US20160369411A1

US20160369411A1 - Solar powered systems and methods for generating hydrogen gas and oxygen gas from water

Info

Publication number: US20160369411A1
Application number: US15/111,114
Authority: US
Inventors: Nareshkumar Bernard Handagama; Dharik MALLAPRAGADA
Original assignee: SABIC Global Technologies BV
Current assignee: SABIC Global Technologies BV
Priority date: 2015-01-21
Filing date: 2016-01-19
Publication date: 2016-12-22
Also published as: CN107109668A; EP3247820A1; KR20170088932A; EP3247820A4; WO2016118487A1

Abstract

Solar-powered systems and methods of generating hydrogen gas and oxygen gas from water are described. A solar-powered system for generating hydrogen gas and oxygen gas from water includes an electrolysis unit, a first generator unit, and a solar-powered turbine unit. The electrolysis unit is powered by the first generator unit. The solar-powered turbine unit is configured to drive the first generator unit and to supply steam to the electrolysis unit. The solar-powered turbine unit includes a first turbine coupled to and configured to provide shaft work to the first generator unit, a steam generation unit coupled to the steam feed inlet of the electrolysis unit and configured to hold water; and a solar unit configured to generate and provide heat to the steam generation unit.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims benefit to U.S. Provisional Application No. 62/106,056 titled “SOLAR POWERED SYSTEMS AND METHODS FOR GENERATING HYDROGEN GAS AND OXYGEN GAS FROM WATER”, filed Jan. 21, 2015. The entire contents of the above-referenced application is incorporated by reference without disclaimer.

BACKGROUND OF THE INVENTION

A. Field of the Invention
The invention generally concerns a solar-powered system for generating hydrogen gas and oxygen gas from water. In particular, the invention relates to such a system that utilizes a solar powered turbine unit coupled to a generator and an electrolysis unit.
B. Description of Related Art
Hydrogen (H₂) gas is a valuable product and is used as a feed stock in petroleum, chemical, energy and semiconductor industries. For example, hydrogen is used in the processing of hydrocarbons (for example, hydrocracking, hydrodealkylation, and hydrodesulfurization processes), the production of ammonia, the production of methanol, various chemical processes (for example, hydrogenation reactions), and as a coolant. Hydrogen gas can be recovered as a by-product of chemical or biological reactions, or separated from production of fossil fuels. Conventional methods to produce hydrogen include steam reforming of natural gas, thermochemical splitting of water, and electrolysis of water. Hydrogen production as a product of water-splitting offers enormous potential benefits for the energy sector, the environment, and the chemical industry. These processes suffer from the problem that they can generate a large amount of carbon dioxide (CO₂) either from the chemical reaction or from the consumption of electricity derived from fossil fuel. For example, in steam reforming reactions, CO₂can be generated as a reaction product when excess water is used as shown in equation (I).
CH₄+2H₂O→CO₂+4H₂ (I)
Other processes that generate hydrogen require electrical energy which generates CO₂through the combustion of fossil fuel as illustrated in equation (II).
CH₄+2O₂→CO₂+2H₂O (II)
Carbon dioxide is recognized by government agencies as the primary greenhouse gas produced through human activity and the emission of carbon dioxide is regulated by many governmental agencies.
Conventional systems and methods attempt to reduce the carbon dioxide production through the use of solar energy. U.S. Patent Application Publication No. 20130234069 describes solar receivers to generate electricity for an electrolysis unit, and then use the heat rejected from the electrolysis process as a heat source for the working fluid to be used elsewhere in the power cycle. U. S. Patent Application Publication No. 20120171588 to Fan et al. describes the use of solar energy to power a reforming/water splitting block. These systems are not self-sufficient, however, suffer from reliance on carbon-based feedstocks or fuel to meet the energy requirements for their systems.

