FR3029190A1 - DESSALING UNIT COMPRISING AT LEAST ONE EVAPORATION BASIN AND ASSOCIATED SALT EXTRACTION PROCESS - Google Patents

Abstract

The invention relates to a desalination unit (1) of an initial aqueous solution (SO) containing an initial salt concentration, comprising at least one desalting device (10) adapted to receive, at an inlet (101), this solution aqueous solution and to reject separately, at first and second outlets (102, 103), a first aqueous solution (S1) containing a first concentration of salts greater than said initial concentration, and a second aqueous solution (S2) containing a second concentration in salts lower than the initial concentration. According to the invention, said desalination unit further comprises at least one evaporation basin (20) and means for pouring (12) exclusively said first aqueous solution discharged by the desalination device into the evaporation basin. The invention also relates to a process for extracting salts using such a desalination unit.

Description

TECHNICAL FIELD TO WHICH THE INVENTION RELATES The present invention relates generally to the field of desalination units. It relates more particularly to a desalination unit of an initial aqueous solution containing an initial concentration of salts, comprising at least one desalting device adapted to receive, at an inlet, this initial aqueous solution and to reject separately, at first and second outlets, a first aqueous solution containing a first concentration of salts greater than said initial concentration, and a second aqueous solution containing a second salt concentration lower than the initial concentration. The invention finds a particularly interesting application in salt marsh type installations. It also relates to a process for extracting salts from an aqueous solution. BACKGROUND OF THE INVENTION Various techniques are known that can be implemented in desalination units to obtain a fresh, possibly potable water from an aqueous solution concentrated in salts such as seawater. various techniques are generally based on the removal of the concentrated aqueous solution of salts, generally in the sea, then its separation into two solutions: an aqueous solution more concentrated in salts and aqueous solution less concentrated in salts, called fresh water. The seawater withdrawn can optionally be chemically treated before this separation into two solutions. Fresh water is recovered and eventually treated to obtain drinking water. The aqueous solution, more concentrated in salts, is most often discharged into the sea or buried underground. Discharge to the sea poses environmental problems because the salt concentration of the discarded aqueous solution greatly disturbs the local salinity of the sea. Local flora and fauna can be threatened by this rejection.

In addition, disposal at sea requires the use of pumping systems adapted to reject the more concentrated aqueous salt solution far from the shore, these pumping systems being very energy intensive. Similarly, underground burial can disrupt the ecosystem.

OBJECT OF THE INVENTION In order to overcome the aforementioned drawback of the state of the art, the present invention proposes a new optimized desalination unit allowing the recovery of at least a portion of the more concentrated aqueous solution of salts from operation of the desalination unit and avoiding its discharge to the sea or its burial. More particularly, according to the invention there is provided a desalination unit as described above, said desalination unit further comprising at least one evaporation basin and means for discharging exclusively said first aqueous solution discharged by the desalination device into the evaporation basin. Other non-limiting and advantageous characteristics of the desalination unit according to the invention are as follows: the evaporation basin comprises several elements of basins whose bottom and walls are watertight; the desalination device comprises a reverse osmosis pump; the desalination device comprises a device for the distillation of the initial aqueous solution; the desalination device comprises a device for electrodialysis of the initial aqueous solution; - there is provided a pre-concentration device adapted to concentrate in salt a preliminary aqueous solution containing a preliminary concentration of salts so as to form, at least partially, the initial aqueous solution received by the desalting device at its inlet; said pre-concentration device comprises at least one other desalination device placed upstream of said desalination device, this other desalination device receiving at another inlet said preliminary aqueous solution and rejecting at another first outlet said initial aqueous solution; said pre-concentration device comprises a pipe for recirculating at least a portion of the first aqueous solution from the first outlet of said desalination device to the inlet of said desalination device, such that said initial aqueous solution supplying the Desalting device is here formed by a mixture between said first aqueous solution and said preliminary aqueous solution. The invention also proposes a method for extracting salts using a desalination unit as described above, according to which: a) a desalination device of the desalination unit is fed with an initial aqueous solution, b) said first aqueous solution containing the first concentration of salts greater than said initial concentration in the evaporation basin of the desalination unit; c) evaporating the water of the first aqueous solution; d) recovering the salts of the first solution. aqueous.

A further feature of the extraction method described above is that in step a), the initial aqueous solution is obtained by concentrating a preliminary aqueous solution with salts using a pre-concentration device of the unit. desalination. Said pre-concentration device being as defined above, namely either one or more other desalination units placed upstream of the main desalination unit, or a recirculation line. DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT The following description with reference to the accompanying drawings, given as non-limiting examples, will make it clear what the invention consists of and how it can be achieved. In the accompanying drawings: FIG. 1 is a schematic representation of a first embodiment of a desalination unit according to the invention; FIG. 2 is a schematic view of a second embodiment of a desalination unit according to the invention; and - Figure 3 is a schematic view of a third embodiment of a desalination unit according to the invention. In the following description, the terms "upstream" and "downstream" will be used in the direction of the flow of aqueous solutions, to locate the elements of the desalination unit with respect to each other. Similarly, the terms "inlet" and "outlet" will be used in the flow direction of the aqueous solutions to describe the mounting direction of the elements of the desalination unit.

