PLANT AND PROCESS FOR DESALINATION OF SEAWATER BY EVAPORATION USING SOLAR ENERGY

Abstract

The present invention relates to a seawater desalination plant comprising a boiling boiler (34) receiving a heat transfer fluid heated by solar energy, generating a primary water vapor (46) sent into condensers (72) consisting of a bundle of tubes arranged in each of the tanks (78) of a succession of cells (60, 62, 64) in order to carry out condensation in said condensers producing distilled water (74), this condensation heating seawater sprayed into the tanks (78), above the condensers, generating a low pressure secondary water vapor (50) which is added to the primary water vapor (46).Such an installation is characterized in that it comprises a device for heating the heat transfer fluid to a very high temperature, greater than 300°C, which is circulated in the boiling boiler (34), a suction device (42) maintaining a low pressure of less than 1 bar in the boiling boiler (34), a heat exchanger device (32) capable of bringing the water received by the boiling boiler to a very high temperature greater than 300°C, a thermal compressor (48) for obtaining a high-pressure primary water vapor (52), and a circuit delivering to each of the cells (60, 62, 64) of the succession a high-pressure and very high-temperature primary water vapor (50, 56), greater than 300°C. Figure for the abstract: Figure 3.

Description

Title of the invention: PLANT AND METHOD FOR DESALINATING SEAWATER BY EVAPORATION USING SOLAR ENERGY Technical field of the invention

[0001] The present invention relates to a seawater desalination plant using solar energy. It also relates to the desalination process implemented within said plant. Prior art

[0002] A known type of seawater desalination plant, presented in particular by document US-A1-2017151507 published on June 1, 2017, comprises a boiling boiler heated by fuel oil which, from water coming from condensation, forms a primary vapor of pure water passing inside a condenser consisting in this example of a tube (in other examples, the condenser consists of a bundle of multiple parallel tubes) integrated in the tank of a first cell (also called "effect") supplied by untreated seawater, which is sprayed onto said tube or tubes from nozzles arranged at the upper part of said cell.

[0003] In said condenser, an exothermic condensation of the primary steam is carried out, which, by the latent heat of phase change, releases heat energy which vaporizes the seawater mist sprayed in said first cell, this steam then being transferred to the condenser of a following cell whose construction is similar to that of the first cell. The two cells thus communicate with each other by means of openings provided in their upper parts. The same manner is then continued with a succession of identical cells (four to twenty in number depending on the installations, and most often between ten and fifteen in number), which therefore present at each transfer a progressive drop in the temperature of the condensation water in the direction from the first cell to the last cell of the installation.Thus, in each of the communicating cells of such a succession, on the one hand, water vapor is obtained from the evaporation of the sea water projected from the upper part of the cell after contact with the condenser in which the condensing water vapor circulates and, on the other hand, a deposit of the part of sea water which has not come into contact with the condenser. The water vapor resulting from the vaporization of the sea water is sent to the condenser arranged in the tank of the following cell, the water in liquid form, distilled, obtained by condensation in the condenser is . directed to a storage tank (placed at the end of the installation) while the deposited seawater, resting at the bottom of the tank, is pumped and sent from the bottom of the first cell to the upper part of the second cell, to be sprayed there, and so on from the second cell to the last cell to finally be discharged into the sea while the highly concentrated brine contained in the deposit of the last cell has the disadvantage of being a toxic product. In the last cell, the quantity of distilled water which flows from what is then the last condenser is also directed to the storage tank while the resulting water vapor is returned downstream of the boiling boiler in order to be reinjected into the first cell.In conclusion, all the sea water sprayed in the upper part of the different cells of the installation is separated by evaporation into distilled water vapor and a deposit of untreated sea water which is less and less concentrated in brine, the distilled water and the deposit of brine mixed with untreated sea water being recovered at the end of said installation, exploited for the first and unfortunately, since harmful, discharged into the sea for the second even though it is loaded more with water, therefore sees its concentration in brine decrease from the first towards the last cell of the installation.

