Abstract:
Methods for using a hydrophobic liquid, such as mineral oil, to compress steam include using a compressor to compress a mixture of steam and the hydrophobic liquid. One embodiment includes the steam to be compressed coming from a boiling aqueous solution in an evaporator. The steam compressed with a hydrophobic liquid is routed to a heat exchanger which thermally communicates with the evaporator to create more steam. The resulting mixture of condensed steam and hydrophobic liquid from the heat exchanger is routed to a water/hydrophobic liquid separator. The hydrophobic liquid is also recycled to the compressor from the water/hydrophobic liquid separator.

Description:
TECHNICAL FIELD 
     The present invention pertains generally to the compression of steam, and more particularly to the use of a hydrophobic liquid in the compression process. 
     BACKGROUND OF THE INVENTION 
     Ordinary water evaporators are notoriously expensive to operate since evaporating water requires large quantities of energy because of its high heat of vaporization. To evaporate large quantities of water a heat pump is often employed to efficiently recycle the heat of vaporization. One heat pump method is the mechanical vapor recompression process that when applied to the evaporation of water requires the direct compression of steam. The need for a rugged and simple steam compressor would greatly expand the use of mechanical vapor recompression for water evaporation. Other applications for a rugged and simple steam compressor might arise in any instance where the pressure of the steam available is too low for its intended purpose and must be upgraded by compression. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to methods for using a hydrophobic liquid to compress steam. The methods are most often used in the context of mechanical vapor recompression (MVR), which is a method for evaporating water. In MVR, a compressor is used to boost the pressure of steam from the evaporator so that it will condense at a higher temperature. This enables the latent heat in the steam to be returned to the evaporator thus generating more steam. In this way the same heat is continuously reused. Other uses for the present invention include the general upgrading of steam pressure for general heating purposes. 
     In the methods of the present invention, a compressor evacuates steam, created in a heat exchanger. In the compressor, such as a liquid piston pump, the steam is compressed to a higher pressure and discharged along with a hydrophobic liquid, such as mineral oil, into the other side of the same heat exchanger. There the steam is condensed to water (condensate) giving up its heat of vaporization. The condensate and hydrophobic liquid are drained from the heat exchanger and into a water/hydrophobic liquid separator where the hydrophobic liquid is taken off the top of the condensate and evacuated back into the compressor. 
     In a useful embodiment of the invention, mineral oil, a material with a very high vapor pressure and immiscibility with water and with low viscosity, is used as a liquid compressant allowing the liquid piston pump to operate without flashing liquid compressant or absorbing the compressed vapor. Also, the mixture of oil and steam is allowed to pass directly to the heat exchanger without attempting to first separate the steam from the oil. 
     Further, liquid piston pumps are inexpensive, rugged, and quiet compared to positive two-lobed blower that is normally used in this application. The liquid piston pump is inexpensive and rugged compared to the centrifugal compressor that is also used in this application. 
     In accordance with an embodiment of the invention, a method for using a hydrophobic liquid to compress steam includes:
         (a) providing steam;   (b) providing a hydrophobic liquid;   (c) providing a compressor having a steam input, a hydrophobic liquid input, and a compressed steam-hydrophobic liquid output;   (d); routing the steam to the steam input of the compressor;   (e) routing the hydrophobic liquid to the hydrophobic liquid input of the compressor; and,   (f) obtaining a mixture of compressed steam and hydrophobic liquid from the compressed steam-hydrophobic liquid output of the compressor.       