The flow direction of the aqueous solutions is represented by arrows in FIGS. 1, 2 and 3. In the rest of the description, the references will be the same in all the embodiments in which the elements described are identical, so that only the different elements of one embodiment to another will have different references. Furthermore, in the remainder of the description, the term "salts" designates, unless otherwise stated, salts dissolved in an aqueous solution, while the terms "salt crystals" denote salts in solid form. Device In Figures 1, 2 and 3, there is shown first, second and third embodiments of a desalination unit 1. Regardless of the embodiment considered, the desalination unit 1 comprises a desalination device 10 principal. This main desalination device 10 comprises an inlet 101 adapted to receive an initial aqueous solution SO containing an initial concentration CO salts. It is suitable for separating this initial aqueous solution SO into first and second aqueous solutions 51, S2 respectively containing a first concentration C1 of salts greater than said initial concentration CO, and a second concentration of salts C2 less than said initial concentration CO. It is adapted to evacuate by a first outlet 102 the first aqueous solution 51, and a second outlet 103 the second aqueous solution S2. By convention, the aqueous solution entering the desalting device 10 through the inlet 101 is called the initial aqueous SO solution. Similarly, the aqueous solution exiting through the first outlet 102 of the desalination device 10 and having a salt concentration greater than that of the initial solution SO is called the first aqueous solution 51 and the aqueous solution exiting through the second outlet 103 of the desalination 10 and having a salt concentration lower than that of the initial solution SO is called second aqueous solution S2. In the example described here, the initial aqueous solution SO is seawater which can be, according to the second and third embodiments, pre-concentrated from a preliminary aqueous solution. In general, the initial solution SO or preliminary SP is taken from a reservoir 2, here the sea. In a conventional manner, the initial CO concentration in salts of seawater varies from 5 grams per liter (g / L), for example in the Baltic Sea, at around 40g / L. On average, the initial CO concentration in salts of the initial aqueous solution SO is of the order of 35 g / l.

The salts are pairs of ions conventionally contained in seawater. Seawater contains, for example, ions such as chloride ions, sulphate ions, hydrogencarbonate or carbonate ions, sodium ions, ions potassium, magnesium ions, or lithium ions. Tables 1 and 2 below show a part of the various ions conventionally contained in seawater having a salinity of 35 g / l. These tables 1 and 2 are taken from: UNESCO, International Oceanographic Tables, quoted by Andrew W. Dickson and Catherine Goyet (eds.), US Department of State of Energy, version 2, September 1994, ORNL / CDIAC-74, Chapter 5, Part 6.1 "The Major Composition of Seawater", p. V-10. Table 1 Anions Quantity in grams per kilogram Chloride (Cl-) 19.3524 Sulphate (5042-) 2.7123 Hydrogen carbonate (HCO3-) 0.1080 Bromide (Br-) 0.0673 Carbonate (C032-) 0.0156 Fluoride ( F) 0.0013 Hydroxide (HO-) 0.0002 Table 2 Cations Quantity in grams per kilogram Sodium ion (Na) 10.7837 Magnesium ion (Mg2 +) 1.2837 Calcium ion (Ca2 +) 0.4121 Potassium ion (K +) 0.3991 Strontium ion (Sr2 +) 0.0079 Lithium ion (Li) 1.73.10-4 Rubidium ion (Rb) 1.20.10-4 Barium ion (Ba2 +) 2.0.10-5 Polyatomic ions (including molybdenum), o o-5 Polyatomic Ions (including uranium) 3.3.106 The ion pairs that are of particular interest to us are lithium chloride (Li +; Cl-), potassium chloride (K +; sodium chloride (Na, Cl-) or lithium carbonate (2Li +; CO32-).

This list of ion pairs is however not exhaustive. In the case where the initial solution SO is seawater, the first aqueous solution Si is a salt-enriched water with respect to this seawater. This first salt-enriched aqueous solution Si is more commonly called a concentrate.

For a seawater whose initial concentration CO in salts is of the order of 35 gram per liter (g / L), the first concentration Cl in salts of the first aqueous solution Si is generally between 60g / L and 80g / L. The second aqueous solution S2 is a water highly salt-depleted compared to seawater. It is desalinated in this way.

As shown in FIGS. 1 to 3, the desalination unit 1 comprises, upstream of the desalination device 10, a pipe 11 for conveying the seawater to the inlet 101 of the desalination device 10. The pipe 11 comprises a first pump 111 adapted to convey the seawater from the sea to the inlet 101 of the desalter device 10.

As described later, the seawater is optionally pretreated and then directly introduced into the main desalting device (first embodiment of the desalting unit), or mixed with another aqueous solution before it enters the desalination device. main desalination (second embodiment of the desalting unit), is concentrated in salts before being introduced into the main desalination device (third embodiment of the desalting unit). According to a first variant of the desalination device 10, it is a reverse osmosis pump. The reverse osmosis pump is a conventional means of desalting aqueous solution and will not be described in detail here. It will be recalled only that the reverse osmosis pump comprises an element in which first and second compartments are separated by a semipermeable membrane. Said element is, in general, a pipe of great length, and the semipermeable membrane is approximately the same length as said pipe, so that the first and second compartments are formed in the direction of the length of said pipe. The inlet 101 of the reverse osmosis pump corresponds to the inlet of the first compartment. The first output 102 of the reverse osmosis pump 25 corresponds to the output of the first compartment. The second output 103 of the reverse osmosis pump corresponds to the output of the second compartment. The reverse osmosis pump is adapted to receive at its inlet 101 the initial aqueous solution SO, and to circulate this initial aqueous solution SO under pressure, namely under a pressure equal to 40 to 60 bars in general, in the first compartment . The first compartment is intended to evacuate at its outlet the first aqueous solution 51. The reverse osmosis pump is adapted to collect in the second compartment the second aqueous solution S2, and to evacuate at the outlet of said second compartment.

