WO2011004416A1

WO2011004416A1 - Thermal desalination plant

Info

Publication number: WO2011004416A1
Application number: PCT/IT2010/000302
Authority: WO
Inventors: Vito Lavanga; Antonio Cesare Sparacino
Original assignee: Esae S.R.L.
Priority date: 2009-07-07
Filing date: 2010-07-06
Publication date: 2011-01-13

Abstract

The present invention concerns a device suitable for producing desalinated water mainly actuated by renewable energy sources. In particular, the present invention concerns a thermal desalination plant comprising at least one chamber (2, 100' ) into which the water to be desalinated (A) is introduced, at least one condensation circuit (F) and at least one evaporation circuit (C), said circuits being independent from one another and crossed by a heat transfer fluid, wherein said condensation circuit (F) comprises a portion positioned beneath the level of the ground or of a body of water and it is in heat exchange relationship with said ground or with said body of water.

Description

DESCRIPTION

Thermal desalination plant

[0001] . The device claimed by the present invention is suitable for producing desalinated water, to be sent to suitable successive integrations that depend upon the destinations and uses. The device is mainly actuated by renewable energy sources.

STATE OF THE ART

[0002] . There are many regions of the world where the availability of fresh water is already or is becoming scarce.

[0003] . Currently, different solutions have been proposed for the desalination of salt water, often dependent upon evaporation/condensation or osmosis processes. 85% of world production of desalinated water is produced through multi-stage flash distillation, based on a vacuum distillation process. There are also many plants based on reverse osmosis technology, where the salts are separated from the water using semi-permeable membranes and pressure. These large desalination plants in order to operate require large amounts of energy as well as specialised infrastructures, making the plant and operating cost- benefit ratio very hard to manage as well as having an environmental impact that is not always acceptable. [0004] . More manageable plants, based on the principle of evaporation/condensation, are described in US 4,235,679 and WO 03/022746. Both documents describe a floating device that uses the sun' s energy as main energy source. US 4,235,679 foresees a single circuit suitable for promoting, in the different steps of its operation, at one stage the evaporation process, at another stage the condensation process. WO 03/022746 foresees a distinct device in two chambers, one light and hot, the other dark and cold, in which the evaporation and the condensation, respectively, take place. The steam goes from the evaporation chamber to the condensation chamber thanks to the presence of a fan.

[0005] . The present invention aims to drastically reduce the cost/benefit ratio in the production of desalinated water to be sent to successive and suitable integration processes, through a more efficient use of the sun' s energy and/or of other renewable energy sources.

SUMMARY OF THE INVENTION

[0006] . The present invention concerns a system that comprises a thermal desalination plant actuated and supplied with power by renewable sources. The thermal desalination plant of the present invention is characterised ^' in that it comprises two highly efficient mutually independent circuits: one, the hot circuit, which exploits the substantial energy provided by the thermo-surfaces (driver of the evaporation) , the other, the cold circuit, which uses the efficacy of the thermo-well to disperse the heat or, in the case in which it is not possible to have said thermo-well, the water to be desalinated itself is used to disperse the heat (driver of the condensation) .

[0007] . The system can be attached to solid earth or floating.

[0008] . In the embodiment attached to solid earth, as a non-limiting example, the system comprises a thermal desalination plant and a thermo-well. The following are provided i) a thermo-well used for condensation, with a main role of exchanging with the subsurface, roughly one metre deep, and on top it is completed with a layer of natural insulation; ii) a regular pentagon-shaped greenhouse, fluid-tight and insulated (made from expanded polystyrene EPS or similar) .

[0009] . Inside said greenhouse there are suitable exchangers (derived from said thermo-surfaces, corrugated plates and tubes containing a heat transfer fluid) on the lower plane and on the upper oblique walls.

[0010] . ^■ Outside of said greenhouse, on the upper layers, there are exchangers, i.e. thermo-surfaces (heliothermal diode, i.e. corrugated plates and tubes containing a heat transfer fluid covered by a cell- structured translucent material) suitable for collecting the heat from solar radiation, direct and diffused.

[0011] . The device is completed by a system for filling, replacing and maintaining suitable levels of water to be desalinated (coming from the sea or brackish water or water for refining) arranged in the lower space of the greenhouse.

[0012] . In the floating embodiment, the device is made up of a fluid-tight and insulated cylindrical structure (with heavy thermal insulation) which performs the functions of a greenhouse, arranged horizontally (so that it floats) on the water to be distilled.

