WO2025043182A1

WO2025043182A1 - Electrolysis system with a geothermally heated feed stream

Info

Publication number: WO2025043182A1
Application number: PCT/US2024/043643
Authority: WO
Inventors: Kimberly C. CONNER; James Michael Browning; Joseph H. HOYT; Philip BENGE
Original assignee: EnhancedGEO Holdings, LLC
Priority date: 2023-08-24
Filing date: 2024-08-23
Publication date: 2025-02-27
Also published as: US20250066927A1

Abstract

A geothermally powered hydrogen production system includes a wellbore that heats a heat transfer fluid, thereby forming heated heat transfer fluid. A heat exchanger heats a feed stream using the heated heat transfer fluid, thereby forming a heated feed stream. An electrolyzer receives the heated feed stream and generates hydrogen from the heated feed stream.

Description

ELECTROLYSIS SYSTEM WITH A GEOTHERMALLY HEATED FEED STREAM

TECHNICAL FIELD

[0001] The present disclosure relates generally to geothermal power systems and related methods and more particularly to an electrolysis system with a geothermally heated feed stream.

BACKGROUND

[0002] Hydrogen is a potential fuel source for existing and emerging technologies. Hydrogen can be obtained through the electrolysis of water. However, the high energy demands of hydrogen production through electrolysis and other means have played a role in limiting the adoption of hydrogen-fueled technologies. Solar power and wind power are available sources of renewable energy that have been considered for driving electrolytic hydrogen production, but both energy sources can be unreliable and have relatively low power densities.

SUMMARY

[0003] Previous technology primarily focuses on the use of solar power for driving electrolytic hydrogen production. While this approach utilizes renewable energy, it suffers from drawbacks in its reliability and overall effectiveness. Solar energy is only intermittently available based on time of day and weather, resulting in considerable amounts of time during which solar- powered electrolysis cannot be performed. Furthermore, the efficiency of these processes (e.g., amount of hydrogen obtained per unit of solar energy) is relatively low, such that solar-generated hydrogen is not viable when compared to other fuels that can be generated at lower costs. This disclosure recognizes these shortcomings of previous technologies and provides solutions in the form of more resilient and efficient approaches to hydrogen generation. This disclosure provides a new geothermally powered and geothermally heated electrolysis system. A geothermal system harnesses heat from a geothermal resource with a sufficiently high temperature that can be used to both reliably power the electrolysis process (e.g., by providing an electrical current) and to heat the process to temperature conditions (e.g., superheated conditions) that not only decreases electrical energy demands but also improves overall reaction efficiency. Solar and wind energy also cannot reliably and efficiently provide the heating-based improvements of this disclosure. For example, solar energy is only available intermittently available to provide direct solar heating, and

1

SUBSTITUTE SHEET (RULE 26) wind power can only indirectly provide heating by using wind-derived electricity to power an electric heater. Thus, these energy sources are not only relatively unreliable but are less efficient because of the need to convert the energy source to electricity (with associated energy losses) and then use the electricity to heat the electrolysis fluid (with additional associated energy losses).

[0004] In some embodiments, the geothermally powered electrolysis system includes a wellbore extending from a surface into an underground magma reservoir. The wellbore heats a heat transfer fluid via heat transfer with the underground magma reservoir, thereby forming heated heat transfer fluid. A heat exchanger heats an electrolysis feed stream (e.g., water) using the heated heat transfer fluid, thereby forming a heated electrolysis feed stream. The electrolysis feed stream may be superheated through this heat transfer process. An electrolyzer receives the heated electrolysis feed stream, generates hydrogen from the received heated feed stream, and provides the generated hydrogen for storage.

[0005] In some cases, the geothermal system of this disclosure may harness a geothermal resource with sufficiently high amounts of energy from magmatic activity such that the geothermal resource does not degrade significantly over time. This disclosure illustrates improved systems and methods for capturing energy from magma reservoirs, dykes, sills, and other magmatic formations that are significantly higher in temperature than heat sources that are accessed using previous geothermal technologies and that can contain an order of magnitude higher energy density than the geothermal fluids that power previous geothermal technologies. In some cases, the present disclosure can significantly decrease hydrogen production costs and/or reliance on nonrenewable resources for hydrogen production operations. In some cases, the present disclosure may facilitate more efficient hydrogen production in regions where access to reliable power is currently unavailable or transport of non-renewable fuels is challenging. The systems and methods of the present disclosure may also or alternatively aid in decreasing carbon emissions. Certain embodiments may include none, some, or all of the above technical advantages. One or more technical advantages may be readily apparent to one skilled in the art from figures, description, and claims included herein.

SUBSTITUTE SHEET (RULE 26) BRIEF DESCRIPTION OF THE FIGURES

[0006] For a more complete understanding of the present disclosure, reference is now made to the following description, taken in conjunction with the accompanying drawings and detailed description, in which like reference numerals represent like parts.

[0007] FIG. 1 is a diagram of underground regions near a tectonic plate boundary in the Earth.

[0008] FIG. 2 is a diagram of a conventional geothermal system.

[0009] FIG. 3 is a diagram of an example improved geothermal system of this disclosure.

[0010] FIG. 4 is a diagram of an example system in which hydrogen production is powered by the improved geothermal system of FIG. 3.

[0011] FIG. 5 is a diagram of an example hydrogen generation system for use in the system of FIG. 4.

[0012] FIG. 6 is a diagram of another example hydrogen generation system for use in the system of FIG. 4.

[0013] FIG. 7 is plot illustrating the improvement of electrolysis efficiency that may be achieved through geothermal heating.

[0014] FIG. 8 is a flowchart of an example method for operating the systems of FIGS. 4- 6.

[0015] FIG. 9 is a diagram of an example system for performing thermal processes of

FIGS. 3 and 4.

SUBSTITUTE SHEET (RULE 26) DETAILED DESCRIPTION

[0016] Embodiments of the present disclosure and its advantages will become apparent from the following detailed description when considered in conjunction with the accompanying figures. In the figures, each identical, or substantially similar component that is illustrated in various figures is represented by a single numeral or notation. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment shown where illustration is not necessary to allow those of ordinary skill in the art to understand the disclosure.

