Reverse electrodialysis or pressure delayed osmosis unit with heat pump

Abstract

Methods and systems 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, and mixing the first saline solution and the second saline solution in a controlled manner, the first saline solution being separated from the second saline solution as a salinity difference between the first saline solution and the second saline solution decreases. At least some salinity gradient energy is captured as electrical power. The method further includes transferring thermal energy from the first saline solution to the second saline solution by a heat pump (320), causing an increase in salinity difference between the first saline solution and the second saline solution. The methods and systems may include regeneration processes such as membrane distillation, forward osmosis, electrodialysis, salt evaporation, 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 energy generated by the difference in salt concentration between two naturally occurring fluids (usually fresh water and salt water), for example, when a river flows into the ocean. Reverse electrodialysis (RED) can be used to recover energy from salinity gradients, for example, by passing a salt solution and fresh water through alternating cation and anion exchange membrane stacks. The chemical potential difference between salt water and fresh water generates a voltage across each membrane, and the total potential of the system is the sum of the potential differences across all membranes. Open-loop RED cells require a continuous source of salt water and fresh water to maintain the salinity gradient. This constraint may limit the practical location of commercial-scale RED cells. In addition, open-loop RED cells are susceptible to contamination by minerals, microorganisms, or other foreign matter or substances in the water source. Closed-loop RED cells do not require a continuous source of concentrated and dilute salt solutions, but require continuous regeneration of the salinity difference between the concentrated solution and the dilute solution, which can be energy-intensive and / or inefficient.

[0003] This document describes methods and systems directed to solving the above-referenced problems and / or other important problems. Summary of the invention

[0004] A method for generating electricity from thermal energy is disclosed. The method includes: separating a first salt solution from a second salt solution by a selectively permeable membrane; transferring thermal energy to the first salt solution and / or the second salt solution by a heat pump; mixing the first salt solution and the second salt solution in a controlled manner, and capturing at least some salinity gradient energy as electricity as the salinity difference between the first salt solution and the second salt solution decreases. It may include regenerating the salinity difference between the first salt solution and the second salt solution by applying a regeneration process selected from the following: salt decomposition, electrodialysis, membrane distillation, evaporation, forward osmosis, salt precipitation, or any combination thereof.

[0005] The salt decomposition process may include providing at least a portion of a spent dilute solution formed from a first salt solution, wherein the spent dilute solution contains 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 as a salt precipitate in the cold solution. When the method includes generating a third salt solution by membrane distillation, the method may further include mixing the third salt solution into the first salt solution and / or the second salt solution. The first salt solution and second salt solution method may include circulating the solutions in a substantially or completely closed closed system.

[0006] The selectively permeable membrane may include graphene, graphene oxide, or reduced graphene oxide, optionally with nanopores therein. The selectively permeable membrane may be a single-layer sheet, a multi-layer sheet, or a cylinder.

[0007] The method may further include capturing the salinity gradient energy using reverse electrodialysis or using pressure-retarded osmosis to drive a generator.

[0008] The method may include transferring heat energy from the first salt solution to the second salt solution causing the first salt solution to precipitate salt, and optionally further including introducing the precipitated salt into the second salt solution causing an increase in the salinity difference between the first salt solution and the second salt solution.

[0009] The method may include using a portion of the generated electricity to produce hydrogen by electrolysis.

[0010] The method may include a regeneration process including applying a salt decomposition, the salt decomposition including: providing a spent dilute solution formed from a first salt solution, wherein the spent dilute solution contains salt; heating the spent dilute solution to decompose the salt to form a gaseous product; and transferring the gaseous product to an absorber; and solidifying the gaseous product to reform as a salt precipitate in a spent concentrated solution within the absorber. By transferring the gaseous product to the absorber, the salt content of the spent dilute solution may be reduced to regenerate the first salt solution. The salt precipitate may be dissolved in the spent concentrated solution to regenerate a second salt solution, and optionally the spent dilute solution has a higher salt content than the first salt solution;

[0011] The method may include a regeneration process, the regeneration process including electrodialysis, the electrodialysis including: providing a spent dilute solution formed from a first salt solution, wherein the spent dilute solution contains salt; providing a spent concentrated solution formed from a second salt solution; supplying electricity to separate the salt into ions and to move the ions from the spent dilute solution to the spent concentrated solution. The salt content of the spent dilute solution is reduced to regenerate the first salt solution, while the salt content of the spent concentrated solution is increased to regenerate the second salt solution.

[0012] The method may include a regeneration process including applying an evaporation process including: providing a spent concentrated solution formed from a second salt solution; heating the spent concentrated solution to generate water vapor; and transferring the water vapor to mix with the spent dilute solution. The salt content of the spent dilute solution is reduced to regenerate the first salt solution, while the salt content of the spent concentrated solution is increased to regenerate the second salt solution.

[0013] The method may include a regeneration process including applying a membrane distillation process including: providing a membrane distillation vessel including a hydrophobic membrane having a waste concentrated solution on one side of the membrane and a waste dilute solution on an opposite side of the membrane; and warming the waste concentrated solution to generate water vapor. The water vapor permeates the hydrophobic membrane to mix with the waste dilute solution to regenerate a first salt solution, and the salt content of the waste concentrated solution is increased to regenerate a second salt solution.

[0014] The method may include a regeneration process including applying a forward osmosis process including: circulating the spent concentrate solution and the draw solution through a forward osmosis system to regenerate the second brine and produce a spent draw solution; and circulating the spent draw solution through a switchable solubility system to regenerate the draw solution and produce water.

[0015] The method may include applying a pressure delayed osmosis (PRO) system, a capacitive mixing (CAP) system, or both PRO and CAP systems to generate additional electricity.

[0016] A system for generating electricity is disclosed. The system includes: a first salt solution; a second salt solution, wherein the salinity of the second salt solution is different from the salinity of the first salt solution; a heat pump configured to transfer thermal energy to the first salt solution and / or the second salt solution; and a selectively permeable membrane that separates the first salt solution from the second salt solution. The system may further include: at least one regeneration system. The selectively permeable membrane may be configured to control mixing of the first salt solution and the second salt solution, and further configured to capture at least some salinity gradient energy as electricity when the first salt solution and the second salt solution are mixed. The selectively permeable membrane may include graphene, graphene oxide, or reduced graphene oxide, and optionally contain nanopores therein. The selectively permeable membrane may be a single-layer sheet, a multi-layer sheet, or a cylinder containing graphene, graphene oxide, and / or reduced graphene oxide. The heat pump may be a vapor compression cycle, a thermoelectric refrigerator, a chemical absorption refrigerator, or other devices known in the art for simultaneous heating and cooling. The regeneration system includes one or more of the following: a salt precipitation system, a membrane distillation system, a salt decomposition system, an electrodialysis system, a forward osmosis system, evaporation, or any combination thereof.

[0017] 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 by a hydrophobic membrane; and a heat pump (or alternatively a second heat pump) configured to warm the container and cool the opposite side of the hydrophobic membrane. The membrane distillation system is configured to generate a salt gradient at the membrane after warming and generate a third salt solution in the container. The hydrophobic membrane may include polytetrafluoroethylene, polypropylene, or polyvinylidene fluoride, and may optionally be configured in a sandwich unit stack configuration.

[0018] 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 a first salt solution, wherein the spent dilute solution contains salt; a heat pump (or alternatively a second heat pump) configured to warm the container; and a cold water stream configured to receive at least one gaseous product released from the container. The salt decomposition system can be configured to decompose the salt and then reform the salt precipitate in the cold water stream.

[0019] The salt decomposition system may include: a container configured to receive a spent dilute solution from a reverse electrodialysis cell, wherein the spent dilute solution contains salt; a heat pump configured to warm the container and generate a gaseous product containing salt in the container; and an absorber configured to receive a spent concentrated solution from the reverse electrodialysis cell and receive the gaseous product. The salt in the gaseous product can be absorbed by the spent concentrated solution to regenerate a concentrated salt solution.

[0020] 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.

[0021] 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 warm the container and cool one side of the hydrophobic membrane. The membrane distillation system may be configured to generate a salt gradient at the hydrophobic membrane after warming, and to generate an ultra-dilute solution and regenerate a concentrated salt solution. The membrane distillation system may further include: a concentrate tank configured to receive a waste concentrated solution from a reverse electrodialysis cell and connected to the membrane distillation container; a diluent tank configured to receive a waste dilute solution from a reverse electrodialysis cell and connected to the membrane distillation container. The concentrate tank may be configured to receive a concentrated solution from the membrane distillation container, and the diluent tank may be configured to receive an ultra-dilute solution from the membrane distillation container. The hydrophobic membrane may include polytetrafluoroethylene, polypropylene, or polyvinylidene fluoride, and is configured to form a sandwich unit stack structure.

[0022] When the regeneration system includes an evaporation system, the evaporation system may include: an evaporator configured to receive the spent concentrated solution from the reverse electrodialysis cell and generate water vapor to regenerate the concentrated salt solution; a heat pump configured to provide heat energy to the evaporator; and a condenser configured to receive the spent dilute solution from the reverse electrodialysis cell and receive the water vapor generated by the evaporator. The water vapor condenses and mixes with the spent dilute solution to regenerate the dilute salt solution.

[0023] When the regeneration system includes an electrodialysis system, the electrodialysis system may be configured to receive the spent dilute solution and the spent concentrated solution. Power is supplied to the electrodialysis system to cause ions to move from the spent dilute solution to the spent concentrated solution to regenerate the dilute salt solution and the concentrated salt solution.

[0024] The regeneration system may include a salt precipitation system and an electrodialysis system, wherein the salt precipitation system includes: a salt precipitator configured to receive a waste dilute solution from a reverse electrodialysis cell and precipitate salt from the waste dilute, and then supply the waste dilute to the electrodialysis system; a concentrate tank configured to receive a waste concentrated solution from the reverse electrodialysis cell and receive salt generated by the salt precipitator. The concentrate tank may be configured to receive a concentrated solution, and the diluent tank is configured to receive a dilute salt solution from the electrodialysis system.

[0025] The regeneration system may include a forward osmosis system configured to receive a waste concentrated solution from a reverse electrodialysis cell and to regenerate a concentrated salt solution using a switchable solubility system. In the case of a forward osmosis system, the regeneration system may further include a diluent tank configured to receive a waste dilute solution from the reverse electrodialysis cell and to receive water from the switchable solubility system, wherein the water is mixed with the waste dilute solution to regenerate the dilute salt solution. The switchable solubility system may include: a draw solution that circulates through the forward osmosis system and produces a waste draw solution; a recovery device configured to receive the waste draw solution and add heat, wherein CO2 is released and water is produced; and a generator configured to receive a solution from the recovery device and add CO2 to regenerate the draw solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings, which are incorporated herein and constitute a part of this specification, are illustrations of specific embodiments of the present disclosure and do not limit the scope of the present disclosure.

[0027] Figure 1 An exemplary reverse electrodialysis (RED) system is shown.

[0028] Figure 2 An exemplary regeneration system is shown.

[0029] Figure 3 An exemplary thermal optimization system is shown.

[0030] Figure 4 An exemplary pressure delayed permeation (PRO) system is shown.

[0031] Figure 5 An exemplary hydrogen generation system is shown.

[0032] Figure 6 A flow chart of a method for generating electricity from thermal energy.

[0033] Figure 7 A block diagram is shown of an example of internal hardware that may be used to contain or implement program instructions according to one embodiment.

[0034] Figure 8is an example of a system and method of the present disclosure that includes a RED or PRO battery in combination with a salt precipitation system, and which is connected to an external heat source.

[0035] Fig. 9 is another example of a system and method of the present disclosure that includes a RED or PRO battery in combination with a salt precipitation system. The system does not include an external heat source system, but heat is added to the diluent tank, for example, via a heat pump loop and / or waste heat.

[0036] Fig.10 is an example of a system and method of the present disclosure comprising a RED or PRO battery in combination with a salt decomposition system.

[0037] Fig.11 is an example of a system and method of the present disclosure that includes a RED or PRO battery in combination with a evaporation system.

[0038] Fig.12 is an example of a system and method of the present disclosure comprising a RED or PRO cell coupled with an electrodialysis system and salt precipitation.

[0039] Fig.13 is an example of a regeneration system incorporating a membrane distillation system and salt precipitation.

[0040] Fig.14 is an example of a regeneration system incorporated into a membrane distillation system.

[0041] Fig.15 is an example of a batch system for regeneration, where all process tanks are operational.

[0042] Fig.16 An example of water production using a steam condenser and a heat pump.

[0043] Fig.17 How to use Fig.16 Example of a system to generate cold and hot fluid tanks for use in a salinity gradient energy thermal system.

[0044] Fig.18 is an example of a system and method of the present disclosure that includes a RED or PRO cell combined with atmospheric water generation using a liquid desiccant dehumidification process.

