Salt difference cycle power generation system and method based on phase change material and solar thermal

Abstract

The present disclosure discloses a salinity difference cycle power generation system based on phase change materials and solar thermal energy, comprising: a solution supply device, a power generation device and an electric energy output device, wherein the solution supply device provides high and low concentration seawater as a salinity difference source for the power generation device; the power generation device realizes a day and night cycle of salinity difference power generation effect; the electric energy output device stores the electric energy, a portion of which is used internally to provide pumping work, and a portion of which is used as system output. The present disclosure also provides a salinity difference cycle power generation method based on phase change materials and solar thermal energy. The present disclosure utilizes the photothermal effect to increase the solution temperature, and at the same time utilizes phase change materials to store heat, and releases heat in the absence of solar radiation to maintain a high temperature environment, thereby maintaining the directional migration rate of cations. Heat storage and heat release can be repeated, thereby achieving low-cost, continuous electric energy output gain.

Description

Technical Field

[0001] The present disclosure belongs to the field of power generation technology, and in particular relates to a salinity cycle power generation system and method based on phase change materials and solar thermal energy. Background Art

[0002] Solar energy is a clean, inexpensive, renewable energy source with advantages such as wide distribution, high energy density, and large storage capacity. Its utilization methods mainly include: photothermal conversion, photovoltaic conversion, and photochemical conversion. Near the ocean, solar thermal conversion is widely used in fields such as seawater desalination. The chemical potential difference between seawater and freshwater contains enormous energy. The method of using the intersection of seawater and freshwater to generate electricity is called "blue energy." When seawater of different concentrations is separated by an ion-selective membrane, ions flow in a directional manner, and the electrodes and external circuit form a closed loop, and the salinity difference can be converted into electrical energy. Phase change materials are widely used in heat storage, energy conservation, temperature control, and other fields due to their high latent heat, good temperature uniformity, and reversible phase change.

[0003] In recent years, salinity difference power generation technology has developed rapidly, focusing mainly on the fields of ion-selective membrane materials and structural design, power generation device structural design, etc., to improve the efficiency and power density of salinity difference power generation, and a power generation method that uses solar energy to enhance salinity difference power generation has been proposed. However, regardless of the one-dimensional, two-dimensional or three-dimensional structure, although various ion-selective membranes can improve the power density of the electroosmotic power generation system, they also greatly increase the system cost and have problems such as service life, which is not conducive to engineering application. At the same time, various power generation devices and systems that use solar energy to enhance salinity difference power generation will not be able to continuously enhance efficiency under conditions such as darkness or rainy days due to the intermittent and unstable sunlight. Therefore, stable, efficient and continuous electroosmotic power generation devices and power generation methods are needed.

[0004] The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Summary of the Invention

[0005] In response to the deficiencies in the prior art, the purpose of the present disclosure is to provide a salt difference cycle power generation system and method based on phase change materials and solar thermal energy. By utilizing the photothermal effect of solar energy and the heat storage and heat release characteristics of phase change materials, continuous electroosmosis power generation efficiency enhancement and day and night cycle power generation performance can be achieved, thereby improving the power generation power density of the entire system.

[0006] To achieve the above objectives, the present disclosure provides the following technical solutions:

[0007] A salinity difference cycle power generation system based on phase change material and solar thermal energy, characterized in that the system comprises:

[0008] A power generation device includes a first chamber storing a high-concentration solution and a second chamber storing a low-concentration solution, wherein a nanoporous ion-selective membrane is provided between the first chamber and the second chamber. Cations in the first chamber are directionally migrated to the second chamber through the nanoporous ion-selective membrane under the action of the solution concentration difference, forming an ion flux; at the same time, a first electrode is provided in the first chamber, and a second electrode is provided in the second chamber. Electrons on the first electrode flow to the second electrode through an external circuit to form an electric current.

[0009] The system also includes a phase change material chamber, which is located outside the first chamber and the second chamber. Phase change material is arranged in the phase change material chamber. During the phase change process, the phase change material repeatedly stores and releases heat to provide thermal energy to the first chamber and the second chamber to maintain the directional migration rate of cations and realize cyclic power generation.

