Process and system for recovery of energy from geothermal brines and other water containing sources by direct contact with a working fluid below the critical pressure

Claim 2

Process for recovery of energy from elevated temperature or hot water containing fluids including geothermal brines and other elevated temperature water sources, which comprises introducing said water containing fluid in a heat transfer zone in heat exchange relation therein with a working fluid in liquid form, and heating said working fluid at temperature to produce boiling thereof in the upper portion of said heat transfer zone, said heat transfer zone being maintained at a pressure below the critical pressure of said working fluid, and corresponding to operation at a point on the saturated vapor curve of the Mollier enthalpy-entropy diagram for said working fluid, close to the apex on said saturated vapor curve, expanding the boiling vapors of working fluid in an expander to produce work, cooling and condensing said expanded working fluid, separating said condensed working fluid from condensed water and uncondensible gas, and returning said condensed working fluid under pressure to said heat transfer zone for reheating therein.

Claim 3

The process as defined in claim 1, said operation being carried out at a point on said saturated vapor curve which is 0 to about 10% less than the enthalpy value at said apex, on a water free basis.

Claim 4

The process as defined in claim 2, wherein said operation is carried out at a point on said saturated vapor curve to maximize the amount of work produced by said expander and wherein not more than about 10% by weight of the vapors expanded in said expander is converted to the liquid phase.

Claim 5

The process as defined in claim 3, wherein said working fluid is a paraffinic or olefinic hydrocarbon containing from about 1 to about 8 carbon atoms, or mixtures thereof.

Claim 6

The process as defined in claim 1, wherein said operation is carried out at a point on said saturated vapor curve to maximize the amount of work produced by said expander and wherein not more than about 10% by weight of the vapors expanded in said expander is converted to the liquid phase.

Claim 7

The process as defined in claim 1, wherein said working fluid is a substance in the form of a hydrocarbon selected from the group consisting of aromatics, paraffins, naphthenes and olefins, and mixtures thereof.

Claim 8

The process as defined in claim 1, including the step of removing at least a portion of uncondensible gas in said water containing fluid prior to introduction thereof into said heat transfer zone.

Claim 9

The process as defined in claim 1, said working fluid being passed upwardly in countercurrent heat exchange relation with said hot water containing fluid being passed downwardly, in said heat transfer zone, and the flow of said working fluid being maintained at a rate sufficient to avoid temperature pinch between said working fluid and said water containing fluid along the length of said heat transfer zone.

Claim 10

The process as defined in claim 8, wherein said working fluid is introduced into the bottom of said heat transfer zone and is the continuous phase, and said water containing fluid is distributed into the top of said heat transfer zone and is the discontinuous phase, the interface between said phases being at the bottom of said heat transfer zone, and including a boiling zone for said working fluid in the top of said heat transfer zone.

Claim 11

The process as defined in claim 1, wherein said working fluid is a substance in the form of a hydrocarbon selected from the group consisting of aromatics, paraffins, naphthenes and olefins, and mixtures thereof.

Claim 12

The process as defined in claim 1, wherein said working fluid is a hydrocarbon containing 2 to 5 carbon atoms, selected from the group consisting of methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane and neopentane, and the analogous olefins, and mixtures thereof.

Claim 13

The process as defined in claim 1, said water containing fluid being in direct contact heat exchange relation with said working fluid in said heat transfer zone, said water containing fluid being introduced into said heat transfer zone at a temperature ranging from about 60° to about 600° F, and said heat transfer zone being maintained at a pressure ranging from about 200 to about 700 psia.

Claim 14

The process as defined in claim 1, said working fluid being passed upwardly in countercurrent heat exchange relation with said hot water containing fluid being passed downwardly, in said heat transfer zone, and the flow of said working fluid being maintained at a rate sufficient to avoid temperature pinch between said working fluid and said water containing fluid along the length of said heat transfer zone.

Claim 15

The process as defined in claim 1, including withdrawing cooled water containing fluid from said heat transfer zone, flashing said last mentioned fluid to flash off working fluid contained in said cooled water containing fluid, compressing the resulting vaporized working fluid, and mixing said compressed working fluid with the working fluid discharged from said expander and prior to cooling and condensation thereof.

