WO2012104787A1

WO2012104787A1 - Apparatus and method for freeze desalination

Info

Publication number: WO2012104787A1
Application number: PCT/IB2012/050449
Authority: WO
Inventors: Tomer EFRAT; Hadar GOSHEN
Original assignee: I.D.E. Technologies Ltd.
Priority date: 2011-01-31
Filing date: 2012-01-31
Publication date: 2012-08-09
Also published as: JP5855682B2; GB201112065D0; JP2014508268A; GB2485864B; GB2485864A; CN103459324A; CN103459324B

Abstract

Coldness generated by gasifying liquid natural gas is utilized to freeze desalinate sea water using a specially designed ice slurry generator (110) that generates fine ice with high energy efficiency using plates (111), of which subgroups are periodically warmed during the continuous operation of the ice slurry generator (110) to flake of ice. Brine is washed from ice slurry produced by the generated coldness on an ice concentrator (130), and the resulting rinsed ice is melted in a precooling unit (140) to pre-cool sea water feed (101). Heating the cooling fluid from the gasification alleviates the heating need from the gasifying plant.

Description

APPARATUS AND METHOD FOR FREEZE DESALINATION

BACKGROUND

1. TECHNICAL FIELD

[0001] The present invention relates to the field of desalination, and more particularly, to energetically coupling a cooling source with a freeze desalination system via a vacuum ice machine (VIM) with an integrated water vapor deposition process.

2. DISCUSSION OF RELATED ART

[0002] It is well known in the art that ice production, either for cooling, desalination, and other purposes can be carried out in large scale, quite economically, by causing water or brine in a chamber to simultaneously boil and freeze under specified pressure conditions at the triple point of water, being 0°C and 613 Pa (4.6 mmHg).

[0003] In order to maintain the aforementioned triple point conditions, it is crucial to remove the water-vapor as they are being produced. One known solution for treating the very large volume of water-vapor has been to compress the water-vapor to pressures and temperatures at which it can be condensed into liquid water by readily available means, such as water from conventional chiller or cooling-tower, and redeposit the liquid water into the chamber.

[0004] Freeze desalination has been used to extract product water from sea water by generating a low pressure to freeze water and extract brine therefrom, as disclosed e.g. by U.S. Patent No. 3121626. [0005] U.S. Patent No. 4474031 describes a heat pump in which cooling is achieved by desublimation of water vapor from water at the triple point upon evaporator tubes that are kept at -3°C by freon vapor. The heat pump utilizes the heat pump in order to transfer heat towards the source circuit.

[0006] U.S. Patent No. 4420318 discloses an improved vacuum freezing process that is useful in separating solvent from a solution that contains one or more non-volatile solutes in which the desublimated vapor is melted and then evaporated again.

[0007] U.S. Patent No. 4236382 discloses an improved vacuum-freezing high pressure ice melting process in which desublimated vapor is used to provide heat to the ice melting operation within the tubes, and the resulting ice is washed away to allow further desublimation.

[0008] U.S. Patent No. 3859069 discloses a unitary apparatus for minimum heat exchange with the environment is described, with the interior divided into a plurality of chambers. In U.S. Patent No. 3859069 the water vapor is drawn out of the chamber by a compressor and is then fluidized and melted.

[0009] U.S. Patent No. 3714791 discloses a batch evaporative desalination method and apparatus having a pair of similar systems for substantially continuous output is described. Each system has three evacuated chambers in vapor communication with each other. In the first chamber, precooled seawater is sprayed for partial vaporization and consequent formation of ice crystals as latent heat is removed from the seawater.

[0010] All of the above mentioned documents are incorporated herein by reference. BRIEF SUMMARY

[0011] Embodiments of the present invention provide a desalination system comprising an ice slurry generator arranged to produce ice slurry, the ice slurry generator comprising a heat exchanger arranged to extract heat from a pre-cooled feed by a cooling fluid under maintained flow, thereby heating the cooling fluid while producing ice slurry from the feed, an ice concentrator arranged to remove brine from the ice slurry to yield product ice, and a pre-cooling unit arranged to cool feed water by melting the product ice, to yield the pre-cooled feed and product water.