The reverse osmosis pump is thus adapted to exert a pressure, greater than the osmotic pressure, on the initial aqueous solution SO contained in the first compartment, so as to force a part of the water contained in said initial aqueous solution SO towards the second compartment. The semi-permeable membrane is adapted to retain in the first compartment the vast majority of the salts, so that only the water can be transferred to the second compartment. Thus, the reverse osmosis pump is adapted to separate the initial aqueous solution SO in the first and second aqueous solutions Si, S2, the latter being distinct. According to a second variant of the desalination device 10, it may be a distillation device. The distillation device is a conventional means of desalting aqueous solution and will not be described in detail here.

It will be recalled only that the distillation device comprises first and second circuits for circulating aqueous solutions. The inlet of the first circuit corresponds to the inlet 101 of the distillation device. The output of the first circuit corresponds to the first output 102 of the distillation device. The output of the second circuit corresponds to the second output 103 of the distillation device. The distillation device is adapted to receive at its inlet 101 the initial aqueous solution SO, and to circulate said initial aqueous solution SO in the first circuit. The first circuit is intended to heat at a selected temperature and under a selected pressure said initial aqueous solution SO. The first circuit is also intended to evacuate the first aqueous solution S1 at its output. The heating temperature and the pressure are chosen to evaporate part of the water contained in the initial aqueous solution SO. The distillation device is adapted to recover in the second circuit the water vapor originating from said initial aqueous solution SO and to condense it so as to form the second aqueous solution S2. The distillation device is also adapted to evacuate the second aqueous solution S2 at the outlet of the second circuit. Thus, advantageously, the distillation device is adapted to separate the initial aqueous solution SO in the first and second aqueous solutions Si, S2, the latter being distinct. According to a third variant of the desalination device 10, it is an electrodialysis device.

The electrodialysis device is a conventional means of desalting aqueous solution and will not be described in detail here. The electrodialysis device comprises two electrodes separated by a plurality of compartments, each compartment being formed on one side by a cation-permeable membrane, and on the other side by an anion-permeable membrane. The input 101 of the electrodialysis device corresponds to all the inputs of the compartments. The first output 102 of the electrodialysis device corresponds to the output of one compartment out of two. The second output 103 of the electrodialysis device corresponds to the output of the other compartments. The electrodialysis device is adapted to apply a voltage between the two electrodes so as to create an electric field between these two electrodes, and to circulate the initial aqueous solution SO in the compartments. A compartment out of two is intended to evacuate at its outlet the first aqueous solution 51. The other compartments are intended to evacuate at their outlet the second aqueous solution S2. Thus, advantageously, the electrodialysis device is adapted to separate the initial aqueous solution SO in the first and second aqueous solutions 51, S2, the latter being distinct. Each of the variants of the desalination device 10 can be used in all the embodiments of the desalination unit 1, or be associated in part or in whole. The desalination device can in particular comprise a combination of these variants. Whatever the embodiment of the desalination unit and the variant of the main desalination device 10 used, the desalination unit 1 also remarkably comprises at least one evaporation pond 20 and a means for pouring exclusively said first aqueous solution Si rejected by the main desalination device 10 into the evaporation basin 20.

Thus, as shown in FIGS. 1 to 3, the evaporation basin 20 is connected to the first outlet 102 of the main desalination device 10 via a discharge pipe 12. The evaporation basin 20 is adapted to collect the first solution aqueous If that was until then discharged into the sea or buried. The marine fauna and flora are protected, as well as the subsoils. In addition, the evaporation basin 20 is adapted to evaporate all or part of the water contained in the first aqueous solution Si. For this purpose, it is preferably arranged in the sun and / or in the wind, so as to facilitate evaporation of water. The desalination unit 1 according to the invention is thus preferably installed in a region having a hot and dry climate, in a zone subject to the winds. The desalination unit 1 can in particular be installed in the Middle East, a region in which the rate of evaporation of water is of the order of 3500 millimeters per year. In addition, this region offers large free spaces for the installation of the evaporation basin 20. The evaporation basin 20 is adapted to collect salt crystals contained in the first aqueous solution Si. It then plays the role of a basin for settling salts. It also acts as a concentration pool of salts of the first aqueous solution Si. In a variant, it is possible to recover, downstream of the evaporation basin, a final aqueous solution which is much more concentrated in salts than the first aqueous solution Si, in order to post-treat this final aqueous solution to extract salt crystals. Thus, thanks to the desalination unit 1 according to the invention, the first aqueous solution Si is recovered, which limits the harmful effects of its discharge on the environment, and this first aqueous solution Si is recovered by the extraction of salt crystals that can then be exploited.

