Geothermal Extractor

Abstract

The geothermal extractor includes a heat transfer fluid and a heat transfer fluid supply conduit. The heat transfer fluid is maintained in the supply conduit in a liquid state at a pressure equal to or greater than its saturation pressure. The geothermal extractor further includes a heat transfer fluid return conduit, a geothermal heat source coupled thereto, at least one flow control valve configured to control a flow of the heat transfer fluid from the supply conduit to the return conduit, and an external load coupled to the return conduit. As the heat transfer fluid is supplied in a liquid state to the return conduit, the heat transfer fluid is vaporized in the return conduit by heat supplied from the geothermal heat source to the return conduit. The vaporized heat transfer fluid is supplied from the return conduit to the external load.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims priority to U.S. Provisional Application No. 63 / 292,055, filed December 21, 2021, the disclosure of which is incorporated herein by reference in its entirety. [Background technology]

[0002] Geothermal energy is of growing interest due to its potential to reduce emissions and consumption of non-renewable resources. Geothermal energy sources, such as abandoned oil wells, provide a readily available source of heat that does not have the constraints of needing batteries for energy storage, as do wind and solar power systems. Geothermal energy is continuous and does not require battery storage.

[0003] The thermal loads for which geothermal systems supply heat can be for residential and / or commercial / industrial heating and / or power generation. Water flow loops are a very common and widespread method for heat extraction. Closed loop liquid systems can be gravity driven, with the difference in density between heated and unheated liquids creating buoyancy that drives circulation. In this case, the resulting flow rate and therefore the amount of heat extracted may be increased by the use of pumps. However, a major drawback of water flow loops is the limited amount of heat extracted per unit mass flow rate and the gradually diminishing temperature at which heat transfer occurs.

[0004] Electricity generation from geothermal energy resources is typically achieved through the use of conventional steam turbines or binary plants. Conventional steam turbines require a fluid to be above 150° C. This hot, high-pressure fluid (e.g., water) is "flashed" to produce steam that drives a turbine to generate electricity. However, the thermodynamic properties of water limit the application of this type of generator to high-temperature geothermal resources.

[0005] Intermediate and low temperature geothermal sources are of interest due to their widespread availability. Historically, a challenge with such sources has been the difficulty of meeting the cost / economic requirements for a practical system. For example, the water drawn from a low temperature geothermal source may not contain enough energy to flash enough water steam at sufficient pressure to drive a turbine. Thus, such systems require a large amount of pumping power to extract enough heat to produce the high levels of water flow required to meet operational requirements. However, the thermal energy held in the water is transferred to a secondary fluid (thermal oil or silicone-based oil) that has an even lower boiling point. The secondary fluid is "flashed" to generate enough steam and pressure to drive a turbine. This process, commonly referred to as the Organic Rankine Cycle (ORC), allows for the generation of electricity from a low temperature fluid at 75°C.

[0006] However, the amount of heat that can be transferred from the heat source to the converter at a given mass flow rate is limited by the specific heat capacity of the water. In addition to being constrained by the need for large amounts of pumping power, there is a decreasing gradient temperature change as the water absorbs and releases heat. Because the heat transfer water cools as heat is transferred to the converter, the temperature of the heat coupled to the converter can be significantly lower than the geothermal source temperature, resulting in less than optimal system efficiency. Therefore, a balance must be struck between the flow rate (pumping power consumed) and the temperature change of the water used to couple the geothermal heat from the heat source to the converter.

[0007] Heat extraction can be enhanced using buoyancy driven water currents. Heat transport can be enhanced using specialized working fluids that evaporate at geothermal source temperatures at pressure levels sufficient to drive the return flow to the surface in vapor form. The heat transfer rate is enhanced by a phase change in the working fluid. However, these fluids are organic liquids or other materials that are expensive and impractical for use in many heat extraction situations.

[0008] It would therefore be desirable to provide improved methods and systems for efficiently and practically extracting heat from geothermal sources. Summary of the Invention

[0009] In general, one embodiment comprises a geothermal heat extractor including a heat transfer fluid and a heat transfer fluid supply conduit. The heat transfer fluid is maintained in the heat transfer fluid supply conduit in a liquid state at a pressure equal to or greater than its saturation pressure. The geothermal heat extractor further includes a heat transfer fluid return conduit, a geothermal heat source coupled to the heat transfer fluid return conduit, at least one flow control valve configured to control a flow of the heat transfer fluid from the heat transfer fluid supply conduit to the heat transfer fluid return conduit, and an external load coupled to the heat transfer fluid return conduit. As the heat transfer fluid is supplied in a liquid state to the heat transfer fluid return conduit, the heat transfer fluid is vaporized in the heat transfer fluid return conduit by heat supplied from the geothermal heat source to the heat transfer fluid return conduit. The vaporized heat transfer fluid is supplied from the heat transfer fluid return conduit to the external load.

[0010] In one embodiment, the heat transfer fluid is water.

