Abstract:
Power generation systems and methods are disclosed for use with medium to high temperature heat source stream, gaseous or liquid, where the systems and methods permit efficient energy extraction for medium and small scale power plants.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to power systems and methods designed for the utilization of heat sources with high or medium initial temperatures (from 1076° F. to 400° F.) in medium and small scale power plants. 
         [0003]    More particularly, the present invention relates to power systems and methods designed for the utilization of heat sources with high or medium initial temperatures (from 1076° F. to 400° F.) in medium and small scale power plants, where the systems include complete at least one turbine, six heat exchange apparatus, a heat recovery vapor generator, at least three working fluid pumps, a separator and optionally an admission valve along with a plurality of mixing and dividing valves. The method includes converting a portion of heat in at least one vaporized, superheated working fluid stream, using a spent stream to heat a rich or basic working fluid stream and lean working fluid stream, combining the cooled superheated stream with a portion of the lean stream and using the combined stream to preheat the rich working fluid stream and the lean working fluid stream and separating a resulting partially condensed combined stream into a vapor stream and a lean working fluid liquid stream, forming the basic working fluid stream from the vapor stream and a portion of the lean working fluid liquid stream, where the cycle is closed and an external coolant stream is used to condense the basic working fluid stream and an external heat source stream is used to fully vaporize and superheat the at least one working fluid stream prior to the converting step. 
         [0004]    2. Description of the Related Art 
         [0005]    In U.S. Pat. Nos. 5,095,708, and 5,572,871, power systems were presented that were designed to serve as bottoming cycles for combined cycle systems. These systems both had a specific feature which was the key to their high efficiency; both systems used intercooling of the working fluid in between turbine stages. Because the heat released during intercooling was recuperated, it was then used as an additional source of heating for the process of vaporization. This resulted in a drastic increase in the thermodynamical reversibility and correspondingly in higher efficiency of the power cycle. 
         [0006]    However, in the prior art, this process of intercooling was performed in a special heat exchanger, a so-called “intercooler.” Such an intercooler requires that the streams of working fluid in both the tubes and the shell of the intercooler be at high pressure. Moreover, the intercooled stream in the prior art is in the form of a vapor, and therefore the heat transfer coefficient from the vapor to the intercooler tubes is low. As a result, such an intercooler must be a very large and very expensive high pressure heat exchanger. This in turn has a very negative impact on the economics of the entire system. 
         [0007]    Thus, there is a need in the art for a system designed to utilize high to medium temperatures sources in small to medium power plants to convert a portion of the thermal energy from these heat sources into electrical power. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention provides a system for extracting electrical power from high to medium temperature heat source streams, where the system includes at least on energy conversion apparatus or turbine (T 1 ), six heat exchange apparatuses, at least three pumps, a heat recovery vapor generator (HRVG), and a separator (S 1 ), where at least five different compositional multicomponent streams are circulated through a closed cycle to permit cost effective power extraction from the high to medium temperature heat source streams in medium to small scale power plants, where energy can be extracted from a single combinational stream or from a combinational stream and a lean stream both fully vaporized and superheated by the HRVG after being heated by five of the heat exchanger apparatuses while the sixth heat exchange apparatus is a condenser, which fully condenses a starting basic working fluid stream. 
         [0009]    The present invention provides a method for extracting electrical energy from a medium to high temperature heat source stream (gas or liquid), the where method includes converting a portion of heat in at least one vaporized, superheated working fluid stream in a turbine to form a spent stream. The method also includes using the spent stream to heat a rich or basic working fluid stream and a first lean working fluid substream, combining the cooled spent stream with a second lean working fluid substream and using the combined stream to preheat the rich working fluid stream and the first lean working fluid substream. The method also includes separating a resulting partially condensed combined stream into a vapor stream and a lean working fluid liquid stream. The method also includes dividing the lean working fluid liquid stream into the first lean working fluid substream, the second lean working fluid substream and a third lean working fluid substream. The method also includes forming the basic working fluid stream from the vapor stream and the third the lean working fluid liquid substream, where the cycle is closed and an external coolant stream is used to condense the basic working fluid stream and an external heat source stream is used to supply the heat for the cycle and to fully vaporize and superheat the at least one working fluid stream prior to the converting step. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    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: 
           [0011]      FIG. 1A  depicts an embodiment of a system of this invention including dual superheated streams, a lean stream and a rich stream and a dual turbine subsystem, one turbine for a lean stream and one turbine for a rich stream. 