The means for discharging the first aqueous solution Si into the evaporation pond 20 is here the discharge pipe 12 adapted to transport the first aqueous solution Si from the first outlet 102 of the main desalination device 10 to the evaporation basin 20. Preferably, as shown in FIG. 1, the gravity is sufficient to circulate the first aqueous solution Si from the first outlet 102 of the main desalination device 10 towards the evaporation basin 20. Thus, advantageously, the addition of pumping systems increasing the energy consumption of the desalination unit 1 Alternatively, the discharge pipe 12 may be provided with a second pump 121 adapted to circulate the first aqueous solution Si from the first outlet 102 of the device 10 to the evaporation pond 20. The discharge pipe 12 is here provided with a suitable spill valve 120 in order to regulate the flow rate of the first aqueous solution Si in said discharge line 12. The desalination unit 1 also comprises a discharge line 13 of the second aqueous solution S2 outside the desalination unit 1. The recovery of this second aqueous solution being conventional, we will not discuss it further here. The discharge pipe 13 here comprises a third pump 131 adapted to circulate the second aqueous solution S2 from the second outlet 103 of the desalination device 10 to the outside of the desalination unit 1. Alternatively, the gravity may be sufficient to circulating the second aqueous solution S2 from the second outlet 103 of the desalination device 10 to the outside of the desalting unit 1. In addition, the discharge line 13 is here provided with a reject valve 130 adapted to regulating the flow rate of the second aqueous solution S2 in the discharge line 13. The discharge and discharge pipes 12, 13 are distinct, as are the first and second outlets 102, 103 of the desalination device 10, so that the desalination device 10 is adapted to separate the first and second aqueous solutions Si, S2 separately. In the first and second embodiments of the desalination unit, shown in FIGS. 1 and 2, the evaporation pond 20 comprises a single pond element 21. In the third embodiment, shown in FIG. it can be provided that the evaporation basin 20 comprises several basin elements 21, here upper basin elements 21a, 21b intermediate and 21c lower.

These elements of upper, intermediate and lower basins 21a, 21b, 21c are placed in the direction of flow of the aqueous solution, so that the upper basin element 21a is positioned directly downstream of the discharge pipe 12 and upstream of the intermediate and lower basin elements 21b, 21c, and so that the intermediate basin element 21b is positioned directly downstream of the upper basin element 21a and upstream of the lower basin element 21c. The upper basin elements 21a, 21b intermediate and 21c lower are adapted to receive different by-products from the first aqueous solution Si. These by-products are, for example, aqueous solutions girls from the first aqueous solution Si or crystals of salts. As shown in FIG. 3, the upper basin elements 21a, 21b intermediate and 21c lower can be cascaded relative to each other so as to facilitate the extraction of the various salt crystals. It will also be possible to envisage bearings, filters, or airlocks for passage from one pelvic element 21 to the other. Upper and lower link valves 213a, 213b may also be provided to regulate the flow of aqueous solution transferred from one pond member 21 to another. Advantageously, the gravity is sufficient to transfer the concentrated aqueous solution of salts from one basin element 21 to another. This limits the use of pumps that consume energy. According to a variant not shown, it can be provided that the pelvic elements 21 are arranged next to one another, or one after the other, on the same level, and not in cascade. Advantageously, the evaporation basin 20 comprising several basin elements 21 is adapted to the implementation of specific treatment steps in each basin element 21. The multiple basin elements 21 provide a certain flexibility of use. since the treatment steps can be modulated from one basin element 21 to another depending on the wishes of an operator of the desalination unit 1. Thus, for example the basin elements 21 are suitable for a single type of salt crystals, called "mono-salt" extraction, or the extraction of several salt crystals of different chemical compositions, called "multi-salt" extraction. Whatever the embodiment variant of the evaporation basin 20, the bottom 211 and the walls 212 of the basin element or elements 21, 21a, 21b, 21c are sealed.

For example, the bottom 211 and the walls 212 of the basin element or elements 21, 21a, 21b, 21c are made of a plastic material that is watertight and resistant to high concentrations of salts. Thus, advantageously, the bottom 211 or the sealed walls 212 of the evaporation basin 20 are adapted to prevent the water or the salts contained in the first aqueous solution Si from escaping from said evaporation basin 20. It is note that, whatever the embodiment of the desalination unit 1, the evaporation basin 20 and the desalination device 10 are distinct and different. They are separated by a spill line 12.

In the first embodiment of the desalination unit, the desalination device is directly fed with seawater conveyed, for example, by the delivery line 11 to the inlet 101 of this desalination device 10. According to second and third embodiments of the desalination unit 1, shown in Figures 2 and 3, the desalination unit 1 further comprises a pre-concentration device 30, 40 of a preliminary aqueous solution SP containing a preliminary concentration of salts. This pre-concentration device 30, 40 is adapted to concentrate in salt the initial aqueous solution SO before it arrives in the inlet 101 of the main desalination device 10. The first aqueous solution 51 discharged at the outlet of the main desalination device 10 of these two embodiments of the desalination unit 1 is then also more concentrated in salts. The extraction of salts by evaporation of water from the aqueous solution is thus faster.

According to the second embodiment of the desalination unit 1 shown in FIG. 2, the desalination unit 1 is in all respects identical to the desalination unit of the first embodiment, except that it further comprises the pre-concentration device 30. The pre-concentration device 30 is a recirculation line 30 adapted to take all or part of the first aqueous solution Si at the first outlet 102 of the desalination device 10 to reintroduce it into the conveying duct 11, upstream of the inlet 101 of the main desalination device 10.