[0045] Fig.19 is an example of a system and method of the present disclosure comprising a RED or PRO cell in combination with a forward osmosis system. DETAILED DESCRIPTION

[0046] The present disclosure relates to salt gradient heat engine systems that utilize heat and generate electricity from thermal energy. A salt gradient heat engine may be any system that utilizes thermal energy to generate or regenerate a salinity gradient and produce usable energy (e.g., electricity and / or hydrogen). Examples of salt gradient heat engine systems include RED and PRO cells. RED cells may incorporate more than one selectively permeable membrane and one or more electrodes, and are discussed in more detail below. PRO cells may incorporate a membrane and do not require one or more electrodes. PRO cells generate pressure rather than directly generating electricity from the salinity difference between a concentrated salt solution and a solution as RED cells do. The selectively permeable membrane of a PRO cell may be configured to preferentially allow a solvent rather than a solute to pass through the membrane, for example, from a dilute solution to a concentrated salt solution, so as to reduce the salinity difference between the solutions.

[0047] Both RED and PRO cells may include a concentrated salt solution separated from a dilute solution by a selectively permeable membrane. Also in both systems, the power ratio generated by the system is at least a function of the salinity 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.

[0048] A reverse electrodialysis system is disclosed, the reverse electrodialysis system comprising an anode, a cathode, and one or more units disposed between the anode and the cathode. At least one of the one or more units comprises a first membrane configured to selectively permeate cations, and a second membrane configured to selectively permeate anions, the second membrane being spaced apart from the first membrane. The unit further comprises a concentrated salt solution disposed between the first membrane and the second membrane, the first membrane and the second membrane separating the concentrated salt solution from the dilute salt solution, such that the first membrane selectively allows cations to migrate toward the cathode and the second membrane selectively allows anions to migrate toward the anode, causing a voltage difference between the cathode and the anode. The first selectively permeable membrane and the second selectively permeable membrane may comprise an ion exchange membrane.

[0049] Disclosed herein are multiple (e.g., 2-500, 2-200, 10-400, or 2-100) selective permeable membranes used in reverse electrodialysis systems. Some selective permeable membranes limit the ability of ionic components to diffuse freely. In contrast, cation exchange membranes (and anion exchange membranes) allow cationic components and anionic components to migrate or move in opposite directions, respectively. Each selective permeable membrane can be made of an organic or inorganic polymer (e.g., ion exchange resin) having a charged (ionic) side group. Each selective permeable membrane can be made of graphene, reduced graphene oxide, or graphene oxide. The selective permeable membrane may include graphene in a single-layer structure or a multilayer sheet optionally stacked, and optionally including nanopores. The selective permeable membrane may include graphene, reduced graphene oxide, or graphene oxide, and may be a cartridge, such as those commonly used in reverse osmosis water filtration systems. The permeability of the membrane may depend on the construction or other aspects of the graphene sheet. The single-layer or multilayer sheet may be stretched or otherwise constructed to change the permeability of the membrane.

[0050] The selectively permeable membrane may be a bipolar membrane (e.g., anionic on one side and cationic on the opposite side) which, when used, generates acids and bases from salts present in solution. The selectivity of the selectively permeable membrane may be based on size, charge, charge density, phase (e.g., hydrophobic / hydrophilic), or polarity.

[0051] The selectively permeable membrane may be a polymer composite membrane with oriented nanochannels, such as those disclosed in WO 2022 / 032236, which is incorporated herein by reference in its entirety. For example, the selectively permeable membrane may be a thin film composite membrane comprising: (i) a polymer membrane, film or coating comprising a layer having a first surface, a second surface and a film thickness therebetween, and comprising cylindrical polymer fibers, the cylindrical polymer fibers being at least partially ordered as hexagonal stacked cylinders within the membrane, oriented parallel to the membrane surface, and existing as an H1 mesophase; wherein the cylinders are internally cross-linked within the cylinders; and wherein the cylinders are spatially arranged to provide channels between the cylinders for fluid flow through the membrane, film or coating; and (ii) a porous support layer in contact with the polymer membrane, film or coating. In an embodiment, the porous support layer is polyacrylonitrile, polyvinylidene fluoride, polysulfone, polyamide, polyimide, polypropylene, anodized aluminum oxide, cellulose acetate, or a nonwoven fabric.

[0052] The salt gradient heat engine system may include a heat source configured to transfer heat energy to a concentrated salt solution or a dilute salt solution; and a regeneration system including a heat pump. The heat pump may be any device known in the art for simultaneous heating and cooling, and optionally produces a coefficient of performance greater than about 1, or 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 refrigerator, a chemical absorption refrigerator, etc. The vapor compression cycle may be a screw type, an acoustic wave type, an air conditioner. The heat pump used herein may include a refrigerant with or without phase change. The refrigerant may be CO2, helium, or any other refrigerant known for heat pumps. The heat pump may include a thermodynamic cycle. The thermodynamic cycle may include any combination of refrigerants and / or non-refrigerant cycles that provide the ability to heat and cool simultaneously. The heat pump may be a thermoacoustic heat pump, such as a thermoacoustic heat pump ( 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 entitled "Heat Source Optimization System" or U.S. Patent No. 11,067,317 entitled "Heat Source Optimization System". Each of the foregoing patents is incorporated herein by reference in its entirety. In some embodiments, a humidifier, a dehumidifier, a two-way ventilation fan, and / or a wet refrigerator may be used in conjunction with a heat pump to drive reverse electrodialysis. The heat pump may be fueled by any known heat exchange fluid, such as, but not limited to, water, a refrigerant, ethylene glycol, or oil.

[0053] Traditionally, humidity is detrimental to HVAC cooling because it adds a dead load to the system; energy is consumed to condense water vapor, wasting energy and resulting in energy inefficiency. Typically, when the desired temperature for cooling is set on the thermostat, any energy spent condensing the water vapor is energy that could otherwise be used to cool the air. In this case, energy is consumed to condense the vapor into condensate, and the HVAC unit works against the latent heat of evaporation.

[0054] In contrast, according to the present disclosure, humidity in the environment can be highly advantageous because humidity provides additional energy to the system, which can be used to drive the reverse electrodialysis process and generate electricity, hydrogen, oxygen, and any combination thereof. For example, humidity can be introduced into the system, and the latent heat of water vapor can be captured and used to drive the reverse electrodialysis and generate electricity. Similarly, with the formation of ice, the thermal crystallization of water can be used to drive the reverse electrodialysis process to generate electricity, hydrogen, oxygen, or any combination thereof.

[0055] The regeneration system may be configured to receive a dilute salt solution from at least one of the one or more units and remove heat from the dilute salt solution (via a heat pump), causing the dilute salt solution to precipitate salt. The regeneration system may be configured to, after causing the dilute salt solution to precipitate salt, circulate the dilute salt solution to at least one of the one or more units, introduce the precipitated salt into a concentrated salt solution, and cause the precipitated salt to dissolve in the concentrated salt solution.

[0056] The regeneration system may be configured to transfer at least some of the heat removed from the dilute salt solution back to the dilute salt solution after causing the salt dissolved in the dilute salt solution to precipitate. The regeneration system may be configured to transfer at least some of the heat removed from the dilute salt solution to the concentrated salt solution, causing the precipitated salt to dissolve in the concentrated salt solution. The heat source may be configured to transfer heat to the concentrated salt solution, causing the precipitated salt to dissolve in the concentrated salt solution. The concentrated salt solution may include an endothermic solution or an exothermic solution. The concentrated salt solution may include a substance having a nonlinear temperature-dependent solubility.

[0057] One or more other regeneration systems can be adopted. The regeneration system may include electrodialysis. In addition to the reverse electrodialysis system, electrodialysis can be further used for water purification. In the case of electrodialysis, the dilute salt solution can be further desalinated using electrodialysis. For example, when precipitating salt, the concentration of the dilute salt solution is limited by the solubility curve. In order to further dilute the dilute salt solution, electrodialysis can be used. Any renewable electricity (e.g., solar / wind energy, etc.) can be used to force electrodialysis to separate salt from the dilute salt solution and produce a further diluted stream. This provides energy storage. During the hours when the sun is out, the salt gradient using electrodialysis can be fully utilized, and then the energy from the salt gradient is utilized after sunset. The battery / tank that can be used for electrodialysis is the same as that used for reverse electrodialysis. Fig.12 is an example of a system including electrodialysis and a RED / PRO cell, which is discussed further below.

[0058] The reverse electrodialysis system may further include a control system configured to coordinate heat transfer between the one or more heat sources and the reverse electrodialysis system based on one or more measurements of the state of the one or more heat sources or the reverse electrodialysis system. The heat source includes one or more of geothermal, industrial waste heat, or solar heat.

[0059] The salt gradient heat engine system may include a salt decomposition system to produce a salt gradient. Salt decomposition may be used with reverse electrodialysis instead of the salt precipitation process disclosed herein. For example, a waste dilute solution (supplied by a RED cell) may be heated to a temperature above the temperature at which the salt decomposes (e.g., ammonium bicarbonate decomposes into CO2 and ammonia at about 60°C). When the solution is heated, the salt decomposes and leaves the waste dilute solution as a gaseous product, which reduces the salt concentration in the waste dilute solution, thereby producing a regenerated dilute solution. A vacuum or optional application of a fan may help the gaseous product move toward the cold stream. The gaseous products (e.g., CO2 and ammonia) may be driven into a cold water stream to react and precipitate back into a solid salt form (e.g., CO2, ammonia and cold water into ammonium bicarbonate salt). The solid salt precipitated in the solution (e.g., ammonium bicarbonate) may be delivered to a concentrated salt solution in a RED cell. In this process, a heat pump may be used to heat and cool the waste dilute solution and cold water vapor, respectively. The heat pump may be the same or different from the heat pump used in other steps of the reverse electrodialysis system disclosed herein. Optionally, when the gaseous product is precipitated in the cold stream, heat energy can be extracted and transferred to the spent dilute solution to decompose the salts. In addition, heat energy can be used to increase the temperature of the precipitated solution to increase solubility and allow for super concentrated solutions. Fig.10 is an example of a salt splitting process, which shows the solution flow between the RED cell and the vessel of the salt splitting process, and is discussed in further detail below.By applying the salt splitting process, it is possible to regenerate concentrated and dilute salt solutions by incorporating salt splitting.

[0060] The reverse electrodialysis system may include a second unit. The second unit may include a third membrane configured to be selectively permeable to cations and a fourth membrane configured to be selectively permeable to anions, the fourth membrane being spaced apart from the third membrane. The second unit may include 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. 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.

[0061] The reverse electrodialysis system may include a membrane distillation system. Membrane distillation (MD) is a heat-driven separation process in which liquids are repelled and only vapor molecules permeate through a porous hydrophobic membrane. The driving force in the MD process is the vapor pressure difference generated by the temperature difference across the hydrophobic membrane. The hydrophobic membrane must be hydrophobic in nature, or its surface can be modified to be hydrophobic. The hydrophobic membrane used for MD may be polytetrafluoroethylene (PTFE), polypropylene (PP), polyvinylidene fluoride (PVDF), or any combination thereof. Large surface area hydrophobic membranes can be used in sandwich unit stack designs similar to RED stacks. The stack of hydrophobic membranes may include only one or more types of hydrophobic membranes without electrodes. The use of a heat pump can improve the efficiency of the MD process by heating and cooling simultaneously, thereby generating a strong temperature gradient driving force. For example, a heat pump can be used to heat a waste concentrated solution or a waste dilute solution to about 40°C to about 80°C on one side of a hydrophobic membrane simultaneously, while providing a cooling means (e.g., a cooling stream heat exchanger, an evaporator with a refrigerant, or cooling water) on the other side of the hydrophobic membrane to produce a dilute solution and obtain heat, such as from ambient conditions, geothermal, solar, industrial waste heat. Membrane distillation allows the power of a heat pump to be used to efficiently produce a salt gradient that can be used in the reverse electrodialysis system disclosed herein. The heat pump can be the same or different from the heat pump used in other steps of the reverse electrodialysis system disclosed herein. Membrane distillation can be used to generate a concentrated salt solution and optionally a dilute salt solution for introduction into a RED cell. Fig.13 is an example of a membrane distillation system, which shows the solution flow between the MD system and the RED system. It is possible to regenerate concentrated and dilute salt solutions by introducing membrane distillation.

[0062] The membrane distillation process used in this article can be direct contact MD (DCMD), air gap MD (AGMD), vacuum MD (VMD), sweep gas MD (SWGMD), vacuum multi-effect membrane distillation (V-MEMD), permeate gap MD (PGMD), or a combination thereof.

[0063] The membrane distillation system may include: a container containing at least a portion of the first or second salt solution, the container being covered by a hydrophobic membrane that allows vapor permeation; a heat pump configured to warm the container; and cooling the opposite side of the membrane. The membrane distillation system may be configured to generate a salt gradient at the membrane after warming and generate a third salt solution (i.e., concentrated) in the container. The membrane distillation system may include a second heat pump to warm the container, and optionally a cooling device on the side of the membrane opposite to the container. The cooling device may be a cold stream, a heat exchanger, a refrigerant circuit, or otherwise operated, for example, to condense the vapor back into a liquid. Fig.13is an example of a membrane distillation process, which shows a hydrophobic membrane that creates a salt gradient between a warm concentrated solution and a cold dilute solution, as discussed in further detail below. The membrane distillation system may include: at least a portion of a first or second salt solution separated by a hydrophobic membrane that allows vapor permeation. In this embodiment, the solution is provided on either side of the hydrophobic membrane, and a 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.