[0010] Preferably, a first light-to-heat conversion structure is provided in the first chamber, and a second light-to-heat conversion structure is provided in the second chamber. The first light-to-heat conversion structure and the second light-to-heat conversion structure are used to convert solar energy into thermal energy.

[0011] Preferably, a first heat-conducting porous structure is further provided in the first chamber, and a second heat-conducting porous structure is further provided in the second chamber. The first heat-conducting porous structure and the second heat-conducting porous structure are used to conduct the heat energy to the first chamber and the second chamber respectively to increase the absolute temperature of the solution.

[0012] Preferably, a high light-transmittance heat-insulating layer is provided on the phase-change material chamber.

[0013] Preferably, the phase change material is a composite phase change material.

[0014] Preferably, the system further comprises a solution supply device, wherein the solution supply device comprises a first solution storage chamber for supplying a high-concentration solution to the first chamber, and the solution supply device further comprises a second solution storage chamber for supplying a low-concentration solution to the second chamber.

[0015] Preferably, a concentrator is provided on the first solution storage chamber.

[0016] Preferably, the first electrode and the second electrode are both silver-silver chloride electrodes.

[0017] Preferably, the system further comprises an electric energy output device, and the electric energy output device comprises a battery and an electric energy transmission component.

[0018] The present disclosure also provides a method for generating electricity through a salinity cycle based on phase change materials and solar thermal energy, comprising the following steps:

[0019] S1: Cations in the first chamber migrate toward the second chamber through the nanoporous ion selective membrane under the action of the solution concentration difference between the first chamber and the second chamber to form an ion flux, and electrons flow from the first electrode to the second electrode through the external circuit to form an electric current to generate external power;

[0020] S2: The first photothermal conversion structure and the second photothermal conversion structure convert solar energy into thermal energy, and the first thermal conductive porous structure and the second thermal conductive porous structure transfer the thermal energy to the first chamber and the second chamber, respectively, to increase the absolute temperature of the solution, thereby increasing the directional migration rate of the cations;

[0021] S3: The phase change material in the phase change material chamber stores heat through phase change under the action of solar energy, and releases heat through phase change again when solar energy is insufficient to maintain the directional migration rate of cations.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. This invention utilizes solar thermal energy, thermal storage of composite phase change materials, and the ion-selective properties of nanoporous ion-selective membranes to achieve efficient, continuous, day-and-night cycled electrical energy output.

[0024] 2. This disclosure achieves low-cost, continuous, day-and-night cycle power output gain by combining solar thermal utilization with thermal storage utilization of composite phase change materials;

[0025] 3. The present invention can stably and continuously output high-power-density electric energy without changing the nanoporous ion-selective membrane and increasing a lot of costs, has significant social and economic benefits, and can be widely used in the field of salinity difference power generation. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic structural diagram of a salinity difference cycle power generation system based on phase change materials and solar thermal energy provided by an embodiment of the present disclosure;

[0027] Figure 2 yes Figure 1 A schematic diagram of the structure of the power generation device in the system shown;

[0028] Figure 3 yes Figure 1 Schematic diagram of the effect of the experiment to verify the thermal insulation effect of the phase change material in the system shown;

[0029] Figure 4 yes Figure 1 Schematic diagram comparing the short-circuit currents measured in the system with and without phase change material;

[0030] The symbols in the accompanying drawings are as follows:

[0031] 1. First solution storage chamber; 2. Concentrator; 3. Second solution storage chamber; 4. High-transmittance thermal insulation layer; 5. First chamber; 6. Nanoporous ion-selective membrane; 7. Second chamber; 8. Phase change material chamber; 9-1. First photothermal conversion structure; 9-2. Second photothermal conversion structure; 10-1. First thermally conductive porous structure; 10-2. Second thermally conductive porous structure; 11. Second electrode; 12. External circuit; 13. First electrode; 14. Second inlet valve; 15. First inlet valve; 16. Outlet valve; 17. Main inlet valve; 18. Main outlet valve; 19. First inlet pump; 20. Second inlet pump; 21. Outlet pump; 22. Main outlet pump; 23. Main inlet pump. DETAILED DESCRIPTION