[0004] It is also possible to provide that at the outlet of a cell, most often the first or the last, part or all of the water in liquid form delivered after condensation by the tube or bundle of tubes constituting the condenser of the cell concerned is returned to the boiling boiler in order to supply it with distilled water which, added to the sea water, will be transformed into water vapor.

[0005] Generally speaking, it is in any case known from document US-Al-2017151507 to produce in the boiling boiler a primary water vapor at a temperature of approximately 70°C and at ordinary pressure, this temperature then also being that of the vapor entering the first cell and then descending progressively in the succession of communicating cells to reach approximately 40°C during the last condensation.

[0006] A large number of cells can be used so that the temperature differences are smaller. This process, involving multiple effect distillation, is called "Multiple effect distillation" in English, or "MED" for short.

[0007] Thus, from a primary pure water vapor having a temperature generally lower than 70°C, a production of distilled water is achieved with a gain between the mass of water produced and the mass consumed by the primary vapor, called "Gain output ratio" in English, or "GOR" for short, which is approximately 6.

[0008] In similar known installations, heat production is carried out, not by the combustion of fuel oil, but by means of solar panels, power plants thermal, generators or even by the combustion of any other fossil fuel.

[0009] However, all these types of installation using a low primary steam temperature (equal to or less than 70°C) with a low pressure have the first disadvantage of causing problems of limescale formation, in particular in the boiling boiler and on the surface, or even inside the tubes of the different condensers arranged in each of the cells, limescale which ends up being deposited on these surfaces by forming an insulating layer, in particular on the internal and external surfaces of the condenser tubes, thus reducing the passage sections and, in any case, reducing the heat exchanges.

[0010] Furthermore, the temperature of the water vapor circulating in the tube bundles for the purpose of condensation and, consequently, the temperature of the water vapor obtained by evaporation of the sea water in each of the cells both fall from the first to the last of the cells in the installation, due to the absence of heating elements under the cell tanks, which has the consequence of causing a notable progressive drop in the efficiency of the installation at the level of the cells closest to the outlet of the installation.

[0011] Finally and above all, since the cells of known desalination installations communicate with each other to allow the passage of primary water vapor from one to the other, any defective or abnormal operation inside a cell resulting in a shutdown of this cell generates the shutdown of all the cells of the installation and therefore the temporary cessation of the desalination treatment until the defective cell is repaired. Presentation of the invention

[0012] The present invention aims in particular to avoid these problems of the prior art.

[0013] For this purpose, it proposes a seawater desalination installation comprising a boiling boiler receiving a heat transfer fluid heated by solar energy, generating a primary water vapor sent into condensers consisting of a bundle of tubes arranged in each of the tanks of a succession of cells in order to carry out condensation in said condensers producing distilled water, this condensation heating sea water sprayed into the tanks, above the condensers, generating a low pressure secondary water vapor which is added to the primary water vapor, said installation being characterized in that it comprises a device for heating at very high temperature, greater than 300°C, the heat transfer fluid circulated in the boiling boiler, a suction device maintaining a low pressure of less than 1 bar in the boiling boiler, a heat exchanger device capable of bringing the water received by the boiling boiler to a very high temperature above 300°C, a thermal compressor to obtain high-pressure primary water vapor, and a circuit delivering to each of the cells in the succession high-pressure primary water vapor at a very high temperature, above 300°C.

[0014] An essential advantage of the installation according to the invention compared to current installations is that, since the cells are now completely partitioned and independent of each other, in the event of a shutdown occurring on a cell, whether it be an operational failure or a voluntary shutdown for maintenance purposes, only the cell concerned will be taken out of service while all the other cells of the installation will continue to operate normally. It is then reasonable to conclude from the above that the installation according to the invention will be able to comprise fewer cells than current installations while ensuring equivalent efficiency because shutdowns will be less frequent. In addition to the savings resulting from the fact that the quantity of cells to be constructed will be smaller, it is understood that the footprint of the installation according to the invention will be significantly reduced.

[0015] Another advantage of this installation is that the low pressure in the boiling boiler leads to the formation of vapors which greatly limits the formation of limescale, which makes it possible to reduce maintenance operations and maintain good system performance thanks to the reduction of deposits.

