Closed-circuit continuous seawater desalination device

Abstract

The invention relates to a reverse-osmosis water treatment device (2) comprising: - at least one reverse-osmosis membrane unit configured to extract a permeate from water to be desalinated; - at least one feed pipe for conveying water to be treated (8) to the membrane unit; - at least one outlet pipe (16) for a concentrate from the membrane unit; - at least one tank (24); - at least one discharge pipe (26) for discharging the concentrate into the tank (24); - at least one refill pipe for refilling the tank (24) with water to be treated, wherein the desalination device (2) is characterised in that the tank (24) extends mainly along a first, substantially vertical axis and further comprises a lower connection (52) connected to the discharge pipe (26) for the concentrate and an upper connection (54) fluidically connected to the pipe (32) for sending the water to be treated.

Description

Continuous closed-circuit seawater desalination device

[0001] The invention relates to devices for treating water to be treated, and more particularly to devices for treating seawater in a closed circuit.

[0002] It is known to desalinate seawater by reverse osmosis. Reverse osmosis desalination occurs when a saltwater solution is compressed against semi-permeable membranes at a water pressure greater than the osmotic pressure of the water. This pressure difference is the driving force behind the reverse osmosis seawater desalination process. Currently, the conventional reverse osmosis configuration involves feeding seawater into one or more pressure tubes in parallel, with the pressure tube(s) consisting of several membrane modules arranged in series. Seawater is fed under pressure at the top of the pressure tube, flows through the membrane modules in series, and exits at the other end of the pressure tube. Under the effect of the water pressure, only water passes through the semi-permeable reverse osmosis membranes while the salts are retained.The water that passes through the membrane, called permeate, is desalinated. The flow that has not passed through the membrane is called concentrate. The concentrate at the outlet of the first module becomes the feed for the second module and so on along the pressure tube. The water pressure allowing the water to pass through the membrane must be higher than the osmotic pressure, which depends in particular on the salt concentration. Osmotic pressure increases with the concentration of dissolved salts. As the seawater flows through the pressure tube, it becomes concentrated in salts, due to the extraction of non-saline water, which leads to an increase in osmotic pressure. Therefore, the highest osmotic pressure is found at the end of the pressure tube.The water pressure at the inlet of the pressure tube is therefore calculated to be higher than the osmotic pressure at the end of the pressure tube in order to be able to extract water along the entire length of the pressure tube.

[0003] Such operation generates significant energy consumption. Indeed, since the osmotic pressure is lower at the inlet of the pressure tube, the feed pressure of the first membranes could be lower in order to guarantee the driving force necessary for their production of permeate.

[0004] The concentrate extracted at the end of the pressure tube is always at a high pressure, corresponding to the feed pressure from which the pressure losses related to the flow through the membrane modules are subtracted. This residual pressure also represents a significant energy loss. In order to recover this energy, energy recovery equipment allows the pressure of the concentrate to be transferred to a portion of the seawater supplying the module(s) and thus reduce energy consumption. However, these systems remain expensive, which impacts the total cost of a seawater installation. In addition, the efficiency of these energy recovery installations is not 100%.

[0005] It is known, to overcome this drawback, to use a seawater desalination device, operating in a closed circuit by recirculating the concentrate at the feed level of the pressure tube(s) so that it passes through the pressure tube(s) several times. The recirculated flow is mixed with the continuous pressurized feed of fresh seawater which makes it possible to maintain the volume of the recirculation loop constant by compensating for the water loss linked to the production of permeate. Each time water passes through the pressure tube(s) (seawater or concentrate), the water pressure is adjusted in order to maintain the driving force constant and thus allow permeate production despite the gradual increase in the salinity of the seawater as the recirculation cycles progress.

[0006] Once the concentrate has reached a defined salt concentration and / or the feed pressure has reached the set value, and / or the system conversion rate has reached the desired value, the concentrate is discharged and replaced with fresh seawater to recharge the desalination circuit with raw seawater to be desalinated and start a new concentration cycle. This sequential operation leads to a reduction or even a stoppage of permeate production due to the aforementioned replacement because the pressure in the desalination device is significantly reduced during this purge step, which reduces the driving force applied and therefore the permeate production. The frequency of recharging the desalination circuit depends on the concentration cycle duration, the salinity of the feed water, the permeate flow rate, the free volume in the recirculation loop or the recirculation flow rate.In the case of seawater desalination or concentrate treatment applications, the recharging frequency is high, the loss of production during the concentrate purging stages is therefore significant on the productivity of this process.

[0007] In order to overcome this pressure loss, it is known to provide, in parallel with the concentrate recirculation loop, the presence of a parallel pipe equipped with one or more pressure tanks containing seawater connected to the recirculation loop. When the recirculation loop needs to be recharged with seawater, the concentrate is sent to the tank in the parallel pipe containing fresh seawater at an identical pressure and expels the seawater stored inside the latter.The latter is sent into the recirculation loop, which allows the filtration device to be recharged while evacuating the concentrate, while adapting the water pressure to always apply a net driving pressure defined for the given permeate production and therefore maintaining constant permeate production (the concentrate will be replaced by seawater for a new desalination cycle in parallel with the operation of the recirculation loop) and thus reducing the impact of seawater recharging on the productivity of the whole.

