EP4433427A1 - Method and device for desalinating water - Google Patents

Abstract

The invention relates to a method for desalinating seawater, comprising a step of cooling incoming seawater to a temperature of between -2 and 0 degrees Celsius in order to obtain ice crystals suspended in concentrated seawater. The method further comprises: a decanting step (215) for enabling an initial removal of concentrated seawater; a centrifuging step (220) to separate the ice crystals from the concentrated seawater; a step (230) of collecting the ice crystals; and a step (240) of obtaining freshwater by melting the ice crystals.

Description

Description

Title of the invention: Process and device for the desalination of pomaine water Technique

[0001] The present invention relates to a method and a device for desalinating seawater using more particularly a cryocrystallization method.

Technological Background

[0002] Water is more and more coveted around the world. Indeed, the demand for water has only increased in recent years and is destined to continue to grow strongly, in particular due to the needs of industry, energy, with, among other things, the production of hydrogen and also due to population growth. This is why water has become a global issue. However, about ninety-seven percent of the water on Earth is salty. Thus, the industrial development of the production of fresh water or even pure water by desalination processes has taken off in recent years.

[0003] The desalination of sea water makes it possible to obtain fresh water or even pure water from brackish or salt water, such as sea water or ocean water having an average of 35 grams of salt per liter of water. To date, there are two main methods employed in seawater desalination plants. As such, seawater can be desalinated either by vaporizing it through thermal distillation or by jetting it through a ultra-thin membrane that retains salt by reverse osmosis.

[0004] Thermal distillation, the oldest method, consists of sifting seawater to remove its largest impurities and then heating it until it evaporates in tanks where the salts settle. The evaporated water then passes into a condensation tank where it returns in a liquid form.

[0005] Reverse osmosis, the method most commonly used today, consists of carefully filtering seawater through layers of sand and coal. This makes it possible to remove micro-algae and particles in suspension, to so that only the salts remain. The water is then projected under high pressure through very fine semi-permeable membranes. These membranes trap salt and only allow water molecules to pass.

[0006] However, these proven methods for seawater desalination have several drawbacks, particularly in terms of environmental impact. Indeed, thermal distillation is very energy intensive. Reverse osmosis, on the other hand, uses less energy but requires continuous cleaning of the membranes using chemicals. However, the major environmental impact remains the discharge, most often at sea, of effluent from plants using these desalination methods. The main characteristic of these discharged effluents is their high salinity, thus qualified as brine. However, when the brine is discharged without dilution or treatment, it induces an increase in the salt concentration around the discharge zone which can lead to modifications of the local environment, such as anoxia and/or the reduction of light at the seabed level, thus affecting marine ecosystems. At the same time, such effluents may contain chemicals, used for the operation of the plant, and present a high temperature modifying the temperature of the sea water at the level of the brine discharge zone.

[0007] To respond to this problem, a seawater desalination process that does not generate brine discharge is of great interest.

[0008] As such, the American patent US 3,377,814 and the patent application FR 2 334 627 disclose processes for the production of fresh water by cryo-crystallization. Seawater is cooled to form ice crystals. The ice crystals suspended in the seawater are then separated from the seawater by decantation. The ice crystals are then collected and transformed, by melting, into liquid fresh water. Nevertheless, such processes require a relatively long settling separation time which is very often incompatible with industrial requirements and/or rates.

[0009] Patent application WO 2005/015008 discloses another process for producing fresh water by cryo-crystallization in which the ice crystals in suspension in the water are separated by centrifugation. In this process, the decantation is replaced by passage through a centrifuge to separate the ice from the seawater. Such a process makes it possible to treat a larger volume of ice crystals but requires a significant energy input for the separation of the ice crystals.

Summary of the invention

The present invention therefore aims to remedy the aforementioned drawbacks, in particular to propose a method for extracting fresh water from seawater by cryo-crystallization by coupling decantation and centrifugation technologies. Freezing makes it possible to obtain both ice crystals with a high level of purity and residual seawater with a sodium concentration of a few parts per million. This concentration is much lower than that of brine from known desalination methods described above. The combination of decantation and centrifugation makes it possible to obtain a high throughput while reducing the energy required to separate the ice crystals from the seawater.