SUMMARY OF THE INVENTION

A solution to the problems of producing energy with minimal amount of carbon dioxide production (i.e., a low carbon dioxide footprint) has been discovered. In particular, the solution resides in the ability to eliminate the use of fossil fuel as a source of electricity during the electrolysis of water to generate hydrogen and oxygen. The chemical reaction of water-splitting is shown in Equation (III).
2H₂O→2H₂+O₂ (III)
Notably, the invention is capable of elevating the temperature and pressure of the water, which can then be used in an electrolysis unit. By elevating the water temperature and pressure the overall electrical energy needed for the water splitting reaction is reduced, which in certain aspects, can be at the expense of using additional heat input from either solar energy or internal heat dissipation. The electrical energy is produced using a generator that is coupled to a solar powered turbine unit capable of driving the generator unit and providing steam to the electrolysis unit. This can be done without the use of fossil fuel and without producing carbon dioxide during the water-splitting reaction (see Equation (III) above and compare with Equations (I) and (II)).
In one particular aspect of the invention, a solar-powered system for generating hydrogen gas and oxygen gas from water is described. The system can include (a) an electrolysis unit configured to produce hydrogen gas and oxygen gas from water, (b) a first generator unit configured to provide electricity to the electrolysis unit; and (c) a solar-powered turbine unit configured to drive the first generator unit and to supply steam to the steam feed inlet. In a particular aspect, the system includes an air supply unit that feeds compressed air to the oxygen evolution side of the electrolysis unit to maintain less than pure oxygen in the outlet stream. A non-limiting example of an air supply unit is an air compressor. The electrolysis unit can include a steam feed inlet and at least a first product outlet for hydrogen gas or oxygen gas, or both. In a preferred aspect, the hydrogen gas and the oxygen gas exits the electrolysis unit as separate streams through two product outlets. The oxygen gas can through a second product outlet and the hydrogen gas can exit through the first product outlet. In a particular aspect, the stream exiting the second product outlet is an oxygen-rich stream that includes oxygen and air. The solar-powered turbine unit can include (i) a first turbine coupled to and configured to provide shaft work to the first generator unit; (ii) a steam generation unit coupled to the steam feed inlet of the electrolysis unit and configured to hold water; and (iii) a solar unit configured to generate and provide heat to the steam generation unit. In some aspects of the invention, the solar unit is configured to generate and provide heat to the working fluid of the turbine. The steam produced by the steam generation unit can include pressurized steam. Notably, carbon dioxide is not produced in the water splitting reaction (see Equation (III)), thereby reducing or eliminating carbon dioxide production when the system is in use. The produced hydrogen gas, oxygen gas, or both can each be used in a downstream chemical process. In a preferred aspect, both the produced hydrogen gas and the oxygen gas are used in a downstream chemical process. In some aspects of the invention, the system can also include a product cooling unit coupled to the electrolysis unit and configured to receive and reduce the temperature of the produced hydrogen gas or oxygen gas, or both. In a preferred aspect, the system can also include a product cooling unit coupled to the electrolysis unit and configured to receive and reduce the temperature of the produced hydrogen gas and oxygen gas. The product cooling unit can include (i) a second turbine coupled to and configured to provide power to a second generator unit, wherein the second turbine is configured to receive the produced hydrogen gas or oxygen gas, or both; and (ii) a heat transfer unit coupled to and configured to transfer heat produced from the product cooling unit to the steam generator unit. The second generator unit can be configured to provide electricity to the electrolysis unit. In some aspects, the product cooling unit includes a third turbine coupled to and configured to provide power to the second generator unit or to a third generator unit, wherein the third turbine is configured to receive the produced hydrogen gas or oxygen gas, or both, and wherein the third generator unit is configured to provide electricity to the electrolysis unit.
In some aspects of the invention, the solar powered turbine unit can include (i) the first turbine coupled to and configured to provide shaft work to the first generator unit; (ii) the steam generation unit coupled to the steam feed inlet of the electrolysis unit, (iii) the solar unit configured to generate and provide heat to the steam generation unit; and (iv) a condenser. The steam generation unit can include a boiler that is configured to hold water and produce steam. The boiler can be coupled to the first turbine and configured to transfer the produced steam from the boiler to the first turbine. The first turbine can be coupled to the condenser and configured to transfer steam from the turbine to the condenser. The condenser can be configured to condense the steam transferred from the turbine into liquid, and be coupled to and configured to transfer the liquid to the boiler.
In some aspects of the invention, the solar powered turbine unit is a closed-loop gas turbine unit that can include (i) the first turbine coupled to and configured to provide shaft work to the first generator unit; (ii) the steam generation unit coupled to the steam feed inlet of the electrolysis unit, and (iii) the solar unit configured to generate and provide heat to a cooled fluid (for example, a gas) produced from the steam generation unit. The steam generation unit can include a first heat exchanger coupled to the first turbine to receive heated fluid from the first turbine. Heat can be transferred in the first heat exchanger from the heated fluid to water to produce steam and cooled fluid. The heat exchanger can also be coupled to a compressor and configured to transfer the cooled fluid to the compressor. The compressor can be coupled to a second heat exchanger that is configured to heat the cooled fluid with heat produced by the solar unit. The second heat exchanger can be coupled to the first turbine to transfer the heated fluid to the first turbine. In some aspects of the invention the closed-loop gas turbine unit includes a back pressure steam turbine unit coupled to the first heat and configured to receive heat from the first heat exchanger. The back pressure steam turbine can include a fourth turbine couple to and configured to provide shaft work to the first generator unit. In some instances of the present invention, the first turbine and the fourth turbine are set-up in series of another. In other aspects of the invention, the back pressure steam turbine unit can include a fourth turbine coupled to and configured to provide power to a fourth generator unit in which the fourth generator unit is configured to provide electricity to the electrolysis unit.
Methods of generating hydrogen gas and oxygen gas from water using the systems described throughout this specification are described. The methods can include subjecting water to electrolysis conditions sufficient to produce hydrogen gas and oxygen gas, preferably as separate streams. The hydrogen gas can be separated from the oxygen gas. The hydrogen gas, the oxygen gas, or both can be provided to one or more storage units, chemical process units, transportation units, or any combination thereof.