[0013] . On the inner and outer walls, four diametrically opposite exchangers are applied (derived from said thermo-surfaces, corrugated plates and tubes containing a heat transfer fluid) .

[0014] . The cylinder is equipped on the two side circles (one acts as a removable lid) with two inlet- outlet holes for the water to be desalinated, so as not to have a salinity that is too high inside the cylinder, avoiding incrustations and difficulty of evaporation of the water.

[0015] . The movement of the water and of the salt can occur passively, through the differences in saline concentrations that are present between the inside and the outside of the floating thermal desalination plant .

[0016] . The cylinder is completed by suitable weights and floats so as to fill until the lower inner exchanger is covered.

[0017] . In the embodiments attached to solid earth and floating, said outer and inner exchangers are joined by crossed and circulating water connections.

[0018] . The two circulating water connections are activated by electrical energy coming from a photovoltaic panel of suitable power, slaved to a twilight device, or directly from direct voltage, the circulators will be associated with inverters to deal with variable voltage loads.

[0019] . Said upper inner exchangers are completed by water trays to collect and convey to the outside the condensation water percolated downwards. [0020] . Said upper outer exchangers are covered with a sheet of POLIBOLL of the type used for packaging with aluminium foil (alternatively cell-structured polycarbonate or in general a cell-structured translucent material with high radiation transmittance and substantial overall heat resistance) .

[0021] . The energy (hot water) deriving from the upper outer exchangers is brought by mere circulation (in closed circuit) into the lower inner exchangers and this will substantially raise the temperature of the salted water contained in the tank, allowing evaporation and environment saturation pressures to be reached.

[0022] . The inner upper exchangers are kept at lower temperatures thanks to the exchange with the cold well below, in the case of the thermal desalination plant attached to solid earth, or the body of water on which the thermal desalination plant itself floats, where said body of water is a body of brackish water or the sea, in the floating embodiment (through mere circulation) .

[0023] . The steam will condense on the inner upper exchangers and will percolate to the collection point, where it will be conveyed outside.

BRIEF DESCRIPTION OF THE FIGURES [0024] . Further characteristics and advantages of the present invention will become clearer from the following description of embodiments given purely as a non-limiting example, in which:

Figure 1 shows a schematic side section view of a thermal desalination plant attached to solid earth with a thermo-well according to the invention;

Figure 2 shows a perspective section view of a different .embodiment of the thermal desalination plant of the invention;

Figure 3 shows a perspective section view of a detail of the exchanger according to the invention.

[0025] . With reference to figure 1, the thermal desalination plant of the invention, wholly indicated with reference numeral 1, comprises a chamber 2, typically in the form of a greenhouse, with which two mutually independent closed circuits are associated, a condensation circuit F, which comprises a thermo-well

20, and an evaporation circuit C.

[0026] . Such a chamber 2 will have a shape such as to allow it to have a flat lower part 3 and an upper part 4 having a configuration capable of allowing the water to be run off and collected; as a non-limiting example, the upper part 4 can consist of one or more valances, i.e. a convex surface. In a preferred embodiment the^' chamber 2 is regular pentagon shaped.

[0027] . In said regular pentagon shaped embodiment, the chamber 2 comprises a flat lower part 3, an upper part 4 with two valances, two side walls 2a and 2b, a front face and a rear face (not shown) .

[0028] . The chamber 2 is fluid-tight and insulated, and in an embodiment it consists of panels typical of refrigerator cells or else masonry made impermeable on the inside and coated on the outside with suitable insulating material, typically EPS.

[0029] . The greenhouse 2 has one or more sealed openings on the side walls 2a and/or 2b and/or on the front or rear face. In particular, in the embodiment described in figure 1 there are two sealed openings 11 and 11' on the top part of the side walls 2a and 2b and two sealed openings 12 and 12' on the bottom part of the same side walls 2a and 2b. Said sealed openings are used to pass pipes.

[0030] . Inside the chamber 2 there is the water to be desalinated A, up to a level M.

[0031] . The water to be desalinated A enters into the chamber 2 through one or more pipes that pass through the sealed openings arranged on the bottom part of the side walls. In the example shown in figure 1, the water to be desalinated A enters through the pipe 17 that passes through the sealed opening 12' arranged on the bottom part of the side wall 2b.