[0011] To this end, the invention discloses, as a first object, a seawater desalination process comprising a step of cooling incoming seawater to a temperature between -2 and 0 degrees Celsius in order to to obtain ice crystals suspended in concentrated sea water. Said method further comprises:

- a settling step allowing for a first withdrawal of concentrated seawater,

- a centrifugation step carried out after the settling step to separate the ice crystals from the concentrated seawater;

- a step for collecting ice crystals;

- a stage for obtaining fresh water, by melting ice crystals.

[0012] In order to reduce the necessary energy consumption, the step of cooling the incoming seawater of said method may comprise a first step of cooling the incoming seawater to a temperature substantially equal to 5 degrees Celsius and a second stage of cooling the incoming sea water to a temperature between -2 and 0 degrees Celsius. [0013] In order to have a continuously closed process and thus to achieve energy savings, the first step of cooling the incoming seawater can be carried out by heat exchange with the concentrated seawater then with the ice crystals collected at the end of the centrifugation step to cool the incoming seawater.

[0014] To prevent the ice crystals from melting too quickly, the concentrated seawater containing the ice crystals can be maintained at a temperature of between -2 and 0 degrees Celsius during the settling and centrifugation steps.

As a second object, the invention discloses a seawater desalination device comprising:

- at least one chiller cooling incoming seawater to a temperature between -2 and 0 degrees Celsius in order to cause ice crystals to appear in suspension in concentrated seawater;

- a settling tank allowing by settling, after the generation of ice crystals, to eliminate a first part of the concentrated seawater,

- a refrigerated centrifuge, maintained at a temperature between -2 and 0 degrees Celsius, said centrifuge receiving the concentrated seawater and the ice crystals in suspension coming from the at least one cooler, in order to separate the ice crystals from the concentrated sea water.

[0016] In a preferred embodiment making it possible to reduce the energy consumption necessary for the implementation of said device, the at least one cooler may comprise a first cooler cooling the incoming sea water to a temperature of 5 degrees Celsius and a second cooler consisting of an ice crystal generator cooling the seawater leaving the first cooler to a temperature of -2 degrees Celsius.

[0017]Preferably, in order to increase productivity, the ice crystal generator may comprise a cooling tube and a rotating scraper which scrapes the internal walls of said tube on which the ice crystals form.

[0018]Preferentially, the refrigerated centrifuge may comprise a tank with at least one mobile disc rotated in order to rotate the ice crystals and concentrated sea water, the disc being connected to the tank by anti-friction bearings.

[0019] In a preferred embodiment, in order to increase the active surface of the centrifuge, the at least one mobile disc may comprise a plurality of conical discs.

Brief Description of Figures

The invention will be better understood and other characteristics and advantages thereof will appear on reading the following description of particular embodiments of the invention, given by way of illustrative and non-limiting examples, and referring to the attached drawings, among which:

Figure 1 shows a preferred example of implementation of a seawater desalination device according to the invention,

[0022] Figure 2 shows a representative flowchart of steps of the seawater desalination process according to the invention,

[0023] Figure 3 shows a sectional view of a centrifuge, along the axis of revolution of said centrifuge according to the invention,

[Detailed description

In order to simplify the description, the same reference is used in different figures to designate the same object. Thus, when the description cites a referenced object, this object may be identified in several figures. In addition, the figures as well as the description are given by way of non-limiting examples of embodiment.

[0025] As a preamble, it is important to remember that sea water, being salty, freezes at a lower temperature than fresh water, which has a very low salinity. In fact, salt lowers the solidification temperature of water by a few degrees, depending on the amount of salt.

The solidification of water is the transition from a liquid state, disordered water molecules, to a solid state, water molecules neatly arranged next to each other, in an orderly fashion. In a so-called liquid state, fresh and/or pure water has molecules that are relatively free to move relative to each other: they bind together and then quickly undo these molecules. links, and so on. By lowering the temperature of fresh and/or pure water to a temperature between -2 and 0 degrees Celsius, the movements of the water molecules will slow down until they stop, the water molecules will manage to organize themselves and will then bind together in a sufficiently durable manner, to freeze in the form of ice.