Claim 16

The process as defined in claim 1, said separating said cooled and condensed working fluid from condensed water and uncondensible gas taking place in an accumulator zone, including withdrawing a vent gas containing uncondensibles and some working fluid from said accumulator zone, withdrawing cooled water containing fluid from said heat transfer zone, flashing said last mentioned fluid to flash off working fluid contained in said cooled water containing fluid, compressing the resulting vaporized working fluid, and mixing said compressed working fluid with the working fluid discharged from said expander and prior to cooling and condensation thereof, said flashing said cooled water containing fluid being carried out in a flash zone at a pressure less than the pressure in said accumulator zone.

Claim 17

The process as defined in claim 1, said water containing fluid being in direct contact heat exchange relation with said working fluid in said heat transfer zone, said water containing fluid being introduced into said heat transfer zone at a temperature ranging from about 60° to about 600° F, and said heat transfer zone being maintained at a pressure ranging from about 200 to about 700 psia.

Claim 18

The process as defined in claim 16, the expander outlet pressure being in the range of about 1 to about 600 psia, said working fluid being cooled and condensed to a temperature in the range of about 80° to about 140° F.

Claim 19

The process as defined in claim 7, said separating said cooled and condensed working fluid from condensed water and uncondensible gas taking place in an accumulator zone, including withdrawing a vent gas containing uncondensibles and some working fluid from said accumulator zone.

Claim 20

The process as defined in claim 1, wherein said working fluid is a paraffinic or olefinic hydrocarbon containing from about 1 to about 8 carbon atoms, or mixtures thereof.

Claim 21

The process as defined in claim 19, said hydrocarbon containing 2 to 5 carbon atoms, selected from the group consisting of methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane and neopentane, and the analogous olefins, and mixtures thereof.

Claim 22

The process as defined in claim 19, said heat transfer zone being a heat transfer column, said water containing fluid being in direct contact heat exchange relation with said working fluid in said heat transfer column, said hot water containing fluid being introduced into said heat transfer column at a temperature ranging from about 150° to about 400° F, and said heat transfer column being maintained at a pressure ranging from about 200 to about 700 psia.

Claim 23

The process as defined in claim 21, wherein said working fluid is distributed in the bottom of said heat transfer zone and is the discontinuous phase and said water containing fluid is introduced into the top of said heat transfer zone and is the continuous phase, the interface between said phases being in the upper portion of said heat transfer zone, and including a boiling zone for said working fluid in the top of said heat transfer zone.

Claim 24

The process as defined in claim 21, the expander outlet pressure being in the range of about 30 to about 250 psia, said working fluid being cooled and condensed to a temperature in the range of about 80° to about 140° F.

Claim 25

The process as defined in claim 23, including the step of removing at least a portion of uncondensible gas in said hot water containing fluid prior to introduction thereof into said heat transfer column.

Claim 26

The process as defined in claim 24, said separating said cooled and condensed working fluid from condensed water and uncondensible gas taking place in an accumulator zone, including withdrawing a vent containing uncondensibles and some working fluid from said accumulator zone, said removal of at least a portion of uncondensible gas in said hot water containing fluid prior to introduction into said heat transfer column and the pressure in said accumulator zone being controlled to obtain a predetermined balance between energy recovery in said expander and working fluid loss in said vent gas from said accumulator zone.

Claim 27

Process for recovery of energy from elevated temperature or hot water containing fluids including geothermal brines and other elevated temperature water sources, which comprises introducing said water containing fluid in a heat transfer zone in heat exchange relation therein with a working fluid in liquid form, and heating said working fluid at temperature to produce boiling thereof in the upper portion of said heat transfer zone, said heat transfer zone being maintained at a pressure below the critical pressure of said working fluid, and corresponding to operation at a point on the saturated vapor curve of the Mollier enthalpy-entropy diagram for said working fluid, close to the apex on said saturated vapor curve, expanding the boiling vapors of working fluid in an expander to produce work, cooling and condensing said expanded working fluid, separating said condensed working fluid from condensed water and uncondensible gas, and returning said condensed working fluid under pressure to said heat transfer zone for reheating therein, said separating said cooled and condensed working fluid from condensed water and uncondensible gas taking place in an accumulator zone, including withdrawing a vent gas containing uncondensibles and some working fluid from said accumulator zone, withdrawing cooled water containing fluid from said heat transfer zone, flashing said last mentioned fluid to flash off working fluid contained in said cooled water containing fluid, compressing the resulting vaporized working fluid, and mixing said compressed working fluid with the working fluid discharged from said expander and prior to cooling and condensation thereof, said flashing said cooled water containing fluid being carried out in a flash zone at a pressure less than the pressure in said accumulator zone.

