Abstract:
Distillation apparatus comprises a condensing chamber and a heating chamber arranged on an enclosure. Liquid feed into the condensing chamber is pre-heated and flows to the heating chamber where it is boiled to produce vapor. Gas sparging in the condensing chamber enhances heat transfer and absorbs additional vapor generated by pre-heating. The condenser is a helical or other horizontal tube heat exchanger.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    In U.S. Pat. Nos. 4,976,824; 5,030,327; and 5,332,476, several embodiments of a fluid distillation system are disclosed. For the most part, these embodiments provide effective operation and a reasonable yield of distilled water. However, with improved design of such a system, the operation and yield can be enhanced, and the present invention is directed to apparatus and method for providing an increase in the yield of distilled water from such a system while keeping the system relatively simple in construction.  
           [0002]    U.S. Pat. No. 5,490,906 describes several embodiments of a fluid distillation system wherein each embodiment uses a primary container or chamber for water or fluid to be distilled and a secondary water container or chamber. The two chambers are adjacent to each other, and the secondary chamber cooperates with the primary chamber to direct water vapor generated in the system to travel to a reservoir for collection.  
           [0003]    An example of such a fluid distillation apparatus was built under the instruction of Naisin Lee, an inventor herein, and is described in an updated manuscript authored by B. J. Huang and available from the National Taiwan University, Taipei, Taiwan, prior to the invention described and claimed herein. The distillation apparatus includes separate heating and condensing chambers where the vapor is condensed in a plurality of vertical chambers.  
           [0004]    Thus, it remains desirable to provide further improved distillation apparatus and methods useful for water and other liquids. Such apparatus should preferably be compact, provide highly efficient distillation, i.e. minimum energy input per unit amount of distilled water produced, and be scalable from small units to large units. At least some of these objectives will be met by the inventions described hereinafter.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention provides improved liquid distillation apparatus and methods. The apparatus can take a variety of forms, but will preferably have a highly compact form which is easily manufacturable at a relatively low cost, as described in more detail below. Apparatus of the present invention permit distillation of water and other liquids to be performed on a highly efficient basis, typically with an energy consumption of 380 kcal/l of water distilled or less, preferably being 320 kcal/l of water distilled or less.  
           [0006]    In a first aspect, distillation apparatus according to the present invention comprise an enclosure defining a heating chamber and a condensing chamber. The enclosure is usually a single shell or housing having internal structure for defining the separate chambers, but could less desirably be formed from separate housings or structures joined together by pipes, ducts, and the like. The enclosure defines a vapor space above and common to the heating and condensing chambers and has a liquid feed inlet into the condensing chamber.  
           [0007]    A horizontal tube condenser, such as a helical or spiral tube condenser, is disposed in the condensing chamber and has a vapor inlet at an upper end thereof and a clean distal outlet at a lower end thereof. To enhance efficiency, a gas sparger, such as an aerator, is disposed within the condensing chamber to direct air or other gas bubbles upwardly through the condensing chamber. Such bubbles provide two distinct benefits. First, the bubbles scrub the heat transfer surfaces of the condenser to enhance heat transfer. Second, the bubbles absorb vapor directly from the liquid feed which is being heated as the vapor is condensed within the condenser. The vapor in the bubbles is carried upwardly into the vapor space where it combines with the steam vapor from the heating chamber, which will include an electrical or other heating element for boiling the water or other liquid therein.  
           [0008]    The combined vapors which collect in the vapor space pass downward through the horizontal tube condenser, where the vapors are condensed by heat exchange with the relatively cold liquid feed, typically cold water, coming into the condensing chamber. After condensing, the clean distillate may be collected from an outlet at the lower end of the condenser.  
           [0009]    The high efficiencies achieved by the apparatus and methods of the present invention are believed to be derived, at least in part, from the interaction between the upwardly flowing gas bubbles from the gas sparger and the horizontally arranged heat exchange surfaces of the horizontal tube condenser. In the preferred spiral and other close-packed configurations of the horizontal tub condensers, the bubbles will pass upwardly through multiple tortuous paths where the directional flow is constantly changing and intimate contact between the bubbles and the exposed surfaces of the tube condensers is maintained. The ability to close pack the horizontal tubes is also an advantage since it allows a highly compact distillation unit to be constructed.  
           [0010]    In preferred aspects of the apparatus, the enclosure is a cylinder having a vertical axis. The heating chamber comprises a tubular wall arranged coaxially with the vertical axis of the cylindrical enclosure, and the condensing chamber is disposed annularly about the tubular wall of the heating chamber. Thus, the horizontal tube condenser may preferably comprise a coiled tube arranged in the annular condensing chamber, more preferably comprising a plurality of coiled tubes arranged spirally within the condensing chamber and passing from the upper end to the lower end thereof. The plurality of condensing tubes may be joined at the bottom in a manifold or other collection chamber for collecting the clean distillate.  
