Mixed working fluid power system with incremental vapor generation

[0002] This invention relates to power generation systems in general and more specifically to power generation systems utilizing mixed working fluids.

[0003] Power generation systems or power plants are well-known in the art and are widely used to generate electricity. Most such power generation systems generate electricity from heat energy derived from burning fossil fuels (e.g., coal or natural gas) and are referred to herein as thermal power plants. In addition to using heat energy derived from burning fossil fuels, thermal power plants can also be used with a wide variety of other heat sources, such as solar, geothermal, and nuclear sources.

[0004] Traditionally, thermal power plants have operated in accordance with the well-known Rankine thermodynamic cycle. In the Rankine cycle, a so-called pure working fluid, such as water, is heated to produce vapor or steam. The steam is then expanded, typically through a turbine, in order to convert heat energy contained therein into mechanical work. In the case of an electric power generation system, the turbine is operatively connected to an electrical generator which produces the electricity. While power plants operating in accordance with the Rankine cycle are well-known and widely used, certain characteristics of the Rankine cycle impose fundamental limitations on the thermodynamic efficiency of the cycle. For example, a Rankine cycle operating with a pure working fluid suffers some thermodynamic irreversibilities due to the fact that the pure working fluid vaporizes at substantially constant temperature. These irreversibilities can be larger or smaller depending on the temperature difference between the heating medium and working fluid.

[0005] Partly in an effort to solve some of the limitations associated with the use of a pure working fluid in the Rankine cycle, other types of thermodynamic cycles (e.g., any of the so-called Kalina cycles) have been developed which utilize mixed working fluids. Briefly, a mixed component working fluid comprises two or more vaporizable components which vaporize and condense progressively over a temperature range rather than at the relatively constant temperature of a so-called pure working fluid (e.g., water). Accordingly, thermodynamic cycles utilizing mixed working fluids can, if properly designed, realize increased efficiencies over similar thermodynamic cycles (e.g., the Rankine cycle) that utilize pure working fluids, such as water.

[0006] One design consideration for mixed working fluid systems relates to the boiler or vapor generator that is used to vaporize the mixed working fluid. That is, since the mixed working fluid vaporizes over a temperature range, it is generally preferred to design the vapor generator so that heating function of the mixed working fluid closely follows the cooling function of the heating medium. Closely matching the heating and cooling functions of the working and heating fluids reduces the thermodynamic irreversibilities during the heating cycle, thus increasing the overall thermodynamic efficiency of the system. In accordance with this consideration, thermodynamic cycles utilizing mixed fluids often make use of countercurrent heat exchangers, in which the heating medium and mixed working fluid flow in opposite directions. In this manner, the heating function of the mixed working fluid can be made to more closely follow the cooling function of the heating medium.

[0007] While such countercurrent heat exchangers have been used in mixed working fluid systems to achieve some performance and efficiency gains, there is still room for improvement, particularly in light of other requirements or limitations of the particular type of power generation system in which the heat exchanger is to be used. For example, a primary consideration of geothermal power generation systems relates to the so-called brine effectiveness, that is, the amount of useful work that can be extracted or derived from a given brine flow rate. A desirable geothermal power generation system will seek to maximize brine effectiveness.

[0008] A power generating system according to the present invention may comprise a heat source and an incremental vapor generator system operatively associated with the heat source. The incremental vapor generator system includes a first heating section and a second heating section. The first heating section receives a mixed working fluid and generates a first heated working fluid stream comprising a vapor portion and a liquid portion. The second heating section is operatively associated with the first heating section and receives the liquid portion from the first heated working fluid stream. The second heating section generates a second heated working fluid stream comprising a vapor portion. An energy conversion device operatively associated with the incremental vapor generator system converts into useful work heat energy contained in the vapor portions of the first and second heated working fluid streams.

[0009] Also disclosed is a method for generating power from a mixed working fluid that comprises the steps of incrementally heating the mixed working fluid to produce a first vapor stream and a second vapor stream; and converting into useful work heat energy contained in the first and second vapor streams.

[0010] Illustrative and presently preferred embodiments of the invention are shown in the accompanying drawings in which:

[0011] FIG. 1 is a schematic diagram of a power generating system according to the present invention utilizing parallel flow incremental vapor generation;

[0012] FIG. 2 is an equilibrium/phase diagram of the mixed working fluid at the various stations of the power generating system shown in FIG. 1;

[0013] FIG. 3 is a graphical representation of the heating and cooling functions of the mixed working fluid and the heating fluid for the power generating system shown in FIG. 1;

[0014] FIG. 4 is a schematic diagram of a second embodiment of a power generating system according to the present invention utilizing serial flow incremental vapor generation;

[0015] FIG. 5 is an equilibrium/phase diagram of the mixed working fluid at the various stations of the power generating system shown in FIG. 4; and

[0016] FIG. 6 is a graphical representation of the heating and cooling functions of the mixed working fluid and the heating fluid for the power generating system of FIG. 4.

[0017] A power generating system 110 according to one embodiment of the present invention is shown in FIG. 1 and may comprise an incremental vapor generator system 112 for vaporizing a mixed working fluid 114. The incremental vapor generator system 112 incrementally vaporizes the mixed working fluid 114 with heat energy extracted from a heat source, such as, for example, geothermal brine 116. Alternatively, and as will be described in greater detail below, the present invention may be utilized with other types of heat sources and/or other types of heating fluids.

[0018] In the embodiment shown in FIG. 1, the incremental vapor generator system 112 comprises a parallel flow incremental vapor generation system 118 in which the mixed working fluid 114 is incrementally vaporized to form a first vapor portion 120 and a second vapor portion 122. The first and second vapor portions 120 and 122 thereafter may be combined in a vapor mixer 124 before being directed to an energy conversion system 126, which converts energy contained in the first and second vapor portions 120 and 122 into useful work heat. In the embodiment shown in FIG. 1, energy conversion system 126 comprises a turbine 128 and an electrical generator 130. Accordingly, heat energy contained in the first and second vapor portions 120, 122 is converted into electrical energy by the energy conversion system 126. In an alternate embodiment described below, the incremental vapor generator system may comprise a series flow incremental vapor generation system 218 (FIG. 4) in which the mixed working fluid is incrementally vaporized in a serial manner.

[0019] The parallel flow incremental vapor generating system 118 utilized in the first embodiment 110 of the power generating system according to the present invention is shown in FIG. 1 and may comprise a heat exchanger or vaporizer 132 having a primary loop 134 through which is caused to flow the heating fluid, e.g., geothermal brine 116. The heat exchanger or vaporizer 132 may also comprise first and second heating sections 136 and 138 that are in thermal communication with the primary loop 134 so that heat energy contained in the heating fluid (e.g., brine 116) is transferred to the mixed working fluid 114 flowing through the first and second heating sections 136 and 138, respectively. The heat exchanger 132 may also be provided with a third heating section 140 suitable for additionally heating the first and second vapor portions 120 and 122 in a manner that will be described in more detail below.