Claim 28

Process for recovery of energy from elevated temperature or hot water containing fluids including geothermal brines and other elevated temperature water sources, which comprises introducing said water containing fluid in a heat transfer zone in heat exchange relation therein with a working fluid in liquid form, and heating said working fluid at temperature to produce boiling thereof in the upper portion of said heat transfer zone, said heat transfer zone being maintained at a pressure below the critical pressure of said working fluid, and corresponding to operation at a point on the saturated vapor curve of the Mollier enthalpy-entropy diagram for said working fluid, close to the apex on said saturated vapor curve, expanding the boiling vapors of working fluid in an expander to produce work, cooling and condensing said expanded working fluid, separating said condensed working fluid from condensed water and uncondensible gas, and returning said condensed working fluid under pressure to said heat transfer zone for reheating therein, said separating said cooled and condensed working fluid from condensed water and uncondensible gas taking place in an accumulator zone, including withdrawing a vent gas containing uncondensibles and some working fluid from said accumulator zone, withdrawing cooled water containing fluid from said heat transfer zone, flashing said last mentioned fluid to flash off working fluid contained in said cooled water containing fluid, compressing the resulting vaporized working fluid, and mixing said compressed working fluid with the working fluid discharged from said expander and prior to cooling and condensation thereof, said flashing said cooled water containing fluid being carried out in a flash zone at a pressure less than the pressure in said accumulator zone.

Claim 29

The process as defined in claim 26, including withdrawing cooled water containing fluid at a moderately elevated temperature from said flash zone, introducing said last mentioned water containing fluid into a second heat transfer zone in heat exchange relation with a second working fluid in liquid form, and heating and boiling said second working fluid in said second heat transfer zone, said second heat transfer zone being maintained at a pressure below the critical pressure of said second working fluid, and corresponding to operation at a point close to the apex on the saturated vapor curve of the Mollier enthalpy-entropy for said second working fluid, said second working fluid being different from said first working fluid, expanding the boiling vapors of said heated second working fluid in a second expander to produce work, cooling and condensing said expanded second working fluid, separating the resulting condensed working fluid from condensed water and uncondensible gas, and returning said condensed second working fluid under pressure to said second heat transfer zone.

Claim 30

The process as defined in claim 27, wherein the working fluid in the first heat transfer zone is a single paraffin or olefin hydrocarbon containing from about 1 to about 8 carbon atoms, and said second different working fluid is a mixture of such hydrocarbons.

Claim 31

The process as defined in claim 28, said separating said cooled and condensed second working fluid from condensed water taking place in a second accumulator zone, including withdrawing a vent gas from said second accumulator zone, withdrawing cooled water containing fluid from said second heat transfer zone, flashing said last mentioned fluid to flash said working fluid contained in said last mentioned water containing fluid, compressing the resulting vaporized second working fluid, and mixing said compressed second working fluid with the second working fluid discharged from said second expander.

Claim 32

The process as defined in claim 26, including withdrawing condensed water from said accumulator zone and passing said condensed water into said flash zone.

Claim 33

The process as defined in claim 30, including passing a portion of said vent gas containing uncondensibles and some working fluid withdrawn from said accumulator zone, into said flash zone.

Claim 34

The process as defined in claim 31, including the step of removing at least a portion of uncondensible gas in said water containing fluid prior to introduction thereof into said heat transfer zone.

Claim 35

The process as defined in claim 32, said working fluid being a paraffinic or olefinic hydrocarbon selected from the group consisting of methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane and neopentane, and the analogous olefins, and mixtures thereof.

Claim 36

The process as defined in claim 26, including withdrawing condensed water from said accumulator zone, passing said condensed water into another separate flash zone, flashing said condensed water therein to flash off working fluid in said condensed water, mixing the resulting vaporized working fluid with vaporized working fluid from the first flash zone prior to compression thereof, and withdrawing relatively pure water from said separate flash zone.

