Abstract:
The invention relates to a device for the distillation of a liquid, with at least one mirror surface ( 24, 24   a,    124 ) for focusing solar radiation onto an absorber tube ( 14, 14   a,    114 ) which can be filled at least partly with the liquid, wherein the absorber tube ( 14, 14   a,    114 ), is provided, for taking up energy from the solar radiation and for evaporating the liquid, and to at least one first condensation tube ( 22, 22   a,    122 ) for condensing the evaporated liquid, the first condensation tube ( 22, 22   a,    122 ) being disposed at a distance from the absorber tube ( 14, 14   a,    114 ), to which it is coupled by at least one distillation bridge ( 20, 20   a,    120 ). In order to make a simple and cost effective distillation device possible, with which a particularly efficient utilization of the solar energy for a high distillation performance is achieved, it is provided that a transparent sleeve ( 16, 16   a,    116 ) is coupled thermally with the condensation tube ( 22, 22   a,    122 ) and surrounds the absorber tube ( 14, 14   a,    114 ), a space ( 18, 18   a,    118 ) remaining between the sleeve ( 16, 16   a,    116 ), and the absorber tube ( 14, 14   a,    114 ).

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a device and to a method for distilling a liquid. In particular, the invention relates to a distillation device and a distillation method which is supplied with energy by solar radiation. 
       BACKGROUND OF THE INVENTION 
       [0002]    As a separation method, the distillation has manifold applications in technology. Distillation is utilized with different starting liquids, particularly in the chemical industry area. 
         [0003]    Distilled water finds extensive use in various industrial areas, such as solvents or cleaning agents. However, a high input of energy is required for the distillation. 
         [0004]    The use of solar energy for operating a distillation device is known per se. The DE-OS 26 04 978 describes a distillation device which can be operated with solar energy and for which the liquid which is to be distilled, such as water, is separated from an air space by a silicone membrane. The silicone membrane is sinusoidal in shape and glued to a cover of glass or a different material which transmits solar energy. The solar energy which is radiated through the cover, is absorbed by the silicone membrane, so that vapor can penetrate through the membrane and condense at the underside of the cover. 
         [0005]    The AT 507 782 A4 describes a portable solar thermal device for producing fresh water from effluent or salt water. The device exhibits a closed fluid cycle. This consists of tube or hose elements which are connected with one another, with a waste water inlet and a fresh water outlet. The fluid cycle comprises a heating section for heating and evaporating the effluent. The heating section has a partially transparent, insulating casing, so that solar radiation can pass through the casing and reach a solar collector. The solar collector is able to concentrate the thermal energy of the solar radiation on an evaporation surface located in the interior of the heating section. A perpendicular condensing section, in which the freshwater can condense and the effluent may be pre-heated, adjoins the heating section. 
         [0006]    A light and compact solar still which has a two-part distillation chamber and an adjustable solar collector is described in US 2008/0 073 198 A1. The distillation chamber comprises mainly two parts, a trough and a cover. Liquid which is to be distilled is disposed in the trough. Preferably, the underside is blackened, so that heating the liquid for distillation is simplified. The distillate can condense at the cover and is discharged via troughs. The cover may be transparent and have cooling ribs which improve condensation. 
         [0007]    A solar still for sea water is disclosed in U.S. Pat. No. 4,504,362 A. Preferably, the solar still is configured so that the solar collector which focuses light on an absorber tube can function as a float. The sea water is heated and evaporated by solar radiation in the absorber tube which is connected via distillation bridges with a condensation tube. The condensation tube preferably is arranged below the water line, so that it is cooled by seawater and the condensation of the vapor can be improved. 
         [0008]    In the U.S. Pat. No. 4,749,447 A, a solar still is described, for which the absorber tube and the condensation tube are coupled thermally with one another, so that the heat of condensation can be used to heat the liquid in the absorber tubes. The coupling is accomplished directly via heat-conducting elements, such as metal ribs, the walls of the tubes or a concentric arrangement of a condensation tube in an absorber tube. The absorber tubes and the condensation tubes are connected with one another via distillation bridges. The distillation bridges have valves and pumps, so that the pressure is higher in the condensation tubes than in the absorber tubes. As a result, condensation of the distillate can also become possible at higher temperatures. The tubes may be disposed in a partly or completely transparent casing which preferably is gas tight. 