[0020] The first and second heating sections 136 and 138 are operatively associated with respective first and second separator systems 142 and 144. The first and second separator systems 142 and 144 separate liquid and vapor portions from the heated mixed working fluid introduced therein by the first and second heating sections 136 and 138, respectively. More specifically, a first inlet 146 of the first separator 142 is connected to the outlet 148 of the first heating section 136, whereas a liquid outlet 150 of the first separator 142 is connected to the inlet 152 of the second heating section 138. A second inlet 154 of first separator 142 is connected to a high temperature recuperator 156. A vapor outlet 158 of first separator 142 is connected to the vapor mixer 124.

[0021] The second separator 144 is provided with an inlet 160 that is connected to the outlet 162 of the second heating section 138. A liquid outlet 164 of second separator 144 is connected to the high temperature recuperator 156, whereas a vapor outlet 166 is connected to the vapor mixer 124.

[0022] The vapor mixer 124 is provided with a vapor outlet 168 which, in the embodiment shown and described herein, is connected to the third heating section 140. The third heating section 140 is used to further heat (e.g., superheat) the vaporized mixed working fluid 114 exiting the mixer 124. The outlet 170 of the third heating section 140 is connected to the energy conversion system 126. As mentioned above, the energy conversion system 126 may comprise a turbine 128 and electrical generator 130. The exhaust outlet 172 of turbine 128 is connected to a low temperature recuperator 174. The low temperature recuperator 174 is in turn connected to a condenser 176 via a mixer 178. The condenser 176 is operatively connected to the heat exchanger 132 via a pump 180 and the high and low temperature recuperators 156 and 174, respectively.

[0023] The power generation system 110 may be operated as follows to convert into useful work heat energy contained in the heating fluid (e.g., geothermal brine 116). As was briefly described above, the mixed working fluid 114 utilized herein vaporizes progressively over an increasing temperature range. That is, the temperature of the vapor and liquid comprising the heated mixed working fluid 114 increases with increasing quality. The point at which vaporization begins (i.e., at 0% quality) is referred to herein as the bubble point, whereas the point at which vaporization is complete (i.e., at 100% quality) is referred to herein as the dew point. By way of example, the mixed working fluid 114 utilized in the preferred embodiments shown and described herein comprises a mixture of ammonia and water. Alternatively, other mixed working fluids could be used as well.

[0024] Referring now to FIGS. 1 and 2 simultaneously, the mixed working fluid feed stream 114 exits the condenser 176 at about the bubble point for the mixture. This corresponds to station L₀ in FIG. 1 and the corresponding point L₀ in FIG. 2. Before proceeding with the description, it should be noted that various points in the system 110 that are of interest thermodynamically are referred to herein as stations and are indicated in FIGS. 1 and 4 as encircled numbers or encircled letter-number combinations. Such stations are indicated on the equilibrium/phase diagrams (e.g., FIGS. 2 and 5) as points having corresponding numbers or letter-number combinations. Hence, station L₀ is designated in FIG. 1 as encircled legend L₀. The corresponding point in the equilibrium/phase diagram illustrated in FIG. 2 is also designated L₀.

[0025] Continuing now with the description, the pump 180 increases the pressure of the mixed working fluid 114 to a point suitable for use in the high pressure side of the power generation system 110. The flow of the working fluid 114 is then split, with a first stream 182 being directed through the high temperature recuperator 156 and a second stream 184 being directed to the low temperature recuperator 174. The heating characteristics of the high temperature recuperator 156 and the flow rate of the first stream 182 are selected so that the first stream 182 is heated to a point above its bubble point at the particular pressure involved (e.g., about 425 pounds per square inch absolute (psia)). That is, the first stream 182 is heated to a quality greater than zero. By way of example, in one preferred embodiment, the first stream 182 is heated to a quality in the range of about 10% to about 40% (30% preferred). This quality corresponds to a vapor portion in the range of about 80% to about 96% (90% preferred) on a volume basis. The heated first stream 182 is then directed to the inlet 154 of first separator system 142. This is identified as station 2₁ in FIG. 1 and as point 2₁ in FIG. 2.

[0026] The second stream 184 is heated by the low temperature recuperator 174 and thereafter is directed to the first heating section 136 of heat exchanger 132 where it is additionally heated to a temperature that exceeds the bubble point. This corresponds to station 2₃ in FIG. 1 and to point 2₃ in FIG. 2. It is generally preferred that the heating characteristics of the low temperature recuperator 174 and the first heating section 136, as well as the flow rate of the second stream 184 be such that the mixed working fluid 114 comprising the second stream 184 is heated to about the same quality as the first stream 182. That is, it is preferred that the points 2₁ and 2₃ on FIG. 2 be approximately coincident. The heated second stream 148 from the first heating section 136 is then directed to the first inlet 146 of the first separator 142.

[0027] The first separator system 142 receives the first and second heated streams 182 and 184 and separates the two streams 182 and 184 into a liquid portion and a vapor portion. The liquid portion exits the liquid outlet 150 of the separator 142 and is directed to the inlet 152 of the second heating section 138. The vapor portion exits the vapor outlet 158 of the first separator 142 as first vapor stream 120. The first vapor stream 120 is at about the dew point (i.e., 100% quality) for the particular concentration of the mixed working fluid 114 comprising the vapor portion stream 120. This corresponds to station v₁ in FIG. 1 and to point v₁ in FIG. 2.

[0028] Before proceeding with the description it should be noted that the concentrations of the constituents (e.g., ammonia and water) comprising the mixed working fluid 114 are different for the liquid and vapor portions. For example, with reference now to FIG. 2, in one preferred embodiment wherein the mixed working fluid 114 comprises a mixture of ammonia and water, the first vapor portion stream 120 (corresponding to point v₁ in FIG. 2) of the mixed working fluid 114 comprises a higher concentration of ammonia (e.g., slightly greater than about 0.95 on a mass basis) than does the liquid portion (point 3 in FIG. 2) of the mixed working fluid 114. The liquid portion of the mixed working fluid 114 at point 3 has an ammonia concentration that is slightly less than about 0.55 (on a mass basis). Consequently, any characteristics (e.g., quality) specifically recited herein for the mixed working fluid 114 at a particular station refer to the working fluid 114 in the particular state (e.g., vapor or liquid) and at the corresponding concentration at the referenced station. For example, at station v₁, the mixed working fluid 114 comprises a vapor having an ammonia concentration that is slightly greater than about 0.95 and is at about the dew point (i.e., a quality of about 100%) for the mixture at that particular ammonia concentration. At station 3, the mixed working fluid 114 comprises a liquid having an ammonia concentration that is slightly less than about 0.55 and is at about the bubble point (i.e., a quality of about 0%) for the mixture at the lower ammonia concentration. The ammonia concentrations (i.e., mass fractions) for the ammonia/water mixed working fluid 114 that may be utilized in the preferred embodiments of the present invention are shown in FIGS. 2 and 4 for the corresponding liquid and vapor portions of the mixed working fluid at the various stations.