Claim 37

The process as defined in claim 26, said heat transfer zone being a heat transfer column, said water containing fluid being in direct contact heat exchange relation with said working fluid in said heat transfer column, said water containing fluid being introduced into said heat transfer column at a temperature ranging from about 100° to about 600° F, and said heat transfer column being maintained at a pressure ranging from about 200 to about 700 psia, the expander oulet pressure being in the range of about 1 to about 600 psia, said working fluid being cooled and condensed to a temperature in the range of about 80° to about 140° F, and said flash zone being maintained at a pressure ranging from about 15 to about 250 psia and at a temperature ranging from about 80° to about 140° F.

Claim 38

The process as defined in claim 35, including withdrawing condensed water from said accumulator zone and passing said condensed water into said flash zone, and passing a portion of said vent gas containing uncondensibles and some working fluid withdrawn from said accumulator zone, into said flash zone.

Claim 39

The process as defined in claim 36, including the step of removing at least a portion of uncondensible gas in said water containing fluid prior to introduction thereof into said heat transfer column.

Claim 40

The process as defined in claim 37, said removal of at least a portion of uncondensible gas in said water containing fluid prior to introduction thereof into said heat transfer column, and the pressure in said accumulator zone being controlled to obtain a predetermined balance between energy recovery in said expander and working fluid loss in said vent gas from said accumulator zone.

Claim 41

Process for recovery of energy from hot water containing fluids including geothermal brines and other hot water sources, which comprises pumping said fluid into the top zone of a heat transfer column in direct contact heat exchange relation with a working fluid in liquid form, said working fluid being a paraffinic or olefinic hydrocarbon containing from about 1 to about 8 carbon atoms, or mixtures thereof, and heating said working fluid at temperature to produce boiling thereof in the upper portion of said heat transfer zone, said working fluid in said top zone of said heat transfer column being at a pressure below the critical pressure of said working fluid, and corresponding to operation at a point on the saturated vapor curve of a Mollier diagram plotting enthalpy as ordinate and entropy as abscissa, for said working fluid, said point being near the apex of said saturated vapor curve, said operation being carried out at a point on said saturated vapor curve which is 0 to about 5% less than the enthalpy value at said apex, withdrawing the boiling vapors of working fluid from said column and expanding said vapors in an expander to produce work, not more than about 10% by weight of the vapors expanded in said expander being converted to the liquid phase, cooling and condensing said expanded working fluid, separating said condensed working fluid from condensed water and uncondensible gas in an accumulator zone, returning said condensed working fluid to the lower zone of said heat transfer column for reheating therein, withdrawing a vent gas containing uncondensibles and some working fluid from said accumulator zone, withdrawing cooled water containing fluid from the bottom zone of said heat transfer column and passing said fluid to a flash zone, withdrawing condensed water from said accumulator zone and passing said condensed water into said flash zone, flashing the fluids in said flash zone to flash off working fluid, compressing the resulting vaporized working fluid, and mixing said compressed working fluid with the working fluid discharged from said expander and prior to cooling and condensation thereof, said flashing said cooled water containing fluid and said condensed water from said accumulator zone, in said flash zone, being carried out at a pressure therein less than the pressure in said accumulator zone.

Claim 42

Process for recovery of energy from hot water containing fluids including geothermal brines and other hot water sources, which comprises pumping said fluid into the top zone of a heat transfer column in direct contact heat exchange relation with a working fluid in liquid form, said working fluid being a paraffinic or olefinic hydrocarbon containing from about 1 to about 8 carbon atoms, or mixtures thereof, and heating said working fluid at temperature to produce boiling thereof in the upper portion of said heat transfer zone, said working fluid in said top zone of said heat transfer column being at a pressure below the critical pressure of said working fluid, and corresponding to operation at a point on the saturated vapor curve of a Mollier diagram plotting enthalpy as ordinate and entropy as abscissa, for said working fluid, said point being near the apex of said saturated vapor curve, said operation being carried out at a point on said saturated vapor curve which is 0 to about 5% less than the enthalpy value at said apex, withdrawing the boiling vapors of working fluid from said column and expanding said vapors in an expander to produce work, not more than about 10% by weight of the vapors expanded in said expander being converted to the liquid phase, cooling and condensing said expanded working fluid, separating said condensed working fluid from condensed water and uncondensible gas in an accumulator zone, returning said condensed working fluid to the lower zone of said heat transfer column for reheating therein, withdrawing a vent gas containing uncondensibles and some working fluid from said accumulator zone, withdrawing cooled water containing fluid from the bottom zone of said heat transfer column and passing said fluid to a flash zone, withdrawing condensed water from said accumulator zone and passing said condensed water into said flash zone, flashing the fluids in said flash zone to flash off working fluid, compressing the resulting vaporized working fluid, and mixing said compressed working fluid with the working fluid discharged from said expander and prior to cooling and condensation thereof, said flashing said cooled water containing fluid and said condensed water from said accumulator zone, in said flash zone, being carried out at a pressure therein less than the pressure in said accumulator zone.

