WO1985004159A1

WO1985004159A1 - Method and apparatus for desalination and/or purification of water

Info

Publication number: WO1985004159A1
Application number: PCT/SE1985/000115
Authority: WO
Inventors: Sven Runo Vilhelm Gebelius
Original assignee: Sven Runo Vilhelm Gebelius
Priority date: 1984-03-15
Filing date: 1985-03-13
Publication date: 1985-09-26
Also published as: SE8401503D0; SE8401503L; JPS61501439A; AU4065885A; EP0203926A1

Abstract

A method and an apparatus for desalination and/or purification of water, comprising a buoyant enclosure having restricting side walls (2, 2') spanned by an upper wall (1). The enclosure is partly or completely immersed in water, the restricting side walls (2, 2') being arranged to suspend same floating on a water surface. The enclosure is provided with air inlets (5, 5'), and an air stream is forced by means of wind force, wave energy and/or solar energy through the enclosure to a cooler (8), from which the condensate is transferred to a storage tank (19) or similar. A second and lower wall surface is suspended floating adjacent to the water surface, but below same, arranged to absorb heat imposed by solar energy. The enclosure is advantageously arranged to partly cover a beach, washed by waves, to obtain an increased evaporization. By arranging the upper wall with a number of lense elements, incoming solar rays are concentrated to the surface to be heated. A solar heated stack is advantageously arranged connected to the air outlet from the cooler (8), thereby increasing the air flow rate within the enclosure. Rain water, collected on the outer surface of the upper wall, is diverted through a substantially centrally located outlet via a conduit to the storage tank (19) used for the condensate.

Description

METHOD AND APPARATUS FOR DESALINATION AND/OR PURIFICATION OF WATER

The present invention relates to a method and an apparatus for desalination and/or purification of water.

It is previously known to use vertical tube evaporators, vapor compression, solar distillation, refrigeration methods, reverse osmosis and electrodialysis for desalination and/or purification of water. All previously known types of plants are expensive to install and maintain, and as a result, the water is produced at a high cost. Another obvious disadvantage with previously known methods, apart from possibly solar distillation, is the fact that they are power-consuming processes, and thus require a supply of electricity, oil or any other suitable energy source. As a result, low costs are those of large nuclear reactor schemes that generate electricity and use low-pressure steam in distillation plants, whereas high costs are obtained for small and medium-sized plants. To reduce the costs involved for desalination or purification of water, it has previously been proposed to use solar energy or wind energy, as disclosed in US, A, 2820 744, US, A, 3 334 026, and US, A, 4172 767.

With regard to US, A, 2 820 744, a floating solar still is disclosed, comprising of a dome shaped buoyant outer casing having a continous side wall spanned at its upper end by a top enclosure, a continous inner wall within said casing extending upwardly from the lower portion of the outside wall to provide an upwardly open trough between the side walls, and also having a liquid pervious barrier spanning the interior of the inner wall. This buoyant casing is intended to be floated upon the open sea, with the side walls, and the lower portion of the trough, immersed beneath the surface of the sea water, and sea water will rise within the inner wall above the pervious barrier, acting as a filter to remove solids and animal life. The top enclosure, having a dark coated surface, will absorb the solar rays, and the increase in heat will cause the water above the barrier to evaporate. When the the vapor thus formed contacts the inside of the outer wall, which is chilled by the sea water, the condensate will be accumulated within the trough, from which it is withdrawn through a conduit. The output from this device would be small, but no energy apart from solar energy is required, except for the .

energy required for moving the pur fied water from the trough through the conduit.

US, A, 3334026 discloses a method to produce potable water, based on the combination of solar energy and wind force. A relatively humid stream of atmospheric air, the humidity of which could be increased in a first stage by passing through a duct with wick members saturated by and communicating with sea water, is heated and expanded, whereafter it passes through a cooler in which the water vapor of the air stream is condensed out, and pumped to a fresh water reservoir.