[0032] . The water to be desalinated A enters into the chamber 2 through the pipe 17 without using up energy where the lower part 3 of the chamber 2 is advantageously positioned at a lower level than the level of the water present in the body of water from which the water to be desalinated A (not shown) is taken. By the principle of communicating vessels, inside the chamber 2 the water A will reach a level M that will be equal to the level of the water in said body of water.

[0033] . In a further embodiment, where the lower part 3 of the greenhouse 2 is positioned at a level equal to or higher than the level of the water in the body of water, the water A will be let into the chamber 2 until it reaches the level M using suitable pumping means, for example submerged pumps.

[0034] . It is foreseen for there to be a valve device 18 positioned on the pipe 17 to modulate the entry of the water to be desalinated A.

[0035] . Said condensation circuit F and evaporation circuit C comprise exchangers equipped with a coil crossed by a fluid that has the characteristics of a heat transfer fluid. [0036] . Said condensation circuit F comprises one or more heat exchangers arranged on the inner upper part 4' of said chamber 2. In the example shown in figure 1 two heat exchangers 5 and 5' are depicted arranged on the inner upper part 4' of the chamber 2, connected together by the tube 10.

[0037] . Said evaporation circuit C comprises one or more heat exchangers arranged on the inner lower part 3' of said chamber 2 and one or more heat exchangers on the outer upper part of the same chamber 2. The example shown in figure 1 shows a heat exchanger 6 arranged on the inner lower part 3' of the chamber 2 and two heat exchangers 7 and 7' arranged on the outer upper part connected together by the tube 9.

[0038] . In said evaporation circuit C the heat exchanger 6 arranged on the inner lower part of the chamber 2 is connected to the heat exchangers 7, 7' positioned on the outer upper part through the tubes 8, 8' . The tubes 8 and 8' cross the walls of the chamber 2 through the sealed openings 12 and 12' .

[0039] . Said condensation circuit F, in the embodiment depicted in figure 1, also comprises a thermo-well 20.

[0040] . In said condensation circuit F the heat exchangers 5 and 5' arranged on the inner upper part 4' of the chamber 2 are connected to the thermo-well 20 through draw pipes 29 and feeding pipes 30. Said pipes 29 and 30 come out from the side walls of the chamber 2 through the sealed openings 11 and 11' .

[0041] . Said evaporation circuit C and condensation circuit F are connected to pumping means.

[0042]. Said heat transfer fluid is typically water.

[0043]. The tubes 8, 8', 9, 10 and the pipes 29 and 30 are built from any material suitable for containing water. In a preferred embodiment said tubes are made from PVC.

[0044] . The heat exchangers 5, 5' -and 6 arranged inside the chamber 2 are built from plate with corrugated section. The plate can be made from aluminium, galvanized steel or highly thermally conductive alloys. The plate has throats arranged horizontally in which said coil is inserted. ^'

[0045] . The coil can be made with tubes, corrugated and not, possibly multi-layer, of PVC (woven, meshed or with metal cores), polyethylene, copper, steel.

[0046] . Suitable anchoring means take care of fixing the whole thing to the upper and lower inner parts of the chamber 2.

[0047]. _,In an embodiment, the heat exchangers 7, T arranged on the outer upper part of the chamber 2 comprise a plate with corrugated section that has throats in which the coil is inserted. Plate and coil are built from the same materials used for the exchangers arranged in the inner part of the greenhouse. The throats allow the heat captured by the plate to be concentrated on the edges of the throats themselves, thus promoting the heat exchange with the heat transfer fluid circulating inside the coil. Moreover, the exchangers arranged on the outer upper part of the chamber 2 are coated, totally or only on some portions, with a layer of non-reflective aluminium painted or treated in a suitable manner to transform light into heat and, further outside, with a layer of honeycombed translucent material, for example a film of POLIBOLL of the type used for packaging. Such a film has the function of easily allowing solar radiation to pass by irradiation, but blocking heat dispersion by conduction towards the outside, thanks to the presence of the cells full of air.

[0048] . Suitable anchoring means 60 take care of fixing the outer heat exchangers 7, 1' to the outer upper part 4 of the chamber 2.

[0049] . Said thermal desalination plant in the embodiment attached to solid earth comprises at least one thermo-well in the condensation circuit F. The thermo-well 20 comprises a casing 21 that comprises side walls 23 and a bottom 24. The casing 21 is sealed fluid-tight. Such a casing 21 can have any shape: cubic, parallelepiped, cylindrical, etc. and in particular a shape will be selected that maximises the surface area to promote the heat exchange towards the outside.