[0012] These, additional, and/or other aspects and/or advantages of the present invention are: set forth in the detailed description which follows; possibly inferable from the detailed description; and/or learnable by practice of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention will be more readily understood from the detailed description of embodiments thereof made in conjunction with the accompanying drawings of which:

Figures 1A, IB and 2 are high level schematic block diagrams of a desalination system that utilizes an external industrial cooling source, according to some embodiments of the invention,

Figures 3A, 3B and 4A-4C are illustrations of a vacuum ice machine operable in the slurry generation sub-system according to some embodiments of the present invention, and Figure 5 is a high level flowchart illustrating a desalination method according to some embodiments of the invention.

DETAILED DESCRIPTION

[0014] Prior to setting forth the detailed description, it may be helpful to set forth definitions of certain terms that will be used hereinafter.

[0015] The term "deposition" or "desublimation" as used herein in this application refers to physical state-of-matter transformation from gas phase into solid phase without first transforming into liquid phase.

[0016] The term "condensation" as used herein in this application refers to physical state- of-matter transformation from gas phase into liquid phase.

[0017] The term "evaporation" as used herein in this application refers to physical state- of-matter transformation from liquid phase into gas phase.

[0018] The term "hard Ice" refers to well-known methods of producing static ice on heat transfer surfaces, such as plate ice, tube ice, or flake ice. Removal of the ice layers in these methods is being done thermally (by introducing hot media internally or externally) or mechanically (by scraping).

[0019] Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is applicable to other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.

[0020] With the increasing use of natural gas, Liquefied Natural Gas (LNG) is becoming more extensively used to ease the gas storage and transportation. The process of gasifying LNG to its natural gaseous state (regasification), prior to distribution in pipelines, absorbs large quantities of heat and therefore provides a readily available and inexpensive source of "coldness" at low temperatures.

[0021] This available "coldness" source is used to return to the technology of desalination by freezing, i.e., utilizing the "coldness" resulting from the LNG regasification process to freeze seawater (using a cooling fluid as a secondary heat transfer fluid), forming ice slurry, and then separating the ice from the brine, washing the residual brine and melting the ice, a process reminiscent to the vacuum freezing vapor compression (VFVC) processes, but without having to use a water vapor compressor to achieve a sufficient condensation pressure.

[0022] Figures 1A, IB and 2 are high level schematic block diagrams of a desalination system that utilizes an external industrial cooling source, according to some embodiments of the invention. Desalination system 100 comprises a vacuum desalination system that utilizes a cooling fluid that is cooled in an external industrial process such as the coupled processes of gasifying natural gas.

[0023] Figures 1A and IB illustrates the use of an external industrial cooling source 125 to generate cooling in an ice slurry generation sub-system 200. Industrial cooling source 125 may be used to cool either a feed 105 to an icy slurry 230, e.g. via a dynamic ice slurry generator 126 (Figure 1A) or to cool a heat exchanger 111 that is used to desublimate water vapor from ice slurry 230 (Figure IB), as explained below. Ice, desalinated water or snow may then be produced from ice slurry 230 as explained below.

[0024] Desalination system 100 comprises an ice slurry generation sub-system 200 comprising a slurry generator 110 (coupled to a vacuum system 260, see below) arranged to produce ice slurry by freezing pre-cooled feed 102 by evaporating a part thereof (while under the triple point, and when no heat sink available, another part of the feed provides this heat for evaporation and freezes), and extracting the deposition heat of the evaporated part by a heat exchanger 111 (such as a heat exchanging surface) toward a cold cooling fluid 121, thereby heating cooling fluid 120. Heated cooling fluid 122 is then pumped back to a gasifier 125 or to the regasification plant for re-cooling.