[0017] The present disclosure includes unexpected observations, which include the following: (1) magma reservoirs can be located at relatively shallow depths of less than 2.5 km;

(2) the top layer of a magma reservoir may have relatively few crystals with little or no mush zone;

(3) a magma reservoir does not decline in thermal output over at least a two-year period; (4) eruptions have never been observed as a result of drilling into magma reservoirs (e.g., eruptions have not happened at African and Icelandic drill sites in over 10,000 years and it is believed a Kilauea, Hawaii drill site has never erupted); and (5) drilling into magma reservoirs can be reasonably safe.

[0018] As used herein, “magma” refers to extremely hot liquid and semi-liquid rock under the Earth’s surface. Magma is formed from molten or semi-molten rock mixture found typically between 1 km to 10 km under the surface of the Earth. As used herein, “borehole” refers to a hole that is drilled to aid in the exploration and recovery of natural resources, including oil, gas, water, or heat from below the surface of the Earth. As used herein, a “wellbore” refers to a borehole either alone or in combination with one or more other components disposed within or in connection with the borehole in order to perform exploration and/or recovery processes. In some cases, the terms “wellbore” and “borehole” are used interchangeably. As used herein, “heat transfer fluid” refers to a fluid, e.g., a gas or liquid, that takes part in heat transfer by serving as an intermediary in cooling on one side of a process, transporting and storing thermal energy, and heating on another side of a process. Heat transfer fluids are used in processes requiring heating or cooling.

[0019] FIG. 1 is a partial cross-sectional diagram of the Earth depicting underground formations that can be tapped by geothermal systems of this disclosure (e.g., for generating geothermal power). The Earth is composed of an inner core 102, outer core 104, lower mantle 106, transitional region 108, upper mantle 110, and crust 112. There are places on the Earth where magma reaches the surface of the crust 112 forming volcanoes 114. However, in most cases,

4

SUBSTITUTE SHEET (RULE 26) magma approaches only within a few miles or less from the surface. This magma can heat ground water to temperatures sufficient for certain geothermal power production. However, for other applications, such as geothermal energy production, more direct heat transfer with magma is desirable.

[0020] FIG. 2 illustrates a conventional geothermal system 200 that harnesses energy from heated ground water for power generation. The conventional geothermal system 200 is a “flashplant” that generates power from a high-temperature, high-pressure geothermal water extracted from a production well 202. The production well 202 is drilled through rock layer 208 and into the hydrothermal layer 210 that serves as the source of geothermal water. The geothermal water is heated indirectly via heat transfer with intermediate layer 212, which is in turn heated by magma reservoir 214. Magma reservoir 214 can be any underground region containing magma such as a dike, sill, or the like. Convective heat transfer (illustrated by the arrows indicating that hotter fluids rise to the upper portions of their respective layers before cooling and sinking, then rising again) may facilitate heat transfer between these layers. Geothermal water from the hydrothermal layer 210 flows to the surface 216 and is used for geothermal power generation. The geothermal water (and possibly additional water or other fluids) is then injected back into the hydrothermal layer 210 via an injection well 204.

[0021] The configuration of conventional geothermal system 200 of FIG. 2 suffers from drawbacks and disadvantages, as recognized by this disclosure. For example, because geothermal water is a multicomponent mixture (i.e., not pure water), the geothermal water flashes at various points along its path up to the surface 216, creating water hammer, which results in a large amount of noise and potential damage to system components. The geothermal water is also prone to causing scaling and corrosion of system components. Chemicals may be added to partially mitigate these issues, but this may result in considerable increases in operational costs and increased environmental impacts, since these chemicals are generally introduced into the environment via injection well 204.

Example improved geothermal system

[0022] FIG. 3 illustrates an example magma-based geothermal system 300 of this disclosure. The magma-based geothermal system 300 includes a wellbore 302 that extends from the surface 216 at least partially into the magma reservoir 214. The magma-based geothermal system 300 is a closed system in which a heat transfer fluid is provided down the wellbore 302 to

5

SUBSTITUTE SHEET (RULE 26) be heated and returned to a thermal process system 304 (e.g., for power generation and/or any other thermal processes of interest). As such, geothermal water is not extracted from the Earth, resulting in significantly reduced risks associated with the conventional geothermal system 200 of FIG. 2, as described further below. Heated heat transfer fluid is provided to the thermal process system 304. The thermal process system 304 is generally any system that uses the heat transfer fluid to drive a process of interest. For example, the thermal process system 304 may include an electricity generation system and/or support thermal processes requiring higher temperatures/pressures than could be reliably or efficiently obtained using previous geothermal technology, such as the conventional geothermal system 200 of FIG. 2. Further details of components of an example thermal process system 304 are provided with respect to FIG. 9 below.

[0023] The magma-based geothermal system 300 provides technical advantages over previous geothermal systems, such as the conventional geothermal system 200 of FIG. 2. The magma-based geothermal system 300 can achieve higher temperatures and pressures for increased energy generation (and/or for more effectively driving other thermal processes). For example, because of the high energy density of magma in magma reservoir 214 (e.g., compared to that of geothermal water of the geothermal fluid layer 210), wellbore 302 can generally create the power of many wells of the conventional geothermal system 200 of FIG. 2. Furthermore, the magmabased geothermal system 300 has little or no risk of thermal shock-induced earthquakes, which might be attributed to the injection of cooler water into a hot geothermal zone, as is performed using the conventional geothermal system 200 of FIG. 2. The heat transfer fluid is generally not substantially released into the geothermal zone, resulting in a decreased environmental impact and decreased use of costly materials (e.g., chemical additives that are used and introduced to the environment in great quantities during some conventional geothermal operations). The magmabased geothermal system 300 may also have a simplified design and operation compared to those of previous systems. For instance, fewer components and reduced complexity may be needed at the thermal process system 304 because only clean heat transfer fluid (e.g., steam) reaches the surface 216. There may be no need or a reduced need to separate out solids or other impurities that are common to geothermal water. The example magma-based geothermal system 300 may include further components not illustrated in FIG. 3.