       SUMMARY OF THE INVENTION 
       [0009]    It is an object of the invention to propose a simple and cost effective distillation device, with which a high distillation performance will be achieved with a particularly efficient utilization of the energy of the sun. 
         [0010]    According to the invention, this objective is accomplished by a device of claim  1  and a method of claim  14 . Dependent claims relate to advantageous embodiments of the invention. 
         [0011]    The device according to the invention first of all has an absorber tube. This can be filled at least partly with the liquid which is to be distilled, so that the liquid reservoir formed is in thermal contact with the wall of the absorber tube. 
         [0012]    A mirror surface serves to focus solar radiation in the area of the absorber tube, so that the absorber tube is warmed up by absorbing energy from the radiation of the sun. With sufficient warming up, a portion of the liquid evaporates in the absorber tube. 
         [0013]    The absorber tube is coupled via a distillation bridge at least with one first condensation tube, so that vapor is passed into the first condensation tube. The vapor condenses in the first condensation tube. It is disposed at a distance from the absorber tube to which it preferably is parallel. 
         [0014]    According to the invention, a transparent sleeve is provided which is coupled thermally with the condensation tube and encloses the absorber tube. Moreover, the sleeve passes at a distance from the absorber tube, so that an interstice remains as a space between the sleeve and the absorber tube. As is evident in conjunction with preferred embodiments, the sleeve need not be formed continuously from one material; instead, different elements and materials may jointly form a sleeve which encloses the absorber tube. 
         [0015]    Due to the transparency of the sleeve, light radiation from the latter can unimpededly hit the absorber tube. The transparent sleeve does not need to be transparent over the whole of its area, but it has to be transparent at least partly. The sleeve is transparent at least in the area of the thermal coupling with the condensation tube. Furthermore, the sleeve is transparent in those regions from which light rays can hit the absorber tube. If light radiation is not to be expected from certain regions of the sleeve, since these regions, for example, are covered by other parts of the device, such as the condensation tube, the sleeve need not necessarily also be transparent at these sites. It may even be appropriate that the sleeve or parts thereof have reflecting properties at such sites, so that incident light beams from a different side can be reflected onto the absorber. 
         [0016]    Due to the device according to the invention, it becomes possible to utilize the heat of condensation and the increase the efficiency. During the condensation at the condensation tube, the latter is heated by the released heat of condensation. The sleeve, surrounding the absorber tube, is also being heated due to the thermal coupling with the condensation tube. Preferably, the sleeve is gas tight, so that, a closed insulated space is formed from which essentially no heat escapes by convection. For this, it may already be sufficient if the insulated space is closed off to such an extent that, for example, it is wind tight. Moreover, the insulated space can be closed off so tightly, that a gas which fills it is contained at a pressure higher or lower than atmospheric pressure, down to a vacuum. 
         [0017]    Accordingly, the absorber tube is in an insulated space within the sleeve which is kept at a higher temperature than the surroundings due to the heating. Because of this, there is also a higher temperature at the absorber tube, since the direct environment of the latter is heated and the absorber tube therefore emits less heat to its surroundings. 
         [0018]    Due to this additional utilization of the heat of condensation, a particularly efficient distillation process is possible with the device according to the invention. As a result of the increased temperature of the absorber tube, less intensive solar radiation is already sufficient for distilling water and it is also possible to evaporate liquids with a higher boiling point. 
         [0019]    Moreover, due to the tubular construction and preferred parallel arrangement of an absorber and a condenser, the construction of the device according to the invention is particularly efficient and the device can be produced cost-effectively. 
         [0020]    In advantageous embodiments, the absorber tube, the condensation tube and the sleeve may be constructed as tubes with different cross-sectional shapes. These comprise round or predominately round, cross-sectional shapes as well as, for example, triangular or other cross-sectional shapes. For example, in a round sleeve, the absorber tube may be disposed centrally, so that if, for example, the cross-section of the absorber tube is also round, the sleeve always has the same distance from the wall of the absorber tube. Temperature difference in the absorber tube can be avoided by these means. 