[0027] On the other hand, if the water contains salt, as is the case for EM1 seawater, containing both water molecules and salt ions, the process is different. As such, the volume of a salt ion is roughly equal to the volume of a water molecule. However, such ions appreciate the proximity of water molecules. Thus, by slipping between the water molecules, the salt ions separate and separate the water molecules from each other, locally disturbing the arrangement of the latter. The constituents of the salt will come between the water molecules, introducing disorder. Thus, for seawater to solidify, this disorder must be compensated with a temperature lower than 0 degrees Celsius, because the lowering of temperature favors the arrangement of molecules in order to form a solid. For example, sea water containing approximately 35 grams of salt per liter solidifies around -2 degrees Celsius. As a result, at a temperature between -2 and 0 degrees Celsius, only a part of the water molecules of EM1 seawater, i.e. water molecules with no nearby salt ion, go thus able to crystallize. Conversely, salt ions will prevent the crystallization of water molecules in their surrounding area. Thus, by cooling the incoming seawater EM1 to a temperature between -2 and 0 degrees Celsius, this has the effect of crystallizing part of the fresh water contained in the seawater, thus forming ice crystals CG suspended in EM2 sea water with a higher concentration of salt.

[0028] A preferred example of a seawater desalination device 100, in accordance with the invention, is shown in FIG. Said seawater desalination device 100 is composed of at least one cooler 110, a settling tank 160 and a refrigerated centrifuge 120 and is implemented by a method of desalination of seawater. sea 200, illustrated in the flowchart in FIG. 2. Said device 100 is thus implemented by said method 200 in order to desalinate so-called incoming seawater EM1, taken, preferably offshore, at sea.

A first step 210 of said method 200 consists in cooling the incoming seawater EM1. To do this, said incoming seawater EM1 is thus routed to the cooler 110. The communication between the seawater EM1 and the cooler 110 can be done by means of a pipe 113, as illustrated in the figure 1 . However, the person skilled in the art may use any other type of water connection compatible with the use made of it within said device 100, such as for example a tap or a valve. It is also possible that the incoming seawater EM1 is pre-filtered to remove any contaminants.

The cooler 110 is sized to cool the incoming seawater EM1 to a temperature between -2 and 0 degrees Celsius. Such a cooler 110 can consist, for example, of a cooling tube 111 . Such a refrigerant tube 111 can be a hollow structure which receives and conveys a refrigerant or otherwise called a refrigerant. The refrigerant can be any type of fluid that can be used in a refrigeration device. Such a refrigerant, circulating in said tube 111, makes it possible to lower the temperature of the latter to a temperature favoring the freezing of part of the incoming sea water EM1 in order to obtain the formation of ice crystals CG in suspension in concentrated sea water EM2. Thus, the temperature of the cooling tube 111 must be lower than or equal to the freezing point of fresh water but higher than that of salty sea water. As a reminder, such a temperature is between -2 and 0 degrees Celsius. As such, the cooler tube 111 can be made of a material that facilitates heat transfer. By way of illustrative examples, such a material may be stainless steel, copper, aluminum, nickel, tin, or any other material, or any combination thereof. The concentrated seawater EM2, in the liquid phase, then drives said CG crystals formed, towards the outlet of the cooler 110. Nevertheless, the invention is not limited to the choice of the type of cooler 110 nor even to the types of elements of which it is made. A person skilled in the art may use any other type of cooler compatible with the use made of it. within the invention, namely allowing at least one cooling of the seawater EM1 to a temperature between -2 and 0 degrees Celsius.

In a preferred embodiment, the cooler 110 can preferably consist of an ice crystal generator, making it possible to regulate the temperature of the incoming seawater EM1 between -2 and 0 degrees Celsius. Such an ice crystal generator may be composed mainly of a cooling tube 111, allowing the formation of ice crystals CG, in particular on the walls of said tube 111 and of a rotary scraper 112 allowing said ice crystals CG to be detached from the walls of the cooling tube 111. This thus makes it possible to isolate purified fresh water in solid form on the walls of said cooler 110. Said tube 111 and scraper 112 can be in a vertical position or in a horizontal position. According to this preferred mode, the refrigerant passes inside the walls of said tube 111 or outside the thermally conductive walls of said tube 111. The incoming seawater EM1, for its part, passes through said tube 111. CG ice crystals will form on all refrigerated surfaces in contact with liquid EM1 seawater. However, the incoming seawater EM1 will tend to crystallize, preferentially, on the walls of the cooling tube 111.