In the context of the present invention, twenty-one (21) embodiments are described. Embodiment 1 includes a solar-powered system for generating hydrogen gas and oxygen gas from water. The system can include (a) an electrolysis unit configured to produce hydrogen gas and oxygen gas from water, the electrolysis unit can include a steam feed inlet and at least a first product outlet for hydrogen gas, oxygen gas or both; (b) a first generator unit configured to provide electricity to the electrolysis unit; and (c) a solar-powered turbine unit configured to drive the first generator unit and to supply steam to the steam feed inlet, the solar-powered turbine unit that includes (i) a first turbine coupled to and configured to provide shaft work to the first generator unit; (ii) a steam generation unit coupled to the steam feed inlet of the electrolysis unit and configured to hold water; and (iii) a solar unit configured to generate and provide heat to the steam generation unit. Embodiment 2 is the system of embodiment 1, further including a product cooling unit coupled to the electrolysis unit and configured to receive and reduce the temperature of the produced hydrogen gas or oxygen gas, or, preferably, both. Embodiment 3 is the system of embodiment 2, wherein the product cooling unit that includes (i) a second turbine coupled to and configured to provide power to a second generator unit, wherein the second turbine is configured to receive the produced hydrogen gas or oxygen gas, or, preferably, both; and (ii) a heat transfer unit coupled to and configured to transfer heat produced from the product cooling unit to the steam generator unit. Embodiment 4 is the system of embodiment 3, wherein the second generator unit is configured to provide electricity to the electrolysis unit. Embodiment 5 is the system of embodiment 4, wherein the product cooling unit includes a third turbine coupled to and configured to provide power to the second generator unit or to a third generator unit, wherein the third turbine is configured to receive the produced hydrogen gas or oxygen gas, or, preferably, both, and wherein the third generator unit is configured to provide electricity to the electrolysis unit. Embodiment 6 is the system of any one of embodiments 1-5, wherein the solar powered turbine unit can include (i) the first turbine coupled to and configured to provide shaft work to the first generator unit; (ii) the steam generation unit coupled to the steam feed inlet of the electrolysis unit, wherein the steam generation unit includes a boiler that is configured to hold water and produce steam; (iii) the solar unit configured to generate and provide heat to the boiler; and (iv) a condenser; wherein the boiler is coupled to the first turbine and configured to transfer steam from the boiler to the first turbine, wherein the first turbine is coupled to the condenser and configured to transfer steam from the turbine to the condenser, wherein the condenser is configured to condense the steam transferred from the turbine into liquid, and wherein the condenser is coupled to and configured to transfer the liquid to the boiler. Embodiment 7 is the system of any one of embodiments 1-5, wherein the solar powered turbine unit is a closed-loop gas turbine unit that includes (i) the first turbine coupled to and configured to provide shaft work to the first generator unit; (ii) the steam generation unit coupled to the steam feed inlet of the electrolysis unit, wherein the steam generation unit can include a first heat exchanger coupled to the first turbine to receive heated fluid from the first turbine, wherein heat is transferred in the first heat exchanger from the heated fluid to water to produce steam and cooled fluid; and (iii) the solar unit configured to generate and provide heat to the cooled fluid; and wherein the heat exchanger is coupled to a compressor and configured to transfer the cooled fluid to the compressor, wherein the compressor is coupled to a second heat exchanger that is configured to heat the cooled fluid with heat produced by the solar unit, and wherein the second heat exchanger is coupled to the first turbine to transfer the heated fluid to the first turbine. Embodiment 8 is the system of embodiment 7, further including a back pressure steam turbine unit. Embodiment 9 is the system of embodiment 8, wherein the back pressure steam turbine is coupled to the first heat exchanger and configured to receive steam from the heat exchanger. Embodiment 10 is the system of embodiment 9, wherein the back pressure steam turbine unit can include a fourth turbine coupled to and configured to provide shaft work to the first generator unit. Embodiment 11 is the system of embodiment 9, wherein the back pressure steam turbine unit can include a fourth turbine coupled to and configured to provide power to a fourth generator unit, and wherein the fourth generator unit is configured to provide electricity to the electrolysis unit. Embodiment 12 is the system of any one of embodiments 1 to 11, wherein the steam produced by the steam generation unit is pressurized steam. Embodiment 13 is the system of any one of embodiments 1 to 12, wherein the system does not produce carbon dioxide during use. Embodiment 14 is the system of any one of embodiments 1 to 13, wherein the produced hydrogen gas or the produced oxygen gas, or both, are each used in a downstream chemical process. Embodiment 15 is the system of any one of embodiments 1 to 14, wherein the electrolysis unit can include at least two product outlets, wherein the first product outlet is for hydrogen gas and a second product outlet is for oxygen gas. Embodiment 16 is the system of embodiment 15, further can include an air supply coupled to the electrolysis unit, wherein the air supply provides air to an oxygen evolution side of the electrolysis unit such that a mixture of oxygen and air are produced from the second outlet.
Embodiment 17 is a method of generating hydrogen gas and oxygen gas from water with any one of the systems of embodiments 1 to 16. The method can include subjecting water to electrolysis conditions sufficient to produce hydrogen gas and oxygen gas. Embodiment 18 is the method of embodiment 17, further including providing the hydrogen gas to one or more storage units, chemical process units, transportation units, or any combination thereof. Embodiment 19 is the method of any one of embodiments 17 to 18, further including providing the oxygen gas to one or more storage units, chemical process units, transportation units, or any combination thereof. Embodiment 20 is the method of any one of embodiments 17 to 19, wherein the produced hydrogen gas or the produced oxygen gas, or both, are each used in a downstream chemical process. Embodiment 21 is the method of any one of embodiments 17 to 20, wherein no carbon dioxide is produced by the system. Embodiments 22 is the method of any one of embodiments 17 to 21, wherein the water is in the form of steam produced by the steam generation unit.
The following includes definitions of various terms and phrases used throughout this specification.
The term “coupled” means either a direct connection or an indirect connection (for example, one or more intervening connections) between one or more objects or components, and not necessarily mechanically; two items that are “coupled” may be unitary with each other.
The term “fluid” refers to a substance or a mixture of compounds that exist in a gas phase, liquid phase, or a mixture thereof and are capable of flowing. Non-limiting examples of a fluid include air, liquid carbon dioxide, gaseous carbon dioxide, water, steam, or mixtures thereof.
The term “about” or “approximately” are defined as being close to as understood by one of ordinary skill in the art, and in one non-limiting embodiment the terms are defined to be within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5%.
The term “substantially” and its variations are defined as being largely but not necessarily wholly what is specified as understood by one of ordinary skill in the art, and in one non-limiting embodiment substantially refers to ranges within 10%, within 5%, within 1%, or within 0.5%.
The terms “inhibiting” or “reducing” or “preventing” or “avoiding” or any variation of these terms, when used in the claims and/or the specification includes any measurable decrease or complete inhibition to achieve a desired result.
The term “effective,” as that term is used in the specification and/or claims, means adequate to accomplish a desired, expected, or intended result.
The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.”
The words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.
The systems of the present invention can “comprise,” “consist essentially of,” or “consist of” particular ingredients, components, compositions, etc. disclosed throughout the specification. With respect to the transitional phase “consisting essentially of,” in one non-limiting aspect, a basic and novel characteristic of the systems of the present invention are their use of solar energy and the reduced amount of carbon dioxide produced when the system is in use.
Other objects, features and advantages of the present invention will become apparent from the following figures, detailed description, and examples. It should be understood, however, that the figures, detailed description, and examples, while indicating specific embodiments of the invention, are given by way of illustration only and are not meant to be limiting. Additionally, it is contemplated that changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and B are schematics of a solar-powered system of the present invention for generating hydrogen gas and oxygen gas from water.