           [0012]      FIG. 1B  depicts the embodiment of a system of  FIG. 1A , where the heat exchangers HE 5  and HE 6  have been combined into a single, dual flow heat exchanger DHE 1 . 
           [0013]      FIG. 1C  depicts the embodiment of a system of  FIG. 1A , where the heat exchangers HE 3  and HE 4  have been combined into a single, dual flow heat exchanger DHE 2 . 
           [0014]      FIG. 1D  depicts the embodiment of a system of  FIG. 1A , where the heat exchangers HE 5  and HE 6  have been combined into a single, dual flow heat exchanger DHE 1  and the heat exchangers HE 3  and HE 4  have been combined into a single, dual flow heat exchanger DHE 2 . 
           [0015]      FIG. 2  depicts an embodiment of a system of this invention including dual superheated streams, a lean stream and a rich stream and a single turbine subsystem. 
           [0016]      FIG. 3  depicts an embodiment of a system of this invention including a single superheated stream and a single turbine subsystem. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    These system are designed to operate with a multi-component working fluid including at least two components at least one lower boiling component and at least on higher boiling component. 
         [0018]    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. In certain embodiments, the 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 certain embodiments, the fluid comprises a mixture of water and ammonia. 
         [0019]    The present invention broadly relates to a system for high or medium initial temperature heat sources in medium and small scale power plants comprising a turbine subsystem including at least one turbine adapted to convert a portion of thermal energy contained in at least one vaporized, superheated stream to form a spent stream. The system also includes a heat recovery vapor generator adapted to fully vaporize and superheat at least one heated stream to form the at least one vaporized, superheated stream. The system also includes a first heat exchange apparatus adapted to heat a partially heated rich working fluid stream and a preheated first lean working fluid substream with heat from the spent stream to form a heated rich working fluid stream and a heated lean working fluid stream and a cooled spent stream. The system also includes a first combining valve adapted to combine the cooled spent stream with a higher pressure second lean working fluid stream to form a leaner spent stream. The system also includes a second heat exchange apparatus adapted to heat a preheated rich working fluid stream and a high pressure first lean working fluid substream with heat from the leaner spent stream to form the partially heated rich working fluid stream and the preheated first lean working fluid substream and a partially condensed leaner spent stream. The system also includes a separator adapted to separate the partially condensed leaner spent stream into a vapor stream and a lean liquid working fluid stream. The system also includes a first dividing valve adapted to divide the lean liquid working fluid stream into a first lean liquid working fluid substream, a second lean liquid working fluid substream, and a third lean liquid working fluid substream. The system also includes a first pump (P 2 ) adapted to raise a pressure of the first lean liquid working fluid substream to a high pressure to form the high pressure first lean working fluid stream. The system also includes a second pump (P 3 ) adapted to raise a pressure of the second lean liquid working fluid substream to a higher pressure to form the higher pressure second lean working fluid stream. The system also includes a second combining valve adapted to combine the vapor stream and the third lean liquid working fluid substream to form a basic working fluid stream. The system also includes a third heat exchange apparatus to heat an intermediate pressure basic working fluid stream to form the preheated basic working fluid stream and a cooled basic working fluid stream. The system also includes a fourth heat exchange apparatus adapted to condense the cooled basic working fluid stream with an external coolant stream to form a fully condensed basic working fluid stream. The system also includes a third pump (P 1 ) adapted to raise a pressure of the fully condensed basic working fluid stream to form the intermediate pressure basic working fluid stream. 
