Photothermal material and preparation method thereof and solar multi-effect flash evaporation seawater desalination system

Abstract

The present invention proposes a photothermal material and a preparation method thereof and a solar multi-effect flash evaporation seawater desalination system. The prepared photothermal material has a simple method and strong practicality, and can double the light absorption capacity of graphite; a high-temperature molten salt storage tank is arranged behind the first-stage flash tank and the second-stage flash tank to heat the steam generated in the flash tank, which is used to drive the steam turbine to generate electricity and then drive the system operation; the set photothermal heat accumulator absorbs solar heat during the day for the first-stage preheating of seawater. This process directly absorbs solar heat and stores it in the heat accumulator, reducing the heat transfer steps and effectively improving the solar energy utilization rate; the seawater is subjected to multi-stage preheating and multi-stage heating to gradually increase the temperature of the seawater and steam, thereby maximizing the heat utilization efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field related to solar seawater desalination, and in particular relates to a photothermal material and a preparation method thereof, and a solar multi-effect flash evaporation seawater desalination system. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Freshwater resources are scarce on islands, and freshwater production and consumption requires desalination equipment. Currently, most desalination equipment on islands relies on reverse osmosis technology, which is costly and complex. Furthermore, desalination systems that rely on seawater evaporation incur significant grid electricity costs, necessitating cost-saving measures such as self-generated heat or reliance on other processes. Inland, multi-effect flash evaporation desalination systems rely on processes that generate steam, harnessing the heat from the steam to desalinate seawater.

[0004] Desalination is the only water resource development technology unaffected by climate change, directly providing fresh water for human life and production. In the long run, desalination is the fundamental solution and direction for addressing water shortages on islands. However, islands farther offshore have a single, limited energy source, relying primarily on diesel generators. Even with power plants, the electricity supply is often insufficient.

[0005] The inventors discovered that energy storage devices will become a future energy hub during the energy transition. New, high-performance thermal storage materials are also a current research hotspot. The rational deployment of multi-stage phase change thermal storage technology can not only address the intermittent nature of solar energy but also effectively improve the energy efficiency of solar desalination systems. Since there are few processes capable of generating steam on islands, multi-effect flash desalination technology can only be used in conjunction with renewable energy systems. The key challenge is to rationally design the system structure to reduce dependence on diesel generation and improve energy efficiency.

[0006] Therefore, how to prepare high-performance photothermal materials for application in the field of seawater desalination, and set up a reasonable seawater desalination system, solve the problems of high operating costs, additional power input and low energy utilization of existing island freshwater systems, and maximize energy utilization efficiency, is a problem that needs to be solved at present. Summary of the Invention

[0007] To overcome the deficiencies of the above-mentioned prior art, the present invention provides a photothermal material, a preparation method thereof, and a solar multi-effect flash evaporation seawater desalination system. The method for preparing the photothermal material is simple and practical, and can double the light absorption capacity of graphite; the seawater desalination system can maximize the heat utilization efficiency.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a method for preparing a photothermal material, comprising:

[0010] The Max phase material is added to a mixed solution of concentrated hydrochloric acid and lithium fluoride, stirred, centrifuged, and the upper layer solution is collected to obtain a MXene colloidal solution;

[0011] Adding graphite and dopamine hydrochloride to a solution of anhydrous ethanol and deionized water, adjusting the pH value, stirring, and drying to obtain modified graphite;

[0012] The MXene colloidal solution and the modified graphite are mixed and dried at low temperature to obtain the modified graphite;

[0013] The modified graphite is mixed with a phase change material, a thickener and a nucleating agent to obtain a photothermal material.

[0014] In a second aspect, the present invention provides a photothermal material obtained by the above-mentioned method for preparing the photothermal material.

[0015] In a third aspect, the present invention provides a solar multi-effect flash evaporation seawater desalination system, comprising: a photothermal heat accumulator filled with the photothermal material obtained by the above preparation method;

[0016] It also includes: a shell and tube gas-liquid heat exchanger, a low-temperature molten salt storage tank, a first-level flash tank, a medium-temperature molten salt storage tank and a second-level flash tank connected to the photothermal heat accumulator in sequence through a seawater pipeline;

[0017] The solar thermal system is cyclically connected to the high-temperature molten salt storage tank, the medium-temperature molten salt storage tank and the low-temperature molten salt storage tank in sequence through the oil pipeline;

[0018] The steam generated by the first-stage flash tank and the second-stage flash tank enters the high-temperature molten salt storage tank, which heats the steam and drives the steam turbine to generate electricity; the steam exhausted by the steam turbine exchanges heat with the seawater flowing into the shell and tube gas-liquid heat exchanger.