FIG. 2 is a schematic of a solar-powered turbine unit of the present invention.

FIG. 3 is a schematic of the solar-powered system of the present invention that includes a cooling unit.

FIG. 4 is a schematic of the solar-powered turbine unit of the present invention that includes a boiler and a condenser.

FIG. 5 is a schematic of the solar-powered turbine unit of the present invention that includes a closed-loop gas turbine unit.

FIG. 6 is a schematic of the solar-powered turbine unit of the present invention that includes a closed-loop gas turbine unit and a back-pressure steam turbine unit set-up in series with one another.

FIG. 7 is a schematic of the solar-powered turbine unit of the present invention that includes a closed-loop gas turbine unit and a back-pressure steam turbine unit and a fourth generator unit set-up in parallel with one another.

FIG. 8 is a schematic of the solar-powered turbine unit of the present invention that includes a closed-loop gas turbine unit.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. The drawings may not be to scale. It should be understood that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but to the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims

DETAILED DESCRIPTION OF THE INVENTION

The currently available water-splitting systems require a significant amount of electrical energy. Most of the electrical energy is produced by combustion of fossil fuel, which produces carbon dioxide, a known greenhouse gas. By comparison, the present invention allows for reduced or limited carbon dioxide production by relying on the water-splitting reaction of Equation (III). The discovery lies in the combination of solar power, heat recovery, and steam generation to produce sufficient heat and electricity to power an electrolysis unit. Use of the steam in the electrolysis unit reduces the electrical energy needed for the water splitting reaction compared to the electrical energy required when using an electrolysis unit operating at or near ambient temperature fed with water.
These and other non-limiting aspects of the present invention are discussed in further detail in the following sections with references to FIGS. 1-7. In FIGS. 1-7, mechanical or thermal energy is depicted using a line with an open-headed arrow. Mass flow is depicted with a line and a closed-headed arrow. Electrical power is depicted with a dashed line and a closed-headed arrow. It should be understood that inlets, outlets, valves and connectors are known to one of ordinary skill.
A. Solar-Powered System for Generating Hydrogen Gas and Oxygen Gas from Water
FIGS. 1A and 1B are schematics that depict a solar-powered system of the present invention. The solar-powered system 100 can include an electrolysis unit 102, a first generator unit 104, and a solar-powered turbine unit 106. Steam feed 108 generated in the solar-powered turbine unit 106 can exit the solar-powered turbine unit 106 and enter the electrolysis unit 102. The use of steam instead of water in electrolysis unit 102 lowers the amount of electrical energy required for the electrolytic water-splitting reaction as compared to room temperature electrolytic water-splitting conditions. The steam feed may be delivered to the electrolysis unit 102 at a pressure of 1 to 10 bar or 10 bar. In electrolysis unit 102, the steam is split into hydrogen gas and oxygen gas. Electrolysis unit 102 can be a high steam temperature electrolysis unit. In a preferred embodiment, electrolysis unit 102 can be a solid oxide electrolysis system using a solid electrolyte of one or more materials such as, for example, yttria-stabilised zirconia, scandia stabilized zirconia, ceria-based electrolytes, or lanthanum gallate materials. Electrolysis conditions sufficient to split water into hydrogen and oxygen can include temperatures of 50 to 1000° C., 250 to 950° C., or from 600 to 900° C. and pressures of 0.1 to 1 MPa. Hydrogen gas stream 110 can exit electrolysis unit 102 and be used in downstream chemical process, transportation units. Oxygen gas stream 112 can exit electrolysis unit 102 and be used in downstream chemical process and/or transportation units. The hydrogen gas stream and/or oxygen gas stream can also be stored, transported, or sold. Electrolysis unit 102 is capable of converting 50 to 90 mol % water to hydrogen gas and oxygen gas. In some embodiments, hydrogen gas and oxygen gas generated during water splitting can be collected in a hydrogen collector and an oxygen collector in the electrolysis unit 102. The collectors can each provide hydrogen gas or oxygen gas to downstream units, transportation units, storage units, or the like.
As shown in FIG. 1B, air supply unit 114 is coupled to electrolysis unit 102. Air supply unit 114 can provide air stream 116 (for example, compressed air) to the oxygen evolution side of the electrolysis unit to maintain less than pure oxygen in the outlet stream. The air entering electrolysis unit 102 can be compressed air. In some embodiments, the oxygen stream 112 exiting electrolysis unit is an oxygen-rich stream having at least 10 to 90 vol % oxygen, 50 to 80 vol % oxygen, or 60 to 70 vol % oxygen.
In FIGS. 1A and 1B, first generator unit 104 is coupled to electrolysis unit 102 and solar-powered turbine unit 106. Solar-powered turbine unit 106 can include a first turbine. The first turbine can be one or more solar-powered gas turbine, steam turbines, back pressure steam turbines or any combination thereof. Turbines in solar-powered turbine unit generate mechanical energy (shaft work), which is supplied to first generator unit 104. First generator unit 104 uses the mechanical energy to generate and provide electrical energy 118 to electrolysis unit 102. Referring to FIG. 2, system 200 depicts a system to make hydrogen and oxygen gases from water that incorporates a steam turbine. Solar-powered turbine unit 106 can include first turbine 200, solar heat collection unit 202, and steam generation unit 204. First turbine 200 can provide mechanical energy 120 to first generator 104. In FIG. 2, first turbine 200 is a steam turbine. Solar heat collection unit 202 can generate and