Abstract:
When fresh water is produced from salt water or similar by evaporation of untreated or crude liquid in an evaporation device under partial vacuum and by vapor condensation in a condensation device connected with the vapor outlet of the evaporation device a high degree of evaporation and cost effectiveness can be obtained in that the evaporation device and the condensation device in a disconnected condition, are filled with crude or clean liquid, respectively, and are subsequently exposed to a partial vacuum created by volume enlargement under hermetically sealed conditions and that the evaporation device and the condensation device are not flow-connected with each other until they are under partial vacuum.

Description:
FIELD OF THE INVENTION 
     This invention relates to a process for producing clean liquid from untreated liquid, in particular for producing fresh water from salt water, by means of evaporation of the untreated liquid under partial vacuum in an evaporation device and condensation of the vapour in a condensation device connected with the vapour output of the evaporation device. 
     The invention further relates to a device suitable for carrying out the process, having at least one evaporation device which can be supplied with untreated liquid and in which a partial vacuum can be produced, and further having at least one condensation device which can via a connecting line be supplied with vapour from at least one upstream evaporation device. 
     BACKGROUND OF THE INVENTION 
     Such a process and device is known from DE 33 45 937 A1 where the connecting line between an evaporation device and a condensation device cannot be shut off. To produce the desirable partial vacuum, the evaporation device is connected with at least one tank which is filled with untreated liquid, and provided at a height that is at least by the water column producible by the ambient air pressure above a water level, which tank is provided with a downpipe that is immersed in the water level and can be shut off. By opening the downpipe, liquid flows off causing a partial vacuum in the evaporation device if venting thereof is prevented, which partial vacuum is in this case passed on to the condensation device via the open connecting line. The required location of the tank at a high level and the immersing of the bottom end of the downpipe in an existing water level result in a relatively large overall height of the device and high constructional expenditure. Nevertheless, due to the existing connection between the evaporation device and the condensation device, the obtainable partial vacuum is relatively small. In addition, the liquid in which the downpipe is immersed may contain gas bubbles produced by gas emission etc., which may accumulate at the bottom end of the downpipe and then rise in it, which may result in a further deterioration of the obtainable partial vacuum. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a process and a device as described initially above which ensure high evaporation output at a low boiling point and thus a high degree of cost effectiveness. 
     According to the invention, this object is achieved, in conjunction with a process whereby an evaporating device and a condenser device have crude or clean liquid therein exposed to a partial vacuum created by volume enlargement under hermetically sealed conditions and further, in conjunction with the device whereby each evaporating device forms a vessel system comprising a pump unit connected with the bottom area of the evaporator device and having an operating chamber of variable size which vessel system can be filled with crude liquid when the operating chamber is reduced in size and is exposed to a partial vacuum in hermetically closed condition by enlarging the operating chamber, whereby the side of the condensation device forms a vessel system comprising a pump unit connected with the bottom area of the evaporation device and having an operating chamber of variable size, which vessel system can be filled with a clean liquid when the operating chamber of the condensation device vessel system is reduced in size and is exposed to a partial vacuum in hermetically closed condition by enlarging the operating chamber of the condensation device vessel system, and whereby a shut-off device is provided in the connecting line for releasing the connecting line only when the operating chambers are enlarged to maximum size. 
     The measures according to the present invention advantageously result in a high degree of evacuation and thus in a high evaporation output at relatively low temperatures as can advantageously be obtained using simple solar collectors or the like. The measures according to the invention may further also be realised in an advantageous manner by a highly compact and correspondingly easy-maintenance arrangement. Thus, the measures according to the invention serve to achieve the above-mentioned object of the invention in a most simple and low cost manner. 
     The evaporation device may advantageously comprise a heater and a separator provided downstream thereof. Such an arrangement permits the direct or indirect heating of the raw water to be vaporised outside the separator, thus allowing a high degree of freedom of design. 