[0032] Said rotary scraper 112 scrapes, by mechanical action, all the internal walls of said cooling tube 111 in order to detach the ice crystals CG which have formed there to bring them back into the concentrated sea water EM2. Such a scraper 112 makes it possible to increase the crystallization yield. Said scraper 112 is preferably formed of at least two blades arranged along the length of the scraper so that said scraper 112 has a helical shape. However, the invention is not limited to the shape of the scraper or even to the tool and/or the manner used to detach the ice crystals CG from the walls of the cooling tube 111. The ice crystals CG can be removed from the walls said tube 111 in various ways, such as, for example, by gravity, with the use of a lever or even by thermally reducing the strength of the connection between the tube 111 and the ice crystals CG.

[0033] With such a cooler 110, it is possible to control the quantity of ice crystals CG in suspension in the concentrated seawater EM2 by varying the flow rate of seawater EM1 passing through the cooler 110. As for example, a variation in the flow rate can make it possible to have a proportion of the order of 5% to 40% of ice crystals CG. In order to avoid too high a concentration of salt in the concentrated seawater while ensuring a significant production of ice crystals, it is preferred to regulate the flow of seawater to obtain at the outlet of the cooler 110 approximately 10% of ice crystals for 90% EM2 concentrated seawater.

[0034] Once the cooling step 210 has been carried out and the ice crystals CG in suspension in the sea water EM2 have been obtained, a settling step 215 is carried out followed by a centrifugation step 220. The step decantation 2115 consists in carrying out a first withdrawal of concentrated seawater EM2 before the centrifugation step 220 in order to reduce the volume to be treated by centrifugation.

The settling step 215 uses the natural separation which takes place when a solid is contained in suspension in a liquid under the effect of gravity and buoyancy. The settling step 215 is carried out in the settling tank 160, as shown in Figure 1. Such a tank 160 is dimensioned to allow by decantation to eliminate a first part of the concentrated seawater EM2 obtained after passing through the cooler 110. Under the effect of gravity, the ice crystals CG will rise to the surface and a first part of the concentrated seawater EM2 will be removed from the mixture of CG ice crystals suspended in the concentrated seawater EM2 before passing through the centrifuge 120. An upward grip will recover crystals of CG ice in suspension in the concentrated seawater EM2 which will then be transported to the centrifuge 120. A downward intake will recover part of the concentrated seawater EM2 which contains no or very few ice crystals CG in order to throw it back into the sea.

According to the invention and unlike a decantation of the state of the art, the decantation step is not intended to extract the ice crystals CG but to extract part of the concentrated seawater EM2. Therefore, it is not necessary to wait for the ice crystals CG to rise completely to the surface but only for them to rise sufficiently in an upper part of the tank while remaining in suspension in the water of the tank. concentrated sea EM2. Obviously, it is necessary to maintain the temperature of the mixture of EM2 concentrated seawater and CG ice crystals at a temperature between -2 and 0 degrees Celsius during settling.

In order to accelerate settling, such a settling tank 160 may comprise a grid or a particle filter in order to prevent the CG ice crystals from going towards the outlet at the bottom of said tank 160. A pump may also suck up EM2 concentrated seawater which is removed through the bottom intake. Thus, the decantation can be forced at the level of the withdrawal of concentrated seawater EM2 and it is possible to withdraw up to 90% of the concentrated seawater EM2, which makes it possible to considerably reduce the volume of water from concentrated sea and ice crystals to be treated during the centrifugation step 220.