[0024] Further details and examples of different configurations of geothermal systems and methods of their preparation and operation are described in U.S. Patent Application No.

6

SUBSTITUTE SHEET (RULE 26) 18/099,499, filed January 20, 2023, and titled “Geothermal Power from Superhot Geothermal Fluid and Magma Reservoirs”; U.S. Patent Application No. 18/099,509, filed January 20, 2023, and titled “Geothermal Power from Superhot Geothermal Fluid and Magma Reservoirs”; U.S. Patent Application No. 18/099,514, filed January 20, 2023, and titled “Geothermal Power from Superhot Geothermal Fluid and Magma Reservoirs”; U.S. Patent Application No. 18/099,518, filed January 20, 2023, and titled “Geothermal Power from Superhot Geothermal Fluid and Magma Reservoirs”; U.S. Patent Application No. 18/105,674, filed February 3, 2023, and titled “Wellbore for Extracting Heat from Magma Chambers”; U.S. Patent Application No. 18/116,693, filed March 2, 2023, and titled “Geothermal systems and methods with an underground magma chamber”; U.S. Patent Application No. 18/116,697, filed March 2, 2023, and titled “Method and system for preparing a geothermal system with a magma chamber”; and U.S. Provisional Patent Application No. 63/444,703, filed February 10, 2023, and titled “Geothermal systems and methods using energy from underground magma reservoirs”, the entirety of each of which is hereby incorporated by reference.

Geothermally powered hydrogen production

[0025] FIG. 4 illustrates an example combined geothermal and hydrogen production system 400 of this disclosure. The combined geothermal and hydrogen production system 400 includes all or a portion of the components of the magma-based geothermal system 300 described above with respect to FIG. 3 as well as geothermally powered hydrogen production system 410 for producing hydrogen. Examples of the geothermally powered hydrogen production system 410 are described in greater detail below with respect to FIGS. 5 and 6 (see example systems 500 and 600, described below). The combined geothermal and hydrogen production system 400 may include all or a portion of the thermal process system 304. In operation, heat transfer fluid is injected into the wellbore 302, which extends from the surface 216 into the magma reservoir 214 underground. The heated heat transfer fluid can be conveyed to the thermal process system 304 as heat transfer fluid 404a that can be used to drive processes, such as the generation of electricity 408 by turbines (see, e g., sets of turbines 904 and 908 in FIG. 9). Heat transfer fluid 404a may be referred to as a stream of heat transfer fluid 404a. Heat transfer fluid 404c, which can be formed from any remaining amount of heat transfer fluid 404a (e.g., steam) exiting from the thermal process system 304 and/or a wellbore bypass stream (i.e., heat transfer fluid 404b) is provided to the geothermally powered hydrogen production system 410. The electricity 408 may be used in

7

SUBSTITUTE SHEET (RULE 26) addition to or in place of heat transfer fluid 404c for powering electrical and mechanical processes in the geothermally powered hydrogen production system 410, as described in greater detail below with respect to the examples of FIGS. 5 and 6.

[0026] As described in greater detail below with respect to FIG. 5, the geothermally powered hydrogen production system 410 uses the heat transfer fluid 404c, which may be waste heat from thermal process system 304 and/or heated fluid directly from the wellbore 302, to improve the process for generating hydrogen through the electrolysis of water. For example, an electrolysis feed stream may be heated using the heated heat transfer fluid 404c before it is provided to an electrolyzer. The electrolyzer may also or alternatively be heated using the heated heat transfer fluid 404c. Electricity 408 provides an electrical current to the electrolyzer to facilitate the electrolytic splitting of water to form hydrogen and oxygen. The produced hydrogen is stored or transported to some downstream process. In some cases, a motor of the geothermally powered hydrogen production system 410 may be powered by the heat transfer fluid 404c and/or the electricity 408. For example, a motor of a fluid pump used to provide the flow of electrolysis feed stream into the electrolyzer may be powered by electricity 408.

[0027] Heat transfer fluid 406a (e.g., condensed steam) that is cooled and/or or decreased in pressure after powering the geothermally powered hydrogen production system 410 may be returned to the wellbore 302. For instance, as shown in the example of FIG. 4, a stream of return heat transfer fluid 406c may be provided back to the thermal process system 304, optionally used to drive one or more reactions or processes, and then expelled as heat transfer fluid 406a for return to the wellbore 302. The heat transfer fluid 406a can also include a bypass stream of heat transfer fluid 406b. Restated, thermally processed return stream of heat transfer fluid 406a includes heat transfer fluid (e.g., condensed steam) from the thermal process system 304 and/or the bypass stream of heat transfer fluid 406b. Thermally processed return stream of heat transfer fluid 406a that is sent back to the wellbore 302 may be water (or another heat transfer fluid), while the stream of heat transfer fluid 404a received from the wellbore 302 is steam (or another heat transfer fluid at an elevated temperature and/or pressure). While the example of FIG. 4 includes the thermal process system 304 of FIG. 3, in some cases, the combined geothermal and hydrogen production system 400 may exclude all or a portion of the thermal process system 304. For example, the wellbore stream of heat transfer fluid 404a from the wellbore 302 may be provided directly to the geothermally powered hydrogen production system 410 (see wellbore bypass stream of heat

8

SUBSTITUTE SHEET (RULE 26) transfer fluid 404b described above).