     A further advantageous measure to improve the output may consist in cooling the condensation device during the condensation process. The heat thus generated may advantageously be used for preheating the raw water to be vaporised. 
     A further, particularly preferential measure may consist in that the condensation device is stimulated to perform vibrating movements during the condensation process. Thus, the formation of water droplets on the condensate side of the condensation device is prevented, which may affect the thermal transfer and thus condensation. Instead, the vibrating movement ensures that the droplets run off rapidly leaving only a very thin water layer on the condensate side. 
     A further advantageous measure may consist in that the vapour coming from the evaporation device is pumped into the condensation device by means of an injection device. This advantageously permits an increase in pressure within the condensation device, having a positive effect on the acceleration of the condensation process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantageous embodiments and expedient developments of the main-claim measures are evident from the remaining sub-claims and can be derived from the description of an example given below in conjunction with the accompanying drawings wherein: 
         FIG. 1  shows a functional diagram of a seawater desalination plant having an evaporation and a condensation device, 
         FIG. 2  shows a functional diagram of a seawater desalination plant having several evaporation and condensation devices, 
         FIG. 3  shows a section of an injection device associated with a condensation device, and 
         FIG. 4  shows a side view of a vibratable condenser. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention is mainly used for seawater desalination, that is to say for producing fresh water from salt water. The plant according to the invention is thus advantageously installed at the sea shore so that practically unlimited amounts of the required salt water can be taken from the sea. 
     Plants as described in the present invention comprise an evaporator and a condenser side each.  FIG. 1  contains a dot-dash separation line A, with the evaporator side on the right-hand side of such line, and the condenser line on the left-hand side thereof. The evaporator side comprises a raw water tank  1 , designed as a trough which is open towards the top, which is suppliable with seawater via a pump  2 . Below the raw water tank  1  provision is made for a lower-level cylinder-piston unit  3  comprising a piston  4  provided in a cylinder, which piston is connected via a piston rod  5  with a piston  6  of an equal-stroke cylinder-piston unit  7 , which is actuatable by hydraulic or preferably pneumatic force, which unit is connected with a suitable energy source not shown in detail here, but shown in the present example in the form of a pressurized oil source and controllable by a control valve  8 . The cylinder-piston unit  3  comprises an operating chamber  9 , limited by the piston  4 , which can be reduced or increased in size within the associated cylinder by a movement of the piston  4 . 
     Above the level of the cylinder-piston unit  3  provision is made for an evaporation device  10  comprising a heater  11  and a downstream separator  12 . In the example illustrated, the heater  11  is designed as a solar collector ensuring practically direct heating by solar energy. It would of course be also conceivable to integrate the heater into a heat exchanger and to supply the heat via a secondary heating circuit, as is indicated for example on the right-hand side of  FIG. 2 . The separator  12 , where water is separated from vapour, is provided above the level of the heater  11  but still below the raw water tank  1 . The evaporation unit  10  comprising the heater  11  and the separator  12  together with the operating chamber  9  constitute an inter-connected vessel system which can be shut off towards the outside. For this purpose, connecting lines exist between the operating chamber  9  and the bottom side of the heater  11 , between the top side of the heater  11  and the separator  12  and between the separator and the operating chamber  9 . The line leading from the separator  12  to the operating chamber  9  extends from the bottom of the separator  12 . The line from the heater  11  to the separator  12  exits into the top area of the separator  12 . 
     A supply line  13  which can be shut off by a valve arrangement is provided from the raw water tank  1  to the bottom side of the operating chamber  9 . In the example illustrated, the valve arrangement associated with the supply line  13  comprises two parallel branches provided with a valve  14  and a valve  15 , respectively, one of which, in this example valve  15 , being controllable by a level controller  16  associated with the separator  12 . An outlet nozzle  13   a , which can be shut off by a valve  17 , extends from the bottom area of the supply line  13 . A venting line  19  which can be shut off by a valve  18  extends from the top area of the separator  12 . 