[0016] Furthermore, the fact that all the cells of the installation according to the invention receive water vapor at very high temperature and under the same high pressure contributes to operations and results that are almost identical from one cell to another. Thus, the efficiencies being the same, it will be possible to reduce the number of such cells in comparison with the installations currently in operation.

[0017] The desalination installation according to the invention may further comprise one or more of the following characteristics, which may be combined with each other.

[0018] Thus, the suction device may comprise a vacuum pump.

[0019] Advantageously, the cells will comprise partitioned steam circuits, separated from each other, and therefore not delivering steam from one to the other.

[0020] Preferably, the installation according to the invention may comprise a set of reflectors forming an arc-shaped surface whose focal point is centered on a tube for circulating the heat transfer fluid which is heated by solar energy.

[0021] In this construction, said installation may further comprise a thermal reserve receiving the heat transfer fluid heated by solar energy, thus making it possible to regulate the temperature of the fluid delivered to the boiling boiler over entire days.

[0022] According to another preferred construction, the installation according to the invention may comprise a circuit of the heated heat transfer fluid successively passing through the brines deposited at the bottom of the tanks of each of the cells.

[0023] Still according to this other construction, the heated heat transfer fluid circuit will be able to cross the succession of cells in counter-current, from the last cell to the first cell.

[0024] Ideally, the heat transfer fluid will be chosen from fluids based on molten salts.

[0025] According to yet another construction variant, the installation according to the invention may comprise a final condensation chamber receiving the portion of secondary steam (50) which is then delivered to the thermal compressor.

[0026] In this case, the final condensation chamber may include a cold seawater circuit cooling this chamber and then supplying the cells with cold seawater to be sprayed onto their condenser.

[0027] Very advantageously, the invention may comprise a device for cleaning at least the condensers and the heat exchanger device internal to the boiling boiler, said cleaning device operating by ultrasound.

[0028] It may also include at least one flash generator making it possible to suddenly and abruptly increase the temperature of the high-pressure primary water vapor delivered by the thermal compressor, which has already reached a very high temperature.

[0029] Preferably, the heat transfer fluid circulation circuit may comprise two parts extending one from the other, a primary circuit and a secondary circuit, the second being able to be isolated from the first in the event of insufficient sunlight.

[0030] The second subject of the invention is a process for desalinating seawater comprising, in a known manner, the heating by solar energy of a heat transfer fluid circulated in a boiling boiler capable of producing a primary water vapor sent into condensers consisting of a bundle of tubes arranged in each of the tanks of a succession of cells in order to carry out in said condensers a condensation producing distilled water, this condensation heating seawater sprayed in the tanks, above the condensers, by generating a low-pressure secondary water vapor which is added to the high-temperature primary water vapor, said process being characterized in that it further consists in heating to a very high temperature, greater than 300°C, the heat transfer fluid circulated in the boiling chamber, in maintaining by suction a pressure lower than 1 bar in said boiling boiler,to bring into contact the sea water received by the boiling chamber and a heat exchanger in which the heat transfer fluid circulates in order to produce primary water vapor whose temperature is greater than 300°C, to send this primary water vapor at very high temperature, produced by said boiler in a thermal compressor in order to obtain high pressure primary water vapor, and to deliver this water vapor under high pressure and at very high temperature into each of the cells in the succession of cells. Brief description of the drawings

[0031] The invention will be better understood and other characteristics and advantages will appear more clearly on reading the description below given by way of example, with reference to the appended drawings in which:

[0032] [Fig-1] is a front view diagram of a solar mirror system generating the heat energy for heating the boiling boiler of a desalination plant according to the invention;

[0033] [Fig.2] is a cross-sectional diagram of this solar mirror system; and

[0034] [Fig.3] is a diagram of the desalination unit of this installation.

