Method and facility for desalinating water by reverse osmosis

Abstract

The invention relates to a facility and a method for desalinating a water flow by reverse osmosis, which comprises injecting a pressurised gas inside at least one tank that is filled with water to be desalinated, said pressure driving the water flow to the outlet of the tank and towards a semi-permeable membrane frame. Osmosis thus occurs and two water currents are generated, one being treated and desalinated and the other being brine that concentrates all the salt from the original water flow and is a by-product that can be used in the present process. The water flow to be desalinated can be pre-treated by filtration before coming into contact with the driving gas inside the tank, and it is also possible to pass the brine generated by backwashing through the filters before being discarded.

Description

[0001] METHOD AND INSTALLATION FOR DESALINATION OF WATER BY REVERSE OSMOSIS

[0002] DESCRIPTION

[0003] FIELD OF INVENTION

[0004] The present invention falls within the field of water treatment, such as desalination and purification, and specifically refers to a method and installation for desalination of water by reverse osmosis, such as seawater and other brackish waters containing salts such as urban wastewater.

[0005] BACKGROUND OF THE INVENTION

[0006] Water desalination is a treatment process that converts seawater or brackish water into potable water. There are several methods to minimize salinity levels in water: distillation or evaporation, and semipermeable membranes.

[0007] Evaporation processes include the following techniques: flash evaporation and multi-effect distillation. In the case of membrane desalination, which is the most widely used method, reverse osmosis, nanofiltration, and electrodialysis stand out. Currently, the most widely used technique is reverse osmosis, accounting for almost 80% of the total volume of desalinated water.

[0008] Reverse osmosis desalination involves applying mechanical pressure, which varies depending on the saline concentration of the water to be desalinated, from, for example, 25 atmospheres to over 50-60 atmospheres. It typically uses high-pressure pumping equipment that directs the flow to be treated with this force to the membranes, counteracting the natural osmotic pressure and thus filtering the water through semipermeable membranes, which allow the passage of water molecules but not the salts dissolved in them. Nanofiltration, on the other hand, has a very similar principle to reverse osmosis, but there is a substantial difference in the type of semipermeable membranes used, since in this case they allow working with lower pressures, although with a higher cost / performance.

[0009] A conventional seawater treatment plant for desalination is usually made up of the following elements (see Figure 1, state of the art): a collection-feeder tank, which directs the flow of water to be treated towards physical-chemical pre-treatment means, which are usually comprised of: a physical pre-treatment device, for the removal of impurities and solids such as sand, carbon, nanometric filters...and means for post-pretreating the pre-filtered water with chemical additives; before directing the pretreated flow to a high-pressure pump, which increases the pressure of the pretreated water flow to be desalination to above 25 atmospheres, and directs it to a module of one or more semipermeable reverse osmosis membranes, said module comprising two outlets, one for the discharge and another for the desalinated water; the discharge, which is the water concentrated in salt or brine, is either discharged into the sea or recirculated at the inlet of the high-pressure pump, mixing with the pretreated water flow to be desalination; and the water desalinated in the membranes can be subjected to post-treatment, for example with mineral dosing, before completing the treatment process, for its purification.

[0010] Given the high cost of pressurizing the water flow in conventional desalination plants, they are usually equipped with energy recovery systems, through which the generated brine, which is at high pressure, is reintroduced into the water treatment circuit. This reuse is more cost-effective than introducing water with a lower salt concentration into the process. Furthermore, since the brine exits the osmosis process at a still high pressure, this pressure can be recovered by passing the brine flow through energy recovery systems.

[0011] The main disadvantages and problems of osmosis in water treatment are: high cost of installations, a high energy cost per m 3(in addition to the high-pressure pump, the system includes low-pressure pumps in the feed tank and in the receiving tank for desalinated and post-treated water), high maintenance costs for the machinery due to contact with the water to be desalinated and the corrosion it causes; and the high level of pollution generated by the discarded water, the brine, with its high salt content (desalinated water after undergoing osmosis treatment accounts for approximately 40% of the total treated water; the remaining 60% is disposable, with an increased salt content).

[0012] Given these problems detected in conventional methods already known, the present invention proposes an alternative that improves the performance of the desalination process, reducing infrastructure and energy costs.

