Reverse electrodialysis or pressure retarded osmosis cell and method of using same

Abstract

A method and system for generating electricity or hydrogen from thermal energy are disclosed. The method includes separating a first saline solution from a second saline solution by a selective permeable membrane (104), receiving thermal energy from a heat source by the first saline solution and / or the second saline solution, mixing the first saline solution and the second saline solution in a controlled manner, and capturing at least a portion of the salinity gradient energy as electricity as the salinity concentration difference between the first saline solution and the second saline solution decreases. The method further includes transferring thermal energy from the first saline solution to the second saline solution by a heat pump (320) to increase the salinity concentration difference between the first saline solution and the second saline solution. The method may include processes of membrane distillation, electrodialysis, and / or salt decomposition for further energy efficiency and power generation.

Description

Technical Field

[0001] The present technology generally relates to salt gradient heat engine systems and methods for generating electricity and / or hydrogen from thermal energy.

Background Art

[0002] Salinity gradient power is the energy generated from the salinity difference between two fluids (usually fresh water and salt water) that occurs naturally, such as when a river flows into the sea. Reverse electrodialysis (RED) can be used to extract energy from the salinity gradient, for example, by passing salt water and fresh water through a stack of alternating cation exchange membranes and anion exchange membranes. A voltage is generated across each membrane due to the chemical potential difference between the salt water and fresh water, and the overall potential of the system is the sum of the potential differences across all the membranes. In an open-loop RED battery, a continuous supply of salt water and fresh water is required to maintain the salinity gradient. This constraint can limit the practical installation locations of commercial-scale RED batteries. Additionally, open-loop RED batteries are more susceptible to contamination by minerals, microorganisms, and other foreign substances and materials in the water source. In a closed-loop RED cell, a continuous supply source of concentrated saline solution and dilute saline solution is not required, but the salinity difference between the concentrated and dilute solutions needs to be continuously regenerated, which can be energy-intensive and / or inefficient.

[0003] This specification describes methods and systems for addressing the above problems and / or other problems.

Summary of the Invention

[0004] A reverse electrodialysis system is disclosed. The reverse electrodialysis system includes an anode, a cathode, and one or more cells disposed between the anode and the cathode. At least one of the one or more cells includes a first membrane configured to selectively permeate cations, a second membrane configured to selectively permeate anions, the second membrane being spaced apart from the first membrane, and a concentrated salt solution disposed between the first membrane and the second membrane. The first membrane enables cations to selectively move towards the cathode, and the second membrane enables anions to selectively move towards the anode, such that the first membrane and the second membrane separate the concentrated salt solution from the dilute salt solution to create a voltage difference between the cathode and the anode. The system includes a thermal optimization system configured to transfer thermal energy to the concentrated salt solution or the dilute salt solution, and a regeneration system including a heat pump. The regeneration system includes one or more of a salt precipitation system, a membrane distillation system, a salt decomposition system, an electrodialysis system, a forward osmosis system, evaporation, or any combination thereof. When the regeneration system includes a membrane distillation system, the membrane distillation system includes a container containing at least a portion of the first or second salt solution, the container being covered with a hydrophobic membrane, and a heat pump (or alternatively, a second heat pump) configured to heat the container and cool the opposite side of the hydrophobic membrane.

[0005] When the regeneration system includes a salt decomposition system, the salt decomposition system includes a container configured to receive at least a portion of a spent dilute solution formed from the first salt solution, the spent dilute solution containing salt, a heat pump (or alternatively, a second heat pump) configured to heat the container, and a cold water stream configured to receive at least one gaseous product released from the container. The salt decomposition system may be configured to decompose the salt and then reform a salt precipitate in the cold water stream.

[0006] A method of generating electricity from thermal energy is also disclosed. The method includes separating a first saline solution from a second saline solution by a selective permeable membrane, receiving thermal energy from a thermal optimization system by the first saline solution and / or the second saline solution, mixing the first saline solution and the second saline solution in a controlled manner, and capturing at least a portion of the salinity gradient energy as electricity as the salinity concentration difference between the first saline solution and the second saline solution decreases, transferring thermal energy from the first saline solution to the second saline solution by a heat pump to increase the salinity concentration difference between the first saline solution and the second saline solution, and can include one or more of the following: (i) applying a salt decomposition process, (ii) applying electrodialysis to remove salt from the first saline solution, the second saline solution, or both saline solutions, and / or (iii) generating a third saline solution by membrane distillation. When the method includes generating a third saline solution by membrane distillation, the method can further include mixing the third saline solution with the first saline solution and / or the second saline solution.

[0007] The salt decomposition process can include providing at least a portion of a spent dilute solution formed from the first saline solution, the spent dilute solution containing salt, heating the spent dilute solution to decompose the salt to produce at least one gaseous product, transferring the at least one gaseous product to a cold solution, and solidifying the gaseous product to reform it as a salt precipitate in the cold solution.

[0008] The method can include applying a pressure retarded osmosis (PRO) system, a capacitive mixing (CAP) system, or both a PRO system and a CAP system to generate additional electricity.

[0009] A salt gradient heat engine system is disclosed, which system includes an anode, a cathode, and one or more cells disposed between the anode and the cathode, at least one of the one or more cells including a first membrane configured to selectively permeate cations, a second membrane configured to selectively permeate anions, the second membrane being spaced apart from the first membrane, and a concentrated salt solution disposed between the first membrane and the second membrane, the first membrane enabling cations to selectively move toward the cathode and the second membrane enabling anions to selectively move toward the anode such that a voltage difference is created between the cathode and the anode, the first and second membranes separating the concentrated salt solution from a dilute salt solution. The regeneration system includes one or more of a salt precipitation system, a membrane distillation system, a salt decomposition system, an electrodialysis system, a forward osmosis system, evaporation, or any combination thereof. When the regeneration system includes a membrane distillation system, the membrane distillation system includes a container containing at least a portion of the first or second salt solution and covered with a hydrophobic membrane, and a heat pump (or alternatively, a second heat pump) configured to heat the container and cool the opposite side of the hydrophobic membrane. The membrane distillation system is configured to form a salt gradient across the membrane after heating and produce a third salt solution within the container. The hydrophobic membrane may include polytetrafluoroethylene, polypropylene, or polyvinylidene fluoride and may optionally be configured in a sandwich cell stack configuration.

[0010] When the regeneration system includes a salt decomposition system, the salt decomposition system includes a container configured to receive at least a portion of a spent dilute solution formed from the first salt solution, the container in which the spent dilute solution contains salt, a heat pump (or alternatively, a second heat pump) configured to heat the container, and a cold water stream configured to receive at least one gaseous product released from the container. The salt decomposition system may be configured to decompose the salt and then reform a salt precipitate in the cold water stream.

[0011] The salt decomposition system may include a container configured to receive a used dilute solution from a reverse electrodialysis battery, the used dilute solution containing salts, the container, a heat pump configured to heat the container and generate a gaseous product containing salts therein, and an absorber configured to receive a used concentrated solution from the reverse electrodialysis battery and receive the gaseous product. The salts in the gaseous product are absorbed by the used concentrated solution, and a concentrated salt solution can be regenerated.

[0012] The salt gradient heat engine system may include a salt precipitation system and a membrane distillation system, or an electrodialysis system and a salt precipitation system. The salt gradient heat engine system may further include a liquid desiccant dehumidification process.

[0013] When the regeneration system includes a membrane distillation system, the membrane distillation system may include a membrane distillation container including a hydrophobic membrane, and a heat pump configured to heat the container and cool one side of the hydrophobic membrane. The membrane distillation system can be configured to form a salt gradient with the hydrophobic membrane after heating, generate an ultra-dilute solution, and regenerate a concentrated salt solution. The membrane distillation system may further include a concentrated solution tank configured to receive a used concentrated solution from the reverse electrodialysis battery and connected to the membrane distillation container, and a dilute solution tank configured to receive a used dilute solution from the reverse electrodialysis battery and connected to the membrane distillation container. The concentrated solution tank may be configured to receive a concentrated solution from the membrane distillation container, and the dilute solution tank may be configured to receive an ultra-dilute solution from the membrane distillation container. The hydrophobic membrane may be composed of polytetrafluoroethylene, polypropylene, or polyvinylidene fluoride, and may be configured in a sandwich cell stack configuration.

[0014] When the regeneration system includes an evaporation system, the evaporation system may include an evaporator configured to receive a used concentrated solution from the reverse electrodialysis battery and to generate steam for regenerating the concentrated salt solution, a heat pump configured to supply thermal energy to the evaporator, and a condenser configured to receive a used dilute solution from the reverse electrodialysis battery and to receive the steam generated by the evaporator. The steam condenses and mixes with the used dilute solution to be regenerated as a dilute salt solution.

[0015] When the regeneration system includes an electrodialysis system, the electrodialysis system may be configured to receive a used dilute solution and a used concentrated solution. Electricity is supplied to the electrodialysis system, ions move from the used dilute solution to the used concentrated solution, and a dilute salt solution and a concentrated salt solution are regenerated.

[0016] The regeneration system may include a salt precipitation system and an electrodialysis system. The salt precipitation system includes a salt precipitation device configured to receive a used dilute solution from the reverse electrodialysis battery and to precipitate salts from the used dilute solution before the used dilute solution is supplied to the electrodialysis system, and a concentrated solution tank configured to receive a used concentrated solution from the reverse electrodialysis battery and to receive the salts generated by the salt precipitation device. The concentrated solution tank may be configured to receive a concentrated solution, and the dilute solution tank is configured to receive a dilute salt solution from the electrodialysis system.

[0017] The regeneration system may include a forward osmosis system configured to receive a spent concentrated solution from a reverse electrodialysis battery and to regenerate the concentrated salt solution using a switchable solubility system. In the forward osmosis system, the regeneration system may further include a dilute solution tank configured to receive a spent dilute solution from the reverse electrodialysis battery and to receive water from the switchable solubility system, where the water is mixed with the spent dilute solution to regenerate the dilute salt solution. The switchable solubility system is circulated through the forward osmosis system and includes a draw solution that produces a spent draw solution, and a recovery device configured to receive the spent draw solution and apply heat, where CO 2 is released and water is produced, and a generator configured to receive the solution from the recovery device and add CO 2 to regenerate the draw solution.

[0018] A method of generating electricity from thermal energy is also disclosed. The method includes separating a first salt solution from a second salt solution by a selective permeable membrane, receiving thermal energy from a heat optimization system by the first salt solution and / or the second salt solution, mixing the first salt solution and the second salt solution in a controlled manner, and capturing at least a portion of the salt concentration gradient energy as electricity as the salt concentration difference between the first salt solution and the second salt solution decreases, transferring thermal energy from the first salt solution to the second salt solution by a heat pump to increase the salt concentration difference between the first salt solution and the second salt solution, and may include one or more of the following: (i) applying a process of salt decomposition, (ii) applying electrodialysis to remove salt from the first salt solution, the second salt solution, or both salt solutions, and / or (iii) generating a third salt solution by membrane distillation. When the method includes generating a third salt solution by membrane distillation, the method may further include mixing the third salt solution with the first salt solution and / or the second salt solution. The first salt solution and the second salt solution method may include circulating the solution in a substantially or completely closed system.

[0019] The salt decomposition process may include providing a spent dilute solution formed from a first saline solution, the spent dilute solution containing salt, heating the spent dilute solution to decompose the salt to produce at least one gaseous product, transferring the at least one gaseous product to a cold solution, and solidifying the gaseous product to reform it as a salt precipitate in the cold solution. By applying a regeneration process selected from the group consisting of salt decomposition, electrodialysis, membrane distillation, evaporation, forward osmosis, salt precipitation, or any combination thereof, the salt concentration difference between the first saline solution and the second saline solution is regenerated.

[0020] This method may further include capturing salinity gradient energy using reverse electrodialysis or pressure retarded osmosis to drive a generator.

[0021] This method may include transferring thermal energy from the first saline solution to the second saline solution to precipitate salt in the first saline solution, and further optionally introducing the precipitated salt into the second saline solution to increase the salt concentration difference between the first saline solution and the second saline solution.

[0022] This method may include using a portion of the generated electricity to produce hydrogen gas by electrolysis.

[0023] This method may include a regeneration process that involves applying a salt decomposition process. The salt decomposition process may include providing a spent dilute solution formed from a first saline solution, the spent dilute solution containing salt; heating the spent dilute solution to decompose the salt and generate a gaseous product; transferring the gaseous product to an absorber; and solidifying the gaseous product to reform it as a salt precipitate in the spent concentrated solution in the absorber. By transferring the gaseous product to the absorber, the salt content of the spent dilute solution can be reduced to regenerate the first saline solution. The salt precipitate can dissolve in the spent concentrated solution to regenerate a second saline solution, and optionally, the salt content of the spent dilute solution may be higher than that of the first saline solution.

[0024] This method may include a regeneration process that involves applying an electrodialysis process. The electrodialysis process may include providing a spent dilute solution formed from a first saline solution, the spent dilute solution containing salt; providing a spent concentrated solution formed from a second saline solution; supplying electricity to separate the salt into ions and transfer the ions from the spent dilute solution to the spent concentrated solution. As the salt content of the spent dilute solution decreases, the first saline solution is regenerated, and as the salt content of the spent concentrated solution increases, the second saline solution is regenerated.

[0025] This method may include a regeneration process that involves applying an evaporation process. The evaporation process may include providing a spent concentrated solution formed from a second saline solution; heating the spent concentrated solution to generate water vapor; and transferring the water vapor for mixing with the spent dilute solution. As the salt content of the spent dilute solution decreases, the first saline solution is regenerated, and as the salt content of the spent concentrated solution increases, the second saline solution is regenerated.

[0026] This method may include a regeneration process that includes applying a membrane distillation process, which may include providing a membrane distillation vessel that includes a hydrophobic membrane having a used concentrated solution on one side of the membrane and a used dilute solution on the opposite side of the membrane, and heating the used concentrated solution to generate water vapor. The water vapor permeates through the hydrophobic membrane and mixes with the used dilute solution to regenerate a first salt solution, while increasing the salt content of the used concentrated solution and regenerating a second salt solution.

[0027] This method may include a regeneration process that includes applying a forward osmosis process, which may include circulating a used concentrated solution and a draw solution through a forward osmosis system to regenerate a second salt solution and generate a used draw solution, and circulating the used draw solution through a switchable solubility system to regenerate the draw solution and generate water.