[0035] [Fig.4]] is a diagram of an ultrasonic cleaning device operating in continuous, capable of being associated with the installation according to the invention, which therefore allows the latter to avoid the stops required for cleaning to eliminate any possible limescale deposits

[0036] [Fig.5] is a diagram of an example of construction arranged at the exit of the desalination plant illustrating the latest treatments applied to distilled water and brine. Description of preferred embodiments

[0037] Figures 1 and 2 show masts 2 each supporting a horizontal pivot 4, these pivots being aligned to form a pivot axis of a tubular structure 12 supporting reflectors consisting of mirror panels 6 arranged between two masts. Each reflecting mirror 6 has a cross-section in the shape of an arc of a circle receiving the pivot 4 on its outer face, so as to leave free its concave inner face facing a tube 10 arranged in the center of the arc of a circle.

[0038] A motorization installed at the top of each mast 2, controlled by a control box 28 arranged in the mast, drives the horizontal pivot 4 so as to turn the set of reflecting mirrors 6 facing the sun to receive maximum energy from its radiation, and concentrate these rays so that their focal points permanently coincide with the central tube 10, and this in order to always heat to the maximum a high temperature heat transfer liquid fluid circulating in this tube 10. Under this last expression, it must be understood that it is a very high temperature heat transfer support liquid which also turns out, for the needs of the implementation and with regard to the destination of the invention, to be a non-toxic, non-flammable liquid, of low viscosity and of very high thermal conductivity. As an example, the product marketed under the brand name "Globaltherm" will be cited. Omnistore MS-600" with a flash point of 680°C, its safe operating range extending from 149°C to 600°C.

[0039] This heat transfer fluid, marketed by the British company Global Oil Company (Europe) Limited, is based on molten salts and is known for its use in very high temperature solar storage applications.

[0040] The heat fluid passes through a closed primary circuit comprising a circulation pump 14 delivering the fluid to an inlet end 16 of the central tube 10, fluid which comes out, heated to a very high temperature, at the other end of said tube to then pass through a heat exchanger 18 arranged in a thermal reserve 20 accumulating heat energy by heating the heat fluid already contained in a secondary closed circuit.

[0041] The heat exchanger is advantageously provided upstream with two valves, one at its inlet and the other at its outlet, in order to be able to isolate the secondary circuit from the primary circuit, in the absence of sun and in any case at night, the circulation pump 14 of the primary circuit then being stopped, the two aforementioned valves being closed while the circulation pump 22 of the fluid arranged in the secondary circuit continues to operate, thus allowing the installation according to the invention to be constantly in operation.

[0042] Via the heat exchanger, the secondary circuit thus comprises an outlet for heat fluid 24 heated to a very high temperature, having an optimized regularity, towards the desalination unit, heat fluid which, after its use, returns colder via an inlet 26 into the thermal reserve 20, and is reheated there even in the case where the primary circuit is isolated from the thermal reserve 20 and, therefore, from the secondary circuit.

[0043] It should be noted here that the solar energy heating device and the heat transfer fluid are specifically chosen for the purpose of being able to operate the desalination installation, and more particularly its cells, at temperatures that current installations do not provide.

[0044] This is the case with reflective mirrors which concentrate the sun's rays and which therefore make it possible to reach temperatures above 500°C, which are impossible to obtain using solar panels.

[0045] Similarly, current installations operate with water vapor whose temperature is close to 70°C, whereas the installation according to the invention operates with water vapor whose temperature is at least 300°C, and preferably of the order of 400°C (as will be used as an example throughout the remainder of this description), thanks as will be described in the following paragraphs to the use of the aforementioned heat fluid which, itself, can be heated to this temperature of at least 400°C delivered by the reflecting mirrors.

[0046] A control unit of the installation manages control boxes 28 arranged in each mast 2 to regulate the operation of the motorization of the pivots 4 and of the circulation pump 14 of the primary circuit, in order to optimize the capture of thermal energy during the day by orienting the reflecting mirrors 6, and to deliver the most constant heat energy possible during the whole days in order to regulate the operation of the desalination unit over time.

[0047] In particular, the circular arc-shaped reflecting mirrors 6 make it possible to concentrate the solar radiation on the central tube 10, using a total surface area which is not limited thanks to the addition of masts 2 and the use of successive panels along a length which can be very significant.