[0064] The reverse electrodialysis system may include a microbial reverse electrodialysis electrolysis unit (MREC), as disclosed in U.S. Pat. No. 9,112,217, which is incorporated herein by reference in its entirety. In this embodiment, the microorganisms generate electricity to drive the RED system. The MREC may include a variety of power-producing microorganisms disposed in a RED cell, which can assist in the production of hydrogen and electricity by oxidation of organic matter on the anode and reduction of oxygen on the cathode. Since microorganisms thrive under warmer conditions, the use of a heat pump may increase the ability of microorganisms to remove electrode overpotentials. Due to thermodynamically unfavorable electrode reactions, electrode overpotentials promote significant energy losses. In addition, the leveraged heat energy provided by the heat pump promotes greater reaction kinetics, which reduces the amount of membrane required to produce the same amount of energy in the RED. For example, in a residential environment, organic waste (e.g., sewage from a septic tank) can be converted into usable energy using microbial reverse electrodialysis. Ultraviolet light can be used for any salt gradient thermal engine system disclosed herein to limit any microbial growth / fouling within the system.

[0065] In a salt gradient thermal engine system, the RED and PRO can be operated together continuously or in a batch system. When operating in a batch system, the reverse electrodialysis system may include multiple precipitators, and / or multiple tanks arranged in parallel or stacked. When operating in a batch system, the precipitators, tanks, and stacks as a whole may be of different sizes and operated in series, parallel, or a combination of the two, and may be operated in countercurrent, crosscurrent, or co-flow. For example, the system may include two or more precipitators, each of which produces a regenerated dilute solution that is combined before flowing into the RED cell; and / or the system may include two or more dissolution tanks, each of which produces a regenerated concentrated salt solution that is combined before flowing into the RED cell. When operating as a batch system, the salt solution can pass through the RED cell stack several times (multiple passes) to improve efficiency. This provides the ability to stop operation in one part of the system, such as for maintenance, while maintaining operation in the rest of the system.

[0066] In one embodiment, one vessel can be both a precipitator (e.g., precipitates salts from spent solution and removes a regenerated weak solution) and a dissolution tank (e.g., adds spent solution to a vessel containing precipitated salts and then dissolves the salts into the solution so that a concentrated solution can be regenerated). Here, the salts are retained in the vessel and used to prepare a regenerated concentrated salt solution, rather than removing the precipitated salts.

[0067] The concentrated solution and the dilute solution will be in separate circuits. However, there may be some controlled mixing of the two solutions (controlled mixing in the RED / PRO stack). In addition, some uncontrolled mixing permeation (water flow) may occur between the concentrate and the dilute solution within the RED / PRO stack. Due to permeation, some portion of the water in the dilute solution may be transferred or migrated to the concentrated solution in the RED / PRO stack. Because of this movement of water due to permeation, there may be a controlled flow that balances the total volume in the diluent tank and the concentrate tank. Otherwise, the volume in the concentrate tank continues to increase. The controlled mixing or flow between the circuits can be controlled by incorporating a valve that operates to ensure that both circuits have the same volume of solution.

[0068] A method for generating electricity from thermal energy is disclosed. The method includes separating a first salt solution from a second salt solution by a selectively permeable membrane. The method includes receiving thermal energy from a heat source through the first salt solution and / or the second salt solution. The method includes mixing the first salt solution with the second salt solution in a controlled manner, capturing at least some salinity gradient energy as electricity as the salinity difference between the first salt solution and the second salt solution decreases. The method includes transferring thermal energy from the first salt solution to the second salt solution by a heat pump, causing the salinity difference between the first salt solution and the second salt solution to increase.

[0069] The method may include using reverse electrodialysis to capture salinity gradient energy. The method may further include using pressure-retarded osmosis to drive a generator to capture salinity gradient energy. In some embodiments, the first salt solution and the second salt solution are each circulated in a closed system. Transferring heat energy from the first salt solution to the second salt solution may cause the first salt solution to precipitate salt. The method may include introducing the precipitated salt into the second salt solution, causing the salinity difference between the first salt solution and the second salt solution to increase. The method may include using a portion of the generated electricity to produce hydrogen and optionally oxygen through electrolysis. In some examples, transferring heat energy from the first salt solution to the second salt solution includes transferring heat energy from a first salt solution that is cooler than the second salt solution.

[0070] The method may further include coordinating heat transfer from one or more heat sources to the first salt solution and / or the second salt solution based on one or more heat sources or one or more measurements of the state of the first salt solution and / or the second salt solution. The heat source may include one or more of geothermal heat, industrial waste heat (e.g., power plants), exhaust from transportation vehicles (e.g., cars, ships, trucks), or solar heat.

[0071] The method may include reversing the circulation flow of the first salt solution and the second salt solution in the closed system. This may be achieved by applying solenoid valves at both ends of the closed loop system. The reversal of the circulation flow does not stop the generation of energy and prolongs the use of the selectively permeable membrane so that the membrane wears substantially equally on its two opposite lateral sides.

[0072] The following discussion omits or only briefly describes conventional features of the disclosed technology that are obvious to those skilled in the art. Reference to various embodiments does not limit the scope of the appended claims. In addition, any examples set forth in this specification are intended to be non-limiting and only set forth some of the many possible embodiments of the appended claims. In addition, specific features described herein may be used in combination with other described features in each of a variety of possible combinations and arrangements. One of ordinary skill in the art will know how to use the present invention in combination with routine experimentation to achieve other results not specifically disclosed in the examples or embodiments.

[0073] It is also understood that the terms used in this specification are only for the purpose of describing a specific form or embodiment, and are not intended to limit the scope of the present disclosure, which will be limited only by the appended claims. Unless specifically defined otherwise herein, all terms should be given their broadest possible interpretation, including the meaning implied by this specification and the meaning understood by those skilled in the art and / or the meaning defined in dictionaries, papers, etc. Unless otherwise defined, all technical and scientific terms used herein have the same meanings as those of ordinary skill in the art are generally understood. Although 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, preferred methods, devices and materials are now described. All references mentioned herein are incorporated by reference in their entirety.

[0074] As used in the specification and including the appended claims, the singular forms "a (kind) (indefinite articles a, an)" and "the" include plural forms, and unless the context clearly dictates otherwise, references to a particular numerical value include at least that particular value. Ranges may be expressed herein 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 other particular values. Similarly, when a value is expressed as an approximation by using the antecedent "about", it will be understood that the particular value forms another embodiment. It is also understood that all spatial references, such as horizontal, vertical, top, upper, lower, bottom, left and right, are for illustrative purposes only and may be changed within the scope of the present disclosure. For example, references to "upper" and "lower" are relative and are used only relative to one another in the context, and are not necessarily "upper" and "lower". Generally, similar spatial references to different aspects or components indicate similar spatial orientation and / or positioning, ie, each "first end" is located at or directed toward the same end of the device.

[0075] The systems and methods described in the present disclosure generally relate to effectively extracting usable energy from the salt concentration difference between two solutions via the precise arrangement and controlled mixing of two solutions. The system can be used to directly generate electricity, or generate hydrogen, or hydrogen and oxygen, which can be used as a fuel for generating mechanical (and / or electrical) power, or generate pressure and / or gravitational potential energy, any of which can be used to drive a turbine or perform other useful work. The system covers a range of sizes and power outputs. Some embodiments can be configured to generate power on the scale of a single residential or commercial building. In some instances, the system includes an industrial power generation system that provides electricity to a regional or national power grid. In some instances, the system provides hydrogen fuel, for example, to provide power for a fleet, and (or instead of) generating electricity.

[0076] Figure 1 An exemplary system 100 for generating power from a salinity gradient is shown. The exemplary system 100 includes a reverse electrodialysis (RED) cell 110. The RED cell 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 that has been dissolved into its anionic and cationic constituents such that the ionic components are free to move relative to each other. Each ion can have a single charge, or can have multiple variations. In some examples, the solvent and solute are water and sodium chloride (NaCl), respectively. The dissociated ions of NaCl are NaCl, each having a single charge. + and Cl -. Other solvents and solutes may be used that also form a liquid mixture including anions and cations that are free to move relative to each other. The solvent may be an organic or inorganic liquid, including but not limited to water, alcohol, benzene, glycerol. The salt solution may be exothermic or endothermic. That is, when a solution is formed, the solution may absorb heat, such as when potassium chlorate (KClO3) or potassium nitrate (KNO3) is dissolved in water, or release heat, such as when calcium chloride (CaCl2) is dissolved in water.

[0077] like Figure 1 As shown, a salt solution 130 is separated from a dilute solution 140 (i.e., a solution having a lower solute concentration than the salt solution) by a selective permeable membrane 104 (104a-d). The salt solution 130 is separated from the dilute solution 140 by a cation exchange membrane (104a, 104c) on one side of the unit 150 and by an anion exchange membrane (104b, 104d) on the other side of the unit 150, and the anion exchange membrane is spaced apart from the cation exchange membrane (104a, 104c). The salt solution 130 is disposed in the space between the cation exchange membrane (104a, 104c) and the anion exchange membrane (104b, 104d). In the absence of these membranes 104, the salt solution 130 will diffuse freely into the dilute solution 140, thereby making the salinity of the two solutions equal. The movement of negatively charged ions to the anode 114 and the movement of positively charged ions to the cathode 112 cause a potential difference (voltage) across the unit 150. The total voltage of the battery 110 includes the voltage of each cell 150 .

[0078] Ions may tend to accumulate near the membrane 104. This accumulation may hinder the process of power generation. To counteract this accumulation, the system 100 may apply agitation or mixing forces to the salt solution 130 and / or the dilute solution 140, causing the ions to be more evenly (uniformly) distributed throughout the solutions 130, 140. In some examples, the system 100 applies acoustic vibrations to one or more solutions 130, 140 to enhance the uniformity of the solutions 130, 140. The system 100 may apply acoustic vibrations to ion accumulation areas of the cell 150 (e.g., near one or more membranes 104) to effectively enhance the uniformity of the one or more solutions 130, 140.

[0079] like Figure 1As shown, the electrodes (e.g., cathode 112, anode 114) are surrounded by a dilute solution 140. Alternatively, the electrodes 112, 114 may be surrounded by a rinse solution (aqueous solution) that circulates in a closed loop between the electrodes 112, 114 so that the rinse solution is separated from the salt solution 130 and the dilute solution 140. In such an arrangement, the outer selectively permeable membranes 104 (i.e., the membranes 104 closest to the respective electrodes 112, 114 of the RED cell 110) are of the same type (e.g., two anion exchange membranes or two cation exchange membranes). For example, the cation exchange membrane 104 may separate the rinse solution around the cathode 112 from the salt solution 130, and the cation exchange membrane 104 may also separate the rinse solution around the anode 114 from the dilute solution 140. In this arrangement, cations that migrate from the salt solution 130 to the electrolyte around the cathode 112 are recycled to the anode 114, where the cations may pass through the cation exchange membrane 104 and enter the dilute solution 140. Similarly, the membranes 104 closest to the respective electrodes 112, 114 may both be anion exchange membranes, in which case the anions circulate (in the rinse solution) from the anode 114 to the cathode 112, where the anions pass through the anion exchange membrane 104 into the dilute solution 130. In either configuration, a reduction reaction occurs at the cathode 112, and a balanced oxidation reaction occurs at the anode 114. In some examples, the rinse solution includes a supporting electrolyte to enhance the reactions at the electrodes 112, 114. Because both electrodes 112, 114 are surrounded by the same electrolyte (rinse solution) in this arrangement, the rinse solution may form a resistive load between the electrodes 112, 114 through which current may flow, resulting in a reduction in the power output of the RED cell 110. In some examples, the rinse solution and / or associated circulation system may be configured to have a high resistance relative to the output load of the RED cell 110 or the internal resistance of the cells 150 of the RED cell 110. For example, the rinse solution circulation path may be configured to be relatively long.

[0080] The current generated by the cell 110 is a function of the rate at which ions move, and the rate at which ions move is a function of several factors, including the salinity gradient (i.e., the difference in salinity between the salt solution 130 and the dilute solution 140) and (at least) the temperature of the salt solution 130, as well as aspects of the membrane 104. The temperature of the salt solution 130 affects the rate at which ions in the salt solution 130 move toward (and across) the membrane 104, due to the increased kinetic energy of the ions at higher temperatures. According to the Nernst equation, the power generated is a function of the logarithm of the ratio of the salinities of the salt solution 130 and the dilute solution 140. However, as ions move from the salt solution 130 to the dilute solution 140, the salinity of the dilute solution 140 increases, while the salinity of the salt solution 130 decreases. Thus, the gradient between the "spent" salt solution 130 and the "spent" dilute solution 140 decreases. In order to maintain the current (and therefore, power output) of the cell 110, the salinity difference can be continuously regenerated by renewing the spent salt solution 130 and / or the spent dilute solution 140. To this end, spent salt solution 130 and / or spent dilute solution 140 may be circulated between RED cell 110 and the regeneration system (e.g., in a closed loop). Alternatively, spent salt solution 130 and / or spent dilute solution 140 may be continuously replenished, for example, from a natural source such as a river and ocean or bay.