           [0011]    In the preferred constructions, the heating chamber and the condensing chamber will both open at their upper ends into the common vapor space, and the heating chamber will open at its lower end to the condensing chamber to allow the flow of pre-heated liquid from the condensing chamber to the heating chamber. Most simply, the lower end of the condensing chamber will form an open plenum and at least one opening or passage will be provided in the tubular wall of the heating chamber to permit liquid flow. Usually, only a single passage or opening at the lower end will be provided to permit liquid flow between the condensing chamber and the heating chamber. In this way, flow of the inlet liquid must first pass through the condensing chamber before entering the heating chamber. The sparging air or gas may be provided in any conventional manner. Typically, a perforated tube, usually a perforated coiled tube, is disposed in a bottom space or plenum of the condensing chamber to pass the sparging bubbles upwardly therethrough.  
           [0012]    In a second aspect, methods of the present invention comprising feeding a liquid feed through a condensing chamber to a heating chamber. The liquid feed is boiled in the heating chamber to form a first vapor phase. Air or other gas is sparged upwardly through condensing chamber to provide a second vapor phase carried upwardly by the gas bubbles. The first vapor and second vapor phase combine and are condensed in a horizontal tube condenser in the condensing chamber. The gas bubbles enhance heat transfer between the inlet liquid feed and the condensing vapor to both enhance condensation and enhance pre-heating of the liquid feed. A clean distillate may then be collected from the bottom of the condenser.  
           [0013]    In a third aspect, the present invention provides an improved method for distilling water. The method is of the type where water is boiled to produce steam and the steam is condensed in a condenser by a heat exchange with feed water. The improvement of the present invention comprises sparging the condenser with air to enhance heat transfer and produce additional water vapor which is condensed with the steam. The improvement optionally further comprises condensing the vapor in a horizontal tube heat exchanger. The improved method produces water with a very high distillation efficiency.  
           [0014]    The energy consumption per liter of water produced by the methods and apparatus of the present invention is typically below 380 kcal/l, preferably below 320 kcal/l. Such improved methods usually utilize a horizontal tube condenser to provide the benefits discussed above. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a schematic illustration of a distillation apparatus constructed in accordance with the principles of the present invention showing exemplary liquid and gas flows.  
         [0016]    [0016]FIG. 2 illustrates a specific embodiment of apparatus constructed in accordance with the principles of the present invention with portions being broken away to illustrate internal components. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]    Referring to FIG. 1, apparatus  10  according to the present invention comprise an enclosure  12  having at least a condensing chamber  14  and a heating chamber  16  therein. A liquid feed inlet  18  is provided into the condensing chamber  14 , and an electrical resistance heating element  20 , or other heating element, is provided within the heating chamber  16 . The condensing chamber  14  and heating chamber  16  are divided by an internal partition  24  but are generally connected or open at their upper and lower ends to permit an internal flow or movement of liquids and vapors as will be described in more detail below. In particular, a vapor space  26  defined in the upper end of the enclosure  12  and an opening or passage  28  is provided in the lower region of the enclosure.  
         [0018]    A horizontal tube condenser  30  is disposed in the condensing chamber  14  and includes a plurality of generally horizontal heat exchange tubes which serve to condense vapor entering from an upper end  32  thereof and to pre-heat the liquid feed inlet entering through inlet  18 . The horizontal tube condenser  30  may take a variety of forms and is shown schematically as a generally serpentine structure having a number of reversing flow sections. More usually, however, the condenser will be arranged as a helical coil or spiral, as described in more detail with reference to FIG. 2 below.  
         [0019]    An important feature of the present invention is the inclusion of an air or gas sparger  38  at or near the bottom of the condensing chamber  14 . Sparging gas is introduced through the sparger  38 , and bubbles are generated which pass upwardly through the liquid feed in a direction generally countercurrent to the liquid flow, at least at the bottom of the chamber  14 . Since the liquid feed is heated by the vapor flow through the horizontal tube condenser  30 , vapor will be generated in the liquid feed which will generally coalesce with the gas bubbles. As the gas bubbles pass upwardly through upper liquid surface  40 , the vapor will be released into the vapor space  26 , together with vapor from the heating chamber as will be discussed in more detail below. The bubbles also act to enhance the heat transfer between the liquid feed coming in and the vapor passing downwardly through the horizontal tube condenser  30 , as discussed above.  
