FR2484391A1 - Desalination of sea-water by reverse osmosis under hydrostatic pressur - via membrane into vessel submerged at more than 300 m in sea-water - Google Patents

Abstract

A process and equipment for desalination of seawater etc. to provide drinking water takes place by reverse osmosis via a semi-permeable membrane leading into a pressure vessel. The vessel is immersed in the water at a depth which provides a hydrostatic pressure on the membrane in excess of the osmotic pressure of the seawater. The initial pressure inside the vessel before entry of purified water is adjusted to a value which is less than the difference between the hydrostatic and the osmotic pressure. This value is pref. equal to atmospheric pressure. Pref. the vessel with membrane is submerged to a depth of more than 300 metres in seawater having a salinity of between 30 and 40 g/l. Esp. the vessel is submerged at a depth between 350 and 750 m. The equipment is self-contained, requiring no power supply for pumps etc. The equipment is simple to operate and requires negligible maintenance.

Description

PRODUCTION PROCESS AND DEVICE
FRESHWATER FROM SEAWATER
The invention relates to a method for producing fresh water from sea water; it extends to devices for implementing this process.

 There are many methods for desalinating seawater, but these methods are generally complex to implement, require bulky and expensive installations, and a high power source of energy.

 For example, none of these methods is suitable for obtaining fresh water from a small-gauge boat and no existing desalination plant lends itself to miniaturization which would allow its use as a survival accessory in case of sinking.

 The present invention proposes to indicate a new process for ~ production of fresh water from sea water, which has great flexibility to adapt to the requirements of multiple applications with many advantages such as low cost , miniaturization faculty, possibility of implementation without energy source for miniaturized installations, reduced operating and maintenance costs for larger installations ...

 The process of the invention calls upon the now well known phenomenon of reverse osmosis through a selective semi-permeable membrane. Currently, the known methods which make use of this phenomenon consist in sending a flow of salt water at high pressure, greater than the osmotic pressure in an envelope equipped with a membrane of an appropriate nature, and the essential conditions for implementing these processes lie in the high value of the flow pressure (the osmotic pressure proportional to the salinity being very high for seawater) and in the obligation to create a continuous current of water at the surface of the membrane (to avoid increase in the salinity of the water in the vicinity of said membrane); these conditions impose the presence of powerful pumping groups from which the essential drawbacks of these installations arise.

 For example, for seawater with an average salinity of 35 g / l, the osmotic pressure is 25 bars and, if we assume a conversion rate of around 25%, it is necessary for each m3 of fresh water produced, to pump 4 m3 of salt water and bring it to a pressure of the order of 50 to 60 bars.

 It is obvious that these subjects would lead to costly and energy-consuming installations and, in practice, solutions other than reverse osmosis are currently chosen by specialists when it is necessary to desalinate seawater or neighboring salinity.

In addition, it is completely inconceivable that the current reverse drosmosis processes can be implemented on small boats which would not have the necessary power and, all the more reason, on rescue boats devoid of any energy source.

 An object of the invention is to indicate a new process which uses the phenomenon of reverse osmosis, but is not subject to the above-mentioned drawbacks or limitations of conventional processes.

 An object of the invention is in particular to provide a device of small bulk which makes it possible to produce fresh water on a boat in the absence of energy source, such a device being able in particular to equip rescue boats to constitute a survival accessory in case of sinking.

 Another objective is to allow the production of installations providing medium or high freshwater flow rates under very improved operating conditions compared to conventional installations.

 In particular, the invention aims to reduce, for a given flow rate, the cost, size and energy consumption of said installations by eliminating the pumping units which are necessary in conventional methods.

To this end, the process according to the present invention for the production of fresh water from sea water, consists in carrying out a reverse osmosis in the heart of sea water through at least one selective semi-permeable membrane. , submerged at a depth H corresponding to a pressure
P greater than the osmotic pressure PO of the sea water, to collect the fresh water having diffused through the membrane in a sealed tank whose internal pressure is initially adjusted to a value p less than P-PO, and to rise the tank on the surface to take fresh water.

 The invention extends to a device suitable for implementing this method; this device essentially comprises a sealed reservoir and at least one module with selective semi-permeable membrane, fixed on said reservoir so that one active face of the membrane communicates with the interior of the reservoir and that the other active face communicates with the outdoor environment.