         [0021]    In some embodiments, the sleeve can also be formed partly by regions of the mirror, for example, the base thereof. For example, a transparent pane in, for example, a trough-shaped or parabolic mirror can be inserted so that this pane, as an outer pane, together with the mirror, can form a sleeve about the absorber tube which is transparent in the direction of the incident light rays. This makes a simplified construction of the sleeve possible and, nevertheless, irradiation of light from many directions onto the absorption tube. 
         [0022]    It is advantageous if the sleeve consists at least partly of a glass, preferably with advantageous heat conduction properties, and a high transmission, such as borosilicate glass. Furthermore, transparent plastic, such as Plexiglas for example, may also be used. 
         [0023]    Advantageously, the absorber tube is disposed in the device so that it is at a focal point of the mirror surfaces. Preferably, it may have a circular or polygonal cross-section. According to a further embodiment of the invention, the cross-section of the absorber tube is triangular, especially equilaterally triangular. In this connection, an acute angled triangle, for example, with an angle of less than 60° between the sides of equal length, is preferred. With such a cross-section, the long sides of the triangle may be aligned with respect to the mirror surfaces, so that the greatest amount of radiation can strike the absorber tube. The efficiency of the device can be increased further in this way. 
         [0024]    In preferred further embodiments of the device, the absorber tube consists of a corrosion resistant and vapor resistant material which preferably is thermally stable, such as stainless steel, glass or certain polymers. For an improved absorption of light, it is advantageous if the absorber tube is blackened or, in the case of a metal tube, galvanized. 
         [0025]    Preferably, the first condensation tube is disposed in direct contact with the transparent sleeve in order to transfer the heat, resulting from the condensation, to the sleeve by conduction. If the sleeve is constructed as a tube, the condensation tube may, for example, be arranged at the inside of the tube. For a further embodiment of the invention, in which the sleeve consists at least partly of a transparent plate, for example, a glass plate in the optical path, the condensation tube may be disposed directly in contact with the transparent plate. In a preferred embodiment, two transparent plates are disposed at an angle to one another, the condensation tube being disposed in contact with one of the transparent plates. 
         [0026]    It is particularly preferred if in the last-mentioned case the second transparent plate, as an inner pane, extends from the first transparent plate which is disposed as an outer pane, up to the mirror, preferably to its base. By these means, two insulated spaces can be formed. The absorber tube, distillation bridge and condensation tube may then be disposed in a first insulated space. In the second insulated space, either this construction may be repeated or this chamber may be used, for example, for storing heat. During operation of the device, this reservoir may be supplied, to begin with, by excess heat. If there are fluctuations in the solar radiation, for example, due to cloudiness, the stored heat may be used as a buffer and intercept these fluctuations. As a result, the distillation can proceed more uniformly which represents a gain in efficiency. 
         [0027]    In order to achieve passive cooling, the first condensation tube may be disposed in thermal coupling with the mirror surface, preferably in direct contact with the mirror surface. According to a further embodiment of the invention, the first condensation tube may, moreover, be connected to a second condensation tube, so that vapor which does not condense in the first condensation tube reaches the second condensation tube. The second condensation tube may be disposed so that it is in thermal contact with the mirror surface. An efficient, passive cooling, namely the delivery of heat of the second condensation tube, is made possible in this way, so that the condensation of the still remaining vapor, is achieved. Alternatively or additionally, active cooling can also be used. 
         [0028]    According to a further embodiment of the invention, it is furthermore preferred if a desired liquid level is achieved in the absorber tube by means of a valve. In particular, provisions can be made here so that the valve permits liquid to flow in only as far as a desired maximum level. For example, the valve may be controlled with a float. 
         [0029]    In a further embodiment of the invention, the mirror surface is constructed in the shape of a trough, the absorber tube being disposed within the trough-shaped mirror surface. Such a structure can be realized particularly well in large installations, wherein several troughs which are to be disposed parallel to one another over an area being preferred. The trough-shaped arrangement, moreover, is particularly advantageous if at least the mirror surface and preferably also the absorber tube is disposed so that it can be rotated about a longitudinal axis, in order to enable tracking relative to the sun. A rotation of the whole unit of a mirror surface, absorber tube, sleeve, and first condensation tube is particularly preferred. 
         [0030]    Advantageously, a heat exchanger may be provided in order to preheat the liquid, supplied to the absorber tube, by means of the condensate. The efficiency of the device is increased herewith. 