[0081] Figure 2An exemplary regeneration system 200 is shown. The exemplary regeneration system 200 includes a salt removal subsystem 210. The regeneration system 200 circulates the spent dilute solution 140 from the RED cell 110 through the salt removal subsystem 210 in a closed loop and back to the RED cell 110 as a renewed dilute solution 140. In some examples, the salt removal subsystem 210 evaporates and then condenses the solvent of the dilute solution 140 and then circulates the condensed solvent back to the RED cell 110 as a renewed dilute solution 140. The system can evaporate the solvent until the remaining dilute solution 140 is close to or even less than the solubility limit. The remaining dilute solution 140 can then be reintroduced into the spent salt solution 130 to renew the salt solution 130. In some examples, the salt removal subsystem 210 evaporates and then condenses the solvent of the salt solution 130 and then circulates the condensed solvent back to the RED cell 110 as a renewed dilute solution 140. In the closed loop RED cell 110, the salt removal subsystem 210 can evaporate both the salt solution 130 and the dilute solution 140, then condense, circulate the condensed solvent from both solutions back to the RED cell 110 as a renewed dilute solution 140, and circulate the remaining solution back to the RED cell 110 as a renewed (concentrated) salt solution 130. In some examples, the salt removal subsystem 210 reduces the salinity of the dilute solution 140 by a process of salt precipitation instead of evaporation (or in addition) to regenerate the salinity difference between the salt solution 130 and the dilute solution 140 in the RED cell 110. Other methods of regenerating the salinity gradient include freezing the spent dilute solution 140, such as by eutectic chilled crystallization (ECC), or using microfiltration and / or membrane separation. In some examples, multiple methods are advantageously combined. For example, the precipitation or freezing stage can be enhanced by a subsequent membrane filtration stage to optimize the total energy required to separate salt from the spent dilute solution 140.

[0082] like Figure 2 As shown, the exemplary salt removal subsystem 210 removes salt from the spent dilute solution 140 by causing the salt to precipitate. In general, the ability of a solvent to dissolve a solute increases with increasing temperature. Conversely, lowering the temperature of a solution below a temperature known as the saturation point (the temperature at which the solution is at its maximum salinity) generally causes the solute to precipitate. The exemplary salt removal subsystem 210 includes a heat transfer device 216 that is configured to cool the spent dilute solution 140 to a temperature below the saturation point. If the spent dilute solution 140 is an exothermic solution, the dilute solution 140 will cool further as the salt precipitates. In some examples, the heat transfer device 216 also heats the renewed dilute solution 140, for example back to the temperature of the spent dilute solution 140 prior to cooling. That is, the heat transfer device 216 may transfer some or all of the heat energy removed from the spent dilute solution 140 back to the renewed dilute solution 140, such as with Figure 2As shown by the arrows associated with the heat transfer device 216 of the RED cell 110, the temperature of the refreshed dilute solution 140 entering the RED cell 110 is substantially the same as the temperature of the spent dilute solution 140 leaving the RED cell 150.

[0083] In the exemplary salt removal subsystem 210, the precipitated salt 212 settles to the bottom of the salt removal subsystem 210, for example in a dense solid form. In some instances, the salt removal subsystem 210 includes a conveyor 230, which is configured to transport the precipitated salt 212 away from the salt removal subsystem 210. The conveyor 230 may be a conveyor belt, a pump, an Archimedean screw, or other devices or systems configured to physically transport the precipitated salt 212 away from the salt removal subsystem 210. For example, if the salt is in solid form, the conveyor 230 may be a mechanical system capable of transporting solid materials. In some instances, the removed salt 212 is transported to the salt replenishment subsystem 220, where the salt is reintroduced (e.g., redissolved) into the waste salt solution 130, thereby renewing the waste salt solution 130. In a manner similar to how the regeneration system 200 circulates the dilute solution 140, the regeneration system 200 may also circulate the spent salt solution 130 from the RED cell 110 through the salt replenishment subsystem 220 in a closed loop and back to the RED cell 110 as a renewed salt solution 130. The salt replenishment subsystem 220 may increase the salinity of the salt solution 130 by a process of re-dissolving the salt removed by the salt removal subsystem 210, thereby regenerating the salinity difference between the salt solution 130 and the dilute solution 140 in the RED cell 110.

[0084] As described above, the ability of a solvent to dissolve a solute generally increases with increasing temperature. Thus, a higher temperature of the salt solution 130 allows for a higher salinity level and is accompanied by a larger difference between the salinity of the salt solution 130 and the dilute solution 140. A solubility curve is a graph of the amount of solute that a particular amount of solvent can dissolve as a function of temperature. In some instances, the solubility curve associated with a solution is linear. That is, the amount of solute that a solvent can dissolve can change linearly with temperature changes over a wide temperature range (e.g., the entire range over which the solvent is a liquid). In some instances, the amount of solute that a solvent can dissolve does not change linearly with temperature changes. In these cases, even within a narrow temperature range, the amount of solute that a solvent can dissolve can increase, for example, five times or more. The system 100 can be configured to operate the RED cell 110 over a temperature range of high salt solution 130 salinity. Dissolving additional salt may require transferring additional heat to the salt solution 130. Additionally, the system 100 can maintain the temperature of the RED cell 110 at a point above the solubility point to provide a "safety margin" to avoid undesirable precipitation if the salt solution 130 cools below the solubility point.

[0085] The salt replenishment subsystem 220 may receive thermal energy from one or more heat sources configured to increase the temperature of the salt solution 130, for example, to allow additional salt to dissolve. For example, the salt replenishment subsystem 220 may receive waste heat from the heat transfer device 216 of the salt removal subsystem 210. The salt replenishment subsystem 220 may also be configured to receive thermal energy from other heat sources, such as Figure 2 220. Examples of heat sources include, but are not limited to, geothermal heat, industrial waste heat, solar heat, combustion heat, vapor compression cycle waste heat (e.g., from a heat pump), chemical reaction heat, or other forms of heat that cannot be easily or efficiently converted to a usable form by conventional means (e.g., by driving a turbine).

[0086] The thermal optimization system can be used to optimize the use of thermal energy for the power generation system 100 described herein. The thermal optimization system is further described in U.S. Patent No. 11,067,317, which is incorporated by reference in its entirety. The thermal optimization system can transfer thermal energy from one or more heat sources to one or more radiators. Examples of radiators include the interior of a living or office space during the colder seasons of the year, a heated swimming pool, a sauna, and a steam room. In these examples, the system can be configured to regulate the temperature by regulating the transfer of thermal energy to the radiator. For example, the thermal optimization system can monitor the temperature of the heated space and / or the heated water, and use processor-based logic to regulate heat transfer, such as (but not limited to) running one or more PID feedback loops and / or expert systems. During the hotter seasons, the interior space can be a heat source. In this case, the processor-based control system can regulate the transfer of thermal energy leaving these spaces, thereby regulating the temperature.

[0087] Figure 3An exemplary thermal optimization system 300 is shown. The exemplary optimization system 300 includes one or more heat sources 305, one or more heat sinks 310, and one or more RED cells 110 as described above. In some examples, the power generation system 100 includes a pressure delayed osmosis (PRO) system (discussed in more detail below), or other systems that generate electricity from a salinity gradient (e.g., capacitive hybrid (CAP)) instead of (or in addition to) RED cells 110. The optimization system 300 may include one or more pumps 320 configured to transfer heat from one location to another. In some examples, the optimization system 300 uses vapor compression refrigeration to transfer heat from a heat source to a heat sink. That is, the optimization system 300 may compress a refrigerant to transfer thermal energy from the refrigerant to a heat sink (e.g., through a heat exchanger configured for the purpose of absorbing and distributing thermal energy). The optimization system 300 may then transfer the compressed refrigerant (e.g., by pumping the compressed refrigerant through piping configured for that purpose) to the heat source and allow the refrigerant to expand, thereby absorbing thermal energy from the heat source (e.g., via a heat exchanger configured for the purpose of providing thermal energy from the heat source). The vapor compression refrigeration system may include a reversing valve or other controllable device that redirects the transfer of thermal energy. The optimization system 300 may control 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 as the ambient temperature drops.

[0088] The operation of the thermal optimization system 300 may be coordinated by a control system 350 having a processor, for example, as described below with respect to Figure 7 The processor executes instructions that cause the control system 350 to coordinate heat transfer between the heat source 305, the heat sink 310, and the RED battery 110 (or PRO or CAP system), for example, based on prevailing conditions. The control system 350 may also coordinate heat transfer within the power generation system 100, for example, between subsystems such as the salt removal subsystem 210 and the salt replenishment subsystem 220. The control system 350 may transmit or receive signals 352 (352a-c) to or from the heat source 305, the heat sink 310, and the RED battery 110 (or PRO or CAP system). The control system 350 may receive signals 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 PRO system). For example, the signal 352 may indicate a measured quantity, such as temperature and / or pressure, or the signal may indicate a user input, such as a target temperature for the heated interior space. Temperatures associated with power generation system 100 may include temperatures of salt solution 130 and dilute solution 140 in RED cells, in salt removal subsystem 210, and / or in salt replenishment subsystem 220, respectively.

[0089] The control system 350 can be used to transmit control signals, for example, to control the speed of the compressor and / or pump, the direction of the reversing valve, the operating speed of the salt delivery / transfer device 230, etc., to achieve a specified 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 solubility limit. In this way, the control system 350 can effectively control and adjust the heat transfer between several heat sources 305 and the heat sink 310 based on the current conditions and user settings, while optimizing the output of the power generation system 100. In addition, the control system 350 can affect the level of vapor compression cycle waste heat generated by one or more heat pumps 320 and transfer the waste heat to one or more heat sinks and / or RED batteries 110, thereby effectively recapture its own waste heat for power generation or other purposes. In this way, the optimization system 300 can transfer heat from any or all of the multiple heat sources under a variety of dynamic conditions (e.g., as conditions change throughout the year or throughout the day) and / or based on the needs of the RED battery 110. In addition, the control system 350 can configure the power generation system 100 to store excess energy. For example, when the demand for electrical energy is low, the control system 350 may configure the RED cell 110 to generate a portion of its energy output as hydrogen for use as fuel at a later time, rather than as electrical energy for use at the time of generation. Additionally, in the case of a PRO system, the control system 350 may configure the rate at which pressure is converted to electricity, such as by controlling the rate of flow through the turbine. In this way, the control system 350 may retain some energy in the form of, for example, gravitational potential energy when the demand for electricity is low, and convert a larger amount of gravitational potential energy to electricity when the demand for electricity is high.

[0090] In some embodiments, system 100 includes a PRO system instead of (or in addition to) the RED battery 110 described above. Figure 4An exemplary PRO system 120 is shown. The exemplary PRO system 120 also includes a salt solution 130 separated from a dilute solution 140 by a selectively permeable membrane 104c, similar to the RED battery 110 described above. However, instead of generating electricity directly from the salinity difference between the salt solution 130 and the dilute solution 140, the PRO system generates pressure that can take the form of gravitational potential energy. Therefore, the PRO system may not include electrodes. The selectively permeable membrane of the PRO system can be configured to preferentially allow solvents rather than solutes to pass through the membrane, such as from the dilute solution 140 to the salt solution 130, so as to reduce the salinity difference between the solutions. In the PRO system, the selectively permeable membrane can be a hollow fiber membrane that allows water rather than salt to permeate. In the PRO system, the selectively permeable membrane can be a hollow fiber membrane, a spiral wound membrane, a flat membrane, or a combination thereof. As a result, as the solvent migrates across the membrane 104c 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 gravitational potential energy 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 through a turbine, paddle wheel, or other mechanical device suitable for generating electricity. The system 100 can then circulate the spent salt solution 130 through a solvent removal system similar to the salt removal subsystem 210 described above. For example, the solvent recovery system can remove excess solvent by evaporation (optionally in a partial vacuum to reduce the boiling point) and subsequent condensation. The solvent recovery system can then circulate the condensed solvent back to the PRO system 120 as a renewed or "top-up" dilute solution 140, and circulate the renewed salt solution (after removing excess solvent) back to the PRO system 120 as a renewed salt solution 130. Alternatively (or additionally), the solvent recovery system may cause solutes to precipitate out of the spent brine 130, then recycle the spent brine back to the PRO system 120 as “make-up” weak solution 140, and introduce the precipitated salts back into the brine 130, e.g., via Figure 2 As with the RED battery 110 described above, the rate at which the PRO system 120 generates electricity is a function of at least the salinity difference between the salt solution 130 and the dilute solution 140 and at least the temperature of the salt solution 130.