     The condenser side comprises a clean water tank  20  provided at the same level as the raw water tank  1 , which clean water tank can be supplied with clean water via an inlet  22  which is connected with a clean water source and can be shut off by a valve  21 . Below the level of the clean water tank  20  provision is made for a condensation device  23  which in this example comprises a multitubular condenser  24 . Below the condenser  24  provision is made for a cylinder-piston unit  25  whose piston  26  limits an operating chamber  27  and is connected via a piston rod  28  with the piston  29  of an equal-stroke cylinder-piston unit  30  which is preferably actuatable in the same manner as the cylinder-piston unit  7 , which cylinder-piston unit  30  can be connected with the same hydraulic pressure medium source as the cylinder-piston unit  7  and is controllable by a control valve  31 . 
     A supply line  32  is provided from the clean water tank  20  to the bottom area of the operating chamber  27 . The supply line  32  can be shut off by a valve  33 . An outlet line  32   a  which can be shut off by a valve  34  extends from the supply line  32 . A venting line  36  which can be shut off by a valve  35  extends from the inlet of the condenser  24 . In addition, the inlet of the condenser  24  is connected with the clean water tank  20  via an outlet line  37  comprising a check valve  38 . The check valve  38  is designed in such a manner that it opens in the direction of the clean water tank  20 . 
     The condenser  24  and the operating chamber  27  of the cylinder-piston unit  25  constitute a connected vessel system which can be shut off towards the outside. For this purpose, the operating chamber  27  is connected with the bottom area of the condenser  24 . The maximum volume enlargement of the operating chamber  27  obtainable by a movement of the piston  26 , which in this example is performed to the right-hand side, is expediently larger than the capacity of the condenser  24  on the condensate side. 
     In the embodiment shown, this cooling device contains a sprayer device  39  which can be fed with cooling water, preferably raw water, supplied by an associated cooling water pump  40 . The jet of the sprayer device impinges on the outside of the condenser  24  whose inside is exposed to vapour. A cooling water tank  41  is therefore associated with the cooling water pump  40  and can be supplied with raw water via a supply line extending from the raw water tank  1 . The cooling water flowing off from the condenser  24  is collected in a collecting trough  42  arranged underneath the condenser  24 , with a return line leading back to the cooling water tank  41 . 
     Associated with the vapour inlet of the condenser  24  is an injection device  43  which will be described in further detail below in conjunction with by means of  FIG. 3 . This injection device comprises a venturi tube supplied with clean water. For this reason, a supply line  44  is associated with the injection device  43  , which supply line is provided with a pump  45  whose suction side is arranged adjacent to the operating chamber  27 . The injection device  43  brings about a pressure increase within the condenser  24 , thus resulting in an improved condensation effect. 
     To further improve the condensation effect, the condenser  24  may be designed as a vibrating condenser which during the condensation process is stimulated by a vibration generator  46  to perform vibrating movements which will be described in further detail in connection with  FIG. 4 . 
     The evaporator side is connected with the condenser side by a connecting line  47  leading from the exit of the separator  12  to the inlet of the condenser  24 . The connecting line  47  can be shut off by a valve  48  which is expediently controllable by a controll unit preferably in the form of a PLC. This also applies accordingly to the valves  15 ,  17  and  33 . The other valves may expediently be designed as manually controlled valves. 
     To start the plant, the raw water tank  1  is first filled with seawater by means of the associated pump  2 . The cooling water tank  41  is connected with the overflow of the raw water tank  1 . All valves are closed while the manual venting valve  17  is opened. The piston  4  of the cylinder-piston unit  3  is in its end position, here on the left-hand side, which corresponds to the smallest volume of the operating chamber  9 , as indicated in  FIG. 1 . Upon opening the manual valve  14 , the condenser side is flooded until the raw water flows off at the venting line  19 . As soon as this is the case, the valves  18  and  14  will be closed. 