[0011] In another embodiment, the external load is a heat load and the vaporized heat transfer fluid supplied to the heat load is condensed back into a liquid state, thereby releasing its latent heat of condensation.

[0012] In another aspect, a liquid phase heat transfer fluid pump is coupled to the heat transfer fluid supply conduit and configured to supply heat transfer fluid to the at least one flow control valve at a pressure equal to or greater than the vapor pressure of the heat transfer fluid at the temperature of the heat source.

[0013] In another aspect, at least one sensor monitors the contents of the heat transfer fluid return conduit and a controller is coupled to the at least one sensor and the at least one flow control valve, and the controller is configured to operate the at least one flow control valve to regulate a flow of the heat transfer fluid in a liquid state into the heat transfer fluid return conduit at a predetermined rate such that the heat transfer fluid in a liquid state is vaporized in the heat transfer fluid return conduit by heat transferred from the geothermal source and liquid accumulation in the heat transfer fluid return conduit is prevented.

[0014] In another aspect, the external load is a power generating load. In yet another aspect, the power generating load is an electrochemical heat-to-electric converter. In yet another aspect, the electrochemical heat-to-electric converter includes a hydrogen chamber, a working fluid chamber coupled to a heat transfer fluid return conduit and configured to receive a vaporized heat transfer fluid from the heat transfer fluid return conduit, the vaporized heat transfer fluid being a working fluid flowing through the working fluid chamber, a condensation chamber coupled to the hydrogen chamber to supply hydrogen to the hydrogen chamber and coupled to the working fluid chamber to receive the working fluid from the working fluid chamber, and a plurality of membrane electrode assemblies. Each membrane electrode assembly includes an anode, a cathode, and a proton conducting membrane sandwiched between the anode and the cathode. The anode of the membrane electrode assembly is disposed in the hydrogen chamber and exposed to a flow of hydrogen provided from the condensation chamber. The cathode of the membrane electrode assembly is disposed in the working fluid chamber and exposed to the working fluid flowing through the working fluid chamber.

[0015] In another embodiment, the membrane electrode assemblies are electrically connected in series.

[0016] In another aspect, the vaporized heat transfer fluid condenses in a condensation chamber under isothermal or near isothermal conditions.

[0017] In another aspect, the working fluid is passed sequentially through the cathodes of the membrane electrode assemblies, where the working fluid gradually and sequentially releases its latent heat of vaporization to each membrane electrode assembly, thereby generating electricity while approximating constant or near constant temperature condensation of the working fluid. [Brief description of the drawings]

[0018] [Figure 1] 1 is a schematic diagram of a geothermal extraction system according to an embodiment of the present invention in a pre-operational mode. [Diagram 2] FIG. 2 is a schematic diagram of the geothermal extraction system shown in FIG. 1 in an operational mode supplying heat to a heat load. [Diagram 3]FIG. 1 is a diagram of a geothermal heat extraction system according to an embodiment of the present invention using a single well with a distributed flash control valve to generate steam to drive an expansion turbine. [Figure 4a] FIG. 2 is a top cross-sectional view of a geothermal heat extraction system according to an embodiment of the present invention, the system having a concentric tube heat extractor and utilizing a distributed flush flow control valve. [Figure 4b] FIG. 4b is a side cross-sectional view of the geothermal extraction system shown in FIG. 4a. [Diagram 5] FIG. 1 is a schematic cross-sectional view of a geothermal heat extraction system according to an embodiment of the present invention, in which the external load is a power generating load in the form of an electrochemical heat-to-electric converter. [Figure 6] FIG. 6 is a schematic cross-sectional view of the geothermal extraction system shown in FIG. 5 with an expanded view of the electrochemical heat-to-electric converter. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The following detailed description of the preferred embodiments of the invention will be better understood when read in connection with the accompanying drawings, in which: For the purpose of illustrating the invention, there is shown in the drawings embodiments which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.

[0020] In one aspect, the present invention relates to a geothermal system that operates on a low to medium temperature heat source and has improved efficiency and cost-effectiveness compared to conventional geothermal systems. The extractor of the present invention flash-evaporates a heat transfer fluid, preferably water, at the heat source. The heat of vaporization of water and other liquids is generally significantly greater than the specific heat of a given fluid. Thus, the process allows a larger amount of heat to be extracted at a given mass flow rate. The resulting steam is supplied to a heat load where it is condensed and releases its latent heat without significant temperature loss (i.e. isothermally or nearly isothermally) so that the temperature at which the water vapor releases its latent heat is the same or nearly the same as the temperature of the geothermal source. Also, the transport of water vapor from the geothermal source can be performed with very limited pressure loss.