[0028] The accompanying drawings, which are incorporated herein and constitute a part of this specification, illustrate specific embodiments of the disclosure and, together with the description, serve to explain the principles of the disclosure without limiting its scope.

Brief Description of the Drawings

[0029]

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DETAILED DESCRIPTION OF THE INVENTION

[0030] The present invention relates to a salt gradient heat engine system that utilizes heat to generate electricity from thermal energy. A salt gradient heat engine can be a system that utilizes thermal energy to generate or regenerate a salinity gradient and generate usable energy such as electricity and / or hydrogen. Examples of salt gradient heat engine systems include RED batteries and PRO batteries. A RED battery may incorporate a plurality of selective permeable membranes and one or more electrodes, which will be described in detail below. A PRO battery incorporates one membrane and does not require one or more electrodes. A PRO battery generates pressure rather than directly generating electricity from the salinity concentration difference between a concentrated (or enriched) salt solution and a solution, unlike a RED battery. The selective permeable membrane of a PRO battery is configured such that, for example, the solvent rather than the solute can preferentially pass through the membrane from a dilute (or diluted) solution to a concentrated salt solution, reducing the salinity concentration difference between the solutions.

[0031] Both RED batteries and PRO batteries may contain a concentrated salt solution separated from a dilute solution by a selective permeable membrane. Also, in both systems, the rate (or speed) of the force (or electricity) generated by the system is a function of at least the salinity concentration difference between the concentrated salt solution and the dilute solution, and optionally also a function of at least the temperature of the concentrated salt solution.

[0032] A reverse electrodialysis system is disclosed that includes an anode, a cathode, and one or more cells disposed between the anode and the cathode. At least one of the one or more cells includes a first membrane configured to selectively permeate cations and a second membrane configured to selectively permeate anions, and the second membrane is spaced apart from the first membrane. The cell further includes a concentrated salt solution disposed between the first membrane and the second membrane, and the first membrane selectively moves cations toward the cathode and the second membrane selectively moves anions toward the anode such that the first membrane and the second membrane separate the concentrated salt solution from the dilute salt solution to create a voltage difference between the cathode and the anode. The first selective permeable membrane and the second selective permeable membrane may include ion exchange membranes.

[0033] The plurality of selective permeable membranes used in the reverse electrodialysis system disclosed herein can be, for example, 2 to 500, 2 to 200, 10 to 400, or 2 to 100. A particular selective permeable membrane limits the ability of ionic components to diffuse freely. Instead, a cation exchange membrane (and an anion exchange membrane) enables the cationic component and the anionic component to move or travel in opposite directions, respectively. Each selective permeable membrane can be made of an organic or inorganic polymer having charged (ionic) side chains such as an ion exchange resin. Each selective permeable membrane can be made from graphene, reduced graphene oxide, or graphene oxide. The selective permeable membrane can include graphene, optionally laminated, optionally including nanopores, configured as a single layer or a thin multilayer sheet. The selective permeable membrane can include graphene, reduced graphene oxide, or graphene oxide and can be a cartridge such as commonly used in a reverse osmosis filtration system. The permeability of the membrane can depend on the configuration and other characteristics of the graphene sheet. The single layer or thin multilayer sheet can be stretched or otherwise configured to vary the permeability of the membrane.

[0034] The selective permeable membrane may be a bipolar membrane (e.g., anions on one side and cations on the opposite side) that generates an acid and a base from salts present in the solution during use. The selectivity of the selective permeable membrane is determined by size, charge, charge density, phase (e.g., hydrophobicity / hydrophilicity), or polarity.

[0035] The selective permeable membrane may be a polymer composite membrane having oriented nanochannels, such as those disclosed in WO2022 / 032236, which is hereby incorporated by reference in its entirety. For example, the selective permeable membrane may include (i) a polymer membrane, film, or coating including a layer having a first surface, a second surface, and a film thickness therebetween, and including cylindrical polymer fibers that are at least partially aligned as hexagonally packed cylinders within the film, aligned parallel to the film surface, and present as an H1 mesophase, the cylinders being internally cross-linked within the cylinders, and the cylinders being spatially arranged to provide channels between the cylinders for the flow of fluid through the membrane, film, or coating, and (ii) a porous support layer in contact with the polymer membrane, film, or coating, and may be a thin film composite membrane. In embodiments, the porous support layer is polyacrylonitrile, polyvinylidene fluoride, polysulfone, polyamide, polyimide, polypropylene, anodized aluminum, cellulose acetate, or a non-woven fabric.

[0036] A salinity gradient heat engine system can include a heat source configured to transfer thermal energy to a concentrated salt solution or a dilute salt solution, and a regeneration system including a heat pump. The heat pump can be any device known in the art for simultaneous heating and cooling, and optionally provides a coefficient of performance greater than about 1, or from about 1 to about 10, about 1 to about 6, or about 3 to about 4. The heat pump may be a vapor compression cycle, a thermoelectric chiller, a chemical absorption chiller, etc. The vapor compression cycle may be a screw, acoustic, air conditioner. The heat pump used herein may include a refrigerant that undergoes a phase change or a refrigerant that does not undergo a phase change. The refrigerant is CO 2 , helium, or other refrigerants known for use in heat pumps. The heat pump may include a thermodynamic cycle. The thermodynamic cycle can include any combination of a refrigerant cycle and a non-refrigerant cycle that provides the function of heating and cooling simultaneously. The heat pump can be a thermoacoustic heat pump such as developed by Equium (https: / / www.pv-magazine.com / 2023 / 01 / 02 / residential-thermo-acoustic-heat-pump-produces-water-up-to-80-c / ). The heat pump may be a system disclosed in U.S. Patent No. 9,915,436, "Heat Source Optimization System", or U.S. Patent No. 11,067,317, "Heat Source Optimization System". Each of the above patents is hereby incorporated by reference in its entirety. In certain embodiments, a humidifier, a dehumidifier, a two-way exhaust fan, and / or a swamp cooler can be used in combination with the heat pump to drive reverse electrodialysis. The heat pump can be fueled by known heat exchange fluids such as, but not limited to, water, refrigerant, glycol, oil, etc.

[0037] Traditionally, humidity is not preferred in HVAC cooling. This is because humidity adds dead weight to the system. Energy is consumed by the condensation of water vapor, resulting in wasted energy and reduced energy efficiency. Typically, when a desired temperature is set with a thermostat for cooling, the energy used to condense the water vapor is energy that could have been used to cool the air. In this scenario, energy is consumed to condense the vapor into condensate, and the HVAC unit operates against the latent heat of evaporation.

[0038] In contrast, according to the present disclosure, humidity can be highly desirable in the environment because it drives the reverse electrodialysis process and provides the system with additional energy that can be used to generate electricity, hydrogen, oxygen, and any combination thereof. For example, moisture can be introduced into the system to capture the latent heat of water vapor and drive reverse electrodialysis for use in generating electricity. Similarly, in ice formation, the heat crystallization of water can be utilized to drive the reverse electrodialysis process to generate electricity, hydrogen, oxygen, or a combination thereof.

[0039] The regeneration system can be configured to receive a dilute salt solution from at least one of the one or more cells, remove thermal energy (by a heat pump) from the dilute salt solution, and precipitate salt in the dilute salt solution. After precipitating the salt with the dilute salt solution, the regeneration system can be configured to circulate the dilute salt solution to at least one of the one or more cells, introduce the precipitated salt into a concentrated salt solution, and dissolve the precipitated salt in the concentrated salt solution.

[0040] The regeneration system can be configured to return at least a portion of the thermal energy removed from the dilute saline solution to the dilute saline solution after precipitating the salts dissolved in the dilute saline solution. The regeneration system can be configured to transfer at least a portion of the thermal energy removed from the dilute saline solution to the concentrated saline solution to dissolve the precipitated salts in the concentrated saline solution. The heat source can be configured to transfer thermal energy to the concentrated saline solution to dissolve the precipitated salts in the concentrated saline solution. The concentrated saline solution can include an endothermic solution or an exothermic solution. The concentrated saline solution can include a substance having a solubility with non-linear temperature dependence.

[0041] One or more other regeneration systems may be employed. The regeneration system may include electrodialysis. In addition to reverse electrodialysis systems, electrodialysis can be used for water purification. In electrodialysis, the dilute saline solution can be further desalinated by electrodialysis. For example, when precipitating salts, the concentration of the dilute saline solution is limited by the solubility curve. Electrodialysis can also be utilized to further dilute the dilute saline solution. Renewable electricity (such as solar or wind power) can be used to perform electrodialysis to separate salts from the dilute saline solution and form a further diluted stream. This enables energy storage. For example, during sunlight hours, electrodialysis can be used to charge the salt gradient, and the energy from the salt gradient can be utilized after sunset. The same battery / tank used for reverse electrodialysis can be used for electrodialysis. FIG. 12 is an example of a system including electrodialysis and a RED / PRO battery, which will be described in more detail below.

[0042] The reverse electrodialysis system may further include a control system configured to adjust the heat transfer between one or more heat sources and the reverse electrodialysis system based on one or more heat sources or one or more measured values of the state of the reverse electrodialysis system. The heat source includes one or more of geothermal heat, industrial waste heat, and solar heat.

[0043] The salt gradient heat engine system may comprise a salt decomposition system for generating a salt gradient. The decomposition of the salt may be carried out by reverse electrodialysis, instead of the salt precipitation process disclosed herein. For example, the used dilute solution (supplied from the RED battery) can be heated to a temperature higher than the temperature at which the salt decomposes (e.g., ammonium bicarbonate decomposes into CO 2 and ammonia around 60 °C). When the solution is heated, the salt decomposes, leaving the used dilute solution as a gaseous product, and the concentration of the salt in the used dilute solution decreases, producing a regenerated dilute solution. The application of a vacuum or an optional fan helps to move the gaseous product to a cold stream. When the gaseous product (e.g., CO 2 and ammonia) is fed into a cold water stream, it reacts and precipitates back in the form of solid salt (e.g., CO 2 ammonia and cold water form ammonium bicarbonate salt). The solid salt precipitated in the solution (e.g., ammonium bicarbonate) can be transferred to the concentrated salt solution in the RED battery. In this process, a heat pump can be used for heating and cooling the used dilute solution and the cold water stream respectively. The heat pump may be the same as or different from the heat pump used in other processes of the reverse electrodialysis system disclosed herein. Optionally, when the gaseous product precipitates in the cold stream, thermal energy can be extracted and transferred to the used dilute solution to decompose the salt. Furthermore, thermal energy can also be used to increase the temperature of the precipitated solution, enhance the solubility, and obtain a super-concentrated solution. Figure 10 is an example of a salt decomposition process showing the flow of the solution between the RED battery and the vessel of the salt decomposition process, which will be described in more detail below. By applying the salt decomposition process, the regeneration of the concentrated salt solution and the dilute salt solution becomes possible by incorporating salt decomposition.

[0044] A reverse electrodialysis system may include a second cell. The second cell includes a third membrane configured to selectively permeate cations and a fourth membrane configured to selectively permeate anions, and the fourth membrane is disposed spaced apart from the third membrane. The second cell includes a second concentrated salt solution disposed between the third membrane and the fourth membrane, and the third membrane and the fourth membrane separate the second concentrated salt solution from the second dilute salt solution. The concentrated salt solution may include an endothermic solution, the second concentrated salt solution may include an exothermic solution, and the heat pump may be configured to transfer heat between the concentrated salt solution and the second concentrated salt solution.

[0045] A reverse electrodialysis system may include a membrane distillation system. Membrane distillation (MD) is a heat-driven separation process in which liquids are excluded and only vapor molecules permeate through a porous hydrophobic membrane. The driving force of the MD process is the vapor pressure difference caused by the temperature difference across the hydrophobic membrane. The hydrophobic membrane needs to be essentially hydrophobic or modified so that its surface becomes hydrophobic. The hydrophobic membrane for MD can be polytetrafluoroethylene (PTFE), polypropylene (PP), polyvinylidene fluoride (PVDF), or any combination thereof. The large surface area of the hydrophobic membrane can be used in a sandwich-type cell stack design similar to the RED stack. The stack of hydrophobic membranes may contain only one or more types of hydrophobic membranes without electrodes. By using a heat pump, heating and cooling can be performed simultaneously to create a strong temperature gradient driving force, thereby enhancing the efficiency of the MD process. For example, the heat pump heats the spent concentrated solution or the spent dilute solution to about 40°C to about 80°C on one side of the hydrophobic membrane, and at the same time provides a cooling means such as a cooling stream heat exchanger, an evaporator with refrigerant, or cold water on the other side of the hydrophobic membrane to generate a dilute solution, which can be used to obtain heat from, for example, ambient conditions, geothermal energy, solar heat, industrial waste heat, etc. Membrane distillation can efficiently generate the salt gradient that can be used in the reverse electrodialysis system disclosed herein by leveraging the power of the heat pump. The heat pump may be the same as or different from the heat pump used in other processes of the reverse electrodialysis system disclosed herein. Membrane distillation can be used to produce a concentrated salt solution for introduction into the RED battery and, optionally, a dilute salt solution. FIG. 13 is an example of a membrane distillation system showing the flow of solutions between the MD system and the RED system. By incorporating membrane distillation, regeneration of the concentrated salt solution and the dilute salt solution becomes possible.

[0046] The membrane distillation process utilized herein can be direct contact MD (DCMD), air gap MD (AGMD), vacuum MD (VMD), sweeping gas MD (SWGMD), vacuum multi-effect membrane distillation (V-MEMD), permeation gap MD (PGMD), or a combination thereof.

[0047] A membrane distillation system may include a container containing at least a portion of a first or second saline solution, the container being covered with a hydrophobic membrane that allows the permeation of vapor, and a heat pump configured to heat the container and cool the opposite side of the membrane. The membrane distillation system may be configured to form a salt gradient across the membrane after heating and produce a third saline solution (i.e., a concentrated or enriched one) within the container. The membrane distillation system may include a second heat pump for heating the container and, optionally, a cooling device on the opposite side of the container and the membrane. The cooling device may be a cold stream, a heat exchanger, a refrigerant loop, etc., or may operate, for example, by condensing vapor back into a liquid. FIG. 13 is an example of a membrane distillation process, showing how a hydrophobic membrane forms a salt gradient between a warm concentrated solution and a cold dilute solution, which will be described in more detail below. The membrane distillation system can include at least a portion of a first or second saline solution separated by a hydrophobic membrane that allows the permeation of vapor. In this embodiment, the solution is supplied to both sides of the hydrophobic membrane, the heat pump is configured to warm one side of the membrane, while a cooling device is provided on the opposite side of the membrane to cool the solution.