 By "active faces" of the membrane is meant the parts of these which, in the process of reverse osmosis, form, on the one hand, the interface with salt water, on the other hand, the interface with pure water. For a flat membrane formed by layers of selective semi-permeable material, these active faces are formed by the two opposite flat faces of the membrane. For a membrane wound on itself in a spiral, they are constituted, on the one hand, by the two external walls in the form of a spiral of the membrane and, on the other hand, by the two internal walls of the latter. For a capillary hollow fiber membrane, they are formed, on the one hand, by the external cylindrical surfaces of the fibers, on the other hand, by the internal cylindrical surfaces of their capillary channel.

 The invention can be implemented with any type of osmotic membrane, made using any type of suitable material, in particular material based on cellulose acetate or aromatic polyamides.

 The device in accordance with the invention is immersed from the surface in sea water to the depth H and is left at this depth for the time necessary to fill the reservoir at least partially, the fresh water then being collected, by raising the tank to the surface and by withdrawing the water contained therein with the aid of withdrawal means with which said tank is equipped.

 Initially, it is possible to establish inside the tank a legal pressure at atmospheric pressure; this pressure is established naturally when the tank is on the surface.

 For example, for seawater with a usual salinity of between 30 g / l and 40 g / l, the reservoir and its osmotic membrane (s) are submerged to a depth greater than 300 meters, in particular between 350 and 750 meters . Immersion and ascent can be easily carried out using a wire or cable to which said tank is suspended.

 Thus, the method of the invention eliminates the pumping groups of the known installations and the associated drawbacks. It can be implemented by means of a simple structure device, which; is adapted in each case to the desired bit rates and can be miniaturized for applications requiring low bit rates.

For example, this device can constitute an equipment anodes. small gauge boat or emergency boat to ensure the occupants' water consumption in the absence of any source of power. The reservoir then has a capacity of between approximately 0.5 and 15 liters with one or more small osmotic modules mounted thereon; it is attached to a thin and resistant wire, length greater than 300 meters, in particular between 300 and 600 meters, this wire being in particular wound on a reel. The user lets the wire unwind to immerse the device, the weight is a few kilo ram es After
e es minu es immersion at the desired depth for a few tens of minutes, the user reassembles the device to take fresh water, the operation can be repeated as necessary.

 The device can also be made on a larger scale to be used from floating devices, such as a floating platform or a boat, and provide large quantities of water either for daily consumption in the case of a boat, or for produce fresh water in the vicinity of the coasts for irrigation or for supplying cities.

 The capacity of the tank can then be between approximately 0 # 5 and 1.5 hot3, a winch and cable system allowing to carry out the descents and ascents. The expiry case of the said necessary will be obtained by providing several posit s operating simultaneously.

 Note that the device according to the invention can also be used in coastal wells of appropriate depth, communicating with the sea.

 It should be noted in the case of installations with high flow rates, that the energy expended to raise each tank is reduced compared to that which would be consumed in the pumping groups of conventional installations of comparable flow rates, in particular because in the process of the invention, the overconsumption of energy due - in conventional processes - to the pumping of volumes of salt water much greater than the volumes of fresh water obtained <conversion rate less than 1) is completely eliminated. Indeed, in the invention, the phenomenon of reverse osmosis is carried out in the heart of the marine environment of infinite extent and no salt saturation is to be feared in the vicinity of the membrane, which eliminates the influence of the factor conversion and limits the energy consumption to that strictly necessary to bring the fresh water produced deep into the surface. In addition, it is possible in the invention to associate the winches with one another to recover the energy for lowering some tanks in order to raise others.

 Note that, in order to avoid any increase, even a slight increase in the salinity near the membrane, it is possible to communicate to the submerged device a movement relative to the other or a rotational movement on itself (especially in the case of implementation on a floating platform), a displacement in the heart of the water (device dragged behind a boat).

 Furthermore, the implementation of the process at significant depths greater than 3U0 meters makes it possible to operate reverse osmosis on unpolluted water and considerably reduces the risks of clogging of the membranes compared to conventional type installations which would use water surface; in practice, these latter installations should be supplemented by means of pretreatment to rid the waters of their pollution before operating reverse osmosis, which would constitute an additional factor of increase in costs.

