Abstract:
A new thermodynamic cycle is disclosed for converting energy from a low temperature stream, external source into useable energy using a working fluid comprising of a mixture of a low boiling component and a higher boiling component and including a higher pressure circuit and a lower pressure circuit. The cycle is designed to improve the efficiency of the energy extraction process by recirculating a portion of a liquid stream prior to further cooling. The new thermodynamic processes and systems for accomplishing these improved efficiencies are especially well-suited for streams from low-temperature geothermal sources.

Description:
RELATED APPLICATIONS 
     This application is a Continuation-in-Part of U.S. patent application Ser. No. 10/357,328 filed 3 Feb. 2003. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a system and method for the utilization of heat sources with moderate to low initial temperature, such as geothermal waste heat sources or other similar sources. 
     More particularly, the present invention relates to a system and method for the utilization of heat sources with moderate to low initial temperature, such as geothermal waste heat sources or other similar sources involving a multi-staged heating process and at least one separation step to enrich the working fluid which is eventually fully vaporized for energy extraction. 
     2. Description of the Related Art 
     In the prior art, U.S. Pat. No. 4,982,568, a working fluid is a mixture of at least two components with different boiling temperatures. The high pressure at which this working fluid vaporizes and the pressure of the spent working fluid (after expansion in a turbine) at which the working fluid condenses are chosen in such a way that at the initial temperature of condensation is higher than the initial temperature of boiling. Therefore, it is possible that the initial boiling of the working fluid is achieved by recuperation of heat released in the process of the condensation of the spent working fluid. But in a case where the initial temperature of the heat source used is moderate or low, the range of temperatures of the heat source is narrow, and therefore, the possible range of such recuperative boiling-condensation is significantly reduced and the efficiency of the system described in the prior art diminishes. 
     Thus, there is a need in the art for a new thermodynamic cycle and a system based thereon for enhanced energy utilization and conversion. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method for extracting thermal energy from low to moderate temperatures source streams including the step of transforming thermal energy from a fully vaporized boiling stream into a usable energy form to produce a lower pressure, spent stream. The fully vaporized boiling stream is formed by transferring thermal energy from an external heat source stream to a boiling stream to form the fully vaporized boiling stream and a cooled external heat source stream. The method also includes the steps of transferring thermal energy from the spent stream to a first portion of a heated higher pressure, basic working fluid stream to form a partially condensed spent stream and a first pre-heated, higher pressure, basic working fluid stream and transferring thermal energy from the cooled external heat source stream to a second portion of the heated higher pressure, basic working fluid stream to form a second pre-heated, higher pressure, basic working fluid stream and a spent external heat source stream. The method also includes the steps of combining the first and second pre-heated, higher pressure basic working fluid streams to form a combined pre-heated, higher pressure basic working fluid stream and separating the partially condensed spent stream into a separated vapor stream and a separated liquid stream. The method also includes the steps of pressurizing a first portion of the separated liquid stream to a pressure equal to a pressure of the combined pre-heated, higher pressure basic working fluid stream to form a pressurized liquid stream and combining the pressurized liquid stream with the combined pre-heated, higher pressure basic working fluid stream to form the boiling stream. The method also includes the steps of combining a second portion of the separated liquid stream with the separated vapor stream to from a lower pressure, basic working fluid stream and transferring thermal energy from the lower pressure, basic working fluid stream to a higher pressure, basic working fluid stream to form the heated, higher pressure, basic working fluid stream and a cooled, lower pressure, basic working fluid stream. The method also includes the steps of transferring thermal energy cooled, lower pressure, basic working fluid stream to an external coolant stream to from a spent coolant stream and a fully condensed, lower pressure, basic working fluid stream; and pressurizing the fully condensed, lower pressure, basic working fluid stream to the higher pressure, basic working fluid stream. 
     In a more efficient implementation of the present invention, the method provides the additional steps of separating the boiling stream into a vapor stream and a liquid stream; combining a portion of the liquid stream with the vapor stream and passing it through a small heater exchanger in contact with the external heat source stream to insure complete vaporization and superheating of the boiling stream. A second portion of the liquid stream is depressurized to a pressure equal to a pressure of the spent stream. 
