Plant and method for desalinating seawater by evaporation using solar energy

Abstract

The present invention relates to a plant for desalinating seawater of the type made up of a succession of cells (60, 62, 64) each provided with a tank (78), the plant comprising: a condenser (72) consisting of a bundle of tubes open at their two ends; a first pump (40) capturing the seawater by suction ducts (36) and supplying a boiler (34) capable of heating this seawater in order to generate a primary pure steam (46) sent via a circuit (44, 52, 56) to the inlet of each of the condensers (72); a second pump (76) supplying the tanks (78) of the cells (60, 62, 64) with seawater which is sprayed onto the condensers (72) via nozzles (84) arranged at the top of the tanks (78); nozzles (85) also arranged at the top of the tanks (78) to discharge the secondary pure steam (50) resulting from the contact between the sprayed seawater and the condensers (72). Such a plant is characterised in that: it further comprises a heat exchanger device (32) inside the boiler (34) allowing the latter to generate a primary pure steam (46) at a temperature of at least 300°C; in that the cells (60, 62, 64) include partitioned steam circuits which are separated from one another and do not deliver steam from one to the other; and in that it also comprises means for supplying the cells (60, 62, 64) with primary pure steam (46) and seawater, respectively.

Description

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-A1-2017 / 0151507 published on June 1, 2017, comprises a boiling boiler heated by oil which, from seawater, forms a primary vapor of pure water, therefore not yet condensed in its liquid form, which is conducted to the interior of 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 supplied with untreated seawater. This seawater is sprayed onto said tube or tubes from nozzles arranged at the upper part of said cell.

[0003] In this way, an exothermic condensation of the primary steam is carried out in the said condenser, which, through the latent heat of phase change, releases heat energy which creates a water mist hereinafter referred to as "secondary steam".

[0004] While the primary steam is directed in liquid, distilled form, to a storage tank placed at the end of the installation, the secondary steam is then transferred to the condenser of a following cell whose construction is similar to that of the first cell, and there to be condensed. The two cells thus communicate with each other by means of openings provided in their upper parts. We then continue in the same way with a succession of identical cells (four to twenty in number depending on the installation, and most often between ten and fifteen in number), which therefore present at each transfer a progressive drop in the temperature of the secondary steam in the direction of the first cell towards the last cell of the installation.Thus, in each of the communicating cells of such a succession, there are present, on the one hand, sea water, which will be projected from the upper part of the cell in order, after contact with the condenser of the cell, to condense the secondary vapor of pure water, which circulates in said condenser and, on the other hand, a deposit of the fraction of sea water which has not come into contact with the condenser. In other words, the secondary water vapor. produced within a cell is sent to the condenser located in the tank of the next cell, and the water in liquid form, distilled, obtained by condensation in this condenser, is directed to the storage tank. At the same time, the deposited seawater, resting at the bottom of the tank of a cell, is pumped and sent from this bottom to the upper part of the next cell, to be sprayed there, and so on, from the second cell to the last cell of the installation, to finally be discharged into the sea while the very concentrated brine which is thus 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 flowing from what is then the last condenser is also directed towards the storage tank while the resulting water vapor is returned upstream of the boiling boiler in order to be reinjected into the first cell.In conclusion, all the seawater sprayed in the upper part of the various cells of the installation is separated by evaporation into distilled water vapour which then condenses and into a deposit of seawater which is less and less concentrated in brine, the liquid distilled water and the deposit of brine mixed with seawater which could not be treated being both recovered at the end of said installation, to be exploited there as regards the distilled water and unfortunately, since it is harmful, discharged into the sea as regards the brine even though this deposit has become more loaded with water, therefore seeing its brine concentration decrease from the first cell towards the last cell of the installation.

[0005] It is also possible to provide that at the outlet of one of the cells of the installation, most often the first or the last cell, 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 primary water vapour.

[0006] Generally speaking, it is in any case known from document US-A1-2017 / 0151507 to produce in the boiling boiler a primary water vapour at a temperature of approximately 70°C and at ordinary pressure, this temperature then also being that of the vapour entering the condenser of the first cell of the installation and then descending progressively in the succession of communicating cells to reach approximately 40°C during the last condensation in the last cell of the installation.

[0007] A large number of cells can be used so that the temperature differences between them are smaller. This process, which involves multiple-effect distillation, is called "Multiple Effect Distillation" or "MED" for short.

[0008] This produces distilled water from a primary steam of pure water with a temperature generally lower than 70°C at the first cell of the installation, with a gain between the mass of water produced and the mass consumed by the primary steam, called "Gain output ratio" in English, or "GOR" for short, which is approximately 6.