[0048] The reverse electrodialysis system includes a microbial reverse-electrodialysis electrolysis cell (MREC) disclosed in U.S. Patent No. 9,112,217, the entire text of which is incorporated herein by reference. In this embodiment, microorganisms generate electricity to drive the RED system. The MREC includes a plurality of electricity-generating microorganisms disposed within the RED battery and can assist in the generation of hydrogen and electricity through the oxidation of organic matter at the anode and the reduction of oxygen at the cathode. Since microorganisms reproduce in a warm environment, the use of a heat pump can improve the ability of the microorganisms to remove the overvoltage of the electrodes. The electrode overvoltage leads to significant energy losses due to thermodynamically unfavorable electrode reactions. Furthermore, by utilizing the thermal energy supplied by the heat pump, the reaction rate is improved and the amount of membrane required to generate the same amount of energy in the RED is reduced. For example, in a residential environment, organic waste such as sewage from a septic tank can be converted into usable energy using microbial reverse electrodialysis. The use of ultraviolet light in any of the salt gradient heat engine systems disclosed herein can limit the growth and contamination of microorganisms within the system.

[0049] In a salinity gradient heat engine system, the RED and the PRO can operate together either continuously or in a batch system. When operating in a batch system, the reverse electrodialysis system can include a plurality of precipitation devices and / or a plurality of tanks in a parallel or stacked arrangement. When operating in a batch system, the precipitation devices, tanks, and stacks can be of different sizes overall and can be operated in series, parallel, or a combination of both, and can be operated in countercurrent, crossflow, or cocurrent. For example, the system can include two or more precipitation devices, each of which produces a regenerated dilute solution, and these precipitation devices are combined before flowing into the RED battery. And / or, the system can include two or more dissolution tanks, each of which produces a regenerated concentrated salt solution, and these dissolution tanks are combined before flowing into the RED battery. When operating as a batch system, in order to improve efficiency, the salt solution can pass through the RED battery stack multiple times (multiple passes). This allows for the operation of a part of the system to be stopped, for example, for maintenance, while maintaining the operation of the rest of the system.

[0050] In one embodiment, one container can be both a precipitation device (e.g., precipitating salt from a used solution and removing the regenerated dilute solution) and a dissolution tank (e.g., adding a used solution to a container containing precipitated salt and then dissolving the salt in the solution to make a regenerated concentrated solution). Here, instead of removing the precipitated salt, the salt is left in the container and used to make the regenerated concentrated salt solution.

[0051] The concentrated solution and the dilute solution form separate loops. However, the two solutions can be mixed in a controlled manner (controlled mixing within the RED / PRO stack). Additionally, uncontrolled mixing osmosis (water flow) can occur between the concentrated and dilute solutions within the RED / PRO stack. Due to osmosis, a portion of the water in the dilute solution can be transferred or moved to the concentrated solution within the RED / PRO stack. This movement of water due to osmosis can result in a flow that is controlled to balance the total amounts in the dilute and concentrated solution tanks. Otherwise, the volume in the concentrated solution tank would continue to increase. The controlled mixing or flow between the loops can be controlled by incorporating valves that operate to have the same volume of solution in both loops.

[0052] A method for generating electricity from thermal energy is disclosed. The method includes separating a first saline solution from a second saline solution by a selectively permeable membrane. The method includes receiving thermal energy from a heat source by the first saline solution and / or the second saline solution. The method includes mixing the first saline solution and the second saline solution in a controlled manner and capturing at least a portion of the salinity gradient energy as electricity as the salinity concentration difference between the first saline solution and the second saline solution decreases. The method includes transferring thermal energy from the first saline solution to the second saline solution by a heat pump to increase the salinity concentration difference between the first saline solution and the second saline solution.

[0053] This method may include capturing salinity gradient energy using reverse electrodialysis. This method may further include capturing pressure retarded osmosis of salinity gradient energy to drive a generator. In some embodiments, each of the first saline solution and the second saline solution circulates within a closed system. When heat energy is transferred from the first saline solution to the second saline solution, salt may precipitate in the first saline solution. This method can include introducing the precipitated salt into the second saline solution to increase the salinity concentration difference between the first saline solution and the second saline solution. This method may include using a portion of the generated electricity to generate hydrogen gas and, optionally, oxygen gas by electrolysis. In some examples, transferring heat energy from the first saline solution to the second saline solution includes transferring heat energy from the first saline solution that is at a lower temperature than the second saline solution.

[0054] This method can further include adjusting the transfer of heat from one or more heat sources to the first saline solution and / or the second saline solution based on one or more heat sources or one or more measured values of the state of the first saline solution and / or the second saline solution. The heat sources include one or more of geothermal heat, industrial waste heat (such as power plants), exhaust from transportation vehicles (such as automobiles, ships, trucks, etc.), solar heat, and the like.

[0055] This method can include reversing the circulation flow of the first saline solution and the second saline solution within the closed system. This can be achieved by applying solenoid valves at both ends of the closed-loop system. Reversing the circulation flow does not stop the generation of energy, and the membrane wears evenly on both opposite sides, which can extend the service life of the selective permeable membrane.

[0056] In the following description, conventional features of the disclosed technology that are apparent to those skilled in the art will be omitted or described only briefly. References to various embodiments are not intended to limit the scope of the claims appended hereto. Further, all of the examples described herein are non-limiting and merely illustrate some of the many possible embodiments of the appended claims. Additionally, the specific features described herein can be used in combination with the other features described, in each of the various possible combinations and permutations. Those skilled in the art will know how to achieve other results not specifically disclosed in the examples or embodiments by using the present invention in combination with ordinary experimentation.

[0057] It is also understood that the terms used in the description are for the purpose of describing particular versions or embodiments only and are not intended to limit the scope of the present disclosure, which is limited only by the appended claims. Unless otherwise specifically defined herein, all terms are to be construed as broadly as possible, including any meaning implied from the specification, any meaning understood by those skilled in the art, and / or any meaning defined in dictionaries, treatises, etc. Unless otherwise specifically defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Any methods, devices, and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present disclosure, but the preferred methods, devices, and materials are described herein. All references mentioned herein are incorporated by reference in their entirety.

[0058] As used in this specification and the appended claims, the singular forms "a", "an", and "the" include the plural, and references to a particular numerical value include at least that particular value unless the context clearly indicates otherwise. In this specification, ranges may be expressed as from "about" or "approximately" a particular value and / or to "about" or "approximately" another particular value. When such a range is expressed, another embodiment includes from one particular value and / or to the other particular value. Similarly, when a value is expressed as an approximation by use of the antecedent "about", it will be understood that the particular value forms another embodiment. Also, it is understood that all spatial references, such as for example horizontal, vertical, above, upper, below, lower, left, right, etc., are for illustrative purposes only and can be varied within the scope of the disclosure. For example, the terms "above" and "below" are relative and used only in the context of one another and not necessarily in the sense of "superior" and "inferior". Generally, similar spatial references to different features or components indicate similar spatial directions and / or arrangements. That is, each "first end" is located or oriented at the same end of the device.

[0059] The systems and methods described in this disclosure are generally directed to efficiently extracting useful energy from a salt concentration difference between two solutions by precisely regulating and controlling the mixing of the two solutions. The systems can be used to directly generate electricity, or to generate hydrogen gas or a combination of hydrogen gas and oxygen gas, which can be used as fuel to generate mechanical (and / or electrical) power, or to generate potential energy due to pressure and / or gravity, both of which can be used to drive a turbine or perform other useful work. The systems come in a variety of sizes and outputs. Some embodiments may be configured to generate electricity on the scale of a single residence or commercial building. In some examples, the system includes an industrial power generation system that supplies electricity to a regional or national power grid. In some examples, the system not only generates electricity (or instead of generating electricity), but also supplies hydrogen fuel, for example, to power a fleet of vehicles.

[0060] FIG. 1 shows an example of a system 100 for generating electricity from a salinity gradient. The exemplary system 100 includes a reverse electrodialysis (RED) battery 110. The RED battery 110 includes a cathode 112 and an anode 114 separated by one or more cells 150, 150a, 150b. Each cell 150 contains a salt solution 130, i.e., a liquid mixture of a solvent and a salt, which is dissolved into anionic and cationic components, and the ionic components are free to move relative to each other. Each ion may carry a single charge or multiple charges. In some examples, the solvent and solute are water and sodium chloride (NaCl), respectively. The dissociation ions of NaCl are Na + and Cl -and each carry a single charge. Other solvents and solutes can also be used to form a liquid mixture containing anions and cations that can move freely with respect to each other. The solvent can be an organic or inorganic liquid including, but not limited to, water, alcohol, benzene, and glycerin. The salt solution may be exothermic or endothermic. That is, when the solution is formed, the solution absorbs heat as in the case where potassium chlorate (KClO 3 ) or potassium nitrate (KNO 3 ) dissolves in water, or releases heat as in the case where calcium chloride (CaCl 2 ) dissolves in water.

[0061] As shown in FIG. 1, the salt solution 130 is separated from the dilute solution 140 (i.e., a solution having a lower solute concentration than the salt solution) by the selective permeable membranes 104, 104a to 104d. The salt solution 130 is separated from the dilute solution 140 by cation exchange membranes (104a, 104c) on one side of the cell 150, and is separated from the dilute solution 140 by anion exchange membranes (104b, 104d) spaced apart from the cation exchange membranes (104a, 104c) on the other side of the cell 150. The salt solution 130 is disposed in the space between the cation exchange membranes (104a, 104c) and the anion exchange membranes (104b, 104d). In the absence of these membranes 104, the salt solution 130 diffuses freely into the dilute solution 140 and the salt concentrations of the two solutions become equal. When negatively charged ions move toward the anode 114 and positively charged ions move toward the cathode 112, a potential difference (voltage) is generated across the cell 150. The total voltage of the battery 110 includes the voltage of each cell 150.

[0062] Ions may tend to accumulate near the membrane 104. This accumulation may interfere with the power generation process. To counteract this accumulation, the system 100 can apply a stirring force or a mixing force to the salt solution 130 and / or the dilute solution 140 so that the ions are more uniformly (homogeneously) dispersed throughout the solutions 130, 140. In some examples, the system 100 applies acoustic vibrations to one or more of the solutions 130, 140 to enhance the homogeneity of the solutions 130, 140. The system 100 can effectively enhance the homogeneity of one or more of the solutions 130, 140 by applying acoustic vibrations to the region of the cell 150 where ions accumulate, for example, in the vicinity of one or more of the membranes 104.

[0063] As shown in FIG. 1, electrodes (e.g., cathode 112, anode 114) are surrounded by a dilute solution 140. Alternatively, electrodes 112, 114 may be surrounded by a rinse solution, and the rinse solution may be circulated in a closed loop between electrodes 112, 114 such that the rinse solution is separated from the salt solution 130 and the dilute solution 140. In such an arrangement, the outer selective permeable membrane 104 (i.e., the membrane 104 closest to each electrode 112, 114 of the RED battery 110) is of the same type (e.g., both anion exchange membranes, or both cation exchange membranes). For example, the cation exchange membrane 104 can separate the rinse solution surrounding the cathode 112 from the salt solution 130, and the cation exchange membrane 104 can separate the rinse solution surrounding the anode 114 from the dilute solution 140. In this arrangement, cations moving from the salt solution 130 to the electrolyte surrounding the cathode 112 can be recycled to the anode 114, and the cations can pass through the cation exchange membrane 104 and enter the dilute solution 140. Similarly, the membranes 104 closest to each electrode 112, 114 may both be anion exchange membranes, in which case anions are circulated (within the rinse solution) from the anode 114 to the cathode 112, and the anions pass through the anion exchange membrane 104 and enter the dilute solution 130. In either configuration, a reduction reaction occurs at the cathode 112 and a balancing oxidation reaction occurs at the anode 114. In some examples, the rinse solution contains a supporting electrolyte to enhance the reactions at electrodes 112, 114. In this arrangement, since both electrodes 112, 114 are surrounded by the same electrolyte (rinse solution), the rinse solution can form a resistive load between electrodes 112, 114, and current can flow through that load, resulting in a decrease in the output of the RED battery 110. In some examples, the rinse solution and / or the associated circulation system may be configured to have a high resistance to the output load of the RED battery 110 or the internal resistance of the cells 150 of the RED battery 110. For example, the rinse solution circulation path may be configured to be relatively long.

[0064] The current generated by the battery 110 is a function of the ion migration speed, and the ion migration speed is a function of several factors including the salt concentration gradient (i.e., the salt concentration difference between the salt solution 130 and the dilute solution 140), the temperature of the salt solution 130 (at least), and the characteristics of the membrane 104. The temperature of the salt solution 130 affects the speed at which ions in the salt solution 130 move towards (and across) the membrane 104 due to the increase in the kinetic energy of the ions at high temperatures. According to the Nernst equation, the generated power is a function of the logarithm of the salt distribution ratio between the salt solution 130 and the dilute solution 140. However, as ions move from the salt solution 130 to the dilute solution 140, the salt concentration of the dilute solution 140 increases and the salt concentration of the salt solution 130 decreases. Therefore, the gradient between the "used" salt solution 130 and the "used" dilute solution 140 decreases. To maintain the current (and thus the power output) of the battery 110, the salt concentration difference can be continuously regenerated by refreshing the used salt solution 130 and / or the used dilute solution 140. For this purpose, the used salt solution 130 and / or the used dilute solution 140 can be circulated between the RED battery 110 and the regeneration system (e.g., within a closed loop). Alternatively, the used salt solution 130 and / or the used dilute solution 140 may be continuously replenished from natural sources such as rivers, seas, bays, etc.