         [0031]    According to a further embodiment of the invention, a collection container for the condensate may be provided, preferably underneath the mirror surface. In this context, it is particularly preferred if the collection container is provided as a foundation for carrying at least the mirror surface and the absorber tube. 
         [0032]    According to a further embodiment of the invention, the distillation bridges can form a connection space between absorber tube and condensation tube, through which vapor from the absorber tube can be passed into the condensation tube in which it condenses. Preferably, in the space between the absorber tube and the condensation tube through which the evaporated fluid flows, a material may be disposed which is to be extracted, that is, dissolved by the vapor flowing through. Preferably, a material which contains another material that is to be extracted, for example, as a constituent or as an impurity, may be disposed in the connection space. Accordingly, the vapor flowing through can be utilized for the extraction. It dissolves the material to be extracted and transports it along. 
         [0033]    According to a further embodiment, an insert for accommodating the substance or material contained by this may be disposed in the connection space. It may be possible to insert this or slide it in. 
         [0034]    According to a further embodiment, the insert may be constructed as a container with a wall which is permeable for the evaporated liquid, for example, as a screen (also as a perforated sheet of metal), for example, of steel, or by using a silicone membrane. In general, an insert should be impermeable for the material itself, but permeable for the vapor and, with that, for the transported extracted materials. 
         [0035]    Accordingly, the substance or the material to be treated can be held in the transition between the absorber reservoir and the condensation space and passage of the vapor through this region can be enabled. 
         [0036]    A method according to the invention for solar distillation comprises a focusing of solar radiation through the mirror surface onto the absorber tube filled at least partly with liquid. The absorber tube takes up the energy from the solar radiation and evaporates the liquid. The vapor flows through a distillation bridge from the absorber tube to the condensation tube. The condensation tube is coupled thermally with a transparent sleeve which encloses the absorber tube so that a space remains between the absorber tube and the sleeve. The vapor condenses in the condensation tube. During the condensation, heat is released which heats up the condensation tube. Heat is transferred to the sleeve via the thermal coupling of the condensation tube and the transparent sleeve. The heated sleeve heats the space in-between, as a result of which the absorber tube delivers less thermal energy to the latter. The method according to the invention therefore makes condensation enthalpy usable for increasing the efficiency of solar distillation. Due to this increase in efficiency, a solar still can still be operated effectively even at higher latitudes or with less solar radiation and the distillation of materials with a higher boiling point is possible. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]    Embodiments of the invention are described in greater detail in the following by means of drawings, in which 
           [0038]      FIG. 1  shows a diagrammatic representation of a first embodiment of a solar distillation device in cross section and 
           [0039]      FIG. 2  shows a diagrammatic representation of a longitudinal section through the device of  FIG. 1   1 . 
           [0040]      FIG. 3  shows a diagrammatic representation of a second embodiment of a solar distillation device in cross section 
           [0041]      FIG. 4  shows a diagrammatic representation of a third embodiment of a solar distillation device in cross section, with a possibility for extraction 
           [0042]      FIG. 5  shows an enlargement of a portion of the representation of  FIG. 4  and 
           [0043]      FIG. 6  shows a diagrammatic representation of a longitudinal section through the device of  FIGS. 4 and 5 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0044]    In the drawings, the various embodiments of distillation installations are shown in diagrammatic representations, with which a liquid which has been supplied, can be distilled by using only the energy of solar light. In this connection, utilization to obtain distilled water is just as possible as the distillation of other starting liquids. For the sake of simplification, the distillation is always started out from water in the following; however, the invention is not limited to this. 
         [0045]      FIGS. 1 and 2  show a first embodiment of a distillation installation  10 . As is evident, first of all from the diagrammatic cross-sectional representation in  FIG. 1 , the water  12  which is to be distilled is in the interior of an absorber tube  14 . The absorber tube  14  is disposed within a gas tight transparent sleeve  16  which may be formed, for example, from glass. The absorber tube  12  accordingly is located in a closed-off insulated space  18  in the interior of the sleeve  16 . 