     In a more yet more efficient implementation of the present invention, the method provides in addition to the additional steps described in paragraph 0006, the steps of separating the depressurized second portion of the liquid stream of paragraph 0006 into a vapor stream and a liquid stream, where the vapor stream is combined with the pressurized liquid stream having the parameters of the point  9  and repressurized before being combined with the stream having the parameters of the point  8 . While the liquid stream is depressurized to a pressure equal to a pressure of the spent stream having the parameters of the point  18 . 
     The present invention provides a systems as set forth in  FIGS. 1A-C  adapted to implement the methods of this invention. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The invention can be better understood with reference to the following detailed description together with the appended illustrative drawings in which like elements are numbered the same: 
         FIG. 1A  depicts a schematic of a preferred thermodynamic cycle of this invention; 
         FIG. 1B  depicts a schematic of another preferred thermodynamic cycle of this invention; 
         FIG. 1C  depicts a schematic of another preferred thermodynamic cycle of this invention; and 
         FIG. 1D  depicts a schematic of another preferred thermodynamic cycle of this invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     he inventors have found that a novel thermodynamical cycle (system and process) can be implemented using a working fluid including a mixture of at least two components. The preferred working fluid being a water-ammonia mixture, though other mixtures, such as mixtures of hydrocarbons and/or freons can be used with practically the same results. The systems and methods of this invention are more efficient for converting heat from relatively low temperature fluid such as geothermal source fluids into a useful form of energy. The systems use a multi-component basic working fluid to extract energy from one or more (at least one) geothermal source streams in one or more (at least one) heat exchangers or heat exchange zones. The heat exchanged basic working fluid then transfers its gained thermal energy to a turbine (or other system for extracting thermal energy from a vapor stream and converting the thermal energy into mechanical and/or electrical energy) and the turbine converts the gained thermal energy into mechanical energy and/or electrical energy. The systems also include pumps to increase the pressure of the streams at certain points in the systems and a heat exchangers which bring the basic working fluid in heat exchange relationships with a cool stream. One novel feature of the systems and methods of this invention, and one of the features that increases the efficiency of the systems, is the result of using a split two circuit design having a higher pressure circuit and a lower pressure circuit and where a stream comprising spent liquid separated for spent vapor from the higher pressure circuit is combined with a stream comprising the spent lower pressure stream at the pressure of the spent lower pressure stream prior to condensation to from the initial fully condensed liquid stream and where the combined stream is leaner than the initial fully condensed liquid stream. The present system is well suited for small and medium signed power units such as 3 to 5 Mega Watt power facilities. 
     The working fluid used in the systems of this inventions preferably is a multi-component fluid that comprises a lower boiling point component fluid—the low-boiling component—and a higher boiling point component—the high-boiling component. Preferred working fluids include an ammonia-water mixture, a mixture of two or more hydrocarbons, a mixture of two or more freon, a mixture of hydrocarbons and freon, or the like. In general, the fluid can comprise mixtures of any number of compounds with favorable thermodynamic characteristics and solubility. In a particularly preferred embodiment, the fluid comprises a mixture of water and ammonia. 
     It should be recognized by an ordinary artisan that at those point in the systems of this invention were a stream is split into two or more sub-streams, the valves that effect such stream splitting are well known in the art and can be manually adjustable or are dynamically adjustable so that the splitting achieves the desired improvement in efficiency. 
     Referring now to  FIG. 1A , a preferred embodiment of a system of this invention, generally  100 , is shown. The system  100  is described in terms of its operation using streams, conditions at points in the system, and equipment. A fully condensed working fluid stream at a temperature close to ambient having parameters as at a point  1 , enters a feed pump P 1 , where it is pumped to an elevated pressure, and obtains parameters as at a point  2 . The composition of the working fluid stream having the parameters of the point  2  will be hereafter referred to as a “basic composition” or “basic solution.” The working fluid stream having the parameters of the point  2 , then passes through a recuperative pre-heater or heat exchanger HE 2 , where it is heated in counter flow by a returning stream of the basic solution as described below, and obtains parameters as at a point  3 . The state of the basic working solution at the point  3  corresponds to a state of saturated, or slightly sub-cooled liquid. 