provide heat 208 to the steam generation unit 204 as described throughout this specification. Solar heat collection unit 202 can be a high-temperature solar collector that includes a mirror and/or lens system (for example, a solar farm) for sunlight collection and is capable of providing sufficient heat to heat water in to 300 to 1000° C. at 20 to 200 bar of pressure or air to temperatures of about 720 to 1350° C. at 1 to 20 bar. In a preferred embodiment, the solar collectors are computer controlled mirrors (e.g., heliostats) that orient themselves according to the changing direction of the sunlight over the course of the day. Steam generator 204 is coupled to first turbine 200 as described throughout this Specification. For example, when first turbine 200 is a steam turbine, steam generator 204 may generate steam feed 210 and steam feed 108. Steam feed 210 can be provided to the first turbine, which generates mechanical energy 120 and reduced pressure steam stream 212. In the steam generation unit 204, water 214 enters steam generation unit 204 and can be pressurized and/or heated to produce the steam feed 210.
B. Solar-Powered System with a Cooling Unit
In some aspects of the invention, a solar-powered system of the present invention can include a cooling unit. FIG. 3 depicts a schematic of the solar-powered system 300 having solar-powered turbine unit 106 and electrolysis unit 102 coupled to cooling unit 302. The cooling unit 302 can include second turbine 304, second generator unit 306, third turbine 308, third generator unit 310, and heat transfer unit 312. In another aspect of the invention, the electrolysis unit is fed with a compressed air stream 116 (See, for example FIG. 1B) that is used to sweep the oxygen produced at one of the electrodes of the electrolysis unit, to produce an oxygen-rich gas stream 112. In system 300, hydrogen gas stream 110 can exit electrolysis unit 102 at a temperature of 800 to 1000° C. and pressure of 1 to 10 bar, and be expanded in second turbine 304. Expansion of hydrogen gas stream 110 in second turbine 304 generates mechanical energy 316 and hot hydrogen gas stream 318. Generated mechanical energy 316 is provided to second generation unit 306, which produces electrical energy 320 that is provided to electrolysis unit 102. Electrical energy 320 can be used to power electrolysis unit 102 or other equipment such as, for example, air supply unit 114. Hot hydrogen gas stream 118 can exit second turbine 304 and undergo heat exchange in heat transfer unit 312 to form cooled hydrogen gas stream 322 and recovered heat energy 324. Recovered heat energy 324 can be transferred to steam generation unit 106. Similarly, oxygen-rich gas stream 112 can exit electrolysis unit 102 having a temperature of 800 to 1000° C. and a pressure of to 10 bar, and be expanded in third turbine 308. Expansion of the oxygen in the third turbine 308 generates mechanical energy 326 and hot oxygen-rich gas stream 328. Generated mechanical energy 326 is provided to third generation unit 310, which produces electrical power 330. Electrical power 330 can be used to power the electrolysis unit 102 or other equipment. In some embodiments, electrical power 320 and electrical power 330 can enter electrolysis unit at the same inlet. It should be understood that the electrical power can be connected to the electrolysis unit through one or more inlets. Hot oxygen-rich gas stream 318 can exit third turbine 308 and undergo heat exchange in heat transfer unit 312 to form cooled oxygen gas stream 332 and recovered heat energy 324′. Recovered heat energy 324′ from heat recovery unit 312 can be transferred to steam generation unit 106. As shown in FIG. 3, recovered heat energy 324′ is combined with recovered heat energy 324, however, it should be understood that heat energy 324′ can be provided separately to steam generation unit 106. Cooled hydrogen gas stream 322 and cooled oxygen-rich gas stream can have a final temperature at or near ambient temperatures, for example, a temperature from 20 to 30° C., or 25° C. While heat transfer unit 312 is shown as one unit more than one unit may be necessary to maintain sufficient temperature difference for heat transfer. For example, heat transfer unit 312 can include one or more heat exchangers with each heat exchanger performing heat exchange with hot hydrogen stream 318 and hot oxygen stream 328 to produce cooled hydrogen stream 322 and cooled oxygen-rich stream 332, or multiple heat exchangers arranged in series or parallel. Cooled hydrogen gas stream 314 can be used in downstream chemical process, stored, transported, or sold. Cooled oxygen gas stream 318 can be used in downstream chemical processes and/or transportation units, stored, transported, or sold. Produced electrical energy 320 and 330 can be used to power the electrolysis unit 102, combined with electrical energy 118, or used to power other equipment requiring electrical energy.
C. Solar-Powered System with a Solar-Powered Steam Turbine Unit
In some aspects of the invention, solar-powered system 400 includes a first turbine that converts heat into electrical power. Referring to FIG. 4, the solar-powered turbine unit 106 can include first turbine 200, solar unit 202, boiler 402, condenser 404, and pump 406. In system 400, first turbine 200 is a steam powered turbine. Solar unit 202 can be a high-temperature solar collector for sunlight collection that is capable of providing sufficient heat to heat water in boiler 402 to 300 to 600° C. at 20 to 200 bar of pressure.
Pump 406 pumps water steam 408 from condenser 404 into boiler 402. Pump 406 pressurizes water stream 408 such that it enters the boiler 402 as a high pressure water stream 410. In boiler 402, high pressure water stream 410 is heated by solar heat energy 208 and, optionally, by the thermal heat energy 322 (See, for example, heat recovery system described in FIG. 3), to a temperature that vaporizes the water to form steam, which is provided to other units as steam feed 210 and steam feed 108. In a preferred aspect, the generated steam is high pressure steam. The boiler 402 can be any conventional solar boiler. In some instances, the boiler 402 can be a series of boilers such as when the first boiler converts pumped water to saturated steam and then subsequently, a second boiler heats the steam beyond its saturation temperature to produce superheated steam.