         [0020]    The present invention broadly relates to a method for high or medium initial temperature heat sources in medium and small scale power plants comprising the step of converting a portion of heat from at least one vaporized, superheated stream to electrical power to form a spent stream. The method also includes the step of fully vaporizing and superheating at least one heated stream in a heat recovery vapor generator to form the at least one vaporized, superheated stream. The method also includes the step of heating, in a first heat exchange apparatus, a partially heated rich working fluid stream and a preheated first lean working fluid substream with heat from the spent stream to form a heated rich working fluid stream and a heated lean working fluid stream and a cooled spent stream. The method also includes the step of combining, in a first combining valve, the cooled spent stream with a higher pressure second lean working fluid stream to form a leaner spent stream. The method also includes the step of heating, in a second heat exchange apparatus, a preheated rich working fluid stream and a high pressure first lean working fluid substream with heat from the leaner spent stream to form the partially heated rich working fluid stream and the preheated first lean working fluid substream and a partially condensed leaner spent stream. The method also includes the step of separating, in a separator, the partially condensed leaner spent stream into a vapor stream and a lean liquid working fluid stream. The method also includes the step of dividing, in a first dividing valve, the lean liquid working fluid stream into a first lean liquid working fluid substream, a second lean liquid working fluid substream, and a third lean liquid working fluid substream. The method also includes the step of raising, in a first pump (P 2 ), a pressure of the first lean liquid working fluid substream to a high pressure to form the high pressure first lean working fluid stream. The method also includes the step of raising, in a second pump (P 3 ), a pressure of the second lean liquid working fluid substream to a higher pressure to form the higher pressure second lean working fluid stream. The method also includes the step of combining, in a second combining valve, the vapor stream and the third lean liquid working fluid substream to form a basic working fluid stream. The method also includes the step of heating, in a third heat exchange apparatus, an intermediate pressure basic working fluid stream to form the preheated basic working fluid stream and a cooled basic working fluid stream. The method also includes the step of condensing, in a fourth heat exchange apparatus, the cooled basic working fluid stream with an external coolant stream to form a fully condensed basic working fluid stream. The method also includes the step of raising, in a third pump (P 1 ), a pressure of the fully condensed basic working fluid stream to form the intermediate pressure basic working fluid stream. 
         [0021]    In all of the embodiments, mixing or combining valves are used to combine stream as each point where two or more streams are combined and dividing valves are used to divide a stream at each point where a stream is divided into two or more substreams. Such valves are well known in the art. 
       FIRST EMBODIMENT 
       [0022]    Referring to  FIG. 1A , a first embodiment of the present system and method designated CSQ- 21  is described. A fully condensed basic working fluid stream S 10  having parameters as at a point  1  is pumped by a first or feed pump P 1  to an elevated intermediate pressure to form an intermediate pressure, basic working fluid stream S 12  having parameters as at a point  2 , where the basic working fluid stream comprises a fluid having at least one higher boiling component and at least one lower boiling component. The stream S 12  having the parameters as at the point  2  then passes through a second heat exchanger or preheater HE 2  in counterflow with a returning basic working fluid stream S 14  having parameters as at a point  26  in a second heat exchange process  26 - 27  or  2 - 3  as described below to form a heated basic working fluid stream S 16  having parameters as at a point  3  and a cooled returning basic working fluid stream S 18  having parameters as at a point  27 . The stream S 16  having the parameters as at the point  3  corresponds to a state of saturated or slightly subcooled liquid. 
         [0023]    The stream S 16  having the parameters as at the point  3  then passes through a third heat exchanger or a boiled-condenser HE 3 , where it is heated and vaporized in counterflow with a second condensing lean combined working fluid substream S 20  having parameters as at a point  11  in a third heat exchange process  11 - 14  or  3 - 8  as described below to form a heated, vaporized basic working fluid stream S 22  having parameters as at a point  8 , which corresponds to a state of wet vapor and a cooled second condensing combined working fluid substream S 24  having parameters as at a point  14 . 