[0013] DESCRIPTION OF THE INVENTION

[0014] The present invention proposes improving the water desalination treatment process through the use of gas pressure, which makes it possible to replace the high-pressure pumping equipment commonly used (see Figure 1; as previously mentioned, above 25 atmospheres, and more preferably equal to or greater than 50 atmospheres, depending on the degree of salt contained in the water), and thus also avoid the incorporation of energy recovery equipment. Essentially, the high-pressure pump is replaced by a high-pressure system that runs on gas.

[0015] Thus, in a first aspect, the invention relates to a water treatment and purification facility by desalination, comprising: an inlet flow of water to be desalined, with a salt concentration of at least 0.05% by weight of the total weight of water, which may be brackish (salt concentration between 0.05% and 3%) or salty (salt concentration greater than 3%) to be treated; connected to a physical-chemical pre-treatment equipment; connected at its outlet to at least one pressurized water tank, configured to house and propel under pressure the flow of pretreated water to be desalinated, to a module or frame that is formed by one or more semipermeable reverse osmosis membranes, said membranes comprising two outlets, a first one for waste water or brine, which is a discharge, and a second one for desalinated water, which is connected to a post-treatment equipment, configured for the purification of desalinated water;characterized in that: the pressurized water tank comprises, in addition to an inlet for the pretreated water flow: o a gas inlet at a pressure of at least 25 atmospheres (which is the pressure required to perform reverse osmosis with brackish water), preferably at least 50 atmospheres (which is the pressure required to perform reverse osmosis with salt water), which connects the tank to equipment for injecting gas (or a mixture of gases, such as air) under pressure; o an outlet for the pressurized water flow to be desalinate, towards the membrane module or frame, once the gas has transferred its pressure to the water to be desalinate; and / or a pressurized gas outlet, to evacuate the pressurized gas once it has transferred its pressure;and where the pressurized gas injection equipment is formed by: or at least one pressurized tank of high pressure gas (understood as greater than 25 atmospheres), comprising a pressurized gas outlet, said outlet being connected to safety means, such as a valve, which direct the pressurized gas to the gas inlet of the pressurized water tank.;

[0016] For the purposes of this specification, the terms "source water", "water to be treated", "process water", "water to be desalinated" or similar refer to water captured from its source (the sea, a factory) and introduced into the desalination plant described here due to its salt concentration, which may be at least 0.05% by weight of the total water weight, although lower values ​​do not prevent said water from also being treated in the process. The terms used thus generally, but not exclusively, include salt water and brackish water, which differ in their salt concentration.This feature, when explaining the invention, is essential, insofar as, as has already been said, the pressure required to drive the flow of water in the reverse osmosis process will depend on the concentration of salts it contains, with a lower pressure of at least 25 atmospheres being required in the case of brackish water, understood as containing salts in a percentage between 0.05% and 3%, and a higher pressure of at least 50 atmospheres for sea salt water, understood as containing salts in a percentage greater than 3%.

[0017] All percentage values ​​of salts given in the report must be understood as weight of solute per total weight of water (for example, if the water flow has 0.05% salt, it is brackish water in which there are 0.5 grams of salt per 1000 grams of water to be treated).

[0018] Preferably, the high-pressure gas tank is a gas condensation boiler. There are two relevant alternatives for using the injection gas: first, the installation as described can include cryogenic liquefied gas as the injection gas. This gas, housed within the pressurized tank, does not require external pressure input. However, in other embodiments, certain gases that require external pressure input can be used as the injection gas. This is the case, for example, of an air stream, which is a mixture of gases, which is preferred as the most accessible and economical method. However, any other gas or gas mixture that a person skilled in the art knows meets the essential requirements for carrying out the process, that is, for use as a pressure transmission element to the water to be desalinated within the water tank where both fluids are mixed, is not ruled out.In the case of these gases other than cryogenic liquefied gas, the pressurized gas injection equipment also comprises at least one compressor connected to the pressurized gas tank.