A portion of the steam feed, steam feed 210, can exit boiler 402 and enter first turbine 200. First turbine 200 expands steam 210 to generate mechanical energy 120 and low pressure expanded steam 212. Mechanical energy (shaft work) 120 can be provided to first generator 104, which generates and supplies electrical power 118 to electrolysis unit 102. Expanded steam 212 can exit the first turbine 200 and enter condenser 404. In condenser 404, expanded steam 212 is cooled at a constant pressure to condense the steam to water. In some embodiments, the steam 212 is cooled to a temperature and pressure to produce saturated steam. A portion of the generated steam, steam feed 108, exits boiler 402 and enters electrolysis unit 202. The amount of steam provided to the electrolysis unit 102 can be regulated by a valve 412. As shown in FIG. 4, all the heat and electrical energy needed to run the electrolysis unit 102 is provided without the use of fossil fuel, and thus no carbon dioxide is generated during use. In some embodiments, cooling unit 302 is not used.
D. Solar-Powered System with a Solar-Powered Gas Turbine Unit
In some aspects of the invention, the solar-powered turbine unit 106 includes a solar-powered gas turbine using a suitable working fluid such as air or carbon dioxide. FIG. 5 depicts a schematic of a solar-powered system 500 that includes first turbine 200 in combination with the first generator 104, electrolysis unit 102, solar unit 202, steam generation unit 204, and cooling unit 302. As shown in FIG. 5, first turbine 200 is a gas turbine. First turbine 200 provides mechanical energy 120 to generator 104, which produces electrical power 118 that is supplied to electrolysis unit 102. The electrolysis unit 102 produces the hydrogen gas stream 110 and the oxygen-rich gas stream 112 as described throughout this Specification. For example, oxygen-rich gas stream is a mixture of compressed air stream 116 and oxygen generated in electrolysis unit 102. As previously described, the generated hydrogen gas stream 110 and/or the oxygen-rich gas stream 112 is expanded through the turbines 304 and 308 and the expanded gases undergo heat exchange as they pass through the heat transfer unit 312. The recovered heat 324, 324′ from the heat transfer unit 312 can be transferred to the steam generation unit 204 and used as a source of heat in the generation of steam in System 500.
In system 500, solar unit 106 includes first turbine 200, steam generation unit 204 and solar units 202. Steam generation unit 204 can be a heat recovery steam generation unit capable of recovering heat from more than one source and producing steam. Steam generation unit 204 can include any pumps and/or water inlets and outlets necessary to provide sufficient steam (e.g., high pressure steam) to electrolysis unit 102. As shown in FIG. 5, steam generation unit 204 includes first heat exchanger 502, which receives heated fluid 504 (for example, heated air or carbon dioxide) from first turbine 200. Heated fluid 504 can be used as a working fluid in first heat exchanger 502 to provide heat for steam generation from water. Although only one heat exchanger is shown in steam generation unit 204, one or more heat exchangers can be used to maintain sufficient heat exchange. For example, steam generation unit 204 can have one or more shell and tube heat exchangers. Steam 208 generated in steam generation unit 204 exits and enters electrolysis unit 102, where it is subjected to conditions sufficient to electrolytically dissociate the steam into hydrogen and oxygen.
Partially cooled fluid 506 exits heat exchanger 502 and enters compressor 508. In compressor 508, the partially cooled fluid 506 is compressed to form compressed fluid 510. Compressed fluid 510 exits compressor 508 at a pressure of 1 to 20 bar, and enters second heat exchanger unit 512. The compressed air can have a temperature of about 250 to 300° C. upon entering second heat exchanger unit 512. Second heat exchanger unit 512 can include one or more heat exchangers. As shown in FIG. 5, second heat exchanger unit 512 includes three heat exchangers 514, 516 and 518. Heat exchangers 514, 516 and 518 are coupled to solar units 202. Solar units 202 can include multiple solar collectors, mirrors and lens that collect solar heat at sufficiently high temperatures near 500° C. to greater than 1000° C., and provide the heat to each of heat exchangers 514, 516 and 518. Solar units 202 are capable of providing a desired amount of heat to heat exchangers 514, 516 and 518. For example, as compressed fluid 510 passes through heat exchangers 514, 516 and 518, the compressed fluid is heated progressively in each heat exchanger until a temperature of the compressed fluid is about 720 to 1350° C. at a pressure of 1 to 20 bar. Hot compressed fluid 520 exits the heat exchanger unit 514 and enters first turbine 200. In first turbine 200, hot compressed air 520 is sufficiently expanded to generate mechanical energy 120, which is provided to the first generator 104 and the compressor 508. Hot exhaust stream 504 exits first turbine 200 and enters heat exchanger 502 to continue the thermodynamic cycle. As shown in FIG. 5, the combination of the first heat exchanger 502, the compressor 508, heat exchanger 514, and first turbine 200 can constitute a closed Brayton cycle; however other thermodynamic heat recovery cycles can be used. In some embodiments, a portion or all of compressed fluid 510 may be at a sufficient temperature that heat exchanger unit 512 is not necessary, thus compressed fluid stream 510′ may be sent directly to first turbine 200. A portion of compressed fluid 510 flow can be regulated by valve 522. Solar powered turbine unit 106 as described for system 500 provides a thermally efficient “green” system to produce the energy required for electrolysis of water with minimal to no generation of carbon dioxide emissions.

