Abstract:
An evaporation device for increasing evaporation from a surface of a body of liquid, comprises at least one evaporation element having at least one evaporation surface wettable by the liquid and at least partially exposable to wind when wetted, so as to allow evaporation of the liquid from the evaporation surfaces whereby the total evaporation area of the surface of the body of liquid is increased.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to an evaporation device using wind to increase the rate of evaporation from outdoor ponds.  
         BACKGROUND OF THE INVENTION  
         [0002]    Devices of the above kind can be used in outdoor ponds where wastewater is stored and where evaporation is needed to concentrate the waste for further treatment. These ponds present an environmental challenge, as leakage from such ponds can lead to serious groundwater contamination. The requirements of environmental authorities regarding the quality of lining of such ponds are becoming more stringent and therefore the costs thereof tend to increase. For these reasons, there exists a need to reduce the number and size of such evaporation ponds by increasing the rate of evaporation therefrom.  
           [0003]    Increasing the evaporation from ponds is also advantageous in the production of solid products like salts and minerals.  
           [0004]    Known means of increasing evaporation from ponds of the above specified kinds include the use of spray nozzles to force the pond water into the air as a spray. Spraying, however, has been found to be environmentally dangerous as the wind can carry the spray drops beyond the catchment area of the pond to open ground, where the drops can then percolate down to the water table with their load of contaminants.  
           [0005]    It is the object of the present invention to provide a new evaporation device.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention makes use of the known phenomenon that increasing the surface area of a liquid exposed to wind, increases the rate of evaporation of the liquid.  
           [0007]    In accordance with the present invention, there is provided an evaporation device for increasing evaporation from a surface of a body of liquid, comprising at least one evaporation element having at least one evaporation surface wettable by said liquid and at least partially exposable to wind when wetted, so as to allow evaporation of said liquid from said evaporation surface, whereby the total evaporation area of said surface of the body of liquid is increased.  
           [0008]    By virtue of the present invention, the body of liquid is provided with auxiliary evaporation surfaces, which make use of wind to allow for effective heat and mass transfer, both of which are involved in increasing the evaporation process.  
           [0009]    Preferably, the device further comprises means for periodically wetting said evaporation surface.  
           [0010]    Preferably, said evaporation surface is constructed from a porous fabric.  
           [0011]    Alternatively, the evaporation surface can be an irregularly or regularly shaped wettable solid such as volcanic rock (tuff), ceramic rings, Berl saddles, or other fill materials used in gas liquid contactors.  
           [0012]    Preferably, said evaporation surface is exposable to wind in a position transverse to said surface of the body of liquid. Still more preferably, said evaporation surface is exposable to wind in a position substantially perpendicular to said surface of the body of liquid.  
           [0013]    Preferably, the device further comprises orientation means for orienting said evaporation surface in the direction at least approximately parallel to the wind&#39;s direction.  
           [0014]    Preferably, each evaporation element has at least two evaporation surfaces.  
           [0015]    Preferably, the device comprises a plurality of evaporation elements. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    In order to understand the invention and to see how it may be carried out in practice, preferred embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:  
         [0017]    [0017]FIG. 1 is a perspective view of an evaporation device according to one embodiment of the present invention;  
         [0018]    [0018]FIG. 2 is a perspective view of an evaporation device according to another embodiment of the present invention;  
         [0019]    [0019]FIG. 3 is a perspective view of an evaporation device according to a further embodiment of the present invention;  
         [0020]    [0020]FIG. 4 is a perspective view of an evaporation device according to a still further embodiment of the present invention;  
         [0021]    [0021]FIG. 5 is a top view of an evaporation device according to a still further embodiment of the present invention;  
         [0022]    [0022]FIG. 6A is a top view of a possible arrangement of an evaporation device according to the present invention in a pond;  
         [0023]    [0023]FIG. 6B is a side view of a possible arrangement of an evaporation device according to the present invention, in a pond;  
         [0024]    [0024]FIG. 7A illustrates an alternative design of evaporation surfaces of an evaporation device of the present invention;  
         [0025]    [0025]FIG. 7B illustrates another alternative design of evaporation surfaces of an evaporation device of the present invention;  
         [0026]    [0026]FIG. 7C illustrates a still other alternative design of evaporation of an evaporation device of the present invention;  
         [0027]    [0027]FIG. 8 is an alternative embodiment of the device shown in FIG. 4;  
         [0028]    [0028]FIG. 9 illustrates an evaporation device of the present invention particularly suitable for mounting the device on a pond&#39;s bank;  
         [0029]    [0029]FIG. 10 is an enlarged illustration of detail J in FIG. 9;  
         [0030]    [0030]FIG. 11 illustrates an another embodiment of an evaporation suitable for mounting on a pond&#39;s bank; and  
         [0031]    [0031]FIG. 12 illustrates a side view of a multistory arrangement of the device shown in FIG. 11. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0032]    [0032]FIGS. 1, 2,  3 ,  4  and  5  illustrate different embodiments of an evaporation device designed in accordance with the present invention, to increase the evaporation from a surface  3  of a liquid pond  5  shown in FIGS. 6A and 6B.  