         [0046]    The absorber tube  14  is connected with a first condensation tube  22  via several distillation bridges  20 , of which one is shown in  FIG. 1 . Sunlight radiation, shown here by arrows, is reflected by a suitably curved mirror surface  24  and focused in the direction of the absorber tube  14 . By these means, the absorber tube  14 , is heated up for evaporating the liquid  12  contained therein, the vapor of which then passes through the distillation bridge  20  into the condensation tube  22 . 
         [0047]    The sleeve  16  is fastened directly to the condensation tube  22 , with which it is in direct thermal contact. If the vapor condenses in the condensation tube  22 , an amount of heat of condensation, corresponding to the evaporation enthalpy, is transferred to the condensation tube  22  and to the sleeve  16  which is coupled thermally thereto. 
         [0048]    Accordingly, the sleeve  16  is heated, so that the absorber tube  14  is in the interior of the heated insulated space  18 . Due to this arrangement of the absorber tube  14  in the heated insulated space  18  within the also heated sleeve  16 , the absorber tube  14  emits less thermal energy to the surroundings. With that, the absorber tube  14  attains a higher temperature with the same solar radiation, than would be the case with an arrangement without the sleeve  16 , that is, if the absorber tube  14  were to be exposed directly to the external environment. 
         [0049]    Accordingly, by utilizing the heat of condensation, the distillation installation  10  with the construction shown diagrammatically in  FIG. 1  achieves a clear increase in efficiency due to the utilization of the heat of condensation. This can be used, on the one hand, in order to achieve a high throughput during the distillation, even if the solar radiation is relatively slight. On the other hand, the higher temperature at the absorber tube  14  can also be used for the distillation of liquids, the boiling point of which is above that of water. 
         [0050]    The further construction of the installation  10  is shown in longitudinal section in  FIG. 2 . The mirror reflector  24  is constructed in the shape of a trough. The absorber tube  14  and the first condensation tube  22  are disposed at a distance from and parallel to one another and coupled with one another by several distillation bridges  20 . 
         [0051]    Water (or a different liquid which is to be distilled) is passed via an inlet  26  and through a float valve  28  to the absorber tube  14 . With the help of the float valve  28 , it is ensured that a desired liquid level is always maintained within the absorber tube  14 . 
         [0052]    If the whole of the liquid does not condense in the first condensation tube  22 , the excess vapor can be passed into a second condensation tube  30 . The second condensation tube  30  extends parallel to the first condensation tube  22 , as well as to the absorber tube  14  and is disposed directly at the mirror surface  24 , so that it is in thermal contact with the mirror surface  24 . By these means, a large surface for delivering heat is available to the second condensation tube  30 , so that it is ensured that the excess vapor will condense. 
         [0053]    The distillate, obtained in the first condensation tube  22  and in the second condensation tube  30 , is passed via a pipeline  32  into a collection container  36 . Moreover, a heat exchanger  34  is provided, the details of which are not shown, with which the fresh water, supplied to the absorber tube  14 , is heated by the condensate. 
         [0054]    The collection container  36  forms a foundation for the installation  10 . The mirror surface  24  and the unit of absorber tube  14 , first condensation tube  22 , and the sleeve  16 , are supported on the collection container  36 . Moreover, the whole trough from the mirror reflector  24  and the sleeve  16 , with the tubes  14 ,  22  therein, can be rotated about a longitudinal axis, so that tracking relative to the position of the sun is made possible. 
         [0055]    A second embodiment of a distillation device  10   a  is shown in  FIG. 3 . The water  12   a  which is to be distilled is disposed in an absorber tube  14   a  with a triangular cross-section, the center of which is at the focal point of a curved mirror  24   a . The absorber tube  14   a  is connected with a condensation tube  22   a  which extends parallel to the absorber tube  14   a  and has a rectangular cross-section in the example shown, via distillation bridges  20   a  one of which is shown here. The absorber tube  14   a , as well as the condensation tube  22   a  is disposed in an insulated space  18   a  which is surrounded by a partially transparent sleeve  16   a.    
         [0056]    A partition  21   a  extends into the absorber tube  14   a  and leaves a region in the tip of the latter free. In the absorber tube  14   a , this partition  21   a  differentiates a region with liquid from a passage to the distillation bridge  20   a . As a result, the liquid cannot reach the distillation bridge  20   a  directly. 