E. Solar-Powered Combined Cycle System

In some embodiments, a solar-powered combined cycle system can be used to generate steam and electricity for the electrolysis unit 102. FIGS. 6 and 7 depict schematics of the solar-powered combined cycle stream system 600. System 600 incudes the features of the solar powered turbine system described in FIG. 5 in combination with a back-pressure steam turbine 602. Referring to FIG. 6, back-pressure steam turbine 602 is used to provide additional mechanical energy to first generator unit 104. The back-pressure steam turbine 602 receives steam feed 604 from steam generation unit 204. Steam feed 604 can be generated in steam generation unit 204 as described throughout this Specification. Expansion of steam feed 604 in back-pressure steam turbine 602 generates additional mechanical energy 606 that can be provided to power generator unit 104. Expanded steam stream 608 exits the back-pressure steam turbine 602 and enters the electrolysis unit 102 to be used as a source of heated water in the generation of hydrogen and oxygen. In some embodiments, expanded steam stream 608 is mixed with steam feed 108 entering the electrolysis unit 102.
Referring to FIG. 7, solar-powered system 700 includes back-pressure steam turbine 702 and fourth generator unit 704 in combination with solar heat generation unit 106, first generator unit 104, electrolysis unit 102, and cooling unit 300. Back-pressure steam turbine 702 provides mechanical energy to fourth generator unit 704, which then generates electrical energy 706 for electrolysis unit 102. A portion of steam feed 108, steam feed 708, is used in back-pressure steam turbine 702. Steam feed 708 is expanded in steam generation unit 204 to produce mechanical energy 710 and hot expanded steam 712, which can be used as water source in electrolysis unit 102. As shown in FIG. 7, hot expanded steam 712 is combined with steam feed 108 prior to entering electrolysis unit 102. It should be understood that hot expanded steam 712 can be provided directly to electrolysis unit. In some embodiments, cooling unit 302 is not used in the systems 600 and 700 depicted in FIGS. 6 and 7. The combined cycle power generation systems described in FIGS. 6 and 7 provides a thermally efficient, and novel “green” system to produce the energy required for water-splitting reactions without generating carbon dioxide emissions.

F. Method of Making Hydrogen Gas and Oxygen Gas

Hydrogen gas and oxygen gas can be produced from water using systems 100 through 700 described throughout this specification. In one non-limiting method, water in the form of steam can be provided from solar-powered turbine unit 106 to the electrolysis unit 102. The steam can be produced using the systems 400 through 700 described in Sections C-E of this specification. In electrolysis unit 102, the steam is subjected to conditions sufficient to generate hydrogen and oxygen. In some embodiments, the hydrogen and oxygen can be collected individually in the electrolysis unit 102 and/or collected as one gas stream and separated in a unit coupled to the electrolysis unit. The hydrogen gas, the oxygen gas, or both can be provided to one or more storage units, chemical processing units, transportation units, or any combination thereof. Since no fossil fuel is used to generate electricity in systems 100 to 700 and no carbon-based feed stocks are use, the system generates minimal or no carbon dioxide.
The systems 100 to 700 can be automated with suitable sensors and/or thermocouples to acquire data during the process. The acquired data can be transmitted to one or more computer systems. The computer systems can include components such as CPUs or applications with an associated machine readable medium or article which may store an instruction or a set of instructions that, if executed by a machine, may cause the machine to perform a method and/or operations in accordance with the methods of the present invention. For example, upon input of data from the sensors and/or thermocouples, the flow of the fluids, opening or closing of valves associated with the inlets and outlets for the various turbines, compressors, heat exchangers, generators, electrolysis unit, etc. can be controlled. Such a machine may include, for example, any suitable processing platform, computing platform, computing device, processing device, computing system, processing system, computer, processor, or the like, and may be implemented using any suitable combination of hardware and/or software. The machine-readable medium or article may include, for example, any suitable type of memory unit, memory device, memory article, memory medium, storage device, storage article, storage medium and/or storage unit, for example, memory, removable or non-removable media, erasable or non-erasable media, writeable or re-writeable media, digital or analog media, hard disk, floppy disk, Compact Disk Read Only Memory (CD-ROM), Compact Disk Recordable (CD-R), Compact Disk Rewriteable (CD-RW), optical disk, magnetic media, magneto-optical media, removable memory cards or disks, various types of Digital Versatile Disk (DVD), a tape, a cassette, or the like. The instructions may include any suitable type of code, such as source code, compiled code, interpreted code, executable code, static code, dynamic code, and the like. The instructions may be implemented using any suitable high-level, low-level, object-oriented, visual, compiled and/or interpreted programming language, such as C, C++, Java, BASIC, Perl, Matlab, Pascal, Visual BASIC, assembly language, machine code, and so forth. The computer system may further include a display device such as monitor, an alphanumeric input device such as keyboard, and a directional input device such as mouse.

EXAMPLES

The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters which can be changed or modified to yield essentially the same results.

Prophetic Example 1

Calculations Demonstrating Efficiency of a Solar Powered System with a Solar-Powered Gas Turbine Unit

Calculations to demonstrate the efficacy and benefits of the invention are presented below with reference to FIG. 8. FIG. 8 is a schematic of the solar-powered turbine unit of the present invention that includes a closed-loop gas turbine unit and is a simplified schematic of FIG. 5.
A total of 214.82 kWh solar energy is collected by solar units 202. In heat exchangers 514, 516, and 518 coupled to solar units 202, those solar energy are further transferred to the working fluid. Considering a 50% efficacy in the heat exchanges, the thermal energy carried by fluid 520 is:
214.82 kWh×50%=120.91 kWh (IV)
Fluid 520 enters the first turbine 200, where the hot compressed air 520 is sufficiently expanded to generate mechanical energy 120. Assuming an 80% of gas turbine efficiency, the total amount of energy in stream 120 can be calculated as:
120.91 kWh×80%=96.73 kWh (V)
The mechanical energy in stream 120 is provided to the first generator 104 and the compressor 508 at a ratio of 85% to 15%, respectively. With that, the mechanical energy provided to the first generator 104 is:
96.73 kWh×85%=82.22 kWh (VI)
Normally an electric generator has an efficiency about 90%. Thus, the electrical power 118 produced is:
82.22 kWh×90%=74 kWh (VII)
The electrical power 118 finally goes into the electrolysis unit 102. For a simplest case, we assume that 18 kg water in stream 108 directly enters electrolysis unit 102. With the water and the electrical power, hydrogen and oxygen gas are produced in the electrolysis unit 102. A lower heating value (LHV) of hydrogen, 33.31 kWh/kg, and a 90% efficiency of electrolysis are used to calculate the amount of hydrogen generated:
74 kWh×90%/33.31 kWh/kg=2 kg (VIII)
Finally, the amount of oxygen generated can be quantified based on the chemical reaction of water-splitting given in Equation (III) and the molecular weight of each chemical component:
(2 kg/0.2 g/mol)×0.5×32 g/mol=16 kg (IX)
In summary of this example, by using the invented method, a total of 214.82 kWh solar energy and 18 kg water are used to produce 2 kg hydrogen gas and 16 kg oxygen gas. Note that there is no carbon dioxide formed in the entire process. As a simple comparison, if we produce the same amount of hydrogen and oxygen gas using thermochemical splitting of water, where the energy supply is not solar but fossil fuels of natural gas, then about 117 pounds of CO₂will be generated; if the energy supply is gasoline, then about 157 pounds of CO₂will be generated; if the energy supply is coal (lignite), then about 215 pounds of CO₂will be generated.