         [0033]    The evaporation device  1  shown in FIG. 1 has a plurality of evaporation elements E each having two evaporation surfaces  7  made from porous fabric which is stretched over vertical frames  9  in a sail-like manner. The evaporation device  1  is designed so as to enable the support of the evaporation elements E above the pond&#39;s surface  3  by means of a float structure  11  which is made from buoyant material. The float structure  11  is provided with a weight  13  which is suspended from it along an imaginary vertical axis  14  of the evaporation device  1  to ensure a low centre of gravity for the device  1  thereby keeping it upright on the pond&#39;s surface  3 .  
         [0034]    The evaporation device  1  has a wetting arrangement comprising a pump  15  having an inlet pipe  17  to the pond  5  and an outlet pipe  19  to a distribution system  21  mounted atop the evaporation surfaces  7 . The pump  15  can be operated by a battery or by a solar power pack, each being controlled by a control circuit, mounted in a watertight box  23  placed on the float structure  11 . To provide orientation of the evaporation surfaces  7  parallel to the direction of wind W, the evaporation device  1  has a wind vane  25  mounted thereatop.  
         [0035]    In use, the evaporation device  1 , or a plurality of such devices, is placed upon the surface  3  of the pond  5  preferably so that each is kept in position, while being free to rotate about its vertical, axis  14  in accordance with the wind direction. Such positioning arrangements may be in the form of float rings  27  tied between opposite banks  29  of the pond  5  (as in FIGS. 6A and 6B). The pump  15  periodically sucks liquid from the pond  5  and discharges it to the distribution system  21 , which acts to pour the liquid over the evaporation surfaces  7 . The liquid on the evaporation surfaces  7  is exposed to wind and therefore evaporates.  
         [0036]    [0036]FIG. 2 shows the evaporation device  30  according to another embodiment of the present invention, wherein the wetting is achieved by periodical submerging the evaporation elements E into the pond  5 . In the evaporation device  30 , the wetting arrangement comprises a hollow ballast chamber  31  capable of regulating the buoyancy of the evaporation device  30  by alternatingly receiving thereinto air or liquid. The ballast chamber  31  is connected with an air compressor  33  via a conduit  35  and a vent valve  37  to enable a flow of compressed air into and out of the ballast chamber  31 . The ballast chamber  31  is disposed underneath the float structure  11  and is provided with holes  39  on its underside  41  to enable a flow of liquid into and out of the ballast chamber  31 . A weight  13  is attached to the underside  41  of the ballast chamber  31  to ensure a low centre of gravity and thereby keep the evaporation device  30  upright. The evaporation device  30  is designed so that the buoyancy of the ballast chamber  31  when filled with air, together with that of the float structure  11 , slightly overbalances the evaporation device&#39;s weight to keep the evaporation device  30  buoyant. The air compressor  33  and the vent valve  37  can be activated in the same manner as the pump  15  in the previous embodiment.  
         [0037]    In use, the periodic immersion of the evaporation elements E is performed by opening the vent valve  37  allowing the air initially trapped in the ballast chamber  31  to escape via the conduit  35 . Liquid from the pond  5  enters the ballast chamber  31  via the holes  39  causing the evaporation device  30  to sink, thereby immersing the evaporation surfaces  7 . When the evaporation surfaces  7  have been wetted they are raised by closing the vent valve  37  and activating the air compressor  33  which forces air into the ballast chamber  31 . The air forces the liquid out of the ballast chamber  31  via the holes  39 . The liquid on the evaporation surfaces  7  is exposed to wind and therefore evaporates. The evaporation device  30  is kept in position by the float ring  27  which in this embodiment is provided with a subsurface cage  43  to prevent the evaporation device  30  from sinking too deep, thereby keeping the air compressor  33  and the vent valve  37  above the pond&#39;s surface  3 .  