     In accordance with another embodiment of the invention, a method for using a hydrophobic liquid to remove water soluble material from an aqueous solution includes:
         (a) providing an aqueous solution containing water soluble material;   (b) providing a hydrophobic liquid;   (c) providing a system for removing the water soluble material from the aqueous solution, the system including:
           An evaporator for receiving the aqueous solution, the evaporator having an aqueous solution input, a steam output, and a concentrated aqueous solution output. A heat exchanger transfers heat to the evaporator, the heat exchanger having a compressed steam-hydrophobic liquid input and a water-hydrophobic liquid output. The system further includes a water/hydrophobic liquid separator having a water-hydrophobic liquid input, a hydrophobic liquid output, and a water condensate output. A compressor has a steam input, a hydrophobic liquid input, and a compressed steam-hydrophobic liquid output. The steam input of the compressor is connected to the steam output of the evaporator, the hydrophobic liquid input of the compressor is connected to the hydrophobic liquid output of the water/hydrophobic liquid separator, the compressed steam-hydrophobic liquid output of the compressor is connected to the compressed steam-hydrophobic liquid input of the heat exchanger, and the water-hydrophobic liquid input of the water/hydrophobic liquid separator is connected to the water-hydrophobic liquid output of the heat exchanger.   
           (d) delivering the aqueous solution to the aqueous solution input of the evaporator;   (e) the compressor compressing a mixture of steam from the evaporator and hydrophobic liquid, thereby increasing the temperature of the mixture;   (f) routing the mixture from the compressed steam-hydrophobic liquid output of the compressor to the compressed steam-hydrophobic liquid input of the heat exchanger and thence through heat exchanger, thereby evaporating the aqueous solution and causing steam to be routed from the steam output of the evaporator to the steam input of the compressor;   (g) routing water and hydrophobic liquid from the water-hydrophobic liquid output of the heat exchanger to the water-hydrophobic liquid input of the water/hydrophobic liquid separator; and,   (h) routing the hydrophobic liquid from the hydrophobic liquid output of the water/hydrophobic liquid separator to the hydrophobic liquid input of the compressor.       