[0025] Desalination system 100 further comprises an ice concentrator 130 arranged to remove brine from the ice crystals received from ice slurry generator 110 via pipe 114 to yield product ice 144 and wash product ice 144 from the residual brine after concentration, e.g. utilizing a hydraulic-piston-counter-washer (HPCW), and a pre- cooling unit 140 arranged to cool feed water 105 with product ice 144, to yield pre- cooled feed 102 and thereby melt product ice to product water 145. Additional heat, e.g. from the natural gas may be used to melt product ice 144. Alternatively of additionally, cooling fluid 120 may further be used to cool the feed (either initial feed 105 or pre- cooled feed 102) via additional dynamic ice slurry generator 126.

[0026] For example, desalination system 100 may comprise a gasifier 125 arranged to re-gasify Liquefied Natural Gas (LNG) to cool a cooling fluid 120. Heat exchanger 111 is used to re-heat the cooling fluid, and relieve the gasifying plant of the need to heat up cooling fluid 120, which currently exploit a large amount of energy. [0027] Cooling fluid 120 may comprise a water glycol solution acting as an intermediate fluid between the LNG and slurry generator 110. Cooling fluid 120 may comprise C0₂ or even the LNG itself, which are directly evaporated by heat from heat exchanger 111 of slurry generator 110.

[0028] For example, cooling fluid 120 may be C0₂, which upon absorbing heat inside evaporate, and would be transferred back to the coupled process.

[0029] The considered desalination process by freezing is based on using cold water- glycol solution from the LNG regasification process to freeze pre-cooled seawater. To efficiently separate ice from brine and wash it to achieve the required water quality, the ice should be generated in ice slurry form.

[0030] The water to be introduced into ice slurry generator 110 may be, as indicated in Figure 2, a mixture of pre-cooled seawater 102 and residual brine 90 from the concentration and rinsing unit (ice concentrator 130). From ice slurry generator 110 the slurry is pumped towards concentration and rinsing unit 130, which operates on the hydraulic-piston-counter-washer (HPCW) principle. The principle behind HPCW is using the potential energy provided to the ice slurry by the slurry pump to lift the ice cake (generated in the concentrator) above the water level. Naturally, ice that enters a vessel starts to float, forming an ice cake at the top of the vessel 130. Due to the difference between the densities of water and ice, ice rises above water level for approximately 10% of the ice cake volume. However, due to the capillary effect, a 10% rise does not allow the required drainage of brine from the ice cake and does not enable washing the ice to achieve drinking water quality. By using HPCW, the ice cake can be raised for approximately 50% of its volume above water level, providing enough leverage for the ice cake to be drained from the brine.

[0031] The ice generated in this process contains approximately 75% ice and 25% water and is very similar to spring snow, which contains small ice crystals of approximately 0.5 mm-1 mm, surrounded by a very thin layer of water. Since the ice is produced from seawater, the thin film of water contains brine from the process. In the second step, the concentrated ice in the concentration and rinsing unit is rinsed from the residual brine using part of the product water. The rinsing process actually results in the "replacement" of the brine film with a film of fresh water. This occurs as part of the brine returns to the ice slurry generator, while the rest of it is evacuated from the plant as process brine. The amount of brine evacuated from the process is controlled by the brine stream salinity, which actually determines the concentration factor or the yield of the process.

[0032] Since the rinsing process is not 100% efficient, some salinity remains in the end product which can reach 200 ppm TDS of mainly NaCl. The efficiency of the rinsing process depends mainly on the size of the HPCW unit and the amount of washing water used, among other parameters. Product ice 144 is scraped from the top of the HPCW unit and fed into the product tank, where it is melted to produce product water 145.

[0033] The melting process in the product tank 140 is achieved by heat exchange between the ice 144 and the feed water 105 and, as a result, it also serves as a heat recovery mechanism in which the seawater is pre-cooled by melting the ice.

[0034] Thermodynamically, the freezing process can utilize the "coldness" from the cooling fluid most efficiently, due to the low latent heat of freezing compared to the latent heat of evaporation. Minimal energy is provided to the process pumps and the ice scraper at the top of the HPCW unit.