[0091] The RED system may be a capacitive (CAP) system instead of (or in addition to) the RED battery and / or PRO system. The CAP system is an electrode-based technology for generating electrical energy from a salinity gradient. Electricity generation using a CAP system is based on cycles of charging and discharging electrodes. The electrodes in a CAP system are sequentially exposed to two solutions with a large salinity difference. The CAP system charges energy in the form of a salinity gradient and extracts energy from the salinity difference, and benefits from the voltage rise that occurs between two electrodes immersed in a saline solution when the salt concentration of the saline solution changes. Power generation depends primarily on the following properties of each electrode: the magnitude of the potential rise when the salinity changes, and the potential in the high salinity solution. The electrodes can be identical so that the flow of the system can be reversed and the polarity can be changed without stopping electricity generation. The CAP system may include one or more selectively permeable membranes as disclosed herein.

[0092] like Figure 1 As shown, the salt solution 130 is separated from the dilute solution 140 by cation exchange membranes (104a, 104c) on one side of the unit 150 and by anion exchange membranes (104b, 104d) on the other side of the unit 150. Alternatively, the salt solution 130 and the dilute solution 140 can be separated by a single selectively permeable membrane 140 (e.g., a cation exchange membrane or an anion exchange membrane). The selective movement of ions across the single membrane 140 causes a potential difference (voltage) across the membrane 140. Figure 1 Similar to the embodiments, the current generated by a single membrane embodiment of the RED unit 150 (e.g., a flow pump) is also a function of the rate of ion movement, and the rate of ion movement is a function of several factors, including the salinity gradient between the salt solution 130 and the dilute solution 140, (at least) the temperature of the salt solution 130 (due to the increase in kinetic energy of ions at high temperatures), and aspects of the single membrane 104.

[0093] In some embodiments, the system includes a first RED battery 110a configured to use an exothermic salt solution 130a, and a second RED battery 110b configured to use an endothermic salt solution 130b. The system can transfer heat generated by dissolving solutes in the exothermic salt solution 130a to the endothermic solution 130b to replace the heat absorbed while dissolving the solutes.

[0094] In some embodiments, a portion of the generated electricity is used to produce hydrogen, for example, by decomposing water by electrolysis. For example, when the dilute solution is water, a potential difference of 1.23 volts may be applied to the water to decompose the water into hydrogen and oxygen. The oxygen may be supplied and pumped to a space such as a building or other indoor area. The hydrogen and / or oxygen may be stored for later use, for example as a battery. The salt solution or the dilute solution (or both) may be decomposed by electrolysis. Figure 5An exemplary RED cell 110 configured to generate hydrogen is shown. The released hydrogen and oxygen may "bubble" to surfaces near the respective cathode 112 and anode 114 of the RED cell 110. The system 100 may separate the oxygen and hydrogen (e.g., by physically separating the cathode 112 and anode 114), capture and store the hydrogen (e.g., by capturing the hydrogen as it bubbles to surfaces near the cathode), and then transport the hydrogen to an appropriate location by appropriate means for use as a fuel. In these cases, the system 100 must replenish or "top up" the solvent lost by electrolysis, for example, from a stream or other fresh water source. The RED cell 110 may be configured so that electrolysis occurs naturally. That is, the RED cell 110 may be configured to generate sufficient potential difference to cause electrolysis of its solvent. In some examples, the regeneration system uses electrolysis to renew the salinity of the spent salt solution 130 while replenishing fresh water as a renewed dilute solution 140 circulated to the RED cell 110 (or PRO or CAP system). In some examples, the system includes a separate reservoir of water for generating hydrogen by electrolysis (e.g., not a solvent for the electrolysis RED Cell or PRO or CAP system). The separate water reservoir can have its own "make-up" source when the RED Cell or PRO system remains in a closed loop. In these embodiments, the reservoir of water can also serve as a heat reservoir or play other roles in the thermal optimization process.

[0095] Figure 6 A flow chart 600 of an exemplary method for generating electricity from thermal energy is shown. At step 602, the exemplary method includes separating a first salt solution 130 from a second salt solution 140 by a selectively permeable membrane 104. The selectively permeable membrane 104 can be configured to provide controlled mixing of the first salt solution 130 and the second salt solution 140 so as to capture salinity gradient energy in a more useful form when mixing occurs. In some examples, the selectively permeable membrane 104 is configured to preferentially allow a solvent of the first salt solution 130 to pass through the membrane and into the separated second salt solution 140, for example, as in a PRO system. In some examples, the selectively permeable membrane 104 is configured to preferentially allow anions or cations of the first salt solution 130 to pass through the membrane and into the separated second salt solution 140, for example, as in a RED battery 110.

[0096] At step 604, the exemplary method includes receiving thermal energy from a heat source. The power generated by the RED battery 110 (or PRO system) is a function of temperature. The received thermal energy may allow the RED battery 110 to continue to operate (e.g., generate electricity). In some examples, the control system 350 is configured to regulate the amount of thermal energy received and 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 to operate the one or more heat pumps 320. As a prophetic example, the RED battery 110 may have an efficiency of approximately 30% (i.e., 30% of the thermal energy transferred to the RED battery 110 is converted into electricity or other usable energy forms). The heat pump 320 may have a coefficient of performance (COP) between 3 and 4 (i.e., the heat pump 320 may require 1 KW of power to absorb 2-3 KW of power from the heat source and transfer 3-4 KW to the heat sink (the sum of the input power and the heat power absorbed from the heat source). For example, a heat pump 320 with a COP of 4 may require 1 KW of power to transfer a total of 4 KW of heat to the RED battery 110. The heat pump 320 may transfer heat from a low-grade or "waste" heat source (e.g., a source that is not easily converted to a useful form of energy, such as a heat source less than 300°C). In some predicted examples, the heat source may be the result of an industrial process that would otherwise simply export waste heat to the environment. At 30% efficiency, the RED battery 110 may generate 1.2 KW of electricity from the 4 KW of transferred heat. In this predicted example, 1 KW of electricity may be used to power the heat pump 320, leaving 200 3 KW of electricity is used for other purposes. Thus, in this predictive example, the combined system 100 of RED battery 110 and heat pump 320 produces a net output of 200 W of electricity, and has no net power input other than 3 KW of "waste" heat. In the case where the waste heat is the result of an industrial process, the combined system 110 of RED battery 110 and heat pump 320 is expected to produce a net output of 200 W while providing the benefit of cooling the waste heat by 3 KW before exporting it to the environment. The expected net efficiency of the combined system 110 can be further amplified with improvements to the efficiency of the RED battery 110.

[0097] In addition, the power generation system 100 can improve the effective coefficient of performance (COP) of a heat pump 320 (e.g., a heat pump used to heat or cool a living space) by capturing some of the waste energy generated by one or more heat pumps and converting the waste energy into electrical energy to power the heat pump 320. For example, a heat pump with a heating COP of 3 may require 1.5 KW of power to pump 3 KW of heat from a source to a heat sink. If the heat sink does not require the full 4.5 KW of power (3 KW of pumped heat plus 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 for conversion into power for the heat pump 320, increasing the effective COP of the heat pump 320. In addition, the control system 350 can configure the power generation system 100 to convert some amounts of waste energy into a form that can be stored for later use, for example, if the instantaneous demand for electricity is greater than the amount of electricity that can be generated. For example, the PRO system can retain waste energy in the form of unreleased pressure and / or gravitational potential energy to be released at a future time, for example, when the demand for electrical energy is greater. Similarly, instead of generating a certain amount of electrical energy, the RED cell 110 can generate hydrogen for use as a fuel at a future time. Thus, waste heat from the heat pump 320 can be flexibly captured and released, thereby further increasing the effective COP of the heat pump.

[0098] At step 606, the exemplary method includes mixing the first salt solution 130 with the second salt solution 140 in a controlled manner. At 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 so that as the solutions (130, 140) mix, the salinity gradient energy is converted into a more useful form. At step 610, the exemplary method includes transferring heat energy from the first salt solution to the second salt solution via the heat pump 320. At step 612, the exemplary method includes causing the salinity difference between the first salt solution and the second salt solution to increase. As described above, the heat pump 320 can cool the spent dilute solution 140, causing salt to precipitate from the dilute solution 140, thereby renewing the dilute solution. The heat pump can transfer heat from the spent dilute solution 140 to the spent salt solution 130, enhancing the process of dissolving the salt introduced into the salt solution 130. Alternatively (or additionally), heat pump 320 may heat spent salt solution 140, causing salt solution 140 to evaporate, thereby renewing the salt solution. The evaporated solvent may be condensed (eg, cooled by the heat pump) as the solvent vapor is circulated back to RED cell 110 as a renewed dilute solution.

[0099] Figure 8An exemplary regeneration system including a salt precipitation system is shown. In this embodiment, the salt precipitation system includes a salt precipitator 880, three heat exchangers 882, 884, 838 (although alternative embodiments may include one heat exchanger, two heat exchangers, or more than three heat exchangers), and an external heat source system 890. The regeneration system circulates the spent dilute solution 840 from the RED or PRO battery 810 through the salt precipitation system in a closed loop and returns to the RED or PRO battery 810 as a renewed dilute solution 845. Optionally, the renewed dilute solution 845 may be stored for a period of time in a tank 846 for holding dilute solution before being directed to the RED or PRO battery 810. The spent dilute solution 840 is directed to the salt precipitator 880, where a heat exchanger 884 is applied to remove heat energy from the spent dilute solution 840, causing the precipitation of salt 885, which further dilutes the solution within the salt precipitator 880, thereby providing a regenerated dilute solution 845 (which may also be referred to as a renewed dilute solution). The salt 885 is directed to a concentrate tank 836 (or a tank configured to regenerate the spent concentrate solution) containing the spent concentrate solution 830. Within the concentrate tank 836, the salt 885 is dissolved in the spent concentrate solution 830, optionally with the application of thermal energy via a heat exchanger 838 or the like, to increase the salt concentration and produce a regenerated concentrate solution 835 (which may also be referred to as a renewed concentrate solution).

[0100] The salt precipitation system reduces the salinity of the spent dilute solution 840 by a salt precipitation process rather than (or in addition to) evaporation, and uses the precipitated salt 885 to increase the salinity of the spent concentrated solution 830 to regenerate the salinity difference between the concentrated solution 835 and the dilute solution 845 so that the feed stream can be directed to and used in the RED or PRO cell 810.

[0101] like Figure 8 As shown, an exemplary salt precipitation system removes salt from a spent dilute solution 840 by causing the salt to precipitate. Reducing the temperature of the solution below a temperature known as the saturation point (the temperature at which the solution is at its maximum salinity) generally causes the solute to precipitate. The system includes a heat transfer device (shown as a heat exchanger 884) Figure 8), the heat transfer device is configured to cool the spent dilute solution 840 to a temperature below the saturation point. The heat exchanger 882 passively exchanges heat between the renewed dilute solution 845 and the spent dilute solution 840. The heat exchanger 882 heats the renewed dilute solution 845, for example, back to the temperature of the spent dilute solution 840 before cooling, because the temperature of the solution in the diluent tank 846 can be optimally about 30°C to about 50°C. That is, the heat exchanger 882 can transfer some or all of the heat energy removed from the spent dilute solution 840 back to the renewed dilute solution 845. The spent dilute solution 840 can be about 30°C to about 40°C, and it will be reduced to about 5°C in the precipitator. In this way, the temperature of the renewed dilute solution 845 entering the battery 810 is substantially the same as the temperature of the spent dilute solution 840 leaving the battery 810. The heat exchanger 882 can play both the role of cooling and heating as described above, or it can be positioned in the system to heat the regenerated dilute solution 845 only after it leaves the precipitator 880. For example, it can heat the stream of the regenerated weak solution 845 by blowing hot air over it. Control valves 811, 812 are included in the system to control and balance the volume of the solution flow. Pumps 813, 814 are included in the system to move the solution and allow it to flow to the RED or PRO battery 810. Pumps 813, 814 can be any such pump or device known in the art for working on a fluid to move the fluid, such as but not limited to a diaphragm pump or a centrifugal pump, a peristaltic pump. The number of control valves and heat pumps may vary between the systems of the present disclosure. Those skilled in the art will understand that one or more control valves may be added to any embodiment of the present disclosure. Heat exchangers 884, 838 transfer heat from the precipitator 880 or the tank 836 to the heat source system 890, respectively. Heat exchangers 884, 838 may be coils immersed in the precipitator 880 or the tank 836, respectively, wherein the liquid circulates in the coils, or each heat exchanger may be any other heat exchanger known in the art, such as a shell or tube heat exchanger.

[0102] Figure 8 An external heat source system 890 is included, which includes a heat exchanger 891 and a heat pump 892 to add heat to the system. The external heat source system 890 can be used with the salt precipitation system to supply thermal energy to the concentrate tank 836. The external heat source system 890 is described as having a closed loop, optionally a refrigerant loop, to generate warming and cooling of the precipitator 880 and the concentrate tank 836. The heat exchanger 891 optionally draws low-grade heat (e.g., below about 100°C, or below about 200°C) or ultra-low-grade heat (e.g., ambient air, or below about 80°C) directly from the air or an external heat source. The external heat source supplies external heat to the heat source system 890, which can ultimately be converted into electricity by the RED / PRO battery 810.