     Thereafter, the stream of basic solution having the parameters of the point  3  is divided into two sub-streams having parameters as at points  4  and  5 , respectively. The sub-stream having the parameters of the point  4 , then passes through a heat exchanger HE 4 , where it is heated and partially vaporized by a stream of a heat source fluid (e.g., geothermal brine stream) having parameters as at a point  42  as described below, and obtains parameters as at a point  6 . While, the stream of basic solution having the parameters of the point  5  passes though a heat exchanger HE 3 , where it is heated and partially vaporized by a condensing stream having parameters as at a point  20  in a condensing process  20 - 21  also described below and obtains parameters as at a point  7 . Thereafter, the sub-streams having parameters as at points  6  and  7  are combined, forming a combined stream having parameters as at a point  8 . The stream of basic solution having the parameters of the point  8  is then combined with a stream of a recirculating solution having parameters as at a point  29  as described below, and forms a stream of a boiling solution having parameters as at a point  10 . The stream having the parameters of the point  29  is in a state of sub-cooled liquid, and, therefore, as a result of the mixing of the streams having the parameters of the points  8  and  29 , a substantial absorption of vapor occurs, and the temperature rises substantially. Thus, a temperature of the stream having the parameters of the point  10  is usually significantly higher than that of the stream having the parameters of the point  8 . The composition of the stream having the parameters of the point  10  is referred to herein as a “boiling solution.” 
     The stream of boiling solution having the parameters of the point  10 , then passes through a heat exchanger HE 5 , where it is heated and vaporized by the stream of the heat source fluid having parameters as at a point  41 . The vaporized stream exiting the heat exchanger HE 5  now has parameters as at a point  11 . The stream having the parameters of the point  11  then enters into a gravity separator S 2 , where it is separated into a vapor stream having parameters as at a point  13  and a liquid stream having parameters as at a point  12 . The liquid stream having the parameters of the point  12  is then divided into two sub-streams having parameters as at points  14  and  15 , respectively. The sub-stream having the parameters of the point  14  usually represents a very small portion of the total liquid stream, and is combined with the vapor stream having the parameters of the point  13  as described below, forming a stream of working solution with parameters as at a point  16 . The stream of working solution having the parameters of the point  16 , then passes through a heat exchanger HE 6  (a small heat exchanger sometimes called a vapor drier to insure that the state of the stream exiting the heat exchanger is a superheated vapor), where it is further heated by the stream of the heat source fluid having parameters as at a point  40 , to form a fully vaporized and slightly superheated stream having parameters as at a point  17 . Thereafter, the stream of working solution having the parameters of the point  17  passes through a turbine T 1 , where it is expanded, producing useful power (conversion of thermal energy into mechanical and electrical energy) to form a stream having parameters as at a point  18 . 
     The recirculating liquid having the parameters of the point  15  as described above passes through a throttle valve TV 1 , where its pressure is reduce to an intermediate pressure to form a stream having parameters as at a point  19 . As a result of throttling, the parameters of the stream at the point  19  correspond to a state of a vapor-liquid mixture. The stream having the parameters of the point  19 , then enters into a gravity separator S 3 , where it is separated into a vapor stream having parameters as at the point  30 , and a liquid stream having parameters as at a point  31 . The liquid stream having the parameters of the point  31  passes through a second throttle valve TV 2 , where its pressure is further reduced to a pressure to form a stream having parameters as at a point  32 , where the pressure of the stream having the parameters of the point  32  is equal to a pressure of the stream having the parameters of the point  18  as described above. Thereafter, the stream having the parameter of the point  32  and the stream having the parameters of the point  18  are combined forming a stream of a condensing solution having the parameters of the point  20 . The stream having parameters of the point  20  passes through the heat exchanger HE 3 , in counter flow to the stream having the parameters of the point  5 , in a cooling process  5 - 7 . After passing through the heat exchanger HE 3 , the stream having the parameters of the point  20  is partially condensed, releasing heat for the heating process  20 - 21  described above and obtains parameters as at a point  21 . 
     The stream having the parameters of the point  21  then enters into a gravity separator S 1 , where it is separated into a vapor stream having parameters as at a point  22  and a liquid stream having parameters as at a point  23 . The liquid stream having the parameters of the point  23  is in turn divided into two sub-streams having parameters as at points  25  and  24 , respectively. The liquid sub-stream having the parameters of the point  25  is then combined with the vapor stream having the parameters of the point  22 , forming a stream of the basic solution having parameters as at a point  26 . 
     The liquid sub-stream having parameters of the point  24  enters a circulating pump P 2 , where its pressure is increased to a pressure equal to a pressure in gravity separator S 3 , i.e., equal to a pressure of the vapor stream having the parameters of the point  30  described above, and obtains parameters as at point  9 . The liquid stream having the parameters of the point  9  is in a state of a sub-cooled liquid. The liquid stream having the parameters of point  9  is then combined with the vapor stream having the parameters of the point  30  described above. A pressure of the streams having the parameters of the points  9  and  30  is chosen in such a way that the sub-cooled liquid having the parameters of the point  9  fully absorbs all of the vapor stream having the parameters of the point  30 , forming a liquid stream having parameters as at point  28 . The liquid stream having the parameters of the point  28  is in a state of saturated or sub-cooled liquid. Thereafter, the stream having the parameters of the point  28  enters into a circulating pump P 3 , where its pressure is increased to a pressure equal to a pressure of the stream having the parameters of the point  8 , and obtains parameters of the point  29  described above. The stream having the parameters of the point  29  is then combined with the stream of basic solution having the parameters of the point  8 , forming the stream of the boiling solution having the parameters of the point  10  described above. 