[0021] 1-2, in one embodiment, the geothermal heat extractor of the present invention comprises a heat source 4, a heat transfer fluid supply conduit 16, a heat transfer fluid return conduit 10, and one or more flow control valves. The conduits 10, 16 may be made from standard steel oil well piping, although other similar materials may be used. The heat transfer return conduit is optionally insulated to avoid cooling and condensation of water vapor by the surrounding soil as it rises in the piping. The heat transfer fluid supply conduit 16 and the heat transfer fluid return conduit 10 preferably extend in a single or separate wells or boreholes formed in and through the earth. Thus, a portion of each of the supply conduit 16 and the return conduit 10 is preferably located below ground, and another portion of each conduit 16, 10 is located above ground. The wells may extend vertically, horizontally, or a combination of vertical and horizontal.

[0022] In one embodiment, each well is an abandoned well, preferably an abandoned oil well, although it should be understood by those skilled in the art that the present invention is not limited to abandoned wells. The wells may be other types of abandoned wells, or may be actively formed near a geothermal source, such as a hot spring, specifically for the purpose of constructing the heat extraction system of the present invention.

[0023] The heat source 4 is preferably a geothermal source such as a hot spring. The heat source 4 is preferably coupled to the return conduit 10 such that it is configured to supply heat to the return conduit 10. The heat source may range from about 50° C. to about 600° C. or higher. For abandoned oil wells, the temperature range may be as low as about 50° C. to about 250° C.

[0024] 1-2, the geothermal heat extractor of the present invention preferably further comprises a pump 12 configured to remove liquid from the return conduit 10, a port 14 coupled to a source of heat transfer fluid, an external load 18 in fluid communication with the return conduit 10, a condenser 42, and a controller 32. In the embodiment of Figures 1-2, the external load 18 is a heat load.

[0025] In particular, the extractor preferably includes at least one fluid flow control valve 26 that controls the supply of heat transfer fluid from the supply conduit 16 to the return conduit 10. Such valves are referred to herein as flush flow control valves 26. More preferably, the extractor includes first and second flush flow control valves 26 that control the supply of heat transfer fluid from the supply conduit 16 to the return conduit 10. The flush flow control valves 26 are provided at spaced locations along the underground length of the supply conduit 16. The distribution of the flush flow control valves 26 is preferably selected to optimize steam production.

[0026] The heat extractor preferably further comprises a fluid flow control valve 8 disposed between the pump 12 and the return conduit 10 to regulate the flow of fluid removed from the return conduit 10 by the pump 12. The extractor preferably further comprises a fluid flow control valve 11 disposed between the heat transfer fluid supply port 14 and the heat transfer fluid supply conduit 16 to regulate the flow of heat transfer fluid from the source to the supply conduit 16 via the port 14. The extractor preferably further comprises a third fluid flow control valve 30 disposed between the heat transfer fluid supply conduit 16 and the heat transfer fluid return conduit 10 to regulate the flow of fluid from the return conduit 10 to the supply conduit 16.

[0027] The heat transfer fluid is preferably a vaporizable liquid. Preferably, the heat transfer fluid is water, since heat can be conducted to the underground piping by the aquifer around the well or by the surrounding solid soil, although there may be embodiments in which other possible working fluids can be used, such as ammonia, fluorocarbons, organic fluids, etc.

[0028] In a first mode in which the extractor is prepared for operation, as shown in FIG. 1, initially the fluid flow control valves 8, 11 are opened and the fluid flow control valve 30 and the flush flow control valve 26 are closed. In the preparation configuration of FIG. 1, the pump 12 is operated to remove substantially all liquid present in the heat transfer fluid return conduit 10. Heat transfer fluid is supplied to the heat transfer fluid supply conduit 16. More specifically, in the pre-operation mode shown in FIG. 1, initially the fluid flow control valve 8 is opened and the pump 12 is operated to pull liquid from the heat transfer fluid return conduit 10 to bring the heat transfer fluid return conduit 10 to a pressure below the vapor pressure of the heat transfer liquid. The pressure may be dependent on the working fluid being used. The removed liquid may be discarded. The well may be empty when drilling is completed and the well is "completed", in which case only liquid needs to be supplied to the well. The heat transfer fluid return conduit 10 is preferably pumped out completely or nearly completely dry (i.e., completely or nearly completely free of liquid). Once the heat transfer fluid return conduit 10 is at low pressure, valve 8 is closed, thereby ensuring that the heat transfer fluid return conduit 10 remains at low pressure. Additionally, in the pre-operation mode of FIG. 1, the fluid flow control valve 11 is first opened to allow heat transfer fluid, now in liquid state, to be supplied from the source port 14 to the heat transfer fluid supply conduit 16. This may occur before, after and / or simultaneously with pumping out the return conduit 10. The fluid flow control valve 11 is closed after the heat transfer fluid supply conduit 16 is sufficiently filled with heat transfer fluid in liquid state so that the resulting pressure created by the fluid density under gravity may exceed the vapor pressure of the hot side liquid at the bottom of the well. The vapor pressure and fluid density may be dependent on the fluid selected.