[0009] In other similar known installations, heat production is achieved not by the combustion of fuel oil, but by means of solar panels, thermal power plants, generators or even by the combustion of any other fossil fuel.

[0010] However, all these known desalination plants that use a low primary steam temperature (equal to or less than 70°C) with low pressure have the primary disadvantage of causing problems with the formation of limescale, particularly in the boiling boiler and also on the surface, or even inside the tubes of the various condensers arranged in each of the cells, limescale which ends up being deposited on these surfaces, forming an insulating layer, particularly on the inner and outer surfaces of the condenser tubes, thus reducing the passage sections and, in any case, reducing heat exchanges.

[0011] Furthermore, the temperature of the primary water vapour circulating in the bundles of tubes constituting the first condenser of the first cell for condensation and, consequently, the temperature of the secondary water vapour obtained by evaporation in each of the following cells both fall from the first to the last of the cells of the installation (from approximately 70°C to approximately 40°C), due to the absence of heating elements under the tanks of the cells. The negative consequence of this drop in temperature is that it causes a notable progressive drop in the efficiency of the installation, particularly in the cells closest to the outlet of said installation.

[0012] Finally and above all, since the cells of known desalination plants communicate with each other to allow the passage of primary water vapor and / or secondary water vapor and / or sea water from one to the other, any defective or abnormal operation within a cell results in the shutdown of that cell. Since the cells of such plants are placed in an arrangement that is commonly called "in series", it is obvious that the shutdown of the operation of one cell has the disastrous consequence of shutting down all the cells in the plant and therefore the temporary cessation of desalination treatment until the defective cell is repaired.

[0013] Other examples of desalination plants in which the supply of their cells with primary water vapor and / or secondary water vapor and / or seawater is done "in series" are described in US patents US 3,021,265 published on February 13, 1962 and respectively US 5,346,592 published on September 13, 1994 as well as in patent applications US 2019 / 301808 published on October 3, 2019 and respectively US 2023 / 294014 published on September 21, 2023. Presentation of the invention

[0014] The present invention aims in particular to avoid these problems of the prior art.

[0015] To this end, it proposes a seawater desalination plant of the type composed of a succession of cells, each equipped with a tank comprising a condenser consisting of a bundle of tubes open at both ends, a first pump capturing the seawater through suction pipes and feeding a boiling boiler capable of heating this seawater in order to generate primary pure water vapour sent via a circuit to the inlet of each of the condensers, a second pump feeding the tanks of the cells with seawater which is sprayed onto the condensers via nozzles arranged in the upper part of the tanks, nozzles also arranged in the upper part of the tanks to evacuate the secondary pure water vapour resulting from the contact between the sprayed seawater and the condensers,said installation being characterized in that it further comprises a heat exchanger device internal to the boiling boiler allowing the latter to generate primary pure water vapor at a temperature of at least 300°C, in that the cells comprise partitioned steam circuits, separated from each other, which do not deliver steam from one to the other, and in that it also comprises means for supplying the cells in parallel with primary pure water vapor and respectively with sea water.,

[0016] An essential advantage of the installation according to the invention compared to current installations is that, since its cells are now supplied in parallel, both with regard to their supply of primary steam and their supply of sea water, in the event of a shutdown occurring on a cell, whether it be an operating failure or a voluntary shutdown for a maintenance requirement, only the cell concerned will be put 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 higher output and better efficiency because shutdowns will be less frequent.In addition to the savings resulting from the fact that the quantity of cells to be built will be lower, it is understood that the footprint of the installation in accordance with the invention will be significantly reduced.

[0017] Very advantageously, the desalination installation according to the invention comprises a device for cleaning at least the condensers and the heat exchanger device. internal heat to the boiling boiler, said cleaning device operating by ultrasound.

[0018] The desalination installation according to the invention may further comprise one or more of the following characteristics, which may be combined with each other.

[0019] Thus each vaporization cell is composed of three chambers which do not communicate with each other, namely a first chamber through which the primary pure water vapor enters, a second chamber essentially constituting the tank equipped with the condenser formed by the bundle of tubes whose two ends are open and open into the first chamber and respectively into a third chamber intended to collect the distilled water obtained liquid by condensation during the passage of the primary water vapor in the tubes of the condenser of the second chamber.

[0020] Preferably, the installation comprises a thermal compressor placed between the boiling boiler and the condensers capable of distributing primary water vapor in the latter under very high pressure of at least eight bars.

[0021] In this case, such an installation may also include means connecting the inlet of the thermal compressor and the outlet nozzles through which the secondary water vapor is evacuated.