[0065] FIG. 2 shows an example of the regeneration system 200. The exemplary regeneration system 200 includes a salt removal subsystem 210. The regeneration system 200 circulates the used dilute solution 140 in a closed loop and returns it to the RED battery 110 as the refreshed dilute solution 140 from the RED battery 110 via the salt removal subsystem 210. In some examples, the salt removal subsystem 210 evaporates and condenses the solvent of the dilute solution 140 and returns the condensed solvent to the RED battery 110 as the refreshed dilute solution 140 for circulation. The system can evaporate the solvent until the remaining dilute solution 140 approaches or falls below the dissolution limit. The remaining dilute solution 140 can be reintroduced into the used salt solution 130 to refresh the salt solution 130. In some examples, the salt removal subsystem 210 evaporates and condenses the solvent of the salt solution 130 and returns the condensed solvent to the RED battery 110 as the refreshed dilute solution 140 for circulation. In the closed-loop RED battery 110, the salt removal subsystem 210 can evaporate and condense both the salt solution 130 and the dilute solution 140, return the condensed solvent from both solutions to the RED battery 110 as the refreshed dilute solution 140 for circulation, and return the remaining solution to the RED battery 110 as the refreshed (concentrated) salt solution 130 for circulation. In some examples, the salt removal subsystem 210 reduces the salt concentration of the dilute solution 140 through the process of salt precipitation, rather than (or in addition to) evaporation, and regenerates the salt concentration difference between the salt solution 130 and the dilute solution 140 in the RED battery 110. Other methods of regenerating the salt concentration gradient include, for example, freezing the used dilute solution 140 by eutectic chilled crystallization (ECC) or using microfiltration and / or membrane separation. In some examples, multiple methods are advantageously combined. For example, the precipitation stage or the freezing stage may be enhanced by a subsequent membrane filtration stage to optimize the total energy required to separate the salt from the used dilute solution 140.

[0066] As shown in FIG. 2, the exemplary salt removal subsystem 210 removes salt from the spent dilute solution 140 by precipitating the salt. Generally, the ability of a solvent to dissolve a solute increases with increasing temperature. Conversely, when the temperature of a solution is lowered below a temperature called the saturation point (the temperature at which the salt concentration of the solution is maximum), the solute usually precipitates. The exemplary salt removal subsystem 210 includes a heat transfer device 216 configured to cool the spent dilute solution 140 to a temperature below the saturation point. When the spent dilute solution 140 is a heat-generating solution, the dilute solution 140 is further cooled as the salt precipitates. In some examples, the heat transfer device 216 heats the refreshed dilute solution 140 to, for example, the temperature of the spent dilute solution 140 before cooling. That is, the heat transfer device 216 can transfer some or all of the thermal energy removed from the spent dilute solution 140 back to the refreshed dilute solution 140, as indicated by the arrows associated with the heat transfer device 216 in FIG. 2. In this way, the temperature of the refreshed dilute solution 140 entering the RED battery 110 is substantially the same as the temperature of the spent dilute solution 140 exiting the RED cell 150.

[0067] In the exemplary salt removal subsystem 210, the precipitated salt 212 settles to the bottom of the salt removal subsystem 210, for example, in the form of a high-density solid. In some examples, the salt removal subsystem 210 includes a conveyance device 230 configured to carry the precipitated salt 212 out of the salt removal subsystem 210. The conveyance device 230 may be a belt, a pump, an Archimedes screw, or any other device or system configured to physically transport the precipitated salt 212 out of the salt removal subsystem 210. For example, if the salt is a solid, the conveyance device 230 may be a mechanical system capable of transporting solid materials. In some examples, the removed salt 212 is conveyed to the salt replenishment subsystem 220 where the salt is reintroduced (e.g., redissolved) into the spent salt solution 130, thereby refreshing the spent salt solution 130. Similar to the regeneration system 200 circulating the dilute solution 140, the regeneration system 200 can also circulate the spent salt solution 130 in a closed loop from the RED battery 110 through the salt replenishment subsystem 220 back to the RED battery 110 as the refreshed salt solution 130. The salt replenishment subsystem 220 increases the salt concentration of the salt solution 130 through the process of redissolving the salt removed by the salt removal subsystem 210, thereby regenerating the salt concentration difference between the salt solution 130 and the dilute solution 140 within the RED battery 110.

[0068] As described above, the ability of a solvent to dissolve a solute generally increases with increasing temperature. Thus, the higher the temperature of the salt solution 130, the higher the salt concentration, and the greater the difference in salt concentration between the salt solution 130 and the dilute solution 140. A solubility curve is a plot of the amount of solute that can be dissolved in a specific amount of solvent as a function of temperature. In some examples, the solubility curve associated with a solution is linear. That is, the amount of solute that can be dissolved in the solvent can vary linearly with temperature change over a wide range of temperatures (e.g., over the entire range in which the solvent is a liquid). In some examples, the amount of solute that can be dissolved in the solvent varies non-linearly with temperature change. In such cases, the amount of solute that can be dissolved in the solvent can increase, for example, by more than a factor of five even within a narrow temperature range. The system 100 can be configured to operate the RED battery 110 within a temperature range in which the salt concentration of the salt solution 130 is high. To dissolve additional salt, it may be necessary to transfer additional heat to the salt solution 130. Further, the system 100 may maintain the temperature of the RED battery 110 at a point above the solubility point to provide a "safety margin" to avoid undesirable precipitation when the salt solution 130 is cooled below the solubility point.

[0069] The salt replenishment subsystem 220 can receive thermal energy from one or more heat sources configured to raise the temperature of the salt solution 130, for example, to dissolve additional salt. For example, the salt replenishment subsystem 220 can receive waste heat from the heat transfer device 216 of the salt removal subsystem 210. The salt replenishment subsystem 220 can also be configured to receive thermal energy from other heat sources, as indicated by the arrows associated with the salt replenishment subsystem 220 of FIG. 2. Examples of heat sources include, but are not limited to, geothermal heat, industrial waste heat, solar heat, combustion heat, vapor compression cycle waste heat (such as a heat pump), heat of chemical reaction, or other forms of heat that are not easily or efficiently convertible to a form usable by conventional means such as driving a turbine.

[0070] The thermal optimization system can be used to optimize the use of thermal energy by the power generation system 100 described herein. The thermal optimization system is further described in U.S. Patent No. 11,067,317, the entire contents of which are incorporated herein by reference. The thermal optimization system transfers thermal energy from one or more heat sources to one or more heat sinks. Examples of heat sinks include the interior of a living or office space during the cool season of the year, a heated pool, a sauna, a steam room, etc. In these examples, the system can be configured to regulate the temperature by adjusting the transfer of thermal energy to the heat sink. For example, the thermal optimization system can monitor the temperature of the heated space and / or heated water and use processor-based logic (such as, but not limited to, implementing one or more PID feedback loops and / or an expert system) to adjust the transfer of heat. During the hot season, the interior space can be a heat source. In this case, the processor-based regulation system can adjust the transfer of thermal energy from these spaces to regulate the temperature.

[0071] FIG. 3 shows an example of a thermal optimization system 300. The exemplary optimization system 300 includes, as described above, one or more heat sources 305, one or more heat sinks 310, and one or more RED batteries 110. In some examples, the power generation system 100 includes, instead of (or in addition to) the RED battery 110, a pressure-retarded osmosis (PRO) system (details of which are discussed below), or other systems for generating electricity from a salinity gradient (e.g., capacitive mixing (CAP)). The optimization system 300 may include one or more pumps 320 configured to move heat from one location to another. In some examples, the optimization system 300 uses vapor compression refrigeration to transfer heat from the heat source to the heat sink. That is, the optimization system 300 can compress the refrigerant and transfer thermal energy from the refrigerant to the heat sink (e.g., by a heat exchanger configured for the purpose of absorbing and distributing thermal energy). The optimization system 300 transfers the compressed refrigerant to the heat source (e.g., by pumping the compressed refrigerant through piping configured for the purpose) and expands the refrigerant to absorb thermal energy from the heat source (e.g., through a heat exchanger configured to supply thermal energy from the heat source). The vapor compression refrigeration system may include a reversing valve or other controllable device that changes the direction of heat transfer. The optimization system 300 controls the reversing valve to change the direction of heat transfer, for example, to cool the interior space during the day when the ambient temperature is relatively high and then reverse the heat flow to heat the interior space at night when the ambient temperature drops.

[0072] The operation of the thermal optimization system 300 may be adjusted by a control system 350 equipped with a processor, as described below with respect to, for example, FIG. 7. The processor may execute instructions to cause the control system 350 to adjust heat transfer between the heat source 305, the heat sink 310, and the RED battery 110 (or the PRO system or the CAP system), based on, for example, the current situation. The control system 350 may adjust heat transfer within the power generation system 100, between subsystems such as, for example, the salt removal subsystem 210 and the salt replenishment subsystem 220. The control system 350 can transmit and receive signals 352, 352a - c with the heat source 305, the heat sink 310, and the RED battery 110 (or the PRO or CAP system). The control system 350 can receive a signal 352 indicating, for example, one or more conditions or states of the heat source 305, the heat sink 310, and the RED battery 110 (or the PRO system). For example, the signal 352 may indicate a measured quantity such as temperature and / or pressure, or it may indicate a user input such as a target temperature of the heated internal space. The temperatures associated with the power generation system 100 include the temperatures of the salt solution 130 and the dilute solution 140 within the RED battery, the salt removal subsystem 210, and / or the salt replenishment subsystem 220, respectively.

[0073] The control system 350 is used to send control signals and controls, for example, the speed of the compressor and / or pump, the direction of the reversing valve, the operating speed of the salt conveyance / transfer device 230, etc., to achieve the indicated target temperature and / or power output. For example, the control system 350 can adjust the temperature of the salt solution to be at or near its dissolution limit. In this way, the control system 350 can optimize the output of the power generation system 100 while efficiently controlling and adjusting the heat transfer between the plurality of heat sources 305 and the heat sinks 310 based on the current situation and user settings. Further, the control system 350 affects the level of waste heat of the vapor compression cycle generated by one or more heat pumps 320 and transfers the waste heat to one or more heat sinks and / or the RED battery 110, thereby efficiently recovering its own waste heat for power generation and other purposes. In this way, the optimization system 300 can transfer heat from any or all of the various heat sources under various dynamic conditions (e.g., conditions change throughout the year or throughout the day) and / or based on the demand of the RED battery 110. Further, the control system 350 can also configure the power generation system 100 to store surplus energy. For example, when the demand for electrical energy is low, the control system 350 can set the RED battery 110 to generate a portion of its energy output as hydrogen gas to be used later as fuel rather than as electrical energy used during generation. Further, in the case of the PRO system, the control system 350 can configure the rate at which pressure is converted to electricity, for example, by controlling the flow rate through a turbine. In this way, the control system 350 can hold some energy in the form of gravitational potential energy, for example, when the power demand is low, and convert more gravitational potential energy to electrical energy when the power demand is high.

[0074] In some embodiments, the system 100 includes a PRO system instead of (or in addition to) the above-described RED battery 110. FIG. 4 shows an example of a PRO system 120. The exemplary PRO system 120 also includes a salt solution 130 separated from the dilute solution 140 by a selective permeable membrane 104c, similar to the above-described RED battery 110. However, instead of directly generating electricity from the salt concentration difference between the salt solution 130 and the dilute solution 140, the PRO system generates a pressure that can take the form of potential energy due to gravity. Thus, the PRO system may not include electrodes. The selective permeable membrane of the PRO system can be configured such that, for example, the solvent rather than the solute can preferentially pass through the membrane from the dilute solution 140 to the salt solution 130 in order to reduce the salt concentration difference between the solutions. In the PRO system, the selective permeable membrane can be a hollow fiber membrane that allows water to pass through but not salt. In the PRO system, the selective permeable membrane can be a hollow fiber membrane, a spiral wound membrane, a flat sheet membrane, or a combination thereof. As a result, as the solvent passes through the membrane 104c and moves into the salt solution 130, the pressure and / or average height of the solvent in the salt solution 130 can increase over time. The system 100 can convert the increased pressure and / or potential energy due to gravity of the salt solution 130 into a more usable form of power, such as electrical energy, for example, by directing the (elevated) salt solution 130 to a turbine, a paddle wheel, or other suitable mechanism for generating electricity. Next, the system 100 can circulate the used salt solution 130 through a solvent removal system similar to the above-described salt removal subsystem 210. For example, the solvent recovery system can remove excess solvent by evaporation (optionally at a partial vacuum to lower the boiling point) and subsequent condensation. The solvent recovery system then returns the condensed solvent to the PRO system 120 as a refreshed or "make up" dilute solution 140 and circulates it, and returns the refreshed salt solution (after the excess solvent has been removed) to the PRO system 120 as a refreshed salt solution 130 and circulates it.Alternatively (or additionally), the solvent recovery system may precipitate the solute from the used salt solution 130 and then return the used salt solution as a "makeup" dilute solution 140 to the PRO system 120 for circulation, and introduce the precipitated salt back into the salt solution 130, for example, via the transport device 230 of FIG. 2. Similar to the RED battery 110 described above, the rate (or speed) of the electric power generated by the PRO system 120 is a function of at least the salt concentration difference between the salt solution 130 and the dilute solution 140 and at least the temperature of the salt solution 130.

[0075] The RED system can be a capacitive (CAP) system instead of (or in addition to) the RED battery and / or the PRO system. The CAP system is an electrode-based technology used to generate electrical energy from a salt concentration gradient. Power generation using the CAP system is based on the charging and discharging cycles of the electrodes. The electrodes of the CAP system are successively exposed to two solutions with significantly different salt concentrations. The CAP system charges energy in the form of a salt concentration gradient, extracts energy from the salt concentration difference, and utilizes the voltage increase that occurs between two electrodes immersed in the salt solution when its salt concentration changes. The amount of power generated mainly depends on the following characteristics of each electrode, namely the amplitude of the potential increase due to the change in salt concentration and the potential in the high-salt solution. The electrodes may be the same so that the flow of the system can be reversed and the polarity changed without stopping the generation of electricity. The CAP system may include one or more selective permeable membranes as disclosed herein.

[0076] As shown in FIG. 1, the salt solution 130 is separated from the dilute solution 140 by cation exchange membranes (104a, 104c) on one side of the cell 150 and from the dilute solution 140 by anion exchange membranes (104b, 104d) on the other side of the cell 150. Alternatively, the salt solution 130 and the dilute solution 140 may be separated by a single selective permeable membrane 140 (e.g., a cation exchange membrane or an anion exchange membrane). A potential difference (voltage) across the membrane 140 is generated by the selective movement of ions across the single membrane 140. Similar to the embodiment of FIG. 1, the current generated by the single membrane embodiment (e.g., a flow pump) of the RED cell 150 is also a function of the ion migration rate, which is a function of several factors including the salt concentration gradient between the salt solution 130 and the dilute solution 140, (at least) the temperature of the salt solution 130 (since the kinetic energy of the ions increases at high temperatures), and the characteristics of the single membrane 104.