         [0024]    Meanwhile, a lean saturated liquid stream S 26  having parameters as at a point  24  (see below) enters into a second pump P 2 , where it is pumped to a high pressure forming a high pressure lean liquid stream S 28  having parameters as at a point  9 . The stream S 28  having the parameters as at the point  9  is then sent into a fourth heat exchanger HE 4 , where it is heated in counterflow with a first condensing lean combined working fluid substream S 30  having parameters as at a point  12  in a fourth heat exchange process  12 - 13  or  9 - 10 , (see below) to form a preheated high pressure lean liquid stream S 32  having parameters as at a point  10  and a cooled first condensing combined working fluid substream S 34  having parameters as at a point  13 . 
         [0025]    The stream S 22  with the parameters as at the point  8  passes through a fifth heat exchanger HE 5 , where it is heated in counterflow by a first spent vapor substream S 36  having parameters as at a point  30  in a fifth heat exchange process  30 - 31  or  8 - 4  to form a vaporized basic working fluid stream S 38  having parameters as at a point  4  and a first de-superheated vapor substream S 40  having parameters as at a point  31 . 
         [0026]    The preheated high pressure lean liquid stream S 32  having the parameters as at the point  10  is meanwhile sent into a sixth heat exchanger HE 6 , where it is heated in counterflow with a second spent vapor substream S 42  having parameters as at a point  32  in a sixth heat exchange process  32 - 33  or  10 - 5  to form a second de-superheated vapor substream S 44  having parameter as at a point  33  and a heated high pressure lean liquid stream S 46  parameters as at a point  5 , corresponding to a state of saturated or slightly subcooled liquid. 
         [0027]    Thereafter, the vaporized basic working fluid stream S 38  having parameters as at a point  4  and the heated high pressure lean liquid stream S 46  parameters as at a point  5  pass in parallel through a heat recovery vapor generator HRVG, where they are heated in counterflow by a heat source stream S 48  having parameters as at a point  500  (e.g., flue gas stream, hot liquid stream, other heat source or mixtures of such streams). There are a number of HVRG heat exchange processes going on simultaneously in the HRVG. The overall heat exchange processes are  500 - 502  or  5 - 36  and  4 - 15  and the stepwise heat exchange processes are  500 - 535  or  35 - 36  and  34 - 15  and  535 - 502  or  5 - 35  and  4 - 34  (see below) to form a spent heat source stream S 50  having parameters as at a point  502 . The vaporized working fluid stream S 38  having parameters as at a point  4  and the heated high pressure lean liquid stream S 46  parameters as at a point  5  are thus fully vaporized and superheated in the HRVG to form a fully vaporized, superheated basic working fluid stream S 52  having parameters as at a point  15  and fully vaporized, superheated high pressure lean stream S 54  parameters as at a point  36 , respectively. 
         [0028]    The fully vaporized, superheated high pressure lean stream S 54  having the parameters as at the point  36  is then sent into an admission valve TV, where its pressure is reduced to form a reduced pressure fully vaporized, superheated high pressure lean stream S 56  having parameters as at a point  37 . 
         [0029]    Thereafter, the reduced pressure fully vaporized, superheated high pressure lean stream S 56  having the parameters as at the point  37  is sent into a higher pressure turbine T 1 , where it expands and produces electric power to form a spent lean stream S 58  having parameters as at a point  38 . The spent lean stream S 58  having the parameters as at the point  38  is then sent back into an upper portion of the HRVG, where it is reheated to form a reheated lean stream S 60  having parameters as at a point  16 . The pressure and temperature of the reheated lean stream S 60  having parameters as at point  16  are equal to the pressure and temperature of the fully vaporized and superheated basic working fluid stream S 52  having parameters as at the point  15  (see above). 
         [0030]    Thereafter, the reheated lean stream S 60  having the parameters of the point  16  is combined with the fully vaporized and superheated basic working fluid stream S 52  having parameters as at the point  15 , forming a combined working fluid stream S 62  having parameters as at a point  17 . The combined working fluid stream S 62  having the parameters as at the point  17  then passes through a lower pressure turbine T 2 , where it expands and produces electric power to form a spent vapor stream S 64  having the parameters as at the point  18 . The spent vapor stream S 64  having parameters as at the point  18  is in a state of a superheated vapor. 