     The stream of basic solution having the parameters of the point  26  enters into the heat exchanger HE 2 , where it partially condenses releasing heat for a heating process  2 - 3  described above, and obtains parameters as at a point  27 . Thereafter the stream of basic solution having the parameters of the point  27  enters into a condenser HE 1 , where its is cooled and fully condensed by an air or water stream having parameters as at point  51  described below, and obtains parameters of the point  1 . 
     An air (or water) stream having parameters as at a point  50  enters an air fan AF (or compressor in the case of water) to produce an air stream having parameters as at a point  51 , which forces the air stream having the parameters of the point  51  into the heat exchanger HE 1 , where it cools the stream of basic working fluid in a cooling process  27 - 1 , and obtains parameters as at point  52 . 
     The stream of heat source fluid with the parameters of the point  40  passes through the heat exchanger HE 6 , where it provides heat from a heating process  6 - 17 , and obtains the parameters of the point  41 . The stream of heat source fluid having the parameters of the point  41  passes through the heat exchanger HE 5 , where it provides heat for a heating process  10 - 11 , and obtains the parameters of the point  42 . The stream of heat source fluid having the parameters of the point  42  enters into the heat exchanger HE 4 , where it provides heat for a heating process  4 - 6  and obtains parameters as at point  43 . 
     In the previous variants of the systems of this invention, the recirculating stream having parameters as at the point  29  was mixed with the stream of basic solution having parameters as at the point  8 . As a result of this mixing, a temperature of the combined stream having parameters as at the point  10  was substantially higher than a temperature of the streams having parameters as at the points  8  and  29 . 
     Referring now to  FIG. 1D , another embodiment of the system of this invention, generally  100 , is shown to includes an additional heat exchanger HE 7 , i.e., the heat exchanger HE 5  is split into two heat exchangers HE 5 ′ and HE 7  designed to reduce the temperature difference between the stream, having the parameters as at the point  10  and the streams having the parameters as at the points  8  and  29 . 
     In the new embodiment, the stream with parameters as at the point  8  is sent into the heat exchanger HE 7  where it is heated and further vaporized by a heat source stream, such as a geothermal fluid stream, having the parameters as at a point  44  producing the heat source stream having parameters as at the point  42  in a counter flow heat exchange process  44 - 42  and a stream having parameters as at a point  34 . Only then is the steam having the parameters as at the point  34  mixed with a recirculating stream having the parameters as at the point  29  (as described above) forming a combined stream having parameters as at the point  10 . A temperature at of the stream having the parameters as at the point  34  is chosen in such a way that the temperature of the stream having the parameters as at the point  10  is equal or very close to the temperature of the stream having the parameters as at the point  34 . As a result, the irreversibility of mixing a stream of basic solution and a stream of recirculating solution is drastically reduced. The resulting stream having the parameters as at the point  10  passes through the heat exchanger HE 5 ′ where it is heated and vaporized in a counter flow process  41 - 44  by the heat source stream such as a geothermal fluid stream having the parameters as at the point  41 . 
     This embodiment can also include a sub-streams having parameter as at points  14 , a s described above, which usually represents a very small portion of the total liquid stream, and is combined with the vapor stream having the parameters of the point  13  (not shown) as described below, to form the stream of working solution with parameters as at the point  16 . Additionally, this embodiment can also include the AF unit and associated streams as described above. 
     The advantages of the arrangement of streams shown in the present embodiment include at least the following: a temperature difference in the heat exchanger HE 7  (which is, in essence, the low temperature portion of the heat exchanger HE 5  in the previous variants), are substantially increased and therefore the size of the heat exchanger HE 7  is reduced, while the heat exchanger HE 5 ′ of this embodiment works in absolutely the same way as the high temperature portion of the heat exchanger HE 5  of the previous variants. The efficiency of the system of this embodiment is not affected at all. 
     This embodiment of the method of mixing a recirculating stream with a stream of basic solution can be applied to all variants described above. One experienced in the art can easily apply this method without further explanation. 
     An example of calculated parameters for the points described above are given in Table 1 for the embodiment shown in FIG.  1 A. 
     