[0077] In some embodiments, the system includes a first RED battery 110a configured to use the exothermic salt solution 130a and a second RED battery 110b configured to use the endothermic salt solution 130b. The system can transfer the heat generated by dissolving a solute in the exothermic salt solution 130a to the endothermic solution 130b to replace the heat absorbed when dissolving the solute.

[0078] In some embodiments, a portion of the generated power is used to produce hydrogen gas, for example, by splitting water through electrolysis. For instance, when the dilute solution is water, a potential difference of 1.23 volts can be applied to the water to split it into hydrogen and oxygen. Oxygen can be supplied and fed into spaces such as buildings and other indoor areas. Hydrogen and / or oxygen can be stored, for example, for later use as a battery. Either or both of the salt solution or the dilute solution can be decomposed by electrolysis. FIG. 5 shows an example of a RED battery 110 configured to produce hydrogen. The released hydrogen gas and oxygen gas may "bubble" on the surfaces near the respective cathodes 112 and anodes 114 of the RED battery 110. The system 100 separates the oxygen gas and hydrogen gas (for example, by physically separating the cathodes 112 and anodes 114), captures the hydrogen (for example, when the hydrogen gas bubbles on the surface near the cathode and captures it), and then transports the hydrogen to an appropriate location by appropriate means for use as fuel. In such cases, the system 100 needs to replenish or "refill" the solvent lost in electrolysis from, for example, a small stream or other fresh water sources. The RED battery 110 may be configured such that electrolysis occurs naturally. That is, the RED battery 110 can be configured to generate a potential difference sufficient to cause electrolysis of its solvent. In some examples, the regeneration system uses electrolysis to refresh the salt concentration of the spent salt solution 130 when the fresh water for replenishment is circulated to the RED battery 110 (or a PRO or CAP system) as a refreshed dilute solution 140. In some examples, the system includes another water reservoir for producing hydrogen gas by electrolysis (instead of, for example, electrolyzing the solvent of the RED battery or a PRO or CAP system). The RED battery or PRO system remains in a closed loop, and the other water reservoir can have its own "replenishment" source. In these embodiments, the water reservoir can also function as a heat reservoir or play other roles in the heat optimization process.

[0079] FIG. 6 shows a flowchart 600 of an example of a method for generating electric power from thermal energy. In step 602, the exemplary method includes separating a first saline solution 130 from a second saline solution 140 by a selective permeable membrane 104. The selective permeable membrane 104 is configured to provide a controlled mixing of the first saline solution 130 and the second saline solution 140, and when the mixing occurs, the salinity gradient energy can be captured in a more useful form. In some examples, the selective permeable membrane 104 is configured such that the solvent of the first saline solution 130 preferentially passes through the membrane and enters another second saline solution 140, as in the case of a PRO system, for example. In some examples, the selective permeable membrane 104 is configured such that either anions or cations of the first saline solution 130 preferentially pass through the membrane and enter another second saline solution 140, as in the case of a RED battery 110, for example.

[0080] In step 604, the exemplary method includes receiving thermal energy from a heat source. The power generated by the RED battery 110 (or the PRO system) is a function of temperature. With the received thermal energy, the RED battery 110 can continue to operate (e.g., generate electricity). In some examples, the control system 350 is configured to adjust the amount of thermal energy received and to configure which heat source 305 provides the thermal energy. In some examples, the control system 350 is configured to transfer waste heat from one or more heat pumps 320 to the RED battery 110. In some embodiments, the power generation system 100 provides some or all of the power for operating one or more heat pumps 320. As a predictive example, the efficiency of the RED battery 110 can be about 30% (i.e., 30% of the thermal energy transferred to the RED battery 110 is converted into electricity or other usable energy forms). The coefficient of performance (COP) of the heat pump 320 can be 3 to 4 (i.e., the heat pump 320 may require 1 KW of power to take in 2 to 3 KW of power from a heat source and transfer 3 to 4 KW to a heat sink (the sum of the input power and the thermal power taken in from the heat source)). For example, for a heat pump 320 with a COP of 4, 1 KW of power may be required to transfer a total of 4 KW of heat to the RED battery 110. The heat pump 320 can transfer heat from a low-grade or "waste" heat source, such as a heat source below 300 °C, which is not easily converted into a useful energy form. In some predicted examples, the heat source may be provided by an industrial process that would otherwise simply discharge waste heat to the environment. When the efficiency is 30%, the RED battery 110 can generate 1.2 KW of power from the 4 KW of heat transferred. In this predictive example, 1 KW of power can be used to supply power to the heat pump 320, and 200 W of power can be left for other purposes. Thus, in this predictive example, the combined system 100 of the RED battery 110 and the heat pump 320 generates a net output of 200 W of power without a net input of power other than 3 KW of "waste" heat.When the waste heat is from an industrial process, the combined system 110 of the RED battery 110 and the heat pump 320 is expected to provide the advantage of cooling 3 KW of waste heat before releasing it to the environment while generating a net output of 200 W. The expected net efficiency of the combined system 110 can be further amplified by the improvement in the efficiency of the RED battery 110.

[0081] Furthermore, the power generation system 100 can capture a portion of the waste energy generated by one or more heat pumps, convert the waste energy into electrical energy and supply power to the heat pump 320, thereby improving the coefficient of performance (COP) of the heat pump 320, such as a heat pump used for heating or cooling a living space. For example, for a heat pump with a heating COP of 3, 1.5 KW of power may be required to pump 3 KW of heat from a heat source to a heat sink. If the heat sink does not require all 4.5 KW of power (3 KW of pumped heat and up to 1.5 KW of waste heat), the control system 350 can configure the optimization system 300 to transfer some or all of the waste heat to the RED battery 110, convert it into power for the heat pump 320, and improve the effective COP of the heat pump 320. Additionally, the control system 350 can configure the power generation system 100 to convert a portion of the waste energy into a form that can be stored for later use, such as when the instantaneous power demand is greater than the amount of power that can be generated, for example. For example, the PRO system can hold the waste energy in the form of un-released pressure and / or gravitational potential energy and release it in the future, such as when the demand for electrical energy increases. Similarly, the RED battery 110 can generate hydrogen gas to be used as a future fuel instead of generating a certain amount of electrical energy. Therefore, the waste heat from the heat pump 320 can be flexibly captured and released to further increase the effective COP of the heat pump.

[0082] In step 606, an exemplary method includes mixing the first saline solution 130 and the second saline solution 140 in a controlled manner. In step 608, the exemplary method includes capturing at least some of the salinity gradient energy as electricity. As described above, the RED battery 110 or the PRO system or the CAP system can be configured such that as the solutions (130, 140) are mixed, the salinity gradient energy is converted into a more useful form. In step 610, the exemplary method includes transferring thermal energy from the first saline solution to the second saline solution by the heat pump 320. In step 612, the exemplary method includes increasing the salinity difference between the first saline solution and the second saline solution. As described above, the heat pump 320 can cool the used dilute solution 140, precipitate salts from the dilute solution 140, and refresh the dilute solution. The heat pump enhances the process of transferring heat from the used dilute solution 140 to the used saline solution 130 and dissolving the salts introduced into the saline solution 130. Alternatively (or in addition thereto), the heat pump 320 may heat the used saline solution 140 to evaporate the saline solution 140 and refresh the saline solution. The evaporated solvent can be condensed when the solvent vapor is returned to and circulated in the RED battery 110 as the refreshed dilute solution (e.g., cooled by the heat pump).

[0083] FIG. 8 shows an example of a regeneration system including a salt precipitation system. In this embodiment, the salt precipitation system includes salt precipitation apparatuses 880, three heat exchangers 882, 884, 838 (in alternative embodiments, one heat exchanger, two heat exchangers, or more than three heat exchangers may be included), and an external heat source system 890. This regeneration system circulates the used dilute solution 840 from the RED or PRO battery 810 through the salt precipitation system in a closed loop and returns it to the RED or PRO battery 810 as the refreshed dilute solution 845. Optionally, the refreshed dilute solution 845 may be stored in a tank 846 that holds the dilute solution for a certain period of time before being sent to the RED or PRO battery 810. The used dilute solution 840 is sent to the salt precipitation apparatus 880, where the heat exchanger 884 removes heat energy from the used dilute solution 840 to precipitate the salt 885, thereby further diluting the solution in the salt precipitation apparatus 880 and providing the regenerated dilute solution 845 (which may also be referred to as the refreshed dilute solution). The salt 885 is sent to a concentrate tank 836 that holds the used concentrated solution 830 (or a tank configured to regenerate the used concentrated solution). In the concentrate tank 836, by applying heat energy through, for example, the heat exchanger 838 as an option, the salt 885 is dissolved in the used concentrated solution 830, increasing the salt concentration and generating the regenerated concentrated solution 835 (which may also be referred to as the refreshed concentrated solution).

[0084] The salt precipitation system, instead of (or in addition to) evaporation, reduces the salt concentration of the used dilute solution 840 through the process of salt precipitation, uses the precipitated salt 885 to increase the salt concentration of the used concentrated solution 830, regenerates the salt concentration difference between the concentrated solution 835 and the dilute solution 845, and directs the stream towards the RED or PRO battery 810 so that it can be used there.

[0085] As shown in FIG. 8, an exemplary salt precipitation system removes salt from the spent dilute solution 840 by precipitating the salt. When the temperature of the solution is lowered below a temperature known as the saturation point (the temperature at which the salt concentration of the solution is maximum), the solute usually precipitates. This system includes a heat transfer device shown as heat exchanger 884 in FIG. 8, which is configured to cool the spent dilute solution 840 to a temperature below the saturation point. Heat exchanger 882 passively exchanges heat between the refreshed dilute solution 845 and the spent dilute solution 840. Since the temperature of the solution in the dilute solution tank 846 can optimally be about 30° C. to about 50° C., heat exchanger 882 heats the refreshed dilute solution 845 to, for example, the temperature of the spent dilute solution 840 before cooling. That is, heat exchanger 882 can return some or all of the thermal energy removed from the spent dilute solution 840 to the refreshed dilute solution 845. The spent dilute solution 840 can be about 30° C. to about 40° C. and drops to about 5° C. within the precipitation device. In this way, the temperature of the refreshed dilute solution 845 entering the battery 810 is substantially the same as the temperature of the spent dilute solution 840 exiting the battery 810. Heat exchanger 882 can also perform both cooling and heating roles as described above, or can be placed within the system to perform only heating after the regenerated dilute solution 845 leaves the precipitation device 880. For example, hot air can be blown onto the stream of the regenerated dilute solution 845 for heating. Control valves 811, 812 are incorporated into the system to control and balance the flow rate of the solution. Pumps 813, 814 are included in the system to move the solution and flow it into the RED or PRO battery 810. Pumps 813, 814 can be any pump or device known in the art that acts on the fluid to move the fluid, for example, a diaphragm pump, a centrifugal pump, or a peristaltic pump, but are not limited thereto. The number of control valves and heat pumps can vary between the disclosed systems. Those skilled in the art will understand that one or more control valves can be added to any embodiment of the present disclosure.The heat exchangers 884, 838 transfer heat from the precipitation device 880 or the tank 836 to the heat source system 890, respectively. The heat exchangers 884, 838 can be submerged in the precipitation device 880 or the tank 836, respectively, and may be coils through which a liquid circulates, or may be other heat exchangers known in the art, such as shell or tube heat exchangers.

[0086] FIG. 8 includes an external heat source system 890 that includes a heat exchanger 891 that adds heat to the system and a heat pump 892. The external heat source system 890 can supply thermal energy to the concentrated liquid tank 836 in combination with the salt precipitation system. The external heat source system 890 is shown to have a closed loop, optionally with a refrigerant loop, for heating and cooling the precipitation device 880 and the concentrated liquid tank 836. The heat exchanger 891 draws in low-grade heat (e.g., less than about 100° C., or less than about 200° C.) or ultra-low-grade heat (e.g., ambient air, or less than about 80° C.), optionally directly from the air or from an external heat source. The external heat source supplies external heat to the heat source system 890, and the external heat is ultimately converted to electricity by the RED / PRO battery 810.

[0087] In other embodiments, the heat source system 890 is absent, and instead high-grade heat (e.g., steam, or any heat source that supplies heat above about 100° C.) can be directly added to and heated in the concentrated liquid tank. FIG. 9 shows an example of a regeneration system that includes a salt precipitation system, but does not have the external heat source system included in FIG. 8. In FIG. 9, when the salt precipitation device 880 is cooled, thermal energy is optionally released as heat 991. The heat 991 can be removed, sent to any source of generation, released, or returned to the system via heat 992 by any means known in the art. The heats 992, 993 can be introduced into the system from ambient energy, a heat pump, or other locations within the system (e.g., heat 991).

[0088] Figure 10 shows an example of a regeneration system including a salt decomposition system. In this embodiment, the salt decomposition system includes an absorber 1080, a salt decomposition vessel 1081, two heat exchangers 1082, 1084 (in an alternative embodiment, one heat exchanger or more than two heat exchangers may be included), and a heat pump 1013. Heat is applied to decompose the salt. This regeneration system circulates the used dilute solution 1040 from the RED or PRO battery 1010 through the salt decomposition vessel 1081 in a closed loop, applies heat in the salt decomposition vessel 1081 to warm the tank, forms vapor and gaseous salt 1085, and returns it to the RED or PRO battery 1010 as the refreshed dilute solution 1045. The heat exchanger 1084 is arranged to transfer thermal energy between the used dilute solution stream 1040 and the refreshed dilute solution stream 1045. The used concentrated solution 1030 circulates in a closed loop from the RED or PRO battery 1010 through the absorber 1080 and then returns to the RED or PRO battery 1010 as the refreshed concentrated solution 1035. The heat exchanger 1082 is arranged to transfer thermal energy between the used concentrated solution stream 1030 and the refreshed concentrated solution stream 1035. When heat is applied to the vessel 1081, the gaseous product (e.g., decomposed gaseous salt) 1085 is released from the vessel and received by the absorber 1080, where the salt decomposed in the vapor is absorbed by the used concentrated solution 1035, increasing the salt concentration of the solution. Salt is removed from the used dilute solution 1040 in the salt decomposition vessel 1081, leaving the regenerated dilute stream 1045. The heats 992, 993 can be introduced into the system from ambient energy, the heat pump, or other locations within the system. The heat 991 is removed and can be used by the heat pump or released. The heat pump 1013 can perform heating and cooling simultaneously (see heat input 991 and heat output 993) and can also use heat / thermal energy 994 from another source. A control valve 1011 is incorporated into the system to control and balance the flow rate of the solution. The salt decomposition vessel 1081 separates gas from the liquid and may include a flash tank or a stripper column for decomposing the salt in the solution.The salt decomposition container 1081 and the absorber 1080 may be any container that realizes the functions described in this specification and can be easily understood by those skilled in the art, or a group of containers, tanks, and / or columns.

