Patent Publication Number: US-2007095765-A1

Title: Liquid purification system and method for purifying a liquid using liquid-to-liquid heating and cooling

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The invention described herein is related to the treatment of liquid compositions for removing one or more components thereof by successive heating and cooling. More specifically, the invention described herein utilizes liquid-to-liquid heat transfer in both heating and cooling stages of the treatment.  
      2. Description of the Prior Art  
      Purifying liquids, and separation of liquids from various compositions is a large field of technology having many varying applications. The purification of water, for instance, has tremendous importance in many parts of the World. Many populated areas of the World are heavily reliant on desalinization of sea water as the primary source of potable water. As such, numerous desalinization plants have been constructed in those parts of the World where fresh water supplies are scarce.  
      Of course, other applications of desalinization of sea water into potable water exist. A useful example is that of a submarine or other sea-going craft, where desalinization of sea water is preferred over the storage of potable water onboard the craft. The decision to implement a desalinization system as opposed to a fresh water storage system is made in large part with consideration to the space requirement of the respective water sources. Where a large quantity of potable water is required, space requirements may be reduced over those of water tanks by installing a desalinization system. Further complicating an onboard storage tank implementation is that as water is used and the tank is depleted, the empty space in the tank may be undesirable, especially in view of the corresponding temporal variability of the weight of the water. For example, on submarines, the variations in water levels in a tank affects the buoyancy of the ship and can complicate navigation.  
      Although several methods for desalinization exist, the more simpler and popular methods are based on distillation. In such processes, salt water is heated until the water is converted to steam, which is then condensed into potable water. The condensing stage is generally accomplished through a series of copper tubes through which the energy of the steam is given off as heat and eventually is converted back into a liquid. Such condensing systems can be quite large in order to allow enough heat to be removed from the steam so as to meet a continuous water demand. However, not all applications where desalinization is desired can accommodate the size requirements of such large systems. Thus, the need is felt in the liquid purification field for systems requiring smaller installation footprints.  
     SUMMARY OF THE INVENTION  
      The present invention provides a liquid purification system having a first vessel containing a first liquid maintained at a first predetermined temperature. The first predetermined temperature is set to exceed the boiling point of a second liquid, where the second liquid is heated through contact with the first liquid. The first liquid and the second liquid are immiscible with respect to each other. The system further includes a second vessel also containing the first liquid, which is maintained at a second predetermined temperature below the condensation point of the second liquid. The second liquid is cooled through contact with the first liquid. The second liquid, e.g., salt water is input to the first vessel in an unpurified form, and the second liquid is expelled from the second vessel in a purified form, e.g., potable water.  
      In another aspect of the invention, a liquid purification system includes a first vessel containing a first liquid in a first zone thereof and a second liquid in a second zone thereof. The first liquid and the second liquid are immiscible with respect to one another. A heater is coupled to the first vessel and is in communication with the first liquid so as to heat the first liquid to a first predetermined temperature. A second vessel, also containing the first liquid in a first zone thereof and a second liquid in a second zone thereof, is coupled to a cooler for cooling the first liquid to a second predetermined temperature. The system includes a conduit network coupled to the first vessel for inputting the second liquid in an unpurified state thereto and coupled to the second vessel for transporting the second liquid in a first heated state thereto and further coupled to the second vessel for expelling the second liquid in a purified state therefrom.  
      In yet another aspect of the invention, a method is provided for purifying a liquid. A first liquid is provided to a first vessel and a second vessel. The first liquid is heated in the first vessel and is cooled in the second vessel. A second liquid is heated in the first vessel through contact with the first liquid contained therein and is cooled in the second vessel through contact with the first liquid contained therein. The second liquid is input to the first vessel and exits the second vessel in a purified state.  
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
      The FIGURE is a schematic diagram of an exemplary system implemented in accordance with the present invention.  
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
      Various embodiments of the present invention are best described in view of the schematic diagram of the FIGURE. It is to be noted that while the following descriptions are made with reference to a desalinization application of the present invention, the system of the present invention is not so confined and may be used in a wide variety of applications. The desalinization application described below is used for descriptive purposes and is not intended to imply limitation of the invention to any specific application.  
      As shown in the FIGURE, the present invention includes a first vessel, illustrated as liquid column  20  (also referred to herein as tank  20 ), having contained therein a first liquid  24 . In certain embodiments of the present invention, the first liquid is a polysiloxane, such as silicone. Certain silicones have among their beneficial properties stability at high temperature and immiscibility with water.  
      In tank  20 , the silicone  24  is heated to a temperature that exceeds the boiling point of a second liquid, such as water, which is the desired product of the exemplary embodiment of the invention. In certain embodiments of the present invention, the heating is accomplished through an immersion heater  80  to a temperature of approximately 300° F. The second liquid in its unpurified state, such as salt water, is input to column  20  via a conduit  54 . The salt water, having a higher specific gravity than the silicone  24 , and being immiscible with the silicone  24 , descends down the column  20  by force of gravity where it is pooled in a second zone of column  20 , as indicated at  34 . As the salt water descends down the column  20 , it is heated by liquid-to-liquid contact with the silicone  24 . In the steady state the liquid in the tank  20  consists of a first zone of silicone  24  and of a second zone of salt water  34 , the two zones being separated by a meniscus  58 .  