         [0031]    Thereafter, the spent vapor stream S 64  having parameters as at the point  18  is divided into the substream S 36  having the parameters as at the point  30  and the substream S 42  having the parameters as at the point  32 , respectively. As stated above, the substream S 36  having the parameters as at the point  30  passes through the fifth heat exchanger HE 5  and the substream S 42  having the parameters as at the point  32  passes through the sixth heat exchanger HE 6 , where they are cooled and almost completely de-superheated forming the de-superheated substreams S 40  and S 44  having the parameters as at the points  31  and  33 , respectively and providing heat for the heat exchange processes  8 - 4  and  10 - 5 , respectively described above. The de-superheated substreams S 40  and S 44  having the parameters as at the points  31  and  33 , respectively are then combined forming a combined de-superheated stream S 66  having parameters as at a point  19 . 
         [0032]    In an alternate embodiment of the system of this invention shown in  FIG. 1B , the stream S 32  having the parameters as at the point  10  and the stream S 22  having the parameters as at the point  8  can be sent in parallel into a single, dual flow heat exchanger DHE 1 . In such a case, the spent vapor stream S 64  having the parameters as at the point  18  is not divided, but is instead sent in counterflow to both the stream S 32  having the parameters as at the point  10  and the stream S 22  having the parameters as at the point  8  in a dual flow heat exchanger replacing the fifth and sixth heat exchangers HE 5  and HE 6 , exiting as the de-superheated stream S 66  having the parameters as at the point  19 . 
         [0033]    In another alternate embodiment of the system of this invention shown in  FIG. 1C , the stream S 28  having the parameters as at the point  9  and the stream S 16  having the parameters as at the point  3  can be sent in parallel into a single, dual flow heat exchanger DHE 2 . In such a case, the stream S 70  having the parameters as at the point  20  is not divided, but is instead sent in counterflow to both the stream S 28  having the parameters as at the point  9  and the stream S 16  having the parameters as at the point  3  in a dual flow heat exchanger replacing the third and fourth heat exchangers HE 3  and HE 4 , exiting as the partially condensed stream S 72  having the parameters as at the point  21 . 
         [0034]    In yet another alternate embodiment of the system of this invention shown in  FIG. 1D , the heat exchanger HE 5  and HE 6  are combined into a first single, dual flow heat exchanger DHE 1  and the heat exchanger HE 3  and HE 4  are combined into a second single, dual flow heat exchanger DHE 2 . 
         [0035]    The combined de-superheated stream S 66  having the parameters as at the point  19  is in a state of slightly superheated vapor. At this point, the combined de-superheated stream S 66  having the parameters as at the point  19  is mixed with a pressurized liquid stream S 68  having parameters as at a point  29  as described below forming a saturated vapor stream S 70  having parameters as at a point  20 . 
         [0036]    The saturated vapor stream S 70  having the parameters as at the point  20  is then divided into the first substream S 30  having parameters as at a point  12  and the second substream S 20  having parameters as at the point  11 . The second substream S 20  having parameters as at the point  11  passes through the third heat exchanger HE 3 , where it is partially condensed, releasing heat for process  3 - 8  (see above) forming the stream S 24  having the parameters as at the point  14 . 
         [0037]    Meanwhile, the first substream S 30  having parameters as at a point  12  enters into the fourth heat exchanger HE 4 , where it is partially condensed, releasing heat for the heat exchange process  9 - 10  as described above forming the stream S 34  having the parameters as at the point  13 . 
         [0038]    The stream S 34  having the parameters as at the point  13  and the stream S 24  having the parameters as at the point  14  are then combined forming a partially condensed working fluid stream S 72  having parameters as at a point  21  corresponding to a state of vapor-liquid mixture. 