[0035] Figures 3A, 3B and 4A-4C are illustrations of a vacuum ice machine operable in the slurry generation sub-system according to some embodiments of the present invention. The main challenge in the freezing process approach is designing the ice slurry generator 111 to properly balance the required capacity and the production cost. The following figures 3 and 4 offer a design that faces this challenge. Figures 3A and 3B are high level schematic diagrams illustrating a slurry generation sub-system 200 according to some embodiments of the present invention. Figures 4A, 4B and 4C are a perspective cross section, a transverse cross section (across plates 111 A) and a longitudinal cross section (along plates 111A), respectively, of a vacuum ice machine (VIM) that can be used as slurry generator 110.

[0036] Slurry generation sub-system 200 comprises a ice slurry generator 110 that receives liquid water or brine via inlet 121. A pump (not shown) is configured to feed liquid water or brine at a specified temperature via inlet 121 into a first portion 220A of the chamber of ice slurry generator 110. A vacuum system 260, possibly powered by a vacuum pump 265, comprising one or two stages of compression, is configured to generate a pressure of approximately 613 Pa (4.6mmHg) in first portion 220A of the chamber, so that a triple point of water condition is established in first portion 220A. An agitator 240, driven by a motor 245, may constantly stir a mixture of liquid water or brine and ice slurry 230.

[0037] As water vapor evaporates from mixture 230, it flows to the second portion 220B of ice slurry generator 110. Several plates 111A configured as cooling elements are located in a second portion 220B of the chamber. Plates 111A may receive cold cooling fluid 121 and deliver heated cooling fluid 122 according to the following scheme.

[0038] Each plate 111 A may have cold refrigerant inlet 252 and cold refrigerant outlet 258 connected to a cooling unit (such as gasifier 125) configured to cool plates 111A to a temperature which is sufficient for the water-vapor within the second portion 220B to undergo deposition into thin layers of ice that further accumulate on plates 111 A. A heating unit (not shown) is connected to each plate through either hot refrigerant or heated secondary fluid inlet 254 or hot refrigerant/secondary fluid outlet 256 and is pushing hot refrigerant/fluid onto plates 111A on an alternate schedule to heat plates 111 A and remove the ice layers accumulated on plates 111 A and ice falls back into mixture 230. Upon falling, the ice sheets collide onto a deflector 280, which is located above portion 220A, and breaks the ice sheets into smaller particles. A heating sleeve 247 covering at least part of the chamber walls of ice slurry generator 110 sufficiently to avoid accumulation of ice on inner walls of ice slurry generator 110; and through heating water inlet 244 and heating water outlet 247 connected to an auxiliary heating unit (not shown). Ice slurry is removed from mixture 230 through outlet 114.

[0039] In addition to breaking the ice sheets, deflector 280 has two additional functions: Aligning the vapor flow, so that the vapors are equally distributed on the long edge of plates 111A in heat exchanger 111; and preventing water droplets, which may be e.g. sprayed by agitator 240 or carried by the water vapor, from reaching plates 111A.

[0040] Another alternative for removing the ice sheets from plates 111 A is to spray hot water, such as feed water, over the external surface of plates 111A. [0041] A thermodynamic analysis of the aforementioned process carried out by slurry generation sub-system 200 shows that the enthalpy of converting liquid water to water vapor is approximately 2.5 MJ/Kg (600kCal/Kg) and the enthalpy of converting liquid water to ice is approximately 0.33 MJ/Kg (80kCal/Kg). Therefore, for each approximately 7.5Kg of ice produced in first portion 220A, 1 Kg of water-vapors flow into second portion 220B where they turn into ice on cooling elements 111 (by transferring 2.83 MJ/Kg (680 kCal/Kg) deposition enthalpy). Thus, by converting the water-vapors into ice (rather than back to liquid water and back to ice slurry 230), embodiments of the present invention provides approximately 15% more ice than the methods known in the art.