[0032] The following will refer to the attached Figures 1 to 4 Specific embodiments of the present disclosure are described in detail. Although specific embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments described herein. Instead, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0033] It should be noted that certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that technicians may use different nouns to refer to the same component. This specification and claims do not use the difference in nouns as a way to distinguish components, but use the difference in the functions of the components as the criterion for distinction. As mentioned throughout the specification and claims, "including" or "comprising" is an open term, so it should be interpreted as "including but not limited to". The subsequent description of the specification is a preferred embodiment of the present disclosure, but the description is based on the general principles of the specification and is not used to limit the scope of the present disclosure. The scope of protection of the present disclosure shall be as defined by the attached claims.

[0034] To facilitate understanding of the embodiments of the present disclosure, further explanation will be given below using specific embodiments as examples in conjunction with the accompanying drawings, and the accompanying drawings do not constitute a limitation on the embodiments of the present disclosure.

[0035] In one embodiment, if Figure 1 As shown, the present disclosure provides a salinity difference cycle power generation system based on phase change materials and solar thermal energy, characterized in that the system includes:

[0036] A power generation device 1 includes a first chamber 5 storing a high-concentration solution and a second chamber 7 storing a low-concentration solution. A nanoporous ion-selective membrane 6 is provided between the first chamber 5 and the second chamber 7. Cations in the first chamber 5 are directed to migrate to the second chamber 7 through the nanoporous ion-selective membrane 6 under the action of the solution concentration difference, forming an ion flux. At the same time, a first electrode 13 is provided in the first chamber 5, and a second electrode 11 is provided in the second chamber 7. Electrons on the first electrode 13 flow to the second electrode 11 through an external circuit 12 to form an electric current.

[0037] The system also includes a phase change material chamber 8, which is located outside the first chamber 5 and the second chamber 7. A phase change material is arranged in the phase change material chamber 8. During the phase change process, the phase change material repeatedly stores and releases heat to provide thermal energy to the first chamber 5 and the second chamber 7 to maintain the directional migration rate of cations and realize cyclic power generation.

[0038] In this embodiment, when sunlight irradiates the first chamber 5, the second chamber 7, and the phase change material chamber 8, the temperature of the solution in the first chamber 5 and the second chamber 7 rises rapidly until equilibrium is reached. Simultaneously, the phase change material in the phase change material chamber 8 absorbs solar radiation, gradually increasing in temperature until it melts, thereby absorbing solar energy and storing heat. Due to the concentration difference between the solutions in the first chamber 5 and the second chamber 7, cations in the first chamber 5 migrate directionally through the nanoporous ion selective membrane 6 to the second chamber 7, forming an ion flux; electrons flow from the first electrode 13 to the second electrode 11, forming an electric current. Furthermore, due to the sunlight irradiation, the temperature of the solution in the first chamber 5 and the second chamber 7 rises, thereby increasing the activity of the cations, increasing the surface charge density of the nanoporous ion selective membrane 6, and improving the selectivity of the cations, thereby increasing the ion flux and the power generation power density. When solar radiation is insufficient or disappears, the temperature of the solution in the first and second chambers 5 and 7 begins to drop, but the temperature of the phase change material in the phase change material chamber 8 remains unchanged when it reaches the freezing point. When the solution temperature drops below the temperature of the phase change material, the phase change material begins to release heat as a heat source, and the heat is transferred from the phase change material into the first and second chambers 5 and 7 through the outer walls of the first and second chambers 5 and 7 by heat conduction, thereby reducing the rate of temperature drop of the solution, maintaining the high temperature environment of the solution in the chambers, allowing the directional migration rate of cations to be maintained at the level of solar radiation, thereby maintaining the power generation gain effect. When the stored energy in the phase change material is released, it returns to its original state through phase change, and when the sun shines, it changes phase again to store solar energy. The phase change material repeatedly undergoes phase change to store and release heat according to the solar radiation conditions, thereby achieving a day-night cycle power generation effect. This embodiment combines the solar thermal utilization method with the heat storage utilization method of the phase change material to achieve low-cost, continuous, day-night cycle power output gain.