         [0039]    The partially condensed working fluid stream S 72  having parameters as at a point  21  is then sent into a flash tank or gravity separator S 1 , where it is separated into a saturated vapor stream S 74  having parameters as at a point  22  and a saturated liquid stream S 76  having parameters as at a point  23 . The concentration of the lower boiling component (ammonia, in a water-ammonia working fluid) in the stream S 74  having the parameters as at the point  22  is slightly higher than the concentration of the lower boiling component in the stream S 10  having the parameters as at the point  1  (see above). 
         [0040]    The stream S 76  having the parameters as at the point  23  is then divided into three substreams S 26 , S 78 , and S 80  having parameters as at points  24 ,  25  and  28 , respectively. The substream S 80  having the parameters as at the point  28  is then sent into a third pump P 3 , where it is pumped to an increased pressure to form the pressurized liquid stream S 68  having the parameters as at the point  29 . The pressurized liquid stream S 68  having the parameters as at the point  29  is then mixed with the stream S 66  having the parameters as at the point  19  to form the stream S 70  having the parameters as at the point  20  (see above). 
         [0041]    The substream S 26  having the parameters as at the point  24  was meanwhile sent into the second pump P 2 , where its pressure is increased to a high pressure to form the stream S 28  having the parameters as at the point  9  (see above). 
         [0042]    Meanwhile, substream S 80  having the parameters as at the point  25  is mixed with the vapor stream S 74  having the parameters as at the point  22  to form the basic solution stream S 14  having the parameters as at the point  26 . The basic solution stream S 14  having the parameters as at the point  26  is then sent into the second heat exchanger HE 2  where it is further condensed, providing heat for heat exchange process  2 - 3  or  26 - 27  (see above) forming the stream S 18  having the parameters as at the point  27 . 
         [0043]    The stream S 18  having the parameters as at the point  27  is then sent into a first heat exchanger or final condenser HE 1 , where it is cooled and fully condensed by a coolant stream S 82  having parameters as at a point  51  (e.g., air or water) in a first heat exchange process  51 - 52  or  27 - 1  (see below) to form the stream S 10  having the parameters as at the point  1  and a spent coolant stream S 84  having the parameters as at a point  52 . The cycle is closed. 
         [0044]    The coolant stream S 82  having the parameters as at the point  51  used for the heat exchange process  27 - 1 , is prepared from an initial coolant stream S 86  having initial parameters as at a point  50 , which is pumped to a higher pressure by a fourth pump P 4 , to form the coolant stream S 82  having the parameters as at the point  51  before being is sent into the first heat exchanger HE 1  as described above. 
         [0045]    As is seen from this description, the flow rate of the working fluid passing through the second turbine T 2  is equal to the sum of flow rate of the stream S 10  having the parameters as at the point  1  passing through the first heat exchanger or condenser HE 1 , and the flow rate of stream S 26  having the parameters as at the point  24 . As a result of this, the total flow rate through the second turbine T 2  is at least 40% higher than the flow rate of the stream S 10  having the parameters as at the point  1  passing though the condenser HE 1 . This, in turn, substantially improves overall efficiency. 
       SECOND EMBODIMENT 
       [0046]    The system of this invention can also be embodied in a simplified version (designated CSQ- 21   s ) using only one a single turbine. The simplified version can utilize high or medium temperature heat source and is depicted in  FIG. 2 . 
         [0047]    This simplified embodiment of the system of this invention operates in a manner identical to the embodiment of  FIG. 1  described above, until it deviated at the stream S 28  having the parameter as at the point  9 . 
         [0048]    In the simplified embodiment of the system of  FIG. 2 , the pressure at the stream S 28  having the parameter as at the point  9  is approximately the same as the pressure of the stream S 16  having the parameters at the point  3 , in distinction to the embodiment of  FIG. 1 , where the pressure of the stream S 28  having the parameter as at the point  9  is substantially higher than the pressure of the stream S 16  having the parameters at the point  3 . 