[0019] In any case, upon reaching the facility object of the invention, the captured inlet flow of water to be desalination is first passed through the physical-chemical pre-treatment equipment, which may preferably consist of physical treatment means to eliminate impurities as far as possible, which are composed of one or more filters, of those known in the technical field, preferably at least one type of filters selected from the group consisting of: sand filters, carbon filters, nanometric filters and any combination of the foregoing. In addition, it could additionally include chemical pre-treatment means, consisting of tanks configured to add additives to the flow.

[0020] Thus, the initial physical pre-treatment, using conventional methods and equipment and preferably by filtration, aims to achieve as clean of impurities as possible to be desalinated water. The equipment comprises one or more tanks connected in series that operate at the inlet flow pressure, which is a lower pressure than the osmosis pressure required to pass the water to be treated through a filter or a chain of filters, which are selected from the group given above (metal filters, carbon cartridges)... in this way, the clogging of the membranes that carry out osmosis is avoided. Generally, it is important that the selected filters, when connected in series, are ordered from largest to smallest pore diameter, forcing the water through them and generating a selective filtration of impurities from largest to smallest.

[0021] The water tank that receives the pre-treated water for desalination is configured to withstand the pressures required for reverse osmosis. It can be made of any known material that a person skilled in the art knows can withstand the pressures required for the desalination process (for example, steel). The value of this pressure depends on the properties of the water flow to be desalined (primarily its salt content). Thus, the pressure required is proportional to the salt content: the higher the salt content, the more pressure is required to propel the water and achieve the reverse osmosis process. Preferably, the pressure is equal to or greater than 25 atmospheres, for example, when the flow is brackish water (salt content between 0.05% and 3%). Also preferably, the pressure is equal to or greater than 50 atmospheres when the flow is salt water (salt content greater than 3%).This tank (or tanks, which may be connected in parallel, as explained below) receives the pre-treated water and drives it to the frame or module containing the semipermeable membranes at the pressure that, inside, transfers the gas to the flow of water to be desalinated, as follows: once the tank is full of pretreated water, thanks to the injection of gas inside it at the required pressure by means of the injection equipment described above, it experiences an increase in pressure inside it, such that when it reaches the required pressure based on the salt content, the flow of water is injected at said pressure from the outlet, which is preferably located at the base of the tank, to the module or frame of semipermeable membrane(s).

[0022] In a preferred embodiment, the installation comprises two or more tanks connected in parallel. In this case, the advantages are greater, since when the first tank is emptied, it remains filled with pressurized gas, which can be extracted through the tank's gas outlet and introduced through the gas inlet of a second tank, such that the same gas is reused at the same pressure without consuming any energy.

[0023] In another particular embodiment, the pressurized gas outlet of the water tank may be connected to the inlet of water to be desalinated in the facility, applying its pressure to the water flow so that, once captured, it can be pumped to the pretreatment equipment.

[0024] Semipermeable membranes separate water molecules from dissolved salts, producing two streams: one of desalinated water and the other of brine, which is discharged or waste.

[0025] Thanks to this improvement in the desalination plant, an energy expenditure per m² is obtained. 3 much lower than the current one, which is normally around 3kW / m 3 , as the pressurization system acts on the compression of a gas and not on the compression of water, as is usual with a high-pressure pump (Figure 1, state of the art). The transfer of pressure from the gas to the water to be desalinated is very simple, as it is carried out inside the pre-treated water tank by injecting said gas at the required pressure.

[0026] Furthermore, maintenance costs are much lower than current ones, since much of the machinery (especially the air / gas compressor) is not in contact with the water to be desalinated, thus preventing corrosion. Furthermore, the installation cost is significantly lower than that of current desalination plants, as high-pressure pumping equipment and wastewater energy recovery systems are eliminated.

[0027] Thanks to this system, and for the reasons previously mentioned, semipermeable membranes that perform reverse osmosis have a longer lifespan and significantly higher performance: to recover the pressure of 60% of the wastewater (brine), part of it is currently injected into the new water flow to be treated, increasing its salinity and decreasing the membranes' lifespan and performance. These negative effects do not occur in the invention proposed here.