[0022] Very advantageously, the installation according to the invention may include a final condensation chamber receiving the portion of secondary steam which is then delivered to the thermal compressor.

[0023] Ideally, the final condensation chamber will then include a cold seawater circuit cooling this chamber and then supplying the cells with cold seawater to be sprayed onto their condenser.

[0024] According to a preferred construction, the installation according to the invention will comprise at least one flash generator making it possible to increase, suddenly and brutally, the temperature of the high-pressure primary water vapor delivered by the thermal compressor and already brought to a very high temperature.

[0025] According to yet another construction variant, the heat exchanger device, internal to the boiling boiler, can be supplied with heat transfer fluid heated by solar energy.

[0026] In this latter hypothesis, the heat transfer fluid circulation circuit will advantageously 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.

[0027] Preferably, the installation according to the invention will then include a thermal reserve receiving the heat transfer fluid heated by solar energy, thus allowing to regulate the temperature of the fluid delivered to the boiling boiler over entire days.

[0028] Ideally, the installation according to the invention will comprise a set of reflectors forming an arc-shaped surface whose focal point will be centered on a tube for circulating the heat transfer fluid which is heated by solar energy.

[0029] The installation may also include an additional heat transfer fluid circuit which successively passes through the brines deposited at the bottom of the tanks of each of the cells.

[0030] In the latter case, preferably, the auxiliary heat transfer fluid circuit will cross the succession of cells in counter-current, from the last cell to the first cell.

[0031] Always advantageously, the heat transfer fluid is based on molten salts.

[0032] Another advantage of the installation described above is that the low pressure in the boiling boiler leads to the formation of vapors, which greatly limits the formation of limescale, which reduces maintenance operations and maintains good system performance.

[0033] 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 almost identical operations and results 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.

[0034] The second subject of the invention is a process for desalinating seawater comprising heating this seawater in a boiling boiler in order to produce 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 simultaneously heating seawater sprayed in the tanks, above the condensers, by generating a low pressure secondary water vapor which is added to the primary water vapor, said process being characterized in that it further consists in heating to a very high temperature, greater than 300°C, a heat transfer fluid circulated in the boiling boiler, in maintaining by suction a pressure lower than 1 bar in said boiling boiler,to bring into contact the boiling boiler in which the pumped sea water circulates 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 into 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 in each of the cells of the succession of cells. Brief description of the drawings

[0035] 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:

[0036] [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;

[0037] [Fig.2] is a cross-sectional diagram of this solar mirror system; and

[0038] [Fig.3] is a diagram of the desalination unit of this installation.

[0039] [Fig.4]] is a diagram of a continuously operating ultrasonic cleaning device, 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 possible deposits of limestone and multiple other minerals

[0040] [Fig.5] is a diagram of an example of construction arranged at the outlet of the desalination plant illustrating the final treatments applied to the distilled water and brine. Description of preferred embodiments

[0041] 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.

[0042] 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 all the reflecting mirrors 6 facing the sun to receive maximum energy from its radiation, and concentrate its 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 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 "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.

[0043] 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.

[0044] 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 intended to heat the heat fluid already contained in a secondary closed circuit.

[0045] The heat exchanger is advantageously provided upstream with two valves, one at its inlet 10a and the other at its outlet 10b, 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 10a and 10b 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.

[0046] Via the heat exchanger, the secondary circuit thus comprises an outlet 24 of heat fluid always heated to a very high temperature, presenting an optimized regularity in the desalination unit, heat fluid which, after its use, returns colder via an inlet 26 in 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.

[0047] Inside the heat exchanger, the tubes in which the heat liquids of the primary circuit 10 and respectively of the secondary circuit 24, 26 circulate are in direct contact.

[0048] It should be noted here that the solar heating device and the heat transfer fluid are specifically chosen to be able to operate the desalination plant, and more particularly its cells, at temperatures that current installations do not provide.

[0049] This is the case with reflective mirrors which concentrate the sun's rays and therefore make it possible to reach temperatures above 500°C, which are impossible to obtain using solar panels.

[0050] Likewise, it is recalled that, if current installations operate with water vapor whose temperature is close to 70°C, the installation according to the invention is characterized by the fact that it operates with primary water vapor whose temperature is at least 300°C, and preferably of the order of 400°C (as will be retained as an example throughout the remainder of this description), thanks as it 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.

[0051] 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 reflector 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.

[0052] In particular, the 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 over a length which can be very significant.

[0053] Advantageously, all 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 self-sufficient.

[0054] [Fig. 3] shows as a whole the installation in accordance with the invention, excluding the solar mirror system which is only one example, preferential in this circumstance, of a means of heating to a very high temperature the heat transfer fluid which circulates in said installation according to the invention.