[0019] One or more of the above technical solutions have the following beneficial effects:

[0020] The method for preparing the photothermal material of the present invention is simple and practical, and can double the light absorption capacity of graphite.

[0021] In the present invention, a high-temperature molten salt storage tank is arranged behind the first-stage flash tank and the second-stage flash tank to heat the steam generated in the flash tank, which is used to drive the steam turbine to generate electricity and then drive the system operation; the arranged photothermal heat accumulator absorbs solar heat during the day to perform the first-stage preheating of seawater. This process directly absorbs solar heat and stores it in the heat accumulator, reducing the heat transfer steps and effectively improving the solar energy utilization rate; the seawater is preheated and heated in multiple stages to gradually increase the temperature of the seawater and steam, thereby maximizing the heat utilization efficiency.

[0022] Advantages of additional aspects of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0024] Figure 1 Schematic diagram of the overall structure of the solar multi-effect flash evaporation seawater desalination system in Example 2 of the present invention;

[0025] Figure 2 Schematic diagram of the optical path and internal coil structure of the solar thermal heat storage device in the second embodiment of the present invention;

[0026] Figure 3 This is a UV-vis image of the photothermal material in the comparative example of Example 1 of the present invention;

[0027] Figure 4 This is the temperature change curve of the material prepared in Example 1 of the present invention under light;

[0028] In the figure, 1. Solar thermal heat storage tank; 2. Solar thermal system; 3. Shell and tube gas-liquid heat exchanger; 4. Low-temperature molten salt storage tank; 5. Primary flash tank; 6. High-temperature molten salt storage tank; 7. Medium-temperature molten salt storage tank; 8. Steam turbine; 9. Secondary flash tank; 10. Fresh water storage tank; 11. Reflector; 12. Serpentine coil; 13. Solar thermal storage material; 14. Aerogel glass. DETAILED DESCRIPTION

[0029] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0030] It should be noted that the terms used herein are for describing particular embodiments only and are not intended to limit the exemplary embodiments according to the present invention.

[0031] In the absence of conflict, the embodiments of the present invention and the features thereof may be combined with each other.

[0032] Example 1

[0033] This embodiment discloses a method for preparing a photothermal material, comprising: adding a Max phase material, such as Ti2AlC, to a mixed solution of a certain amount of concentrated hydrochloric acid and lithium fluoride, stirring the solution in a water bath at 35-40°C for 48 hours, centrifuging the mixed solution multiple times, washing the precipitate with water, and centrifuging and changing the water multiple times until the upper liquid turns dark green, stopping the water change, and centrifuging again 3-4 times. The solution is then ultrasonicated in an ice bath for 30 minutes to 1 hour, and the upper black solution is obtained as the Maxene colloidal solution.

[0034] Dopamine hydrochloride and graphite EG in a mass ratio of 1:3 were added to a solution of anhydrous ethanol and deionized water in a volume ratio of 1:3, and the pH of the mixed solution was adjusted to 8.5 with ammonia water. The mixture was stirred at 35-45°C for 24 hours. The solid matter was filtered and vacuum dried at 45-50°C to obtain EG modified with polydopamine PDA.

[0035] The suspension of MXene and the EG modified with PDA are mixed in a certain proportion, placed in a vacuum environment for 30 minutes to 1 hour, and then dried in a vacuum at low temperature to obtain the EG modified with PDA and MXene.

[0036] Finally, the phase change material, thickener carboxymethyl cellulose CMC, and nucleating agent disodium hydrogen phosphate dodecahydrate DHPD are mixed together and prepared into a photothermal material by melt co-mixing and vacuum impregnation with the modified EG.

[0037] The phase change material can be any organic, inorganic or hydrated salt phase change material with a temperature between 50° C. and 70° C. As an implementation method, the phase change material in this embodiment is sodium acetate trihydrate (SAT).

[0038] It should be noted that nucleating agents and thickeners are only added when the phase change material is a hydrated salt phase change material with supercooling. When the phase change material is an organic phase change material without supercooling, there is no need to add nucleating agents and thickeners.