[0028] In addition, in a preferred embodiment, the discarded water or brine, which upon exiting the membrane(s) still maintains a high pressure but lower than that of osmosis (it can be around 40-45 atmospheres), can have three destinations: in a first embodiment, the brine can be discharged into the sea, as is conventionally done, but with a perforated pipe that minimizes the contamination caused by the discharge; in a second alternative or embodiment, the brine can be used before being discharged to backwash the filters of the pretreatment equipment; and in a third embodiment, since the brine flow exits the membranes at a considerable pressure, greater than that of the desalinated water flow, this flow can be passed through a device that converts the mechanical force of the water passing through it into electrical force. This could be, for example, a turbine connected to the brine conduction and outlet means.

[0029] In conventional equipment, the brine is sometimes redirected to the high-pressure pump as part of the flow to be treated. This is not the case with this invention. To achieve this, the water outlet from the filters of the pretreatment equipment for the brine to be disposed of is connected to a conveying means that directs the brine to an outlet of the facility, which is a discharge outlet.

[0030] These brine conveyance and discharge means may comprise one or more control valves that allow the direction of the brine waste flow to be changed toward the outlet of the pretreatment equipment, which propels the pretreated water toward the inlet of the water tank to be pressurized. In this embodiment, a valve closes the inlet to the water tank, and thus, the pressurized brine is injected to backwash the filters, cleaning them while the process is stopped, and is expelled through a second outlet of the pretreatment equipment for the backwash water, which can then be directed to the brine discharge outlet of the installation.

[0031] In another embodiment, which is not exclusive to the others, the brine conveying means are connected to equipment for converting mechanical energy into electrical energy, such that its passage through said equipment generates energy that, for example, can be reused in the facility itself. These means can be of many types known in the field, such as a turbine. This allows the operation of the means that typically comprise the water inlet and outlet containers in these circuits and facilities, such as low-pressure pumps, to be stopped thanks to the transformation of the energy produced by the passage of the brine.

[0032] This triple reuse is an advantage, which is further enhanced by the fact that, when returning the brine to the sea, since pressure recovery is not necessary, the outlet can be made through a perforated pipe, allowing the brine to mix with seawater through Venturi exchange, thus reducing or eliminating its toxicity.

[0033] As part of the essential installation, as in already known facilities, this includes post-treatment equipment, to which the desalinated water exiting the semipermeable osmosis membranes can be sent. This equipment can include one or more mineralization and treatment tanks in the absence of booster pumps, since, after passing through the semipermeable membrane, the desalinated water flow still maintains sufficient pressure to be pumped and treated in the post-treatment equipment without the need for external force (it can have a pressure of approximately 5-6 atmospheres).

[0034] In a preferred and particular embodiment of the invention, this installation may have flotation means that allow it to be located on the surface or layer of water to be treated, such as in the sea, which is very advantageous. Thus, preferably, the installation comprises means for anchoring to the bottom of the water surface, such as the sea, and all of its elements (the pretreatment equipment, the pressurized water tank, the pressurized gas injection equipment, the module or frame with the membranes, and the post-treatment equipment) incorporate flotation means that can be floats that support the weight when empty and when filled with water to be desalinated. In this case, there is an advantage in that the water to be desalinated is captured and filtered before entering the pressurized water tank by its own gravity pressure, without the need to exert a driving force.Once processed, the desalinated water is conveyed to the shore through pipelines, and the brine is redirected to the outlet of the pretreatment equipment for backwashing. In this specific and particular case, the installation has a particular configuration and layout: first, the pretreatment filters can be incorporated into the water collection and conveyance systems to be desalinated at the inlet of the pressurized water tank, sorting from the highest to the lowest caliber of solids and impurities, as previously mentioned. Second, the gas injection equipment, the frame with the semipermeable membranes, the post-treatment equipment, and the rest of the installation elements are located on the pressurized water tank itself, which has floats on its upper part to keep it afloat on the surface, whether empty or full of water.

[0035] The installation object of the invention comprises control means for opening and closing the valves that manage the entry and exit of water and gas flows.

[0036] The control means may comprise one or more fill sensors for the water and gas tanks, located on the inlet and outlet valves for the water and gas flows, and for monitoring the filling and emptying of the tanks. Preferably, the sensors are level sensors.