[0055] That being said, other constructions than, precisely, that operating with reflecting mirrors described as an example in the preceding paragraphs are achievable without departing from the scope of the invention.

[0056] [Fig.3] therefore 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].

[0057] 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 fill the coil 32 which, by heat exchange, brings this seawater to a boil. A vacuum pump 42 maintains a low constant pressure of less than one bar in the boiler tank 34 so as to promote the boiling of the sea water, and to avoid, if necessary, a deposit of limestone which, otherwise, would be deposited on the walls, reducing heat exchanges.

[0058] A pure water vapor recovery nozzle 44, arranged in the upper part of the boiling boiler 34, recovers the primary vapor 46 thus generated to send it to a thermal compressor 48 also capable of also receiving a secondary vapor of low pressure and high temperature pure water 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 the desalination installations described in the preamble in the paragraphs reserved for the prior state of the art. Generally speaking, as was also described in the preamble, more than three vaporization cells are used, typically between four and twenty and most often between ten and fifteen.

[0059] 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.

[0060] The thermal compressor 48 is a static compressor producing a mixture of the primary steam 46 with the secondary steam 50 to obtain, by a drive 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.

[0061] 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, that is to say 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, downstream of the first cell, if it proves necessary to introduce into such other cells superheated primary water vapor 56 in place of the water vapor 46-52 which is already brought to a very high temperature, of the order of 400°C, by the boiling boiler 34, then by the thermal compressor 48.

[0062] 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 primary 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 consisting of 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 liquid by condensation during the passage of the primary water vapor in the tubes 72 of the condenser of the second chamber.

[0063] 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 primary water vapor that it receives, 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.

[0064] To carry out the condensation, in the tubes 72, of the primary 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 to be treated and an outlet nozzle 85 through which water vapor is evacuated, called "secondary vapor" in the remainder of this description.

[0065] The circuit bringing the seawater to be treated to each of 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 cool the vapor present in this final chamber to condense it and, concomitantly, keep the seawater as cold as possible in order to then supply in parallel 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, and to be diffused on its condenser 72.

[0066] Optionally, the seawater circuit comprises, after passing through the final condensation chamber 82, a seawater outlet valve to the outside 110 in order to add to the feed flow of the spray nozzles 84 a flow discharged directly through this outlet, which thus makes it possible to adjust the flow of water passing through the chamber to obtain sufficient cooling of the steam contained therein in order to achieve its complete condensation.

[0067] In parallel with the seawater outlet valve 110, an inlet for additional chemicals 112 allows an addition of necessary elements to be sent before the vaporization of this water.

[0068] The final condensation chamber 82 has an upper outlet 114 directed towards a non-condensable gas vacuum extractor 116.

[0069] 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 simultaneously form the secondary pure water vapor at low pressure and high temperature 50 which is recovered and evacuated by the upper outlet nozzle 85 of this second chamber 78. The temperature of this secondary pure water vapor is then between 200°C and 300°C and its pressure is slightly less than one bar.

[0070] 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.

[0071] The unvaporized 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.

[0072] 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 into 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.

[0073] A first distilled liquid 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.

[0074] 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.

[0075] As an accessory, 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 an auxiliary circuit 105 successively passing through the brackish water deposits 88 at the bottom of each second chamber 78, and this with the aim of producing heating this brackish water to dry it and obtain the most dehydrated brine possible.

[0076] Very advantageously, such an additional circulation of the heat transfer fluid will then be 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.

[0077] Each brine stock 88 containing a lot of sea water, such preferential counter-current passage of the heat transfer fluid causes the evaporation rate of this water to become 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.

[0078] In the example shown in [Fig. 3], the heat transfer fluid delivered at 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 accessory construction which allows counter-current passage of the heat transfer fluid, it will be possible to provide for the addition at the outlet of the pump 90 of as many auxiliary pipes 105 as there are cells. This arrangement will have the advantage of allowing such an accessory construction for brine recovery to operate without discontinuity, even in the event that the single pipe proves to be faulty.

[0079] The dehydrated brine recovery and evacuation circuit 92 therefore starts from the brine depot 88 of the first cell 60 to successively pass through the other depots, ending with that of the last cell 64, then comprises a brine evacuation pump 94 which finally delivers the brine into a recovery tank 96.

[0080] Advantageously, this highly dehydrated brine can be recovered by being resold to refineries which, after treatment and separation of the different minerals, can be used in fields such as mining, cosmetics, detergents, pharmaceuticals or even agriculture, by supplying fertilizers.

[0081] Being loaded in particular with sodium chloride, 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.

