Abstract:
The present inventive subject matter is drawn to an apparatus for producing power using geothermal liquid comprising: a geothermal power plant for producing power using heat contained in geothermal liquid supplied thereto; and heating means apparatus for heating a solution and producing a heated solution for use in an electrolysis unit with heat from heat depleted geothermal liquid exiting a vaporizer of the geothermal power plant, wherein the electrolysis unit produces hydrogen for use in producing power.

Description:
This application is a divisional application of Ser. No. 10/861,350, filed Jun. 7, 2004 now abandoned, the contents of which are hereby incorporated in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention relates to a method and apparatus for producing hydrogen using geothermal energy, and more particularly, to a method and apparatus for producing hydrogen via electrolysis using geothermal energy. 
     2. Background of the Invention 
     Recently an increasing interest has been developing in methods of producing renewable energy that produces little or minimal pollution. One of the ways is using hydrogen to produce power or electricity. However, the methods of producing hydrogen at present are rather expensive and also can cause pollution. 
     U.S. Pat. No. 5,661,977 discloses a system for generation of electricity from geothermal energy wherein one or more substances are transported down a well to a depth at which geothermal heat (whether from brine or steam reservoirs or hot, dry rock) is sufficient to cause an endothermic reaction or an electrolysis reaction to occur among substances. In a second embodiment of the invention disclosed in this U.S. patent, a system is disclosed for the generation of electricity from geothermal energy wherein one juncture of a thermocouple is transported down a well to a depth at which geothermal heat is sufficient to create a temperature difference, relative to the temperature of the other juncture of the thermocouple. Such systems are rather complicated to construct so that the costs for constructing such system could be high. 
     Geothermal energy is conventionally produced using a constant flow rate of the geothermal fluid. Due to this, such a geothermal power plant operates at a fixed production level, while on the other hand, consumer power demand varies significantly between peak hours and off-peak hours. As a result, operation of such geothermal power plants is not cost effective. 
     As far as room temperature electrolysis operated at atmospheric pressure is concerned, the energy requirements are relatively high. Thus, electrolysis is a relatively expensive method of producing hydrogen. 
     Fouillac et al. (2003) discuss the use of geothermal heat to pre-heat the solution for high temperature (around 900° C. or more) electrolysis with additional energy sources such as coal- or gas-fired power being combined for such a use. In this paper, it is suggested that the geothermal energy could be combined with nuclear power plant energy. 
     It is therefore an object of the present invention to provide a new and improved method of and apparatus for producing hydrogen and operation of geothermal power plants wherein the disadvantages as outlined above are reduced or substantially overcome. 
     SUMMARY OF THE INVENTION 
     The present inventive subject matter is drawn to apparatus for producing hydrogen using geothermal energy comprising: heating means apparatus for heating a solution for use in electrolysis with heat from geothermal fluid and producing a heated solution; and electrolysis means apparatus for producing hydrogen by electrolysis of said heated solution. 
     The present invention also relates to a method for producing hydrogen using geothermal energy comprising: heating a solution for use in electrolysis with heat from geothermal fluid and producing a heated solution; and producing hydrogen by electrolysis of said heated solution. 
     In a further embodiment of the present invention, apparatus for producing hydrogen using geothermal energy is provided comprising: heating means for heating a solution for use in electrolysis with heat from geothermal fluid and producing a heated solution; electrolysis means apparatus for producing hydrogen by electrolysis of said heated solution; and power producing means utilizing the pressure of said hydrogen for producing power. 
     In this embodiment, a method for producing hydrogen using geothermal energy is also provided comprising: heating a solution for use in electrolysis with heat from geothermal fluid and producing a heated solution; producing hydrogen by electrolysis of said heated solution; and utilizing the pressure of said hydrogen for producing power. 
     The integration of geothermal and electrolysis plants of the present invention as described herein is advantageous since the efficiency of the integrated or combined geothermal and electrolysis plant is higher than independently operated plants. This is achieved by using the heat present in the geothermal fluid for heating the solution prior to electrolysis and also permitting the use of the pressure of the hydrogen and/or oxygen electrolysis products in the pumping of brine to be injected into the injection well of the geothermal power plant. 