         [0038]    [0038]FIG. 3 shows a further embodiment of the present invention, wherein the evaporation device  44  has evaporation elements E that are held by means of a boom  45  capable of movement in the vertical direction to periodically immerse the evaporation elements E in the pond  5 . The evaporation elements F, are attached,to a vertical rod  47  which is rotatably mounted to the boom  45 . A wind vane  25  is mounted on the vertical rod  47  which maintains a parallel orientation of the evaporation surfaces  7  to the wind direction W. In use, the boom  45  is mounted on a bank  29  of the pond  5 , being raised to allow evaporation from the evaporation surfaces  7  and being lowered to immerse them in the pond  5  for rewetting.  
         [0039]    [0039]FIG. 4 shows a further embodiment of the present invention, wherein the evaporation device  48  has evaporation elements E that are of a disk shape and are successively centrally mounted on a horizontal axle  49 . The axle  49  is rotatably mounted on a frame  51  which is attached to a float structure  11 . To control the rotation of the axle  49 , the evaporation device  48  is provided with an anemometer type device  53  which is mounted on the frame  51 , and connected to the axle  49  via a worm gear  55 . A wind vane  25  is attached to the fame  51  to keep the evaporation elements E parallel to the wind direction W. The evaporation device  48  may be centrally mounted relative to the float ring  27  via a vertical shaft  57  attached to the frame  51 .  
         [0040]    In use, when the evaporation device  48  is placed upon the pond&#39;s surface  3 , half of each evaporation surface  7  is immersed and the other half is exposed to the wind at any given time. Wind action causes the evaporation surfaces  7  to be rotated and therefore wetted.  
         [0041]    [0041]FIG. 5 shows the evaporation device  58  according to a still further embodiment of the present invention, wherein the orientation control of the evaporation device  58  is achieved by mutual arrangement of the evaporation elements E, thereby negating the need for a wind vane  25  as in the evaporation devices  1 ,  30 ,  44  and  48 , described previously. The evaporation elements E are mounted on the float structure  11  to be staggered on either side of an imaginary central horizontal axis  59  and to be transverse thereto. Due to this arrangement of the evaporation elements E, there is always a portion thereof that is acted upon by the wind to generate a torque  60  which rotates the evaporation device  58  keeping the horizontal axis  59  parallel to the wind direction W. Preferably, the evaporation elements E are designed so that those placed further downwind extend closer towards the central horizontal axis  59 . The wetting of the evaporation surfaces  7  may be preformed by means of a pump  15  as in the device shown on FIG. 1 or by periodic submerging as in the other embodiments previously described.  
         [0042]    In all the above evaporation devices  1 ,  30 ,  44 ,  48 ,  58 , the evaporation surfaces  7  were shown to be separate planar elements. Alternative embodiments for the evaporation surfaces  7  are now shown in FIGS. 7A, 7B and  7 C. FIG. 7A shows that a porous fabric may be mounted as a single sheet  61  on a series of guides  63 . FIG. 7B shows that a fabric may be mounted as in FIG. 7A for periodic take up on rollers  65 . This arrangement is advantageous for use in ponds that have a high salt concentration to break up salt deposits that accumulate on the evaporation surfaces  7 . As one of the rollers  65  rolls up the sheet  61 , the salt deposits are bent on the small radius of the guides  63  and thereby are broken up. FIG. 7C shows that in order to increase the surface area of the evaporation surfaces  7  without significantly increasing the height of the evaporation elements E, they may be corrugated surfaces. This may be advantageous for use in ponds that have a high salt concentration where accumulated salt deposits may be removed by stretching the folded evaporation surfaces  7  straight.  
         [0043]    The above described embodiments of the evaporation device of the present invention, as shown in FIGS.  1  to  5 , are not restricted to the positioning arrangements shown therewith. These arrangements may be interchangeable or rather they may have other designs instead of float rings, a positioning arrangement may be used such as, for example, a submerged fixed girder  67  which mounts the evaporation device  48  via a vertical shaft  57  as shown in FIG. 8.  
         [0044]    FIGS.  9  to  12  illustrate embodiments of the evaporation device of the present invention, particularly suitable for mounting on a pond&#39;s bank rather than on a surface of a pond as described with respect to the previous embodiments. These devices may have substantially greater number of evaporation elements and/or greater area of evaporation surfaces than the devices of the previously described embodiments, since they do not need to be light as in the case of mounting on a surface of a pond. Also, the devices adapted for mounting on a pond&#39;s bank may be supplied with catwalks or ladders to provide excess to any individual evaporation element.  
