workers skilled in the art will recognize
that changes may be made in form and detail without departing from
the spirit and scope of the invention.
[0194] Various modifications to the invention may be apparent to
one of skill in the art upon reading this disclosure. For example,
persons of ordinary skill in the relevant art will recognize that
the various features described for the different embodiments of the
invention can be suitably combined, un-combined, and re-combined
with other features, alone, or in different combinations, within
the spirit of the invention. Likewise, the various features
described above should all be regarded as example embodiments,
rather than limitations to the scope or spirit of the invention.
Therefore, the above is not contemplated to limit the scope of the
present invention.
* * * * *