[0039] As an example, 2 g of Max phase material Ti2AlC was added to a mixed solution of 40 ml, 9 mol / L concentrated hydrochloric acid and 3.2 g of lithium fluoride, and stirred in a 40 ° C water bath for 48 hours. The mixed solution was centrifuged several times, and the precipitate was washed with water. The water was changed by centrifugation several times until the upper liquid turned dark green. The water was stopped and centrifuged again 3-4 times, and then ultrasonicated in an ice bath for 30 minutes. The upper black solution was taken as the Mxene colloidal solution.

[0040] Dopamine hydrochloride and EG in a mass ratio of 1:3 were added to anhydrous ethanol and deionized water solution in a volume ratio of 1:3, and the pH of the mixed solution was adjusted to 8.5 with ammonia water. The mixture was stirred at 40°C for 24 hours. The solid matter was filtered and vacuum dried at 50°C to obtain EG modified with polydopamine PDA.

[0041] 3 ml, 5 ml or 7 ml of the MXene suspension was mixed with 0.28 g of PDA-modified EG, placed in a vacuum environment for 30 minutes and then dried in a low-temperature vacuum environment to obtain PDA- and MXene-modified EG.

[0042] Finally, the phase change material, thickener carboxymethyl cellulose CMC, and nucleating agent disodium hydrogen phosphate dodecahydrate DHPD are mixed together and prepared into a photothermal material by melt co-mixing and vacuum impregnation with the modified EG.

[0043] Comparative Example: Graphite EG was not modified with PDA and Mxene, and other conditions were the same as above.

[0044] Phase change material, thickener carboxymethyl cellulose CMC, nucleating agent disodium hydrogen phosphate dodecahydrate DHPD are mixed together and prepared into photothermal material by melt mixing and vacuum impregnation with unmodified EG. Its light absorption properties are as follows: Figure 3 As shown, it can be seen that the light absorption performance of the photothermal material prepared in this embodiment is more beneficial.

[0045] Figure 4 The temperature change curve of the prepared material under light. Figure 4 The phase change material used is sodium acetate trihydrate (SAT). The phase change ends when the temperature reaches the point of sudden change, as indicated by the dashed line in the figure. The material with 7ml of MXene has the shortest phase change time and the best photothermal performance. Pure SAT, on the other hand, does not undergo a phase change under illumination. The comparative example, a composite of unmodified EG and SAT, takes a long time to change phase and exhibits poor photothermal performance.

[0046] Example 2

[0047] The purpose of this embodiment is to provide a solar multi-effect flash evaporation seawater desalination system, characterized in that the system uses the photothermal material obtained by the preparation method in Example 1.

[0048] like Figure 1-Figure 2 As shown, a solar multi-effect flash evaporation seawater desalination system proposed in this embodiment includes: a solar thermal heat storage tank 1, a shell and tube gas-liquid heat exchanger 3, a low-temperature molten salt storage tank 4, a primary flash tank 5, a medium-temperature molten salt storage tank 7 and a secondary flash tank 9 connected in sequence through a seawater pipeline;

[0049] The solar thermal system 2 is connected to the high-temperature molten salt storage tank 6, the medium-temperature molten salt storage tank 7 and the low-temperature molten salt storage tank 4 in a circular manner through oil pipelines;

[0050] The steam generated by the first-stage flash tank 5 and the second-stage flash tank 9 enters the high-temperature molten salt storage tank 6, which heats the steam and drives the steam turbine 8 to generate electricity; the steam discharged from the steam turbine 8 exchanges heat with the seawater flowing into the shell and tube gas-liquid heat exchanger 3.

[0051] The solar multi-effect flash evaporation seawater desalination system proposed in this embodiment includes three routes: a water route for seawater flow, a steam route for steam flow, and an oil route for thermal oil flow.

[0052] Water route: The concentrated brine is discharged through the solar thermal heat accumulator 1, the shell and tube gas-liquid heat exchanger 3, the low-temperature molten salt storage tank 4, the first-level flash tank 5, the medium-temperature molten salt storage tank 7 and the second-level flash tank 9 in sequence.

[0053] Steam circuit: The steam generated from the primary flash tank 5 and the secondary flash tank 9 passes through the high-temperature molten salt heat storage tank 6, the steam turbine 8, and the shell and tube gas-liquid heat exchanger 3 in sequence, condenses into fresh water in the shell and tube gas-liquid heat exchanger 3, and is collected in the fresh water tank.