         [0057]    In the example shown, the sleeve  16   a  is formed by a rear wall  25   a  of the mirror  24   a  and two transparent elements  17   a, b  which consists of a glass with a high transmission. The one transparent element  17   a  is disposed as an outer pane between the upper and lower mirror sides, so that rays of light, incident frontally on the distillation installation  10   a , hit them perpendicularly. The other transparent element extends as an inner pane  17   b  from the outer pane  17   a  to the rear wall  25   a  of the mirror  24   a  and forms a right angle with the outer pane  17   a . As a result, the inner pane  17   b  separates the insulated space  18   a  from a region  19 . The inner pane  17  is in contact with the condensation pipe  22   a , with which it is coupled thermally by these means. 
         [0058]    Incident light rays are focused by the mirror  24   a  onto the absorber tube  14   a . Due to the triangular acute angled cross section of the latter, most of the rays, preferably, strike the two long sides and, in this way, heat the absorber pipe  14   a  uniformly. At the same time, the water  12   a  evaporates in the absorber tube  14   a . The vapor flows around the partition  21   a  and reaches the condensation tube  22   a  by way of the distillation bridges  20   a.    
         [0059]    The vapor may condense once again in the condensation tube  22   a . The thereby released energy of condensation can then heat the condensation tube  22   a  which transfers this heat to the inner pane  17   b , and with that to the sleeve  16   a.    
         [0060]    In addition, the condensation tube  22   a  is coupled thermally with the rear wall  25   a . Due to the delivery of the energy of condensation to the mirror  24   a , on the one hand, passive cooling can be achieved and, on the other, the region of the mirror  24   a  which forms part of the sleeve  16   a , is heated with the rear wall  25   a . By these means, the sleeve  16   a  can be heated further. 
         [0061]    In addition to being heated by solar radiation, the insulated space  18   a  is therefore also heated by way of the sleeve  16   a . Owing to the fact that it is disposed within the insulated space  18   a , the absorber tube  14  can therefore reach higher temperatures than if it were outside of this space  18   a . In addition to the thermal insulation by the sleeve  16   a , this effect is increased even more by the thermal coupling of the condensation tube  22   a  with the sleeve  17   a.    
         [0062]    The region  19   a  forms a further insulation chamber which can also be heated and functions as a thermal reservoir for the insulation space  18   a . By these means, weather-related fluctuations in the temperature and solar radiation can be intercepted, so that a more uniform operation of the solar still  10   a  is ensured. 
         [0063]    This second embodiment therefore offers a similar gain in efficiency when the solar radiation is utilized, like the first embodiment shown in  FIGS. 1 and 2 . This gain in efficiency can therefore also be used in order to distill relatively larger amounts in a corresponding time with a relatively low solar radiation or to make possible the distillation of liquids, the boiling points of which is above that of water. 
         [0064]    The second embodiment may also comprise further elements which are described for the first embodiment. For example, a heat exchanger (not shown), with which the freshwater, supplied to the absorber tube, is heated by the condensate, may be provided at a pipeline to a collection container for the distillate. 
         [0065]    In addition, a floating valve may be provided in the inlet to the absorber tube  14   a . With the help of the floating valve, it is ensured that a desired water level (or a level of a different liquid which is to be distilled) is always retained within the absorber tube  14 . 
         [0066]    Moreover, in the second embodiment, a second condensation tube may be provided which extends parallel to the first condensation tube  22   a  as well as to the absorption tube  14   a  and is disposed directly at the mirror surface  24 , so that it is in thermal contact with the mirror surface  24 . A large area for emitting heat is therefore available to the second condensation tube. This ensures that the excess vapor is condensed. 
         [0067]    The decisive improvement of these distillation installations,  10 ,  10   a  over known solar stills lies in the utilization of the heat of condensation. This is achieved by the sleeves  16 ,  16   a . Because of the airtight construction thereof, heat losses are minimized. Moreover, the sleeves  16 ,  16   a , are heated in particular by conduction by being disposed at the first condensation tube  22 ,  22   a . Depending on the design, the sleeve  16 ,  16   a  may consist partly or completely of a special solar glass (such as a low iron glass or a borosilicate glass) for optimized thermal radiation properties. 