[0037] A second aspect of the present invention consists of a process for the desalination treatment of water by means of the installation described herein, which comprises: physically and chemically pre-treating the flow of water to be desalinated; subjecting the pre-treated water flow to a pressure within the water tank sufficient to propel it, after filling the tank, to the module or frame of the at least one semi-permeable reverse osmosis filter; subjecting the pressurized flow of pre-treated water to desalination by osmosis, producing two output flows, one of desalinated water, which is sent to the post-treatment equipment for purification; and another of brine; characterized in that the process comprises: pressurizing a gas within at least one gas tank by means of one or more compressors, until reaching a pressure of at least 25 atmospheres necessary for osmosis, preferably at least 50 atmospheres, depending on the salt content of the water;and inject said pressurized gas into the water tank, transferring the gas pressure to the pre-treated water to be desalinated, which is propelled towards the membranes with the gas pressure upon entering the tank.

[0038] In a preferred embodiment, where the water to be desalinated is seawater, the process comprises collecting said seawater from wells along the coast or by means of pipelines from within the sea. In another embodiment, the water is brackish and is collected from a factory or industrial facility where brackish water is generated as a byproduct.

[0039] All the aspects discussed above for the installation, such as: system pressure values ​​in relation to salt content; properties of the preferred gas, which is air; the pre-treatment stage of the inlet water by filtration and its subsequent purification stage... also apply to the process.

[0040] Thus, in one embodiment, the brine flow is discharged into the sea. In another alternative embodiment, the brine flow is directed to the outlet of the pretreatment equipment, to subject the filters of said equipment to cleaning by counterflow, as explained above (closing the inlet valve of the water tank, and propelling the brine countercurrently from the outlet of the pretreatment equipment to its interior). And in a third alternative not exclusive of the previous ones, the brine flow is passed through equipment for transforming mechanical energy into electrical energy, such as a turbine, to produce energy thanks to the pressure with which the brine exits the membranes after osmosis.

[0041] Preferably, the process also comprises: extracting the pressurized gas flow from the interior of the water tank, once emptied, and transferring it a) to the inlet of the water flow to be desalinated in the installation, or b) to a second water tank to be pressurized, which is connected in parallel with the pressurized gas outlet of the first water tank.

[0042] BRIEF DESCRIPTION OF THE FIGURES

[0043] Below, to facilitate a better understanding of the description of the invention, and as an integral part thereof, some figures are attached in which the object of the invention is represented for illustrative and non-limiting purposes, and compared with embodiments of the state of the art.

[0044] Figure 1 (state of the art). Conventional seawater desalination plant.

[0045] (1) Inlet of water to be desalined

[0046] (2) Water feed tank

[0047] (3) First pressure pump, from the feeder tank (2)

[0048] (4) Means of conveying the flow of water to be desalinated

[0049] (5) Physical-chemical pre-treatment equipment

[0050] (6) Filters and chemical additive tanks of the pre-treatment equipment (5)

[0051] (7) High pressure pump

[0052] (8) High pressure pump outlet (7)

[0053] (9) Semipermeable reverse osmosis membranes (10) First outlet of the membranes (9), for desalinated water

[0054] (11) Second membrane outlet (9), for the brine

[0055] (12) Desalinated water post-treatment equipment

[0056] (13) Mineral dosing unit of the post-treatment equipment (12)

[0057] (13') Potabilization equipment of the post-treatment equipment (12)

[0058] (14) Drinking water container tank

[0059] (15) Second low pressure pump, from the drinking water tank (14)

[0060] (16) Brine discharge outlet to the outside of the facility.

[0061] Figure 2. (present invention).

[0062] (1) Inlet of water to be desalined

[0063] (2) Water feed tank

[0064] (3) First pressure pump, from the feeder tank (2)

[0065] (4) Means of conveying the flow of water to be desalinated

[0066] (5) Physical-chemical pre-treatment equipment

[0067] (6) Filters and chemical additive tanks of the pre-treatment equipment (5)

[0068] (7') Water tank configured to withstand high pressure

[0069] (8) Pressurized water outlet

[0070] (9) Semipermeable reverse osmosis membranes

[0071] (10) First membrane outlet (9), for desalinated water

[0072] (11) Second membrane outlet (9), for the brine

[0073] (12) Desalinated water post-treatment equipment

[0074] (13) Mineral dosing unit of the post-treatment equipment (12)