[0039] In another embodiment, Figure 2 As shown, a first light-to-heat conversion structure 9-1 is provided in the first chamber 5, and a second light-to-heat conversion structure 9-2 is provided in the second chamber 7. The first light-to-heat conversion structure 9-1 and the second light-to-heat conversion structure 9-2 are used to convert solar energy into thermal energy.

[0040] In this embodiment, the surfaces of the first and second light-to-heat conversion structures 9-1, 9-2 facing sunlight are provided with a selective absorption coating, and this coating has high absorptivity and low emissivity within the solar spectrum. Specifically, the first and second light-to-heat conversion structures 9-1, 9-2 can be coated with a copper oxide coating or a metal-ceramic composite coating (including Cr-Cr2O3, Co-Al2O3, Ni-Al2O3, etc.). Preferably, a copper sheet coated with a copper oxide coating is used, and a light-absorbing coating is provided on the upper surface of the copper sheet. The light-absorbing coating absorbs solar radiation and converts it into heat energy through the copper sheet.

[0041] In another embodiment, Figure 2 As shown, a first heat-conducting porous structure 10-1 is further provided in the first chamber 5, and a second heat-conducting porous structure 10-2 is further provided in the second chamber 7. The first heat-conducting porous structure 10-1 and the second heat-conducting porous structure 10-2 are used to conduct the heat energy to the first chamber 5 and the second chamber 7 respectively to increase the absolute temperature of the solution.

[0042] In this embodiment, the first thermally conductive porous structure 10-1 and the second thermally conductive porous structure 10-2 are both made of materials with high thermal conductivity and good electrical insulation, preferably silicon carbide materials, which are respectively bonded to the lower surfaces of the first photothermal conversion structure 9-1 and the second photothermal conversion structure 9-2 by thermally conductive adhesive, and can quickly conduct the heat energy converted by the photothermal conversion structure to the first chamber 5 and the second chamber 7, so that the absolute temperature of the solution in the two chambers rises at the same time, thereby increasing the activity of cations in the solution and the charge density on the surface of the nanoporous ion selective membrane, thereby increasing the migration rate of cations from the first chamber 5 to the second chamber 7, thereby improving the power generation power density.

[0043] In another embodiment, a high light-transmittance heat-insulating layer 4 is provided on the first chamber 5 , the second chamber 7 and the phase-change material chamber 8 .

[0044] In this embodiment, on the one hand, the high-transmittance thermal insulation layer 4 has a high transmittance, which can allow solar radiation to enter the first chamber 5, the second chamber 7 and the phase change material chamber 8 as much as possible to obtain a warming effect; on the other hand, it has good thermal insulation performance, which can prevent the energy in the first chamber 5, the second chamber 7 and the phase change material chamber 8 from being lost through convection, radiation and the like as much as possible.

[0045] In another embodiment, the phase change material is a composite phase change material.

[0046] In this embodiment, the composite phase change material comprises paraffin wax as the phase change material, a metal foam as the support framework, a porosity of no less than 90%, and graphene powder or its derivatives as additives, wherein the mass fraction of the additives is 0.1%-5%. In comparison, pure phase change materials cannot utilize the full range of solar radiation, resulting in extremely low photothermal conversion efficiency. However, composite phase change materials can utilize the full range of solar radiation, resulting in high photothermal conversion efficiency. Therefore, by using the composite phase change material, the temperature uniformity and heat storage capacity of the solution in the first chamber 5 and the second chamber 7 can be enhanced while achieving a photothermal effect, thereby improving the efficiency of converting solar radiation into thermal energy.