[0008] However, when replacing the raw water with the concentrate in the parallel pipe, the two flows tend to mix at the interface of the two liquids. This results in an increase in the salinity of the seawater when a new cycle is restarted (which starts again with a little of the concentrate) and therefore a reduction in the efficiency of the process (higher water pressure at restart because the osmotic pressure is also higher, shorter desalination cycle due to the higher salinity of the seawater introduced into the recirculation loop from the tank).

[0009] The invention aims to remedy this by providing a device for continuous treatment of salt water in a closed loop having a parallel pipe and limiting the concentrate / water mixture to be treated.

[0010] To this end, the invention relates to a device for treating water to be treated by closed-circuit reverse osmosis comprising: a reverse osmosis membrane unit configured to produce a permeate and a concentrate from the water to be treated, at least one conduit for supplying the water to be treated to the reverse osmosis membrane unit, at least one conduit for the outlet of the concentrate from the reverse osmosis membrane unit, at least one conduit forming a recirculation loop and connecting the conduit for supplying the water to be treated and the conduit for the outlet of a concentrate from the reverse osmosis membrane unit so as to allow a return of the concentrate to the reverse osmosis membrane unit, at least one reservoir delimiting a storage volume, at least one conduit for discharging the concentrate to the reservoir, from the conduit for the outlet of the concentrate from the reverse osmosis unit, and at least one conduit for extracting the concentrate from the reservoir,at least one conduit for sending water to be treated stored in the tank to the conduit for supplying the water to be treated and at least one conduit for recharging the tank with water to be treated, the tank extending mainly along a first substantially vertical axis, the tank comprising a lower wall, an upper wall located above the lower wall along the first axis, and a side wall connecting the lower wall to the upper wall,

[0011] the tank further comprising a lower tapping located on the lower wall and fluidly connected to the concentrate extraction pipe and an upper tapping located on the upper wall and fluidly connected to the pipe sending the water to be treated.

[0012] Thus, and by connecting the pipes in the aforementioned manner, we take advantage of the difference in density between the concentrate and the water to be treated to achieve, at the level of the tank, a replacement of one of the two liquids by the other by obtaining a plug flow. Indeed, the concentrate, denser than the water to be treated and entering through the lower wall of the tank, will naturally push the raw seawater upwards to send the latter into the recirculation loop at the time of evacuation of the concentrate from the recirculation loop. Conversely, the water to be treated, less dense than the concentrate, will, by entering through the upper wall of the tank, push all the concentrate downwards to extract it from the treatment device. The use of this filling method makes it possible to limit the concentrate / water to be treated mixtures in the tank by starting from the extreme points of the latter.

[0013] According to other optional characteristics of the treatment device taken alone or in combination: the side wall is of general shape of a cylinder of revolution, the reverse osmosis membrane unit comprises at least a first pressure tube comprising at least one desalination module formed by at least one reverse osmosis membrane, the lower tapping is located at the lowest point of the lower wall of the tank, and the upper tapping is located at the highest point of the upper wall of the tank, the treatment device comprises a set of control members controlled to obtain: - a recirculation configuration in which the water to be treated circulates several times in the reverse osmosis membrane unit by passing through the recirculation loop,

[0014] - a discharge configuration in which the concentrate is brought to the tank through the lower tapping and water to be treated stored in the tank is sent to the water to be treated supply pipe through the upper tapping, and

[0015] - a reloading configuration in which the concentrate is discharged from the treatment device via the lower tapping and the tank is filled with water to be treated via the upper tapping,The treatment device comprises means for regulating an inlet speed of the concentrate and / or the water to be treated into the tank,the means for regulating an inlet speed of the concentrate and / or the water to be treated into the tank are configured to regulate an inlet speed of concentrate and / or water to be treated into the tank between 0.04 m / s and 0.30 m / s,the means for regulating an inlet speed of concentrate and / or the water to be treated into the tank are formed by:at least one flow controller, andat least one actuator installed on a recirculation pump and / or a pressurization member,the treatment device comprises means for regulating a speed of movement of the concentrate and / or the water to be treated in the tank,preferably configured to regulate a speed of movement of the concentrate and / or the water to be treated in the tank is between 1 mm / s and 50 mm / s, the tank comprises at least one hydraulic member configured to straighten speed field lines of a concentrate flow and / or a water flow to be treated so as to make them substantially parallel to each other and parallel to the first substantially vertical axis, and arranged in the tank at the lower tapping and / or at the upper tapping, the hydraulic member extends over at least 20% of the lower wall and / or the upper wall, preferably at least 50% of the lower wall and / or the upper wall, the hydraulic member is formed by at least one perforated plate extending at least partly through an upper opening delimited by the upper tapping and / or a lower opening delimited by the lower tapping,the treatment device comprises several tanks, each tank being connected to the conduit for discharging the concentrate to the tank and to the conduit for extracting the concentrate from the tank, the tanks are sized so as to receive a portion of the concentrate, the cumulative volumes of the tanks being substantially equal to the volume of concentrate to be discharged from the reverse osmosis membrane unit, the treatment device comprises at least one pressurization member configured to increase the pressure of water passing through the conduit for supplying the water to be treated and the reverse osmosis membrane unit so as to obtain a water pressure of the water to be treated greater than the osmotic pressure of the water to be treated, and the treatment device comprises means for measuring a flow rate of permeate extracted from the treatment device,the pressurizing member being configured to adjust the water pressure relative to the flow rate of permeate extracted from the treatment device.,