       
         
               
             
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Parameter of Points in the Embodiment of  FIG. 1A   
               
             
          
           
               
                 Point 
                   
                 Temperature 
                 Pressure 
                 Enthalpy 
                 Enthropy 
                 Weight 
               
               
                 No. 
                 Concentration X 
                 T (° F.) 
                 P (psia) 
                 h (btu/lb) 
                 S(btu/lb° F.) 
                 (g/g1) 
               
               
                   
               
             
          
           
               
                 Parameters of Working Fluid Streams 
               
             
          
           
               
                 1 
                 0.975 
                 73.5 
                 133.4091 
                 37.8369 
                 0.09067 
                 1.0 
               
               
                 2 
                 0.975 
                 75.0186 
                 520.0 
                 40.1124 
                 0.09145 
                 1.0 
               
               
                 3 
                 0.975 
                 165.0 
                 508.2780 
                 147.9816 
                 0.27769 
                 1.0 
               
               
                 4 
                 0.975 
                 165.0 
                 508.2780 
                 147.9816 
                 0.27769 
                 0.6010 
               
               
                 5 
                 0.975 
                 165.0 
                 508.2780 
                 147.9816 
                 0.27769 
                 0.3990 
               
               
                 6 
                 0.975 
                 208.0 
                 498.5 
                 579.1307 
                 0.96196 
                 0.6010 
               
               
                 7 
                 0.975 
                 208.0 
                 498.5 
                 579.1307 
                 0.96196 
                 0.3990 
               
               
                 8 
                 0.975 
                 208.0 
                 498.5 
                 579.1307 
                 0.96196 
                 1.0 
               
               
                 9 
                 0.40874 
                 170.2394 
                 220.0 
                 45.8581 
                 0.21737 
                 0.3880 
               
               
                 10 
                 0.81773 
                 231.1316 
                 498.5 
                 433.8631 
                 0.76290 
                 1.40575 
               
               
                 11 
                 0.81773 
                 300.0 
                 490.0 
                 640.0316 
                 1.04815 
                 1.40757 
               
               
                 12 
                 0.35855 
                 300.0 
                 490.0 
                 200.2510 
                 0.43550 
                 0.1950 
               
               
                 13 
                 0.89168 
                 300.0 
                 490.0 
                 710.8612 
                 1.14682 
                 1.21075 
               
               
                 14 
                 0.35855 
                 300.0 
                 490.0 
                 200.2510 
                 0.43550 
                 0.1655 
               
               
                 15 
                 0.35855 
                 300.0 
                 490.0 
                 200.2510 
                 0.43550 
                 0.17845 
               