[0089] FIG. 11 shows another example of a regeneration system including an evaporation system. The embodiment of FIG. 11 is different from the embodiment of FIG. 10 in that it incorporates an evaporator 1091 and a condenser 1090. In this example, the used concentrated solution 1030 circulates in a closed loop from the RED or PRO battery 1010 through the evaporator 1091. In the evaporator 1091, heat 992, 993 is applied, causing the solution to boil, and water evaporates as vapor 1093. As a result, a more concentrated solution, that is, a refreshed concentrated solution, remains, which is returned towards the RED or PRO battery 1010. The vapor 1093 is sent from the evaporator 1091 to the condenser 1090. In the condenser 1090, the container is cooled, the vapor condenses into water and is mixed with the used dilute solution 1040 to form a refreshed dilute solution 1045, which is returned to the RED or PRO battery 1010 in a closed loop. The heat pump 1013 provides a cooling effect to the condenser 1090. Conventionally, a cold water loop was used instead of this heat pump, and all the heat input to the system was lost. By incorporating a heat pump as shown, heat is recovered and the energy efficiency of the process is improved. The evaporator 1091 and the condenser 1090 may be any tank, container, column, or group thereof that realizes the functions described in this specification and can be easily understood by those skilled in the art.

[0090] FIG. 12 is an example of a regeneration system including electrodialysis and salt precipitation. The dilute solution 1141 and the concentrated solution 1131 are sent to an electrodialysis system 1190, where electricity is supplied and ions move from the dilute solution to the concentrated solution, separating salt from the dilute solution 1141 and producing an ultra-dilute solution 1147. Using electrodialysis, electricity is used to produce a more concentrated solution 1132 and an ultra-dilute solution 1147. The used dilute solution 1140 has salt removed in a precipitation device 1180, leaving a dilute solution 1141 (with a lower salt concentration than the used dilute solution 1140). The dilute solution 1141 is further diluted using electrodialysis beyond the solubility curve, producing an ultra-dilute solution 1147 and forming a larger salt gradient. As shown in FIG. 12, the ultra-dilute solution flows from the electrodialysis tank to a dilute solution storage tank 1146, where it is mixed with the dilute solution 1141 (if present) from the precipitation device 1180. In another embodiment, valves may be employed and arranged to change the flow of the solution, as would be readily envisioned by one of ordinary skill in the art, to configure the system such that the ultra-dilute solution 1147 flows directly to the battery 1110.

[0091] The used dilute solution 1140 is sent to the salt precipitation device 1180 where it is cooled (heat 1191 is removed). When heat energy is removed from the used dilute solution 1140, salt 1185 precipitates, and the solution in the salt precipitation device 1180 is further diluted to produce a dilute solution 1147. This dilute solution may be sent to the storage tank 1146 or further diluted by electrodialysis treatment. The regenerated dilute solution 1145 (which may also be referred to as the refreshed dilute solution) has the same salt concentration as the ultra-dilute solution 1147 or a lower salt concentration than the dilute solution 1141 after being mixed with the ultra-dilute solution 1147 in the tank 1146. The regenerated dilute solution 1145 flows back to the battery 1110 to utilize the salt concentration gradient. The salt 1185 is mixed with the used concentrated solution 1130 to increase its salt concentration and then sent to the concentrated solution storage tank 1136. In the concentrated solution storage tank 1136, optionally, heat 1192 or other heat energy sources are applied so that the salt 1185 is dissolved in the used concentrated solution 1130, the salt concentration increases to produce a concentrated solution 1131, and then the concentrated solution 1131 is sent to the electrodialysis system 1190 where the salt concentration increases to produce a more concentrated solution 1132. The more concentrated solution 1132 may have a salt concentration higher than or equivalent to that of the regenerated concentrated solution 1135 (which may also be referred to as the refreshed concentrated solution). There may be excess salt (not shown) at the bottom of the concentrated solution tank 1136. If excess salt is present, the concentrated solution tank 1136 may function as a battery so that the process can continue to be executed when temporarily no excess heat is available.

[0092] The salt precipitation system reduces the salt concentration of the used dilute solution 1140 through the process of salt precipitation, rather than (or in addition to) evaporation, increases the salt concentration of the used concentrated solution 1130 using the precipitated salt 1185, and increases the salt concentration difference between the concentrated solution 1131 and the dilute solution 1141. In this embodiment, unlike FIG. 2, the concentrated solution 1131 and the dilute solution 1141 are further processed by electrodialysis before being reintroduced into the battery 1110, and the salt concentration difference between the solutions is increased. The electricity 1171 generated by the RED or PRO battery 1110 can be used, stored, and / or used as the electricity 1170 for operating the electrodialysis system 1190 by any means known in the art.

[0093] In FIG. 12, a tank different from the RED or PRO battery 1110 is used for the electrodialysis system 1190, but in other embodiments, the same tank used for reverse electrodialysis can be used for electrodialysis.

[0094] FIG. 13 is an example of a regeneration system incorporating a membrane distillation system 1390 and salt precipitation instead of the electrodialysis system 1190 of FIG. 12. The membrane distillation system 1390 includes a heat pump (not shown) that evaporates water that can penetrate into the dilute solution through a porous hydrophobic membrane (not shown) to lower the salt concentration and produce an ultra-dilute solution 1347. The ultra-dilute solution 1347 can be directly sent to the battery 1110 or the dilute solution tank as shown, with valves arranged to change the flow of the stream. As shown in FIG. 13, the ultra-dilute solution 1137 flows from the membrane distillation system 1390 to the dilute solution storage tank 1146, where it is mixed with the dilute solution 1141 (if present) from the precipitation device 1180. In another embodiment, the system can be configured such that the ultra-dilute solution 1347 flows directly to the battery 1110 by using valves arranged to change the flow of the solution, as can be easily envisioned by those skilled in the art.

[0095] Within the concentrated liquid storage tank 1136, as an option, heat 1192 or other heat energy sources are applied so that salts 1185 are dissolved in the used concentrated solution 1130, the salt concentration increases to produce a concentrated solution 1131. Thereafter, the concentrated solution 1131 is sent to the membrane distillation system 1390 where the salt concentration increases to produce a more concentrated solution 1332. The more concentrated solution 1332 may have a salt concentration higher than or equivalent to that of the regenerated concentrated solution 1135 (which may also be referred to as the refreshed concentrated solution).

[0096] Figure 14 shows an example of a regeneration system incorporating a membrane distillation system 1390 without salt precipitation. The used dilute solution 1140 is sent to the dilute liquid storage tank 1146 where it is cooled (i.e., heat energy 1191 is removed) and then sent to the membrane distillation system 1390. The used concentrated solution 1130 is sent to the concentrated liquid storage tank 1136 where it is heated (i.e., heat energy 1192 is introduced into the system) and then sent to the membrane distillation system 1390. Heating and cooling of the storage tanks can optionally be provided by one or more heat pumps (not shown). The used dilute stream 1140 and the used concentrated stream 1130 are sent to a membrane distillation system 1390 that operates using the vapor pressure difference generated by the temperature difference between the streams across a hydrophobic membrane (not shown). The regenerated dilute solution 1445 and the regenerated concentrated solution 1435 are produced by the operation of the membrane distillation system 1390 and then, as shown in Figure 14, are circulated to the RED or PRO battery 1110 via the storage tanks 1146, 1136 as required.

[0097] FIG. 15 is an example of a RED / PRO tank combined with a playback system in which multiple tanks operate in a batch system. Each of the operation tanks 1501, 1502, 1503, 1504 can be a cooling tank (i.e., a precipitation device), a heating tank (i.e., a dissolution tank), or can be inactive at any point in time. For example, tank 1501 can first operate as a cooling tank, precipitate salts from the used dilute solution, leaving the regenerated dilute solution 1545, and the regenerated dilute solution 1545 can then be sent to the dilute solution tank 1546. Next, the operation of tank 1501 is changed to a heating tank, and the used concentrated solution 1530 is sent to the tank holding the precipitated salts, and then heated so that the salts dissolve in the solution, leaving the regenerated concentrated solution 1535, and the regenerated concentrated solution 1535 can then be sent to the concentrated solution tank 1536. At other times, tank 1501 may be inactive if maintenance is required or for other reasons. This change in operation can be applied to any of the operation tanks within the batch system as needed.

[0098] The valve system 1520 operates by separating the tanks from the RED / PRO battery 1510 and directing all or part of the flow of each of the used dilute solution 1540 and the used concentrated solution 1530 to one or more of the operation tanks 1501, 1502, 1503, 1504. The second valve system 1522 operates by separating the operation tanks 1501, 1502, 1503, 1504 from the storage tanks and directing the flow of the regenerated dilute solution 1545 and the regenerated concentrated solution 1535 to the respective storage tanks 1546, 1536. The dilute solution tank 1546 receives and holds the regenerated dilute solution 1545, and the concentrated solution tank 1536 receives and holds the regenerated concentrated solution 1535. Although FIG. 15 shows the operation of four tanks, it is also possible to connect fewer than four or more than four tanks to the system and operate them in a batch system.

[0099] Figure 16 shows a method of manufacturing water using a steam condenser 1601, a compressor or heat pump 1602, and an evaporator 1603. A refrigerant 1612 circulates through the steam condenser 1601, the heat pump 1602, and the evaporator 1603. As shown, the evaporator 1603 removes water vapor from the ambient air and discharges air that is cooler and drier than the incoming ambient air, along with water. The condenser releases latent heat, which can be used in the salinity gradient energy system 1610 disclosed herein. For example, this system can be used to dehumidify (or remove moisture from) ambient air in a home or other building, or optionally generate heat and convert it to electricity with a RED / PRO battery.

[0100] Figure 17 incorporates the system of Figure 16 as a method of manufacturing a warm water tank 1620 and a cold water tank 1625 that can be used to heat and cool the solution used in a salinity gradient engine thermal system 1610 as disclosed herein, optionally including a regeneration system as shown in Figures 8 - 15. The evaporator 1603 cools water to create the cold water tank 1625, and the condenser 1601 heats water to create the warm water tank 1620. A heat transfer medium 1613 (e.g., water, glycol, oil, refrigerant) flows in a closed loop from the cold tank 1625 through the salinity gradient engine system 1610, and a heat transfer medium 1614 flows in a closed loop from the warm tank 1620 through the salinity gradient engine thermal system 1610. Optionally, a heat sink 1640 is shown and serves to absorb or dissipate excess heat from the system. If the system is generating more heat than necessary, that heat can be transferred to the heat sink, and for example, heat 1631 can be released into the atmosphere. Optionally, another heat source 1630 that supplies heat energy or heat 1631 to the system is also shown. Examples of each of the other heat sources include, but are not limited to, any means known in the art such as heat exchangers, industrial steam, radiators, ambient temperature, coils, convection, etc.

[0101] The salt concentration gradient system disclosed in this specification can generate water (also referred to as atmospheric water generation in this specification). Atmospheric water generation is a process of extracting water from the air using various techniques such as condensation, adsorption, and cooling. The concept of atmospheric water generation is based on the fact that even in dry desert areas, the atmospheric environment contains a significant amount of water vapor. When combined with a RED / PRO battery, a heat pump, and a closed-loop process, energy and water can be generated.

[0102] One means of atmospheric water generation is condensation. In condensation, air is cooled to a temperature below the dew point / condensation temperature, and the water vapor in the air is condensed into liquid water. This method is commonly used in thermodynamic cycles such as dehumidifiers and heat pumps. This process depends on the temperature and humidity of the air, which can be easily understood by those skilled in the art, for example, by referring to a psychometric chart.

[0103] Another means of atmospheric water generation is adsorption. In adsorption, desiccants such as silica gel and zeolite are used to absorb moisture in the air. When the desiccant absorbs moisture and becomes saturated if necessary, it is heated to release water, which can be collected and used. Similarly, liquid desiccants, which are substances with a high affinity for water molecules, can be used to remove moisture from the air in a method that can be called a liquid desiccant dehumidification process. This process can include passing air (optionally, air with a medium to high humidity content exceeding about 30% and not dry air) over a surface coated with a liquid desiccant that absorbs water from the air. When the absorbed water is removed from the liquid desiccant, it can be regenerated to its original state. Any solid desiccant or liquid desiccant known in the art can be used herein.

[0104] The liquid desiccant dehumidification process can be a closed-loop system that includes two independent air treatment units: a dehumidification unit (also called a conditioner) and a regeneration unit (also called a generator). The dehumidification unit typically consists of an absorber where the liquid desiccant is sprayed or coated on a surface and a fan or blower circulates the humid air over the surface. As the air passes over the surface, the liquid desiccant absorbs moisture from the air and the dried air is discharged into the conditioned space.

[0105] The regeneration system can include another container that contains the spent liquid desiccant and a heat source (in this case, a heat pump). In this embodiment, the absorbed moisture is removed from the liquid desiccant through a process called regeneration where heat is applied to the liquid desiccant to remove the absorbed moisture. The removed water vapor can be condensed via the heat pump to produce water (which can be made into potable water by adding filtration (e.g., reverse osmosis or other known systems used in the art)), or added to the dilute solution to increase the salinity gradient of the RED / PRO battery. This produced water can be used as a raw material (or feed) for electrolysis and / or RED and thus can be used to produce hydrogen additionally or alternatively.