[0075] (13') Post-treatment equipment purification equipment (12)

[0076] (14) Drinking water container tank

[0077] (15) Second low pressure pump, from the drinking water tank (14)

[0078] (16) Brine discharge outlet to the outside of the facility

[0079] (17) Connection valve of the brine outlet (16) with the outlet of the pre-treatment equipment (5)

[0080] (18) Pre-treated water inlet from the tank (7')

[0081] (19) Pressurized gas outlet from tank (7')

[0082] (20) Gas compressor

[0083] (21) High pressure boiler

[0084] (22) Safety valves

[0085] (23) Pressurized gas inlet into the tank (7')

[0086] (24) Backwash water outlet of the physical-chemical pre-treatment equipment Figure 3. (present invention). Particular embodiment where the installation object of the invention is floating in the sea.

[0087] (I) Inlet of water to be desalined

[0088] (4) Means of conveying the flow of water to be desalinated

[0089] (5) Physical-chemical pre-treatment equipment, located within the means of conducting the inlet (1) of water to be desalinated

[0090] (6) Pre-treatment equipment filters (5)

[0091] (7') Water tank configured to withstand high pressure

[0092] (8) Pressurized water outlet

[0093] (9) Semipermeable reverse osmosis membranes

[0094] (10) First membrane outlet (9), for desalinated water

[0095] (II) Second membrane outlet (9), for the brine

[0096] (12) Post-treatment equipment for desalinated water, at the end of the pipeline from the first desalinated water outlet (located on land)

[0097] (16) Brine discharge outlet to the outside of the facility, which is connected to the inlet pipe for water to be desalinated.

[0098] (18) Pre-treated water inlet from the tank (7')

[0099] (19) Pressurized gas outlet from tank (7')

[0100] (20) Gas compressor

[0101] (21) High pressure boiler

[0102] (22) Safety valves

[0103] (23) Pressurized gas inlet into the tank (7')

[0104] (25) Floats located in the tank (7')

[0105] (26) Ground anchoring.

[0106] DETAILED DESCRIPTION OF THE INVENTION

[0107] A conventional desalination plant, for example of water captured from the sea, which is salt water, is shown in Figure 1 (State of the art). It consists of an inlet (1) to the water system to be treated, directly to a water feeder tank (2), where it accumulates and by means of a first pressure pump (3) the water flow is driven through conduction means (4) to a physical-chemical pre-treatment equipment (5). Said equipment (5) consists of vapour tanks in series where chemical additives are added, for example, flocculants, and different filters (6) that can be sand, carbon, nanometcos... After the first stage of pre-treatment, the flow of pre-treated water is directed to a high pressure pump (7), which gives the flow the pressure necessary for reverse osmosis, and which leaves the pump (7) through the outlet (8) that connects to the module or frame where the semipermeable reverse osmosis membranes are housed (9).Each membrane (9) has two outlets (10, 11), a first outlet (10) for the flow of desalinated water, which is directed to a post-treatment equipment (12), and a second outlet (11) through which the brine is discharged to the outside of the installation, most likely to the sea, through an outlet (16), or it is taken back to the pressure pump to be treated by osmosis and recover said pressure. The post-treatment equipment (12) consists of a mineral dispenser (13) and a purification equipment (13'). The desalinated and potable water is directed to a drinking water container tank (14), which has a low pressure pump (15) to distribute said drinking water.

[0108] In the case of the present invention, a preferred embodiment of which is shown in Figure 2, the high pressure pump (7) is replaced by a water tank (7') configured to withstand a high pressure (at least 25 atmospheres, for water flows with a lower concentration of salts - brackish water -, and at least 50 atmospheres, preferably around 60 atmospheres, if it is water with a higher concentration of salt - salt water -), which receives the pre-treated water to be desalinated through an inlet (18) and drives the pressurized flow through its outlet (8) to the module comprising the membranes (9), at the pressure required to carry out reverse osmosis. Previously, the flow of water to be desalinated is passed through the physical-chemical treatment equipment and the filters that comprise it.Unlike the system in Figure 1 , said driving pressure towards the membranes (9) is not generated through the pump (8) but through a gas, which is preferably pressurized air, which is injected into the tank (7') through the pressurized gas inlet (23). Thus, a compressor (20), which is connected to a high pressure boiler (21) (at least 25 atmospheres, or at least 50 atmospheres, depending on the salt content of the water flow), pressurizes a gas, which may be air, which is driven by means of safety valves (22) to the gas inlet (23) of the pressurized water tank (7'), the gas transferring the desired pressure to the water, such that, when it is full of water, the water is driven through the outlet (8) at the pressure of the incoming gas.