               
                 16 
                 0.8845 
                 300.0 
                 490.0 
                 703.9808 
                 1.13724 
                 1.2272 
               
               
                 17 
                 0.8845 
                 306.0 
                 488.5 
                 718.3184 
                 1.15637 
                 1.2273 
               
               
                 18 
                 0.8845 
                 213.3496 
                 139.5 
                 642.4511 
                 1.17954 
                 1.2273 
               
               
                 19 
                 0.35855 
                 249.1433 
                 220.0 
                 200.2510 
                 0.44140 
                 0.17845 
               
               
                 20 
                 0.81671 
                 214.6540 
                 139.5 
                 584.8515 
                 1.08437 
                 1.3880 
               
               
                 21 
                 0.81671 
                 170.0 
                 137.5 
                 460.9041 
                 0.89583 
                 1.3880 
               
               
                 22 
                 0.97746 
                 170.0 
                 137.5 
                 624.6175 
                 1.16325 
                 0.99567 
               
               
                 23 
                 0.40874 
                 170.0 
                 137.5 
                 45.4163 
                 0.21715 
                 0.39233 
               
               
                 24 
                 0.40874 
                 170.0 
                 137.5 
                 45.4163 
                 0.21715 
                 0.3880 
               
               
                 25 
                 0.40874 
                 170.0 
                 137.5 
                 45.4163 
                 0.21715 
                 0.00433 
               
               
                 26 
                 0.975 
                 170.0 
                 137.5 
                 622.1123 
                 1.15916 
                 1.0 
               
               
                 27 
                 0.975 
                 93.9659 
                 135.5 
                 514.2431 
                 0.97796 
                 1.0 
               
               
                 28 
                 0.43013 
                 195.9556 
                 220.0 
                 74.5165 
                 0.26271 
                 0.40575 
               
               
                 29 
                 0.43013 
                 196.6491 
                 498.5 
                 75.8407 
                 0.26312 
                 0.40575 
               
               
                 30 
                 0.89772 
                 249.1433 
                 220.0 
                 700.9614 
                 1.21784 
                 0.01775 
               
               
                 31 
                 0.2990 
                 249.1433 
                 220.0 
                 144.9514 
                 0.35565 
                 0.16070 
               
               
                 32 
                 0.2990 
                 233.8807 
                 139.5 
                 144.9514 
                 0.35718 
                 .016070 
               
             
          
           
               
                 Parameters of Geothermal Source Stream 
               
             
          
           
               
                 40 
                 brine 
                 315.0 
                   
                 283.0 
                   
                 3.90716 
               
               
                 41 
                 brine 
                 311.3304 
                   
                 279.3304 
                   
                 3.90716 
               
               
                 42 
                 brine 
                 237.4534 
                   
                 2305.1534 
                   
                 3.90716 
               
               
                 43 
                 brine 
                 170.0 
                   
                 138.0 
                   
                 3.90716 
               
             
          
           
               
                 Parameters of Air Cooling Stream 
               
             
          
           
               
                 50 
                 air 
                 51.7 
                 14.7 
                 122.3092 
                   
                 91.647 
               
               
                 51 
                 air 
                 51.9341 
                 14.72 
                 122.3653 
                   
                 91.647 
               
               
                 52 
                 air 
                 73.5463 
                 14.7 
                 127.5636 
                   
                 91.647 
               
               
                   
               
             
          
         
       
     