The water purification system disclosed in US, A, 4172 767 is a solar energy based system, in which it s proposed to include the use of wind energy included to increase the yield of the system. It is based on the use of a covered tank containing unclean water, heated by solar rays, the vapor being moved by a blower to a condensing apparatus, from which the condensed water is pumped to a storage tank. Wind energy can be used to drive a blower, intended to increase the air flow rate over the water surface in the tank containing unclean water.

The above three examples of prior art disclose previous efforts to find a method for desalination and/or purification of water with use of solar energy, and with a minimum of additional energy required. The floating solar still disclosed in US, A, 2820744 would only require additional energy to pump the water from the trough through a conduit to a storage tank, but the output of fresh water from this apparatus would be small.

An object of the present invention is to disclose a method and apparatus for desalination and/or purification of water having a reasonably high output of purified water, but requiring only natural and thus easily obtainable energy sources.

It is a further object of the present invention to provide a low cost apparatus for the above purpose, easily transported and installed, and requiring a minimum of surveillance and maintenance.

The method for desalination and/or purification of water is based on the use of area restricting wall members, suspended floating on a water surface and spanned by an upper wall, in which an air flow caused by wind force, wave motion or solar heat is forced over the restricted water surface heated by solar rays through the upper wall, the air flow being directed from the restricted area to a cooler, from which the condensate is directed to a storage tank or similar.

The apparatus according to the present invention is character sed in that the restricting wall members include a flexible skirt extending from the lower portion, arranged to extend downwardly below the water surface, the upper wall being arranged with air inlets, facilitating an air flow into the enclosure formed by the restricting wall members, the upper wall and the surface suspending the restricting wall members, said air flow being directed through a conduit to a cooler, from which the condensate is passed to a storage tank or similar. Advantageously, it also comprises a lower second wall surface, preferably having a dark and heat absorbing surface,s arranged located submerged at a small distance below the water surface, including air-filled cushions or similar elements to maintain the second wall surface suspended below the water surface, and also including through apertures facilitating a free flow of water between the upper and. lower surfaces of the second wall surface. The air flow through the enclosure can be enhanced by a substantially vertically extending solar heated stack, connected to the air oulet from the cooler.

Other features and advantages of the present invention will be readily apparent from the following detailed description when considered in connection with the accompanying drawings in which:-

Fig. 1 is a cross-sectional view of a first embodiment of an apparatus according to the invention.

Fig. 2 is a cross-sectional view of the embodiment shown in Fig. 1, but with an additional element included.

Fig. 3 is a frag entory cross-sectional view showing a modified air inlet.

Fig. 4 is a cross-sectional view of a preferred embodiment of an upper covering wall surface.

Fig. 5 is a plan view of the embodiment shown in Fig. 3

Fig. 6 is a cross-sectional view showing a pump member influenced by wave motion, arranged to force air into the apparatus.

Fig. 7 is a cross-sectional view showing a solar heated stack arranged to draw air into the apparatus.

Fig.8 is a cross-sectional view showing how rain water can be retrieved by means of a further modification.

Fig. 9 is a perspective view showing how the apparatus can be arranged partly immersed into water and partly covering a beach, washed by waves.

Fig. 10 is a cross-sectional view of the embodiment shown in Fig. 9.

Fig. 11 is a perspective view, illustrating how a number of immersed or semi-immersed units can be interconnected to cover a larger area.

The method according to the present invention is based on the use of solar energy, but also other natural energy sources, such as energy obtained from wave motion, and/or wind energy.