[0029] With the foregoing points in mind, the liquid portion of the mixed working fluid 114 from the first separator 142 is at about the bubble point of the liquid portion of mixed working fluid 114 at the corresponding ammonia concentration. That is, the liquid portion is at about the bubble point for the lower ammonia concentration of the liquid portion of the mixed working fluid 114. This corresponds to station 3 in FIG. 1 and to point 3 in FIG. 2. The liquid portion is directed into the inlet 152 of the second heating section 138 whereupon it is heated to a temperature in excess of the bubble point. It is generally preferred that the liquid portion be heated in the second heating section 138 to about the same quality as the mixed working fluid at stations 2₁ and 2₃. That is, the quality of the mixed working fluid stream exiting the second heating section 138 should be about the same as the qualities of the working fluid streams exiting the first heating section 136 and the high temperature recuperator 156. For example, in the embodiment shown and described herein, the mixed working fluid stream exits the second heating section 138 at a quality in the range of about 10% to about 40% (30% preferred), which corresponds to a vapor portion in the range of about 80% to about 96% (90% preferred) on a volume basis. This corresponds to station 4 in FIG. 1 and to point 4 in FIG. 2.

[0030] The second separator system 144 receives the heated mixed fluid from the second heating section 138 and separates the heated mixed fluid into a liquid portion and a vapor portion. The liquid portion exits the liquid outlet 164 of the separator 144 and is directed to the high temperature recuperator 156 whereupon it surrenders a portion of its heat to the first working stream 182. The vapor portion from separator 144 exits the vapor outlet 166 as the second vapor portion stream 122. The second vapor portion stream 122 is at about the dew point (i.e., 100% quality) for the higher ammonia concentration of the mixed working fluid 114 that comprises the second vapor portion stream 122. See station v₂ in FIG. 1 and point v₂ in FIG. 2.

[0031] The vapor mixer 124 receives the first and second vapor streams 120 and 122 and combines them into a combined vapor stream 186. The combined vapor stream 186 corresponds to station v₃ in FIG. 1 and to point v₃ in FIG. 2. The combined vapor stream 186 may be additionally heated (e.g., superheated) by the third heating section 140 to a temperature greater than the dew point temperature for the combined vapor stream 186. The superheated stream 188 exiting the third heating section 140 corresponds to station v₄ in FIG. 1 and to point v₄ in FIG. 2. The stream 188 is then directed to the energy conversion system 126.

[0032] The energy conversion system 126 extracts heat energy from the superheated stream 188, converting it into useful work. In the embodiment shown and described herein, heat energy contained in the first and second vapor streams 120 and 122 (which comprise combined stream 186 and superheated stream 188) is converted into electrical work by the turbine 128 and the electrical generator 130 comprising the energy conversion system 126.

[0033] The exhaust stream 172 from the turbine 128 corresponds to station v₅ in FIG. 1 and to point v₅ in FIG. 2 and is at a temperature that is greater than the dew point temperature for the mixed working fluid at the reduced pressure on the low pressure side of the power generating system 110. By way of example, in the embodiment shown and described herein, the mixed working fluid 114 is at a pressure of about 71 psia on the low pressure side. Alternatively, the exhaust stream could exit the turbine 128 at a temperature below the dew point of the mixed working fluid if the turbine is capable of handling wet mixtures. The exhaust stream 172 from turbine 128 is thereafter directed to the low temperature recuperator 174 wherein it surrenders a portion of its heat energy to the second working fluid stream 184. The cooled exhaust stream 172 exits the low temperature recuperator 174 at station v₆ at a temperature between the bubble and dew points for the mixed working fluid. By way of example, in one preferred embodiment, the cooled exhaust stream 172 exits the low temperature recuperator 174 at a quality in the range of about 0% to about 100% (45% preferred). See also point v₆ in FIG. 2.

[0034] The mixed working fluid exiting the low temperature recuperator 174 is then mixed with the liquid portion exiting the high temperature recuperator 156 in the mixer 178. The combined working fluid stream exits mixer 178 at station v₇ which corresponds to point v₇ in FIG. 2. The combined working fluid stream is then condensed to the bubble point (station L₀ in FIG. 1 and point L₀ in FIG. 2) by the condenser 176. The condensed stream is then returned to the high pressure side of the system by pump 180 and the cycle is repeated.

[0035] A significant advantage of the power generating system 110 according to the present invention is that it results in closely matched heating and cooling curves for the working and heating fluids, respectively. For example, with reference now to FIG. 3 the heating curve or function 190 of the mixed working fluid closely follows the cooling curve or function 192 of the heating fluid (e.g., brine 116). The closely matched heating and cooling functions 190 and 192, improves thermodynamic efficiency by reducing the irreversibilities occurring in the heat exchanger 132. The closely matched heating and cooling functions also allow the brine 116 to be cooled to a lower temperature, closer to the bubble point of the working fluid, than is possible with prior systems. Consequently, the power generating system 110 of the present invention substantially reduces the heating fluid (e.g., brine 116) flow rate required for a given amount of useful work. Accordingly, the power generating system 110 can be used with considerable advantage in geothermal power generation systems wherein it is desired to minimize the brine flow rate per kilowatt of electricity produced.

[0036] Having briefly described one embodiment of the power generating system 110, as well as some of its more significant features and advantages, the various embodiments of the power generating system according to the present invention will now be described in detail. However, before proceeding with the description, it should be noted that while the various embodiments of the power generating system are shown and described herein as they could be used in a geothermal electrical generating system utilizing hot brine 116 as the heating fluid, the present invention is not limited to use in geothermal electrical generating systems. In fact, power generating systems according to the present invention could be used with any of a wide variety of heating fluids and working fluids that are now known in the art or that may be developed in the future, as would be obvious to persons having ordinary skill in the art after having become familiar with the teachings of the present invention. Consequently, the present invention should not be regarded as limited to the particular applications and/or heating and working fluids shown and described herein.

[0037] With the foregoing considerations in mind, one embodiment of a power generating system 110 according to the present invention comprises an incremental vapor generator system 112 for vaporizing a mixed working fluid 114 utilizing heat obtained from a suitable heat source. By way of example, in the embodiments shown and described herein, the heat source may comprise geothermal brine 116. The geothermal brine 116 comprises the heat source or heating fluid and is used to vaporize the working fluid 114 in the incremental vapor generator system 112.

[0038] The working fluid 114 used in the power generation system 110 may comprise any of a wide range of mixed, non-azeotropic fluids now known in the art or that may be developed in the future suitable for use in the particular application. As used herein, the term mixed fluid refers to any fluid wherein the temperature of the vapor and liquid components increases with increasing quality. By way of example, in the embodiment shown and described herein, the mixed working fluid comprises a mixture of ammonia and water.

[0039] As was briefly mentioned above, in one embodiment of the invention the incremental vapor generator system 112 comprises a parallel flow incremental vapor generation system 118. In the parallel flow incremental vapor generation system 118, the mixed working. fluid 114 is incrementally vaporized to form a first vapor portion 120 and a second vapor portion 122. The first and second vapor portions 120 and 122 are combined (i.e., in a parallel manner) before being directed to the energy conversion system 126, hence the designation parallel flow incremental vapor generation system 118.