[0016] The invention also relates to a method for treating water to be treated using a treatment device according to the invention, the treatment method comprising repeating, at least once, the following steps:

[0017] - a recirculation stage in which the water to be treated circulates several times in the reverse osmosis membrane unit by passing through the recirculation loop,

[0018] - a purging step in which the concentrate is brought to the tank via the lower tapping and water to be treated stored in the tank is sent to the water supply pipe to be treated via the upper tapping, and

[0019] - a recharging stage in which the concentrate is evacuated from the treatment device through the lower tapping and the tank is filled with water to be treated through the upper tapping.

[0020] According to other optional features of the treatment device taken alone or in combination: the concentrate is brought to the tank and removed from the tank from a lowest point of the lower wall, and water to be treated is brought to and removed from the tank via a highest point of the upper wall, the treatment method comprises a step of regulating the speed of entry of the concentrate and / or of the water to be treated into the tank, the speed of entry of concentrate and / or of water to be treated into the tank is between 0.04 m / s and 0.30 m / s, and the treatment method comprises a step of straightening the speed field lines of a concentrate flow and / or of a water flow to be treated so as to make them substantially parallel to each other and parallel to the first substantially vertical axis. Brief description of the figures

[0021] The invention will be better understood on reading the following description, given solely by way of example and with reference to the appended drawings in which:

[0022] is a schematic representation of a desalination device according to a first embodiment of the invention, during a concentrate recirculation step,

[0023] is a schematic representation of a desalination device according to a first embodiment of the invention, during a concentrate evacuation step,

[0024] is a schematic representation of a desalination device according to a first embodiment of the invention, during a concentrate extraction step,

[0025] is a schematic representation of a desalination device according to a second embodiment of the invention,

[0026] is a schematic representation of a desalination device according to a third embodiment of the invention, and

[0027] is a flowchart of a treatment method according to the invention. Detailed description

[0028] Reference is now made to the illustrating a treatment device 2 for water to be treated according to a first embodiment of the invention. The water treatment device 2 is a continuous desalination device, in the sense that it allows seawater to be desalinated continuously, and in a closed or semi-closed loop, in the sense that an initial volume of raw water to be treated will be treated several times, and that a replacement of the concentrate is carried out by a supply of a new volume of water to be treated from an additional tank.

[0029] "Water to be treated" means seawater, brackish water or treated water from a treatment plant. More generally, it can be any water that can be treated by desalination (reduction of the ionic charge).

[0030] The treatment device 2 comprises a reverse osmosis unit which may comprise at least one first pressure tube 4 comprising at least one desalination module 6 (two in FIGS. 1 to 6) formed by at least one semi-permeable membrane, for example reverse osmosis, the pressure tube 4 being configured to extract a permeate from water to be desalinated, whether it is water to be treated or recirculated concentrate. The desalination modules 6 comprise semi-permeable membranes allowing water to pass through and retaining, among other things, salt when the water pressure of the water passing through them is greater than the osmotic pressure of this water.The membranes of the different desalination modules 6 may be identical or have different permeabilities and / or rejection rates, for example: membranes with lower permeability may be used at the head of the pressure tube 4, and membranes with higher permeability at the end of the pressure tube 4. A permeate extracted from the water to be desalinated is extracted from the treatment device 2 (arrow 3 in figures 1 to 6).

[0031] The treatment device 2 comprises at least one conduit 8 for supplying water to be treated to the reverse osmosis membrane unit. This conduit can be supplied with water to be treated by a feed pump 10. A first filter 12, for example a cartridge filter, can be placed downstream of the feed pump 10 in order to retain the impurities present in the raw seawater before the water to be treated enters the conduit 8 for supplying water to be treated, and this in order to limit the fouling of the treatment device 2, in particular of the reverse osmosis membrane unit.

[0032] At least one pressurizing member 14 (for example a high-pressure pump) is configured to increase the pressure of water passing through the water supply pipe to be treated 8 and the reverse osmosis membrane unit so as to obtain a water pressure greater than the osmotic pressure of the water passing through the reverse osmosis membrane unit. This pressurizing member 14 is placed, in the figures, downstream of the filter 12 and sends the water to be treated (raw water and / or concentrate) to the reverse osmosis membrane unit with sufficient pressure to allow desalination of the water passing through the pressure tube 4, at least at the head of the pressure tube 4. The treatment device 2 therefore comprises means for measuring the flow rate of permeate extracted from the treatment device 2 to be able to adjust the water pressure in order to ensure extraction of permeate while avoiding excessive energy consumption.More precisely, and after observing a reduction in the permeate flow rate, the flow rate of the pressurizing member 14 is increased so as to increase the water pressure and thus ensure satisfactory permeate extraction by overcoming the production resistance, in particular the osmotic pressure.