The embodiment shown in Fig. 1 includes a floating member, comprising an upper covering wall surface 1, from which inflated sections 2, 2' extend downwardly, having a skirt 3, 3^' extending downwardly from the lower portion. The lower free portion of the skirts 3, 3^" are advantageously arranged including a weight 4, 4^', causing the skirts 3, 3^' to extend in a substantially vertical direction from the inflated sections 2, 2'. Advantageously, the floating member is manufactured as an integral unit of a synthetic plastics material, the inflated sections 2, 2'and the skirts 3, 3^' being formed by folding and welding the outer portions of the upper wall surface 1. A number of air inlets 5, 5' extend uppwardly from the upper covering wall surface 1, communicating with the interior of the floating member. When the above member is placed on a water surface 6, it restricts an area of a size corresponding to the floating member. In Fig. 1, it is shown how a conduit 7 is connected adjacent to one edge portion of the upper wall surface 1, and how the other end portion of said conduit 7 is arranged communicating with a cooler 8, located below the water surface 6, and thus being cooled by the surrounding water. Assuming that the upper wall surface is subjected to sun rays, the water enclosed within the inflated sections 2, 2^' and the skirts 3, 3^' would be heated, and vapor from the heated water could move through the conduit 7 to the cooler 8 to be condensed. However, as previously discussed with regard to the disclosure of US, A, 2820 744, such a solar still has a very small output, and further means would be required to obtain a desired and acceptable output of purified water.

The air inlets 5, 5^" provide such a further means by directing an air flow into the interior of the floating member. These air inlets 5, 5^' can either be arranged with the inlet opening fixed in relation to the floating member, or arranged to facilitate a rotary movement around the vertical axis. In the first case, the floating member is preferably orientated in such a way, that the inlet openings of the air inlets 5, 5^' are facing the wind, and in the second case, the air inlets 5, 5^' are preferably arranged including means, which orientate the air inlets 5, 5^' in such a way, that the inlet openings are constantly located in relation to the wind direction to facilitate a maximum flow of air into the floating structure. According to the present invention, each air inlet 5, 5^' may also include a valve member 9, such as a flap valve or any other valve type permitting an air flow into the interior of the floating member, but restricting an outwardly directed flow (Fig. 3). When the floating member is moved by wave motion, the air volume within the upper wall surface 1 and the inflated sections 2, 2^' is constantly and also alternatively increased/decreased, and when same is increased, the air pressure is reduced in relation to the surrounding atmospheric pressure, whereby the valve member 9 is opened to permit an air flow into the interior of the structure. When the volume is decreased, due to wave motion, the valve member 9 closes, and the air pressure within the structure will now be increased above atmospheric pressure, thus forcing an air stream out through the conduit 7 to the cooler 8. The above described operation is continously repeated, resulting in an intermittent air stream over the water surface enclosed within the floating member, thereby increasing evaporation and also the output of purified water. The increased efficiency is thus^' accomplished by a combination of solar energy heating and a forced air flow passing over the heated water surface, the air flow being accomplished either by wind energy or wave energy, or by a combination of same.

It would also obviously be possible to use wave motion to influence a pump means 10, or a number of such means, anchored to the bottom of the lake or the sea in which the floating member is used, and an example of such an embodiment is illustrated in Fig. 6.

However, if the floating member is used in an environment where there is little and no wave motion, but where there is a hot and sunny climate, such as tropic or subtropic climates, the desired air flow over the water surface restricted by the floating member could be accomplished in other ways. With reference to Fig. 7, it is shown how a transparent stack 11 is arranged connected to an air outlet 12 from the cooler 8. The stack 11 surrounds a body 13, having a dark outer surface, and the space between the outer surface of the body 13 and the internal surface of the stack 11 is continously reduced in direction towards the outlet at the upper portion of the stack 11. When the body 13 is made subject to sun rays, the surface is heated, resulting in an upwardly directed air flow through the stack 11. The continously decreased through-flow area within the stack 11 results in an successively increased velocity for the air stream.