[0048] Advantageously, all of the electricity consumed elsewhere by the installation, in particular by the heat fluid circulation and seawater suction pumps, comes either from traditional photovoltaic solar panels recharging batteries, or from small nuclear reactors (Small Modular Reactors, or SMR for short), these arrangements making it possible to create a desalination installation which is energy-autonomous.

[0049] [Fig. 3] shows a first pump 22 of the secondary heat fluid circuit, connected to the outlet 24 of the thermal reserve 20, which delivers the fluid heated to approximately 400°C into a heat exchanger coil 32 arranged in a tank of a boiling boiler 34 to then exit at a lower temperature and return to the inlet of the thermal reserve marked by the arrow 26 at the top right of [Fig. 3].

[0050] A first seawater feed pump 40 pumps this water through suction pipes 36 arranged at a distance and at a maximum depth adapted to preserve the environment and also to capture the coldest seawater in this environment, in order to cover the coil 32 which, by heat exchange, brings this seawater to a boil. A vacuum pump 42 maintains a constant low pressure in the tank of the boiler 34, less than one bar, so as to promote the boiling of the seawater, and to avoid a deposit of limestone which, otherwise, would be deposited on the walls, reducing heat exchange.

[0051] A water vapor recovery nozzle 44, arranged in the upper part of the boiling boiler 34, recovers the generated primary steam 46 to send it to a thermal compressor 48 also receiving a low pressure and high temperature secondary steam 50, which is produced by a succession of vaporization cells 60, 62, 64, three in this illustrated example, said cells having the particularity of not communicating with each other, unlike those equipping current desalination installations. In general, as has been described As a preamble, more than three vaporization cells are used, typically between four and twenty and most often between ten and fifteen.

[0052] The coil 32, brought to a very high temperature, and the vacuum pump 42 ensure that the temperature of the primary water vapor 46 distributed by the boiler 34 remains close to 400°C.

[0053] The thermal compressor 48 is a static compressor producing a mixture of the secondary steam 50 with the primary steam 46 to obtain, by a driving effect in converging then diverging cones, a steam 52 at high pressure (greater than eight bars) and at very high temperature, always close to 400°C.

[0054] A portion of the high-pressure steam 52 passes through a flash generator 54 to suddenly and abruptly obtain superheated steam 56 at very high temperature and high pressure (at least 400°C and respectively greater than eight bars), which is delivered to the first vaporization cell 60 while the complementary portion of high-pressure steam 52 directly feeds in parallel each of the other vaporization cells 62, 64 of the succession of cells as well as a final condensation chamber 82. Obviously, a flash generator 54 can be added upstream of one or more of the following cells if it proves necessary to introduce into such other cells superheated steam 56 in place of the steam 52 which is already brought to a very high temperature, of the order of 400°C, by the boiling boiler 34.

[0055] Each vaporization cell 60, 62, 64 is composed of three chambers which do not communicate with each other, namely (from left to right in [Fig. 3]): a first chamber 70 through which the water vapor penetrates at very high temperature and high pressure 52, or according to 56; a second chamber 78 constituted essentially in the form of a tank equipped with a condenser constituted by a bundle of parallel and horizontal tubes 72, these tubes being arranged either in an anarchic manner, or organized and placed one above the other by being for example embedded inside one or more plates installed vertically inside the chamber 78 (see [Fig. 3]), or organized and placed inside a cylinder, in the manner of a revolver barrel (see [Fig. 4]); and finally a third chamber 74 provided to collect the distilled water obtained by condensation during the passage of the water vapor in the tubes 72 of the condenser of the second chamber.

[0056] To this end, each of the tubes 72 is open at its two ends, one opening into the first chamber 70 to allow the passage of the water vapor that it contains, the other opening into the third chamber 74 to allow the flow into this third chamber of the water in liquid form that has been condensed in the tubes 72.

[0057] To carry out the condensation, in the tubes 72, of the water vapor delivered into the first chamber 70, it is provided that the second chamber 78 of the installation according to the invention comprises at its upper part nozzles 84 which spray sea water and an outlet nozzle 85 through which water vapor is evacuated, called "secondary vapor" in the remainder of this description.