[0033] The treatment device 2 comprises an outlet conduit 16 for the concentrate from the reverse osmosis membrane unit. This conduit may comprise a recirculation pump 18 for recirculating the concentrate or for evacuating it, as described below.

[0034] The treatment device 2 comprises at least one conduit forming a recirculation loop 20 directly connecting the water supply pipe to be desalinated 8 and the outlet pipe 16 of a concentrate from the reverse osmosis membrane unit so as to allow a return of the concentrate to the latter. By "directly" is meant the fact that the recirculation loop 20 connects the water supply pipe to be desalinated 8 and the outlet pipe 16 of a concentrate without the presence of an intermediate pipe or even a buffer tank. Thus, the concentrate leaving the reverse osmosis membrane unit and which can still be treated passes through the recirculation loop 20, is pressurized by the pressurization member 14 to a pressure allowing an extraction of permeate from the water passing through the reverse osmosis membrane unit.A first valve 22, typically a pneumatic valve, is placed at the level of the recirculation loop 20 in order to authorize or prohibit the recirculation of the concentrate through the recirculation loop and this depending on the achievement of a target for stopping the recirculation of the concentrate: achievement of a ceiling water pressure (for example equal to 60 bars), of a predefined salinity of the concentrate, of a predefined time interval, etc.

[0035] The treatment device 2 further comprises a tank 24 delimiting a storage volume, typically of water to be treated or concentrate. This tank 24 makes it possible to store seawater on standby during recirculation of the concentrate in the desalination device 2. When it is no longer relevant to recirculate the concentrate in the reverse osmosis membrane unit, the latter can be sent to the tank 24 to take the place of the water to be treated, which is in turn sent to the reverse osmosis membrane unit, as will be described later.

[0036] The treatment device 2 also comprises at least one conduit 26 for discharging the concentrate to the tank 24, from the conduit 16 for discharging the concentrate from the reverse osmosis membrane unit, and at least one conduit 26' for extracting the concentrate from the tank 24 and from the treatment device 2. These conduits make it possible to send the concentrate at the outlet of the reverse osmosis membrane unit to the tank 24 or to cause the concentrate to leave the treatment device 2 by extracting it from the tank 24.It comprises a second valve 28 and a third valve 30: The second valve 28 placed on the conduit 26 for discharging the concentrate to the tank 24 and intended to have an open / closed state opposite to that of the first valve 22 and this in order to direct the concentrate leaving the reverse osmosis membrane unit, the latter via the recirculation loop 20 or towards the tank 24 thanks to the conduit for discharging the concentrate to the tank 24 and extracting the concentrate from the tank 24. The third valve 30 present on the conduit 26' for extracting the concentrate from the tank 24 and from the treatment device 2 and which allows, when it is open, to extract the concentrate from the treatment device 2.

[0037] The treatment device 2 further comprises at least one conduit 32 for sending water to be treated stored from the reservoir 24 to the conduit 8 for supplying water to be treated and at least one conduit 32' for recharging the reservoir 24 with water to be treated. The conduit 32 for sending water to be treated stored from the reservoir 24 to the conduit 8 for supplying water to be treated allows, when the concentrate takes the place of seawater in the reservoir 24, to send the latter to the reverse osmosis membrane unit through the conduit 8 for supplying water to be treated. It comprises a fourth valve 34 authorizing or prohibiting the passage of water to be treated from the conduit 32 for sending water to be treated stored from the reservoir 24 to the conduit 8 for supplying water to be treated.The 32' conduit for recharging the tank 24 with water to be treated allows water to be treated to enter the treatment device 2 in order to refill the tank 24 with water to be treated and to replace the concentrate stored inside the tank 24.

[0038] A refill pump 36, placed on the pipe 32' for refilling the tank 24 with water to be treated, is provided in order to refill the tank 24 with water to be treated as will be described later. A second filter 38, for example a cartridge filter, also makes it possible to prevent the entry of impurities present in the water to be treated entering the treatment device 2. Finally, an isolation pump 42 is placed downstream of the second filter 38 so as to allow communication between the pipe for refilling the tank with water to be treated 32' and the tank 24 (with closing of the fourth valve 34) when refilling the tank 24 with water to be treated and replacing the concentrate.

[0039] According to the invention, and as can be seen in the, the reservoir 24 extends mainly along a first substantially vertical axis A. The reservoir 24 comprises a lower wall 46, an upper wall 48 located above the lower wall 46 along the first axis A, and a side wall 50 connecting the lower wall 46 to the upper wall 48.

[0040] The tank 24 further comprises a lower tapping 52 located on the lower wall 52 and fluidly connected to the concentrate discharge conduit 26 and an upper tapping 54 located on the upper wall 48 and fluidly connected to the conduit 32 for sending the water to be treated. In other words, the concentrate discharge conduit 26 is connected below the tank 24, and the conduit 32 for sending the water to be treated is connected above the tank 24.