[0029] 2 illustrates an embodiment of an operating mode of the geothermal extraction system. During operation, the heat transfer fluid contacts the heat source in its liquid form and is subsequently flash evaporated by the flow control valve to achieve a high level of heat extraction per unit mass flow rate, thereby supplying heat to the heat load 18.

[0030] 2, in operation, fluid flow control valves 8, 11 are closed and flush flow control valve 26 and fluid flow control valve 30 are open. The open position of flush flow control valve 26 allows a controlled amount of heat transfer fluid to move in liquid form from heat transfer fluid supply conduit 16 to heat transfer fluid return conduit 10. Operation of flush flow control valve 26 is coordinated to restrict the flow of heat transfer liquid into heat transfer fluid return conduit 10 so that heat transfer fluid return conduit 10 is not flooded with heat transfer liquid.

[0031] The heat transfer liquid transferred to the vapor return conduit 10 is flash evaporated or flash vaporized by the geothermal source 4, which is achieved by the surrounding hot soil or liquid in intimate contact with the conduit. The vaporization temperature is dependent on pressure and is a physical property of the heat transfer fluid / liquid. Valve 26 regulates the liquid into conduit 10 at a rate commensurate with the rate at which heat is delivered to conduit 10 to vaporize all the liquid without allowing a large amount of liquid to build up inside conduit 10, which causes the steam pressure to push the steam up the conduit 10.

[0032] The heat transfer liquid is preferably supplied from the supply conduit 16 to the heat transfer fluid return conduit 10 via the flash flow control valve 26 at a rate such that continuous vaporization, more specifically continuous flash vaporization, can be maintained in the return conduit 10, taking into account the rate at which heat is supplied to the return conduit 10 by the heat source 4. The heat transfer rate varies depending on the geothermal properties of the rock or surrounding liquid surrounding the conduit 10. Thus, the latent heat of vaporization may be a physical property of the material of the heat transfer fluid / liquid selected, extracted from the heat source 4. The heat of vaporization of the heat transfer liquid is greater than the specific heat of the heat transfer fluid. Thus, the geothermal heat extractor is configured to extract a large amount of heat for a given mass flow rate.

[0033] The resulting vaporized heat transfer fluid (e.g., water vapor if the heat transfer fluid is water) travels vertically upward in the return conduit 10 toward the external load 18. In the embodiment of Figs. 1-2 where the external load 18 is a heat load, the heat load 18 preferably includes or is provided with a condenser 42. The vaporized heat transfer fluid condenses at the heat load 18 and releases its latent heat without significant temperature loss (i.e., under isothermal or near isothermal conditions). That is, the vaporized heat transfer fluid condenses at the heat load 18 and releases its latent heat at or near the same temperature as the temperature of the geothermal source. The heat of condensation of the heat transfer fluid is supplied to the heat load 18 for power generation, and the condensed heat transfer fluid is returned to the heat transfer fluid supply conduit 16 via the open fluid flow control valve 30. The heat of condensation is a physical property of the heat transfer fluid used in the system. The system is sized based on the available heat and the rate at which it will be conducted to the conduit 10 by the surrounding soil and liquids (eg, water).

[0034] The use of latent heat as a transport mechanism in this manner provides significantly enhanced performance for geothermal extraction and power generation. In one embodiment, the heat transfer fluid is preferably saturated throughout the geothermal extraction system so that the condensation temperature at the heat load 18 is similar to the vaporization temperature downhole.

[0035] Alternatively, in other embodiments, depending on the temperature of the heat source 4, the rate of heat transfer to the return conduit 10, and the fluid flow rate through the flash flow control valve 26, the vaporized heat transfer fluid reaching the heat load 18 may be superheated. In this case, the condensation temperature at the heat load 18 is only slightly lower than the vaporization temperature downhole due to the higher pressure downhole caused by the gravity load of the steam column in the return conduit 10. The pressure difference is relatively small due to the relatively low density of the steam column in the return conduit 10.

[0036] Thus, in the geothermal heat extraction system of the present invention, the transport of the vaporized heat transfer fluid from the geothermal source 4 (i.e., when it is flash vaporized in the return conduit 10) occurs with minimal pressure loss. Thus, the vaporized heat transfer fluid releases its latent heat at a temperature similar to that of the geothermal source 4.

[0037] In one embodiment, the geothermal extraction system of the present invention includes a controller 32 and one or more sensors 34. The controller 32 is preferably coupled to each of the flush flow control valves 26 and each of the sensors 34. In one embodiment, the controller 32 is also coupled to one or more of the fluid flow control valves 8, 11, and 30. The sensor 34, shown in Figures 1-2, monitors the contents of the heat transfer fluid return conduit 10 for vapor and liquid. Based on the monitoring data received from the sensor 34, the controller operates the flush flow control valve 26 to (i) place the valve 26 in an open position to allow and regulate the flow of heat transfer liquid into the return conduit 10 at a predetermined rate that allows the liquid to vaporize consistent with the rate at which heat is being supplied from the heat source 4 to the return conduit 10, or (ii) place the valve 26 in a closed position to prevent the flow of heat transfer liquid into the return conduit 10, thereby preventing the accumulation of heat transfer liquid in the return conduit 10.