[0047] In addition, it should be noted that the phase change temperature of the composite phase change material is slightly higher than the equilibrium temperature reached by the solution in the first chamber 5 and the second chamber 7 after being exposed to sunlight, thereby ensuring that the heat released during the phase change of the phase change material can maintain the solution at the highest possible temperature.

[0048] In another embodiment, the system further includes a solution supply device II, which includes a first solution storage chamber 1 for providing a high-concentration solution to the first chamber 5 , and a second solution storage chamber 3 for providing a low-concentration solution to the second chamber 7 .

[0049] In this embodiment, the upper surface of the first solution storage chamber 1 is inclined, and a concentrator 2 is mounted on it. When solar radiation is concentrated by the concentrator 2 and irradiates the first solution storage chamber 1, the seawater stored in the storage chamber begins to evaporate, generating steam. The steam rises and hits the upper surface of the first solution storage chamber 1, where it condenses. The condensed water flows along the upper surface of the first solution storage chamber 1 into the second solution storage chamber 3, creating a concentration difference between the solutions in the two storage chambers. Furthermore, an inclined baffle is positioned between the first solution storage chamber 1 and the second solution storage chamber 3 to prevent the condensed water from dripping and flowing back into the first solution storage chamber 1.

[0050] In addition, the first solution storage chamber 1 is connected to the first chamber 5 via the first inlet valve 15, the first inlet pump 19 and the pipeline, and then connected to the main outlet valve 18 and the main outlet pump 22 via the outlet valve 16, the outlet pump 21 and the pipeline; the second solution storage chamber 3 is connected to the second chamber 7 via the second inlet valve 14, the second inlet pump 20 and the pipeline, and then connected to the main outlet valve 18 and the main outlet pump 22 via the outlet valve 16, the outlet pump 21 and the pipeline. Through the combined action of the above-mentioned valves, water pumps and pipelines, the seawater stored in the first solution storage chamber 1 and the fresh water stored in the second solution storage chamber 3 can be respectively transported to the first chamber 5 and the second chamber 7 for power generation.

[0051] In another embodiment, the first electrode 13 and the second electrode 11 are both silver-silver chloride electrodes.

[0052] In this embodiment, the silver-silver chloride electrode is selected because the silver-silver chloride electrode has stable electrochemical properties, is easy to prepare, and has low cost.

[0053] The silver-silver chloride electrode is made by electroplating. The specific preparation method is: placing a smooth silver wire in a 1M KCl solution, with the silver wire as the anode and the inert platinum electrode as the cathode, and passing a constant current of 1-4 mA through the circuit for 0.5-4 hours.

[0054] In another embodiment, the system further comprises an electric energy output device III, and the electric energy output device III comprises a battery and an electric energy transmission component.

[0055] In this embodiment, a battery is connected to the first and second chambers 5, 7 via an external circuit 12. The electrical energy generated by the concentration difference between the first and second chambers 5, 7 is transferred to the battery via an output circuit for storage. A portion of the electrical energy stored in the battery is used to provide intermittent pumping power to the main inlet pump 23, the main outlet pump 22, the first inlet pump 19, the second inlet pump 20, and the outlet pump 21. The remaining energy is used as system output to provide external power.

[0056] Figure 3 Schematic diagram of the thermal insulation effect of the first chamber and the second chamber with and without phase change material. Figure 3 As shown, under illumination conditions, the maximum temperature of the first chamber 5 and the second chamber 7 after the phase change material is set is higher than that without the phase change material. When the illumination is removed, the rate of decrease of the solution temperature in the first chamber 5 and the second chamber 7 with the phase change material is significantly lower than that without the phase change material.

[0057] Figure 4 This is a schematic diagram comparing the short-circuit current between the first chamber and the second chamber measured with and without phase change materials. Figure 4As shown, under illumination conditions, the maximum value of the short-circuit current between the first chamber with the phase change material and the second chamber is greater than that without the phase change material; when the illumination is removed, the decreasing rate of the short-circuit current between the first chamber with the phase change material and the second chamber is lower than that without the phase change material.