In order to further increase the evaporisation within the floating member, the upper covering wall surface 1 can be further improved, as indicated in Figs. 4 and 5. According to this embodiment, the upper ^• covering wall surface 1 comprises of two layers, 1 and 1^' respectively, having a number of lenses 14, 14^', arranged to take up and focus incoming sun rays at a predetermined distance below the lenses 14, 14^", e.g. at the surface of the water, or immediately below same, enclosed within the floating member. The lenses 14, 14^" are advantageously formations of a suitable liquid, enclosed between the layers 1, 1^", diametrically restricted by means of a surrounding welded joint between the two layers 1, 1^". It is also possible to arrange a second wall surface 15, preferably dark and heat absorbing, located extending between the internal surfaces of the inflated sections 2, 2^", or the skirts 3, 3^", and arranged to be immersed in the water enclosed by the floating member. As shown in Fig. 6, apertures 16, 16^" are taken up in this second wall surface 15, to facilitate a water flow into the area restricted by same. When used for desalination of sea water, it would be possible to arrange valve members in this apertures 16, 16^" to prevent a return flow out from the space restricted by the second wall surface 15, and thus achieve formation or sedimentation upon same of salt, which could be recovered and used. In this case, either the covering wall surface 1, or the second wall surface 15, should be arranged detachable.

The second wall surface 15 can advantageously include a number of gas or air filled sections or "bubbles", which serve to maintain the second wall surface 15 at a predetermined distance below the water surface enclosed by the floating member.

When used in areas where rain can be expected, it is also possible to make a further modification, intended to facilitate possibility to recover rain water, as shown in Fig. 8. Since the upper covering wall surface 1 covers a fairly large area, and is manufactured from a flexible material, the rain water will deflect the surface and be stored on same. The central portion of each covering wall surface 1 may thus be provided with a water outlet 17, communicating with a conduit 18 connected to the cooler 8, or a fresh water reservoir 19, to which water from the cooler 8 also is passed for storage and subsequent use. Since the upper covering wall surface 1 may be covered by a deposit of dirt or ^• other substances when the rains starts, a valve member 20 may be arranged at the water outlet 17, arranged to be operated when the pressure from the water located on top of the upper covering wall surface 1 indicates that said surface is substantially covered by water. When a sufficient amount of water has accumulated on top of the the upper covering wall surface 1, the valve member 20 is opened to facilitate a free flow into the interior of the floating member, and after a predetermined time limit, or when a certain and prdetermined volume of water has passed through the valve member 20, the flow is diverted into the conduit 18. The floating member may advantageously include a number of supporting inflated sections 2, 2^" with associated skirts 3, 3^", located in a spaced relationship from each other, and serving to form a number of restricted areas adjacent to each other. Obviously, it would also be possible to interconnect a number of floating members, in order to get desired surface coverage (Fig. 11).

With a plant according to the present invention, located in water and arranged to utilize a combination of solar energy with an air stream over the heated water surface, output over a period of 24 hours would be in the region of 10 - 40 1/m , i.e. a plant covering a water surface having an area of 200 m would result in an output of 2 - 8 purified water.

However, this output could be considerably increased, by locating the floating member partly covering a water surface and partly covering a beach surface. A beach, having a grain size of 1 mm and in which the water infiltrates to a depth of 10 mm has, due to the capillary effect on the water washed up by waves, an effective surface six times larger per mm of depth than the beach area, i.e. a beach area of 1 m is equivalent to an area of 60 m . As a result, output from a plant partially covering a beach is increased by 10 - 20 times, and if the plant covers a total area of 200 m , total output over a period of 24 hours would be in the region of 30 - 60 m .

When located partly in water, and partly covering a beach surface washed by waves, as shown in Figs. 9 and 10, the inflated sections 2, 2^" serve as distance members locating the upper covering wall surface 1 at a predetermined distance from the beach surface, and the skirts 3, 3^" serve as anchoring and sealing means, e.g. burried in the beach.

The beach acts as a means for storage of solar heat, and the absorption of solar rays can be further improved by preparation of the beach, prior to restricting an area of same by means of the "floating member", which, for this application, only partly is arranged floating. Firstly, it is possible to arrange a second wall surface 15 of the type previously described located burried at a distance below the surface of the beach. Secondly, it would also be possible to cover the beach surface with a dark and heat absorbing material, preferably located in a pocket formed in the beach. These two methods may also be combined.