[0041] As explained previously, this configuration of tank 24 makes it possible to obtain a piston effect limiting the concentrate / water mixture to be treated in tank 24.

[0042] The side wall 50 can advantageously be of the general shape of a cylinder of revolution.

[0043] The lower tapping 52 delimits at least one lower opening for the passage of the concentrate towards the storage volume of the tank 24. The upper tapping 54 delimits at least one upper opening for the passage of the water to be treated towards the storage volume of the tank 24.

[0044] The number of tappings made at the level of the lower 46 and upper 48 walls may be greater than a single tapping, in particular in the case where several tappings would allow a better distribution of the concentrate and / or the water to be treated entering the tank 24.

[0045] The reservoir 24 therefore has a height greater than its width. The fact that the reservoir 24 is taller than it is wide makes it possible to maximize the piston effect described above by minimizing the contact surface between the two liquids in favor of the vertical displacement of the latter. Advantageously, the reservoir 24 is formed by an external casing of a pressure tube placed vertically to meet the aforementioned dimension criterion. Several external casings of pressure tubes placed vertically and connected in parallel can be used as reservoirs 24.

[0046] Advantageously, the lower tapping 52 is located at the lowest point of the lower wall 46 of the tank 24, and the upper tapping 54 is located at the highest point of the upper wall 48 of the tank 24. This makes it possible to amplify the limitation of the mixing by ensuring an absence of water to be treated under the lower tapping 52 and an absence of concentrate above the upper tapping. The terms “top” and “bottom” are understood relative to the vertical direction.

[0047] As explained above, the treatment device 2 comprises several valves and pumps making it possible to obtain different operating configurations. More generally, the treatment device comprises a set of control members configured to obtain: a recirculation configuration in which the water to be treated circulates several times in the reverse osmosis membrane unit by passing through the recirculation loop 20, a purge configuration in which the concentrate is brought to the tank 24 via the lower tapping 52 and water to be treated stored in the tank 24 is sent to the supply pipe for the water to be treated 8 via the upper tapping 54, and a refill configuration in which the concentrate is evacuated from the treatment device 2 via the lower tapping 52 and the tank 24 is filled with water to be treated via the upper tapping 54.

[0048] For example, it is possible to list as control organs of the treatment device 2 means for adjusting the parameters of its operation such as the valves and pumps described above or additional ones, sensors for measuring parameters such as conductivity or water pressure, etc.

[0049] Advantageously, the lower 52 and upper 54 tappings are arranged so as to inject the concentrate and / or the water to be treated inside the tank 24 in a direction substantially parallel to the first axis A. This makes it possible to ensure that liquid enters the tank 24 under conditions conducive to obtaining a plug flow.

[0050] Illustrates a second embodiment of the invention that can be implemented as an alternative to the first embodiment of the invention or as a complement to the latter. In this embodiment of the invention, the reservoir 24 comprises at least one hydraulic member 40 configured to straighten velocity field lines respectively of the concentrate flow and of the water flow to be treated so as to make them substantially parallel to each other and parallel to the first substantially vertical axis. In other words, and upstream of the hydraulic member, the velocity field lines of the concentrate flow and / or water to be treated are disordered. Downstream of the hydraulic member 40, the velocity field lines of the flow are substantially parallel to each other. A certain linearization is therefore obtained in the movement of concentrate and / or water to be treated in the reservoir 24.In the example illustrated in , the tank 24 comprises two hydraulic members 40, one at the concentrate inlet, and arranged at the lower tapping 52, and the other at the water inlet to be treated and arranged at the upper tapping 54. These hydraulic members 40 make it possible to limit the turbulence generated by the inlet of a liquid and therefore to avoid mixing between the two liquids.

[0051] The hydraulic member(s) 40 may also act as a diffusion member for a flow entering the reservoir 24 (concentrate or water to be treated) in order to spread the entry of said flow into the reservoir 24 over a significant portion of the lower wall 46 and / or the upper wall 48 and thus optimize the piston effect. For example, the hydraulic member 40 may extend over at least 20% of the lower wall 46 and / or the upper wall 48, preferably at least 50% of the lower wall 46 and / or the upper wall 48 to distribute the concentrate and / or water to be treated in a plane substantially perpendicular to the first axis A.

[0052] For example, the hydraulic member(s) 40 may be formed by at least one perforated plate extending at least partly through an upper opening delimited by the upper tapping 54 and / or a lower opening delimited by the lower tapping 52. Thus, the liquid entering the reservoir 24 is slowed down and can only pass through the orifices of the perforated plate. The liquid passing through the orifices will only generate slight local turbulence after passing through the perforated plate. Depending on the dimensions of the perforated plate(s), the incoming liquid may also be distributed as explained above.

[0053] Alternatively, the hydraulic member 40 may be formed by a perforated pipe extending inside the tank 24, the perforations being sized to allow the entry of concentrate or water to be treated into the tank 24 while avoiding the formation of turbulence upon entry of the liquid in question. Generally speaking, any type of jet breaker may be considered.