Claims

1. A solar-powered system for generating hydrogen gas and oxygen gas from water, the system comprising:

(a) an electrolysis unit configured to produce hydrogen gas and oxygen gas from water, the electrolysis unit comprising a steam feed inlet and at least a first product outlet for hydrogen gas, oxygen gas or both;

(b) a first generator unit configured to provide electricity to the electrolysis unit;

(c) a solar-powered turbine unit configured to drive the first generator unit and to supply steam to the steam feed inlet, the solar-powered turbine unit comprising:

(i) a first turbine coupled to and configured to provide shaft work to the first generator unit;

(ii) a steam generation unit coupled to the steam feed inlet of the electrolysis unit and configured to hold water; and

(iii) a solar unit configured to generate and provide heat to the steam generation unit; and

(d) a product cooling unit coupled to the electrolysis unit and configured to receive and reduce the temperature of the produced hydrogen gas or oxygen gas, or both

2. (canceled)

3. The system of claim 1, wherein the product cooling unit comprises:

(i) a second turbine coupled to and configured to provide power to a second generator unit, wherein the second turbine is configured to receive the produced hydrogen gas or oxygen gas, or, preferably, both; and

(ii) a heat transfer unit coupled to and configured to transfer heat produced from the product cooling unit to the steam generator unit.

4. The system of claim 3, wherein the second generator unit is configured to provide electricity to the electrolysis unit.

5. The system of claim 4, wherein the product cooling unit comprises a third turbine coupled to and configured to provide power to the second generator unit or to a third generator unit, wherein the third turbine is configured to receive the produced hydrogen gas or oxygen gas, or, preferably, both, and wherein the third generator unit is configured to provide electricity to the electrolysis unit.

6. The system of claim 1, wherein the solar powered turbine unit comprises:

(i) the first turbine coupled to and configured to provide shaft work to the first generator unit;

(ii) the steam generation unit coupled to the steam feed inlet of the electrolysis unit, wherein the steam generation unit comprises a boiler that is configured to hold water and produce steam;

(iii) the solar unit configured to generate and provide heat to the boiler; and

(iv) a condenser;

wherein the boiler is coupled to the first turbine and configured to transfer steam from the boiler to the first turbine,

wherein the first turbine is coupled to the condenser and configured to transfer steam from the turbine to the condenser,

wherein the condenser is configured to condense the steam transferred from the turbine into liquid, and

wherein the condenser is coupled to and configured to transfer the liquid to the boiler.

7. The system of claim 1, wherein the solar powered turbine unit is a closed-loop gas turbine unit comprising:

(ii) the steam generation unit coupled to the steam feed inlet of the electrolysis unit, wherein the steam generation unit comprises a first heat exchanger coupled to the first turbine to receive heated fluid from the first turbine, wherein heat is transferred in the first heat exchanger from the heated fluid to water to produce steam and cooled fluid; and

(iii) the solar unit configured to generate and provide heat to the cooled fluid; and

wherein the heat exchanger is coupled to a compressor and configured to transfer the cooled fluid to the compressor,

wherein the compressor is coupled to a second heat exchanger that is configured to heat the cooled fluid with heat produced by the solar unit, and

wherein the second heat exchanger is coupled to the first turbine to transfer the heated fluid to the first turbine.

8. The system of claim 7, further comprising a back pressure steam turbine unit, wherein the back pressure steam turbine is coupled to the first heat exchanger and configured to receive steam from the heat exchanger.

9. The system of claim 8, wherein the back pressure steam turbine unit comprises a fourth turbine coupled to and configured to provide shaft work to the first generator unit.

10. The system of claim 8, wherein the back pressure steam turbine unit comprises a fourth turbine coupled to and configured to provide power to a fourth generator unit, and wherein the fourth generator unit is configured to provide electricity to the electrolysis unit.

11. The system of claim 1, wherein the steam produced by the steam generation unit is pressurized steam.

12. The system of claim 1, wherein the system does not produce carbon dioxide during use.

13. The system of claim 1, wherein the produced hydrogen gas or the produced oxygen gas, or both, are each used in a downstream chemical process.

14. The system of claim 1, wherein the electrolysis unit comprises at least two product outlets, wherein the first product outlet is for hydrogen gas and a second product outlet is for oxygen gas.

15. The system of claim 14, further comprising an air supply coupled to the electrolysis unit, wherein the air supply provides air to an oxygen evolution side of the electrolysis unit such that a mixture of oxygen and air are produced from the second outlet.

16. A method of generating hydrogen gas and oxygen gas from water with the system of claim 1, the method comprising subjecting water to electrolysis conditions sufficient to produce hydrogen gas and oxygen gas.

17. The method of claim 16, further comprising providing the hydrogen gas to one or more storage units, chemical process units, transportation units, or any combination thereof, and/or providing the oxygen gas to one or more storage units, chemical process units, transportation units, or any combination thereof.

18. The method of claim 16, wherein the produced hydrogen gas or the produced oxygen gas, or both, are each used in a downstream chemical process.

19. The method of claim 16, wherein no carbon dioxide is produced by the system.

20. The method of claim 16, wherein the water is in the form of steam produced by the steam generation unit.