The centrifugation step 220 consists of separating the ice crystals CG formed from the concentrated seawater EM2, due to their difference in density, by subjecting them to centrifugal force. Separation by centrifugation is also known in particular for the skimming of milk or even for the separation of a solid in a liquid according to their density. This same principle is applied to step 220 of said process 200 in accordance with the invention in order to make it possible to accelerate the separation of the ice crystals CG from the concentrated sea water EM2. Indeed, any solid contained in a liquid is subject to gravity, a force which is exerted from top to bottom, and to the buoyancy force, a force which is exerted from bottom to top. Thus over time, a solid suspended in a liquid ends up either falling to the bottom of the container in which it is located or rising to the surface depending on its mass density relative to that of the liquid. However, carrying out such a centrifugation step 220 makes it possible to accelerate this natural phenomenon of separation. In the case of a centrifugation process, the separation rate Vz is governed by Stokes' law:

[0039] [Math.1]

Vz = where r is the radius of the solid in suspension, Ap is the difference in density between the solid in suspension and the liquid containing the solid in suspension, g is the acceleration due to the centrifugal force in the centrifuge and ri the viscosity of the liquid.

[0040] To do this, as illustrated in Figure 1, the ice crystals CG in suspension in the concentrated sea water EM2 pass through the centrifuge refrigerated 120, maintained at a temperature between -2 and 0 degrees Celsius. CG ice crystals have a density substantially equal to 0.9168 grams per milliliter. Between −2 and 0 degrees Celsius, such crystals CG are lighter than concentrated seawater EM2 which has a density substantially equal to 1.0273 grams per milliliter. Thus, subjected to the centrifugal force combined with gravity, the ice crystals CG, lighter than the concentrated sea water EM2, will be projected and attracted to the top and the center of the refrigerated centrifuge 120 along a diagonal of gravity modified while the concentrated seawater EM2 will be projected towards the periphery of the centrifuge 120.

The centrifuge 120 is thus sized to separate the ice crystals CG from the concentrated seawater EM2 at a temperature between -2 and 0 degrees Celsius. As illustrated in Figure 3, such a centrifuge 120 is composed of a tank 121 having refrigerated fixed walls and partitions and comprising a central axis of rotation 123 making it possible to reach high speed of rotation. For example, the speed of rotation of said centrifuge 120, in the case of the invention, can be between 1,000 and 5,000 revolutions per minute. In order to maintain a temperature between -2 and 0 degrees Celsius, the tank 121 can be refrigerated, for example, by means of an external cooler which surrounds said tank 121 . Nevertheless, the invention is not limited to the means used to cool said tank 121 in order to maintain it between -2 and 0 degrees Celsius: any other equivalent means may be used. In addition, to limit energy losses, the use of relatively neutral and insulating materials is preferred for the design of the centrifuge 120. Thus, by way of example, the tank 121 can be made of stainless steel and/or a material reinforced composite.

In a preferred embodiment, in order to facilitate separation by centrifugation, the tank 121 of the refrigerated centrifuge 120 may comprise one or more mobile discs 122 which are driven in rotation at the level of the central axis of rotation 123 of the tank 121 . Each disk 122 is connected to the tank 121 by bearings in order to support and guide said disk 122 in rotation. To avoid any heating within the tank 121, such bearings can preferably be antifriction bearings such as polytetrafluoroethylene, abbreviated as PTFE. As a variant, the person skilled in the art may use any other type of material for the antifriction bearings such as, for example, materials based on polyester, and/or polyetheretherketone, designated by the abbreviation PEEK.

To ensure better separation efficiency, it is preferable to have several rotating mobile discs 122 stacked on top of each other, preferably having a conical shape. As such, the tank 121 comprises a set of discs arranged in parallel with a cone angle, corresponding to the inclination of the centrifugal force combined with gravity, allowing the speed of separation to be increased. The conical shape allows the CG ice crystals to be guided by the combined force of centrifugal force and gravity. As shown in Figure 3, the tank 121 has an inlet

124 through which flows the mixture of ice crystals CG and concentrated seawater EM2, at the outlet of the cooler 110. Said mixture will then circulate through the discs 122. The separation between the ice crystals CG and the concentrated sea water EM2 is produced at the level of each stacked disk 122. Under the influence of centrifugal force, the heaviest component, namely the concentrated seawater EM2, will be deposited radially towards the outer walls of the tank 121 to emerge at the level of a first outlet 126 of the centrifuge 120. The lighter components, namely the ice crystals CG, will move up and towards the central axis of rotation 123 of the bowl 121 . The ice crystals will then come out at a second exit

125 of said centrifuge 120. Thus, the concentrated seawater EM2 flows from the periphery of the centrifuge 120 to the first outlet 126 while the ice crystals move from the central part of the centrifuge 120 to the second outlet 125.