[0040] With reference now primarily to FIG. 1, the parallel flow incremental vapor generating system 118 utilized in one embodiment of the power generating system 110 according to the present invention comprises a heat exchanger or vaporizer 132 having a primary loop 134 through which is caused to flow the heating fluid. As mentioned above, in the embodiment shown and described herein, the heating fluid comprises geothermal brine 116. Alternatively, other types of heating fluids may be used, as would be obvious to persons having ordinary skill in the art after having become familiar with the teachings of the present invention.

[0041] The heat exchanger or vaporizer 132 may also comprise first and second heating sections 136 and 138 arranged so that they are in thermal communication with the primary loop 134. Accordingly, heat energy contained in the brine 116 is transferred to the mixed working fluid 114 flowing in the first and second heating sections 136 and 138, respectively. The heat exchanger 132 may also be provided with a third heating section 140 suitable for additionally heating the first and second vapor portions 120 and 122. For example, in the embodiment shown and described herein, the third heating section 140 is used to heat the first and second vapor portions 120 and 122 above the dew point, a process that is commonly known as superheating.

[0042] It is generally preferred that the heat exchanger 132 comprise a counter-current heat exchanger in which the inlet end of the primary loop 134 is thermally adjacent the hottest heating section (e.g., the third heating section 140) and in which the outlet end is thermally adjacent the coolest heating section (e.g, the first heating section 136). Such an arrangement makes it easier to more closely match the heating function 190 of the working fluid 114 with the cooling function 192 of the heating fluid (e.g., brine 116). See FIG. 3.

[0043] The exact number of heating sections (e.g., heating sections 136, 138, and 140) comprising the heat exchanger 132 may vary depending on the particular application, the particular heating and working fluids used, as well as on the number of stages (e.g., vapor separators) used to achieve the incremental heating of the working fluid in the manner shown and described herein. That is, the number of heating sections comprising the heat exchanger in any given application could be readily determined by persons having ordinary skill in the art after having become familiar with the teachings of the present invention and by applying the teachings to the particular application. Consequently, the present invention should not be regarded as limited to a heat exchanger having any particular number of heating sections.

[0044] The heat exchanger 132 may be constructed from any of a wide range of materials and in accordance with any of a wide range of techniques that are now known in the art or that may be developed in the future that would be suitable for the particular application. However, since heat exchangers of the type described herein could be readily fabricated by persons having ordinary skill in the art after having become familiar with the teachings of the present invention, and since the details of such heat exchangers are not necessary to understand or practice the present invention, the heat exchangers used in the embodiments shown and described herein will not be described in further detail herein.

[0045] The first and second heating sections 136 and 138 of the heat exchanger 132 are operatively associated with first and second separator systems 142 and 144. As will be described in greater detail below, the first and second separator systems 142 and 144 separate liquid and vapor portions (not shown) from the heated mixed working fluid introduced therein by the first and second heating sections 136 and 138, respectively.

[0046] The first separator system 142 comprises a first inlet 146, a second inlet 154, a liquid outlet 150, and a vapor outlet 158. The first inlet 146 is connected to the outlet 148 of the first heating section 136 so that heated mixed working fluid from the first heating section 136 enters the separator system 142. The second inlet 154 of the first separator system 142 is connected to the high temperature recuperator 156 so that the first mixed working fluid stream 182 from the high temperature recuperator 156 is also directed into the separator system 142. The liquid outlet 150 of the first separator system 142 is connected to the inlet 152 of the second heating section 138 of heat exchanger 132. The vapor outlet 158 of the first separator system 142 is connected to the vapor mixer 124.

[0047] The first separator system 142 may comprise any of a wide range of separator systems that are well-known in the art that would be suitable for separating vapor and liquid portions from an incoming wet mixture stream (e.g., the heated working fluid 114). Consequently, the present invention should not be regarded as limited to any particular type of separator system.

[0048] The second separator system 144 may be similar to the first separator system 142, except that the second separator system 144 is provided with but a single inlet 160 connected to the outlet 162 of the second heating section 138. The arrangement is such that the second separator system 144 receives the heated mixed working fluid 114 from the second heating section 138 of heat exchanger 132. A liquid outlet 164 of the second separator 144 is connected to the high temperature recuperator 156, whereas a vapor outlet 166 is connected to the vapor mixer 124.

[0049] The high temperature recuperator 156 connected to the liquid outlet 164 of second separator system 144 is used to recover heat contained in the liquid portion separated by the second separator 144. The recovered heat is used to pre-heat the first mixed working fluid stream 182. In the embodiment shown and described herein, the liquid outlet 164 of the second separator 144 is connected to a heating loop 155 of the high temperature recuperator 156, whereas a heated loop 157 of high temperature recuperator 156 is connected between the pump 180 and the second inlet 154 of first separator system 142. The separated liquid portion in the heating loop surrenders heat to the first mixed working fluid stream 182 in the heated loop 157, thereby pre-heating the first mixed working fluid stream 182. Thereafter, the separated liquid portion passes through an expansion valve 194 before entering the low pressure side of the system 110.

[0050] The vapor mixer 124 is connected to the vapor outlets 158 and 166 of the respective first and second separator systems 142 and 144 and receives the corresponding first and second vapor portions 120 and 122. A vapor outlet 168 on the mixer 124 is connected to the third heating section 140. The outlet 170 of the third heating section 140 is connected to the energy conversion system 126.

[0051] The vapor mixer 124 may comprise any of a wide range of devices known in the art or that may be developed in the future that would be suitable for mixing together the first and second vapor portions 120 and 122. Consequently, the present invention should not be regarded as limited to any particular type of vapor mixer system.

[0052] The energy conversion system 126 may comprise any of a wide range of systems and devices suitable for converting into useful work heat energy contained in the heated mixed working fluid 114 exiting the parallel flow vapor generator 118 (or third heating section 140, if a third heating section is used). By way of example, in the embodiments shown and described herein, the energy conversion system 126 comprises a turbine 128 and an electric generator 130 connected thereto. The turbine 128 and electric generator 130 may comprise any of a wide range of systems and devices that are well-known in the art and readily commercially available. Consequently, the turbine 128 and electric generator 130 utilized in one preferred embodiment of the invention will not be described in greater detail herein.

[0053] The exhaust outlet 172 of turbine 128 is connected to a low temperature recuperator 174. The low temperature recuperator 174 recovers heat contained in the turbine exhaust stream and uses it to pre-heat the second mixed working fluid stream 184. More specifically, the exhaust outlet 172 of turbine 128 is connected to a heating loop 173 of the low temperature recuperator 174, whereas a heated loop 175 of the low temperature recuperator 174 is connected between the pump 180 and the first heating section 136 of the heat exchanger 132. The turbine exhaust stream in the heating loop 173 surrenders heat to the second mixed working fluid stream 184 in the heated loop 175, thereby pre-heating the second mixed working fluid stream 184 before the same enters the first heating section 136. Thereafter, the exhaust stream is combined in the mixer 178 with the separated liquid portion exiting the expansion valve 194. A condenser 176 connected to the mixer 178 receives the combined cooled mixed working fluid 114, condenses it, and returns it to pump 180.