Other characteristics of the invention are appended which present, by way of nonlimiting examples, several embodiments; on these drawings
FIG. 1 is a partial section view of a device for small flows,
FIG. 2 is a sectional view of another embodiment,
FIG. 3 is a detailed view of the device in FIG. 2,
FIG. 4 is a schematic view illustrating the method of the invention in the case of small flow rates,
FIG. 5 is a diagrammatic section of a device for large flows,
FIG. 6 is a schematic view illustrating the use of the device in FIG. 5 from a floating platform,
- Figure 7 is a schematic view illustrating another embodiment of the invention.

 The device for producing fresh water represented by way of example in FIG. 1 is called upon to supplement the emergency equipment of a small gauge boat, in order to make it possible to supply the fresh water necessary for its occupants in the event of sinking; this device can also be used in the usual way on the boat to produce the fresh water consumed every day by boaters.

This device comprises a reservoir 1, in the spherical example, capable of withstanding pressures greater than 60 bars; this tank is made of an anti-corrosion material, of food quality, in particular stainless steel or glass fibers or any other synthetic material, if necessary transparent. Its capacity is to twist from 1 to 2 liters
it is provided with a ball valve 2 extending by a conduit 3 opening at the bottom of the tank to allow the withdrawal of the water contained therein.

 The reservoir 1 also comprises an opening 1a around which a reverse osmosis module 4 is fixed.

 In the example, this module 4 is essentially constituted by a central tubular manifold 5 which is screwed sealingly on a flange of the reservoir 1, by a membrane 6 wound in a spiral around this manifold and by an external tubular protective element 7 perforated for let the sea water pass freely.

 The central collector 5 is provided permeable (for example pierced with a plurality of holes) to let pass the water having diffused through the membrane 6; it is open at its end situated opposite the opening la and closed at its other end. It is made so as to withstand a pressure greater than 60 bars.

The membrane 6 is a selective semi-permeable osmotic membrane, of a type known per se, in particular Mnembrane ~ en sDiraleS lier / en aceta ee cellulose. Subject to a pressure difference greater than the osmotic pressure between surfaces
external active and internal active faces This membrane is able to let diffuse,
molecules of pure water and retain the salts.

 In addition, a non-return valve 8 of conventional structure is associated with the opening la; this valve is arranged to be opened in the event of overpressure in the manifold 6 and to close in the opposite case when an overpressure appears inside the tank relative to the outside.

 Furthermore, the protective element 7 is fixed at its base to the reservoir and comprises in the upper part a hooking ring 9.

 The reservoir 1 and module 4 assembly is produced so as to have a weight greater than the weight of a volume of water equal to the volume of said assembly. For example, the volume occupied by the assembly can be of the order of 2 to 3 liters, and its weight from 4 to 5 kilograms.

 This assembly is hung by its ring 9 on a wire 10, thin and resistant, (polyamide wire or the like) of length of the order of 500 to 600 meters. This wire is wound on a reel 11 of the fishing reel type, which is carried by the end of a short rod 12; the reservoir 1 and its module 4 are suspended at the other end of the rod by an eyelet through which the wire 10 passes.

 Figures 2 and 3 show another embodiment of a similar device.

 In this embodiment, the reservoir 13 is cylindrical and is associated with a module 14 with hollow capillary fibers. This module comprises a support disc 15 fixed in leaktight manner on the reservoir at the opening of the latter; this support disc 15 which can be seen on an expanded scale in FIG. 3 maintains a multitude of hollow capillary fibers such as 16 made of aromatic polyamide.

 Each fiber 16 forms a loop located in the external medium, with its ends 16a and 16b held by the support disc 15 and passing through it to come opposite the opening of the reservoir 13.

 The support disc 15 can be produced. in a manner known per se in epoxy resin or other material capable of withstanding a pressure greater than 60 bars. The hollow fibers 16 in number of the order of 105 to 106 each have an external diameter of about 80 microns and an internal diameter of 40 microns.

 Such membranes have the advantage of ensuring maximum transfer surfaces per unit of volume and of resisting themselves at high pressures (without having to provide a support of the type of central collector 5 provided in the device of FIG. 1).