[0028] Heat transfer fluid 404a-c, 406a-c may be any appropriate fluid for absorbing heat within the wellbore 302 and driving operations of the geothermally powered hydrogen production system 410 and, optionally the thermal process system 304. For example, the heat transfer fluid may include water, a brine solution, one or more refrigerants, a thermal oil (e.g., a natural or synthetic oil), a silicon-based fluid, a molten salt, a molten metal, or a nanofluid (e.g., a carrier fluid containing nanoparticles). A molten salt is a salt that is a liquid at the high operating temperatures experienced in the wellbore 302 (e.g., at temperatures between 1,600 and 2,300 °F). In some cases, an ionic liquid may be used as the heat transfer fluid. An ionic liquid is a salt that remains a liquid at more modest temperatures (e.g., at or near room temperature). In some cases, a nanofluid may be used as the heat transfer fluid. The nanofluid may be a molten salt or ionic liquid with nanoparticles, such as graphene nanoparticles, dispersed in the fluid. Nanoparticles have at least one dimension of 100 nanometers (nm) or less. The nanoparticles increase the thermal conductivity of the molten salt or ionic liquid carrier fluid. This disclosure recognizes that molten salts, ionic liquids, and nanofluids can provide improved performance as heat transfer fluids in the wellbore 302. For example, molten salts and/or ionic liquids may be stable at the high temperatures that can be reached in the wellbore 302. The high temperatures that can be achieved by these materials not only facilitate increased energy extraction but also can drive thermal processes that were previously inaccessible using previous geothermal technology. The heat transfer fluid may be selected at least in part to limit the extent of corrosion of surfaces of the combined geothermal and hydrogen production system 400. As an example, the heat transfer fluid may be water. The water is supplied to the wellbore 302 as stream of heat transfer fluid 406a in the liquid phase and is transformed into steam within the wellbore 302. The steam is received as stream of heat transfer fluid 404a and used use to drive the geothermally powered hydrogen production system 410.

Example geothermally powered hydrogen production systems

[0029] FIG. 5 shows an example system 500 that may be used as the geothermally powered hydrogen production system 410 of FIG. 4 in greater detail. The configuration of FIG. 5 is provided as an example only. The geothermally powered hydrogen production system 500 may include more or fewer components, and the components may be arranged in different configurations in order to produce hydrogen (see stream 518). Operations of the geothermally powered hydrogen production system 500 may be powered at least partially by geothermal energy

9

SUBSTITUTE SHEET (RULE 26) from the heat transfer fluid 404c (e.g., steam), which obtained its heat from the magma reservoir 214 via the stream of heat transfer fluid 404a. For example, the heat transfer fluid 404c (or a secondary heat transfer fluid heated by heat transfer fluid 404c) may be used to heat components of the geothermally powered hydrogen production system 500 or may be converted to mechanical or electrical energy to perform operations in the geothermally powered hydrogen production system 500, as described further below.

[0030] The geothermally powered hydrogen production system 500 is configured to preheat an electrolysis feed stream 506 that is provided to an electrolyzer 502. The geothermally powered hydrogen production system 500 includes the electrolyzer 502, a heat exchanger 504, a fluid pump 508, an oxygen storage tank 516, a hydrogen storage tank 520, and an absorption chiller 522 (optional). The electrolyzer 502 is configured, when powered by electricity 408, to convert water to hydrogen and oxygen via the reaction 2H2O — ► 2H2 + O2. The electrolyzer 502 may be any appropriate type of electrolyzer, such as an alkaline water electrolyzer, a proton exchange membrane (PEM) electrolyzer, a steam electrolyzer, or the like. In operation, heated electrolysis feed stream 510 enters the electrolyzer 502. The heated electrolysis feed stream 510 may be steam or high temperature water (e.g., heated by the heat exchanger 504, as described below). The electrolyzer 502 may facilitate the electrolysis of steam. The electrolyzer 502 may be maintained at an increased pressure to facilitate high-temperature and high-pressure electrolysis. The electrolyzer 502 may be insulated and/or heated (see, e.g., example of FIG. 6 showing a heated electrolyzer).

[0031] Electricity 408 is used to apply a voltage across one or more electrolytic cells 532 of the electrolyzer 502. In the example of FIG. 5, the electrolyzer includes multiple cells 532. Each cell 532 includes an anode 534, a cathode 536, and a separator 538. The anode 534 and cathode 536 are generally pieces of metal, alloy, or other conductive material (e.g., a carbon-based material) with optionally one or more catalysts deposited thereon. The separator 538 may be an electrolyte, a membrane, or a combination of these. For example, a cell 532 in a PEM electrolyzer may include an anode 534 and cathode 536 with a PEM positioned between the anode 534 and cathode 536 as the separator 538. During an example operation of such a PEM cell, oxygen is generated on the anode side of the PEM separator 538, and hydrogen is generated at the cathode side of the PEM separator 538.

[0032] The heat exchanger 504 uses heat from the heated heat transfer fluid 404c (see FIG.

10

SUBSTITUTE SHEET (RULE 26) 4) to increase the temperature of the electrolysis feed stream 506. The heat exchanger 504 may be any appropriate type of heat exchanger. Examples of the heat exchanger 504 include shell-and- tube or tube-in-tube type heat exchangers. The heated heat transfer fluid 404c may be used directly to heat the electrolysis feed stream 506 (as shown in the example of FIG. 5), or the heated heat transfer fluid 404c may heat a secondary heat transfer fluid that is then provided to the heat exchanger 504. The secondary heat transfer fluid may be any similarly suitable fluid as chosen for the heat transfer fluid 404c.

[0033] The oxygen storage tank 516 is any vessel capable of safely storing oxygen generated by the electrolyzer 502. In some cases, oxygen may not be collected. Instead, oxygen may be released into the atmosphere. In some cases, rather than storing generated oxygen in a tank 516, the oxygen may be provided to a downstream process for use (e.g., to support a chemical process requiring oxygen). Similarly, the hydrogen storage tank 520 is any vessel capable of safely storing hydrogen generated by the electrolyzer 502. In some cases, the hydrogen is provided directly to a downstream process (e.g., to act as a fuel or reactant in a downstream process).