[0054] The condenser 176 may comprise any of a wide range of condensers that are well-known in the art or that may be developed in the future that would be suitable for condensing the combined cooled mixed working fluid 114 from the mixer 178. By way of example, in the embodiment shown and described herein, the condenser 176 comprises an air-cooled condenser in which air 196 is used to condense the mixed working fluid 114 flowing in the condenser 176. Alternatively, other cooling media besides air may be used to condense the mixed working fluid 114.

[0055] The power generation system 110 may be operated as follows to convert into useful work heat energy derived from the heating fluid. Consider, for example, a geothermal power generation system which generates electricity from geothermal brine 116 extracted from the earth. The geothermal brine 116 serves as the heating fluid and, in the example described herein, enters the primary loop 134 of the heat exchanger 132 at a temperature of about 335 F., although other temperatures are possible. The mixed working fluid 114 may comprise a mixture of ammonia and water and is maintained at a pressure of about 425 pounds per square inch absolute (psia) on the high pressure side of the power generating system 110. The low pressure side of the power generating system 110 is maintained at a pressure of about 71 psia. Alternatively, other mixed fluids may be used at other pressures, as would be obvious to persons having ordinary skill in the art after having become familiar with the teachings of the present invention. The ammonia/water mixture that comprises the mixed working fluid 114 vaporizes progressively over an increasing temperature range. That is, the temperature of the vapor and liquid comprising the heated mixed working fluid increases with increasing quality.

[0056] Referring now to FIGS. 1-3, the mixed working fluid feed stream 114 exits the condenser 176 at station L₀ at about the bubble point for the mixture 114. This station corresponds to point L₀ in FIG. 2. The pump 180 increases the pressure of the mixed working fluid 114 to a pressure suitable for use in the high pressure side of the power generating system 110. In the embodiment shown and described herein, the high pressure side of the system 110 is maintained at a pressure of about 425 psia. Therefore, the pump 180 increases the pressure of the mixed working fluid 114 to a pressure of about 425 psia. The mixed working fluid stream 114 exiting the pump 180 is then split into a first working fluid stream 182 and a second working fluid stream 184. The first working fluid stream 182 is directed through the heated loop 157 of the high temperature recuperator 156 whereupon it is heated by the liquid portion from the second separator 144 passing through the heating loop 155. The heating characteristics of the high temperature recuperator 156 and the flow rate of the first stream 182 are such that the first stream 182 is heated to a temperature in excess of its bubble point. This corresponds to station 2₁ in FIG. 1 and to point 2₁ in FIG. 2.

[0057] By way of example, in the embodiment shown and described herein, the first stream 182 is heated to a quality in the range of about 10% to about 40% (30% preferred). This quality range corresponds to a vapor portion range of about 80% to about 96% (90% preferred) on a volume basis. So heating the first working fluid stream 182 to a vapor portion in the range specified herein provides for good heat transfer characteristics in the high temperature recuperator 156. That is, some loss of efficiency in the high temperature recuperator 156 will occur if the first working fluid stream 182 is heated to a vapor portion that is substantially greater than the vapor portion range specified herein. After being heated in the high temperature recuperator 156, the heated first working fluid stream 182 is directed to the inlet 154 of the first separator system 142.

[0058] The second working fluid stream 184 is directed to the heated loop 175 of the low temperature recuperator 174 whereupon it is pre-heated by the exhaust stream 172 exiting the turbine 128. Thereafter, the pre-heated second working fluid stream 184 is directed to the first heating section 136 of heat exchanger 132 which heats the second working fluid stream 184 to a temperature in excess of the bubble point. This corresponds to station 2₃ in FIG. 1 and to point 2₃ in FIG. 2. It is generally preferred that the flow rate of the second stream 184 be matched to the heating characteristics of the low temperature recuperator 174 and the first heating section 136 so that the mixed working fluid 114 comprising the second working fluid stream 184 is heated to about the same quality as the first stream 182. That is, it is preferred that the points 2₁ and 2₃ in FIG. 2 be approximately coincident. Stated another way, the second working fluid stream 184 is heated to a quality in the range of about 10% to about 40% (30% preferred), which corresponds to a vapor portion in the range of about 80% to about 96% (90% preferred).

[0059] In the embodiment shown and described herein, the mass ratio of the first working fluid stream 182 to the second working fluid stream 184 is about 1:4. That is, most of the working fluid 114 is directed to the second stream 184, with only a small amount (i.e., on a mass basis) being directed through the high temperature recuperator 156 as first working fluid stream 182. Of course, the mixed working fluid stream 114 may be divided in accordance with other mass ratios depending on the characteristics of the particular system.

[0060] Referring back now primarily to FIG. 1, the first separator system 142 receives the first and second heated streams 182 and 184 and separates the two streams 182 and 184 into a liquid portion and a vapor portion. The liquid portion exits the liquid outlet 150 of the first separator 142 and is directed to the inlet 152 of the second heating section 138. The vapor portion exits the vapor outlet 158 of the first separator 142 as a first vapor portion stream 120. The first vapor portion stream is at about the dew point (i.e., 100% quality) for the mixed working fluid 114. This corresponds to station v₁ in FIG. 1 and to point v₁ in FIG. 2.

[0061] The liquid portion from the first separator 142 is at about the bubble point of the mixed working fluid 114. See station 3 in FIG. 1 and point 3 in FIG. 2. The liquid portion is directed into the inlet 152 of the second heating section 138 whereupon it is heated to a temperature in excess of the bubble point. It is generally preferred that the liquid portion be heated to about the same quality as the mixed working fluid at stations 2₁ and 2₃. That is, the quality of the mixed working fluid stream exiting the second heating section 138 should be about the same as the qualities of the working fluid streams exiting the first heating section 136 and the high temperature recuperator 156. For example, in the embodiment shown and described herein, the mixed working fluid stream exits the second heating section 138 at a quality in the range of about 10% to about 40% (30% preferred). This corresponds to a vapor portion in the range of about 80% to about 96% (90% preferred). See station 4 in FIG. 1 and point 4 in FIG. 2. As discussed above, heating the mixed working fluid to the quality ranges specified herein provides a good balance between temperature rise and heat transfer efficiency in the second heating section 138.

[0062] The second separator system 144 receives the heated mixed fluid from the second heating section 138 and separates the heated mixed fluid into a liquid portion and a vapor portion. The liquid portion exits the liquid outlet 164 of the separator 144 and is directed to the high temperature recuperator 156 whereupon it surrenders a portion of its heat to the first working fluid stream 182. Thereafter, the cooled liquid portion is expanded through the expansion valve 194 to the low pressure side of the power generating system 110. See station 5₂ in FIG. 1 and point 5₂ in FIG. 2. The cooled, expanded liquid portion is then combined with the turbine exhaust stream in mixer 178.