[0038] Those skilled in the art will appreciate that sensors may be utilized in other conduits and locations within the geothermal extraction system of the present invention to monitor various parameters of the system and its components. Those skilled in the art will also appreciate that the controller 32 may be coupled to other flow control valves 8, 11, 30, ports 14, and / or pumps 12, 17 of the system. For example, in one embodiment, the system includes an additional sensor in the return conduit 10 to monitor the pressure in the conduit 10 such that if a predetermined low pressure condition is achieved during the pre-operation mode, the controller 32 is triggered to close the fluid flow control valve 8 and / or terminate operation of the pump 12. In one embodiment, the system includes a sensor in the heat transfer fluid supply conduit 16 to monitor the liquid contents of the supply conduit 16 such that if the supply conduit 16 fills with heat transfer liquid to a predetermined level, the controller 32 is triggered to close the fluid flow control valve 11 and stop the supply of heat transfer liquid from port 14. The controller 32 is also coupled to the fluid flow control valve 30 and can move it between a closed state and an open state as needed for the pre-operational and operational modes, respectively.

[0039] In one embodiment, the heat transfer fluid conduit 16 may include a pump 17. The pump 17 may assist in increasing the pressure in the heat transfer fluid conduit 16. More specifically, the pump 17 may be coupled to the heat transfer fluid conduit 16 to supply heat transfer liquid to the flush flow control valve 26 at a pressure equal to or greater than the vapor pressure of the fluid at the temperature of the heat source 4. As a result, undesirable sporadic vaporization of the liquid in the conduit 16 may be avoided.

[0040] Referring to Figure 3, an alternative embodiment of a geothermal heat extraction system according to the present invention is shown. The reference numbers given to the various components of the system that are the same as those in Figures 1-2 refer to the same components, and therefore a detailed description of those components will not be repeated.

[0041] The system of Figure 3 is particularly configured for use in a single well configuration for heat extraction, such as an abandoned well. In the system of Figure 3, the heat transfer fluid return conduit 10 and the heat transfer fluid supply conduit 16 are configured in a concentric tube configuration 3, although non-concentric configurations may be used as well. Preferably, the heat transfer fluid supply conduit 16 is configured as an inner tube and the heat transfer fluid return conduit 10 is configured as an outer tube, although those skilled in the art will appreciate that a reverse configuration of the inner and outer tubes may be utilized.

[0042] Preferably, both conduits 16, 10 extend vertically into a single well to a predetermined depth and then bend laterally to extend laterally, i.e., generally horizontally, for a predetermined distance. The required depth / distance may depend on the characteristics of the heat store. For example, geysers are often just below ground level, whereas typical oil wells may be about 5,000 to about 20,000 feet or more deep, and the horizontal distance at depth may be about 5,000 to about 20,000 feet or more. Thus, heat is extracted from the heat source 4 at a predetermined depth (i.e., when the conduits 10, 16 are generally oriented horizontally). The concentric tube arrangement 3, and more specifically the heat transfer fluid supply conduit 16, is provided with a plurality of flush flow control valves 26 at spaced locations along its lateral length. The flush flow control valves 26 are preferably distributed along the length of the concentric tube arrangement 3 at a predetermined depth in locations consistent with the availability of heat from the heat source 4 (i.e., to optimize the use of the heat generated by the heat source 4) for steam generation.

[0043] In FIG. 3, the geothermal extraction system is configured to provide steam, more specifically water vapor, to drive a turbine 44. The water vapor is generated by operation of the heat transfer fluid conduit 16, the heat transfer fluid return conduit 10, the heat source 4, and the valves 8, 11, 26, 30 as described above with respect to FIGS. 1-2 (i.e., as heat transfer liquid is transferred from the supply conduit 16 to the return conduit 10, it is flash vaporized in the return conduit 10 to generate steam). The generated water vapor then travels through the return conduit 10 and is supplied to the expansion turbine 44. The water vapor then enters the condenser 42, and the condensed fluid is returned to the heat transfer fluid supply conduit 16 through the open fluid flow control valve 30.

[0044] 4a and 4b, a diagram of a concentric tube configuration 3 is shown, which may be used, for example, as the concentric tube configuration 3 in the system of FIG. 3. As shown in FIGS. 4a-4b, a heat transfer fluid supply conduit 16, which is preferably at a relatively high pressure, is configured as the inner tube, and a heat transfer fluid return conduit 10, which is at a relatively low pressure, is configured as the outer tube. The inner tube (heat transfer fluid supply conduit) 16 includes a plurality of flush flow control valves 26 distributed along its length in a manner to control the release of liquid heat transfer fluid from the inner tube 16 to the outer tube 10 (i.e., the steam return conduit 10). As discussed above with respect to FIGS. 1-3, when the heat transfer liquid is introduced into the return conduit 10, it vaporizes as heat is transferred from the geothermal source 4 to the steam return conduit 10.