Such a centrifugation step 220 then makes it possible to obtain both ice crystals CG corresponding for example to 10% of the incoming seawater EM1 and both concentrated seawater EM2 thus having a concentration in salt increased significantly by 11% compared to the incoming seawater EM1. By way of example, for an incoming seawater EM1 comprising 35 grams of salt per liter, such an increase of 11% brings the concentrated seawater EM2 to a concentration of approximately 38 grams of salt per liter which is very acceptable compared to brine with significantly higher salt contents. In addition, it is possible to adjust the salt concentration of the concentrated seawater EM2 according to the flow rate of said device 100 but also according to the salt content of the incoming seawater EM1.

As illustrated in Figure 2, after this centrifugation step 220, there follows a step 230 of collecting ice crystals CG. To do this, the CG ice crystals can be, for example, collected in a tank maintained at ambient temperature. Thus, a step 240 for obtaining fresh water ED is then carried out by melting the ice crystals CG. At the same time, the concentrated seawater EM2 is discharged into the sea.

According to a particular embodiment of the invention illustrated in Figures 1 and 2, in order to reduce energy consumption, it is possible to carry out an additional cooling step 211 of the seawater EM1, prior to the step of cooling 210. Preferably, such a step 211 consists in cooling the incoming sea water EM1 to a temperature substantially equal to 5 degrees Celsius. To do this, it is possible to introduce within said device 100 a heat exchanger 150, prior to the cooler 110. Thus, such a heat exchanger 150 is, for its part, sized to cool the incoming sea water EM1 down to at a temperature of 5 degrees Celsius before said seawater EM1 is routed to the cooler 110 which will allow it thermal regulation of the incoming seawater EM1 between -2 and 0 degrees Celsius.

The heat exchange is carried out by first using concentrated sea water EM2 after the removal of the CG ice crystals, then in a second step, using the CG ice crystals collected at the end of the centrifugation step 220. Thus the incoming seawater EM1, warmer than the concentrated seawater EM2 and than the ice crystals CG from the settling 215 and centrifugation 220 steps, will heat the water EM2 sea salt and CG ice crystals while losing calories. Thus, the incoming seawater EM1 will naturally cool down.

To do this, the heat exchanger 150 may comprise a coil-shaped tube immersed in a tank containing the concentrated seawater EM2 after the removal of the CG ice crystals and/or in a container containing the CG ice crystals collected at the end of the centrifugation 220. For the sake of efficiency, it is preferable to do both, namely a passage in the container containing the sea water EM2 then a passage in the tank containing the ice crystals CG, or the reverse. Said submerged tube has an inlet receiving the incoming seawater EM1, for example from a pump, and an outlet connected to the cooler 110. Thus, the incoming seawater EM1 will enter inside the submerged tube and will circulate inside said tube. During the passage of seawater EM1, circulating in said tube, in the tank containing concentrated seawater EM2 after removal of the ice crystals CG, said incoming seawater EM1, warmer, will lose calories, cooling and also heating EM2 concentrated seawater. This makes it possible to lower the temperature of the incoming sea water EM1 but also to bring the temperature of the concentrated sea water EM2 closer to the temperature of the sea. Alternatively or in addition, the concentrated sea water EM2 can be heated naturally by the sun before being discharged into the sea. This has the effect of limiting excessive temperature differentials between the concentrated seawater EM2 discharged and the sea. Subsequently, during the passage of the incoming sea water EM1, circulating in said tube, in the tank containing the ice crystals CG, the incoming sea water EM1 will again lose calories, will further lower its temperature and will heat the ice crystals CG. This makes it possible to once again lower the temperature of the incoming sea water EM1 but also to accelerate the melting of the ice crystals CG in order to obtain liquid fresh water ED.