     Other aspects of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flow diagram of a first system for using a hydrophobic liquid to compress steam; 
         FIG. 2  is a flow diagram showing additional features of the first system; 
         FIG. 3  is a flow diagram of a second system for using a hydrophobic liquid to compress steam; and, 
         FIG. 4  is flow diagram of a third system for using a hydrophobic liquid to compress steam which combines the features of the first and second systems. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring initially to  FIG. 1 , there is illustrated a flow diagram of a first system for using a hydrophobic liquid to compress steam, generally designated as  20 . In the shown embodiment, first system  20  is utilized for removing a water soluble material from an aqueous solution, and includes an evaporator  22  for receiving the aqueous solution  24 , evaporator  22  having an aqueous solution input  26 , a steam output  28 , and a concentrated aqueous solution output  30 . A heat exchanger  32  transfers heat to evaporator  22 , the heat exchanger  32  having a compressed steam-hydrophobic liquid input  34  and a water/hydrophobic liquid output  36 . System  20  further includes a water/hydrophobic liquid separator  38  having a water-hydrophobic liquid input  40 , a hydrophobic liquid output  42 , and a water condensate output  44 . A compressor  46  has a steam input  48 , a hydrophobic liquid input  50 , and a compressed steam-hydrophobic liquid output  52 . Steam input  48  of compressor  46  is connected to steam output  28  of evaporator  22 , hydrophobic liquid input  50 , of compressor  46  is connected to hydrophobic liquid output  42  of water/hydrophobic liquid separator  38 , compressed steam-hydrophobic liquid output  52  of compressor  46  connected to compressed steam-hydrophobic liquid input  34  of heat exchanger  32 , and water-hydrophobic liquid input  40  of water/hydrophobic liquid separator  38  is connected to water-hydrophobic liquid output  36  of heat exchanger  32 . 
     As used herein a hyphen (“-”) means “and”, such as in compressed steam-hydrophobic liquid input  34 . This means that both compressed steam and hydrophobic liquid are present at input  34 . Conversely, a slash (“/”) means “from”, such as in water/hydrophobic liquid separator  38 . This means that water is separated from hydrophobic liquid in separator  38 . 
     In a preferred embodiment of the invention, a hydrophobic liquid having a low viscosity and a low vapor pressure is utilized in system  20 . A mineral oil such as XCELTHERM 600 manufactured by Radeo Industries, P.O. Box 305, La Fox, Ill. 60147 has been found useful. 
     Also in a preferred embodiment of the invention, compressor  46  comprises a liquid piston pump such as is available from Nash Engineering Company, 9 Trefoil Drive, Trumbull, Conn. 06611-1330. Further regarding compressor  46 , it is noted that in the shown embodiment, steam input  48  and hydrophobic liquid input  50  comprise two separate physical inputs to compressor  46 . It is also noted however that the steam  48  and hydrophobic liquid  50  inputs can be combined into one common compressor input with somewhat lessened results. 
     Referring now to  FIG. 2 , there is illustrated a flow diagram showing additional features of the first system  20 . A mist eliminator  54  is disposed between evaporator  22  and compressor  46 . Mist eliminator  54  serves as a filter which captures water soluble material contained within entrained water droplets with the steam. Mist eliminator  54  can be located at any convenient location between evaporator  22  and compressor  46 . Also, an hydrophobic liquid pump  56  is disposed between water/hydrophobic liquid separator  38  and compressor  46 . Hydrophobic liquid pump  56  pumps hydrophobic liquid from hydrophobic liquid output  42  of water/hydrophobic liquid separator  38  to the hydrophobic liquid input  50  of compressor  46 . In the embodiment shown in  FIG. 1 , a vacuum created by compressor  46  pulls hydrophobic liquid from water/hydrophobic liquid separator  38  to compressor  46 . However, in certain applications pump  56  has been found useful. It may be appreciated that mist eliminator  54  and hydrophobic liquid pump  56  may be added individually or in combination to other embodiments of the present invention subsequently discussed herein. 
     In view of the aforementioned system  20 , a method for using a hydrophobic liquid to compress steam includes:
         (a) providing steam;   (b) providing a hydrophobic liquid;   (c) providing a compressor  46  having a steam input  48 , a hydrophobic liquid input  50 , and a compressed steam-hydrophobic liquid output  52 ;   (d) routing the steam to the steam input  48  of compressor  46 ;   (e) routing the hydrophobic liquid to hydrophobic liquid input  50  of compressor  46 ; and,   (e) obtaining a mixture of compressed steam and hydrophobic liquid from the compressed steam-hydrophobic liquid output  52  of compressor  46 .       

     During the compression process, it is the steam and not the hydrophobic liquid which is compressed by compressor  46 . 
     Further in view of system  20 , a method for using a hydrophobic liquid to remove water soluble material from an aqueous solution includes:
         (a) providing an aqueous solution containing water soluble material;   (b) providing a hydrophobic liquid;   (c) providing system  20  (described above) for removing the water soluble material from the aqueous solution;   (d) delivering the aqueous solution  24  to the aqueous solution input  26  of evaporator  22 ;   (e) compressor  46  compressing a mixture of steam from evaporator  22  and the hydrophobic liquid, thereby increasing the temperature of the mixture;   (f) routing the mixture from the compressed steam-hydrophobic liquid output  52  of compressor  46  to the compressed steam-hydrophobic liquid input  34  of heat exchanger  32  and thence through heat exchanger  32 , thereby evaporating the aqueous solution and causing steam to be routed from the steam output  28  of evaporator  22  to steam input  48  of compressor  46 ;   (g) routing water and hydrophobic liquid from the water-hydrophobic liquid output  36  of heat exchanger  32  to the water-hydrophobic liquid input  40  of the water/hydrophobic liquid separator  38 ; and,   (h) routing the hydrophobic liquid from the hydrophobic liquid output  42  of the water/hydrophobic liquid separator  38  to the hydrophobic liquid input  50  of compressor  46 .       

     The, method further including:
         removing a concentrated aqueous solution containing water soluble material from the concentrated aqueous solution output  30  of evaporator  22 . The concentrated solution can be disposed of in conventional ways or, as appropriate, recycled.       