         [0020]    The liquid feed, after having been pre-heated in the condenser chamber  14 , flows to the heating chamber, generally as indicated by arrow  44 . The liquid entering the heating chamber  16  is heated by heating element  20  to cause boiling and vapor generation. The vapor generated in the heating chamber  16  also passes into the vapor space  26  where it combines with the vapor from the sparged gas in the condensing chamber. Thus, vapor from the heating chamber  16 , as generally indicated by arrow  46 , and vapor from the condensing chamber  14 , as generally indicated by arrow  48  pass into the upper end  32  of the horizontal tube condenser  30 , where the combined vapors then pass down the tube and are condensed by heat exchange with the liquid feed. The condensed vapor provides a “clean distillate” which may then be collected from outlet  50  of the condenser. An exemplary mass and energy balance is shown below.  
                                             EXEMPLARY MASS AND ENERGY BALANCE                                    Total volume in enclosure 12    6 l           Volume in Coils 30    3.5 l           Volume in Heating Chamber 16    1.5 l           Surface Area of Coils 30    0.9 m 2             Water Flow    4.6 l/hr.           Sparging Air Flow   360 l/hr.           Specific Power   318 kcal/l           Condenser Efficiency    0.2 m 2 hr/l                      
 
         [0021]    Referring now to FIG. 2, a presently preferred embodiment of the distillation apparatus of the present invention will be described. A cylindrical enclosure  100  is adapted to contain water or other liquid at a level  111 . Water or other liquid feed to be distilled  112  may be introduced into the enclosure  100  through an inlet  113 . The liquid level  111  in the enclosure may be maintained by conventional apparatus, such as level sensors and inlet feed controls (not shown). A drain  114  is provided for periodic removal of brackish condenser liquid which collects at the bottom of the enclosure  100  over time.  
         [0022]    A vapor space  116  is formed at an upper end of the interior of enclosure  100  generally over the liquid surface  111 . A plurality of spiral condensing tubes  117  (with five being illustrated) are disposed annularly at the outer periphery of the interior of the enclosure  100 . While the condensing tubes  117  will typically have a circular cross section, it is possible that the tubes could have other cross sections, such as oval, square, polygonal, or like. It is generally preferred, however, that the coils be arranged so that the tubes are generally horizontal in order to enhance contact with the sparged gas bubbles as generally described above. The spiral tubes  117  are, of course, not truly horizontal and by “horizontal” it is meant only that the tubes will have an angle less than 45° relative to horizontal, usually less than 25°, and more preferably less than 15°. An exemplary angle is in the range from 1.5° to 2.5°.  
         [0023]    Vapor from the vapor space  116  will enter into the condensing tubes  117  as indicated by arrows  126  and  130 . As the vapor passes downwardly through the condensing tubes  117 , heat exchange with the liquid inlet will condense the vapor producing the desired distillate. The distillate is preferably removed through a reservoir or manifold  118  which combines the outflow from each of the condensing tubes  117  and provides a common outlet  119  from which the distillate may be withdrawn.  
         [0024]    Gas sparging over the heat exchange tubes  117  preferably provided by gas injection tube  122  having holes  123  which produce bubbles  124 . Bubbles pass upwardly through the condensing tubes  117  in an annular condensing chamber  120 . For convenience, the bubbles  124  are shown in only a portion of the condensing space. In actual operation, the bubbles would be passing upwardly through the entire annular condensing chamber  120 . It will also be appreciated that a wide variety of other gas spargers could be used, including perforated manifolds, porous stones, and the like. It will also be appreciated that the sparging may be done with air (in which case it may be referred to as aeration), or with a wide variety of other gasses.  
         [0025]    The heating chamber  127  is defined by a tubular wall  131  surrounding a heating element  128 . Water from the condensing chamber  120  passes into the interior of the heating chamber  127  through an opening  133  at the bottom thereof. The heating element  128  produces liquid vapor bubbles  132  which pass upwardly through an upper opening  129  in the heating chamber into the vapor space  116 . The vapor then passes into the tops of the condensing tubes, as indicated by arrow  130  and described previously.  
         [0026]    It will be appreciated that construction and operation of the distillation apparatus of FIG. 2 is relatively straightforward. In particular, the liquid level in both the condensing chamber  120  and heating chamber  131  will be the same, thus requiring only a single liquid level control system. Heat into the apparatus is provided principally by the amount of energy delivered to the heating element  28 . Evaporation of water into the gas bubbles cools the incoming water, and a cooler condenser will condense more vapor. Thus, a colder feed water will be desirable. Humidity of the sparging gas is preferably maintained at a relatively low level, although this will often be difficult to control.  
         [0027]    While the above is a complete description of the preferred embodiments of the invention, various alternatives, modifications, and equivalents may be used. Therefore, the above description should not be taken as limiting the scope of the invention which is defined by the appended claims.