     Furthermore, the method and apparatus of the present invention permits the integrated or combined geothermal and electrolysis plant to have flexible modes of operation during peak and off-peak demand hours. In particular, the hydrogen and oxygen produced by the electrolysis system of the present invention are energy storage vehicles that enable the shift of off-peak geothermal power to be sold and consumed during periods of peak power demand. The local use of the electrolysis hydrogen and oxygen products make it unnecessary to use high-pressure storage or transportation of these gases. Consequently, the available pressure of the electrolysis produced hydrogen and oxygen can be used for other purposes. More importantly, the above-mentioned flexibility of operation of the integrated or combined plant is achieved while the geothermal fluid pumping rate remains substantially constant. This is achieved by using a combination of valves that permits the variable diversion of the geothermal fluid from the geothermal power plant to the electrolysis system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A description of the present inventive subject matter including embodiments thereof is presented and with reference to the accompanying drawings, the description is not meant to be considered limiting in any manner, wherein: 
         FIG. 1  is a graphical representation of a combined power plant; 
         FIG. 2  is a graphical representation of a further embodiment of a combined power plant; 
         FIG. 3  is a graphical representation of an additional embodiment of a combined power plant; and 
         FIG. 4  is a graphical representation of a still further embodiment of a combined power plant. 
     
    
    
     Like reference numerals and designations in the various drawings refer to like elements. 
     DETAILED DESCRIPTION 
     Turning now to the Figures,  FIG. 1  represents an embodiment of a combined power plant that operates in accordance with the present invention. As can be seen from the figure, numeral  10 A designates a combined power plant for the production of hydrogen using geothermal energy. Combined power plant  10 A includes vaporizer  12 A of geothermal power plant  15 A for vaporizing working fluid present in the vaporizer using heat present in geothermal liquid or brine supplied thereto, the geothermal liquid or brine being produced by a separator (not shown) that separates the geothermal liquid or brine as well as geothermal steam from geothermal fluid extracted from production well  11 A. Working fluid vapor exiting vaporizer  12 A is supplied to vapor turbine  14 A where it is expanded and power is produced as well as expanded working fluid. Preferably, vapor turbine  14 A drives electric generator  16 A for producing electric power. Expanded working fluid vapor exiting vapor turbine  14 A is supplied to condenser  17 A, which is an air-cooled condenser or a water-cooled condenser, and working fluid condensate is produced which is supplied to vaporizer  12 A using cycle pump  18 A. Preferably, an organic working fluid is used for working fluid of geothermal power plant  15 A. Examples of such organic working fluids are butane, i.e. n-butane, or iso-butane, pentane, i.e. n-pentane, or iso-pentane, hexane, i.e. n-hexane, or iso-hexane, etc. and mixtures of the above-mentioned fluids, preferably, pentane, i.e. n-pentane, or iso-pentane. 
     In accordance with this embodiment of the present invention, heat depleted geothermal liquid or brine exiting vaporizer  12 A is supplied to heat exchanger  22 A of electrolysis system  25 A for heating water or solution supplied thereto. Specific advantages of using electrolysis together with a fuel cell are described in U.S. Pat. No. 6,127,055. Thereafter, the further heat-depleted geothermal liquid or brine is supplied to injection well  21 A using pump  20 A. The heated water or heated solution exiting heat exchanger  22 A is supplied to electrolysis unit  24 A wherein electrolysis of the heated water or heated solution is carried out. During electrolysis of the heated water or heated solution using electrodes  26 A hydrogen and oxygen are produced in hydrogen supply means  28 A and oxygen supply means  29 A. Hydrogen may be used in utilization device  30 A to produce e.g. in electricity using e.g. fuel cells, combustion processes such as in gas turbines, steam turbines, internal combustion engines, etc. Alternatively, the hydrogen produced can be used to produce methanol or ammonia. Oxygen produced can be used in utilization device  32 A e.g. in combustion processes such as in gas turbines or steam turbines, or used together with hydrogen in a fuel cell to produce electricity. 