         [0049]    Thereafter, the stream S 28  having the parameter as at the point  9  enters into the fourth heat exchanger HE 4 , where it is heated to form the stream S 32  having the parameters as at the point  10 . The stream S 32  having the parameters as at the point  10  then passes through the sixth heat exchanger HE 6 , to form the stream S 46  having the final parameters as at the point  5 , corresponding to a state of saturated liquid. But in this simplified system of  FIG. 2 , the pressures of the streams S 38  and S 46  having the parameters as at the points  4  and  5 , respectively, are approximately equal, in distinction from the embodiment of  FIG. 1 , where the pressure the stream S 38  having the parameters as at the at point  4  was substantially higher than the stream S 46  having the parameters as at the point  5 . 
         [0050]    In the cases where the heat source stream used has a relatively low temperature, the stream S 42  having the parameters as at the point  32  may not be hot enough to convert the stream S 32  having the parameters as at the point  10  into the stream S 46  having the parameters as at the point  5  so that it is in a state of saturated liquid in the heat exchange process  32 - 33  or  10 - 5 . In this case, the stream S 38  having the parameters as at the point  4  is divided into a first substream a substream S 88  having parameters as at a point  7  and a second substream S 90  having parameters as at a point  6 . The first substream S 88  having the parameters as at the point  7  is then mixed with the stream S 46  having the parameters as at the point  5  to form a richer stream S 92  having the parameters as at a point  39 . The substream S 88  having the parameters as at the point  7  which is a portion of the stream S 38  having the parameters as at the point  4  is a stream of rich solution which was previously vaporized in the third heat exchanger HE 3  and the fifth heat exchanger HE 5  as set described in the embodiment of  FIG. 1 . The richer stream S 92  having the parameters as at the point  39  is now in the desired state of saturated liquid. 
         [0051]    After being heated in the HRVG in the embodiment of  FIG. 1 , the streams S 38  and S 46  having the parameters as at the points  4  and  5 , respectively, produce the stream S 52  having the parameters as at the point  15  and the stream S 60  having the parameters as at the point  16 , correspondingly. At this point, the stream S 52  having the parameters as at the point  15  and the stream S 60  having the parameters as at the point  16  are combined to form the stream S 62  having the parameters as at the point  17 . The stream S 62  having the parameters as at the point  17  then passes through the single turbine T 1 , producing electric power, and forming the stream S 64  having the parameters as at the point  18 . 
         [0052]    In the simplified embodiment of  FIG. 2 , the richer stream S 92  having the parameters as at the point  39  and the basic working fluid substream S 90  having the parameters as at the point  6  are passed through the HRVG in parallel, where they are fully vaporized and superheated by the heat source stream S 48  having the parameters as at the point  500  to form a vaporized, superheated richer stream S 94  having parameters as at a point  40  and a vaporized, superheated basic working fluid substream S 96  having parameters as at a point  41 . The vaporized, superheated richer stream S 94  having the parameters as at the point  40  and the vaporized, superheated basic working fluid substream S 96  having the parameters as at the point  41  are combined to form the stream S 62  having the parameters as at the point  17 . Thereafter the operation of the embodiment of  FIG. 2  does not differ from the operation of the embodiment of  FIG. 1  described above. 
         [0053]    In the embodiment of  FIG. 1  and the simplified embodiment of  FIG. 2  both described above, the lean stream S 46  having the parameters as at the point  5  or the lean stream S 92  having the parameters as at the point  39  and the rich stream S 38  having parameters as at the point  4  or the rich substream S 90  having the parameters as at the point  6  are simultaneously heated as they pass through the HRVG as two parallel streams. In the embodiment of  FIG. 1 , the streams are combined after the lean stream is passed through the first turbine T 1  of  FIG. 1  and reheated in an upper part of the HRVG, while in the embodiment of  FIG. 2 , the streams are directly combined after exiting the HRVG, where the combined stream is passed through the single turbine T of  FIG. 2 . This arrangement is convenient in the case that both streams have to pass through the tubes of the HRVG, while the heat source stream S 48  having the parameters as at the point  500  passes through a shell space of the HRVG resulting in simultaneous superheating of the two streams and reheating of the spent lean stream in the embodiment of  FIG. 1 . 