The various features disclosed may be combined in a number of ways, to suit existing conditions at each location. When used in areas where no wind or wave conditions are to be expected, a combination of floating members having a submerged lower surface and including at least one solar heated stack for accomplishing an air stream over the heated water is a preferred and suitable embodiment. When used at locations where a sufficient air flow can be obtained through wind force, the solar heated stack can often be omitted.

The method and apparatus according to the present invention can also be used to recover salt, when used for desalination of water. By making the apertures 16, 16^" in the second wall surface 15 small, and thereby also preventing a free flow of water which continously washes away the salt, said second wall surface 15 could be used as a means to collect salt. If used in connection with a beach surface, it would also be possible to arrange a barrier near the water front, which prevents salt from being washed away by the waves from the restricted area.

With regard to the inflated sections 2, 2^", same are advantageously a number of independent sections, closed off from each other, in order to secure that the floating member is not adversely affected if punctured locally. These sections 2, 2^" may obviously also be manufactured from other materials than synthetic and flexible plastic materials, i.e. more rigid materials, both non-metallic and metallic.

The solar heated stack 11 may also be manufactured in a number of ways and from a variety of materials. A simple design includes a tubular- structure, forming a frame, onto which a flexible plastics material is applied. However, a more rigid construction may also be used, based on both metallic and non-metallic materials.

Claims

C L A I M S

1. A method for desalination and/or purification of water based on the use of area restricting wall members, at least partly being suspended floating on a water surface and spanned by an upper wall, in which an air flow caused by wind force, wave motion or solar heat is forced over the restricted surface heated by solar rays through the upper wall, the air flow being directed from the restricted area to a cooler, from which the condensate is directed to a storage tank or similar.

2. An apparatus for desalination and/or purification of water according to the method disclosed in claim 1, in which the restricting wall members include a flexible skirt extending from the lower portion, arranged to extend downwardly below the suspending surface, the upper wall being arranged with air inlets, facilitating an air flow. into the enclosure formed by the restricting wall members, the upper wall and the surface suspending the restricting wall members, said air flow being directed through a conduit to a cooler, from which the condensate is passed to a storage tank or similar.

3. An apparatus as disclosed in claim 2, in which a lower second wall surface, preferably having a dark and heat absorbing surface, is arranged located submerged at a small distance below the suspending surface, including air-filled cushions or similar elements to maintain the second wall surface suspended below a water surface, and also including through apertures facilitating a free flow of water between the upper and lower surfaces of the second wall surface.

4. An apparatus as disclosed in claim 2, in which the air flow through the enclosure is enhanced by a substantially vertically extending solar heated stack, connected to the air oulet from the cooler.

5. An apparatus as disclosed in claim 4, in which the solar heated stack comprises an outer tubular member, preferably at least partially being of transparent material, enclosing a preferably dark and heat absorbing member, an air flow channel between the outer tubular member and the enclosed heat absorbing member preferably being arranged having a decreased through-flow area in direction towards the air outlet from the stack.

6. An apparatus as disclosed in claim 2, in which the upper wall is arranged with an outlet means, substantially centrally located and connected by means of a conduit to a storage tank or similar.

7. An apparatus as disclosed in claim 6, in which a valve member is arranged to facilitate a free flow into the enclosure of a first volume of water from the outlet means, before diverting the flow into the conduit communicating with a storage tank or similar.

8. An apparatus as disclosed in claim 2, in which the upper wall includes a number of lense devices, arranged to focus incoming sun rays at a predetermined distance below the upper wall, said lense devices preferably being enclosed volumes of l quid between two transparent sheets forming the upper wall.

9. An apparatus as disclosed in claim 2, in which the enclosure partly is immersed in water, thereby restricting a certain water area, partly is arranged to enclose an adjacent beach area, washed by incoming waves.

10. An apparatus as disclosed in claim 9, in which the beach area covered is arranged covered by a dark and heat absorbing and granulated material, and/or a substantially impenetrable sheet member located at a distance below the beach surface.