     In an additional embodiment, see  FIG. 2 , part of the heat of condensation of the organic Rankine cycle turbine can be used for pre-heating the water to be used in electrolysis. Thus, this embodiment is very similar to the embodiment of the present invention described with reference to  FIG. 1  except that heater  19 B can be used for pre-heating water with heat present in expanded vapors exiting turbine  14 B prior to supplying the water to heat exchanger  22 B for further heating the water with geothermal fluid. In this embodiment combined power plant  10 B includes vaporizer  12 B of geothermal power plant  15 B for vaporizing working fluid present in the vaporizer using heat present in geothermal liquid or brine supplied thereto, the geothermal liquid or brine being produced by a separator (not shown) that separates the geothermal liquid or brine as well as geothermal steam from geothermal fluid extracted from production well  11 B. Working fluid vapor exiting vaporizer  12 B is supplied to vapor turbine  14 B where it is expanded and power is produced as well as expanded working fluid. Preferably, vapor turbine  14 B drives electric generator  16 B for producing electric power. Expanded working fluid vapor exiting vapor turbine  14 B is first of all supplied to pre-heater  19 B where it heats water supplied to pre-heater  19 B and heat depleted working fluid vapor exiting pre-heater  19 B is supplied to condenser  17 B, which is an air-cooled condenser or a water-cooled condenser. The working fluid condensate produced in condenser  17 B is then supplied to vaporizer  12 B using cycle pump  18 B. Preferably, an organic working fluid is used for working fluid of geothermal power plant  15 B. Examples of such organic working fluids are butane, i.e. n-butane, or iso-butane, pentane, i.e. n-pentane, or iso-pentane, hexane, i.e. n-hexane, or iso-hexane, etc., and mixtures of the above-mentioned fluids, preferably, pentane, i.e. n-pentane, or iso-pentane. 
     In accordance with this embodiment of the present invention, heat depleted geothermal liquid or brine exiting vaporizer  12 B is supplied to heat exchanger  22 B of electrolysis system  25 B for further heating water or solution supplied thereto from pre-heater  19 B. Thereafter, the further heat-depleted geothermal liquid or brine is supplied to injection well  21 B using pump  20 B. The further heated water exiting heat exchanger  22 B is supplied from heat exchanger  22 B to electrolysis unit  24 B wherein electrolysis of the heated water or heated solution is carried out. During electrolysis of the further heated water or further heated solution using electrodes  26 B, hydrogen and oxygen are produced in hydrogen supply means  28 B and oxygen supply means  29 B. Hydrogen may be used in utilization device  30 B to produce e.g. in electricity using e.g. fuel cells, combustion processes such as in gas turbines, steam turbines, internal combustion engines, etc. Alternatively, the hydrogen produced can be used to produce methanol or ammonia. Oxygen produced can be used in utilization device  32 B e.g. in combustion processes such as in gas turbines or steam turbines, or used together with hydrogen in a fuel cell to produce electricity. In accordance with the present invention, the embodiment of the present invention can be used in any of the other embodiments of the present invention. 
       FIG. 3  represents a further embodiment of a combined power plant that operates in accordance with the present invention. As can be seen from the figure, numeral  10 C designates a combined power plant for the production of hydrogen using geothermal energy. Combined power plant  10 C includes vaporizer  12 C of geothermal power plant  15 C for vaporizing working fluid present in the vaporizer using heat present in geothermal liquid or brine supplied thereto, the geothermal liquid or brine being produced by a separator (not shown) that separates the geothermal liquid or brine as well as geothermal steam from geothermal fluid extracted from production well  11 C. Working fluid vapor exiting vaporizer  12 C is supplied to vapor turbine  15 C where it is expanded and power is produced as well as expanded working fluid. Preferably, vapor turbine  14 C drives electric generator  16 C for producing electric power. Expanded working fluid vapor exiting vapor turbine  14 C is supplied to condenser  17 C, which is an air-cooled condenser or a water-cooled condenser, and working fluid condensate is produced which is supplied to vaporizer  12 C using cycle pump  18 C. Preferably, an organic working fluid is used for working fluid of geothermal power plant  15 C. Examples of such organic working fluids are butane, i.e. n-butane, or iso-butane, pentane, i.e. n-pentane, or iso-pentane, hexane, i.e. n-hexane, or iso-hexane, etc., and mixtures of the above mentioned fluids, preferably, pentane, i.e. n-pentane, or iso-pentane. 