[0034] The example geothermally powered hydrogen production system 500 includes an absorption chiller 522. The absorption chiller 522 uses geothermal energy from the heated heat transfer fluid 404c to provide cooling to components of the geothermally powered hydrogen production system 500. This approach to cooling improves efficiency, for example, because a separate energy source is not needed to provide cooling. In the example of FIG. 5, the absorption chiller 522 provides cooling to the oxygen storage tank 516 and the hydrogen storage tank 520. The absorption chiller 522 receives the heated heat transfer fluid 404c and generates a cooling fluid provided in cooling fluid streams 524 to the storage tanks 516, 520. The streams 524 cool the tanks 516, 520 (e.g., by passing through a heat exchanger wrapped around or otherwise in contact with the tanks 516, 520). A warmed cooling fluid is generated in this process and provided back to the absorption chiller 522 via fluid streams 526. The cooling fluid may be water, a refrigerant, or any other appropriate fluid for cooling the tanks 516, 520 and/or other components of the geothermally powered hydrogen production system 500. While shown cooling the tanks 516, 520, the absorption chiller 522 may cool more or fewer components of the geothermally powered hydrogen production system 500.

[0035] In an example operation of the geothermally powered hydrogen production system 500, an electrolysis feed stream 506 is pumped toward the heat exchanger 504 using fluid pump

11

SUBSTITUTE SHEET (RULE 26) 508. The electrolysis feed stream 506 may be water. The electrolysis feed stream 506 may be purified or ultra-pure water. The electrolysis feed stream 506 may include one or more electrolytes or other components to facilitate electrolysis. For example, the electrolysis feed stream 506 may be an alkaline solution (e.g., a KOH solution). The fluid pump 508 may be powered by electricity 408 that is geothermally generated. Electricity demand may be decreased by heating the electrolysis feed stream 506, as described further throughout this disclosure (see, e.g., FIG. 7 and the corresponding description below).

[0036] The electrolysis feed stream 506 enters the heat exchanger 504 and is heated by the heated heat transfer fluid 404c. A heated electrolysis feed stream 510 from the heat exchanger 504 enters the electrolyzer 502. The heated electrolysis feed stream 510 may be steam, high temperature water, superheated water (i.e., liquid water above its boiling point at the current pressure), superheated steam (i.e., steam at a temperature greater than the boiling point of water at the current pressure), or a mixture of these. The heated electrolysis feed stream 510 may be pressurized to maintain the heated electrolysis feed stream 510 in the liquid phase. The electrolyzer 502 causes the water to be split to form hydrogen and oxygen, as described above. By performing electrolysis at an increased temperature, the amount of electricity 408 needed to drive the water-splitting process may be decreased. This disclosure also recognizes that pre-heating the electrolysis feed stream 506 may provide unexpected improvements to the overall efficiency of the electrolysis process (see FIG. 7 and corresponding description below).

[0037] An oxygen stream 514 that includes oxygen generated in the electrolyzer 502 exits the electrolyzer 502 and is stored in the oxygen storage tank 516. A hydrogen stream 518 that includes hydrogen generated in electrolyzer 502 exits the electrolyzer 502 and is stored in the hydrogen storage tank 520. The absorption chiller 522 may provide cooling to maintain the storage tanks 516, 520 at appropriately cool temperatures for safe storage of oxygen and hydrogen. Although not illustrated for conciseness, the geothermally generated electricity 408 may also power other components used for oxygen and/or hydrogen purification and storage. For example, electricity 408 may be used at least in part to power cryogenic processes for liquefaction of the oxygen and/or hydrogen. Such processes may be aided by the absorption chiller 522.

[0038] FIG. 6 shows another example system 600 that may be used as the geothermally powered hydrogen production system 410 of FIG. 4. The example geothermally powered hydrogen production system 600 includes the same or similar components to those described above

12

SUBSTITUTE SHEET (RULE 26) with respect to FIG. 5. The geothermally powered hydrogen production system 600 of FIG. 6 also includes a heat exchanger 602 that heats the electrolyzer 502. The heat exchanger 602 may be coil heat exchanger wrapped around the electrolyzer 502 and/or that passes through an interior of the electrolyzer 502. For example, one or more coils of the heat exchanger 502 may pass along the surface and/or through an internal volume of the electrolyzer 502. Heated heat transfer fluid 404c flowing through the heat exchanger 602 heats the electrolyzer 502 to increase the temperature of the electrolysis process. The geothermally powered hydrogen production system 600 could also include the heat exchanger 504 of FIG. 5 (not shown for conciseness) to preheat the electrolysis feed stream 506 before it enters the heated electrolyzer 502 with heat exchanger 602.

[0039] In an example operation of the geothermally powered hydrogen production system 600, an electrolysis feed stream 506 is pumped toward the electrolyzer 502 using fluid pump 508. The electrolysis feed stream 506 enters the electrolyzer 502 where it is heated by the heated heat transfer fluid 404c via heat exchanger 602. Water in the electrolysis feed stream 506 is electrolytically split to form hydrogen and oxygen, as described above. By performing electrolysis at an increased temperature in the heated electrolyzer 502 with heat exchanger 602, the amount of electricity 408 needed to drive the water-splitting process may be decreased and overall reaction efficiency may be improved (see FIG. 7). As described above with respect to the example operation of the system 500 of FIG. 5, an oxygen stream 514 that includes oxygen generated in the electrolyzer 502 exits the heated electrolyzer 502 and is stored in the oxygen storage tank 516. A hydrogen stream 518 that includes hydrogen generated in the heated electrolyzer 502 exits the electrolyzer 502 and is stored in the hydrogen storage tank 520. The absorption chiller 522 may provide cooling to maintain the storage tanks 516, 520 appropriately cool temperatures for safe storage of oxygen and hydrogen.

[0040] FIG. 7 is a plot 700 illustrating electrolysis efficiency improvements that may be achieved at increased reaction temperatures. Plot 700 shows a calculated percent change in energy input (electrical and heat energy input) to drive water splitting via electrolysis. Negative percentage values in plot 700 indicate a percentage decrease in energy input needed to drive electrolysis. Calculations performed to obtain plot 700 are summarized below. Plot 700 reveals the unexpected results that increasing electrolysis temperature not only decreases electricity demand (i.e., the amount of electrical energy needed to drive electrolysis) but also decreases the overall energy input needed to drive electrolysis. For example, plot 700 shows an energy input

13

SUBSTITUTE SHEET (RULE 26) reduction exceeding 33% at temperatures of about 240 °C and greater. As such, this disclosure encompasses the recognition of previously unrecognized benefits of performing electrolysis at increased temperature that can be realized through the unique geothermally powered electrolysis systems and operations of this disclosure.