[0106] Typically, atmospheric water generation consumes a great deal of energy because it works against the latent heat of vaporization of water to produce water. When combined with a closed-loop salinity gradient engine system such as RED, the latent heat can be utilized and converted into hydrogen and / or electricity instead of being released into the atmosphere. Advantages of the liquid desiccant dehumidification process include the ability to extract water from low humidity levels even in hot and humid climates, and the ability to utilize waste heat, solar energy, and / or a heat pump for regeneration. Condensing water vapor using only a heat pump in a hot and dry climate region would be much more difficult than using a combination of a heat pump and a desiccant. Combining the liquid desiccant dehumidification process with a heat pump and a salinity gradient engine system can produce a significant amount of water and energy even in very hot and dry climates.

[0107] Figure 18 is an example of atmospheric water generation using a liquid desiccant dehumidification process. In this example, water is removed from the air and absorbed by the desiccant in conditioner 1812. The used (weakened) desiccant 1820 is transferred to generator 1811, where the desiccant is regenerated by the evaporation of water, thereby regenerating strong desiccant 1821, and the strong desiccant 1821 is returned to conditioner 1812. Heat pump 1882 is used to transfer heat between the stream of weakened desiccant 1820 and the stream of regenerated strong desiccant 1821. The vapor 1884 removed from generator 1811 is sent to vapor condenser 1815, where it is cooled and liquefied, and water 1885 for any purpose, including drinking water (with a filtration system applied), is generated.

[0108] Figure 18 utilizes the manufacturing methods of hot water tank 1813 and cold water tank 1814, which can be used to heat and cool a solution (e.g., water) used in the salt concentration gradient engine heat system 1810 disclosed herein, which optionally includes a regeneration system as shown in FIGS. 8 - 15. Heat exchanger 1884 cools the water to create cold tank 1814, and heat exchanger 1883 heats the water to create hot water tank 1813. The heat transfer medium 1816 (e.g., water, glycol, oil, refrigerant) flows in a closed loop from heat exchangers 1883, 1884 to heat pump 1802. One or more heat sinks and other heat sources can be incorporated to provide heating or cooling to one or both of hot water tank 1813 or cold water tank 1814. Hot water tank 1813 supplies hot water to generator 1811 and salt gradient engine heat system 1810 as hot supply stream 1830 in a closed loop, and the hot supply stream 1830 returns to hot water tank 1813 as a lower temperature stream 1831. Cold water tank 1814 supplies cold water as cold supply stream 1832 to vapor condenser 1815, to conditioner 1812, and to salt gradient engine heat system 1810 in a closed loop, and the cold supply stream 1832 returns to cold water tank 1814 as a higher temperature stream 1833.

[0109] The salt concentration gradient system disclosed in this specification may include forward osmosis (FO) as a means of regenerating the spent dilute solution and the spent concentrated solution from the RED / PRO battery, i.e., as a regeneration system. In a forward osmosis system, a feed solution such as a spent concentrated solution can be placed on one side of a semi-permeable membrane, and a draw solution (or driving solution) can be placed on the opposite side of the semi-permeable membrane. The draw solution can be any solution as long as it has a higher osmotic pressure than the feed solution. The draw solution can contain different salts, synthetic salts, or can be essentially the same as the feed solution but at a higher concentration. A salt gradient is formed to draw water out of the spent concentrated solution and then regenerated by a switchable solubility system incorporating the draw solution. Due to the osmotic pressure gradient generated by the draw solution, water molecules are drawn through the membrane from the feed solution while salts and other contaminants remain on the feed solution side. Thereby, the concentrated solution can be regenerated and returned to the RED / PRO battery. The membrane used in the FO system can be any membrane that may be used in the PRO battery. However, in the case of FO, the membrane does not need to be designed to withstand as high a pressure as the PRO membrane.

[0110] A forward osmosis system may incorporate a switchable solubility system, and the switchable solubility system includes a draw solution and carbon dioxide (CO 2A reversible reaction between [substance] and water is utilized to form a solution with switchable solubility characteristics. These switchable solubility solutions can switch between hydrophobic and hydrophilic forms. The method of forming a switchable solubility solution includes dissolving an amine in water to form a solution at a specific pH level. For example, amines include 1-cyclohexylpiperidine, N-methyldipropylamine, ethyl 4-(diethylamino)butanoate, N,N-dimethylphenethylamine, N,N-diethylbutylamine, etc. The draw solution mentioned in this specification is a solution with a high osmotic pressure or concentration for drawing water across a semipermeable membrane. Therefore, the switchable solubility solution may be a draw solution in a forward osmosis system. When CO 2 is introduced, it reacts with the amine to form a salt, and the pH of the solution decreases. This change in pH causes a change in the solubility of the amine, increasing or decreasing its solubility in water. Therefore, the solubility of the amine can be changed by the presence of CO 2 , and it is reversible by applying heat. Specifically, when the pH is low (e.g., less than about 7, or between 7 and 1), the amine is more soluble in the solution. Conversely, when the pH is high (e.g., above 7), the amine is less soluble in water and the amount dissolved in the solution also decreases. The solubility of CO 2 depends on temperature. As the temperature rises, the solubility of CO 2 decreases, and water and CO 2 separate from the amine solution. After the water is removed, the solution is cooled to increase the solubility of CO 2 so that the amine dissolves completely and the solubility increases.

[0111] Using the switchable solubility system as described above, the draw solution can be regenerated, and the power of a heat pump that can provide both heating and cooling can also be utilized. When the solubility of the draw solution decreases, water can be separated and sent, and mixed with the used dilute solution from the RED / PRO battery. By removing water, the draw solution used in the forward osmosis system is concentrated and regenerated, and the used concentrated solution from the RED / PRO battery is regenerated.

[0112] Operating a salinity gradient engine system near industrial facilities such as power plants offers various advantages. In power plants, both excess waste heat and the release of undesirable by-products such as CO 2 occur during the process. This industrial CO 2 can be used in the forward osmosis systems disclosed herein to control the solubility of the draw solution.

[0113] In Figure 19, this regeneration system circulates the used dilute solution 1940 in a closed loop from the RED or PRO battery 1910 through the dilute solution tank 1946. Water 1970 is added in the dilute solution tank 1946 to form the regenerated dilute solution 1945, which is then returned to the RED or PRO battery 1910. The used concentrated solution 1930 also circulates in a closed loop from the RED or PRO battery 1910 through the forward osmosis system 1980 to produce the regenerated concentrated solution 1935, which is returned to the RED or PRO battery 1910. A switchable solubility system 1920 is also shown. The draw solution 1955 circulates through the forward osmosis system 1980 and is used in the operation of the system, generating the used draw solution 1950. In the recovery device 1960, heat 1992 is applied to the used draw solution 1950, releasing CO 2 so that the solubility of the used draw solution decreases and water 1970 can be separated and decanted. When CO 2 is returned to the system in the generator 1965, the solubility of the solute in the draw solution increases (for example, salt can be redissolved in the solution and the solution needs to be concentrated to increase the osmotic pressure). To increase the solubility of CO 2 , the solution is cooled (thermal energy 1991 is removed from the system).

[0114] It should be understood that the various features (or aspects) disclosed in this specification can be combined in combinations different from those specifically presented in the description and the accompanying drawings. Also, by way of example, any particular act or event of any of the processes or methods described herein can be performed in a different order, added, combined, or completely omitted (for example, it may be possible that not all acts or events described are necessary to practice the technique). Further, although a particular feature of the present disclosure is described as being performed by a single module or unit for clarity, the techniques of the present disclosure can be performed, for example, by a combination of units or modules associated with, for example, a RED battery, a PRO system, a CAP system, a hydrogen generation subsystem, a salt precipitation subsystem, an evaporation subsystem, and the like.

[0115] In one or more examples, the techniques described can be implemented in hardware, software, firmware, or any combination thereof. When implemented in software, the functions can be stored as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. The computer-readable medium can include non-transitory computer-readable media corresponding to tangible media such as data storage media (e.g., RAM, ROM, EEPROM, flash memory, or other media that can be used to store desired program code in the form of instructions or data structures and that are accessible by a computer).

[0116] The commands can be implemented by one or more processors such as one or more digital signal processors (DSPs), general-purpose microprocessors, application-specific integrated circuits (ASICs), field-programmable logic arrays (FPGAs), or other equivalent integrated logic circuits or discrete logic circuits. Thus, the term "processor" as used herein can refer to any of the foregoing structures, or other physical structures suitable for performing the described techniques. Also, this technique can be fully performed with one or more circuits or logic elements.

[0117] FIG. 7 shows an example of hardware that can be used to store or execute program instructions. Bus 710 functions as a main information highway interconnecting the other illustrated components of the hardware. Central processing unit (CPU) 705 is the central processing unit of the system and performs the computations and logical operations necessary for program execution. CPU 705 is an example of a processor as the term is used within the present disclosure, either alone or in combination with one or more of the other elements disclosed in FIG. 7. Read-only memory (ROM) and random access memory (RAM) constitute examples of non-transitory computer-readable storage media 720, memory devices, or data storage bodies as the terms are used within the present disclosure.

[0118] Program instructions, software, or interactive modules for providing an interface and performing queries or analysis related to one or more data sets can be stored in memory device 720. Optionally, the program instructions can be stored on tangible non-transitory computer-readable media such as compact discs, digital discs, flash memories, memory cards, universal serial bus (USB) drives, optical disc storage media, and / or other storage media.

[0119] The optional display interface 730 can display information from the bus 710 on the display 735 in audio, visual, graphic, or alphanumeric form. Communication with external devices can be performed using various communication ports 740. The communication ports 740 can be connected to communication networks such as the Internet or an intranet.

[0120] The hardware can also include an input device such as a keypad 750, or an interface 745 that enables receipt of data from other input devices 755 such as a touch screen, a remote control, a pointing device, a video input device, and / or an audio input device.

[0121] It will be understood that the various or other features and functions disclosed above, or alternative means thereof, can be desirably combined into many other different systems or applications, or combinations of systems and applications. Also, various alternatives, modifications, changes, or improvements not presently anticipated or expected may subsequently be made by those skilled in the art, and these are also intended to be encompassed by the following claims.

Claims

1. 1. An electrodialysis reversal system comprising: an anode; a cathode; one or more cells disposed between the anode and the cathode; wherein at least one of the one or more cells comprises: a first membrane configured to be selectively permeable to cations; a second membrane configured to selectively permeate anions, the second membrane being spaced apart from the first membrane; a concentrated salt solution disposed between the first membrane and the second membrane, the first membrane selectively allowing cations to migrate toward the cathode and the second membrane selectively allowing anions to migrate toward the anode, the first membrane and the second membrane separating the concentrated salt solution from the dilute salt solution such that a voltage differential is created between the cathode and the anode; a thermal optimization system configured to transfer thermal energy to the concentrated salt solution or the diluted salt solution; 1. A regeneration system including a heat pump, receiving the dilute salt solution from the at least one of the one or more cells; removing heat energy from the dilute salt solution with the heat pump to precipitate salt in the dilute salt solution; After precipitating the salt in the dilute salt solution, circulating the dilute salt solution through the at least one of the one or more cells; introducing the precipitated salt into the concentrated salt solution; and Dissolving the precipitated salt in the concentrated salt solution. A playback system configured as follows: Including, the system.

2. 2. The electrodialysis reversal system of claim 1, wherein the regeneration system is further configured to transfer at least a portion of the heat energy removed from the dilute salt solution back to the dilute salt solution after precipitating salts dissolved in the dilute salt solution.

3. 2. The electrodialysis reversal system of claim 1, wherein the regeneration system is further configured to transfer at least a portion of the thermal energy removed from the dilute salt solution to the concentrated salt solution to dissolve the precipitated salts in the concentrated salt solution.

4. 2. The electrodialysis reversal system of claim 1, wherein the heat source is configured to transfer thermal energy to the concentrated salt solution to dissolve the precipitated salts in the concentrated salt solution.

5. 10. The electrodialysis reversal system of claim 1, wherein the concentrated salt solution comprises an endothermic or exothermic solution.

6. 2. The electrodialysis reversal system of claim 1, wherein the concentrated salt solution includes a substance having a solubility with a nonlinear temperature dependence.

7. 10. The electrodialysis reversal system of claim 1, wherein the first membrane and the second membrane comprise ion exchange membranes.

8. further comprising a second cell, said second cell comprising: a third membrane configured to be selectively permeable to cations; a fourth membrane configured to selectively permeate anions, the fourth membrane spaced apart from the third membrane; a second concentrated salt solution disposed between the third membrane and the fourth membrane, the third membrane and the fourth membrane separating the second concentrated salt solution from the second dilute salt solution; and wherein the concentrated salt solution comprises an endothermic solution; the second concentrated salt solution comprises a pyrogenic solution; and 2. The electrodialysis reversal system of claim 1, wherein the heat pump is configured to transfer heat between the concentrated salt solution and the second concentrated salt solution.

9. 10. The electrodialysis reversal system of claim 1, wherein the thermal optimization system includes a control system configured, by a processor, to adjust the transfer of heat between the one or more heat sources and the electrodialysis reversal system based on one or more measurements of conditions of the one or more heat sources or the electrodialysis reversal system.

10. 10. The electrodialysis reversal system of claim 9, wherein the heat source comprises one or more of geothermal, industrial waste heat, or solar heat.

11. 1. A method for generating electrical power from thermal energy, comprising: separating the first salt solution from the second salt solution by a permselective membrane; receiving thermal energy from a thermal optimization system by the first salt solution and / or the second salt solution; mixing the first salt solution and the second salt solution in a controlled manner to capture at least a portion of the salinity gradient energy as electrical power as a salinity difference between the first salt solution and the second salt solution decreases; and transferring heat energy from the first salt solution to the second salt solution with a heat pump to increase the salinity difference between the first salt solution and the second salt solution; A method comprising:

12. 12. The method of claim 11, further comprising capturing the salinity gradient energy using electrodialysis reversal.

13. 12. The method of claim 11, further comprising capturing the salinity gradient energy using pressure retarded osmosis to drive an electrical generator.

14. 12. The method of claim 11, wherein each of the first salt solution and the second salt solution circulates in a closed system.

15. 12. The method of claim 11, wherein salt is precipitated in the first salt solution by transferring thermal energy from the first salt solution to the second salt solution.

16. 16. The method of claim 15, further comprising increasing the salinity difference between the first salt solution and the second salt solution by introducing the precipitated salt into the second salt solution.