     Also in accordance with this embodiment of the present invention, heat present in heat depleted geothermal liquid or brine exiting the vaporizer of the geothermal power plant is used in the electrolysis system. Thus, heat depleted geothermal liquid or brine exiting vaporizer  12 C is supplied to heat exchanger  22 C of electrolysis system  25 C for heating water or solution supplied thereto. Thereafter, the further heat-depleted geothermal liquid or brine is supplied to injection well  21 C using pump  20 C. The heated water or heated solution exiting heat exchanger  22 C is supplied to electrolysis unit  24 C wherein electrolysis of the heated water or heated solution is carried out. During electrolysis of the heated water or heated solution using electrodes  26 C hydrogen and oxygen are produced in hydrogen supply means  28 C and oxygen supply means  29 C. The hydrogen or portion thereof may be used also here to produce e.g. electricity using e.g. fuel cells, combustion processes such as in gas turbines, steam turbines, internal combustion engines, etc. Alternatively, also here, the hydrogen produced or portion thereof can be used to produce methanol or ammonia. Oxygen produced or portion thereof can be used also here e.g. in combustion processes such as in gas turbines or steam turbines, or used together with hydrogen in a fuel cell to produce electricity. However, in accordance with this embodiment of the present invention, hydrogen produced or portion thereof is used to operate expander  34 C for expanding the hydrogen from its present pressure to a lower pressure such that expander  34 C runs pump  19 C for supplying at least portion of further heat-depleted geothermal liquid exiting heat exchanger  22 C to the injection well. Likewise, oxygen produced or portion thereof is used to operate expander  36 C for expanding the oxygen from its present pressure to a lower pressure such that expander  36 C runs pump  19 C for supplying at least portion of further heat-depleted geothermal liquid exiting heat exchanger  22 C to the injection well. 
     In a further embodiment, see e.g.  FIG. 4 , the hydrogen and/or oxygen produced by the electrolysis system can be stored for use at a different time e.g. during peak hours of electricity demand rather than using the hydrogen online as produced. Basically, the operation of this embodiment is similar to that of the embodiment described with reference to  FIG. 1  utilizing geothermal power plant  15 D and electrolysis system  25 D except that the hydrogen and/or oxygen produced by electrolysis system  25 D is stored in hydrogen storage apparatus  40 D and in oxygen storage apparatus  42 D respectively for later use. Such later use can be e.g. during peak hours of electricity demand and the hydrogen and/or oxygen produced can be used in utilization devices  30 D and  32 D for producing electricity using e.g. fuel cells or combustion apparatus such as gas turbines or steam turbines, internal combustion engines, etc. Oxygen produced can be used in utilization device  32 D e.g. in combustion processes such as in gas turbines or steam turbines, or used together with hydrogen in a fuel cell to produce electricity. In such a case, the hydrogen and/or oxygen can be stored for local used to that low-pressure (e.g. approximately between 3-10 atmospheres) storage can be used. Combined power plant  10 D includes vaporizer  12 D of geothermal power plant  15 D for vaporizing working fluid present in the vaporizer using heat present in geothermal liquid or brine supplied thereto, the geothermal liquid or brine being produced by a separator (not shown) that separates the geothermal liquid or brine as well as geothermal steam from geothermal fluid extracted from production well  11 D. Working fluid vapor exiting vaporizer  12 D is supplied to vapor turbine  14 D where it is expanded and power is produced as well as expanded working fluid. Preferably, vapor turbine  14 D drives electric generator  16 D for producing electric power. Expanded working fluid vapor exiting vapor turbine  14 D is supplied to condenser  17 D, which is an air-cooled condenser or a water-cooled condenser, and working fluid condensate is produced which is supplied to vaporizer  12 D using cycle pump  18 D. Preferably, an organic working fluid is used for working fluid of geothermal power plant  15 D. Examples of such organic working fluids are butane, i.e. n-butane, or iso-butane, pentane, i.e. n-pentane, or iso-pentane, hexane, i.e. n-hexane, or iso-hexane, etc., and mixtures of the above-mentioned fluids, preferably, pentane, i.e. n-pentane, or iso-pentane. 