[0041] The electrolysis of water is an endothermic process requiring both electricity and heat to sustain the reaction. In the calculations used to prepare plot 700, the electricity requirement is given by the Gibbs free energy of the reaction which varies as a function of temperature and pressure. The required heat is given by the difference between the higher heating value (HHV) and the Gibbs free energy, and this quantity also depends upon temperature and pressure. Further, increasing the temperature of water requires further heat. The amount of heat needed to increase the temperature of water also depends upon the fluid’s temperature and pressure. To obtain plot 700, energy from a geothermal source was assumed to superheated water (e.g., in electrolysis stream 506) to a temperature of 240 °C at a pressure greater than its saturation pressure via a heat exchanger (see, e.g., heat exchangers 504 and 602 of FIGS. 5 and 6, respectively) at an efficiency of 78%. The remaining thermal energy is converted to electricity at an efficiency of 42.2%. A model for electrical efficiency as a function of temperature was developed using available data (see Allebrod, Frank, et al. “Alkaline electrolysis cell at high temperature and pressure of 250 C and 42 bar.” Journal of Power Sources 229 (2013): 22-31.). This model facilitated the estimation of the total input thermal energy required for electrolysis at any temperature below the critical point, as shown in FIG. 7 as a percentage change in the total energy needed at 25 °C.

Example method of geothermally powered hydrogen production

[0042] FIG. 8 shows an example method 800 of operating the geothermally powered hydrogen production systems 500 and 600 of FIGS. 5 and 6. The method 800 may begin at step 802 whereby heated heat transfer fluid 404c is received. The heated heat transfer fluid 404c may include fluid output by the thermal process system 304 and/or heat transfer fluid 404a directly from the wellbore 302 (see FIG. 4). At step 804, the heated heat transfer fluid 404c is used to heat the electrolysis feed stream 506. The heated heat transfer fluid 404c can be used to heat the electrolysis feed stream 506 before being received by the electrolyzer 502 (see FIG. 5) and/or the heated heat transfer fluid 404c can be used to heat the electrolysis feed stream 506 after being received by the electrolyzer 502 (see FIG. 6). At step 806, the heated electrolysis feed stream 510 is electrolyzed by the electrolyzer 502 using electricity 408 generated using geothermal energy

14

SUBSTITUTE SHEET (RULE 26) (see FIGS. 5 and 6). This process results in the formation of hydrogen and oxygen in a manner that may provide an additional or alternative means for improving electrolysis efficiency. At step 810, the electrolysis products are stored. For example, hydrogen may be stored in the hydrogen storage tank 520.

[0043] Modifications, omissions, or additions may be made to method 800 depicted in FIG. 8. Method 800 may include more, fewer, or other steps. For example, at least certain steps may be performed in parallel or in any suitable order. While at times discussed as geothermally powered hydrogen production systems 500, 600 performing steps, any suitable component or components of the geothermally powered hydrogen production systems 500, 600 or other components used for geothermal and/or electrolytic processes may perform or may be used to perform one or more steps of the method 800.

Example thermal process system

[0044] FIG. 9 shows a schematic diagram of an example thermal process system 304 of FIGS. 3 and 4. The thermal process system 304 includes a steam separator 902, a first turbine set 904, a second turbine set 908, a high-temperature/pressure thermochemical process 912, a medium-temperature/pressure thermochemical process 914, and one or more lower temperature/pressure processes 916a,b. The thermal process system 304 may include more or fewer components than are shown in the example of FIG. 9. For example, a thermal process system 304 used for power generation alone may omit the high-temperature/pressure thermochemical process 912, medium-temperature/pressure thermochemical process 914, and lower temperature/pressure processes 916a, b. Similarly, a thermal process system 304 that is not used for power generation may omit the turbine sets 904, 908. As a further example, if heat transfer fluid is known to be received only in the gas phase, the steam separator 902 may be omitted in some cases. The ability to tune the properties of the heat transfer fluid received from the unique wellbore 302 of FIGS. 3 and 4 facilitates improved and more flexible operation of the thermal process system 304. For example, the depth of the wellbore 302, the residence time of heat transfer fluid in the magma reservoir 214, the pressure achieved in the wellbore 302, and the like can be selected or adjusted to provide desired heat transfer fluid properties at the thermal process system 304.

[0045] In the example of FIG. 9, the steam separator 902 is connected to the wellbore 302 that extends between a surface and the underground magma reservoir. The steam separator 902

15

SUBSTITUTE SHEET (RULE 26) separates a vapor-phase heat transfer fluid (e.g., steam) from liquid-phase heat transfer fluid (e.g., condensate formed from the vapor-phase heat transfer fluid). A stream 920 received from the wellbore 302 may be provided to the steam separator 902, In some cases, all of stream 918 is provided in stream 920. In other cases, a fraction or none of stream 918 is provided to the steam separator 902. Instead, all or a portion of the stream 918 may be provided as stream 928 which may be provided to the first turbine set 904 and/or to a high-pressure thermal process 912 in stream 929. The thermal process 912 may be a thermochemical reaction requiring high temperatures and/or pressures (e.g., temperatures of between 500 and 2,000 °F and/or pressures of between 1,000 and 4,500 psig), such as the geothermally powered hydrogen production system 500. One or more valves (not shown for conciseness) may be used to control the direction of stream 920 to the steam separator 902, first turbine set 904, and/or thermal process 912. A vapor-phase stream 922 of heat transfer fluid from the condenser may be sent to the first turbine set 904 and/or the thermal process 912 via stream 926. A liquid-phase stream 924 of heat transfer fluid from the steam separator 902 may be provided back to the wellbore 302 and/or to condenser 742. The condenser 942 is any appropriate type of condenser capable of condensing a vapor-phase fluid. The condenser 942 may be coupled to a cooling or refrigeration unit, such as a cooling tower (not shown for conciseness).