[0103] In other embodiments, heat source system 890 is not present, and instead high grade heat (eg, steam, or from any source that supplies heat above about 100° C.) may be added directly to the concentrate tank to heat it. Fig. 9 Shows a system including salt precipitation without Figure 8 An example of a regeneration system for an external heat source system included in . Fig. 9 As the salt precipitator 880 is cooled, thermal energy is released, optionally as heat 991. Heat 991 may be removed by any means known in the art and directed to any source, released, or directed back into the system via heat 992. Heat 992, 993 may be introduced into the system from ambient energy, a heat pump, or elsewhere in the system (e.g., heat 991).

[0104] Fig.10An exemplary regeneration system including a salt decomposition system is shown. In this embodiment, the salt decomposition system includes an absorber 1080, a salt decomposition vessel 1081, two heat exchangers 1082, 1084 (although alternative embodiments may include one heat exchanger, or more than two heat exchangers), and a heat pump 1013. Heat is added to the salt decomposition. The regeneration system circulates the spent dilute solution 1040 from the RED or PRO cell 1010 through the salt decomposition vessel 1081 in a closed loop, where heat is applied to warm the tank and form vapor and gaseous salt 1085, and returns to the RED or PRO cell 1010 as a renewed dilute solution 1045. The heat exchanger 1084 is positioned between the spent dilute solution stream 1040 and the renewed dilute solution stream 1045 to transfer thermal energy. The spent concentrated solution 1030 circulates from the RED or PRO cell 1010 through the absorber 1080 in a closed loop, and then returns to the RED or PRO cell 1010 as a renewed concentrated solution 1035. Heat exchanger 1082 is positioned to transfer thermal energy between waste concentrated solution stream 1030 and renewed concentrated solution stream 1035. When heat is applied to container 1081, gaseous products (e.g., decomposed gaseous salts) 1085 are released from the container and received by adsorber 1080, where the salt decomposed in the vapor is absorbed into the waste concentrated solution 1035 to increase the salt concentration of the solution. In salt decomposition container 1081, salt is removed from waste dilute solution 1040, leaving a regenerated dilute stream 1045. Heat 992, 993 can be introduced into the system from ambient energy, heat pumps, or other places in the system. Heat 991 can be removed and used in the heat pump, or released. Heat pump 1013 can heat and cool simultaneously (see heat input 991 and heat output 993), and use heat / thermal energy 994 from another source. Control valve 1011 is included in the system to control and balance the volume of solution flow. The salt decomposition vessel 1081 separates gas from liquid; it may include a flash tank or a stripping tower to decompose the salt in solution. The salt decomposition vessel 1081 and the absorber 1080 may be any container or group of containers, tanks and / or towers, and perform the functions described herein and are readily understood by those skilled in the art.

[0105] Fig.11 is another example of a regeneration system that includes an evaporation system. Fig.11 and Fig.10The embodiment of is different in that it incorporates an evaporator 1091 and a condenser 1090. In this example, the spent concentrated solution 1030 is circulated from the RED or PRO cell 1010 through the evaporator 1091 in a closed loop, where heat 992, 993 is applied, causing the solution to boil and the water to evaporate as vapor 1093, leaving a more concentrated solution, i.e., a renewed concentrated solution that is directed back to the RED or PRO cell 1010. The vapor 1093 is directed from the evaporator 1091 to the condenser 1090, where the container is cooled and the vapor is condensed into water and mixed with the spent dilute solution 1040 to make a renewed dilute solution 1045, which is directed back to the RED or PRO cell 1010 in a closed loop. The heat pump 1013 produces a refrigeration effect on the condenser 1090. Traditionally, a chilled water loop would be used instead of this heat pump, and any heat put into the system would be lost. By incorporating a heat pump as shown, the heat is recovered, which makes the process more energy efficient. The evaporator 1091 and the condenser 1090 can be any tank, container, tower, or combination thereof that achieves the functions described herein and is readily understood by those skilled in the art.

[0106] Fig.12 is an example of a regeneration system including electrodialysis and salt precipitation. Dilute solution 1141 and concentrated solution 1131 are directed to electrodialysis system 1190, where electricity is supplied to force salt to separate from dilute solution 1141 by moving ions from the dilute to the concentrate, which produces an ultra-dilute solution 1147. By using electrodialysis, electricity is used to generate a more concentrated solution 1132 and an ultra-dilute solution 1147. The spent dilute solution 1140 is desalted in precipitator 1180, leaving dilute solution 1141 (having a lower salt concentration than spent dilute solution 1140). By using electrodialysis, dilute solution 1141 is further diluted outside the solubility curve to produce an ultra-dilute solution 1147 and create a larger salt gradient. As shown in FIG. Fig.12 As depicted in FIG. 1 , the ultra-dilute solution flows from the electrodialysis tank to the diluent storage tank 1146 where it is mixed with the dilute solution 1141 (if any) from the precipitator 1180. In an alternative embodiment, the system may be configured to flow the ultra-dilute solution 1147 directly into the cell 1110, with valves employed and positioned to alter the flow of the solution, as will be readily apparent to one skilled in the art.

[0107] The spent dilute solution 1140 is directed to a cooled (heat removed 1191) salt precipitator 1180. The removal of heat from the spent dilute solution 1140 causes precipitation of salt 1185, which further dilutes the solution within the salt precipitator 1180, thereby providing a dilute solution 1147, which can be sent to a storage tank 1146 and / or further diluted by treatment with electrodialysis. The regenerated dilute solution 1145 (which may also be referred to as a renewed dilute solution) has the same salt concentration as the ultra-dilute solution 1147, or has a lower salt concentration than the dilute solution 1141 after mixing with the ultra-dilute solution 1147 in the tank 1146. The regenerated dilute solution 1145 flows back to the cell 1110 to take advantage of the salinity gradient. The salt 1185 is combined with the spent concentrated solution 1130 to increase its salinity and then directed to the concentrate storage tank 1136. In the concentrate storage tank 1136, salt 1185 is dissolved in the spent concentrate solution 1130, optionally by applying any heat 1192 or other thermal energy source, to increase the salt concentration and produce a concentrated solution 1131, which is then directed to the electrodialysis system 1190 to increase its salt concentration and produce a more concentrated solution 1132. The more concentrated solution 1132 may have a higher or equal salt concentration than the regenerated concentrated solution 1135 (which may also be referred to as a renewed concentrated solution). The concentrate tank 1136 may have excess salt (not shown) at its bottom, which, if present, can be used as a battery to allow the process to continue operating when excess heat is temporarily unavailable.

[0108] The salt precipitation system reduces the salinity of the spent dilute solution 1140 by a salt precipitation process, rather than (or in addition to) evaporation, and uses the precipitated salt 1185 to increase the salinity of the spent concentrated solution 1130 to increase the salinity difference between the concentrated solution 1131 and the dilute solution 1141. Figure 2 Differently, concentrated solution 1131 and dilute solution 1141 are further processed by electrodialysis to increase the salinity difference between the solutions before being reintroduced into cell 1110. The electricity 1171 generated by RED or PRO cell 1110 can be used, stored, and / or used as electricity 1170 for operating electrodialysis system 1190 by any means known in the art.

[0109] And in Fig.12 In some embodiments, the electrodialysis system 1190 uses a different tank than the RED or PRO cell 1110, while in other embodiments, the electrodialysis may use the same tank as the reverse electrodialysis.

[0110] Fig.13 is incorporated into the membrane distillation system 1390 (the electrodialysis system 1190 is Fig.12The membrane distillation system 1390 includes a heat pump (not shown) that evaporates water that is able to permeate through a porous hydrophobic membrane (not shown) into a dilute solution to reduce its salt concentration, thereby producing an ultra-dilute solution 1347. The ultra-dilute solution 1347 can go directly into the cell 1110 or into a dilute tank as shown, where valves are used and positioned to change the flow of the stream. Fig.13 , the ultra-dilute solution 1137 flows from the membrane distillation system 1390 to the diluent storage tank 1146 where it is mixed with the dilute solution 1141 (if any) from the precipitator 1180. In an alternative embodiment, the system can be configured to allow the ultra-dilute solution 1347 to flow directly into the cell 1110, wherein valves are employed and positioned to change the flow of the solution, as will be readily apparent to one skilled in the art.

[0111] In the concentrate storage tank 1136, salt 1185 is dissolved in the spent concentrate solution 1130, optionally by applying any heat 1192 or other thermal energy source, to increase the salt concentration and produce a concentrated solution 1131, which is then directed to the membrane distillation system 1390 to increase its salt concentration and produce a more concentrated solution 1332. The more concentrated solution 1332 can have a higher or equal salt concentration than the regenerated concentrated solution 1135 (which can also be referred to as a renewed concentrated solution).

[0112] Fig.14 is an example of a regeneration system that is incorporated into the membrane distillation system 1390 without salt precipitation. The spent dilute solution 1140 is directed to the diluent storage tank 1146, where it is cooled (i.e., heat energy 1191 is removed) and directed to the membrane distillation system 1390. The spent concentrated solution 1130 is directed to the concentrate storage tank 1136, where it is warmed (i.e., heat energy 1192 is put into the system) and directed to the membrane distillation system 1390. Heating and cooling of the tanks may optionally be supplied by one or more heat pumps (not shown). The spent dilute stream 1140 and the spent concentrated stream 1130 are directed to the membrane distillation system 1390, which operates using the vapor pressure difference generated by the temperature difference between the streams across the hydrophobic membrane (not shown). Regenerated dilute solution 1445 and regenerated concentrated solution 1435 are produced by operation of the membrane distillation system 1390, which are then circulated back to the RED or PRO cell 1110, optionally returned through the storage tanks 1146, 1136, as shown. Fig.14 shown.

[0113] Fig.151501 is an example of a RED / PRO tank combined with a regeneration system, wherein multiple tanks are operated in a batch system. Operation tanks 1501, 1502, 1503, 1504 may each be a cooling tank (i.e., a precipitator), a heating tank (i.e., a dissolving tank), or may not be in operation at any given time. For example, tank 1501 may first be operated as a cooling tank to precipitate salt from a waste dilute solution, leaving a regenerated dilute solution 1545, which may then be directed to a diluent tank 1546. Then, the operation of tank 1501 may be changed to a heating tank, wherein a waste concentrated solution 1530 is directed to a tank containing precipitated salts, which is then warmed to dissolve the salts into the solution, leaving a regenerated concentrated solution 1535, which may then be directed to a concentrate tank 1536. At other times, tank 1501 may not be in operation when it needs maintenance or for any other reason. This change in operation may be applied to any operating tank in a batch system as needed.

[0114] A valve system 1520 separates the tank from the RED / PRO cell 1510 and operates by directing the flow of all or a portion of each of the spent dilute solution 1540 and the spent concentrated solution 1530 to one or more operating tanks 1501, 1502, 1503, 1504. A second valve system 1522 separates the operating tanks 1501, 1502, 1503, 1504 from the storage tanks and operates by directing the flow of the regenerated dilute solution 1545 and the regenerated concentrated solution 1535 to respective storage tanks 1546, 1536: the diluent tank 1546 receives and holds the regenerated dilute solution 1545, and the concentrate tank 1536 receives and holds the regenerated concentrated solution 1535. Although the Fig.15 Four operating tanks are shown, but fewer or more than four tanks may be connected to the system and operated in a batch system.

[0115] Fig.16 A method of producing water using a vapor condenser 1601, a compressor or heat pump 1602, and an evaporator 1603 is shown. A refrigerant 1612 circulates through the vapor condenser 1601, the heat pump 1602, and the evaporator 1603. As shown, the evaporator 1603 removes water vapor from the ambient air, releasing water and air that is cooler and drier than the incoming ambient air. The condenser releases latent heat, which can be used in the salinity gradient energy system 1610 disclosed herein. For example, the system can be used in a home or other building to dehumidify the ambient air (or extract water from the ambient air) and optionally generate heat, which can be converted into electricity by the RED / PRO battery.

[0116] Fig.17 Incorporation Fig.16as a method of producing a hot water tank 1620 and a cold water tank 1625, which can be used to warm and cool the solution used in the salinity gradient heat engine system 1610 disclosed herein; optionally including a regeneration system (e.g. Figure 8-15 16). The evaporator 1603 cools the water to make a cold tank 1625, while the condenser 1601 heats the water to make a hot tank 1620. A heat transfer medium 1613 (e.g., water, glycol, oil, refrigerant) flows from the cold tank 1625 through the salinity gradient engine system 1610 in a closed loop, and a heat transfer medium 1614 flows from the hot tank 1620 through the salinity gradient heat engine system 1610 in a closed loop. Although optional, a radiator 1640 is shown and used to absorb or dissipate excess heat from the system. If the system generates more heat than required, it can be transferred to the radiator, which can, for example, release heat 1631 to the atmosphere. Although optional, other heat sources 1630 are shown that provide thermal energy or heat 1631 to the system. Each other heat source can be any means known in the art, such as, but not limited to, a heat exchanger, industrial steam, radiator, ambient, coil, convection.