     The method further including:
         removing water condensate from the water condensate output  44  of water/hydrophobic liquid separator  38 . The condensate typically comprises water of a quality which can be recycled or routed to a water drain.       

     The method further including:
         in step (c), a mist eliminator  54  disposed between evaporator  22  and compressor  46 . Mist eliminator  54  capturing water soluble material contained within entrained water droplets with the steam.       

     The method further including:
         in step (c), an hydrophobic liquid pump  56  disposed between water/hydrophobic liquid separator  38  and compressor  46 ; and,   hydrophobic liquid pump  56  pumping hydrophobic liquid from hydrophobic liquid output  42  of water/hydrophobic liquid separator  38  to hydrophobic liquid input  50  of compressor  46 .       

     Referring now to  FIG. 3 , there is illustrated a flow diagram of a second system for using a hydrophobic liquid to compress steam, generally designated as  120 . In the shown embodiment, second system  120  is utilized for removing a water soluble material from an aqueous solution, and includes an evaporator  122  for receiving the aqueous solution  124 , evaporator  122  having an aqueous solution input  126 , a steam output  128 , and a concentrated aqueous solution output  130 . A heat exchanger  132  transfers heat to evaporator  122 , the heat exchanger  132  having a compressed steam input  134  and a water output  136 . A steam/hydrophobic liquid separator  137  has a compressed steam-hydrophobic liquid input  139 , a hydrophobic liquid output  141 , and a compressed steam output  143 . System  120  further includes a compressor  146  having a steam input  148 , a hydrophobic liquid input  150 , and a compressed steam-hydrophobic liquid output  152 . Steam input  148  of compressor  146  is connected to steam output  128  of evaporator  122 , hydrophobic liquid input  150  of compressor  146  is connected to hydrophobic liquid output  141  of steam/hydrophobic liquid separator  137 , compressed steam-hydrophobic liquid output  152  of compressor  146  connected to compressed steam-hydrophobic liquid input  139 , of steam/hydrophobic liquid separator  137 , and compressed steam output  143  of steam/hydrophobic liquid separator  137  is connected to compressed steam input  134  of heat exchanger  132 . 
     In view of system  120 , a method for using a hydrophobic liquid to remove water soluble material from an aqueous solution includes:
         (a) providing an aqueous solution containing water soluble material;   (b) providing a hydrophobic liquid;   (c) providing system  120  (described above) for removing the water soluble material from the aqueous solution;   (d) delivering the aqueous solution  124  to the aqueous solution input  126  of evaporator  122 ;   (e) compressor  146  compressing a mixture of steam from evaporator  122  and the hydrophobic liquid, thereby increasing the temperature of the mixture;   (f) routing the mixture from the compressed steam-hydrophobic liquid output  152  of compressor  146  to the compressed steam-hydrophobic liquid input  139  of the steam/hydrophobic liquid separator  137 ;   (g) routing compressed steam from compressed steam output  143  of the steam/hydrophobic separator  137  to the compressed steam input  134  of heat exchanger  132  and thence through heat exchanger  132 , thereby evaporating the aqueous solution and causing steam to be routed from the steam output  128  of evaporator  122  to the steam input  148  of compressor  146 ; and,   (h) routing the hydrophobic liquid from the hydrophobic liquid output  141  of steam/hydrophobic liquid separator  137  to the hydrophobic liquid input  150  of compressor  146 .       

     The method further including:
         removing a concentrated aqueous solution containing water soluble material from the concentrated aqueous solution output  130  of evaporator  122 .       

     The method further including:
         removing water condensate from the water output  136  of heat exchanger  132 .       