[0045] In one embodiment, the heat extractor may include a layer of insulation 28 between the supply conduit 16 and the return conduit 10, for example wrapped around at least a portion of the exterior of the supply conduit 16, to limit heat transfer from the vaporized fluid to the liquid phase contained within the supply conduit 16. In one embodiment, the heat extractor may include insulation (not shown) along at least a portion of the exterior of the return conduit 10 to limit heat loss from the vaporized fluid to the cooler surroundings in the vertical portion of the return conduit 10 as the steam returns to the surface.

[0046] With reference to Figures 5-6, an embodiment is shown in which the external load is a power generating load. More specifically, in the embodiment of Figures 5-6, the power generating load is an electrochemical heat-to-electricity converter (electrochemical converter) 43, which is connected to a geothermal extractor according to the invention, such as the system of Figures 1-4. In the embodiment of Figures 5-6, the electrochemical converter 43 is coupled to a geothermal extractor of the type shown in Figures 3-4. The electrochemical converter 43 is configured to convert steam, more specifically water vapor, generated by the geothermal extractor into electrical power. In addition to the components of the geothermal extractor as described above, the electrochemical converter 43 comprises a plurality of membrane electrode assemblies 48, more specifically bipolar membrane electrode assemblies 48, configured in a housing 45.

[0047] The membrane electrode assemblies 48 are electrically connected in series. Each membrane electrode assembly (MEA) 48 includes a first electrode 50, a second electrode 54, and a proton conducting membrane 52 sandwiched between the electrodes 50, 54. One of the electrodes 50, 54 is a cathode, and the other of the electrodes 54, 50 is an anode. Hereinafter, the electrode 50 will be referred to as the cathode, and the electrode 54 will be referred to as the anode.

[0048] 6, the series of MEAs 48 may be bounded by an enclosure 60, a portion of which is formed by a proton conducting membrane 52. The area within the enclosure 60 containing the anode (electrode) 54 of the MEA 48 is the first chamber 56, and the area between the enclosure 60 and the housing 45 containing the cathode (electrode) 50 is the second chamber 36. The first chamber 56 is referred to herein as the hydrogen chamber or anode chamber. The second chamber 36 is referred to herein as the working fluid chamber or cathode chamber.

[0049] The electrochemical converter 43 further comprises a gas separation chamber (condenser) 40, also referred to herein as a condenser, which contains the hydrogen and water 38. The electrochemical converter 43 utilizes a working fluid. Preferably, the working fluid is provided from a geothermal heat extractor.

[0050] A conduit 33 couples the condenser 40 to the hydrogen chamber 56. The conduit 33 may be a separate component from the enclosure 60, which is coupled to the enclosure 60, or the conduit 33 may be an extension of the enclosure 60 (i.e., integral with the enclosure 60). A first end, i.e., the inlet, of the working fluid chamber 36 is coupled to the heat transfer fluid return conduit 10 such that vaporized heat transfer fluid from the return conduit 10 is supplied to the first end of the working fluid chamber 36. A second end, i.e., the outlet, of the working fluid chamber 36 is coupled to the condenser 40 such that a flow of working fluid 32 is supplied from the working fluid chamber 36 to the condenser 40.

[0051] Referring to FIG. 6, the electrochemical converter 43 is shown in an operating mode. In operation, hydrogen 34 from the condenser 40 is fed to the hydrogen chamber 56, more specifically to the anode 54 of the series of MEAs 48, thereby forming the high partial pressure state or side of the MEA 48. As the hydrogen 34 passes over the anode 54, protons are conducted through the proton conducting membrane 52 to the cathode 50 and electrons are delivered to the load 58. At the same time, the working fluid 32, more specifically water vapor, produced by the geothermal extractor is fed from the geothermal extractor return conduit 10 to the working fluid chamber 36, more specifically to the cathode 50 of the series of MEAs 48, thereby forming the low partial pressure state or side of the MEA 48. The released protons and electrons are reduced to low pressure hydrogen in the cathode 50, while the produced hydrogen is released into the flow of the working fluid (water vapor) 32.

[0052] More specifically, as hydrogen moves between each MEAs 48 under a pressure differential, current flows through the external load 58, hydrogen is oxidized in the anode 54, protons pass through the proton conducting membrane 52 to the cathode 50, and are reduced back to hydrogen as electrons are delivered to the cathode 50 through the load 58. The resulting hydrogen is released into the working fluid chamber 36. A hydrogen pressure differential is created between the MEAs 48 because the working fluid 32, preferably water vapor, entering the working fluid chamber 36 from the return conduit 10 is substantially free of hydrogen. Thus, as the cathode 50 extracts the heat of expansion from the gas stream in the working fluid chamber 36, hydrogen expands from the high pressure conduit, the hydrogen chamber 56, to the low pressure conduit, the working fluid chamber 36. In the working fluid chamber 36, the produced hydrogen mixes with the gas stream 32 from the geothermal extractor, thereby reducing its partial pressure.