The recirculation line 30 may be provided with a recirculation valve 31 adapted to regulate the flow rate of the first aqueous solution Si flowing in said recirculation line 30. Alternatively, the recirculation line 30 may comprise a filter element adapted to allow passing the first aqueous solution Si in said recirculation line 30 when the first concentration C1 of this first aqueous solution Si is below a predetermined concentration threshold value, for example 80 g / L. This filter element is for example a semi or semi-permeable membrane. It can also be envisaged that the filter element comprises a sensor allowing the determination of the first concentration C1 of the first aqueous solution and control means for controlling the recirculation valve 31 as a function of the first concentration C1 of said first aqueous solution. If. Thus, according to this second embodiment, the initial aqueous solution SO introduced by the delivery line 11 to the inlet 101 of the desalination device 10 is formed of a mixture of sea water taken directly from the sea, which here forms the preliminary aqueous solution SP, and the first aqueous solution Si taken by the recirculation line 30 at the outlet of the desalting device 10.

This second embodiment of the desalination unit 1 is simple to implement and inexpensive. According to the third embodiment of the desalination unit 1 shown in FIG. 3, the desalination unit is similar to that described in the first embodiment, except that it further comprises, upstream of the main desalination device 10 previously described, the pre-concentration device 40. According to this third embodiment, the pre-concentration device 40 is another desalination device 40, hereinafter referred to as the preliminary desalination device 40.

Thus, here the first pump 111 of the conveying conduit 11 is adapted to take the preliminary aqueous solution SP, namely seawater, and to route it to an inlet 401 of the preliminary desalination device 40. preliminary desalination device 40 produces, at each of its two outlets 402, 403, as the main desalting device 10, on one side an aqueous solution more concentrated in salts than the preliminary aqueous solution SP, and on the other side, an aqueous solution less concentrated in salts than the preliminary aqueous solution SP. A connecting line 42 connects a first outlet 402 of the preliminary desalination device 40 to the inlet 101 of the main desalination device, so as to introduce the more concentrated aqueous solution of salts than the preliminary aqueous solution SP produced by the desalination device. preliminary desalination 40 at the inlet of the main desalination device 10. Another discharge line 43 is intended to reject the less concentrated aqueous solution than the preliminary aqueous solution SP produced by the preliminary desalination device 40 from a second outlet 403 of the preliminary desalination device 40 to the outside of the desalination unit. According to this third embodiment of the desalination unit 1, the main desalination device 10 and the preliminary desalination device 40 are not necessarily identical. In other words, the preliminary desalination device 40 may be a distillation device, and the main desalination device 10 may be a reverse osmosis pump for example.

Alternatively, it can also be provided that the preconcentration device comprises multiple desalination devices arranged in series from each other, upstream of the main desalination device, so as to concentrate the initial aqueous solution SO by a succession of desalination devices.

It could also be envisaged to place upstream of the main desalination device any pre-concentration device known to those skilled in the art so as to concentrate the initial aqueous solution SO entering into said desalination device. Preliminary desalination 40 upstream of the main desalination device 10 is particularly advantageous in the case where the main desalination device 10 is a reverse osmosis pump. Indeed, the reverse osmosis pump being relatively low energy consuming, the assembly comprising the preliminary desalination device 40 and the main desalination device 10 keeps a reasonable power consumption. Alternatively, one could consider combining the different pre-concentration devices described above. In particular, it can be provided that the recirculation line which withdraws at least a portion of the first aqueous solution at the outlet of the main desalination device returns this first aqueous solution to the inlet of the pre-concentration device formed by the preliminary desalination device. or at the inlet of the main desalination device, downstream of this preliminary desalination device. In addition, regardless of the embodiment of the desalination unit 1, it is possible to place upstream of the main desalting device 10 different pretreatment elements of the initial aqueous solution SO. These pretreatment elements are suitable for removing any particles suspended in seawater, or to avoid the development of microorganisms for example.

Typically, these pretreatment means of the initial aqueous solution SO are mechanical means such as sand filters or cartridge filters, for example, as well as chemical means. These pretreatment elements are preferably used in desalination units 1 whose desalination device 10 is a reverse osmosis pump. Also, whatever the embodiment of the desalination unit 1, it is possible to place downstream of the discharge line 13, post-treatment elements of the second aqueous solution S2. These post-treatment elements are intended to treat this second aqueous solution S2 in order to obtain a drinking water solution. Process The desalination unit 1 is used to carry out the salt extraction process according to the invention. According to the salt extraction method according to the invention, the operator performs the following steps: a) he controls the supply of the desalination device 10 of the desalination unit 1 with the initial aqueous solution SO, b) he controlling the pouring of said first aqueous solution Si containing the first concentration C1 salts higher than said initial concentration CO, obtained at the outlet of the desalination device 10, in the evaporation basin 20 of the desalination unit 1, c) it the water is evaporated from the first aqueous solution Si, d) it recovers the salts of the first aqueous solution Si, in the form of salt crystals. According to a first embodiment of the extraction method according to the invention, implementing the first embodiment of the desalination unit according to the invention (FIG. 1), in step a), the operator the first pump 111 of the conveying pipe 11 so as to take the initial aqueous solution SO in a tank 2, here the sea. The first pump 111 of the conveying pipe 11 conveys said initial aqueous solution SO to the inlet The desalting device 10 separates the initial aqueous solution SO into the first aqueous solution 51 and the second aqueous solution S2.