[0050] . Said casing 21 is externally coated by a suitable plate, for example a corrugated plate, which maximises the heat exchange area per unit surface.

[0051] . Said thermo-well 20 is completely buried up to a few metres deep, so as to be able to exploit the substantial temperature stability of the ground in the various seasons .

[0052] . The casing 21 is preferably made from cement, both for reasons of strength and of low cost, but it can also be manufactured from a different material that is suitable for remaining a long time underground.

[0053] . The casing 21 is closed on top by a lid 25 that has a hole so as to pass through a vertical duct 26 that extends from the bottom 24 of the thermo-well 20 and protrudes above it up to the surface S of the ground. The vertical duct 26 can be made from the same material from which the casing 21 is manufactured or from a different material and it can have any shape in section. At ground level, the duct 26 comprises an inspection hatch 27, whereas near to the base it comprises one or more openings 28 that place the inside of the duct 26 in communication with the thermo-well 20.

[0054] . The drawing 29 and feeding 30 pipes, part of the closed condensation circuit F that passes through the upper inner heat exchangers 5 and 5' of the chamber 2, are housed inside the duct 26.

[0055] . The feeding pipe 30 comprises an elbow portion 32 that is arranged in the upper portion of the thermo-well 20, beneath the lid 25. Such an elbow portion 30 has holes that allow the fluid circulating inside the pipes 29, 30 to come out.

[0056] . The inside of the casing 21 of the thermo- well 20 is filled with inert material G in granular form, which constitutes the heat exchange medium inside the thermo-well. Such a material preferably has a granulometry of between 5 mm and 50 mm; preferably, the inert material G will consist of a mixture of grains of different size, i.e. 5-10 mm/10-25 mm/25-40 mm, in suitable ratios. More preferably, the mixture comprises about 1/3 of each of the sizes indicated above . [0057] . In order to be able to perform the heat exchange function, the inert material G must have high heat conductivity.

[0058] . The inert material G has a heat conductivity, measured at room temperature, preferably over 0.6 Kcal/m.⁰C, more preferably over 1.2 Kcal/m.⁰C.

[0059] . The inert material G is preferably selected from stones, gravel, marble or synthetic resins suitable for remaining in contact with water.

[0060] . The filling with the inert material G can, in the lower and/or upper portion of the casing 21, comprise a portion with material having a larger piece size Gl, for example a size of about 100 mm. In this way, homogenisation areas of the fluid are formed at the inlet and/or at the outlet of the thermo-well 20.

[0061] . Figure 1 shows the elbow portion 32 of the feeding pipe 30 and the relative homogenisation area 33 in the upper portion of the thermo-well 20, but in other embodiments the feeding of the fluid can be arranged at the base of the thermo-well 20 and its drawing with the pumping means can be arranged in the upper portion.

[0062] . In use conditions, the thermo-well 20 is typically filled with the heat transfer fluid. In figure 1 L indicates the level of the heat transfer fluid in the thermo-well 20. In this way, by arranging the pumping means near to the bottom 24, a high head is obtained that decreases the need for power of the pumping means .

[0063] . As shown in the embodiment of figure 1, the heat transfer fluid, entered into the thermo-well 20 through the feeding pipe 30, which has holes in the homogenisation area 33, fills the homogenisation area 33 and then percolates through the material G and Gl as shown by the arrows. In this way the heat transfer fluid gives up heat to the inert material G, is collected at the bottom and, through the openings 28, enters into the duct 26 that, through the principle of communicating vessels, will be filled to the same level as the thermo-well 20. The pumping means will then take care of drawing the heat transfer fluid and of circulating it through the drawing pipe 29.

[0064] . In order to promote the heat exchange between thermo-well 20 and surrounding earth, the casing 21 will advantageously not be insulated and will also have a shape such as to maximise the heat exchange surface with the surrounding earth.

[0065] . From what has been stated above, it is clear that the heat transfer fluid must have a good heat exchange with the inert material G. For this purpose it is useful for the path of the fluid, from when it comes into contact with the inert material G to when it comes out from the thermo-well 20, to be maximised. It is also important for all of the mass of the inert material G to be involved in the heat exchange, avoiding the formation of preferential paths. It is for this reason that the homogenisation areas 33 have been provided and it has been foreseen to completely fill the casing 21 with the heat transfer fluid. In general, it will be advantageous for the heat transfer fluid to enter into the thermo-well 20 from one side and come out from the diametrically opposite side.