[0053] In turn, the hydrogen pressure difference creates a voltage difference across each MEA 48. Hydrogen is oxidized in the electrodes 52. The voltage generated by the MEAs 48 is given by the Nernst equation. The voltage is linear with temperature and a logarithmic function of the hydrogen pressure ratio. The voltage is calculated using the Nernst equation (JH Hirschenhofer, DB Stauffer, RR Engleman, and MG Klett, Fuel Cell Handbook, Fourth Edition, p. 2-5, 1999).

number

[0054] In one embodiment, the working fluid, more specifically water vapor, may be supplied to the working fluid chamber 36 as superheated vapor or in a saturated state. In the saturated vapor state, the working fluid 32 condenses in the condenser 40 to a liquid or mist 46 as its heat of condensation is released to the MEA 48 under its decreasing partial pressure. As the heat of condensation of the water vapor is consumed, the heat of expansion of the hydrogen through the MEA 48 is converted to electrical power. The remaining water vapor is condensed in the gas separation chamber 40 by removal of the residual heat of condensation. Meanwhile, as hydrogen gas 39 is supplied to the hydrogen chamber 56 as shown by arrow 34, the working fluid, now in a liquid state as water 38, self-separates and is supplied to the heat transfer fluid supply conduit 16 through the fluid flow control valve 30. As described above with respect to FIGS. 1-2, a pump 17 may be included to supply the liquid working fluid to the heat transfer fluid supply conduit 16 at an elevated pressure.

[0055] A series of electrically connected MEAs 48 provides the advantage of maximizing power output compared to a single MEA. As hydrogen mixes with the gas stream (working fluid) 32 flowing from the inlet of the working fluid chamber 36 (corresponding to the input from the vapor return conduit 10) to the outlet of the working fluid chamber 36 coupled to the condenser 40, the hydrogen increases in partial pressure, thereby reducing the pressure ratio of the MEA 48. The voltage generated at the first MEA 48 in the series in contact with the working fluid with the highest pressure ratio is higher than the voltage at the last MEA in the series in contact with the working fluid with the lowest hydrogen partial pressure ratio. Adding the voltages of the series results in a higher output power for a given amount of hydrogen conduction through the MEA 48. On the other hand, the voltage generated at a single MEA results in less overall power generation. This is because the lower pressure ratio near the outlet of the MEA balances the higher pressure ratio near the inlet. Energy is lost as a single electrode internally conducts current under the induced end-to-end voltage difference. As hydrogen continues to mix with the water vapor flow along the length of a single MEA, the MEA voltage will be lower and will be based on the average pressure difference of the hydrogen. In contrast, in a series of electrically connected MEAs 48 as in the present invention, each MEA 48 in the series will operate at the average peak pressure difference occurring at any given point along the series. Also, the change in water vapor quality as it flows through the MEA series with heat extraction and pressure reduction can approximate a near constant temperature condensation power generation process for maximum energy conversion.

[0056] Thus, according to the embodiment of Figures 5-6, the voltages generated under the hydrogen pressure differential at each MEA are added together to generate the desired voltage output. As the hydrogen expands through each MEA, the vaporized fluid condenses under near-isothermal conditions as the hydrogen generates power by consuming the working fluid's heat of condensation. The multiple MEAs form a series such that the vaporized working fluid passes sequentially through the cathode with the working fluid gradually and sequentially releasing its latent heat of vaporization to each MEA in the series, thereby approximating a constant temperature condensation process to generate electricity.

[0057] The advantageous results achievable by the present invention are described below in comparison with those achieved by conventional systems.

[0058] As an example of a conventional system, the Chena Hot Springs Generating Station is one of the world's lowest temperature geothermal power plants to date. The Chena Generating Station generates electricity using fluids as cold as 164 degrees Fahrenheit. The Chena Generating Station is often referenced in research and corporate proposals as a benchmark for future low-temperature geothermal power development. The heat transfer fluid, specifically water, is supplied from a geothermal source (i.e., hot springs) at a temperature of 164 degrees Fahrenheit. The water temperature is reduced in a step-down gradient to 130 degrees Fahrenheit as heat is transferred to an organic Rankine engine cycle to generate electricity. Heat is input to the Rankine engine cycle at an average temperature of only 147 degrees Fahrenheit, which adversely affects conversion efficiency. Thus, the system generates a 210 kW e 2.58MW needed to generate electricity HEAT To transfer this heat to the Rankine engine, a very high flow rate of water is required - 530 gallons per minute.