      As is shown in the FIGURE, the column  20  has installed therein a coiled conduit  22  having a lower end  23  thereof extending into the lower portion of the column  20 , and particularly into the salt water bath  34  formed below meniscus  56 . The conduit  22  extends upwardly from its lower end  23 , passes through the heated silicone  24  and is coupled to an external conduit  26 . The pre-heated salt water  34  is driven by fluidic pressure through the conduit  22  and flows upwardly against gravitational force toward the external conduit  26 . In so doing, heat is transferred to the salt water therein to the point where the water is converted to steam. The steam in external conduit  26  is then essentially pure water vapor and a brine solution falls toward the lower section of the tank  20  into the salt water bath  34 .  
      Excluding for the moment the description of the center tank  28 , embodiments of the present invention further include a second vessel, illustrated as column  40  (also referred to herein as tank  40 ), for containing a volume  42  of the first liquid, e.g., silicone, in a first zone thereof. In column  40 , the silicone  42  is cooled to a temperature below the condensation point of the purified water entering through conduit  38 . The temperature of the silicone  42  in the second tank  40  is cooled by a cooler such as heat exchange unit  48 . As is typical with heat exchangers of the art, heat exchanger  48  uses a refrigerant device such as the cooling coil  50  to extract heat from the fluid entering by conduit  46  to a predetermined temperature. In certain embodiments of the present invention, the heat exchanger  48  is operable to maintain the silicone bath  42  in the second tank  40  at a temperature of approximately 50° F.  
      As was the case in the first column, the water entering the second column  40  via conduit  38  is both immiscible with and has a higher specific gravity than the silicone  42 . As such, as the water condenses, it falls through the silicone bath  42  and is cooled through liquid-to-liquid contact therewith. The liquid water forms in a second zone in the lower portion of the tank  40  as a pool  44  of potable water having an approximate temperature of 70° F. The potable water is then extracted from the second tank  40  by an output conduit  74 .  
      In certain embodiments of the present invention, the purification system includes a third tank  28  also containing a silicone bath  32  in a region above a purified water bath  36 . The third tank  28  provides a step down in temperature of the purified water prior to proceeding to second tank  40 . As is shown in the FIGURE, steam entering tank  28  through conduit  26  is incident on the silicone bath  32 . The silicone bath  32  is heated by the steam, thereby depleting the steam of some of its energy. The steam entering tank  28  is then at least partially condensed through liquid-to-liquid contact with silicone bath  32  and subsequently falls under the influence of gravity towards the lower zone of the tank  28 . Thus, as shown in the FIGURE, the lower zone of tank  28  is occupied by a potable water bath  36  and the two zones are separated by a meniscus  60 . In the exemplary embodiment, steam entering tank  28  at a temperature in excess of 212° F. can heat the silicone bath  32  to a temperature of 150° F. Thus, the water in the water bath  36  is stored in the lower zone of tank  40  at a temperature of 150° F. Water from the water bath  36  is driven under fluidic pressure into conduit  38 , where it is transported to column  40 . In column  40 , it is further cooled as described above.  
      In certain embodiments of the present invention, the liquid in the tank  28  may be used to preheat the incoming salt water prior to being introduced to tank  20 . As is illustrated in the diagram of the FIGURE, salt water enters the system at inlet  52  and is forced through coiled conduit  30  by an external force, such as a pump (not shown). In conduit  30 , heat from the silicone bath  32 , which is heated by the steam entering tank  28 , is transferred to the solution carried therein. The preheated salt water solution is then transferred to external conduit  54 , which transports the preheated salt water, to tank  20 .  
      As previously described, the steam is created in conduit  22  of tank  20  and concentrated saline solution is left behind by the process. As such, salt water bath  34  may eventually contain an unacceptably high salt concentration so as to chemically over load the silicone. However, a certain salinity is desired because of the heat retention quality of brine. Thus, in certain embodiments of the present invention, means are provided for maintaining a predetermined salinity in the salt water bath  34 . In the embodiment shown in the FIGURE, a pH monitor  92  is coupled to a controller  90  via a transmission line  97 . Through the pH monitor  92 , the pH of the solution  34  is measured. When the pH as measured by the pH monitor  92  reaches a predetermined threshold value which, in certain embodiments, is between 7 and 8, controller  90  transmits a signal over transmission line  96  to a valve  94 . The signal causes the valve  94  to open and a certain volume of brine solution from salt water bath  34  is extracted through outlet  56 . The valve will remain open, under control of controller  90 , until a predetermined pH value, such as 9, is measured by pH monitor  92 . Obviously, there are many ways to maintain a certain salinity in the salt water bath  34 , the foregoing being merely one example thereof.  
      As shown in the FIGURE, certain embodiments of the system include a controller  90  for controlling various aspects of the invention. The controller  90  can be programmed to maintain the salinity of the solution  34 , as described above, as well as many other functions, such as maintaining the temperature of the silicone in one or more of the tanks  20 ,  28 ,  40 . For example, controller  90  may be coupled to a temperature measuring device  100 , such as a thermistor or digital thermometer, through transmission line  102 . Based on the temperature measured by the thermistor  100 , power is provided to immersion heater  80  through conductor  98  so as to maintain the desired temperature in tank  20 . Again, there are several ways of maintaining the temperature in one or more of the tanks  20 ,  28 ,  40 —the foregoing being merely a suggestion of one possible method. Controller  90  may be any known controller circuit, such as an industrial type controller well-known in the art.  
      The descriptions above are intended to illustrate possible implementations of the present invention and are not restrictive. Many variations, modifications, and alternatives will become apparent to the skilled artisan upon review of this disclosure. For example, components equivalent to those shown and described may be substituted therefor, elements and methods individually described may be combined, and elements described as discrete may be distributed across many components. The system may, for example, be used to decontaminate liquids of other contaminates than those exemplified. The scope of the invention should therefore be determined not with reference to the description above, but with reference to the appended Claims, along with their full range of equivalence.