[0066] . The system outlined here operates in the following way: the heat transfer fluid contained in the evaporation circuit C gains heat in passing in the coil arranged inside the heat exchangers 7, 7' to then give it up, through the heat exchanger 6, to the water A contained in the chamber 2. The very structure of .the chamber, fluid-tight and insulated, avoids the dispersion of this heat and thus promotes the heating of the water A contained in it. The portion of water A that reaches a temperature equal to its vapour pressure will become steam that will tend to rise towards the upper part of the chamber. Rising, the steam will come into contact with the condensation circuit F having a lower temperature, in particular with the lower surface 13, 13' of the heat exchangers 5, 5' arranged on the inner upper part 4' of the chamber 2, where it will tend to condense.

[0067] . The lower surface 13, 13' of the heat exchangers 5, 5' arranged on the inner upper part 4' of the chamber 2, preferably coated with an aluminium foil, will act as condensation surface for the water that will then be conveyed in the water trays 14, 14', positioned below said heat exchangers 5, 5' . From the water trays 14, 14' the condensation water will be made to flow through pipes 16, 16' into collection tanks 15, 15' suitably positioned outside of the chamber 2. Said pipes 16, 16' will come out from the chamber through the sealed openings 11, 11' .

[0068] . Said condensation water, through the pipes 16, 16' , will flow to the collection tanks 15, 15' by natural falling should the tanks 15 and 15' be advantageously positioned at a lower level than the water trays 14, 14' .

[0069] . The collection tanks 15 and 15' will be produced in any material suitable for containing water, they may or may not be closed by a lid and they can be placed in connection, through a suitable circuit and by using pumping means, in particular submersible pumps, with the user or with a subsequent processing plant of the water collected in the tanks themselves (not shown) .

[0070] . The thermal desalination plant of the present invention, maximising the efficiency of the condensation and evaporation circuits, allows an extremely favourable operating cost/benefit ratio. The condensation circuit F, thanks to the presence of the thermo-well, can dispose of the heat very quickly, thus avoiding the loss of efficiency of the system that would inevitably be caused by the thermal saturation thereof where it were not possible to effectively dispose of the heat from the cold condensation circuit F.

[0071] . In a second embodiment, represented in figure 3, the thermal desalination plant is a floating device and is represented as a whole with the reference numeral 100.

[0072] . The device 100 comprises a rectangular or square flat surface 101. In an embodiment, said flat surface 101 is rectangular and is arranged in such a way that the two long sides of the rectangle join up along the joining line 101u. The flat surface 101 thus arranged, together with two circular faces 102 and 103, constitutes a cylindrical chamber 100' that performs the functions of a greenhouse. Of course, other shapes that allow the purpose of the invention to be achieved will also be possible.

[0073] . The chamber 100' is arranged horizontally (so that it floats) on the water to be distilled. The chamber 100' , after application for use, comprises two portions: one that stays above and one below the floating line. The flat surface portion 101a and the portions 102a and 103a of the circular faces 102 and 103 will thus remain above the floating line, whereas the portions 101b, 102b and 103b thereof will remain below the floating line.

[0074] . The flat surface 101 foresees one or more sealed openings for the passage of tubes. In particular, in the embodiment represented in figure 2 there are four sealed openings, two openings 111 and 111' , arranged on the flat surface 101a above the floating line, and two openings 112 and 112', arranged on the flat surface 101b below the floating line. The openings 111, 112' and 111', 112 are preferably positioned diametrically opposite one another.

[0075] . Inside the chamber 100' there is the water to be desalinated A, up to a level M that corresponds to the floating line. [0076] . The ^'water to be desalinated A enters into the chamber 100' through the holes 117 and 117' arranged on the circular faces 102 and 103, until it reaches the desired level M.

[0077] . In an alternative embodiment, said holes for the entry of the water to be desalinated are arranged on the flat surface 101.

[0078]. On said holes 117 and 117' there is a gate valve or another suitable closing device (not shown) that allows the entry of water to be adjusted.

[0079] . The chamber 100' is fluid-tight and insulated and it is coated with suitable insulating material, typically PES, and it is structured so as to be able to float.