[0054] Oil circuit: During the day, the thermal oil absorbs heat from the solar thermal system 2, passes through the high-temperature molten salt storage tank 6, the medium-temperature molten salt storage tank 7 and the low-temperature molten salt storage tank 4 in sequence, and finally returns to the solar thermal system 2 to absorb heat again.

[0055] Among them, the flash tank, molten salt storage tank, and steam turbine are all existing structures, and the specific structural forms will not be described in detail here.

[0056] In this embodiment, a solar thermal energy storage tank 1 is connected to pretreated seawater at one end and to a shell-and-tube gas-liquid heat exchanger 3 at the other. The tank 1 is filled with a photothermal material and arranged with multiple rows of vertical serpentine coils 12. Seawater enters and exits the coils 12 from the bottom and the top, encapsulating the outermost portion with aerogel glass 14. Reflectors are arranged around the tank 1 to focus sunlight onto its surrounding surfaces. The aerogel glass 14 provides excellent thermal insulation and boasts a light transmittance exceeding 70%.

[0057] In this embodiment, the shell and tube gas-liquid heat exchanger 3 used is based on the existing shell and tube gas-liquid heat exchanger, and a fresh water valve is provided at the bottom of each steam chamber for discharging and collecting fresh water.

[0058] The fresh water valve may be a water level valve. When the fresh water level in the shell and tube gas-liquid heat exchanger 3 reaches a certain height, the water level valve is opened to discharge the fresh water. After the fresh water is discharged, the water level valve is closed.

[0059] Water flows in the tubes of the shell and tube gas-liquid heat exchanger 3, and steam flows outside the tubes. The steam transfers heat to the water and condenses into fresh water outside the tubes. The fresh water gathers at the bottom of the shell and tube gas-liquid heat exchanger 3. The fresh water valve at the bottom is opened regularly to gather the fresh water in the fresh water storage tank.

[0060] The principle of a solar multi-effect flash evaporation seawater desalination system in this embodiment is described as follows: the pretreated 20-35°C seawater passes through the solar thermal heat accumulator 1 for primary preheating to 45-55°C, then flows into the shell and tube gas-liquid heat exchanger 3 and exchanges heat with the 100-130°C steam discharged from the tail of the steam turbine 8 for secondary preheating to 75-85°C, enters the low-temperature molten salt storage tank 4 for primary heating to 100°C, and then enters the first-level flash tank 5 where part of the seawater evaporates into 80-90°C steam in a negative pressure state, and the temperature of the other part of the seawater is also reduced to 80-90°C; then the seawater enters the medium-temperature molten salt storage tank 7 and is heated to 150-200°C, then enters the second-level flash tank 9, and the concentrated brine is discharged at the tail. The steam generated in the second-level flash tank 9 and the steam generated in the first-level flash tank 5 converge and enter the high-temperature molten salt storage tank 6 for heating while restoring the negative pressure state to standard atmospheric pressure. The steam temperature at the outlet of the high-temperature molten salt storage tank 6 is 250-300°C. The high-temperature steam is then sent to the steam turbine 8 to generate electricity. After power generation, the steam temperature is 100-130°C, and then enters the shell and tube gas-liquid heat exchanger 3 for heat exchange and condensation into fresh water, which is finally collected in the fresh water storage tank 10.

[0061] The electric energy generated by the steam turbine 8 is used to supply the operation of the entire system, including the circulation of seawater and thermal oil and the operation of the vacuum pump in the flash tank, and the excess electric energy is stored.

[0062] During the day, solar thermal system 2 converts solar energy into heat, producing high-temperature thermal oil at 400°C. This oil then stores the heat in high-temperature molten salt storage tank 6, medium-temperature molten salt storage tank 7, and low-temperature molten salt storage tank 4, before returning to solar thermal system 2 to reabsorb the heat. The molten salt in the high-temperature molten salt storage tank has a phase transition temperature of 320-380°C, the medium-temperature molten salt storage tank has a phase transition temperature of 200-250°C, and the low-temperature molten salt storage tank has a phase transition temperature of 110-150°C.

[0063] This embodiment sequentially arranges a solar thermal heat accumulator, a shell and tube gas-liquid heat exchanger, a low-temperature molten salt storage tank, a medium-temperature molten salt storage tank, and a high-temperature molten salt storage tank, and adopts a multi-stage preheating and multi-stage heating method to gradually increase the temperature of seawater and steam to maximize the heat utilization efficiency.