17. 12. The method of claim 11, further comprising using a portion of the generated electrical power to produce hydrogen gas by electrolysis.

18. 12. The method of claim 11, wherein transferring thermal energy from the first salt solution to the second salt solution comprises transferring thermal energy from the first salt solution that is at a lower temperature than the second salt solution.

19. 12. The method of claim 11 , wherein the thermal optimization system is configured to adjust the transfer of heat from one or more heat sources to the first salt solution and / or the second salt solution based on one or more measurements of conditions of the one or more heat sources or the first salt solution and / or the second salt solution.

20. 20. The method of claim 19, wherein the heat source comprises one or more of geothermal, industrial waste heat, or solar heat.

21. 1. A salt gradient engine system comprising: a reverse electrodialysis battery; Playback system and and the reverse electrodialysis battery comprises: an anode; a cathode; one or more cells disposed between the anode and the cathode; wherein at least one of the one or more cells comprises: a first membrane configured to be selectively permeable to cations; a second membrane configured to selectively permeate anions, the second membrane being spaced apart from the first membrane; a concentrated salt solution disposed between the first membrane and the second membrane, the first membrane selectively allowing cations to migrate toward the cathode and the second membrane selectively allowing anions to migrate toward the anode, the first membrane and the second membrane separating the concentrated salt solution from the dilute salt solution such that a voltage differential is created between the cathode and the anode; a thermal optimization system configured to transfer thermal energy to the concentrated salt solution or the dilute salt solution; Including, The salt gradient engine system, wherein the regeneration system is selected from the group consisting of a salt precipitation system, a membrane distillation system, an evaporation system, a forward osmosis system, a salt splitting system, an electrodialysis system, and any combination thereof.

22. the regeneration system includes a salt precipitation system, the salt precipitation system comprising: receiving a spent diluted solution from the reverse electrodialysis battery; removing heat energy from the spent dilute solution with the heat pump, precipitating salt from the spent dilute solution, and regenerating the dilute salt solution; After regenerating the dilute salt solution, circulating the dilute salt solution through the reverse electrodialysis battery; introducing the precipitated salt into the spent concentrated solution; and Dissolving the precipitated salt in the spent concentrated solution and regenerating the concentrated salt solution.

22. The salt gradient engine system of claim 21 configured to:

23. 23. The salt gradient engine system of claim 22, wherein the regeneration system is further configured to transfer at least a portion of the thermal energy removed from the dilute salt solution back to the dilute salt solution after precipitating salts dissolved in the dilute salt solution.

24. 23. The salt gradient engine system of claim 22, wherein the regeneration system is further configured to transfer at least a portion of the thermal energy removed from the spent dilute solution to the spent strong solution to dissolve the precipitated salts in the spent strong solution.

25. 23. The salt gradient engine system of claim 22, wherein the heat source is configured to transfer thermal energy to the spent strong solution to dissolve the precipitated salts in the spent strong solution.

26. 22. The salt gradient engine system of claim 21, wherein the concentrated salt solution comprises a substance having a solubility with a non-linear temperature dependence.

27. the regeneration system includes a salt precipitation system, the salt precipitation system comprising: a salt precipitator configured to receive the spent dilute solution from the reverse electrodialysis battery and precipitate salt from the spent dilute solution to regenerate the dilute salt solution; a concentrate tank configured to receive spent concentrate solution from the reverse electrodialysis battery and salt produced by the salt precipitator to regenerate the concentrated salt solution; one or more heat exchangers; 22. The salt gradient engine system of claim 21, comprising:

28. 28. The salt gradient engine system of claim 27, further comprising a dilute solution tank configured to receive the dilute salt solution from the salt precipitator.

29. 30. The salt gradient engine system of claim 27, further comprising a heat source system configured to provide thermal energy to the concentrate tank.

30. The regeneration system includes a membrane distillation system, and the membrane distillation system comprises: a membrane distillation vessel including a hydrophobic membrane; a heat pump configured to heat the container and cool one side of the hydrophobic membrane; 22. The salt gradient engine system of claim 21, comprising: the membrane distillation system configured to form a salt gradient in the hydrophobic membrane after warming and generate an ultra-dilute solution and regenerate the concentrated salt solution.

31. a concentrate tank configured to receive spent concentrate from the reverse electrodialysis battery and to be connected to the membrane distillation vessel; a dilute solution tank configured to receive the spent dilute solution from the reverse electrodialysis battery and to be connected to the membrane distillation vessel; 31. The salt gradient engine system of claim 30, further comprising: after regeneration in the membrane distillation vessel, the concentrate tank configured to receive the concentrate solution and the dilute tank configured to receive the ultra-dilute solution from the membrane distillation vessel.

32. 31. The salt gradient engine system of claim 30, wherein the hydrophobic membrane comprises polytetrafluoroethylene, polypropylene, or polyvinylidene fluoride and is configured in a sandwich cell stack configuration.

33. The regeneration system includes the salt decomposition system, and the salt decomposition system comprises: a container configured to receive a spent dilute solution from the reverse electrodialysis battery, the spent dilute solution comprising a salt; and a heat pump configured to heat the vessel and generate a gaseous product comprising salt within the vessel; an absorber configured to receive the spent concentrate solution from the reverse electrodialysis battery and to receive the gaseous product, wherein the salt in the gaseous product is absorbed by the spent concentrate solution to regenerate the concentrated salt solution; 32. The salt gradient engine system of claim 31 , comprising:

34. the regeneration system includes the evaporation system, and the evaporation system comprises: an evaporator configured to receive the spent concentrate solution from the reverse electrodialysis battery and generate water vapor to regenerate the concentrated salt solution; a heat pump configured to supply thermal energy to the evaporator; a condenser configured to receive the spent lean solution from the reverse electrodialysis battery and the water vapor produced by the evaporator, the water vapor condensing and mixing with the spent lean solution to regenerate the lean salt solution; 32. The salt gradient engine system of claim 31 , comprising:

35. the regeneration system includes the electrodialysis system; the electrodialysis system is configured to receive a spent dilute solution and a spent concentrate solution; 32. The salt gradient engine system of claim 31 , wherein electricity is supplied to the electrodialysis system to transfer ions from the spent dilute solution to the spent concentrated solution to regenerate the dilute salt solution and the concentrated salt solution.

36. the regeneration system further comprising a salt precipitation system, the salt precipitation system comprising: a salt precipitator configured to receive the spent dilute solution from the reverse electrodialysis battery and to precipitate salts from the spent dilute solution before the spent dilute solution is supplied to the electrodialysis system; a concentrate tank configured to receive spent concentrate solution from the reverse electrodialysis battery and to receive salt produced by the salt precipitator; 36. The salt gradient engine system of claim 35, wherein the concentrate tank is configured to receive the concentrate solution and the dilute tank is configured to receive the dilute salt solution from the electrodialysis system after regeneration by electrodialysis.

37. 32. The salt gradient engine system of claim 31 , wherein the regeneration system comprises the salt precipitation system and the membrane distillation system.

38. 32. The salt gradient engine system of claim 31 , wherein the regeneration system comprises electrodialysis and the salt precipitation system.

39. 32. The salt gradient engine system of claim 31 , wherein the regeneration system comprises the forward osmosis system configured to receive spent concentrate solution from the reverse electrodialysis battery and regenerate the concentrated salt solution using a switchable solubility system.

40. 40. The salt gradient engine system of claim 39, wherein the regeneration system further comprises a dilute solution tank configured to receive spent dilute solution from the reverse electrodialysis battery and to receive water from the switchable solubility system, the water being mixed with the spent dilute solution to regenerate the dilute salinity solution.

41. said switchable solubility system comprising: a draw solution that is circulated through the forward osmosis system and produces spent draw solution; and a recovery device configured to receive the spent draw solution and apply heat to the draw solution; ２ a recovery device into which the gas is released and water is produced; receiving the solution from the recovery device; and ２ a generator configured to regenerate the draw solution by adding 41. The salt gradient engine system of claim 39 or 40, comprising:

42. 22. The salt gradient engine system of claim 21 , wherein the first membrane and the second membrane comprise ion exchange membranes.

43. further comprising a second cell, said second cell comprising: a third membrane configured to be selectively permeable to cations; a fourth membrane configured to selectively permeate anions, the fourth membrane spaced apart from the third membrane; a second concentrated salt solution disposed between the third membrane and the fourth membrane, the third membrane and the fourth membrane separating the second concentrated salt solution from the second dilute salt solution; and wherein the concentrated salt solution comprises an endothermic solution; the second concentrated salt solution comprises a pyrogenic solution; and 22. The salt gradient engine system of claim 21, wherein the heat pump is configured to transfer heat between the concentrated salt solution and the second concentrated salt solution.

44. 22. The salt gradient engine system of claim 21 , wherein the thermal optimization system includes a control system configured by a processor to adjust the transfer of heat between the one or more heat sources and the electrodialysis reversal system based on one or more measurements of conditions of the one or more heat sources or the electrodialysis reversal system.

45. 45. The salt gradient engine system of claim 44, wherein the heat source comprises one or more of geothermal, industrial waste heat, or solar heat.

46. 22. The salt gradient engine system of claim 21, wherein the heat pump is a vapor compression cycle, a thermoelectric refrigerator, a chemical absorption refrigerator, or other device known in the art for use in simultaneous heating and cooling.

47. 1. A salt gradient engine system for producing electricity or hydrogen from thermal energy and producing water, comprising: A system according to claim 21; Liquid desiccant dehumidification process Salt gradient engine system, including:

48. 1. A method for generating electrical power from thermal energy to regenerate a salinity differential between a first salt solution and a second salt solution, comprising: separating the first salt solution from the second salt solution by a permselective membrane; receiving thermal energy from a thermal optimization system by the first salt solution and / or the second salt solution; mixing the first salt solution and the second salt solution in a controlled manner to capture at least a portion of the salinity gradient energy as electrical power as a salinity difference between the first salt solution and the second salt solution decreases; transferring thermal energy from the first salt solution to the second salt solution with a heat pump to increase the salinity difference between the first salt solution and the second salt solution; and regenerating the salinity difference between the first salt solution and the second salt solution by applying a regeneration process selected from the group consisting of salt decomposition, electrodialysis, membrane distillation, evaporation, forward osmosis, salt precipitation, or any combination thereof. A method comprising:

49. 49. The method of claim 48, further comprising applying a pressure retarded osmosis (PRO) system, a volumetric mixing (CAP) system, or both a PRO system and a CAP system to generate additional power.

50. 49. The method of claim 48, wherein the method comprises producing a third salt solution by membrane distillation and further comprises mixing the third salt solution with the first salt solution and / or the second salt solution.

51. 49. The method of claim 48, further comprising capturing the salinity gradient energy using reverse electrodialysis.

52. 49. The method of claim 48, further comprising capturing the salinity gradient energy using pressure retarded osmosis to drive an electrical generator.

53. 49. The method of claim 48, wherein each of the first salt solution and the second salt solution is circulated in a closed system.

54. 49. The method of claim 48, wherein salt is precipitated in the first salt solution by transferring thermal energy from the first salt solution to the second salt solution.

55. 55. The method of claim 54, further comprising increasing the salinity difference between the first and second salt solutions by introducing the precipitated salt into the second salt solution.

56. 49. The method of claim 48, further comprising using a portion of the generated electrical power to produce hydrogen gas by electrolysis.

57. 49. The method of claim 48, wherein transferring thermal energy from the first salt solution to the second salt solution comprises transferring thermal energy from the first salt solution that is cooler than the second salt solution.

58. 49. The method of claim 48, wherein the thermal optimization system is configured to adjust the transfer of heat from one or more heat sources to the first salt solution and / or the second salt solution based on one or more measurements of conditions of the one or more heat sources or the first salt solution and / or the second salt solution.

59. 49. The method of claim 48, wherein the heat source comprises one or more of geothermal, industrial waste heat, or solar heat.

60. The regeneration process comprises: i) providing a spent dilute solution formed from the first salt solution, the spent dilute solution comprising salt; ii) heating the spent dilute solution to decompose the salts and produce gaseous products; iii) transferring said gaseous product to an absorber; and iv) solidifying said gaseous products to reform as salt precipitates in the spent concentrate solution in said absorber; applying a salt decomposition process comprising:

49. The method of claim 48, comprising:

61. the spent dilute solution has a higher salt content than the first salt solution; 61. The method of claim 60, wherein the salt content of the spent lean solution is reduced by transferring the gaseous product to the absorber to regenerate the first salt solution.

62. The regeneration process comprises: i) providing a spent dilute solution formed from the first salt solution, the spent dilute solution comprising salt; ii) providing a spent concentrate solution formed from said second salt solution; iii) applying electricity to separate the salt into ions and transfer the ions from the spent dilute solution to the spent concentrated solution; applying an electrodialysis process comprising: a) reducing the salt content of the depleted dilute solution to regenerate the first salt solution; and b) increasing the salt content of the depleted concentrated solution to regenerate the second salt solution.

49. The method of claim 48, comprising:

63. The regeneration process comprises: i) providing a spent concentrate solution formed from said second salt solution. ii) heating the spent concentrated solution to produce water vapor; and iii) transferring said water vapor for mixing with the spent dilute solution; applying a process of evaporation comprising: a reduction in the salt content of the spent dilute solution to regenerate the first salt solution; and an increase in the salt content of the spent concentrated solution to regenerate the second salt solution.

49. The method of claim 48, comprising:

64. The regeneration process comprises: i) providing a membrane distillation vessel comprising a hydrophobic membrane having a spent concentrated solution on one side of the membrane and a spent diluted solution on the other side of the membrane; ii) warming the spent concentrated solution to generate water vapor; applying a membrane distillation process comprising: the water vapor permeating the hydrophobic membrane and mixing with the depleted dilute solution to regenerate the first salt solution, and the salt content of the depleted concentrated solution is increased to regenerate the second salt solution.

49. The method of claim 48, comprising:

65. The regeneration process comprises: circulating the spent concentrate solution and the draw solution through a forward osmosis system to regenerate the second salt solution and produce a spent draw solution; circulating the spent draw solution through a switchable solubility system to regenerate the draw solution and produce water; Applying the process of forward osmosis, including 49. The method of claim 48, comprising:

66. The process of forward osmosis mixing said water with the spent dilute solution to regenerate said first salt solution; 66. The method of claim 65, further comprising:

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