[0109] Said tank (7') also has a gas outlet (19), which allows it to be reused in the process. This is because, once the pressurized water tank has been emptied, directed to the osmosis membranes, the tank is left filled with pressurized gas. If this gas is extracted through the gas outlet (19) and directed to a second water tank (7'), the pressurized gas can be used to re-pressurize the water flow that fills this other tank (7'), to which it is connected in parallel. In this particular embodiment of the invention, the second outlet (11) of the membranes (9), through which the brine or concentrated salt water is evacuated, not only connects to the brine outlet (16) to the outside of the installation, but also to the outlet of the pre-treatment equipment (5) through which the pre-treated water is propelled to the tank (7').In this way, by means of a valve (17), this branch of the conduit allows the brine to be directed to the pre-treatment equipment (5) under backwash conditions, that is, stopping the desalination process and injecting the brine under pressure to the outlet of the pre-treatment equipment (5), cleaning the filters (6) by backwashing, in countercurrent.

[0110] EXAMPLES

[0111] The following invention is described by means of the following examples, which should be interpreted as merely illustrative and not limiting the scope of the invention. Example 1: Desalination of a seawater flow by means of the process and the installation object of the invention, installed in the sea by floating

[0112] In this example, the system with the pressurized water tank is installed at sea, anchored to the bottom, with floats holding the tank and all other components afloat. Seawater is collected by one or more filling pipes, thanks to its own gravity pressure. This pipe houses the pretreatment equipment, composed of several filters of increasingly smaller caliber to prevent the passage of impurities. The water fills the tank until the level sensor sends a signal to the inlet valve to close it. At this point, the sensor signals the control system, which opens the valve that controls the injection of pressurized air contained in the tank, achieving the desired pressure inside the tank.Thus, the air, which is the gas, is injected at 50 atmospheres or more into the tank, such that the water acquires a pressure of 50 atmospheres or more, which is when the sensor sends a signal to the control means, which close the gas inlet valve to the tank and open the valve that controls the passage of pressurized water to the frame (which are, in this example, swing doors) where the membranes that carry out desalination by reverse osmosis are housed.

[0113] Once the process is finished, the flow of desalinated water, at a pressure of about 6 atmospheres, is channeled towards the coast and the brine, at a pressure of 44 atmospheres, is recirculated countercurrent through the inlet pipe of the water flow to be desalinated, where the pre-treatment filters are located, dragging the impurities towards a diffuser of the brine outlet, which is the seawater inlet itself. The installation has the particularity that all the equipment that accompanies the water tank (gas injection equipment with its compressor and its boiler; the flaps with membranes, control means for opening and closing the various valves that direct the process ...) are located on the water tank itself to be presuñeado with the gas, the tank being the element that includes the floats (25) in the upper part and thus keep it on the surface when filled with seawater.

Claims

CLAIMS 1. A water treatment facility by desalination, comprising: an inlet for a flow of water to be desalinated, with a salt concentration of at least 0.05% by weight of the total weight of the water to be treated; connected to a physical-chemical pre-treatment equipment (5), connected at its outlet to at least one pressurized water tank (7'), configured to house and pressurize the flow of pretreated water to be desalinated, to a module that houses one or more semipermeable reverse osmosis membranes (9), said membranes comprising two outlets (10, 11), one (11) for the brine, and another (10) for the desalinated water that is connected to a post-treatment equipment (12), configured for the purification of the desalinated water;characterized in that: the pressurized water tank (7') comprises, in addition to an inlet (18) for the pretreated water flow: or a gas inlet (23) at a pressure of at least 25 atmospheres, which connects the tank (7') to equipment for injecting a gas or a mixture of gases under pressure; or an outlet (8) for the pressurized water flow to be desalinate, towards the membrane module or frame (9) once the gas has transferred its pressure to the water to be desalinate; and / or a pressurized gas outlet (19), to evacuate the pressurized gas once it has transferred its pressure; and where the pressurized gas injection equipment is formed by: or at least one pressurized gas tank (21) at a pressure of at least 25 atmospheres, comprising a pressurized gas outlet, said outlet being connected to safety means (22) that direct the pressurized gas to the gas inlet (23) of the pressurized water tank (7'); 2. The installation according to claim 1, wherein the water tank (7') to be pressurized is configured to withstand a pressure of at least 50 atmospheres.