[0042] Alternative chamber 110A (Figure 3B) comprises a first portion 510A and a second portion 510B in a different geometric configuration than the one shown in slurry generation sub-system 200. The operation is very similar to the one described above regarding system 100. While ice slurry 230 is being produced in first portion 510A (the so-called "freezer"), water vapors flow into second portion 510B (the so-called "depositioner"), where they are being cooled by cooling elements 111 by incoming cooling refrigerant inlet 252 (and respective outlet 258). Additionally, one or more of cooling elements 111 may be periodically heated by incoming heating refrigerant inlet 254 (and respective outlet 256), or externally water-sprayed, so that the ice accumulated on cooling elements 111 flakes off to the bottom of second portion 510B to a heap of ice 270 from which it may be conveyed by conveying means (not shown) to ice slurry 230 in first portion 510A and from there to further processing as described above in details. [0043] The periodicity of heating or spraying some of plates 111 A may be selected to remove ice off plates 111A when the ice layer reaches a thickness of 2-3 mm. This as opposed to prior art devices that generate hard ice layers of 8-12 mm. The thinner ice layers not only flake better off plates 111A, but also allow ice removal from some of plates 111 A during operation of the rest of plates 111 A, and hence keeping the process continuous within the chamber of slurry generator 110. Furthermore, generating thin layers only allows quicker removal of ice and a smaller reduction in heat transfer to the plates (the ice layer insulating the cold plate from the warmer vapor). The thinner icy layers also allow a closer separation of plates 111A, reaching e.g. 30-40 mm, resulting in a more compact and efficient VIM.

[0044] Furthermore, in prior art hard ice devices, it is necessary to sub-cool the ice (to about -7°C), so that the ice would be brittle enough to be scraped easily. In the present invention, the depositioned ice layer is not sub-cooled, thus resulting in a more thermally efficient process.

[0045] Figure 5 is a high level flowchart illustrating a desalination method 300, according to some embodiments of the invention. It is understood that method 300 may be carried out using another structure than used in system 100 mentioned above.

[0046] Desalination method 300 comprises the following stages: freezing pre-cooled sea water by heat exchange with a cooling fluid and under maintained flow, to yield ice slurry (stage 152), concentrating the ice slurry into an ice cake (stage 153) and washing brine from the ice cake to yield rinsed ice (stage 154), e.g. by a portion of the product water, and melting the rinsed ice to pre-cool the sea water and to yield product water (stage 156). Desalination method 300 may further comprise introducing a portion of the brine into the pre-cooled sea water (stage 158). Brine 90 may be introduced into pre- cooled feed 102 to regulate throughputs in system 100, and especially input to ice slurry generator 110. Desalination method 300 may further comprise re-cooling the cooling fluid by gasifying Liquefied Natural Gas (LNG) (stage 159), without additional energy expense such as steam heating. This method alleviates the need for heating the gasifying plant by additional energy.

[0047] Method 300 may further comprise the following stages, which are being carried out simultaneously and repeatedly: feeding liquid water or brine into a first portion of a chamber in which specified temperature and pressure conditions are established, such that liquid water, water vapor, and ice coexist in a thermodynamic equilibrium (stage 310); cooling one or more elements located at the second portion of the chamber to a deposition temperature which is sufficient for water vapor arriving from the first portion to undergo deposition into layers of ice that further accumulate on the one or more element (stage 320); and removing the accumulated layers of ice from the one or more element (stage 330).

[0048] Consistent with some embodiments of the present invention, method 300 may further comprise the stage of repeatedly and selectively heating at least a part of walls of the chamber sufficiently to avoid accumulation of ice on inner surfaces of the chamber 340. This stage effectively prevents the mixture of brine/water and ice slurry from freezing off entirely.

[0049] Consistent with some embodiments of the present invention, method 300 may further comprise the stage of collecting the produced ice slurry and converting the collected ice slurry into concentrated ice (stage 350). [0050] Method 300 may further comprise repeatedly heating the one or more elements, for a specified period of time which is sufficient for the accumulated layers of ice to flake off the heated element (stage 345). Another alternative is spraying the elements (e.g. plates) with warm water (stage 346) to remove the ice sheets externally.