[0080] . Also in this embodiment, the thermal desalination plant comprises two mutually independent closed circuits: a condensation circuit F and an evaporation circuit C, comprising heat exchangers equipped with a coil crossed by a fluid that has the characteristics of a heat transfer fluid.

[0081] . Said condensation circuit F comprises one or more heat exchangers 105 that cover the inner upper part 104a of said chamber 100' and one or more heat exchangers 108 that cover the outer lower part 101b of the same chamber 100' . Said heat exchangers 105 and 108 are connected through the tubes 129 and 129' that cross the walls of the chamber 100' thanks to the sealed openings 111 and 111' .

[0082] . Said evaporation circuit C comprises one or more heat exchangers 106 that cover the inner lower part 104b of said chamber 100' and one or more heat exchangers 107 that cover the outer upper part 101a of the same chamber 100' . Said heat exchangers 106 and 107 are connected through the tubes 118, 118' that cross the walls of the chamber 100' thanks to the sealed openings 112 and 112' .

[0083] . Said heat exchangers leave two symmetrical flat surface portions 101 free. The floating line is located in the flat surface portion 101 not covered by said heat exchangers. Said flat surface portions 101 not covered by heat exchangers have variable dimensions, of between 1/4 and 1/1000 of the cylindrical surface 101, preferably about 1/100, and they are arranged so as to comprise the floating line.

[0084] . Said evaporation circuit C and condensation circuit F are connected to pumping means.

[0085] . The pumping means are typically electric pumping means and will thus comprise suitable wiring that reaches the electrical power supply.

[0086] . The heat exchangers are built as described for the exchangers, present in the embodiment attached to solid earth first described, i.e. they will comprise a corrugated sheet with throats through which the coil passes.

[0087] . Figure 3 shows a section of the flat surface 101, in particular of the upper portion 101a covered by heat exchangers in the inner part and in the outer part. The inner heat exchanger 105 comprises a corrugated plate 130, a coil 131 and, in the free face facing towards the inside of the chamber 100', it is covered by an aluminium plate 132 suitable for promoting the condensation of the water. There is also a layer of insulating material 133, of the type normally used in the insulation of walls of buildings. Proceeding outwards, there is the outer heat exchanger 107 that comprises a corrugated plate 130, a coil 131 and, in a preferred embodiment, a layer of non- reflective aluminium 134, painted or treated to transform light into heat and a layer of cell- structured translucent material 135, for example a film of POLIBOLL of the type used for packaging.

[0088] . The lower face of the heat exchanger 105 arranged on the inner upper part 104a of the cylindrical surface 101, covered by an aluminium foil 132, will act as condensation surface for the water that will then be conveyed into the water trays 124, 124' . From the water trays, the condensation water will be made to flow through pipes 125 into suitably positioned collection tanks (not shown) . Said pipes 125 will come out from the chamber through the openings 111, 111' .

[0089] . Said collection tanks can be positioned adjacent to the chamber 100' and will also be floating.

[0090] . Alternatively, where the thermal desalination plant is slaved to the needs of desalinated water of a boat, said collection tanks can be arranged on the boat itself.

[0091] . Suitable pumping means will be used if the arrangement of the collection tanks does not allow just the force of gravity to be used to fill them.

[0092] . The system outlined here operates in the following way: the heat transfer fluid gains heat in passing in the coil that crosses the heat exchanger 107 that covers the outer upper surface 101a to then give it up, through the heat exchanger 106 that covers the inner lower surface 104b, to the water A contained in the chamber 100' . The chamber 100' , fluid-tight and insulated, avoids the dispersion of this heat and thus promotes the heating of the water A contained in it. The portion of water A that reaches a temperature equal to its vapour pressure will become steam that will tend to rise towards the upper part of the chamber 100' . Rising, the steam will come into contact with the condensation circuit F, in particular with the aluminium foil 132 arranged on the lower surface of the heat exchanger 105 that covers the inner upper part 104a of the chamber 100' where said steam will tend to condense.

[0093] . The condensation water, collected by the water trays 124, 124', positioned beneath said heat exchanger 105, is made to flow into the collection tanks through the pipes 125 that cross the chamber 100' through said sealed openings 111, 111' .

[0094] . Also in this embodiment, the thermal desalination plant of the present invention, maximising the efficiency of the condensation and evaporation circuits, allows an extremely favourable operating cost/benefit ratio.