[0054] The invention illustrates a third embodiment of the invention which can be implemented as an alternative to the first two embodiments of the invention or in addition to them. According to this embodiment of the invention, the treatment device 2 comprises several tanks 24, each tank 24 being connected to the concentrate discharge conduit 26 towards the tank 24 and to the concentrate extraction conduit 26' from the tank 24 and the treatment device 2. This allows a certain freedom of dimensioning of the treatment device 2.

[0055] It is possible to provide that each of the tanks 24 receives a portion of the concentrate, the cumulative volumes of the tanks 24 being substantially equal to the volume of concentrate to be evacuated from the reverse osmosis membrane unit. Alternatively, it is possible to use only a portion of the tanks 24 when replacing water to be treated with concentrate and to keep the others for later replacement.

[0056] According to a fourth embodiment of the invention (not shown in the figures), and which may be an alternative or a complement to the three previous ones, the treatment device 2 may comprise means for regulating an inlet speed of concentrate and / or water to be treated in the tank 24. The regulation of the inlet speed makes it possible to prevent the liquid entering the tank 24, whether it is concentrate or seawater, from entering with an excessive speed which promotes the mixing of the liquids. Preferably, the means for regulating an inlet speed of concentrate and / or water to be treated in the tank 24 are configured to regulate an inlet speed of concentrate and / or water to be treated in the tank 24 between 0.04 and 0.30 m / s. The speed of movement of the concentrate and / or water to be treated in the tank 24 is preferably between 1 mm / s and 50 mm / s.

[0057] The means for regulating an inlet speed of concentrate and / or water to be treated in the tank 24 can be passive (it is for example possible to adjust the diameter of the different conduits connected to the tank 24 in addition to the configuration of the different pumps sending a liquid to the tank 24) and / or active (use of a pressure and / or flow regulator).

[0058] It should also be noted that the hydraulic member(s) 40 can, depending on their action (for example if it is a perforated plate), also regulate the speed of entry of a liquid into the reservoir 24.

[0059] The different valves of the treatment device 2 lead, as explained above, to isolating different compartments of the latter, which leads to the existence of different, even very different, pressures between different compartments.

[0060] For example, and during the recirculation of the concentrate for extraction of permeate, it is possible that the pressure upstream of the second valve 28 is very high, for example 60 bars, while the pressure downstream of the latter may be equal to atmospheric pressure. To avoid a shock at the time of opening, it is possible to put in place a bypass around the second valve 28, this bypass comprising a valve smaller than the second valve 28. This valve can be opened a few seconds before the second valve 28 so as to balance the pressures on either side of the second valve 28 so that the opening of the latter (at the same time as an opening of the fourth valve 34 to send water to be treated stored in the tank 24 to the first pressure tube 4), at the time when the concentrate is sent to the tank 24, does not lead to a shock.

[0061] A bypass of the same type can be placed around the third valve 30 for activation when the concentrate stored in the tank 24 is replaced by water to be treated. To do this, the isolation valve 42 is opened and the recharging pump 36 is activated to return water to be treated to the tank 24. The third valve 30 must be open to allow the extraction of the concentrate from the treatment device 2. Here again, the pressure upstream of the third valve 30 can be very high, for example 60 bars, while the pressure downstream of the latter can be equal to atmospheric pressure. A bypass can again be arranged on either side of the third valve 30, like the one that can be placed around the second valve 28, in order to rebalance the pressures on either side of the third valve 30.

[0062] We will now describe the processing method 56 resulting from the implementation of a processing device according to the invention with the support of figures 1 to 3 illustrating the operation of the method according to the first embodiment of the invention.

[0063] Illustrates the treatment device during a recirculation step 58 of the concentrate.

[0064] During this step, the water to be treated is recirculated several times in the recirculation loop 20 by means of the recirculation pump 18, as illustrated by the directional arrows 44 present on the. More precisely, it is raw water during the first pass then increasingly concentrated concentrate during the successive passes. The first valve 22 is open to allow the concentrate to pass through the recirculation loop 20, and the second valve 28 is closed to prevent the concentrate from leaving the recirculation loop 20.

[0065] At each passage through the reverse osmosis membrane unit and more precisely the desalination modules 6, the permeate is extracted from the water to be treated and is extracted from the treatment device 2 (directional arrow 44 on the arrow 3). The concentrate, for its part, becomes increasingly concentrated in salt. There is therefore a progressive increase in the salinity of the concentrate, which requires a progressive increase in the pressure in the main loop, an increase ensured by the pressurization member 14. There is also a loss of water volume linked to the production of permeate which is extracted from the recirculation loop 20 through the desalination module(s).In order to compensate for the loss of volume linked to the production of permeate, the feed pump 10 can provide a flow rate of seawater to be treated identical to the flow rate of permeate by ensuring the necessary increase in pressure (with a possible supplement from the pump acting as a pressurization member 14) in order to maintain the production of permeate constant.