[0117] The salinity gradient system disclosed herein can produce water (also referred to herein as atmospheric water generation). Atmospheric water generation is the process of extracting water from the air using a variety of techniques such as condensation, adsorption, and cooling. The concept of atmospheric water generation is based on the fact that even in arid and desert areas, the atmospheric environment contains significant amounts of water vapor. When this is combined with RED / PRO batteries, heat pumps, and closed loop processes, energy and water can be produced.

[0118] One means of atmospheric water generation is by condensation, which involves cooling the air to a temperature below the dew point / condensation temperature so that water vapor in the air condenses into liquid water. This process is commonly used in thermodynamic cycles, such as dehumidifiers and heat pumps. The process depends on the temperature and humidity of the air, which is readily understood by those of ordinary skill in the art, for example, by consulting a psychometric chart.

[0119] Another means of atmospheric water generation is by adsorption, which uses a desiccant material such as silica gel or zeolite to absorb moisture from the air. Once the desiccant material has absorbed moisture and optionally becomes saturated, it can be heated to release water, which can be collected and used. In a similar manner, a liquid desiccant is a substance with a high affinity for water molecules and can be used to remove moisture from the air, which can be referred to as a liquid desiccant dehumidification process. The method may include passing air (optionally having a medium to high humidity content, for example, greater than about 30%; not dry or arid) over a surface coated with a liquid desiccant, which absorbs moisture from the air. When the absorbed water is removed from the liquid desiccant, it can be regenerated to its original state. Any solid desiccant material or liquid desiccant known in the art can be used herein.

[0120] The liquid desiccant dehumidification process can be a closed-loop system that includes two separate air handling units: one unit for dehumidification (also called a conditioner) and the other unit for regeneration (also called a generator). The dehumidification unit typically consists of an absorber where the liquid desiccant is sprayed or coated onto a surface and a fan or blower circulates the humidified air over the surface. As the air passes over the surface, the liquid desiccant absorbs moisture from the air, leaving dry air that is discharged into the conditioned space.

[0121] The regeneration system may include a separate container containing the used liquid desiccant, and a heat source, in this case a heat pump. In this embodiment, the absorbed moisture is removed from the liquid desiccant by a process called regeneration, where heat is applied to the liquid desiccant to drive off the absorbed water. The removed water vapor may be condensed via a heat pump to produce water (which may be potable water in the case of added filtration (e.g., reverse osmosis or any other known system used in the art)), or it may be added to a dilute solution to increase the salinity gradient of the RED / PRO cell. This produced water may additionally or alternatively be used to generate hydrogen, as it may be used as a feed for electrolysis and / or RED.

[0122] Typically, atmospheric water generation is highly energy intensive because it generates water against the latent heat of evaporation of water. In combination with a closed loop salinity gradient engine system such as RED, this latent heat can be utilized and converted into hydrogen and / or electricity rather than discharged into the atmosphere. Some advantages of the liquid desiccant dehumidification process include its ability to extract water from low humidity levels in hot and humid climates, and its ability to regenerate using waste heat, solar energy and / or heat pumps. Using a heat pump alone to condense water vapor from dry and hot climate areas would be far more difficult than using a desiccant in combination with a heat pump. The combination of a liquid desiccant dehumidification process with a heat pump and a salinity gradient engine system allows for the generation of large amounts of water and energy even in very dry and hot climates.

[0123] Fig.18 is an example of atmospheric water generation using a liquid desiccant dehumidification process. In this example, water is drawn from the air and absorbed by the desiccant within the regulator 1812. The used (weakened) desiccant 1820 is transferred to the generator 1811, where the desiccant is regenerated by evaporation of water, thereby regenerating the strong desiccant 1821, which is redirected back to the regulator 1812. A heat pump 1882 is employed to transfer heat between the weakened desiccant stream 1820 and the regenerated strong desiccant stream 1821. The vapor 1884 removed from the generator 1811 can be directed to a vapor condenser 1815, where it is cooled and liquefied to make water 1885 for any purpose, including potable water (using a filtration system).

[0124] Fig.18 Utilizes a method for producing a hot water tank 1813 and a cold water tank 1814 that can be used to warm and cool a solution (e.g., water) used in a salinity gradient heat engine system 1810 disclosed herein; optionally including a regeneration system (e.g., Figure 8-15 1814). Heat exchanger 1884 cools water to make cold tank 1814, while heat exchanger 1883 heats water to make hot tank 1813. Heat transfer medium 1816 (e.g., water, glycol, oil, refrigerant) flows from heat exchangers 1883, 1884 into heat pump 1802 in a closed loop. One or more radiators and other heat sources may be incorporated to provide heating or cooling to one or both of hot tank 1813 or cold tank 1814. Hot tank 1813 provides hot water as heat supply stream 1830 to generator 1811 and salt gradient heat engine system 1810 in a closed loop, which returns to hot tank 1813 as stream 1831 at a lower temperature. Cold tank 1814 provides cold water as cold supply stream 1832 to steam condenser 1815, regulator 1812, and salt gradient heat engine system 1810 in a closed loop, which returns to cold tank 1814 as stream 1833 at a higher temperature.

[0125] The salinity gradient system disclosed herein may include forward osmosis (FO) as a means of regenerating waste dilute solution and waste concentrated solution from the RED / PRO cell, i.e., a regeneration system. In a forward osmosis system, a feed solution (e.g., a waste concentrated solution) may be placed on one side of a semipermeable membrane, and a draw solution may be placed on the other side of the semipermeable membrane. The draw solution may be any solution having a higher osmotic pressure than the feed solution; it may include different salts, synthetic salts, or it may be substantially the same as the feed solution, but at a higher concentration. A salt gradient is generated to draw water from the waste concentrated solution, which is then regenerated by a switchable solubility system incorporated into the draw solution. The osmotic pressure gradient generated by the draw solution draws water molecules from the feed solution through the membrane while leaving salt and other contaminants on one side with the feed solution. This allows the regeneration of the concentrated solution, which can be directed back into the RED / PRO cell. The membrane used for the FO system may be any membrane that can be used for a PRO cell. However, for FO, the membrane does not have to be designed to withstand pressures as high as the PRO membrane.

[0126] The forward osmosis system can be incorporated into a switchable solubility system, which utilizes a draw solution and a reversible reaction between carbon dioxide (CO2) and water to produce a solution with a switchable solubility property. These switchable solubility solutions can switch between a hydrophobic form and a hydrophilic form. The method for preparing a switchable solubility solution may include: dissolving an amine in water and producing a solution with a specific pH level. For example, the amine may be 1-cyclohexylpiperidine, N-methyldipropylamine, 4-(diethylamino)ethyl butyrate, N,N-dimethylbenzeneethylamine, N,N-diethylbutylamine, etc. As mentioned herein, a draw solution is a solution with a high osmotic pressure or concentration to draw water across a semipermeable membrane. Therefore, a switchable solubility solution may be a draw solution in a forward osmosis system. When CO2 is introduced into a switchable solubility solution, it reacts with an amine to form a salt, which causes the pH of the solution to decrease. This pH change causes the solubility of the amine to change, making it soluble or insoluble in water. Therefore, the solubility of the amine can be changed by the presence of CO2 and reversed by applying heat. Specifically, at low pH (e.g., below about 7, or between 7 and 1), the amine becomes readily soluble in solution. In contrast, when the pH is higher (e.g., above 7), the amine becomes poorly soluble in water and is difficult to dissolve in solution. The solubility of CO2 is temperature dependent. As temperature increases, the CO2 solubility decreases, and water and CO2 are allowed to separate from the amine solution. Once the water is removed, the solution is cooled to increase the CO2 solubility to allow the amine to completely dissolve and increase solubility.

[0127] Using a switchable solubility system as described above allows the draw solution to be regenerated while also utilizing the power of a heat pump that can provide both heating and cooling. As the solubility of the draw solution decreases, the water can be separated and sent off and mixed with the spent dilute solution from the RED / PRO cell. This allows the draw solution used in the forward osmosis system to be concentrated and regenerated by removing the water, thereby regenerating the spent concentrated solution from the RED / PRO cell.

[0128] When the salinity gradient engine system is operated near an industrial facility such as a power plant, it can provide a variety of benefits. The power plant generates excess waste heat and releases CO2 as an undesirable byproduct in the process. This industrial CO2 can be used in the forward osmosis system disclosed herein to control the solubility of the draw solution.

[0129] exist Fig.19 , the regeneration system circulates spent dilute solution 1940 from the RED or PRO cell 1910 in a closed loop through a diluent tank 1946 where water 1970 is added to make a regenerated dilute solution 1945 that is directed back to the RED or PRO cell 1910. Spent concentrate solution 1930 is also circulated from the RED or PRO cell 1910 in a closed loop through a forward osmosis system 1980 to make a regenerated concentrate solution 1935 that is directed back to the RED or PRO cell 1910. A switchable solubility system 1920 is also depicted. A draw solution 1955 is circulated through the forward osmosis system 1980 and used to operate the system, producing a spent draw solution 1950. In the recovery unit 1960, heat 1992 is added to the spent draw solution 1950 and CO2 is released, causing the solubility of the spent draw solution to decrease, and the water 1970 can be separated and decanted. When CO2 is added back into the system in the generator 1965, the solubility of the solutes in the draw solution increases (e.g., salts can be redissolved in the solution; it should be concentrated so that the osmotic pressure is high). To increase the solubility of CO2, the solution is cooled (heat energy is removed from the system 1991).

[0130] It should be understood that the various aspects disclosed herein may be combined in combinations different from those specifically presented in the specification and drawings. It should also be understood that, according to examples, some actions or events of any process or method described herein may be implemented in a different order, may be added, combined, or omitted altogether (e.g., all described actions or events may not be necessary to implement the technology). In addition, although for clarity, some aspects of the present disclosure are described as being implemented by a single module or unit, it should be understood that the technology of the present disclosure may be implemented by a combination of units or modules associated with, for example, RED cells, PRO systems, CAP systems, hydrogen generation subsystems, salt precipitation subsystems, evaporation subsystems, etc.

[0131] In one or more instances, the described techniques may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored as one or more instructions or codes on a computer-readable medium and executed by a hardware-based processing unit. A computer-readable medium may include a non-transitory computer-readable medium, which corresponds to a tangible medium such as a data storage medium (e.g., RAM, ROM, EEPROM, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and can be accessed by a computer).

[0132] Instructions may be executed 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 or discrete logic circuits. Therefore, as used herein, the term "processor" may refer to any of the foregoing structures or any other physical structure suitable for implementing the described techniques. Moreover, these techniques may be fully implemented in one or more circuits or logic elements.

[0133] Figure 7 Exemplary hardware that can be used to contain or implement program instructions is shown. Bus 710 serves as the main information path (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 calculations and logical operations required to execute the program. Figure 7 The CPU 705 in combination with one or more other elements disclosed in is an example of a processor (as such term is used in this disclosure). Read-only memory (ROM) and random access memory (RAM) constitute examples of non-transitory computer-readable storage media 720, storage devices, or data storage (as such term is used in this disclosure).

[0134] Program instructions, software, or interactive modules for providing an interface and implementing any query or analysis associated with one or more data sets may be stored in the storage device 720. Optionally, the program instructions may be stored on a tangible, non-transitory computer-readable medium, such as an optical disk, a digital disk, a flash memory, a memory card, a universal serial bus (USB) drive, an optical storage medium, and / or other recording medium.

[0135] An optional display interface 730 may allow information from bus 710 to be displayed in an audio, visual, graphical or alphanumeric format on a display 735. Communications with external devices may occur using various communications ports 740. Communications ports 740 may connect to a communications network, such as the Internet or an intranet.

[0136] The hardware may further include an interface 745 that allows data to be received from input devices such as a keyboard 750 or other input devices 755 such as a touch screen, remote control, pointing device, video input device, and / or audio input device.

[0137] It will be appreciated that various of the above disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications or combinations of systems and applications. Moreover, a variety of presently unforeseen or unanticipated substitutions, modifications, variations or improvements therein may subsequently be made by those skilled in the art, which are also intended to be covered by the following claims.

Claims

1. A method for generating electricity from thermal energy, comprising: separating the first salt solution from the second salt solution by a selectively permeable membrane; transferring heat energy to the first salt solution and / or the second salt solution via a heat pump; as well as The first saline solution is mixed with the second saline solution in a controlled manner to capture at least some salinity gradient energy as electricity as the salinity difference between the first saline solution and the second saline solution decreases.

2. The method of claim 1, further comprising 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.

3. The method of any of the preceding claims, further comprising applying a pressure delayed osmosis (PRO) system, a capacitive mixing (CAP) system, or both a PRO and CAP system to generate additional electricity.

4. The method of any one of the preceding claims, wherein the method comprises generating a third salt solution by membrane distillation, and further comprises mixing the third salt solution into the first salt solution and / or the second salt solution.

5. The method of any preceding claim, wherein the selectively permeable membrane comprises graphene, graphene oxide, or reduced graphene oxide.