[0059] In contrast, a geothermal extractor according to the present invention, such as the geothermal extractor of FIGS. 1 to 6, can generate 2.58 MW of heat. HEAT of geothermal energy can be produced by flowing steam upwards in a 3048 metre vertical well. Assuming a worst case scenario where the steam density at the top of the well is constant, the pressure at the bottom of the well that is required to move the steam to the top must be greater than the water pressure. Saturated steam at 164 degrees Fahrenheit has a mass of about 0.25 kg / m 3 Therefore, the required pressure (calculated by ρ × g × h) is 0.0075 MPa (i.e., 0.25 kg / m 3 ×9.8m / s 2 x 3048 m). The saturated steam pressure at 164°F is 0.04 MPa, which is more than enough pressure to push the steam to the top of the well. At 164°F, the heat of vaporization of water is 2319 kJ / kg. Thus, the present invention provides a 2.58MW HEATTo return the water to the surface, a water flow of 17 gal / min (i.e., 2580 kW) is required, rather than the 530 gal / min required by conventional systems. HEAT gal / 3.79kg). Furthermore, in the geothermal heat extractor of the present invention, the heat transfer temperature is essentially constant as opposed to being on a decreasing gradient, which in turn provides the added benefit of improving overall system efficiency and net power output.

[0060] Those skilled in the art will appreciate that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that the invention is not limited to the particular embodiments disclosed, but is intended to cover modifications within the spirit and scope of the invention as defined by the following claims.

Claims

1. A heat transfer fluid; a heat transfer fluid supply conduit, the heat transfer fluid being maintained in the heat transfer fluid supply conduit in a liquid state at a pressure equal to or greater than the heat transfer fluid's saturation pressure; a heat transfer fluid return conduit; a geothermal source coupled to the heat transfer fluid return conduit; at least one flow control valve configured to control a flow of the heat transfer fluid from the heat transfer fluid supply conduit to the heat transfer fluid return conduit; an external load coupled to the heat transfer fluid return conduit; Equipped with As the heat transfer fluid is supplied in a liquid state to the heat transfer fluid return conduit, the heat transfer fluid is vaporized within the heat transfer fluid return conduit by heat supplied from the geothermal source to the heat transfer fluid return conduit; A geothermal extractor, wherein the vaporized heat transfer fluid is supplied from the heat transfer fluid return conduit to the external load.

2. 2. The geothermal heat extractor of claim 1, wherein the heat transfer fluid is water.

3. 3. A geothermal heat extractor as claimed in claim 1 or 2, wherein the external load is a heat load and the vaporized heat transfer fluid supplied to the heat load is condensed back to a liquid state, thereby releasing its latent heat of condensation.

4. 4. The geothermal heat extractor of claim 1, further comprising a liquid phase heat transfer fluid pump coupled to the heat transfer fluid supply conduit and configured to supply the heat transfer fluid to the at least one flow control valve at a pressure equal to or greater than the vapor pressure of the heat transfer fluid at the temperature of the geothermal source.

5. at least one sensor for monitoring the contents of the heat transfer fluid return conduit; a controller coupled to the at least one sensor and the at least one flow control valve, the controller configured to operate the at least one flow control valve to regulate a flow of the heat transfer fluid in a liquid state to the heat transfer fluid return conduit at a predetermined rate such that the heat transfer fluid in the liquid state is vaporized in the heat transfer fluid return conduit by heat transferred from the geothermal source and such that accumulation of liquid in the heat transfer fluid return conduit is prevented; 5. The geothermal heat extractor of claim 1 further comprising:

6. 2. The geothermal extractor of claim 1, wherein the external load is a power generating load.

7. 7. The geothermal heat extractor of claim 6, wherein the generating load is an electrochemical heat to electricity converter.

8. The electrochemical heat-to-electric converter comprises: A hydrogen chamber; a working fluid chamber coupled to the heat transfer fluid return conduit and configured to receive the vaporized heat transfer fluid from the heat transfer fluid return conduit, the vaporized heat transfer fluid being a working fluid flowing through the working fluid chamber; a condensation chamber coupled to the hydrogen chamber for supplying hydrogen to the hydrogen chamber and coupled to the working fluid chamber for receiving working fluid from the working fluid chamber; a plurality of membrane electrode assemblies, each membrane electrode assembly comprising an anode, a cathode, and a proton conducting membrane sandwiched between the anode and the cathode; Equipped with the anode of the membrane electrode assembly is disposed within the hydrogen chamber and exposed to a flow of hydrogen provided from the condensation chamber; 8. The geothermal heat extractor of claim 7, wherein the cathode of the membrane electrode assembly is disposed within the working fluid chamber and exposed to the working fluid flowing therethrough.

9. 9. The geothermal heat extractor of claim 8, wherein said membrane electrode assemblies are electrically connected in series.

10. 9. The geothermal heat extractor of claim 8, wherein the vaporized heat transfer fluid condenses in the condensation chamber under isothermal or near isothermal conditions.

11. 10. The geothermal heat extractor of claim 9, wherein the working fluid passes sequentially through the cathodes of the membrane electrode assemblies, the working fluid gradually and sequentially releasing its latent heat of vaporization to each membrane electrode assembly, thereby generating electricity while approximating constant or near constant temperature condensation of the working fluid.

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