[0063] The vapor portion from the second separator 144 exits the vapor outlet 166 of separator 144 as the second vapor portion stream 122. The second vapor portion stream 122 is at about the dew point (i.e., 100% quality) and corresponds to station v₂ in FIG. 1 and to point v₂ in FIG. 2.

[0064] The vapor mixer 124 receives the first and second vapor streams 120 and 122 and combines them into a combined vapor stream 186. The combined vapor stream 186 corresponds to station v₃ in FIG. 1 and to point v₃ in FIG. 2. If desired, the combined vapor stream 186 may be additionally heated by the third heating section 140 to a temperature greater than the dew point temperature for the combined vapor stream 186. That is, the combined vapor stream 186 may be superheated in the third heating section 140. The superheated stream 188 exiting the third heating section 140 is designated as station v₄ in FIG. 1 and corresponds to point v₄ in FIG. 2. The stream 188 is then directed to the energy conversion system 126.

[0065] The energy conversion system 126 extracts heat energy from the superheated stream 188, converting it into useful work. In the embodiment shown and described herein, heat energy contained in the first and second vapor streams 120 and 122 (which comprise combined stream 186 and superheated stream 188) is converted into electrical work by the turbine 128 and the electrical generator 130 comprising the energy conversion system 126.

[0066] The superheated stream 188 is expanded in the turbine 128 and exits the turbine 128 as exhaust stream 172. See station v₅ in FIG. 1 and point v₅ in FIG. 2. It is generally preferred that the expansion process be terminated before the mixed working fluid 114 is cooled below the dew point temperature. By way of example, in the embodiment shown and described herein, the mixed working fluid 114 is expanded to a pressure of about 71 psia and to a temperature of about 150 F., which is below the dew point. That is, the mixed working fluid 114 is cooled to a temperature below the dew point temperature since, in the embodiment shown and described herein, the energy conversion device 126 functions effectively with wet mixtures. The exhaust stream 172 is thereafter directed to the low temperature recuperator 174 wherein it surrenders a portion of its heat energy to the second working fluid stream 184 flowing in the heated loop 175 of low temperature recuperator 174. The cooled exhaust stream 172 exits the low temperature recuperator 174 at station v₆ at a temperature between the bubble and dew points for the mixed working fluid. See point v₆ in FIG. 2. By way of example, in the embodiment shown and described herein, the cooled exhaust stream 172 exits the low temperature recuperator 174 at a quality in the range of about 0% to about 100% (45% preferred).

[0067] The mixed working fluid exiting the low temperature recuperator 174 is then mixed in mixer 178 with the liquid portion flowing through the expansion valve 194. The combined working fluid stream that exits mixer 178 is designated as station v₇ and corresponds to point v₇ in FIG. 2. The combined working fluid stream is then condensed by the condenser 176 to about the bubble point, (i.e., at station L₀ in FIG. 1 and point L₀ in FIG. 2). The condensed stream is then returned to the high pressure side of the system by pump 180 and the cycle is repeated.

[0068] The power generating system 110 just described results in the closely matched heating and cooling functions 190 and 192 shown in FIG. 3. That is, the heating curve 190 of the mixed working fluid 114 closely follows the cooling curve 192 of the heating fluid (e.g., geothermal brine 116).

[0069] As mentioned above, the first embodiment 110 of the power generating system according to the present invention utilizes a parallel flow vapor generator system 118 in which the working fluid is incrementally vaporized to produce first and second vapor portion streams 120 and 122 which are then combined in a parallel manner (e.g., by mixer 124) before being superheated (if desired) and directed to the energy conversion system 126. However, other incremental vaporization arrangements are possible in accordance with the teachings of the present invention.

[0070] With reference now to FIGS. 4-6, a second embodiment 210 of a power generating system according to the present invention embodies an incremental vapor generator system 212 that comprises a series flow vapor generator system 218. Briefly, in the series flow vapor generator system 218, the mixed working fluid 214 is incrementally vaporized to form a first vapor portion 220 and a second vapor portion 222. The first vapor portion 220 is then used to condense or separate a liquid portion from a heated mixed working fluid stream 221 from which is derived the second vapor portion 222. Since, in the case of the mixed working fluid 214, the liquid is lean and the first vapor portion 220 is rich, the first vapor portion 220 condenses on the lean liquid. The heat of condensation causes additional vapor to be produced. Accordingly, the series flow vapor generator system 218 produces the vapor streams 220 and 222 in a serial manner.

[0071] With reference now primarily to FIG. 4, the serial flow incremental vapor generating system 218 utilized in the second embodiment 210 of the power generating system according to the present invention comprises a heat exchanger or vaporizer 232 having a primary loop 234 through which is caused to flow the heating fluid. In the embodiment shown and described herein, the heating fluid comprises geothermal brine 216, although other types of heating fluids may be used, as would be obvious to persons having ordinary skill in the art after having become familiar with the teachings of the present invention. The heat exchanger or vaporizer 232 may also comprise first and second heating sections 236 and 238 arranged so that they are in thermal communication with the primary loop 234 so that heat energy contained in the brine 216 is transferred to the mixed working fluid 214 flowing in the first and second heating sections 236 and 238, respectively. The heat exchanger 232 may also be provided with a third heating section 240 suitable for additionally heating the combined first and second vapor portions 220 and 222. For example, and as was the case for the first embodiment 110, the third heating section 240 of the second embodiment 210 is used to heat the first and second vapor portions 220 and 222 above the dew point.

[0072] It is generally preferred that the heat exchanger 232 be of the counter-current type in which the inlet end of the primary loop 234 is thermally adjacent the hottest heating section (e.g., the third heating section 240) and the outlet end is thermally adjacent the coolest heating section (e.g, the first heating section 236). Such an arrangement allows the system 210 to more closely match the heating function 290 of the working fluid 214 with the cooling function 292 of the heating fluid (e.g., brine 216). See FIG. 6.

[0073] The exact number of heating sections (e.g., heating sections 236, 238, and 240) comprising the heat exchanger 232 may vary depending on the particular application, the particular heating and working fluids used, as well as the number of stages used to achieve the incremental heating of the working fluid 214 in the serial manner described herein. The number of heating sections comprising the heat exchanger in any given application could be readily determined by persons having ordinary skill in the art after having become familiar with the teachings of the present invention and by applying the teachings to the particular application. Consequently, the present invention should not be regarded as limited to a heat exchanger having any particular number of heating sections.

[0074] The heat exchanger 232 may be constructed from any of a wide range of materials and in accordance with any of a wide range of techniques that are now known in the art or that may be developed in the future that would be suitable for the particular application. However, since heat exchangers of the type described herein could be readily fabricated by persons having ordinary skill in the art after having become familiar with the teachings of the present invention, and since the details of such heat exchangers are not necessary to understand or practice the present invention, the heat exchangers used in the embodiments shown and described herein will not be described in further detail herein.