[0095] . There are many advantages of the present invention.

[0096] . In the floating embodiment just like the one attached to solid earth, the desalination capability depends upon the temperature that the water A is able to reach inside the chamber 2 or 100' . Regarding this, it is possible to adjust the flow going in by acting upon the closure device present at the level of the holes 117, 117' or of the pipes 17. In this way, the water A can reach or maintain the temperature necessary for evaporation even in conditions of low irradiation.

[0097] . The possibility of adjusting the flow going in is also useful in order to limit the deposit of salt on the bottom of the chamber 2 or 100'^".

[0098] . In most applications it is beyond the purposes of a desalination plant to obtain salt and the inevitable salt deposits inside the plant are periodically removed. This work of removing the salt deposits involves a cost that is added to by the cost linked to the halting of the plant. The thermal desalination plant of the present invention foresees that, particularly in periods where the plant works very little, for example at night, when the residual heat necessary for the evaporation of the water has run out, it be possible to open the closure device present at the level of the holes 117, 117' or of the pipes 17 so as to increase the inlet of water and eliminate the salt deposits without any cost.

[0099] . The water to be desalinated A is then exchanged with the water outside continually, where the plant operates continuously, with the closure devices always open, or else cyclically over a short period, day-night, where the closure devices are kept closed from dusk until the residual heat sufficient for the evaporation of the water has run out. Therefore, the thermal desalination plant of the present invention does not accumulate leftover water to be disposed of. The regulatory need to obtain post- process water having the same composition (within very stringent limits) as that of the water introduced is thus observed without any burden.

[00100] . Optionally, the efficiency of the thermal desalination plant of the present invention can be implemented with contributions from renewable sources such as a wind power station - typically a micro-wind power station - and/or photovoltaic panels. Said renewable source will be able to supply a agenerator suitable to produce the electric power needed for the pumping means to operate so that the thermal desalination plant can operate with complete energy autonomy.

[00101] . The heat energy produced by the same generator can be recovered through a suitable heat exchanger, to heat the evaporation circuit C of the thermal desalination plant. [00102] . Said generator can be coupled with a heat pump, so that the heat pump absorbs the excess energy and converts it into heat energy to be sent to the hot evaporation circuit, in this way extending the hours of use of the thermal desalination plant, for example by exploiting a windy night.

[00103] . The presence of the two highly efficient circuits, hot and cold, allows the thermal desalination plant of the present invention to maintain a temperature gradient sufficient to make the evaporation/condensation process take place in the presence of minimal energy supply.

[00104] . The thermal desalination plant can have many applications both in residential and industrial areas, in areas neighbouring bodies of natural brackish or sea water, rather than waste water intended for purification. It takes care of the preliminary step of producing desalinated water, to be sent with subsequent refinement to the residential or agro- industrial processes. The cost of the plant is very low, it has low operating costs (zero if associated with a photovoltaic and/or wind power kit) essentially due to the hydraulic circulation in closed circuits, without head.

[00105] . The thermal desalination plant, having extremely low installation costs and being totally functional independently from the electrical power mains, can easily be used even in remote areas where there is a great need to have desalinated water.

[00106] . The thermal desalination plant can be sized with suitable sections and volumes, both for the evaporation circuit and the condensation circuit, according to the uses foreseen and its location.

Claims

1. Thermal desalination plant comprising at least one chamber (2, 100') in which the water to be desalinated (A) is introduced, at least one condensation circuit (F) and at least one evaporation circuit (C) , said circuits being independent from one another and crossed by a heat transfer fluid, wherein said condensation circuit (F) comprises a portion positioned beneath the ground or a body of water and it is in heat exchange relationship with said ground or with said body of water.

2. Thermal desalination plant according to claim 1, wherein said chamber (2) has a flat lower part (3) and an upper part (4) having a configuration capable of allowing the water to be run off and collected, preferably said chamber (2) is regular pentagon shaped and constitutes a thermal desalination plant attached to solid earth.

3. Thermal desalination plant according to any one of claims 1 to 2, wherein said chamber (100') is structured so as to be able to float and it is preferably a ' cylindrical structure arranged horizontally on the water to be distilled to constitute a floating thermal desalination plant.

4. Thermal desalination plant according to any one of claims 1 to 3, wherein said chamber (2, 100') is fluid-tight and insulated and has sealed openings (11, 11', 12, 12', 111, 111', 112, 112') used for the passage of pipes.