More specifically, when the desalination device 10 used is the reverse osmosis pump, the operator circulates the initial aqueous solution SO in the first compartment of the pump. It also imposes a pressure in the first compartment so as to force part of the water contained in the initial aqueous solution SO through the semipermeable membrane and in the second compartment. Thus, as the initial aqueous solution SO is circulated in the first compartment, it concentrates in salt until it forms the first aqueous solution 51, conveyed to the first outlet 102 of the desalination device 10.

The forced water through the semipermeable membrane in the second compartment is mixed, in this second compartment, with an aqueous solution already present so as to form the second aqueous solution S2, conveyed to the second outlet 103 of the desalination device 10 When the desalting device 10 used is the distillation device, the operator circulates the initial aqueous solution SO in the first circuit of this distillation device. The operator imposes a pressure and a heating temperature in a portion of the first circuit so as to evaporate a portion of the water contained in the initial aqueous solution SO. Thus, as evaporation of water of the initial aqueous solution SO, said aqueous solution is concentrated in salts so as to form the first aqueous solution Si conveyed to the first outlet 102 of the desalination device 10.

The evaporated water of the first circuit is condensed in the second circuit so as to form the second aqueous solution S2 conveyed to the second outlet 103 of the desalination device 10. When the desalination device 10 used is the electrodialysis device, the The operator circulates the initial aqueous solution SO in the compartments of the electrodialysis device. The operator imposes a voltage between the two electrodes so as to create an electric field in all the compartments. The electric field thus created forces the anions of one compartment out of two to migrate, in the direction of the electric field, towards the nearest neighbor compartment. At the same time, the electric field created forces the cations of the same compartment out of two to migrate in the opposite direction to the nearest neighbor compartment. One in two compartments is enriched with ions, while the other compartments are depleted in ions.

It is the position of the membranes permeable to anions or cations on one side or the other of the compartments which defines which compartments become enriched or deplete in ions. Thus, as the flow of the initial aqueous solution SO in the compartments of the electrodialysis device progresses, it becomes enriched with salts in every other compartment so as to form the first aqueous solution Si, conveyed to the first outlet 102 of the desalination device 10, and is depleted of salts in the other compartments so as to form the second aqueous solution S2, conveyed to the second outlet 103 of the desalination device 10.

Moreover, whatever the desalination device used, the operator controls the third pump 131 and the reject valve 130 of the discharge line 13 so as to reject the second aqueous solution S2 from the second outlet 103 of the desalination device 10 to the outside of the desalting unit 1. The operator can further impose on the second aqueous solution S2 various treatments in the after-treatment elements so as to make this second aqueous solution S2 potable. The second aqueous solution S2 can be used advantageously in agriculture or as drinking water. In step b), the operator also controls the discharge valve 120 of the discharge pipe 12 so as to discharge, under the effect of gravity, the first aqueous solution Si in the evaporation basin 20. In alternatively, in step b), the operator controls the second pump 121 and the overflow valve 120 of the discharge line 12 so as to pump out the first aqueous solution Si into the evaporation basin 20 The water contained in the first aqueous solution Si placed in the pond element 21 evaporates with the aid of sun and wind, so that the first aqueous solution Si concentrates in salts (step c)). . First crystals of salts of a first chemical composition then crystallize in the bottom 212 of the pond element 21. In step d), these first salt crystals are recovered from the bottom 212 of the evaporation pond 20, by example using a rake or any other means known to those skilled in the art to recover salt crystals in an aqueous solution. Then, second salt crystals of a second chemical composition crystallize in the bottom 212 of the pond member 21. These second salt crystals are also recovered from the bottom 212 of the evaporation pond 20 in step d). Indeed, in general, salt crystals crystallize in an aqueous solution concentrated in salts when the concentration of said salts in said aqueous solution is at least equal to the saturation concentration of these salts in this aqueous solution, said concentration saturation mainly depending on the salts and the composition of the aqueous solution.

Thus, the first and second salt crystals crystallize at different times in the first aqueous solution Si since they are present at different concentrations in the first aqueous solution Si. The first and second salt crystals can therefore be recovered separately.

The same applies to all the salt crystals obtainable from the first aqueous Si solution. The salt crystals obtained are then treated so as to obtain one or more desired end products. According to the second and third salt extraction processes, in step a), the initial aqueous solution SO is obtained by concentrating a preliminary aqueous solution SP with salts by means of a pre-concentration device 30, 40 In particular, the initial concentration CO in salts of the initial aqueous solution SO can reach 160 grams per liter (g / L) thanks to the pre-concentration device 30, 40. This concentration corresponds to a overall concentration taking into account all the salts present in the initial aqueous solution. In practice, it may be provided additional steps so as to concentrate in salt the initial aqueous solution SO at the inlet 101 of the desalination device 10, so as to concentrate the first aqueous solution Si at the first outlet 102 of the desalination device 10.

According to the second salt extraction method implementing the second embodiment of the desalination unit (FIG. 2), in step a), the operator controls the first pump 111 of the delivery pipe 11 so as to take the preliminary aqueous solution SP in the tank 2, here the sea.