[0066] Once the maximum salt concentration is reached (or after reaching a predefined conversion rate or a predefined time), the second step (i.e. the purge step 60) of the process is initiated. This step is illustrated in the.

[0067] Once the maximum recovery rate of the cycle has been reached (determined by pressure, conductivity, volume or time), i.e. once it is deemed no longer relevant to circulate the concentrate again in the recirculation loop 20, the concentrate must be evacuated before restarting a new treatment cycle. For this, the recirculation loop 20 is closed (for example by closing the first valve 22, the third valve 30 remaining closed to prevent any exit of the concentrate from the treatment device 2) and the concentrate directed to the concentrate discharge conduit 26 towards the tank 24, from the concentrate outlet conduit 16 of the first pressure tube 4 (for example by opening the second valve 28).

[0068] The conduit 26 allows the concentrate to be directed to the reservoir 24, more particularly to the lower tapping 46, in which water to be treated is stored, preferably pressurized water. When the concentrate reaches the reservoir 24, it pushes the water to be treated from below into the delivery conduit 32 and through the upper tapping. The fourth valve 34 is opened to allow this. The water to be treated extracted from the reservoir 24 therefore replaces the concentrate in the recirculation loop 20, while the latter is now stored in the reservoir 24. The system is therefore both purged (of concentrate) and filled (with fresh water to be treated) in order to reduce this purge time and thus minimize the loss of production. In parallel, water to be treated from the feed pump 10 can also be injected into the treatment device 2 for the reasons mentioned above.

[0069] The structure of the treatment device 2 according to the invention makes it possible, as explained previously, to limit the concentrate / seawater mixture, which makes it possible to limit as much as possible the contribution of salt in the water to be treated replacing the concentrate in the recirculation loop 20, and thus to limit the water pressure to be applied during the first passage of the water to be treated in the reverse osmosis membrane unit while maximizing the number of passages of the water through the latter.

[0070] A recharging step 62 of the tank 24 follows the purging step 60 above. This step can be carried out in parallel with a permeate extraction as described above. Indeed, the second and fourth valves 28 and 34 are closed while the first valve 22 is open, which makes it possible to isolate the recirculation loop 20. In parallel with this, the third valve 30 is open, as is the isolation valve 42, and the recharging pump 36 supplies the recharging pipe 32' of the tank 24 with water to be treated.

[0071] Water to be treated replaces the concentrate in the tank 24, with possible pressurization of the water stored in the tank 24. The invention also makes it possible, during this replacement, to limit a mixture of seawater and concentrate. The opening of the third valve 30 makes it possible to extract the concentrate from the treatment device 2 by passing the concentrate through the lower tapping 52 the conduit 26' for extracting the concentrate from the tank 24 and the treatment device 2. The tank 24 therefore again comprises water to be treated, entered through the upper tapping 54, ready to replace a concentrate that is too concentrated in salt during a subsequent purging step.

[0072] The method according to the invention may further comprise steps of regulating the speed of entry of the concentrate and / or of the water to be treated into the tank 24, and / or a step of straightening the speed field lines of a flow of concentrate and / or of a flow of water to be treated so as to make them substantially parallel to each other and parallel to the first substantially vertical axis.

[0073] The invention is not limited to the embodiments presented and other embodiments will become clear to those skilled in the art. It is in particular possible to provide a conduit architecture different from that shown in the figures, with interdependent or fully separate conduits. It is also possible to provide a set of pumps making it possible to obtain the liquid movements described above. List of references

[0074] 2: processing device

[0075] 3: permeate extraction

[0076] 4: first pressure tube

[0077] 6: desalination module

[0078] 8: water supply pipe to be treated

[0079] 10: feed pump

[0080] 12: first filter

[0081] 14: pressurization organ

[0082] 16: outlet pipe for a concentrate from the reverse osmosis membrane unit

[0083] 18: recirculation pump

[0084] 20: recirculation loop

[0085] 22: first valve

[0086] 24: tank

[0087] 26: Concentrate discharge pipe to the tank

[0088] 26': Concentrate extraction pipe from the tank

[0089] 28: second valve

[0090] 30: third valve

[0091] 32: pipe for sending water to be treated from the tank to the pipe for supplying water to be treated