[0046] The first turbine set 904 includes one or more turbines 906a, b. In the example of FIG. 9, the first turbine set includes two turbines 906a, b. However, the first turbine set 904 can include any appropriate number of turbines for a given need. The turbines 906a, b may be any known or yet to be developed turbine for electricity generation. The first turbine set 904 is connected to the steam separator 902 and is configured to generate electricity from the vapor-phase heat transfer fluid (e.g., steam) received from the steam separator 902 (vapor-phase stream 922). A stream 930 exits the first turbine set 904. The stream 930 may be provided to the condenser 942 and then back to the wellbore 302. The condenser 942 may be cooled using a heat driven chiller, such as the absorption chiller 522 of FIGS. 5 and 6.

[0047] If the heat transfer fluid is at a sufficiently high temperature, as may be uniquely and more efficiently possible using the wellbore 302, a stream 1032 of vapor-phase heat transfer fluid may exit the first turbine set 904. Stream 932 may be provided to a second turbine set 908 to generate additional electricity. The turbines 910a,b of the second turbine set 908 may be the same as or similar to turbines 906a, b, described above.

16

SUBSTITUTE SHEET (RULE 26) [0048] All or a portion of stream 932 may be sent as vapor-phase stream 934 to a thermal process 914. Process 914 is generally a process requiring vapor-phase heat transfer fluid at or near the conditions of the heat transfer fluid exiting the first turbine set 904. For example, the thermal process 914 may include one or more thermochemical processes requiring steam or another heat transfer fluid at or near the temperature and pressure of stream 932 (e.g., temperatures of between 250 and 1,500 °F and/or pressures of between 500 and 2,000 psig). The second turbine set 908 may be referred to as “low pressure turbines” because they operate at a lower pressure than the first turbine set 904. Fluid from the second turbine set 908 is provided to the condenser 942 via stream 936 to be condensed and then sent back to the wellbore 302 via stream 936.

[0049] An effluent stream 938 from the second turbine set 908 may be provided to one or more thermal processes 916a,b. Thermal processes 916a,b generally require less thermal energy than thermal processes 912 and 914, described above (e.g., processes 916a, b may be performed temperatures of between 220 and 700 °F and/or pressures of between 15 and 120 psig). As an example, processes 916a, b may include water distillation processes, heat-driven chilling processes, space heating processes, agriculture processes, aquaculture processes, and/or the like. For instance, an example heat-driven chiller process 916a may be implemented using one or more heat driven chillers. Heat driven chillers can be implemented, for example, in data centers, cryptocurrency mining facilities, or other locations in which undesirable amounts of heat are generated. Heat driven chillers, also conventionally referred to as absorption cooling systems, use heat to create chilled water. Heat driven chillers can be designed as direct-fired, indirect-fired, and heatrecovery units. When the effluent includes low pressure steam, indirect-fired units may be preferred. An effluent stream 940 from all processes 912, 914, 916a,b, may be provided back to the wellbore 952.

[0050] ADDITIONAL EMBODIMENTS

[0051] Embodiment 1. A system, comprising: a wellbore extending from a surface into an underground magma reservoir, the wellbore configured to heat a heat transfer fluid via heat transfer with the underground magma reservoir, thereby forming heated heat transfer fluid; a heat exchanger configured to heat a feed stream using the heated heat transfer fluid, thereby forming a heated feed stream, wherein the feed stream comprises water; and an electrolyzer configured to:

17

SUBSTITUTE SHEET (RULE 26) receive the heated feed stream; generate hydrogen and oxygen from the received heated feed stream; and provide the generated hydrogen for storage, wherein the system optionally includes any one or more of the following limitations:

[0052] one or more turbines configured to use the heated heat transfer fluid to generate electricity;

[0053] wherein the generated electricity provides an electrical voltage between a cathode and an anode of the electrolyzer;

[0054] wherein the generated electricity provides power to a fluid pump providing a flow of the feed stream to the electrolyzer;

[0055] an absorption chiller configured to: receive the heated heat transfer fluid; generate a cooling fluid using the received heat transfer fluid; and provide the cooling fluid for cooling a vessel storing the hydrogen;

[0056] wherein the electrolyzer is configured to perform alkaline water electrolysis; and

[0057] wherein the heated feed stream comprises steam;

[0058] Embodiment 2. A system, comprising: a wellbore extending from a surface into an underground magma reservoir, the wellbore configured to heat a heat transfer fluid via heat transfer with the underground magma reservoir, thereby forming heated heat transfer fluid; an electrolyzer configured to receive a feed stream comprising water; and a heat exchanger coupled to the electrolyzer and configured to heat the feed stream received by the electrolyzer using the heated heat transfer fluid, thereby forming a heated feed stream; wherein the electrolyzer is further configured to: generate hydrogen and oxygen from the heated feed stream received by the electrolyzer; and provide the generated hydrogen for storage, wherein the system optionally includes any one or more of the following limitations:

[0059] one or more turbines configured to use the heated heat transfer fluid to generate electricity;

[0060] wherein the generated electricity provides an electrical voltage between a cathode

18

SUBSTITUTE SHEET (RULE 26) and an anode of the electrolyzer;

[0061] wherein the generated electricity provides power to a fluid pump providing a flow of the feed stream to the electrolyzer;

[0062] an absorption chiller configured to: receive the heated heat transfer fluid; generate a cooling fluid using the received heat transfer fluid; and provide the cooling fluid for cooling a vessel storing the hydrogen;

[0063] wherein the electrolyzer is configured to perform alkaline water electrolysis;

[0064] wherein the heated feed stream comprises steam; and

[0065] wherein the heat exchanger comprises a coil around at least a portion of the electrolyzer.