3. The installation according to any of claims 1 or 2, wherein the high pressure gas tank (21) is a gas condensation boiler, and the pressurized gas injection equipment comprises at least one compressor (20) connected to the pressurized gas tank (21).

4. The installation according to any one of claims 1 to 3, wherein the physical-chemical pre-treatment equipment (5) comprises: physical treatment means (6) for removing impurities, which are composed of one or more filters selected from the group consisting of: sand filters, carbon filters, nanometric filters and any combination of the foregoing; and chemical pre-treatment means (6), which consist of tanks configured to add additives to the flow.

5. The installation according to any one of claims 1 to 4, wherein the outlet (8) of pre-stained water from the tank (7') is located at the base thereof.

6. The installation according to any one of claims 1 to 5, comprising two or more water tanks (7'), connected in parallel, from the pressurized gas outlet (19) of one tank (7') to the pressurized gas inlet (23) of the other tank (7').

7. The installation according to any one of claims 1 to 6, wherein the brine outlet (11) of the membranes (9) is connected to conduction means that are connected at their other end to an outlet (16) to the outside of the installation, which is a perforated brine evacuation pipe; and wherein said conduction means comprise one or several control valves (17) configured to change the direction of the brine flow towards: - the outlet of the pre-treatment equipment (5), and backwash the filters (6) of said equipment (5); or - a device for converting mechanical energy into electrical energy, by passing the brine before it is discharged through the outlet (16) to the outside of the facility.

8. The installation according to any one of claims 1 to 7, comprising means for floating on a surface of water to be treated, as well as anchoring means (26) to the bottom of said water surface.

9. A process for the treatment of water by desalination using the installation described in any one of claims 1 to 8, characterized in that it comprises: physically-chemically pre-treating the flow of water to be desalinated; subjecting the pre-treated water flow to a pressure within the pressurized water tank (6), sufficient to propel it, after filling the tank (7'), to the reverse osmosis semipermeable filter module (9); subjecting the pressurized flow of pre-treated water to desalination by osmosis, producing two output flows, one (10) of desalinated water, which is sent to be purified to the post-treatment equipment (12); and another (11) of brine; characterized in that the process comprises: pressurizing a gas within at least one gas tank (21) by means of one or more compressors (20), until reaching a pressure of at least 25 atmospheres necessary for osmosis;inject said pressurized gas into the water tank (7'), transferring the gas pressure to the pre-treated water to be desalinated, which is propelled towards the membranes (9) with the gas pressure upon entering the tank (7').; 10. The process according to claim 9, wherein the water to be desalinate is selected from brackish water, with a salt content between 0.05% and 3%, or salt water, with a salt content greater than 3% by weight of solute with respect to the total weight of the water flow.

11. The process according to any one of claims 9 or 10, wherein the water to be desalinated is seawater, and the pressurizing gas is air or a cryogenic liquefied gas.

12. The process according to any one of claims 9 to 11, wherein the gas is pressurized to a pressure of at least 50 atmospheres.

13. The process according to any one of claims 9 to 12, wherein, before disposing of the brine flow through the outlet (16) to the outside, said brine is directed to: - the outlet of the pre-treatment equipment (5), which is injected in backwash to clean the filters (6) of the pre-treatment equipment (5), or - a device for converting mechanical energy into electrical energy, passing the brine before it is discharged through the outlet (16) to the outside of the facility.

14. The process according to any one of claims 9 to 13, wherein the pressurized gas It is extracted from the pressurized water tank (7') once it has been emptied of liquid and is directed either to the gas injection equipment for reuse or to a second pressurized water tank (7'), connected in parallel with the first (7').

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