     In the system described above, the liquid produced in separator S 1  eventually passes through heat exchanger HE 5  and is partially vaporized. However, the composition of this liquid is only slightly richer than the composition of the liquid separated from the boiling solution in separator S 2 . In general, the richer the composition of the liquid added to the basic solution as compared to the composition of the liquid added to the spent working solution (point  18 ), the more efficient the system. In the proposed system, the bulk of liquid from separator S 2 , having parameter as point  15  is throttled to an intermediate pressure, and then divided into vapor and liquid in separator S 3 . As a result, the liquid stream having the parameters of the point  32  which is mixed with the spent working solution stream having the parameters of the point  18 , is leaner than the liquid separated from the boiling solution in separator S 2 . In addition, the recirculating liquid which is separated in separator S 1  is mixed with the vapor stream from separator S 3 , and, therefore, is enriched. As a result, the liquid stream having the parameters of the point  29 , which is added to the stream of basic solution having the parameters of the point  10 , is richer than the liquid stream produced from separator S 1 . 
     If the system is simplified, and the liquid stream from the separator S 2  having parameters of the point  15  is throttled in one step to a pressure equal to the pressure of the stream having the parameters of the point  18 , then the system requires less equipment, but its efficiency is slightly reduced. This simplified, but preferred variant of the system of this invention is shown in  FIG. 1B , where the separator S 3  and the throttle valve TV 2  have been remove along with the streams having the parameters of the points  30 ,  31  and  32 . The operation of such a variant of this system of  FIG. 1A  does not require further separate description because all of the remaining features are fully described in conjunction with the detailed description of system and process of FIG.  1 A. 
     If the quantity of liquid from separator S 1  is reduced to such a degree that the composition of the boiling solution stream having the parameters of the point  10  becomes equal to the composition of the working solution which passes through the turbine T 1 , then the separator S 2  can be eliminated along with the throttle valve TV 1 . Therefore, the heat exchanger HE 6  also becomes unnecessary, and is also eliminated because in this implementation there is no risk of liquid droplets being present in the boiling stream due to the absence of the separator S 2 . This even more simplified variant of the system of this invention is presented in FIG.  1 C. Its efficiency is yet again lower that the efficiency of the previous variant described in  FIG. 1B , but it is still more efficient than the system described in the prior art. 
     The choice in between the three variants of the system of this invention is dictated by economic conditions of operations. One experienced in the art can easily compare the cost of additional equipment, the value of additional power output given by increased efficiency and make an informed decision as to the exact variant chosen. 
     A summary of efficiency and performance of these three variants of this invention and the system described in the prior art are presented in Table 2. 
     
       
         
               
             
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Performance Summary 
               
             
          
           
               
                   
                 Systems of This Invention 
                   
               
             
          
           
               
                   
                 Variant 1 
                 Variant 2 
                 Variant 3 
                 Prior Art 
               
               
                   
                   
               
             
          
           
               
                 Heat Input (Btu) 
                 566.5385 
                 565.5725 
                 564.2810 
                 487.5263 
               
               
                 Specific Brine 
                 3.960716 
                 3.9005 
                 3.89159 
                 3.36225 
               
               
                 Flow (lb/lb) 
               
               
                 Heat Rejection (Btu) 
                 476.4062 
                 476.4062 
                 476.4062 
                 414.0260 
               
               
                 Turbine Enthalpy 
                 93.1119 
                 91.7562 
                 90.2988 
                 75.376 
               
               
                 Drop (Btu) 
               
               
                 Turbine Work (Btu) 
                 90.7841 
                 89.4623 
                 88.0413 
                 73.4828 
               
               
                 Pump Work (Btu) 
                 2.9842 
                 2.5812 
                 2.4240 
                 1.867 
               
               
                 Air Fan Work (Btu) 
                 5.1414 
                 5.1414 
                 5.1414 
                 3.5888 
               
               
                 Net Work (Btu) 
                 82.6785 
                 81.7397 
                 80.4759 
                 68.027 
               
               
                 Net Thermal 
                 14.595 
                 14.453 
                 14.262 
                 13.954 
               
               
                 Efficiency (%) 
               
               
                 Second Law 
                 54.23 
                 53.703 
                 52.995 
                 51.85 
               
               
                 efficiency (%) 
               
               
                   
               
             
          
         
       
     
     It is apparent from the simulated data in Table 2 that all three variants of this invention show improvements in net values: net work improvements of 21.54%, 20.16% and 18.30%, respectively; and net thermal and second law efficiency improvements of 4.59%, 3.58% and 2.21%, respectively. 
     All references cited herein are incorporated herein by reference. While this invention has been described fully and completely, it should be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. Although the invention has been disclosed with reference to its preferred embodiments, from reading this description those of skill in the art may appreciate changes and modification that may be made which do not depart from the scope and spirit of the invention as described above and claimed hereafter.