[0058] The circuit supplying sea water to the spray nozzles 84 comprises a second suction pump 76 connected to the suction pipes 36 arranged in the deep sea, giving a flow which passes through a heat exchanger 80 arranged in the final water vapor condensation chamber 82, in order to heat up while carrying out this condensation, then feeds said spray nozzles 84 arranged in the upper part of the tank of each of the second chambers 78 of the vaporization cells 60, 62, 64, above the condenser 72.

[0059] Optionally, the seawater circuit comprises, after passing through the final condensation chamber 82, a seawater outlet valve to the outside 110 making it possible to add to the feed flow of the spray nozzles 84 a flow discharged directly through this outlet, which thus makes it possible to increase the flow of water passing through the chamber to obtain sufficient cooling of the steam contained therein in order to achieve its complete condensation.

[0060] In parallel with the seawater outlet valve 110, an inlet for additional chemical products 112 makes it possible to send an addition of necessary elements before the vaporization of this water.

[0061] The final condensation chamber 82 has an upper outlet 114 directed towards a non-condensable gas vacuum extractor 116.

[0062] The seawater spray mist from the nozzles 84 is projected towards the bottom of the tank of each of the second chambers 78, spraying the bundle of tubes 72, thus releasing the latent heat of condensation in these tubes, to form the low-pressure, high-temperature secondary steam 50 which is recovered and evacuated by the upper outlet nozzle 85 of this second chamber 78. The temperature of this secondary steam is then between 200°C and 300°C and its pressure is slightly less than one bar.

[0063] Most, or even all, of the secondary steam 50 advantageously feeds the thermal compressor 48, any remaining steam being delivered to the final condensation chamber 82 and contributing to the formation of a distilled water condensate which is deposited at the bottom of this chamber.

[0064] The non-vaporized sea water, which is highly charged with salt, descends to the bottom of each second chamber 78 to form a deposit of brackish water 88 charged with mineral salts and in particular sodium chloride.

[0065] Each cell 60, 62, 64 comprises a complementary condensation circuit 120, shown in dotted lines behind the first chamber 70 of the neighboring cell, which recovers the remainder of the non-condensable gases leaving the tubes of the condenser 72 and escaping from the third chamber 74. Each circuit 120 is connected to the upper outlet 114 of the final condensation chamber 82, so that all of these non-condensable gases are finally evacuated by the extractor 116.

[0066] A first distilled water recovery pump 100 recovers via the circuit 101 condensed water at the bottom of the high pressure and very high temperature steam inlet reserve 56 of the first chamber of the first cell 60, by an outlet nozzle which, arranged at the bottom of this reserve, allows it to be partially emptied in order to supply the boiling boiler 34 in addition to the sea water, this to dilute the brine concentration of the water supplying said boiler before the latter produces the primary steam 46.

[0067] A second distilled water recovery pump 102 recovers via the circuit 103 the other part of the condensed water remaining at the bottom of the high-pressure steam inlet reserve 56 of the first chamber 70 of the first cell 60, up to a certain height, and likewise recovers the distilled water condensate which has flowed into the bottom of the reservoirs of the third chambers 74 of each of the cells 60, 62, 64 as well as into the bottom of the final condensation chamber 82, in order to supply a reserve of distilled water 104.

[0068] The outlet 24 of heat transfer fluid, always brought to a temperature close to 400°C, is connected to a second pump 90 for circulating this fluid in order to send it to a circuit 105 successively passing through the brackish water deposits 88 at the bottom of each second chamber 78, and this with the aim of heating this brackish water to dry it and obtain the most dehydrated brine possible.

[0069] Very advantageously, such circulation of the heat transfer fluid is carried out in a reverse direction, that is to say from the last cell (64 in the example shown) to the first cell 60 of the installation.

[0070] Each brine stock 88 comprising a lot of sea water, such a preferential counter-current passage of the heat transfer fluid means that the evaporation rate of this water becomes poorer as the heat transfer fluid circulates from the last cell 78 to the first cell 70, a phenomenon which is illustrated in [Fig. 3] by the level of brine present in each second chamber 78, which increases from the last cell towards the first.