     On the condenser side, all automatic and manual valves are initially closed. First of all, by opening the valve  21 , about one third of the clean water tank  20  is filled with clean water from the outside. Afterwards, the valve  21  is closed again and the venting valve  35  opened. The piston  26  of the cylinder-piston unit  25  is in its end position, here on the left-hand side, which corresponds to the smallest volume of the operating chamber  27 . Upon opening the valve  33  provided in the supply line  32 , the entire condenser system is flooded until raw water flows off at the venting line  36 . As soon as this is the case, the valves  35  and  33  are closed. 
     Due to the activation of the cylinder-piston units  7  and  30  by activating or actuating the associated control valves  8  and  31 , respectively, the pistons  4  and  26  of the cylinder-piston units  3  and  25  are moved into their respective end positions opposite the end position shown in  FIG. 1 , whereby the operating chambers  9  and  27  limited by the pistons  4  and  26 , respectively, are enlarged to their maximum volume. On the evaporator side the liquid level in the separator  12  drops to the operating position as illustrated. The volume enlargement obtainable by the movement of the piston  4  is accordingly smaller than the entire capacity of the separator  12 . On the condenser side the liquid level sinks below the middle of the associated cylinder-piston unit  25 . Accordingly, the volume enlargement obtainable by the movement of the piston  26  of the cylinder-piston unit  25  is greater than the internal capacity, that is to say, the condensate-side capacity, of the condenser  24 . In this case the volume enlargement described above corresponds to more than twice the capacity of the condenser  24 . 
     The vessel systems comprising the operating chamber  9  and the evaporation device  10 , and the operating chamber  27  and the condenser  24 , respectively, are hermetically sealed towards the outside. The volume enlargement of the operating chambers  9  and  27  result in a nearly complete vacuum, or in any case in a very high partial vacuum, in these hermetically sealed-off vessel systems, whereby the water in the entire system will boil at already relatively low temperatures. 
     The heating energy supplied to the evaporator  11 , in this example the directly supplied solar energy, maintains this boiling process. On the condenser side, the cooling device is started by switching on the pump  40 , while simultaneously, by switching on the pump  45 , the injection device  43  is put in operation. By opening the valve  48  provided in the connecting line  47 , vapour pours from the separator  12  into the condenser  24 . The injection device  43  causes a pressure increase which permits condensation at higher temperatures and thus increases the temperature difference between the condensation temperature and the temperature outside of the condenser. The cooling device in the embodiment illustrated, which is designed as a spraying device  39  fed with raw water, reaches a high degree of efficiency, thus improving the condensation output even further. 
     The water evaporating on the outside of the condenser  24  is continually replenished by water flowing from the overflow of the raw water tank  1  to the cooling water tank  41 . To further increase the output, a fan or blower might be associated with the condenser  24  whereby a cooling tower effect could be achieved. 
     To avoid excessive salt concentration in the cooling water tank  41 , the overflow coming from the raw water tank  1  is led directly into the suction-side range of the pump  40 . Thus, the same amount of slightly concentrated salt water in the return line of the cooling circuit will flow into the overflow extending from the cooling water tank  41  as water flows in from the raw water tank  1 . 
     To further increase the output of the condenser  24 , the oscillation generator may be put in operation, which is designed in such a manner that it can stimulate the associated condenser  24  to perform vibrations in a frequency range of 5 to 20,000 Hz, thus considerably increasing the effectiveness of the condenser  24 . 
     The boiling water in the separator  12  is maintained at a constant level by automatically supplying water from the raw water tank  1 . This is achieved by a level controller  16  associated with the separator  12 , which acts to control the valve  15  provided in the supply line  13 . 