[0051] Consistent with some embodiments of the present invention, the heating of stage 345 is carried out based on a specified scheme according to which one or more of the elements are heated while other elements are not heated over different points of time over a repeated heating cycle (stage 347). By using such a scheme, or a similar one, most of the cooling elements are still effectively contributing to the deposition of the ice whereas the heated element is ready for further (and more effective) deposition upon removal of accumulated ice making the process continuous rather than a batch process.

[0052] Advantageously, compared with static ice making machines (e.g. plate ice), a much shorter time is required for heating the cooling elements so that the accumulated ice flakes off. This is because the cooling elements are used to deposit the water vapor as much thinner ice layers compared to static ice machines. In addition, thinning the ice layer reduces its insulating effect and increases the heat transfer coefficient of the cooling elements. This enables to cool the cooling elements according to the present invention to a higher temperature than cooling elements of static ice machines hence increasing the system energy efficiency.

[0053] In addition, the relatively thinner layer of ice, compared to static ice making, allow minimizing the gap between the plates result with the ability of packing much higher number of plates (i.e. heat transfer surface) in a given vessel volume making the vessel smaller and compact. [0054] In case that the accumulated ice that flaked off the cooling elements does not fall directly into the ice slurry, method 300 further comprise the stage of conveying the accumulated layers of ice that flake off the heated element into the ice slurry in the first portion of the chamber (stage 349).

[0055] The present invention uses an elaborate structure of deposition plates to increase the contact area for the vapor, producing vertical ice sheets which readily detach from the plates due to gravity. The relative position of the plates prevents falling ice from clogging the space between the plates.

[0056] In the present invention, the plates are heated to detach the ice sheets is carried out at a relatively high frequency (every 15-20 minutes) and continuously, without interruption of the operation of the ice machine, by switching the heating from one plate module to the next during operation. This heating pattern results in detaching thin ice sheets, thereby diminishing the effect of the reduction in the heat transfer coefficient across the ice sheets (as a result of the ice sheet's conduction resistance) as well as producing easily breakable ice sheets. Additionally, a small amount of heat is required to detach the ice sheets, minimizing energy expenditure and unnecessary melting. Furthermore, the plates may be coated with super-hydrophobic substance, so that the ice flakes would be easily detached, so that the ice accumulation on the plates would be diminished, and the interval between heating of the plates would be longer.

[0057] Agitator 240 and deflector 280 are used to break ice sheets upon impact, and agitator 240 further disintegrates the falling ice sheets. [0058] In addition, agitator 240 increases the heat transfer (of vaporization) by inducing turbulence (by a built-in propeller 290) and by spraying the water through its hollow scoops on the freezer walls thus increasing the heat transfer surface area.

[0059] The chamber of ice slurry generator 110 is optimized for ice production - the heating sleeve 247 prevents wall freezing to keeping free the whole volume for slurry production and efficient stirring, and the vertical orientation of the chamber also allows a more efficient stirring than a horizontal chamber.

[0060] The ice from ice slurry generator 110 is not necessarily deposited back into the chamber, but may be accumulated as a heap to be conveyed away.

[0061] Some of the novel features of the present invention in respect to prior art are: (i) The elaborate structure of plates and the spatial relation between them, (ii) the continuous operation during heating some of the plates to detach ice layers, and carrying out the heating at a high frequency, (iii) breaking ice by detaching thin ice layer which are easily breakable by the deflector and agitator instead of using a milling device, and (iv) the form of the chamber and chamber wall heating.

[0062] Moreover, in the current invention the vapor is depositioned directly, without any intermediate compressor, and removed as solid ice, a feature which maintains the thermodynamic advantage in comparison to a method that melts the desublimated vapor. The ice is accumulated as a heap to be conveyed away.

[0063] Advantageously, although the freezing process is more complex than the evaporation-condensation process, it yields a higher gained output ratio (GOR) as the difference in the latent heat of evaporation and freezing: seawater evaporation requires 7.5 times more thermal energy than freezing does. [0064] Another advantage of system 100, and particularly of presented ice slurry generator 110 in its VIM configuration as illustrated in Figures 3 and 4, is its continuous operation in respect to batch operation of prior art system. Internal heating or external spraying with warm water may be applied to several plates 111A at a time, leaving the large bulk of plates 111 A operative in further vapor desublimation.