[0071] In the example shown in [Fig. 3], the heat transfer fluid delivered to the outlet of the second pump 90 circulates in a single pipe which successively passes through the bottoms of the second chambers of all the cells of the installation. As a variant of this construction which allows a counter-current passage of the heat transfer fluid, it is possible to provide for the addition to the outlet of the pump 90 of as many auxiliary conduits 105 as there are cells. This arrangement will have the advantage of allowing the installation to operate without discontinuity even in the event that the single conduit proves to be faulty.

[0072] The circuit for recovering and removing the dehydrated brine 92 therefore starts from the brine depot 88 of the first cell 60 to successively pass through the others, ending with the last cell 64, then comprises a brine removal pump 94 which finally delivers the brine into a recovery tank 96.

[0073] Advantageously, this highly dehydrated brine can be recovered by being resold to refineries which, after treatment and separation of the different minerals, can be exploited in fields such as mining, cosmetics, detergents, pharmaceuticals or even agriculture, by providing fertilizers.

[0074] Being in particular loaded with sodium chloride, a part of this brine can also be used within the installation according to the invention in the context of the manufacture of the heat transfer fluid, the sodium chloride present in the dehydrated brine then constituting one of the mixed salts included in the composition of the heat transfer fluid.

[0075] The distilled water collected in the reserve 104 can, as is known, be subject to a remineralization treatment by injections of carbonate 130 and calcium bicarbonate 131, an adjustment of its pH indicator in 132, to correct its acidic or basic side, and a purification in order to allow food use.

[0076] According to the invention, it is advantageous to add carbon dioxide 133, preferably recycled, to the distilled water, as well as an adjustment in 134 of mineral salts. By using carbon dioxide recycled from other industries, this makes it possible to have a negative carbon footprint and, at the same time, to increase the yield of the mineralization.

[0077] Still advantageously, if notwithstanding the precautions recommended for the operation of the desalination installation according to the invention, a risk of limescale deposit proves possible, said installation will be supplemented with an ultrasonic generator emitting an electrical signal converted into mechanical vibrations by ultrasonic transducers.

[0078] For example, as shown in [Fig.4], transducers 119, fixed to the support 123 and connected to the generator 121, emit in a known manner high-frequency vibrations 122 shown diagrammatically by arrows in this [Fig.4].

[0079] Such vibrations will continuously generate slight movements on each of the tubes of the condensers 72, thereby preventing the sedimentation of minerals, in particular limestone, as well as the fouling of the installation. The same would apply for the boiling boiler 34, for example by placing the transducers 119 on the coil 32.

[0080] It therefore becomes unnecessary to stop the operation of the installation according to the invention from time to time, whereas such stops were previously required both for cleaning the boiling boiler and for cleaning the condensers and tanks in known installations. This clearly results in a significant improvement in efficiency and significant economic gains compared with prior techniques.

[0081] For a perfect understanding of the operation of the installation according to the invention, some values ​​identified by the letters BT (low temperature), MT (medium temperature), HT (high temperature), BP (low pressure), MP (medium pressure) and HP (high pressure) have been mentioned at the essential stations of said installation.

[0082] Thus, at the outlet of the boiling boiler 34, the primary steam delivered is at a temperature of 400°C and a pressure lower than 1 bar, at the outlet of the thermal compressor 48, the temperature of the primary steam is always 400°C and the pressure is higher than 8 bars, in each of the first chambers 70 of the cells, the temperature is higher than 400°C if these chambers are preceded by a flash generator 54 and the pressure is higher than 8 bars, in the upper part of the second chambers 78 the temperature is between 200°C and 300°C and the pressure is lower than 1 bar, in each of the third chambers 74 the temperature is between 5°C and 20°C and the pressure is higher than 8 bars, and finally in the final condensation chamber 82 the temperature is between 100°C and 200°C and the pressure is between 1 and 4 bars.