         [0068]    A plurality of supplements or respectively modifications is possible in addition, and/or, alternatively to the versions and elements shown. For example, the curved mirror surface  24  may be constructed in different shapes, for example, as a parabolic trough. All parts which are in contact with the liquid or the vapor, may be produced from appropriate stainless steel (such as WNr.1.4301 X5CrNii8-i0, AISI 304 (V2A)) which is resistant to foods as well as to corrosion and, at the same time, has good stability. The absorber tube  14 ,  14   a  may be blackened for better light absorption and, with that, easier heating. 
         [0069]    A third embodiment of an installation  110 , based on the first embodiment shown in  FIG. 1 , is shown in  FIGS. 4-6 . The installation  50  is intended for the extraction of substances from a material, by using the vapor obtained during the distillation. 
         [0070]    In the third embodiment, distillation bridges  120  which connect an absorber tube  114  with a first condensation tube  122 , are expanded into connection spaces  120  in comparison to the distillation bridges  20  of the first embodiment. Sunlight radiation, shown by arrows in  FIG. 4 , is reflected by a suitably curved mirror surface  124  and focused in the direction of the absorber tube  114 . 
         [0071]    The absorber tube  114 , is heated by the sunlight until the liquid  112 , contained therein, starts to evaporate and the vapor of the liquid  112  then passes through the connection space  120  and reaches the condensation tube  122 . In the example shown, the condensation tube has a cross section which, instead of being round, is in the shape of a segment of a circle. 
         [0072]    In the connection space  120  between the absorber tube  114  and the condensation tube  122 , a material (not shown), from which a substance is to be extracted, is disposed in an insert  121 . The insert  121 , is constructed so that the material to be treated is held therein and itself does not reach the absorber tube  114  or the condensation tube  122 . However, the vapor flowing through the connection space  120 , can pass through the insert  121  and comes into contact with the material, resulting in the desired effect of extraction of the material. 
         [0073]    The material which is not shown in the drawings, may, for example, be a plant material, from which contents are to be extracted. This is accomplished by means of the vapor flowing through which in contact with the material within the insert  121  extracts the contents there and transports them into the condensation tube  122 . The extracted substance is then dissolved in the condensate which forms there. 
         [0074]    In a different application example, the insert  121  contains a material which is to be purified, such as spent activated charcoal which previously was used as a filter and therefore is interspersed with impurities. Here also, the vapor, flowing through the connection space  120 , comes into contact with the activated charcoal in the insert  121 , dissolves the impurities there and transports them away. The activated charcoal can be purified and regenerated in this way, so that it can subsequently be used once again as a filter material. 
         [0075]    The inserts  121  in the respective connection spaces  120  are shown only diagrammatically in the Figures between the absorber tube  114  and the condensation tube  122 . Several inserts  121  (four separate inserts  121  in  FIG. 6 ) are shown over the length of the device in the example. Of course, a different number of passages  120  with inserts  121  therein may be provided. Likewise, the connection space  120 , and the insert  121  may extend therein continuously over the whole length. 
         [0076]    The inserts are to be adapted to the material which is to be treated. In the example shown, the inserts  121  are constructed as closed containers with a perforated wall, so that vapor can flow through them, but any solids, such as activated charcoal are retained. 
         [0077]    In general, the wall of the insert  121  should be constructed so that it retains the material which is to be treated, but permits passage of the vapor and of the substance which is to be extracted. 
         [0078]    Depending on the material to be treated and the substance to be extracted, an insert  121  may be equipped, for example, with a membrane which is permeable for the vapor and for the material to be extracted. This membrane may, for example, be a silicone material. 
         [0079]    Preferably, the insert  121  can be exchanged. For example, the tubular or trough-shaped device may be hinged as a whole, so that the inserts  121  can be exchanged in order to remove material which has been treated and to insert new material which is to be treated. The inserts  121  can be used as cartridges so that, for example, filled inserts are removed and replaced by newly filled inserts  121 . 
         [0080]    In an alternative embodiment (not shown), the different inserts  121  or respectively a continuous insert  121  can be pushed in the longitudinal direction into the device. 
         [0081]    There has thus been shown and described a novel device and method for solar distillation which fulfills all the objects and advantages sought therefor. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering this specification and the accompanying drawings which disclose the preferred embodiments thereof. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention, which is to be limited only by the claims which follow.