Claim 43

The process as defined in claim 39, including discharging cooled water containing fluid from said flash zone, and removing any scale from the bottom zone of said heat transfer column.

Claim 44

The process as defined in claim 39, said hot water containing fluid being introduced into said heat transfer column at a temperature ranging from about 150° to about 400° F, and said heat transfer column being maintained at a pressure ranging from about 200 to about 700 psia, the expander outlet pressure being in a range of from about 30 to about 250 psia, said working fluid being cooled and condensed in a cooler to a temperature in the range of about 80° to about 140° F, and said flash zone being maintained at a pressure ranging from about 15 to about 250 psia and at a temperature ranging from about 80° to 140° F.

Claim 45

The process as defined in claim 41, said removal of at least a portion of uncondensible gas in said hot water containing fluid prior to introduction thereof into said heat transfer column and the pressure in said accumulator zone being controlled to obtain a predetermined balance between energy recovery in said expander and working fluid loss in said vent gas from said accumulator zone, including discharging cooled water containing fluid from said flash zone, and removing any scale from the bottom zone of said heat transfer column.

Claim 46

System for recovering energy from hot water containing fluids including geothermal brines and other hot water sources, which comprises in combination a heat transfer column, pump means for pressurizing and introducing said hot water containing fluid into said column, means for introducing a working fluid into said column, means for maintaining said heat transfer column below the critical pressure of said working fluid, and corresponding to operation at a point on the saturated vapor curve of the Mollier enthalpy-entropy diagram for said working fluid, close to the apex on said saturated vapor curve, means providing a boiling zone for said working fluid at the top of the column, an expander, means for withdrawing hot working fluid from said column and introducing said fluid as feed to said expander, cooling means for cooling and condensing said expanded working fluid, accumulator means for separating and condensing working fluid from condensed water and uncondensible gas, conduit means interconnecting said expander, said cooling means and said accumulator means, and means for returning said condensed working fluid to said heat transfer column.

Claim 47

System for recovering energy from hot water containing fluids including geothermal brines and other hot water sources, which comprises in combination a heat transfer column, pump means for pressurizing and introducing said hot water containing fluid into said column, means for introducing a working fluid into said column, means for maintaining said heat transfer column below the critical pressure of said working fluid, and corresponding to operation at a point on the saturated vapor curve of the Mollier enthalpy-entropy diagram for said working fluid, close to the apex on said saturated vapor curve, means providing a boiling zone for said working fluid at the top of the column, an expander, means for withdrawing hot working fluid from said column and introducing said fluid as feed to said expander, cooling means for cooling and condensing said expanded working fluid, accumulator means for separating and condensing working fluid from condensed water and uncondensible gas, conduit means interconnecting said expander, said cooling means and said accumulator means, and means for returning said condensed working fluid to said heat transfer column.

Claim 48

The system as defined in claim 43, including means for removing at least a portion of uncondensible gas in said hot water containing fluid prior to introduction thereof into said heat transfer column.

Claim 49

System for recovering energy from hot water containing fluids including geothermal brines and other hot water sources, which comprises in combination a heat transfer column, pump means for pressurizing and introducing said hot water containing fluid into said column, means for introducing a working fluid into said column, means for maintaining said heat transfer column below the critical pressure of said working fluid, means providing a boiling zone for said working fluid at the top of the column, an expander, means for withdrawing hot working fluid from said column and introducing said fluid as feed to said expander, cooling means for cooling and condensing said expanded working fluid, accumulator means for separating and condensing working fluid from condensed water and uncondensible gas, conduit means interconnecting said expander, said cooling means and said accumulator means, and means for returning said condensed working fluid to said heat transfer column, conduit means for withdrawing cooled water containing fluid from the bottom portion of said heat transfer column, flash means, said conduit means communicating with said flash means for introducing said cooled water containing fluid therein, means for compressing the resulting vaporized working fluid withdrawn from said flash means, conduit means interconnecting said flash means and said compressing means, and conduit means from the discharge of said compressing means for mixing the compressed working fluid with the working fluid discharged from said expander and prior to introduction thereof into said cooling means.