[0065] The freezing process can desalinate seawater to drinking water quality, but not to distillation purity, which is in many applications not needed and even sometimes unwanted.

[0066] Furthermore, the system and method relieve the natural gas plant from the generated coldness, which currently requires energy to heat up.

[0067] In the above description, an embodiment is an example or implementation of the invention. The various appearances of "one embodiment", "an embodiment" or "some embodiments" do not necessarily all refer to the same embodiments.

[0068] Although various features of the invention may be described in the context of a single embodiment, the features may also be provided separately or in any suitable combination. Conversely, although the invention may be described herein in the context of separate embodiments for clarity, the invention may also be implemented in a single embodiment.

[0069] Furthermore, it is to be understood that the invention can be carried out or practiced in various ways and that the invention can be implemented in embodiments other than the ones outlined in the description above. [0070] The invention is not limited to those diagrams or to the corresponding descriptions. For example, flow need not move through each illustrated box or state, or in exactly the same order as illustrated and described.

[0071] Meanings of technical and scientific terms used herein are to be commonly understood as by one of ordinary skill in the art to which the invention belongs, unless otherwise defined.

[0072] While the invention has been described with respect to a limited number of embodiments, these should not be construed as limitations on the scope of the invention, but rather as exemplifications of some of the preferred embodiments. Other possible variations, modifications, and applications are also within the scope of the invention. Accordingly, the scope of the invention should not be limited by what has thus far been described, but by the appended claims and their legal equivalents.

Claims

CLAIMS What is claimed is:

1. A desalination system comprising: an ice slurry generator arranged to produce ice slurry, the ice slurry generator comprising a heat exchanger arranged to extract heat from a pre-cooled feed by a cooling fluid under maintained flow, thereby heating the cooling fluid while producing ice slurry from the feed, wherein the cooling fluid is received from an external industrial source, an ice concentrator arranged to remove brine from the ice slurry to yield product ice, and a pre-cooling unit arranged to cool feed water with the product ice, to yield the pre-cooled feed and product water.

2. The desalination system of claim 1, wherein the cooling fluid is further used to cool the pre-cooled feed via an additional dynamic ice slurry generator.

3. The desalination system of claim 1, wherein the heated cooling fluid is pumped to a gasifier for re-cooling,

4. The desalination system of claim 3, further comprising the gasifier, arranged to re- gasify Liquefied Natural Gas (LNG) to cool a cooling fluid, wherein the heat exchanger is used to re-heat the cooling fluid.

5. The desalination system of claim 1, wherein the cooling fluid is C0₂.

6. The desalination system of claim 1, wherein the heat exchanger comprises heat exchanging plates.

7. The desalination system of claim 1, wherein the ice concentrator comprises a hydraulic-piston-counter-washer arranged to wash brine out of the ice slurry by pushing the ice slurry upwards and rinsing the ice slurry with product water.

8. The desalination system of claim 1, wherein the ice slurry generator comprises: a chamber having an inlet and an outlet; a pump configured to feed liquid water or brine at a specified temperature via the inlet into a first portion of the chamber; a vacuum system configured to generate an under pressure of a specified value within the chamber, so that, combined with the specified temperature a working point is established in which: liquid water, water vapor, and ice coexist in a thermodynamic equilibrium and further such that: (i) ice slurry is being produced within the liquid water or the brine and (ii) water vapors are evaporated into a second portion of the chamber; a plurality of plates located at the second portion of the chamber; a cooling unit configured to cool the plates to a deposition temperature which is sufficient for the water vapor within the second portion to undergo deposition into layers of ice that further accumulate on the plates; and means for removing the accumulated layers of ice from the plates.

9. The desalination system of claim 8, wherein the means for removing the accumulated layers of ice comprises a heat source configured to heat the plates, for a specified period of time which is sufficient for the accumulated layers of ice to flake off the heated plates.