[0066] Embodiment 3. A system, comprising: a wellbore configured to heat a heat transfer fluid, thereby forming heated heat transfer fluid; a heat exchanger configured to heat a feed stream using the heated heat transfer fluid, thereby forming a heated feed stream, wherein the feed stream comprises water; and an electrolyzer configured to: receive the heated feed stream; generate hydrogen and oxygen from the received heated feed stream; and provide the generated hydrogen for storage, wherein the system optionally includes any one or more of the following limitations:

[0067] one or more turbines configured to use the heated heat transfer fluid to generate electricity, wherein the generated electricity provides an electrical voltage between a cathode and an anode of the electrolyzer;

[0068] one or more turbines configured to use the heated heat transfer fluid to generate electricity, wherein the generated electricity provides power to a fluid pump providing a flow of the heated feed stream to the electrolyzer;

[0069] an absorption chiller configured to: receive the heated heat transfer fluid; generate a cooling fluid using the received heat transfer fluid; and provide the cooling fluid for cooling a vessel storing the hydrogen; and

19

SUBSTITUTE SHEET (RULE 26) [0070] wherein the electrolyzer is configured to perform alkaline water electrolysis.

[0071] Although embodiments of the disclosure have been described with reference to several elements, any element described in the embodiments described herein are exemplary and can be omitted, substituted, added, combined, or rearranged as applicable to form new embodiments. A skilled person, upon reading the present specification, would recognize that such additional embodiments are effectively disclosed herein. For example, where this disclosure describes characteristics, structure, size, shape, arrangement, or composition for an element or process for making or using an element or combination of elements, the characteristics, structure, size, shape, arrangement, or composition can also be incorporated into any other element or combination of elements, or process for making or using an element or combination of elements described herein to provide additional embodiments. Moreover, items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface device, or intermediate component whether electrically, mechanically, fluidically, or otherwise.

[0072] While this disclosure has been particularly shown and described with reference to preferred or example embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the disclosure. Accordingly, this disclosure includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Changes, substitutions and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein. Moreover, any combination of the abovedescribed elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

[0073] Additionally, where an embodiment is described herein as comprising some element or group of elements, additional embodiments can consist essentially of or consist of the element or group of elements. Also, although the open-ended term “comprises” is generally used herein, additional embodiments can be formed by substituting the terms “consisting essentially of’ or “consisting of.”

SUBSTITUTE SHEET (RULE 26)

Claims

CLAIMS: What is claimed is:

1. A system, comprising: a wellbore extending from a surface into an underground magma reservoir, the wellbore configured to heat a heat transfer fluid via heat transfer with the underground magma reservoir, thereby forming heated heat transfer fluid; a heat exchanger configured to heat a feed stream using the heated heat transfer fluid, thereby forming a heated feed stream, wherein the feed stream comprises water; and an electrolyzer configured to: receive the heated feed stream; generate hydrogen and oxygen from the received heated feed stream; and provide the generated hydrogen for storage.

2. The system of Claim 1, further comprising one or more turbines configured to use the heated heat transfer fluid to generate electricity.

3. The system of Claim 2, wherein the generated electricity provides an electrical voltage between a cathode and an anode of the electrolyzer.

4. The system of Claim 2, wherein the generated electricity provides power to a fluid pump providing a flow of the feed stream to the electrolyzer.

5. The system of Claim 1, further comprising an absorption chiller configured to: receive the heated heat transfer fluid; generate a cooling fluid using the received heat transfer fluid; and provide the cooling fluid for cooling a vessel storing the hydrogen.

6. The system of Claim 1, wherein the electrolyzer is configured to perform alkaline water electrolysis.

7. The system of Claim 1, wherein the heated feed stream comprises steam.

21

SUBSTITUTE SHEET (RULE 26)

8. A system, comprising: a wellbore extending from a surface into an underground magma reservoir, the wellbore configured to heat a heat transfer fluid via heat transfer with the underground magma reservoir, thereby forming heated heat transfer fluid; an electrolyzer configured to receive a feed stream comprising water; and a heat exchanger coupled to the electrolyzer and configured to heat the feed stream received by the electrolyzer using the heated heat transfer fluid, thereby forming a heated feed stream; wherein the electrolyzer is further configured to: generate hydrogen and oxygen from the heated feed stream received by the electrolyzer; and provide the generated hydrogen for storage.

9. The system of Claim 8, further comprising one or more turbines configured to use the heated heat transfer fluid to generate electricity.

10. The system of Claim 9, wherein the generated electricity provides an electrical voltage between a cathode and an anode of the electrolyzer.

11. The system of Claim 9, wherein the generated electricity provides power to a fluid pump providing a flow of the feed stream to the electrolyzer.

12. The system of Claim 8, further comprising an absorption chiller configured to: receive the heated heat transfer fluid; generate a cooling fluid using the received heat transfer fluid; and provide the cooling fluid for cooling a vessel storing the hydrogen.

13. The system of Claim 8, wherein the electrolyzer is configured to perform alkaline water electrolysis.

14. The system of Claim 8, wherein the heated feed stream comprises steam.

22

SUBSTITUTE SHEET (RULE 26)

15. The system of Claim 8, herein the heat exchanger comprises a coil around at least a portion of the electrolyzer.

16. A system, comprising: a wellbore configured to heat a heat transfer fluid, thereby forming heated heat transfer fluid; a heat exchanger configured to heat a feed stream using the heated heat transfer fluid, thereby forming a heated feed stream, wherein the feed stream comprises water; and an electrolyzer configured to: receive the heated feed stream; generate hydrogen and oxygen from the received heated feed stream; and provide the generated hydrogen for storage.

17. The system of Claim 16, further comprising one or more turbines configured to use the heated heat transfer fluid to generate electricity, wherein the generated electricity provides an electrical voltage between a cathode and an anode of the electrolyzer.

18. The system of Claim 16, further comprising one or more turbines configured to use the heated heat transfer fluid to generate electricity, wherein the generated electricity provides power to a fluid pump providing a flow of the heated feed stream to the electrolyzer.

19. The system of Claim 16, further comprising an absorption chiller configured to: receive the heated heat transfer fluid; generate a cooling fluid using the received heat transfer fluid; and provide the cooling fluid for cooling a vessel storing the hydrogen.

20. The system of Claim 16, wherein the electrolyzer is configured to perform alkaline water electrolysis.

SUBSTITUTE SHEET (RULE 26)