       FIG. 4  is flow diagram of a third system for using a hydrophobic liquid to compress steam, generally designated as  220 , which combines the features of the first  20  and second  120  systems. In the shown embodiment, third system  220  is utilized for removing a water soluble material from an aqueous solution, and includes an evaporator  222  for receiving the aqueous solution  224 , evaporator  222  having an aqueous solution input  226 , a steam output  228 , and a concentrated aqueous solution output  230 . A heat exchanger  232  transfers heat to evaporator  222 , heat exchanger  232  having a compressed steam input  234  and a partially pure water output  236 . A steam/hydrophobic liquid separator  237  has a compressed steam-hydrophobic liquid input  239 , a hydrophobic liquid output  241 , and a compressed steam output  243 . System  220  further includes a compressor  246  having a steam input  248 , a hydrophobic liquid input  250 , and a compressed steam-hydrophobic liquid output  252 . Steam input  248  of compressor  246  is connected to steam output  228  of evaporator  222 , hydrophobic liquid input  250  of compressor  246  is connected to hydrophobic liquid output  241  of steam/hydrophobic liquid separator  237 , compressed steam-hydrophobic liquid output  252  of compressor  246  is connected to compressed steam-hydrophobic liquid input  239  of steam/hydrophobic liquid separator  237 , compressed steam output  243  of steam/hydrophobic liquid separator  237  is connected to compressed steam input  234  of heat exchanger  232 . System  220  further includes a water/hydrophobic liquid separator  238  having an partially pure water input  240 , a hydrophobic liquid output  242 , and a water condensate output  244 . Partially pure water input  240  of water/hydrophobic liquid separator  238  is connected to the partially pure water output  236  of heat exchanger  232 , and the hydrophobic liquid output  242  of water/hydrophobic liquid separator  238  is connected to the hydrophobic liquid input  250  of compressor  246 . 
     In view of system  220 , a method for using a hydrophobic liquid to remove water soluble material from an aqueous solution includes:
         (a) providing an aqueous solution containing water soluble material;   (b) providing a hydrophobic liquid;   (c) providing system  220  (described above) for removing the water soluble material from the aqueous solution;   (d) delivering an aqueous solution  224  to the aqueous solution input  226  of evaporator  222 ;   (e) compressor  246  compressing a mixture of steam from evaporator  222  and the hydrophobic liquid, thereby increasing the temperature of the mixture;   (f) routing the mixture from the compressed steam-hydrophobic liquid output  252  of compressor  246  to the compressed steam-hydrophobic liquid input  239  of steam/hydrophobic liquid separator  237 ;   (g) routing compressed steam from said compressed steam output  243  of the steam/hydrophobic separator  237  to the compressed steam input  234  of heat exchanger  232  and thence through heat exchanger  232 , thereby evaporating the aqueous solution and causing steam to be routed from the steam output  228  of evaporator  222  to the steam input  248  of compressor  246 ;   (h) routing hydrophobic liquid from the hydrophobic liquid output  241  of steam/hydrophobic liquid separator  237  to the hydrophobic liquid input  250  of compressor  246 .       

     (i) routing the partially pure water from the partially pure water output  236  of heat exchanger  232  to the partially pure water input  240  of water/hydrophobic liquid separator  238 ; and,
         (j) routing hydrophobic liquid from the hydrophobic liquid output  242  of water/hydrophobic liquid separator  238  to the hydrophobic liquid input  250  of compressor  246 .       

     The method further including:
         removing a concentrated aqueous solution containing water soluble material from the concentrated aqueous solution output  230  of evaporator  246 .       

     The method further including:
         removing water condensate from the water condensate output  244  of water/hydrophobic liquid separator  238 .       

     It is noted that in system  220 , both the steam/hydrophobic liquid separator  237  and the water/hydrophobic liquid separator  238  are utilized to remove the hydrophobic liquid from the final water condensate. After the first separation, the water emanating from heat exchanger  232  is “partially pure”. The water/hydrophobic liquid separator  238  then serves to further purify the condensate water. 
     The preferred embodiments of the invention described herein are exemplary and numerous modifications, variations, and rearrangements can be readily envisioned to achieve an equivalent result, all of which are intended to be embraced within the scope of the appended claims.