10. The desalination system of claim 9, wherein the heating is carried out based on a specified scheme according to which some plates are heated while other plates are not heated over different points of time over a repeated heating cycle.

11. The desalination system of claim 9, wherein the specified period of time is selected to flake ice off the plates at a thickness of 2 mm of the ice layer.

12. The desalination system of claim 8, wherein the means for removing the accumulated layers of ice comprises sprays of warm water applied for a specified period of time which is sufficient for the accumulated layers of ice to flake off the heated plates.

13. The desalination system of claim 9, wherein the second portion is located above the first portion so that the accumulated layers of ice that flake off the heated plates fall into the ice slurry.

14. The desalination system of claim 8, wherein the first portion is located beside the second portion and wherein the system further comprises a conveyer configured to convey the removed accumulated layers of ice into the ice slurry.

15. The desalination system of claim 9, wherein the heat source is a byproduct of the cooling unit.

16. The desalination system of claim 8, further comprising a collecting unit configured to collect the produced ice slurry and an ice concentrator configured to convert the collected ice slurry into snow.

17. The desalination system of claim 8, further comprising a heating device covering at least a part of the walls of the chamber.

18. The desalination system of claim 8, further comprising an agitator arranged to enhance evaporation by spraying ice slurry on walls of the chamber.

19. The desalination system of claim 18, wherein the agitator further comprises a propeller arranged to enhance stirring of the ice slurry.

20. The desalination system of claim 8, further comprising a deflector positioned between the first and the second portions and is shaped to brake ice falling from the plates and protect the plates from droplets rising from the ice slurry.

21. The desalination system of claim 8, wherein the plates are covered by a super- hydrophobic substance.

22. A desalination method comprising: freezing pre-cooled sea water by heat exchange with a cooling fluid and under maintained flow, to yield ice slurry, concentrating the ice slurry into an ice cake, washing brine from the ice cake to yield rinsed ice, and melting the rinsed ice to pre-cool the sea water and to yield product water.

23. The desalination method of claim 22, wherein washing brine from the ice slurry is carried out by a portion of the product water.

24. The desalination method of claim 21, further comprising introducing a portion of the brine into the pre-cooled sea water.

25. The desalination method of claim 22, further comprising re-cooling the cooling fluid by gasifying Liquefied Natural Gas (LNG) without additional energy expense.

26. The desalination method of claim 22, further comprising feeding liquid water or brine into a first portion of a chamber in which specified temperature and pressure conditions are established, such that liquid water, water vapor, and ice coexist in a thermodynamic equilibrium so that: (i) ice slurry is being produced within the liquid water or the brine and (ii) water vapors are evaporated into a second portion of the chamber; cooling a plurality of plates located at the second portion of the chamber to a deposition temperature which is sufficient for the water vapor within the second portion to undergo deposition into layers of ice that further accumulate on the plates; and removing the accumulated layers of ice from the plates.

27. The desalination method of claim 26, wherein the removing is carried out by repeatedly heating the plates, for a specified period of time which is sufficient for the accumulated layers of ice to flake off the heated plates.

28. The desalination method of claim 27, wherein the heating is carried out based on a specified scheme according to which some plates are heated while other plates are not heated over different points of time over a repeated heating cycle.

29. The desalination method of claim 27, wherein the second portion is located above the first portion so that the accumulated layers of ice that flake off the heated plates fall into the ice slurry.

30. The desalination method of claim 27, wherein the first portion is located beside the second portion and wherein the method further comprises conveying the accumulated layers of ice that flake off the heated plates.

31. The desalination method of claim 27, wherein the cooling and the heating are carried out simultaneously by a single process.

32. The desalination method of claim 26, further comprising collecting the produced ice slurry and converting the collected ice slurry into snow.

33. The desalination method of claim 26, further comprising repeatedly and selectively heating at least a part of walls of the chamber sufficiently to avoid accumulation of ice on inner surfaces of the chamber.