6. The method of claim 5, further comprising applying a stretching force to the selectively permeable membrane to adjust the permeability of the membrane.

7. The method of claim 5, wherein the selectively permeable membrane is a single-layer sheet, a multi-layer sheet, or a cylinder containing graphene, graphene oxide, and / or reduced graphene oxide.

8. The method of claim 5 or 7, wherein the selectively permeable membrane contains nanopores in the graphene, graphene oxide, and / or reduced graphene oxide.

9. The method of claim 1, further comprising applying acoustic vibrations to the first saline solution or the second saline solution to cause the first saline solution or the second saline solution to become more homogenous.

10. The method of claim 9, wherein the acoustic vibration is applied adjacent to the selectively permeable membrane.

11. The method of claim 1 , further comprising coordinating, by a processor, heat transfer from the one or more heat sources to the first saline solution and / or the second saline solution based on one or more measurements of the one or more heat sources or the state of the first saline solution and / or the second saline solution.

12. The method of claim 11, wherein the heat source comprises one or more of geothermal heat, industrial waste heat, or solar heat.

13. The method of claim 1, further comprising capturing the salinity gradient energy using reverse electrodialysis.

14. The method of claim 1 further comprising capturing the salinity gradient energy using pressure-retarded osmosis to drive a generator.

15. The method of any of the preceding claims, wherein the first saline solution and the second saline solution are each circulated in a closed system.

16. The method of any one of the preceding claims, wherein transferring thermal energy from the first salt solution to the second salt solution causes the first salt solution to precipitate salt.

17. The method of any one of the preceding claims, further comprising introducing the precipitated salt into the second saline solution, causing an increase in the salinity difference between the first saline solution and the second saline solution.

18. A method as claimed in any preceding claim, further comprising using a portion of the generated electricity to produce hydrogen by electrolysis.

19. The method of any of the preceding claims, wherein transferring thermal energy from the first saline solution to the second saline solution comprises transferring thermal energy from the first saline solution that is cooler than the second saline solution.

20. The method of any of the preceding claims, wherein a thermal optimization system is configured to coordinate heat transfer from the one or more heat sources to the first and / or second saline solutions based on one or more measurements of the one or more heat sources or a state of the first and / or second saline solutions.

21. The method of any preceding claim, wherein the heat source comprises one or more of geothermal heat, industrial waste heat, or solar heat.

22. The method of claim 2, wherein the regeneration process comprises applying a salt decomposition process, the salt decomposition process comprising: i) providing a spent dilute solution formed from the first salt solution, wherein the spent dilute solution contains salt; ii) heating the spent dilute solution to decompose the salts to produce gaseous products; and iii) transferring the gaseous product to an absorber; and iv) solidifying the gaseous product to reform into a salt precipitate in the spent concentrated solution in the absorber; The salt precipitate is dissolved in the spent concentrated solution, thereby regenerating the second salt solution.

23. The method of claim 22, wherein the spent dilute solution has a higher salt content than the first salt solution; and wherein the salt content of the spent dilute solution is reduced by transferring the gaseous product to the absorber to regenerate the first salt solution.

24. The method of claim 2, wherein the regeneration process comprises applying an electrodialysis process, the electrodialysis process comprising: i) providing a spent dilute solution formed from the first salt solution, wherein the spent dilute solution contains salt; ii) providing a spent concentrated solution formed from the second salt solution; iii) supplying power to separate the salt into ions and to move the ions from the spent dilute solution to the spent concentrated solution; The salt content of the spent dilute solution is reduced to regenerate the first salt solution, while the salt content of the spent concentrated solution is increased to regenerate the second salt solution.

25. The method of claim 2, wherein the regeneration process comprises applying an evaporation process, the evaporation process comprising: i) providing a spent concentrated solution formed from the second salt solution; ii) heating the waste concentrated solution to generate water vapor; as well as iii) transferring said water vapor to mix with the spent dilute solution; and The salt content of the spent dilute solution is reduced to regenerate the first salt solution, while the salt content of the spent concentrated solution is increased to regenerate the second salt solution.

26. The method of claim 2, wherein the regeneration process comprises applying a membrane distillation process, the membrane distillation process comprising: i) providing a membrane distillation vessel comprising a hydrophobic membrane having a spent concentrated solution on one side of the membrane and a spent dilute solution on an opposite side of the membrane; as well as ii) warming the waste concentrated solution to generate water vapor; The water vapor permeates the hydrophobic membrane to mix with the waste dilute solution to regenerate the first salt solution, and the salt content of the waste concentrated solution is increased to regenerate the second salt solution.

27. The method of claim 2, wherein the regeneration process comprises applying a forward osmosis process, the forward osmosis process comprising: circulating the spent concentrate solution and the draw solution through a forward osmosis system to regenerate the second brine and produce a spent draw solution; The spent draw solution is circulated through a switchable solubility system to regenerate the draw solution and produce water.

28. The method of claim 27, wherein the forward osmosis process further comprises: The water is mixed with the spent dilute solution to regenerate the first brine.

29. A salt gradient heat engine system for generating electrical power, comprising: a first saline solution; a second saline solution, wherein the salinity of the second saline solution is different from the salinity of the first saline solution; a heat pump configured to transfer thermal energy to the first salt solution and / or the second salt solution; as well as a selectively permeable membrane that separates the first salt solution from the second salt solution, the selectively permeable membrane being configured to control mixing of the first salt solution and the second salt solution, the selectively permeable membrane being further configured to capture at least some salinity gradient energy as electricity when the first salt solution and the second salt solution mix.

30. The system of claim 29, further comprising a regeneration system selected from the group consisting of a salt precipitation system, a membrane distillation system, an evaporation system, a forward osmosis system, a salt decomposition system, an electrodialysis system, and any combination thereof.

31. The system of claim 29 or 30, wherein the heat pump is a vapor compression cycle, a thermoelectric refrigerator, a chemical absorption refrigerator, or other device for simultaneous heating and cooling.

32. The system of any one of claims 29-31, wherein the selectively permeable membrane comprises graphene, graphene oxide, or reduced graphene oxide.

33. The system of claim 32, wherein the selectively permeable membrane is stretchable.

34. The system of claim 30, wherein the regeneration system comprises the salt precipitation system, the salt precipitation system being configured to: receiving waste dilute solution; removing heat energy from the spent dilute solution by the heat pump, causing the spent dilute solution to precipitate salt and regenerate a dilute salt solution; After regenerating the dilute salt solution, circulating the dilute salt solution; introducing the precipitated salt into the spent concentrated solution; as well as The salt causing the precipitation is dissolved in the spent concentrated solution and a concentrated salt solution is regenerated.

35. The system of claim 34, wherein the regeneration system is further configured to transfer at least some of the heat energy removed from the dilute saline solution back to the dilute saline solution after causing precipitation of dissolved salt in the dilute saline solution.

36. The system of claim 34, wherein the regeneration system is further configured to transfer at least some of the heat energy removed from the spent dilute solution to the spent concentrate solution, causing the precipitated salt to dissolve in the spent concentrate solution.

37. The system of claim 34, wherein the heat source is configured to transfer thermal energy to the spent concentrate solution, causing the precipitated salt to dissolve in the spent concentrate solution.

38. The system of claim 30, wherein the concentrated salt solution includes a substance having a non-linear temperature-dependent solubility.

39. The system of claim 30, wherein the regeneration system comprises the salt precipitation system, and The salt precipitation system comprises: a salt precipitator configured to receive the spent dilute solution and precipitate salt from the spent dilute solution to regenerate a dilute salt solution; a concentrate tank configured to receive the spent concentrated solution and to receive salt generated by the salt precipitator to regenerate a concentrated salt solution; as well as One or more heat exchangers.

40. The system of claim 32, further comprising a dilution tank configured to receive the dilute salt solution from the salt precipitator.

41. The system of claim 32, further comprising a heat source system configured to supply thermal energy to the concentrate tank.

42. The system of claim 30, wherein the regeneration system comprises the membrane distillation system, and Wherein the membrane distillation system comprises: a membrane distillation vessel comprising a hydrophobic membrane; as well as a heat pump configured to warm the container and cool one side of the hydrophobic membrane, The membrane distillation system is configured to generate a salt gradient at the hydrophobic membrane after warming and produce an ultra-dilute solution and a regenerated concentrated salt solution.

43. The system of claim 42, further comprising: a concentrate tank configured to receive the spent concentrate solution and connected to the membrane distillation vessel; a diluate tank configured to receive the spent dilute solution and connected to the membrane distillation vessel; wherein the concentrate tank is configured to receive the concentrated solution after regeneration in the membrane distillation vessel, and the diluent tank is configured to receive the ultra-dilute solution from the membrane distillation vessel.

44. The system of claim 42, wherein the hydrophobic membrane comprises polytetrafluoroethylene, polypropylene, or polyvinylidene fluoride and is configured in a sandwich unit stack configuration.

45. The system of claim 30, wherein the regeneration system comprises the salt decomposition system, The salt decomposition system comprises: a container configured to receive a spent dilute solution, wherein the spent dilute solution contains a salt, a heat pump configured to warm the container and generate a gaseous product containing a salt in the container, and An absorber is configured to receive the spent concentrated solution and the gaseous product, wherein the salt in the gaseous product is absorbed by the spent concentrated solution to regenerate a concentrated salt solution.

46. ​​The system of claim 30, wherein the regeneration system comprises the evaporation system, The evaporation system comprises: an evaporator configured to receive the spent concentrated solution and generate water vapor to regenerate the concentrated salt solution; a heat pump configured to provide thermal energy to the evaporator; A condenser is configured to receive the spent dilute solution and to receive the water vapor generated by the evaporator, wherein the water vapor condenses and mixes with the spent dilute solution to be regenerated into a dilute salt solution.

47. The system of claim 30, wherein the regeneration system comprises the electrodialysis system, wherein the electrodialysis system is configured to receive a spent dilute solution and a spent concentrate solution; and Power is supplied to the electrodialysis system, causing ions to move from the spent dilute solution to the spent concentrated solution to regenerate the dilute salt solution and the concentrated salt solution.

48. The system of claim 47, wherein the regeneration system further comprises a salt precipitation system, wherein the salt precipitation system comprises: a salt precipitator configured to receive a spent dilute solution and precipitate salt from the spent dilute solution and then supply the spent dilute solution to the electrodialysis system; a concentrate tank configured to receive the spent concentrate solution and to receive salt generated by the salt precipitator; Wherein the concentrate tank is configured to receive a concentrated solution after regeneration by electrodialysis, and the diluent tank is configured to receive the dilute salt solution from the electrodialysis system.

49. The system of claim 30, wherein the regeneration system comprises the salt precipitation system and the membrane distillation system.

50. The system of claim 30, wherein the regeneration system comprises electrodialysis and the salt precipitation system.

51. The system of claim 30, wherein the regeneration system comprises the forward osmosis system configured to receive the spent concentrate solution and to regenerate a concentrate brine using a switchable solubility system.

52. The system of claim 51, wherein the regeneration system further comprises a diluate tank configured to receive spent dilute solution and to receive water from the switchable solubility system, wherein the water is mixed with the spent dilute solution to regenerate the dilute salt solution.

53. The system of claim 51 or 52, wherein the switchable solubility system comprises: a draw solution, the draw solution circulating through the forward osmosis system and producing a spent draw solution; a recovery unit configured to receive the spent draw solution and add heat, wherein CO2 is released and water is produced; as well as A generator is configured to receive the solution from the reclaimer and add CO2 to regenerate the draw solution.

54. The system of any one of claims 30-53, wherein the first membrane and the second membrane comprise ion exchange membranes.

55. The system of any one of claims 30-54, further comprising: The second unit comprises: a third membrane configured to be selectively permeable to cations; a fourth membrane configured to be selectively permeable to anions, the fourth membrane being spaced apart from the third membrane; and A second concentrated salt solution is 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, wherein: The concentrated salt solution includes an endothermic solution; The second concentrated salt solution comprises an exothermic solution; and The heat pump is configured to transfer heat between the concentrated saline solution and the second concentrated saline solution.

56. A system as described in any of claims 30-55, wherein the thermal optimization system includes a control system, which is configured to coordinate heat transfer between the one or more heat sources and the reverse electrodialysis system through a processor based on one or more measurement results of the state of the one or more heat sources or the reverse electrodialysis system.

57. The system of claim 37 or 41, wherein the heat source comprises one or more of geothermal heat, industrial waste heat, or solar heat.

58. The system of any of claims 30-57, wherein the heat pump is a vapor compression cycle, a thermoelectric refrigerator, a chemical absorption refrigerator, or other devices known in the art for simultaneous heating and cooling.

59. The system of any of claims 30-55, further comprising a thermal optimization subsystem configured to coordinate heat transfer from the one or more heat sources to the first saline solution and / or the second saline solution based on one or more measurements of the one or more heat sources or the state of the first saline solution and / or the second saline solution.

60. The system of claim 59, wherein the heat source comprises one or more of geothermal heat, industrial waste heat, or solar heat.

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