Claims

Claims

1. Seawater desalination plant comprising a boiling boiler (34) receiving a heat transfer fluid heated by solar energy, generating a primary water vapor (46) sent into condensers (72) consisting of a bundle of tubes arranged in each of the tanks (78) of a succession of cells (60, 62, 64) in order to carry out condensation in said condensers producing distilled water (74), this condensation heating seawater sprayed into the tanks (78), above the condensers, generating a low pressure secondary water vapor (50) which is added to the primary water vapor (46), said plant being characterized in that it comprises a device for heating at a very high temperature, greater than 300°C, the heat transfer fluid circulated in the boiling boiler (34), a suction device (42) maintaining a low pressure less than 1 bar in the boiling boiler (34),a heat exchanger device (32) capable of bringing the water received by the boiling boiler to a very high temperature above 300°C, a thermal compressor (48) for obtaining a high-pressure primary water vapor (52), and a circuit delivering to each of the cells (60, 62, 64) of the succession a high-pressure and very high-temperature primary water vapor (50, 56), above 300°C.,

2. Installation according to claim 1, characterized in that the suction device (42) comprises a vacuum pump.

3. Installation according to claim 1 or 2, characterized in that the cells (60, 62, 64) comprise partitioned steam circuits, separated from each other, which do not deliver steam from one to the other.

4. Installation according to any one of the preceding claims, characterized in that it comprises a set of reflectors (6) forming an arc-shaped surface whose focal point is centered on a heat transfer fluid circulation tube (10) which is heated by solar energy.

5. Installation according to claim 4, characterized in that it comprises a thermal reserve (20) receiving the heat transfer fluid heated by solar energy, thus making it possible to regulate over entire days the temperature of the fluid delivered to the boiling boiler (34).

6. Installation according to any one of the preceding claims, characterized in that it comprises a circuit of the heated heat transfer fluid successively passing through the brines (88) deposited at the bottom of the tanks (78) of each of the cells (60, 62, 64).

7. Installation according to claim 6, characterized in that the heated heat transfer fluid circuit passes through the succession of cells (60, 62, 64) in counter-current, from the last cell (64) towards the first cell (60).

8. Installation according to any one of the preceding claims, characterized in that the heat transfer fluid is based on molten salts.

9. Installation according to any one of claims 1 to 8, characterized in that it comprises a final condensation chamber (82) receiving the portion of secondary steam (50) which is then delivered to the thermal compressor (48).

10. Installation according to claim 9, characterized in that the final condensation chamber (82) comprises a cold seawater circuit (80) cooling this chamber (82) and then supplying the cells with cold seawater to be sprayed onto their condenser.

11. Installation according to any one of the preceding claims, characterized in that it comprises a device for cleaning at least the condensers (72) and the heat exchanger device (32) internal to the boiling boiler, said cleaning device operating by ultrasound.

12. Installation according to any one of the preceding claims, characterized in that it comprises at least one flash generator (54) making it possible to increase, suddenly and abruptly, the temperature of the high-pressure primary water vapor delivered by the thermal compressor (48) already brought to a very high temperature.

13. Installation according to any one of the preceding claims, characterized in that its heat transfer fluid circulation circuit comprises two parts extending one from the other, a primary circuit and a secondary circuit, the second being able to be isolated from the first in the event of insufficient sunlight.

14. A method of desalinating seawater comprising heating by solar energy a heat transfer fluid circulated in a boiling boiler (34) capable of producing primary water vapor (46) sent to condensers (72) consisting of a bundle of tubes arranged in each of the tanks (78) of a succession of cells (60, 62, 64) in order to carry out in said condensers a condensation producing distilled water (74), this condensation heating seawater sprayed in the tanks (78), above the condensers, by generating a low pressure secondary water vapor (50) which is added to the primary water vapor (46), said method being characterized in that it further consists in heating to a very high temperature, greater than 300°C, the heat transfer fluid caused to circulate in the boiling boiler (34), in maintaining by suction a pressure lower than 1 bar in said boiling boiler (34), in bringing into contact the seawater received by the boiling boiler (34) and a heat exchanger (32) in which the heat transfer fluid circulates in order to produce a primary water vapor whose temperature is greater than 300°C,to send this primary water vapor at very high temperature produced by said boiler into a thermal compressor (48) in order to obtain a high pressure primary water vapor (52), and to deliver this water vapor under high pressure and at very high temperature into each of the cells (60, 62, 64) of the succession of cells,

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