[0082] The distilled water collected in the reserve 104 can, as is known, be subject to 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.

[0083] 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 efficiency of remineralization.

[0084] Still advantageously, if notwithstanding the precautions recommended for the operation of the desalination installation according to the invention, a risk of limescale deposits proves possible, said installation will be supplemented with an ultrasonic generator emitting an electrical signal converted into mechanical vibrations by ultrasonic transducers.

[0085] 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].

[0086] Such vibrations will continuously generate slight movements on each of the tubes of the condensers 72 contained in the tanks forming the second chambers of each of the cells, thereby preventing the sedimentation of minerals, in particular limestone, as well as the fouling of the installation. The same would apply to the boiling boiler 34, for example by placing the transducers 119 on the coil 32.

[0087] It will therefore become 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 will obviously result in a significant improvement in efficiency and significant economic gains compared with prior techniques.

[0088] 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 positions of said installation.

[0089] 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 of the type composed of a succession of cells (60, 62, 64) each provided with a tank (78) comprising a condenser (72) consisting of a bundle of tubes open at their two ends, a first pump (40) capturing the seawater via suction pipes (36) and feeding a boiling boiler (34) capable of heating this seawater in order to generate a primary pure water vapor (46) sent via a circuit (44, 52, 56) to the inlet of each of the condensers (72), a second pump (76) feeding the tanks (78) of the cells (60, 62, 64) with seawater which is sprayed onto the condensers (72) via nozzles (84) arranged in the upper part of the tanks (78), nozzles (85) also arranged in the upper part of the tanks (78) for evacuating the secondary pure water vapor (50) resulting from the contact between the sprayed sea water and the condensers (72),said installation being characterized in that it further comprises a heat exchanger device (32) internal to the boiling boiler (34) allowing the latter to generate primary pure water vapor (46) at a temperature of at least 300°C, 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, and in that it also comprises means for supplying the cells (60, 62, 64) in parallel with primary pure water vapor (46) and respectively with sea water.,

2. Installation according to claim 1, 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.

3. Installation according to claims 1 and 2, characterized in that each vaporization cell (60, 62, 64) is composed of three chambers which do not communicate with each other, namely a first chamber (70) through which the primary pure water vapor (46) penetrates, a second chamber (78) essentially constituting the tank equipped with the condenser (72) formed by the bundle of tubes whose two ends are open and open into the first chamber (70) and respectively into a third chamber (74) provided to collect the distilled water obtained liquid by condensation during the passage of the primary water vapor (46) into the tubes of the condenser (72) of the second chamber.

4. Installation according to claims 1 to 3, characterized in that it comprises a thermal compressor (48) placed between the boiling boiler (34) and the condensers (72) capable of distributing in the latter a primary water vapor (52) under very high pressure of at least eight bars.

5. Installation according to claim 4, characterized in that it comprises means connecting the inlet of the thermal compressor (48) and the outlet nozzles (85) through which the secondary water vapor (50) is evacuated.

6. Installation according to claims 1 to 5, 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).

7. Installation according to claim 6, 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.

8. Installation according to claims 6 and 7, 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 (52) delivered by the thermal compressor (48) and already brought to a very high temperature.

9. Installation according to claims 1 to 8, characterized in that the heat exchanger device (32), internal to the boiling boiler (34), is supplied with heat transfer fluid heated by solar energy.

10. Installation according to claim 9, 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.

11. Installation according to claim 10, characterized in that it comprises, between the primary circuit and the secondary circuit, a thermal reserve (20) receiving the heat transfer fluid heated by solar energy, thus making it possible to regulate over days complete the temperature of the fluid delivered to the boiling boiler (34).

12. Installation according to claim 11, 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.

13. Installation according to claims 9 to 12, characterized in that it comprises an additional circuit of heat transfer fluid which successively passes through the brines (88) deposited at the bottom of the tanks (78) of each of the cells (60, 62, 64).

14. Installation according to claim 13, characterized in that the auxiliary 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).

15. Installation according to claims 9 to 14, characterized in that the heat transfer fluid is based on molten salts.

16. A method for desalinating seawater comprising heating this seawater in a boiling boiler (34) in order to produce a 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 simultaneously 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, a heat transfer fluid circulated in the boiling boiler (34), in maintaining by suction a pressure less than 1 bar in said boiling boiler (34),to bring into contact the boiling boiler (34) in which the sea water pumped via the suction pipes (36) circulates and a heat exchanger (32) in which the heat transfer fluid circulates in order to produce a primary water vapor (46) 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 in each of the cells (60, 62, 64) of the succession of cells.

Images