     Due to the constant condensation in the condenser  24 , the liquid level on the condenser side is permanently rising. When this level has reached the bottom side of the condenser  24 , a signal emitted by a suitable level alert causes the valve  48  provided in the connecting line  47  to be closed and the control valve  31  to be reversed, whereby the piston  26  of the cylinder-piston unit  25  is moved in the direction reducing the volume of the operating chamber  27 . Thus, the collected, condensed, and therefore desalted water is pressed into the clean water tank  20  via the discharge line  37  which is provided with the check valve  38 . When the smallest volume of the operating chamber  27  is obtained, the control valve  31  is automatically reversed, thus urging the piston  26  into the opposite direction where it produces a high vacuum again. Then the valve  48  provided in the connecting line  47  can be opened again, so that a new cycle can start. On the evaporator side, the vacuum can likewise be augmented in the above-described manner by activating the cylinder-piston unit  3  while the associated vessel system is hermetically sealed. 
     The arrangement according to  FIG. 2  differs from that in  FIG. 1  merely in that provision is made for two evaporation devices  10   a ,  10   b  and two condenser devices  23   a ,  23   b . The evaporation device  10   a  is connected with the condensation device  23   a  via a connecting line  47   a  having a valve  48   a . The evaporation device  10   b  is connected with the condensation device  23   b  via a connecting line  47   b  having a valve  48   b . A cylinder-piston unit  3   a ,  3   b  and  25   a ,  25   b , is associated with each evaporation device and condensation device, respectively. A particularity in comparison with  FIG. 1  consists here in that the heater  11   a  of the evaporation device  10   a  in this example is not heated directly but, as mentioned above, indirectly. For this purpose, provision is made for a heat exchanger, one side of which forms the heater  11   a  of the evaporation device  10   a  and the other side of which is located in a secondary heating circuit  51  extending via a solar collector  52 . The heater  11   b  of the evaporation device  10   b  and the condenser of the condensation device  23   a  also form a heat exchanger  53  which has the effect that the condensation heat of the condensation device  23  is simultaneously used for heating the raw water flowing through the heater  11   b . It may be expedient to design the heat exchangers  50  and  53  as plate heat exchangers. 
     An injection device  43  may be associated with the vapour inlet of each of the condensation devices, as mentioned above. An example hereof is illustrated in  FIG. 3 . The injection device  43  shown here comprises a venturi tube  55  having a constriction and whose interior is exposed to a clean water jet. For this purpose, the supply line  44  associated with the injection device  43  is provided with a spray nozzle  56  within the area of the above-mentioned constriction. The venturi tube  55 , in the area of the constriction, is provided with radial inlets  57  which constitute a connection with a surrounding annular space  58  communicating with the connecting line  47 . The clear water jet generated by the spray nozzle  56  produces a partial vacuum which sucks the vapour from the annular space  58  into the inside via the radial inlets  57  and presses it into the associated condenser  24  which in the example shown is a multitubular condenser, whose interior is supplied with vapour and whose outside can be cooled by air or an additional coolant. 
     A particularly high condenser output can be achieved, as mentioned above, by using the vibration generator  46  for stimulating the condenser to perform vibrating movements during condensation. This will prevent the formation of water droplets on the inside of the condenser tubes which would affect the condensation process. 
       FIG. 4  shows a condenser  24  which can be stimulated to perform vibrating movements. For this purpose, the condenser is on one side held in an oscillating bearing, and on the other side connected with the vibration generator  46 . In the example illustrated, the condenser  24  is within the area of its upper end suspended in an oscillating manner around a horizontal axis  59  on a fixed bearing bracket  60  while being connected at its bottom end with the vibration generator  46  which is likewise fixed to a bracket and provided with a recuperating spring. The inlet and outlet lines of the condenser  24  are provided with flexible fittings  62  and via those are connectable with firmly installed lines. 
     The frequency of the vibrations generated by the vibration generator  46  may be in the range of 5 to 20.000 Hz. The optimal frequency has to be established in each individual case by experimentation. The effectiveness of the condenser can thus be increased by up to 60%, if an appropriate frequency is selected. The reason for such improvement lies in the fact that, due to the vibrating movements, the water condensing on the inside of the condenser tubes flows off before an excessive formation of droplets, thus preventing a water-caused insulation and improving the heat passage through the condenser tubes.