The first pump 111 of the delivery line 11 conveys said preliminary aqueous solution SP to the inlet 101 of the desalination device 10. The operator controls the overflow valve 120 of the discharge pipe 12 and the recirculation valve 31 of the the recirculation line 30 so as to take a part of the first aqueous solution Si flowing to the first outlet 102 of the desalting device 10. For example, the operator or the filter element controls the recirculation valve 31 so as to take at least a portion of the first aqueous solution Si when its first salt concentration C1 is less than the predetermined concentration threshold value, namely in our example 80g / L. This portion taken from the first aqueous solution Si is conveyed into the recirculation line 30 and reinjected into the delivery line 11 of the desalination device 10, so that said first aqueous solution Si mixes with the preliminary aqueous solution SP to form the initial solution SO. These steps are repeated in a loop, as many times as the operator desires, so as to concentrate in salt the first aqueous solution Si discharged at the first outlet 102 of the desalting device 10.

Meanwhile, the operator controls the discharge valve 120 of the discharge pipe 12 and the recirculation valve 31 of the recirculation pipe 30 so as to discharge, under the effect of gravity, the other part of the first solution If evacuated to the first outlet 102 of the desalter 10 in the evaporation basin 20.

Alternatively, in the case where the discharge pipe 12 is provided with the second pump 121, the operator also controls the second pump 121, so as to discharge, by pumping, the other part of the first aqueous solution Si evacuated to the first outlet 102 of the desalination device 10 in the evaporation basin 20.

The following steps b), c) and d) of the salt extraction process are identical to those described in the first embodiment of the extraction process. Alternatively, it would be possible to recirculate, in the recirculation line 30, all of the first aqueous solution Si from the desalination device 10. In this case, in step a) the operator controls for example the valve discharge device 120 of the discharge pipe 12 and the recirculation valve 31 of the recirculation pipe 30 and possibly the second pump 121, so as to discharge, under the effect of gravity or possibly by pumping, the first aqueous solution Si discharged to the first outlet 102 of the desalination device 10 in the evaporation basin 20 when the first salt concentration C1 of the first aqueous solution Si is greater than or equal to the predetermined concentration threshold value. According to the third salt extraction method using the third embodiment of the desalination unit (FIG. 3), the operator controls, in step a), the first pump 111 of the delivery line 11 of in order to take the preliminary aqueous solution SP in the tank 2, here the sea. The first pump 111 of the delivery line 11 conveys said preliminary aqueous solution SP to the inlet 401 of the preliminary desalination device 40. The desalination device Preliminary 40 separates the preliminary aqueous solution SP into two parts: on one side, an aqueous solution more concentrated than the preliminary aqueous solution, and on the other side, a less concentrated aqueous solution than the preliminary aqueous solution. The more concentrated aqueous solution than the preliminary aqueous solution SP is introduced in step a) in the main desalting device 10, at the inlet 101. In the following, this aqueous solution more concentrated than the preliminary aqueous solution SP is, by convention, called initial aqueous solution SO. The operation of the preliminary desalination device 40 is similar to the operation of the main desalination device 10 already described. The operator controls the desalination unit 1 so as to reject the aqueous solution less concentrated in salts than the preliminary solution SP from the outlet 403 of the preliminary desalination device 40 to the outside of the desalination unit 1. operator can also impose downstream of this outlet 403 various treatments in the post-processing elements of the desalination unit 1 so as to make potable this aqueous solution less concentrated in salts than the preliminary solution SP. As previously described, the desalting device 10 separates the initial aqueous solution SO into the first aqueous solution Si and into the second aqueous solution S2. As described in the first embodiment of the extraction method, in step b) the operator controls the third pump 131 and the reject valve 130 of the discharge line 13 so as to reject the second aqueous solution S2 since the second outlet 103 of the desalination device 10 to the outside of the desalination unit 1. Here, the evaporation basin 20 comprises several basin elements 21 (FIG. 3). In step b), the operator then controls the discharge valve 120 of the discharge pipe 12, and the upper connection valve 213a so as to discharge, under the effect of gravity, the first aqueous solution Si in the upper basin element 21a of the evaporation basin 20.

Alternatively, in step b), the operator also controls the second pump 121, the overflow valve 120 of the overflow pipe 12, and the upper link valve 213a, so as to discharge, by pumping, the first aqueous solution Si in the upper basin element 21a of the evaporation basin 20.

The water contained in the first aqueous solution Si of the upper pond element 21a evaporates with the aid of the sun and the wind (step c)) so that the aqueous solution present in the upper basin element 21a is concentrated in salts. First salt crystals of a first chemical composition then crystallize in the bottom 212 or on the surface of the upper basin element 21a. These salt crystals are recovered (step d)). The operator then controls the upper link valve 213a and the lower link valve 213b so as to transfer the aqueous solution present in the upper basin element 21a, in the intermediate basin element 21b (step b)). The operator evaporates the water contained in the aqueous solution present in the intermediate basin element 21b, here with the aid of sun and wind, so that the latter is concentrated in salts (step c)). Second salt crystals of a second chemical composition then crystallize in the bottom 212 of the intermediate basin element 21b, which are recovered (step d)). The operator then controls the lower link valve 213b so as to transfer the aqueous solution present in the intermediate basin element 21B, into the lower basin element 21c (step b)).