Once the heat exchange has been completed, the incoming seawater EM1 will be recovered at the outlet to be conveyed to the cooler 110 and thus be regulated at a temperature between -2 and 0 degrees Celsius. The heat exchanger 150 may be sized to enable the desired temperature to be reached as precisely as possible for the incoming seawater EM1 before it passes through the cooler 110: such a temperature depending on the length of the tube. Nevertheless, the invention is not limited to the type of heat exchanger used. A person skilled in the art may use any other type of heat exchanger compatible with the use made of it within the invention. [0050] It will be appreciated by those skilled in the art that the present disclosure is not limited to what is particularly shown and described above. Other modifications can be envisaged without departing from the scope of the present invention defined by the appended claims.

Claims

Claims [Claim 1] seawater desalination process (200) comprising a step of cooling (210) incoming seawater (EM1) to a temperature between -2 and 0 degrees Celsius in order to obtain ice crystals (CG) in suspension in concentrated sea water (EM2), characterized in that the method comprises: - a decantation step (215) allowing a first withdrawal of concentrated seawater (EM2), - a centrifugation step (220) carried out at a temperature included after the settling step (215) to separate the ice crystals (CG) from the concentrated sea water (EM2); - a step (230) for collecting ice crystals (CG); - a step for obtaining (240) fresh water (ED), by melting ice crystals (CG). [Claim 2] Process for desalinating seawater according to claim 1, in which the step of cooling (210) the incoming seawater (EM1) comprises a first step of cooling (211) the incoming sea water (EM1) at a temperature substantially equal to 5 degrees Celsius and a second stage of cooling (210) of the incoming sea water (EM1) to a temperature between -2 and 0 degrees Celsius. [Claim 3] Seawater desalination process according to claim 2, in which the first step of cooling (211) the incoming seawater (EM1) is carried out by heat exchange with the concentrated seawater (EM2) then with the ice crystals (CG) collected at the end of the centrifugation step (220) to cool the incoming sea water (EM1). [Claim 4] Seawater desalination process according to one of Claims 1 to 3, in which the concentrated seawater (EM2) containing the ice crystals (CG) is maintained at a temperature between - 2 and 0 degrees Celsius during the decantation (215) and centrifugation (220) steps. [Claim 5] Seawater desalination device (100) characterized in that it comprises: - at least one cooler (110, 150) cooling incoming seawater (EM1) to a temperature between -2 and 0 degrees Celsius in order to cause ice crystals (CG) to appear in suspension in concentrated seawater (EM2); - a settling tank (160) allowing by settling, after the generation of ice crystals (CG), to eliminate a first part of the concentrated seawater (EM2); - a centrifuge (120) refrigerated in order to be maintained at a temperature between -2 and 0 degrees Celsius, said centrifuge (120) receiving the concentrated sea water (EM2) and the ice crystals (CG) in suspension coming from of the settling tank (160) after removal of part of the concentrated seawater, in order to separate the ice crystals (CG) from the concentrated seawater (EM2). [Claim 6] Device for desalinating seawater (100) according to claim 5, in which the at least one cooler comprises a first cooler (150) cooling the incoming seawater (EM1) to a temperature of 5 degrees Celsius and a second cooler (110) consisting of an ice crystal generator cooling the seawater leaving the first cooler (150) to a temperature of -2 degrees Celsius. [Claim 7] Apparatus for desalinating sea water (100) according to claim 6, for which the first cooler (150) is a heat exchanger giving energy to the ice crystals (CG) and to the concentrated sea (EM2) leaving the centrifuge (120) to cool the incoming sea water (EM1). [Claim 8] Seawater desalination device (100) according to one of Claims 6 or 7, for which the ice crystal generator (110) comprises a cooling tube (111) and a rotary scraper (112 ) which scrapes the inner walls of said tube (111) on which the ice crystals (CG) form. [Claim 9] Seawater desalination device (100) according to one of Claims 5 to 8, for which the refrigerated centrifuge (120) comprises a tank (121) with at least one movable disk (122) driven in rotation in order to drive in rotation the ice crystals (CG) and the sea water concentrated (EM2), the disc (122) being connected to the tank (121) by anti-friction bearings. [Claim 10] Seawater desalination device (100) according to claim 9, for which the at least movable disc (122) comprises a plurality of conical discs (122), i