5. Thermal desalination plant according to any one of claims 1 to 4, wherein said water to be desalinated (A) enters into said chamber (2, 100' ) until it reaches a level (M) through holes (117, 117' ) or, alternatively, through one or more pipes (17) that pass through said sealed openings (11, 11', 12, 12') due to the principle of communicating vessels or, where this is not possible, through pumping means.

6. Thermal desalination plant according to any one of claims 1 to 6, wherein on said holes (117, 117') and on said pipes (17) there is a gate valve or another suitable valve device (18).

7. Thermal desalination plant according to any one of claims 1 to 7, wherein said evaporation circuit (C) comprises:

one or more heat exchangers (6, 106) equipped with a coil arranged on the inner lower part of the chamber (2, 100');

one or more heat exchangers (7, 7', 107) equipped with a coil positioned on the outer upper part of the chamber (2, 100');

the tubes that connect said coils together.

8. Thermal desalination plant according to any one of claims 1 to 8, wherein said condensation circuit (F) comprises:

one or more exchangers (105) equipped with a coil arranged on the inner upper part (104a) of said chamber (100');

one or more exchangers (108) equipped with a coil that cover the outer lower part of said chamber (100' ) ;

the tubes that connect said coils together.

9. Thermal desalination plant according to any one of claims 1 to 9, wherein said condensation circuit (F) comprises:

one or more heat exchangers (5, 5' ) equipped with a coil arranged on the inner upper part (4') of said chamber (2) ;

at least one thermo-well (20) ;

the tubes that connect said coils and said thermo-well together.

10. Thermal desalination plant according to any one of claims 1 to 19, wherein said heat transfer fluid is water.

11. Thermal desalination plant according to any one of claims 1 to 10, wherein said heat exchangers (5, 5', 6, 7, 7', 105, 106, 107) are built from plate with corrugated section and said plate has throats arranged horizontally, in which said coil is inserted.

12. Thermal desalination plant according to any one of claims 1 to 11, wherein said heat exchangers (7, 7', 107) arranged on the outer upper surface of the chamber (2, 100' ) are coated, totally or just one some portions, with a layer of non-reflective aluminium painted or treated in a suitable manner to transform light into heat and, further outside, with a layer of cell-structured translucent material, for example a film of POLIBOLL.

13. Thermal desalination plant according to any one of claims 1 to 12, wherein said thermo-well (20) comprises at least one buried casing (21), at least one supply duct of a heat transfer fluid and at least one drawing duct of said heat transfer fluid, wherein said casing (21) is fluid-tight and is not insulated and preferably has a shape in which the outer surface/volume ratio is maximised and comprises, inside of it, an inert material (G) in granular form with which said heat transfer fluid is placed in contact so as to obtain a heat exchange between said heat transfer fluid, said inert material (G) and the ground outside of said casing (21) .

14. Thermal desalination plant according to any one of claims 1 to 13, wherein said evaporation circuit (C) and condensation circuit (F) are connected to pumping means.

15. Thermal desalination plant according to any^¬ one of claims 1 to 14, wherein the lower face of the heat exchangers (5, 5', 105) forming part of the condensation circuit (F) , arranged on the inner upper part (4', 104a) of the chamber (2, 100' ) , is preferably coated with an aluminium foil (132) and acts as a condensation surface for the water that is then conveyed into the water trays (14, 14', 124, 124'); from said water trays said condensed water is made to flow into collection tanks (15, 15') positioned outside of the chamber (2, 100') through pipes (16, 16', 125) that pass through said sealed openings (11, 11' , 111, 111' ) .

16. Thermal desalination plant according to any one of claims 1 to 15, wherein the electrical energy needed for the operation of said pumping means is provided by a generator fed with power by renewable sources such as a wind power station, typically a micro-wind power station, and/or photovoltaic panels.

17. Thermal desalination plant according to any one of claims 1 to 16, wherein the heat energy produced by said generator is recovered through a suitable heat exchanger to heat said hot evaporation circuit (C) .

18. Thermal desalination plant according to any one of claims 1 to 17, wherein said generator is coupled with a heat pump that absorbs the excess energy and converts it into heat energy to be sent to said hot evaporation circuit (C) .

19. Thermal desalination plant according to any one of claims 1 to 18, wherein said body of water is a body of brackish water or the sea.