The operator evaporates the water contained in the aqueous solution of the lower basin element 21c, here with the aid of sun and wind, so that it is concentrated in salts (step c)). Third crystal salts of a third chemical composition then crystallize in the bottom 212 of the lower basin element 21c, which are recovered (step d)). The various salt crystals obtained are finally treated so as to obtain one or more desired end products. As mentioned above, the steps related to the presence of several basin elements can also be performed in the first and second embodiments of the extraction process, when the first and second embodiments of the desalination unit comprise such a device. basin. We can obviously provide two or more basin elements.

The description of the third embodiment of the extraction process emphasizes that steps b), c) and d) can be carried out partly simultaneously, and not only sequentially as is the case in the first embodiment of the method. extraction for example. Alternatively, the extraction process can be applied to any aqueous solutions containing salts, such as aqueous solutions from salt marshes or brines or brackish water. Thus, thanks to the desalination unit 1 according to the invention, and thanks to the salt extraction process according to the invention, it is possible to obtain fresh water, and to avoid the rejection of the solution. aqueous concentrated in salts in nature while promoting this aqueous solution concentrated in salts by extraction of salt crystals. In particular, the described invention is of interest for the extraction of lithium salts and potassium salts. Indeed, since the advent of lithium batteries involved in the industrial processes of manufacturing cell phones, computers or electric or hybrid cars, lithium consumption has increased sharply. Likewise, the potassium extraction is particularly advantageous when potassium is involved in the manufacture of potassium hydroxide, that is to say the various solutions of potassium salts, and in particular aqueous solutions of potassium hydroxide. potassium. Potash is used in the manufacture of fertilizers, with fertilizers accounting for nearly 95% of global potash consumption. By taking the example of the first embodiment of the desalination unit 1, installed in the Middle East, in which the desalination device 10 is a reverse osmosis pump capable of taking seawater with a flow rate of 100,000 cubic meters per day, the concentration of potassium and lithium in this seawater being estimated at 400 grams per cubic meter and 0.17 grams per cubic meter respectively, the quantities of potassium and lithium that can be extracted from The seawater from the desalination unit according to the invention amounts to 40,000 tons of potassium and 20 tons of lithium per year. These amounts represent about 0.1% of the current annual world production of potassium and lithium.

Claims (10)

REVENDICATIONS1. Desalination unit (1) of an initial aqueous solution (S0) containing an initial concentration (CO) of salts, comprising at least one desalting device (10) adapted to receive, at an inlet (101), this initial aqueous solution (SO) and separately rejecting, at first and second outlets (102, 103), a first aqueous solution (51) containing a first concentration (C1) of salts greater than said initial concentration (CO), and a second aqueous solution (S2) containing a second concentration (C2) of salts lower than the initial concentration (CO), characterized in that said desalination unit (1) further comprises at least one evaporation basin (20) and means for discharging (12) exclusively said first aqueous solution (51) discharged by the desalination device (10) into the evaporation basin (20). 2. desalination unit (1) according to claim 1, wherein the evaporation pond (20) comprises several basin elements (21) whose bottom (212) and the walls (211) are sealed. 3. desalting unit (1) according to one of claims 1 and 2, wherein the desalination device (10) comprises a reverse osmosis pump. 4. Desalting unit (1) according to one of claims 1 to 3, wherein the desalting device (10) comprises a distillation device of the initial aqueous solution (SO). 5. desalting unit (1) according to one of claims 1 to 4, wherein the desalting device (10) comprises a device for electrodialysis of the initial aqueous solution (SO). 6. desalting unit (1) according to one of claims 1 to 5, wherein there is provided a pre-concentration device (30, 40) adapted to concentrate in salt a preliminary aqueous solution (SP) containing a preliminary concentration in salts so as to form, at least partially, the initial aqueous solution (SO) received by the desalting device (10) at its inlet (101). The desalting unit (1) according to claim 6, wherein said pre-concentration device (30, 40) comprises at least one other descaling device (40) placed upstream of said desalination device (10), this other device desalting unit (40) receiving at another inlet (401) said preliminary aqueous solution (SP) and discharging at another first outlet (402) said initial aqueous solution (SO). 8. desalination unit (1) according to one of claims 6 and 7, wherein said pre-concentration device (30, 40) comprises a recirculation line (30) of at least a portion of the first aqueous solution (Si) from the first outlet (102) of said desalination device (10) to the inlet (101) of said desalination device (10), such that said initial aqueous solution (SO) feeds the desalination device (10). ) is here formed by a mixture between said first aqueous solution (Si) and said preliminary aqueous solution (SP). 9. A method of extracting salts using a desalination unit (1) according to one of claims 1 to 8, wherein, a) a desalting device (10) of the desalination unit (1) is supplied by an initial aqueous solution (SO), b) pouring said first aqueous solution (Si) containing the first concentration (Cl) salts higher than said initial concentration (CO) in the evaporation basin (20) of the unit of desalination (1), c) the water is evaporated from the first aqueous solution (Si), d) the salts are recovered from the first aqueous solution (Si). The method of extracting salts according to claim 9, wherein in step a), the initial aqueous solution (SO) is obtained by concentrating a preliminary aqueous solution (SP) with salts using a pre-concentration device (30, 40) of the desalting unit (1).