[0075] The first and second heating sections 236 and 238 of the heat exchanger 232 are operatively associated with an integral separator system 241 comprising a first separator section 242 and a second separator section 244. As will be described in greater detail below, the first and second separator sections 242 and 244 comprising the integral separator system 241 separate liquid and vapor portions (not shown) from respective first and second heated mixed working fluid streams 219 and 221.

[0076] The first separator section 242 of integral separator system 241 is provided with an inlet 246 that is connected to the high temperature recuperator 256 and the first heating section 236 in the manner best seen in FIG. 4. The arrangement is such that the first separator section 242 receives the first heated working fluid stream 219. The liquid outlet 250 of the first separator section 242 is connected to an inlet 252 of the second heating section 238.

[0077] The second separator section 244 of integral separator system 241 is provided with an inlet 260 connected to the outlet 262 of second heating section 238 so that the second separator section 244 receives the second heated working fluid stream 221 from the second heating section 238. The second separator section 244 is also provided with a collector 264 for collecting additional amounts of separated liquid. The collector 264 is connected to a heating loop 255 of the high temperature recuperator 256. A vapor outlet 266 provided in the second separator section 244 is connected to the third heating section 240. The outlet 270 of the third heating section 240 is connected to the energy conversion system 226.

[0078] The high temperature recuperator 256 is connected to the collector 264 of the second separator section 244 of integral separator 241. The high temperature recuperator 256 recovers heat contained in the liquid portion separated by the second separator section 244 of the integral separator 241. The recovered heat is used to heat the pre-heated second working fluid stream 282. In the embodiment shown and described herein, the collector 264 is connected to the heating loop 255 of the high temperature recuperator 256, whereas a heated loop 257 of high temperature recuperator 256 is connected in parallel with the first heating section 236 of the heat exchanger 232. The heating loop 255 is connected to an expansion valve 294 which returns the cooled liquid portion to the low pressure side of the power generating system 210.

[0079] As was the case for the first embodiment 110 (FIG. 1) of the power generating system, the energy conversion system 226 of the second embodiment 210 of the power generating system may comprise any of a wide range of systems and devices suitable for converting into useful work heat energy contained in the heated mixed working fluid 214 exiting the series flow vapor generator 218 (or third heating section 240, if a third heating section is used). By way of example, the energy conversion system 226 comprises a turbine 228 and an electric generator 230 connected thereto. The turbine 228 and electric generator 230 may comprise any of a wide range of systems and devices that are well-known in the art and readily commercially available. Consequently, the turbine 228 and electric generator 230 utilized in one preferred embodiment of the invention will not be described in greater detail herein.

[0080] The exhaust outlet 272 of turbine 228 is connected to a low temperature recuperator 274. The low temperature recuperator 274 recovers heat contained in the turbine exhaust stream and uses it to pre-heat the mixed working fluid stream 214. More specifically, the exhaust outlet 272 of turbine 228 is connected to a heating loop 273 of the low temperature recuperator 274, whereas a heated loop 275 of the low temperature recuperator 274 is connected between the pump 280 and the parallel arrangement of the heating loop 257 of the high temperature recuperator 256 and the first heating section 236 of heat exchanger 232. The turbine exhaust stream in the heating loop 273 surrenders heat to the mixed working fluid stream 214 in the heated loop 275, thereby pre-heating the mixed working fluid stream 214 before the same enters the high temperature recuperator 256 and the first heating section 236. Thereafter, the exhaust stream is combined with the separated liquid portion exiting the expansion valve 294. A condenser 276 connected to the low temperature recuperator 274 and expansion valve 294 receives the combined cooled mixed working fluid 214, condenses it, and returns it to pump 280.

[0081] The condenser 276 may comprise any of a wide range of condensers that are well-known in the art or that may be developed in the future that would be suitable for condensing the combined cooled mixed working fluid 214. By way of example, in the embodiment shown and described herein, the condenser 276 comprises an air-cooled condenser in which air 296 is used to condense the mixed working fluid 214 flowing in the condenser 276.

[0082] The second embodiment 210 of the power generation system of the present invention may be operated as follows to convert into useful work heat energy derived from the heating fluid, i.e., geothermal brine 216 extracted from the earth. As was the case for the first embodiment, the geothermal brine 216 may enter the primary loop 234 of the heat exchanger 232 at a temperature of about 335 F., although other temperatures are possible. The mixed working fluid 214 may comprise a mixture of ammonia and water and is maintained at a pressure of about 250 psia on the high pressure side of the power generating system 210. The low pressure side is maintained at a pressure of about 43 psia. Alternatively, other mixed working fluids may be used at other pressures, as would be obvious to persons having ordinary skill in the art after having become familiar with the teachings of the present invention.

[0083] With reference now to FIGS. 4-6, the mixed working fluid stream 214 exits the condenser 276 at station L₀ about the bubble point for the mixture 214. This station corresponds to point L₀ in FIG. 5. The pump 280 increases the pressure of the mixed working fluid 214 to a pressure suitable for use in the high pressure side of the power generating system 210. In the embodiment shown and described herein, the high pressure side of the system 210 is maintained at a pressure of about 250 psia. Therefore, the pump 280 increases the pressure of the mixed working fluid 214 to a pressure of about 250 psia. The mixed working fluid stream 214 exiting the pump 280 is then directed to the heated loop 275 of the low temperature recuperator 274 which pre-heats the mixed working fluid 214. See station 2 of FIG. 4 and corresponding point 2 in FIG. 5. The pre-heated mixed working fluid stream 214 is then split or divided into a first stream 282 and a second stream 284. The first stream 282 is directed through the heated loop 257 of the high temperature recuperator 256 whereupon it is heated by the liquid portion extracted from the second separator section 244 by the collector 264. The heating characteristics of the high temperature recuperator 256 and the flow rate of the first stream 282 are such that the first stream 282 is heated to a temperature in excess of its bubble point. This corresponds to station 3₂ in FIG. 4 and to point 3₂ in FIG. 5.

[0084] In the embodiment shown and described herein, the first stream 282 is heated to a quality in the range of about 10% to about 40% (30% preferred). This quality range corresponds to a vapor portion range of about 80% to about 96% (90% preferred) on a volume basis. So heating the first working fluid stream 282 to a vapor portion in the specified range provides for good heat transfer characteristics in the high temperature recuperator 256. That is, some loss of efficiency in the high temperature recuperator 256 will be experienced if the first working fluid stream 282 is heated to a vapor portion that is substantially greater than the vapor portion range described herein. After being heated in the high temperature recuperator 256, the heated first working fluid stream 282 mixed with the heated working fluid stream 284 exiting the first heating section 236 and directed into the inlet 246 of first separator section 242 as first heated working fluid stream 219. See station 3 in FIG. 4 and corresponding point 3 in FIG. 5.