Claim 50

System for recovering energy from hot water containing fluids including geothermal brines and other hot water sources, which comprises in combination a heat transfer column, pump means for pressurizing and introducing said hot water containing fluid into said column, means for introducing a working fluid into said column, means for maintaining said heat transfer column below the critical pressure of said working fluid, means providing a boiling zone for said working fluid at the top of the column, an expander, means for withdrawing hot working fluid from said column and introducing said fluid as feed to said expander, cooling means for cooling and condensing said expanded working fluid, accumulator means for separating and condensing working fluid from condensed water and uncondensible gas, conduit means interconnecting said expander, said cooling means and said accumulator means, and means for returning said condensed working fluid to said heat transfer column, conduit means for withdrawing cooled water containing fluid from the bottom portion of said heat transfer column, flash means, said conduit means communicating with said flash means for introducing said cooled water containing fluid therein, means for compressing the resulting vaporized working fluid withdrawn from said flash means, conduit means interconnecting said flash means and said compressing means, and conduit means from the discharge of said compressing means for mixing the compressed working fluid with the working fluid discharged from said expander and prior to introduction thereof into said cooling means.

Claim 51

The system as defined in claim 45, including means for withdrawing a vent gas containing uncondensibles and some working fluid from said accumulator means, and conduit means for withdrawing condensed water from said accumulator means and passing said condensed water into said flash means.

Claim 52

The system as defined in claim 46, including conduit means for passing a portion of said vent gas containing uncondensibles and some working fluid from said accumulator means to said flash means.

Claim 53

The system as defined in claim 47, including means for removing at least a portion of uncondensible gas in said hot water containing fluid prior to introduction thereof into said heat transfer column.

Claim 54

Process for recovery of energy from elevated temperature or hot water containing fluids including geothermal brines and other elevated temperature water sources, which comprises introducing said water containing fluid in a heat transfer zone in heat exhange relation therein with a working fluid in liquid form, and heating said working fluid at temperature to produce boiling thereof in the upper portion of said heat transfer zone, said heat transfer zone being maintained at a pressure below the critical pressure of said working fluid, and corresponding to operation at a point on the saturated vapor curve of the Mollier enthalpy-entropy diagram for said working fluid, close to the apex on said saturated vapor curve, expanding the boiling vapors of working fluid in an expander to produce work, cooling and condensing said expanded working fluid, separating said condensed working fluid from condensed water and uncondensible gas, and returning said condensed working fluid under pressure to said heat transfer zone for reheating therein, withdrawing cooled water containing fluid from said heat transfer zone, flashing said last mentioned fluid to flash off working fluid contained in said cooled water containing fluid, compressing the resulting vaporized working fluid, and mixing said compressed working fluid with the working fluid discharged from said expander and prior to cooling and condensation thereof.

Claim 55

Process for recovery of energy from elevated temperature or hot water containing fluids including geothermal brines and other elevated temperature water sources, which comprises introducing said water containing fluid in a heat transfer zone in heat exhange relation therein with a working fluid in liquid form, and heating said working fluid at temperature to produce boiling thereof in the upper portion of said heat transfer zone, said heat transfer zone being maintained at a pressure below the critical pressure of said working fluid, and corresponding to operation at a point on the saturated vapor curve of the Mollier enthalpy-entropy diagram for said working fluid, close to the apex on said saturated vapor curve, expanding the boiling vapors of working fluid in an expander to produce work, cooling and condensing said expanded working fluid, separating said condensed working fluid from condensed water and uncondensible gas, and returning said condensed working fluid under pressure to said heat transfer zone for reheating therein, withdrawing cooled water containing fluid from said heat transfer zone, flashing said last mentioned fluid to flash off working fluid contained in said cooled water containing fluid, compressing the resulting vaporized working fluid, and mixing said compressed working fluid with the working fluid discharged from said expander and prior to cooling and condensation thereof.