[0058] Combine Figure 3 The temperature curve and Figure 4 The current curves in Figure 2 demonstrate that increasing the solution temperature can increase the power density. Furthermore, it demonstrates that the phase change material maintains the power gain by maintaining the solution temperature, enabling this system to achieve day-night cycle power generation.

[0059] The above specific embodiments are used to illustrate the present disclosure, which is only used to help understand the present disclosure and is not intended to limit the present disclosure. Any local modification or replacement within the technical scope disclosed in the present disclosure by any person familiar with the technology should be included in the scope of the present disclosure.

Claims

1. A salt difference cycle power generation system based on phase change materials and solar thermal energy, characterized in that: The system comprises: A power generation device comprising a first chamber storing a high-concentration solution and a second chamber storing a low-concentration solution, wherein a nanoporous ion-selective membrane is disposed between the first chamber and the second chamber. Cations in the first chamber are directed to migrate to the second chamber through the nanoporous ion-selective membrane under the action of a solution concentration difference, thereby forming an ion flux. Simultaneously, a first electrode is disposed in the first chamber, and a second electrode is disposed in the second chamber. Electrons on the first electrode flow to the second electrode through an external circuit to form an electric current. The system further includes a phase change material chamber, the phase change material chamber being located outside the first chamber and the second chamber, the phase change material chamber being provided with a phase change material, and the phase change material repeatedly stores and releases heat during a phase change process, thereby providing thermal energy to the first chamber and the second chamber to maintain a directional migration rate of cations and realize cyclic power generation; The phase change material is a composite phase change material, comprising paraffin as the phase change material, a metal foam as the supporting skeleton, a porosity of not less than 90%, and graphene powder as an additive, the mass fraction of the additive being 0.1%-5%. The phase change temperature of the composite phase change material is slightly higher than the equilibrium temperature reached by the solutions in the first and second chambers after exposure to sunlight, ensuring that the heat released during the phase change of the phase change material can maintain the solution at the highest possible temperature. A first light-to-heat conversion structure is provided in the first chamber, and a second light-to-heat conversion structure is provided in the second chamber, wherein the first light-to-heat conversion structure and the second light-to-heat conversion structure are used to convert solar energy into thermal energy; A first heat-conducting porous structure is also provided in the first chamber, and a second heat-conducting porous structure is also provided in the second chamber. The first heat-conducting porous structure and the second heat-conducting porous structure are used to conduct the heat energy to the first chamber and the second chamber respectively to increase the absolute temperature of the solution.

2. The system according to claim 1, wherein: A high light-transmittance heat-insulating layer is provided on the first chamber, the second chamber and the phase-change material chamber.

3. The system according to claim 1, wherein: The system further includes a solution supply device including a first solution storage chamber for supplying a high-concentration solution to the first chamber, and a second solution storage chamber for supplying a low-concentration solution to the second chamber.

4. The system according to claim 3, characterized in that A concentrator is provided on the first solution storage chamber.

5. The system according to claim 1, wherein: The first electrode and the second electrode are both silver-silver chloride electrodes.

6. The system according to claim 1, wherein: The system further comprises an electric energy output device, which comprises a battery and an electric energy transmission component.

7. A power generation method of the salt difference cycle power generation system based on phase change material and solar thermal energy according to claim 1, comprising the following steps: S1: Cations in the first chamber migrate toward the second chamber through the nanoporous ion selective membrane under the action of the solution concentration difference between the first chamber and the second chamber to form an ion flux, and electrons flow from the first electrode to the second electrode through the external circuit to form an electric current to generate external power; S2: The first photothermal conversion structure and the second photothermal conversion structure convert solar energy into thermal energy, and the first thermal conductive porous structure and the second thermal conductive porous structure transfer the thermal energy to the first chamber and the second chamber, respectively, to increase the absolute temperature of the solution, thereby increasing the directional migration rate of the cations; S3: The phase change material in the phase change material chamber stores heat through phase change under the action of solar energy, and releases heat through phase change again when solar energy is insufficient to maintain the directional migration rate of cations.

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