The other organs of the device are analogous to those already described (draw-off tap, non-return valve, wire, reel and suspension rod),
FIG. 4 illustrates the use of one or the other of the devices described above from an emergency craft 17. The tank of the device being in the open air at atmospheric pressure, the user unlocks the reel 11 to allow the wire 10 to unwind so as to immerse the device at a depth H of the order of 500 meters. It leaves the device thus immersed at this depth for a period of time of the order of ten to twenty minutes and then reassembles it by means of the reel 11.

 It can then collect the pure water desalted under pressure and contained in the tank by opening the withdrawal valve 2. The amount of water collected of the order of 1 liter depends on the depth and the duration of immersion.

The operation can be repeated indefinitely to meet the needs of the occupants of the boat.

 Note that the rod 12 can be associated with an inflatable buoy, preventing accidental loss of the device.

 FIG. 5 shows another device according to the invention suitable for obtaining large # flows.

 This device comprises a reservoir 18 capable of withstanding high pressures greater than 80 bars. This tank, in the example of a spherical shape, has a capacity of the order of 4 m3.

It has on its wall several openings such as 18a, which are each associated with a reverse osmosis module such as 19. Each module 19 has a structure similar to those already described with larger dimensions. The tank can for example be associated with 6 modu
/ hollow / known type with fiber membrane -, diameter of about 30 cm and a length of about 50 cm each module of this type immersed at 700 meters gives a flow of fresh water about 4 m3 / hour, so that the tank 18 is filled in about 10 minutes
As before, each opening 18a of the tank is equipped with a non-return valve closing in the event of internal overpressure; in addition, the tank comprises means for withdrawing fresh water.

 The reservoir 18 is attached to a cable 20 of high resistance, the length of which can be of the order of 700 to 800 meters and which is wound on a winch.

 A floating platform 21 has been drawn in FIG. 6 provided with several winches which each make it possible to raise and lower a device of the type described above to a depth of the order of 70Xd, meèutrOsudeZour a daily production of the order of 3 000 m3g the platform will be equipped with 16 winches, these winches being associated two by two to recover the energy of descent in order to reduce that consumed for the ascent of the devices. The fresh water thus produced near a coast can be transported by any means, tankers or pipelines.

 FIG. 7 illustrates another embodiment of the method in which a device of the type described above is immersed in a well 22 dug in the vicinity of the sea at a depth at least equal to about 500 to 600 meters, this well being brought to communicate with the expanse of salt water by a channel 23. The device, the reservoir of which will preferably be cylindrical, is immersed in the well by means of a winch as before.

 Of course, the invention is not limited to the terms of the preceding description, but includes all variants thereof. In particular, it can be applied to a submersible, in particular a submarine, to produce the water necessary for its occupants or for machines. One or more membrane modules are attached to the hull of the submarine which acts as a pressure tank p. Fresh water can be collected inside the hull by means of an auxiliary container to which a network of pipes can be connected.

Claims (26)