[0085] The second stream 284 is directed to the first heating section 236 of the heat exchanger 232 which heats the second working fluid stream 284 to a temperature in excess of the bubble point. This corresponds to station 3₁ in FIG. 4 and to point 3₁ in FIG. 5. It is generally preferred that the flow rate of the second stream 284 be matched to the heating characteristics of the first heating section 236 so that the mixed working fluid 214 comprising the second working fluid stream 284 is heated to about the same quality as the first stream 282. That is, it is preferred that the points 3₁ and 3₂ in FIG. 5 be approximately coincident. Stated another way, the second working fluid stream 284 is heated to a quality in the range of about 10% to about 40% (30% preferred), which corresponds to a vapor portion in the range of about 80% to about 98% (90% preferred).

[0086] In the embodiment shown and described herein, the mass ratio of the first working fluid stream 282 to the second working fluid stream 284 is about 1:4. That is, most of the working fluid 214 is directed to the second stream 284, with only a small amount (i.e., on a mass basis) being directed through the high temperature recuperator 256 as first working fluid stream 282. Of course, the mixed working fluid 214 may be divided in accordance with other mass ratios depending on the characteristics of the particular system.

[0087] Still referring primarily to FIG. 4, the first separator section 242 in integral separator system 241 receives the first and second heated streams 282 and 284 as combined first heated working fluid stream 219 and separates the stream 219 into a liquid portion and a vapor portion 220. The liquid portion exits the liquid outlet 250 of the first separator section 242 and is directed to the inlet 252 of the second heating section 238. The vapor portion 220 is at about the dew point (i.e., 100% quality) for the mixed working fluid 214. This corresponds to station v₁ in FIG. 4 and to point v₁ in FIG. 5.

[0088] The liquid portion from the first separator 242 is at about the bubble point of the mixed working fluid 214. See station 4 in FIG. 4 and point 4 in FIG. 5. The liquid portion is directed into the inlet 252 of the second heating section 238 whereupon it is heated to a temperature in excess of the bubble point. This corresponds to station 5 in FIG. 4 and to point 5 in FIG. 5. It is generally preferred that the liquid portion be heated to about the same quality as the mixed working fluid at stations 3₁ and 3₂. That is, the quality of the mixed working fluid stream exiting the second heating section 238 should be about the same as the qualities of the working fluid streams exiting the first heating section 236 and the high temperature recuperator 256. For example, in the embodiment shown and described herein, the mixed working fluid stream exits the second heating section 238 at a quality in the range of about 10% to about 40% (30% preferred). This corresponds to a vapor portion in the range of about 80% to about 98% (90% preferred). As discussed above, heating the mixed working fluid to the quality ranges specified herein provides a good balance between temperature rise and heat transfer efficiency in the second heating section 238.

[0089] The second separator section 244 of integral separator system 241 receives the heated mixed fluid from the second heating section 238 as second heated mixed working fluid stream 221. The second separator section 244 separates the second heated working fluid stream 221 into a liquid portion (not shown) and a vapor portion 222. As mentioned earlier, the first vapor portion 220 from the first separator section 242 is used to further separate the vapor portion from the heated mixed working fluid stream 221. Since, the liquid portion to be separated from the second heated mixed working fluid stream is lean (e.g., lower ammonia concentration) and since the first vapor portion 220 is rich (e.g., higher ammonia concentration), portions of the first vapor portion 220 will condense on the lean liquid portion in the second separator section 244. The heat of condensation causes additional amounts of vapor portion 222 to be produced.

[0090] The liquid portion drained from separator 244 is collected by the collector 264 and exits the integral separator system 241. This corresponds to station 6 in FIG. 4 and to point 6 in FIG. 5. The collected liquid portion then proceeds to the high temperature recuperator 256 whereupon it surrenders a portion of its heat to the first working fluid stream 282. See station 7 in FIG. 4 and corresponding point 7 in FIG. 5. Thereafter, the cooled liquid portion is expanded through the expansion valve 294 to the low pressure side of the power generating system 210. See station 8 in FIG. 4 and point 8 in FIG. 5. The cooled, expanded liquid portion is then combined with the turbine exhaust stream at station v₆ and corresponding point v₆ in FIG. 5.

[0091] The vapor portion 222 produced in the second separator portion 244 combines with residual amounts of the first vapor portion 220 from the first separator portion 242 and exits the integral vapor separator system 241 as combined vapor stream 286. This corresponds to station v₂ in FIG. 4 and to point v₂ in FIG. 5. The combined vapor stream 286 may be additionally heated by the third heating section 240 to a temperature that is greater than the dew point temperature for the combined vapor stream 286. That is, the combined vapor stream 286 is superheated in the third heating section 240. The superheated stream 288 exiting the third heating section 240 corresponds to station v₃ in FIG. 4 and to point v₃ in FIG. 5. The stream 288 is then directed to the energy conversion system 226.

[0092] As was the case for the first embodiment 110, the energy conversion system 226 of the second embodiment 210 extracts heat energy from the superheated stream 288, converting it into useful work. In the embodiment shown and described herein, heat energy contained in the first and second vapor streams 220 and 222 (which comprise combined stream 286 and superheated stream 288) is converted into electrical work by the turbine 228 and the electrical generator 230 comprising the energy conversion system 226.

[0093] The superheated stream 288 is expanded in the turbine 228 and exits the turbine 228 as exhaust stream 272. See station v₄ in FIG. 4 and point v₄ in FIG. 5. It is generally preferred that the expansion process be terminated before the mixed working fluid 214 is cooled below the dew point temperature. By way of example, in the embodiment shown and described herein, the mixed working fluid 214 is expanded to a pressure of about 43 psia and to a temperature of about 160 F., which is below the dew point of the mixed working fluid 214 at the designated pressure. The mixed working fluid 214 can be cooled to a temperature below the dew point temperature since the energy conversion device 226 can function effectively with wet mixtures. The exhaust stream 272 is thereafter directed to the low temperature recuperator 274 wherein it surrenders a portion of its heat energy to the working fluid stream 214 flowing in the heated loop 275 of low temperature recuperator 274. The cooled exhaust stream 272 exits the low temperature recuperator 274 at station v₅ at a temperature between the bubble and dew points for the mixed working fluid. See point v₅ in FIG. 5. By way of example, in this embodiment, the cooled exhaust stream 272 exits the low temperature recuperator 274 at a quality in the range of about 0% to about 100% (45% preferred).

[0094] The mixed working fluid exiting the low temperature recuperator 274 is then mixed with the liquid portion flowing through the expansion valve 294. See station v₆ in FIG. 4 and point v₆ in FIG. 5. The combined working fluid stream is then condensed by the condenser 276 to about the bubble point (station L₀ in FIG. 4 and point L₀ in FIG. 5). The condensed stream is then returned to the high pressure side of the system 210 by pump 280 and the cycle is repeated.

[0095] The second embodiment 210 of the power generating system just described results in the closely matched heating and cooling functions 290 and 292 shown in FIG. 6. That is, the heating curve 290 of the mixed working fluid 214 closely follows the cooling curve 292 of the heating fluid (e.g., geothermal brine 216).

[0096] It is contemplated that the inventive concepts herein described may be variously otherwise embodied and it is intended that the appended claims be construed to include alternative embodiments of the invention except insofar as limited by the prior art.