     In accordance with this embodiment of the present invention, heat depleted geothermal liquid or brine exiting vaporizer  12 D is supplied to heat exchanger  22 D of electrolysis system  25 D for heating water or solution supplied thereto. Thereafter, the further heat-depleted geothermal liquid or brine is supplied to injection well  21 D using pump  20 D. The heated water or heated solution exiting heat exchanger  22 D is supplied to electrolysis unit  24 D wherein electrolysis of the heated water or heated solution is carried out. During electrolysis of the heated water or heated solution using electrodes  26 D hydrogen and oxygen are produced in hydrogen supply means  28 D and oxygen supply means  29 D. 
     Also, the embodiments of the present invention described with reference to  FIG. 1 ,  FIG. 2  and  FIG. 3  can also be used in the present embodiment. Thus, e.g. the hydrogen and/or oxygen produced can be first expanded in expanders like  34 C and  36 C (see  FIG. 3 ) for driving pump  19 C for supplying further heat-depleted geothermal liquid or brine to the injection well prior to storing the hydrogen and/or oxygen. However, in a further option, the stored hydrogen and oxygen can be used and often transported, if preferred, in e.g. certain industries, e.g. the manufacture of methanol or ammonia. 
     In addition, in this embodiment, if preferred, the ratio of geothermal liquid supplied to geothermal power plant  15 D and to electrolysis system  25 D can be changed and controlled using valve  50 D (and valve  52 D) so that more geothermal liquid can be supplied to electrolysis system  25 D during e.g. off-peak electricity demand so that more hydrogen can be stored and subsequently used e.g. during peak hours of electricity demand to produce electricity. 
     By use of the present invention to heat the solution to be used in electrolysis with heat from geothermal fluid, the efficiency of the electrolysis process is increased. In addition, by using the pressure of the hydrogen and/or oxygen produced in accordance with the present invention, less electric power has to be used for such a purpose. 
     Furthermore, the present invention, particularly as described in the embodiment of the present invention with reference to  FIG. 4 , permits increased production of electricity during e.g. periods of peak demand for electricity. Moreover, the hydrogen and/or oxygen can be used locally, without having to substantially transport the gases, hydrogen and oxygen can be used at relatively low pressures and their use does not suffer from various market barriers which are often associated with hydrogen transport and prolonged storage. 
     In addition, while the embodiment of the present invention described with reference to  FIG. 4  describes the use of a binary cycle organic Rankline cycle turbine for producing electricity from the geothermal fluid in e.g. a peaking power configuration, other power systems can be used instead, e.g. geothermal Flash Steam Power Plants, geothermal Steam Power plants, Enhanced Geothermal Systems (EGS) Power Plants, Hot Fractured Roc (HFR) and Hot Dry Rock (HDR) Power Plants. In such geothermal Flash Steam Power Plants, geothermal Steam Power plants, geothermal steam produced from the geothermal fluid can be used. 
     It should be pointed out that the present invention is particularly advantageous for use with low to medium temperature geothermal resources and geothermal fluids and does not need to rely on supercritical geothermal steam or vapor. Furthermore, the present invention can be used preferably for low temperature and intermediate temperature electrolysis for solution temperatures up to 350° C. 
     It is believed that the advantages and improved results furnished by the method and apparatus of the present invention are apparent from the foregoing description of the invention. Various changes and modifications may be made without departing from the spirit and scope of the invention as described in the claims that follow.