 1 / - Process for producing fresh water from sea water, characterized in that it consists in carrying out reverse osmosis in the heart of sea water through at least one selective, submerged semi-permeable membrane b a depth H corresponding to a pressure P greater than the osmotic pressure PO of the sea water, to collect X the fresh water having diffused through the membrane in a sealed reservoir whose internal pressure is initially adjusted to a value p lower than P-PO and raise the tank to the surface to take fresh water.  2 / - process for producing fresh water according to claim 1, characterized in that it consists in using a sealed tank provided with at least one selective membrane arranged so that one of the active faces of said membrane communicates with the reservoir and the other active face communicates with the outside, to immerse said reservoir and its selective membrane (s) in seawater at the depth H corresponding to the pressure P greater than the osmotic pressure Po sea water and take the fresh water collected by reverse osmosis in the tank.  3 / - Process for producing fresh water according to one of claims I or 2, characterized in that initially established inside the tank a pressure p equal to atmospheric pressure.  4 / - Process for producing fresh water according to one of claims 1, 2 or 3, characterized in that the reservoir and its membrane (s) are immersed in seawater with a salinity of between 30 g / l and 40 g / l at a depth greater than 300 meters.  5 / - Process for producing fresh water- according to claim 4, characterized in that the reservoir and its or its membranes are immersed at a depth between 350 and 750 meters.  6 / - Process for producing fresh water according to one of claims 1, 2, 3, 4 or 5, characterized in that the tank and its submerged membrane or membranes are subjected to a movement relative to the sea water, in particular movement of movement therein or movement of rotation of the reservoir and its membrane (s) on themselves.  7 / - Process for producing fresh water according to one of claims 1, 2, 3, 4, 5 or 6, characterized in that the reservoir and its or its membranes are immersed in sea water by means of 'A wire or cable to which said tank is suspended, this wire or cable being maintained on the surface.  8 / - A method of producing fresh water according to claim 7, wherein the descent and the ascent of the tank and its membrane (s) are carried out by unwinding or winding the wire or cable on winding means located on the surface.  9 / - A method of producing fresh water according to claim 8, implemented from a floating device, such as a boat or floating platform.  10 / - A method of producing fresh water according to claim 8, implemented from an area located in the vicinity of a body of salt water, characterized in that a well is dug at least deep equal to the depth H, in that this well is brought into communication with the expanse of salt water and in that the tank and its membrane (s) are immersed in this well.  11 / - Process for producing fresh water according to claim 1, characterized in that it is implemented on a submersible, the membrane being fixed on the hull, which acts as a reservoir for the pressure p.  12 / - Device for producing fresh water from sea water, for the implementation of the method according to one of the preceding claims, characterized in that it comprises a sealed tank (1, 18 ) and at least one module (4, 19) with selective semi-permeable membrane, fixed on said reservoir so that one active face of the membrane communicates with the interior of the reservoir and that the other active face communicates with the outside of it.  13 / - Device for producing fresh water according to claim 12, characterized in that each module (4, 19) is fixed around an opening of the reservoir (1, 18) and comprises a membrane support (5, 15 ) tightly secured to the reservoir so that one active face of the membrane (6, 14) communicates with the opening of the reservoir, and that the other active face is located in the external environment.  14 / - Device for producing fresh water according to claim 13, characterized in that each module comprises a membrane (14) constituted by a multitude of hollow capillary fibers (16), each fiber (16) forming a loop located in the external medium with its ends (16a, 16b) held by the support (15) and passing through it to come opposite the opening of the tank.  15 / - Device for producing fresh water according to claim 13, characterized in that each module comprises a membrane (6) wound in a spiral around a central permeable collector (5) forming the above-mentioned support.  16 / - Device for producing fresh water according to one of claims 14 or 15, characterized in that each module comprises an openwork protective external element (7) in which is housed the membrane (6, 14).  17 / - Device for producing fresh water according to one of claims 13, 14, 15 or 16, characterized in that it comprises several modules with semi-permeable membrane, each fixed around an opening of the tank.  18 / - Device for producing fresh water according to one of claims 13, 14, 15, 16 or 17, characterized in that it comprises, associated with each opening of the tank, a non-return valve <8) arranged to close in the event of overpressure inside the tank relative to the outside.  19 / - Device for producing fresh water according to one of claims 12, 13, 14, 15, 16, 17 or 18, characterized in that the tank (1, 18) is equipped with means (2, 3) withdrawal of the water contained therein.  20 / - Device for producing fresh water according to claim 19, characterized in that the withdrawal means comprise a ball valve (2).  21 / - Device for producing fresh water according to one of claims 12, 13, 14, 15, 16, 17, 18, 19 or 20, characterized in that the tank is made so as to withstand higher pressure at around 80 bars.  22 / - Device for producing fresh water according to one of claims 12, 13, 14, 15, 16, 17, 18, 19, 20 or 21, characterized in that the tank and its or its modules are made of so as to have a weight greater than the weight of a volume of water equal to the volume of said tank and its module (s).  23 / - Device for producing fresh water according to one of claims 12, å 22, intended to equip a small gauge boat, in particular to constitute a survival accessory, characterized in that the tank (1, 13) has a capacity approximately between 0.5 and 15 liters and is linked to a thin and resistant wire (10) of length between 300 and 600 meters.  24 / - Device for producing fresh water according to claim 23, characterized in that the wire (10) is wound on a reel (11).  / 25 / - Device for producing fresh water according to claim 24, characterized in that the reel (11) is carried by the end of a short rod (12), the tank and its membrane (s) being suspended from the other end of it by the wire (10>.  26 / - Device for producing fresh water according to one of claims 12 to 22, intended to equip medium or high gauge boats or fixed industrial installations for producing fresh water, characterized in that the tank (18 ) has a capacity approximately between 0.5 and 15 m3 and is linked to a high distance cable (20) wound on a winch.