         [0054]    The streams S 46  having parameters as at the point  5  or the stream S 92  having the parameters as at the point  39  and the stream S 38  having the parameters as at the point  4  or the stream S 90  having the parameters as at the stream  6  are both in single phase state, which makes their distribution to and through the multiple tubes of the HRVG simple. 
       THIRD EMBODIMENT 
       [0055]    In an alternate embodiment, the heat source stream S 48  having the parameters as at the point  500  pass through the tubes of the HRVG. In such an arrangement, the stream S 38  having the parameters as at the point  4  and the stream S 46  having the parameters as at the point  5  can be combined into a single stream S 98  having parameters as at a point  42  before entering into the HRVG as shown in  FIG. 3 . This variant is referred to as variant CS- 21   a . This combined stream S 98  having the parameters as at the point  42 , then exits the HRVG as the vaporized and superheated stream S 62  having the parameters as at the point  17 . 
         [0056]    This simplified version of the system has a lower efficiency than the embodiments of  FIG. 1  and  FIG. 2  described above, but is substantially simpler (having just one turbine) and is able to work with a wider range of initial heat source temperatures. 
         [0057]    The embodiments of  FIG. 2  and  FIG. 3  can also be altered as set forth in  FIGS. 1B-D . 
       Efficiencies and Cost Savings 
       [0058]    The system of the present invention, in its full embodiment form of  FIG. 1A  and its variant embodiments of  FIG. 1B ,  FIG. 1C ,  FIG. 1D ,  FIG. 2  and  FIG. 3 , has an efficiency which is lower than the efficiency of our previously systems for these temperature ranges (See U.S. patent application Ser. Nos. 10/983,970 filed Nov. 8, 2004, 11/099,211 filed Apr. 5, 2005, and 11/235,654 filed Sep. 22, 2005; however, the advantage of the systems of the present invention are their relative simplicity and therefore substantially reduced capital costs. 
         [0059]    The basic system proposed here, working in combination with a recirculating combustion subsystem (RCSS) as set forth in U.S. Pat. No. 7,350,471-B2 incorporated herein by reference (even though all references are incorporated per the last paragraph of the specification), achieves an efficiency of about 39.61% and an LHV efficiency of about 38.99%. These efficiencies are attained with relatively small plants, using turbines with relatively low efficiencies; however, it should be noted that the efficiencies achieved are none the less substantially higher than what is possible with large, base load, Rankine cycle plants. 
         [0060]    The simplified embodiments of the system of this invention, likewise working with an RCSS as set forth in U.S. Pat. No. 7,350,471-B2 incorporated herein by reference, offer efficiencies of about 35.56% and LHV efficiencies of about 34.97%. 
         [0061]    The simplified embodiments of the system of this invention are particularly suitable for small scale plants using a biomass fuel source. By comparison, the most efficient Rankine cycle biomass plant currently in operation has an efficiency of only slightly better than 26%. 
         [0062]    The simplified embodiments of the system of this invention are also suitable for solar-thermal applications. In large scale solar-thermal applications (using high efficiency turbines and a heat source temperature of about 806° F.), the simplified versions attain an efficiency of about 33.15%. For solar thermal applications implemented in a small plant and correspondingly using low efficiency turbines, the simplified embodiments of the system of this invention can result in an efficiency is about 29.76%. By way of comparison, a Rankine cycle solar thermal plant would have an efficiency of about 27% for large scale plant and about 24% for small scale plant. This increase in efficiency over Rankine cycle plants correlates directly to increased power output or decreased solar collection apparatus costs. 
         [0063]    An additional advantage of the simplified embodiments of the system of this invention is that they utilize a single low pressure turbine having an inlet pressure in the range between about 650 psi and 720 psi, with no vacuum stage so that an exit pressure is in the range between about 110 and about 130 psi. 
         [0064]    All references cited herein are incorporated by reference. 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.