         [0045]    As shown in FIG. 9, the evaporation device  70  comprising a scaffold  72  mounted on a bank B of a pond P and provided with a liquid distribution system  74  at the top thereof, a non-porous bottom surface  76  and a plurality of evaporation elements E. The evaporation device  70  is provided with a pump (not shown) for supplying liquid from the pond to the distribution system  74 .  
         [0046]    Each evaporation element E is in the form of a bundle  82  of wettable filaments  83  and as better seen in FIG. 10, the liquid distribution system comprises piping grid  84  with junctions  85  each associated with a tray  86  formed with perforations  87  to which upper ends of the filaments  83  of each such bundle  82  is attached. Each junction  85  has a nozzle  90  through which liquid from the piping grid  84  is supplied to its associated tray  86  to wet tie filaments  83 . Lower ends of the filaments  83  are attached to the bottom surface  76 , as shown in FIG. 9.  
         [0047]    As further shown in FIG. 9, the non-porous bottom surface  76  has a slope  96  inclined downwardly towards the pond P and extending to the pond&#39;s edge so as to guide to the pond excess liquid used for wetting the filaments  83 . The bottom surface  76  preferably bas raised edges (not shown) preventing the excess liquid is from reaching the ground and seeping into the soil. Alternatively, the bottom surface may have drain pipes (not shown) extending towards the pond P and inclined to allow the drainage of tile excess liquid by gravity.  
         [0048]    [0048]FIG. 11 shows a fragment of an evaporation device  100  designed for mounting on a pond&#39;s bank, the device having evaporation surfaces  102  designed similarly to those of the evaporation device shown in FIG. 7B, but arranged in two stories I and II as schematically shown in FIG. 12. It should be mentioned here that the two stories are shown here solely for the purpose of illustration and that devices according to the present invention may clearly have any other number of stories.  
         [0049]    As seen in FIG. 12, the evaporation device has an upper, feeding trough  110  at each story thereof for receiving liquid pumped from the pond and wetting the evaporation surfaces  102  and a lower, collecting trough  111  for collecting herein excess liquid. As shown, the receiving trough  111  of the story I may serve as feeding trough  110  of the story II located thereunder.  
         [0050]    Reverting to FIG. 11, the feeding trough  110  is mounted above the evaporation surfaces  102  and has slots  114  for wetting therethrough these surfaces. The evaporation surfaces  102  are held by stiff horizontal beams  116  in secure contact along the slots  114  with feeding though  110 , and carry weighted bars  118  which keep the evaporation surfaces  102  vertical and from moving far out of place. The evaporation surfaces  102  are in the form of a plurality of strips  120  formed between a plurality of cutouts  122  extending along most of the height of the surfaces  102 . As shown, the strips are relatively narrow to be able to turn in the wind to stay essentially parallel to the wind direction.  
         [0051]    For all embodiments described above, the fabric of the evaporation surfaces may be made of any synthetic or natural fibre that can be wetted by the liquid without significantly reducing the vapour pressure of the liquid as a result of chemical interactions between the liquid and the fibre. The fabric of which the evaporation surfaces are made may also be non-woven, e.g. may be in the form of sleeves such as used in geotextiles and agrotextiles. The same materials may be in the form of strips tin enough to turn in the wend to maintain their surfaces parallel to the wind direction.  
         [0052]    Experimental results, conducted by the authors, demonstrate that die use of an evaporation device according to the present invention can significantly increase the evaporation from a pond&#39;s surface. In one experiment, the ratio of available evaporating area between a device pond and a control pond was 6 to 1. An eight-fold improvement in evaporation over the reference pond&#39;s evaporation was recorded in the device pond during a 24-hour interval.  
         [0053]    The advantages of the present invention include the localised evaporation on the evaporation surfaces thus preventing contamination of surrounding ground, the use of inexpensive materials giving low evaporation costs, low maintenance costs due to the simple construction of the device and a relatively low total weight.  
         [0054]    While the invention has been described with respect to preferred embodiments, it will be appreciated that many variations, modifications and other applications of the invention can be made. The wetting or holding arrangements of the evaporation elements may be of different designs. The evaporation surfaces do not necessarily need to be perpendicular to the pond&#39;s surface or the ground. It is also possible to generate an artificial wind using fans or blowers mounted on the float structures or on the pond&#39;s banks during seasons of little wind. Such fans could be solar powered to save on the use of electricity.