[0092] 32': pipe for recharging the tank with water to be treated

[0093] 34: fourth valve

[0094] 36: refill pump

[0095] 38: second filter

[0096] 40: hydraulic organ

[0097] 42: isolation valve

[0098] 44: directional arrows

[0099] 46: lower wall

[0100] 48: upper wall

[0101] 50: side wall

[0102] 52: lower stitching

[0103] 54: upper stitching

[0104] 56: treatment method

[0105] 58: recirculation stage

[0106] 60: Purge step

[0107] 62: reloading step

[0108] 64: regulation step

[0109] 66: recovery step

[0110] A: vertical axis

Claims

Device (2) for treating water to be treated by closed-circuit reverse osmosis comprising:a reverse osmosis membrane unit configured to produce a permeate and a concentrate from the water to be treated,at least one conduit for supplying the water to be treated (8) to the reverse osmosis membrane unit,at least one outlet conduit (16) for the concentrate from the reverse osmosis membrane unit,at least one conduit forming a recirculation loop (20) connecting the conduit for supplying the water to be treated (8) and the outlet conduit (16) for a concentrate from the reverse osmosis membrane unit so as to allow a return of the concentrate to the reverse osmosis membrane unit,at least one reservoir (24) delimiting a storage volume,at least one evacuation conduit (26) for the concentrate towards the reservoir (24), from the outlet conduit (16) of the concentrate of the reverse osmosis membrane unit, and at least one extraction conduit (26') of the concentrate from the tank (24),at least one conduit (32) for sending water to be treated stored in the tank (24) to the conduit for supplying the water to be treated (8) and at least one conduit (32') for recharging the tank (24) with water to be treated, characterized in that the tank (24) extends mainly along a first substantially vertical axis (A), the tank comprising a lower wall (46), an upper wall (48) located above the lower face (46) along the first axis (A), and a side wall (50) connecting the lower wall (46) to the upper wall (48), the tank (24) further comprising a lower tapping (52) located on the lower wall (46) and fluidly connected to the evacuation conduit (26) of the concentrate and an upper tapping (54) located on the upper wall (48) and fluidly connected to the conduit (32) for sending the water to be treated., Treatment device (2) according to claim 1, in which the side wall (50) is of general shape of a cylinder of revolution. Treatment device (2) according to any one of the preceding claims, in which the lower tapping (52) is located at the lowest point of the lower wall of the tank (24), and the upper tapping (54) is located at the highest point of the upper wall of the tank (24). Treatment device (2) according to any one of the preceding claims, comprising a set of control members (22, 28, 30, 34) controlled to obtain: a recirculation configuration in which the water to be treated circulates several times in the reverse osmosis membrane unit by passing through the recirculation loop (20), a purge configuration in which the concentrate is brought to the reservoir (24) by the lower tapping (52) and water to be treated stored in the reservoir (24) is sent to the supply pipe for the water to be treated (8) by the upper tapping (54), and a recharging configuration in which the concentrate is evacuated from the treatment device (2) by the lower tapping (52) and the reservoir (24) is filled with water to be treated by the upper tapping (54). Treatment device (2) according to any one of the preceding claims, comprising means for regulating an entry speed of the concentrate and / or the water to be treated into the tank (24). Treatment device (2) according to the preceding claim, wherein the means for regulating an inlet speed of the concentrate and / or water to be treated into the tank (24) are configured to regulate an inlet speed of concentrate and / or water to be treated into the tank (24) between 0.04 m / s and 0.30 m / s. Treatment device (2) according to any one of the preceding claims, comprising means for regulating a speed of movement of the concentrate and / or the water to be treated in the tank (24), preferably configured to regulate a speed of movement of the concentrate and / or the water to be treated in the tank (24) is between 1 mm / s and 50 mm / s. Treatment device (2) according to any one of the preceding claims, in which the reservoir (24) comprises at least one hydraulic member (40) configured to straighten velocity fields of a concentrate flow and / or a water flow to be treated so as to make them substantially parallel to each other and parallel to the first axis (A), and arranged in the reservoir (24) at the level of the lower tapping (52) and / or at the level of the upper tapping. Treatment device (2) according to the preceding claim, in which the hydraulic member (40) extends over at least 20% of the lower face (46) and / or the upper face (48), preferably at least 50% of the lower face (46) and / or the upper face (48). Treatment device (2) according to any one of claims 8 or 9, in which the hydraulic member (40) is formed by at least one perforated plate extending at least partly through an upper opening delimited by the upper tapping (54) and / or a lower opening delimited by the lower tapping (52). Treatment device (2) according to any one of the preceding claims, comprising several tanks (24), each tank (24) being connected to the concentrate discharge conduit (26) towards the tank (24) and to the concentrate extraction conduit (26') from the tank (24). A method of treating (56) water to be treated using a treatment device (2) according to any one of the preceding claims, the treatment method (56) comprising repeating, at least once, the following steps: a recirculation step (58) in which the water to be treated circulates several times in the reverse osmosis membrane unit by passing through the recirculation loop (20), a purging step (60) in which the concentrate is brought to the tank (24) via the lower tapping (52) and water to be treated stored in the tank (24) is sent to the supply pipe for the water to be treated (8) via the upper tapping (54), and a recharging step (62) in which the concentrate is evacuated from the treatment device (2) via the lower tapping (52) and the tank (24) is filled with water to be treated via the upper tapping (54). Treatment method (56) according to claim 12, wherein the inlet speed of concentrate and / or water to be treated into the tank (24) is between 0.04 m / s and 0.30 m / s. Treatment method (46) according to one of claims 12 or 13, comprising a step of regulating (64) the speed of entry of the concentrate and / or the water to be treated into the tank (24). Treatment method (56) according to any one of claims 12 to 14, comprising a step of straightening (66) the velocity field lines of a concentrate flow and / or a water flow to be treated so as to make them substantially parallel to each other and parallel to the first axis (A).

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