[0064] In this embodiment, a high-temperature molten salt storage tank is arranged after the first-stage flash tank and the second-stage flash tank to heat the steam generated in the flash tank to drive the steam turbine to generate electricity, and the electrical energy is used to drive the operation of the entire system and drive the vacuum pump in the flash tank.

[0065] This embodiment arranges a photothermal heat storage device that can actively absorb solar heat during the day to perform a primary preheating of the pretreated seawater. This process directly absorbs solar heat and stores it in the heat storage device, reducing the heat transfer steps and effectively improving the utilization rate of solar energy.

[0066] In this embodiment, the shell-and-tube gas-liquid heat exchanger also serves as a freshwater condenser. A freshwater outlet is located at the bottom of each steam chamber of the shell-and-tube gas-liquid heat exchanger. When the freshwater level reaches a certain level, a freshwater valve opens to collect the freshwater. This allows for simpler and more convenient freshwater condensation and collection.

[0067] In this embodiment, the pretreated seawater reaches a temperature of 100°C after primary and secondary preheating and heating in a low-temperature molten salt storage tank, and then enters a flash tank for negative pressure evaporation, which can achieve rapid vaporization of the seawater.

[0068] Although the above describes the specific embodiments of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without any creative work are still within the scope of protection of the present invention.

Claims

1. A method for preparing a photothermal material, characterized in that: include: The Max phase material is added to a mixed solution of concentrated hydrochloric acid and lithium fluoride, stirred, centrifuged, and the upper layer solution is collected to obtain a MXene colloidal solution; Adding graphite and dopamine hydrochloride to a solution of anhydrous ethanol and deionized water, adjusting the pH value, stirring, and drying to obtain modified graphite; specifically, adding graphite and dopamine hydrochloride to a solution of anhydrous ethanol and deionized water, adjusting the pH value to 8.5, stirring at 35°C-45°C for 24 hours, filtering the solid matter, and vacuum drying at 45°C-50°C to obtain graphite modified with polydopamine; wherein the mass ratio of dopamine hydrochloride to graphite is 1:3; and the mass ratio of anhydrous ethanol to deionized water is 1:3; The MXene colloidal solution and the modified graphite are mixed and dried at low temperature to obtain the modified graphite; The modified graphite is mixed with a phase change material to obtain a photothermal material; the phase change material is sodium acetate trihydrate.

2. The method for preparing a photothermal material according to claim 1, wherein: The modified graphite is mixed with a phase change material, a thickener and a nucleating agent to obtain a photothermal material; wherein the thickener is carboxymethyl cellulose and the nucleating agent is disodium hydrogen phosphate dodecahydrate.

3. The method for preparing a photothermal material according to claim 1, wherein: The MXene colloidal solution and the modified graphite are mixed, placed in a vacuum environment for 30 minutes to 1 hour, and then dried in a low-temperature vacuum to obtain the modified graphite.

4. A photothermal material obtained by the preparation method of the photothermal material according to any one of claims 1 to 3.

5. A solar multi-effect flash evaporation seawater desalination system, characterized in that: include: A photothermal heat accumulator, wherein the photothermal heat accumulator is filled with the photothermal material obtained by the preparation method according to any one of claims 1 to 3 or the photothermal material according to claim 4; It also includes: a shell and tube gas-liquid heat exchanger, a low-temperature molten salt storage tank, a first-level flash tank, a medium-temperature molten salt storage tank and a second-level flash tank connected to the photothermal heat accumulator in sequence through a seawater pipeline; The solar thermal system is cyclically connected to the high-temperature molten salt storage tank, the medium-temperature molten salt storage tank and the low-temperature molten salt storage tank in sequence through the oil pipeline; The steam generated by the first-stage flash tank and the second-stage flash tank enters the high-temperature molten salt storage tank, which heats the steam and drives the steam turbine to generate electricity; the steam discharged from the steam turbine exchanges heat with the seawater flowing into the shell and tube gas-liquid heat exchanger.

6. A solar multi-effect flash evaporation seawater desalination system according to claim 5, characterized in that: The photothermal heat storage device includes aerogel glass, and a serpentine coil and the photothermal material arranged inside the aerogel glass.

7. The solar multi-effect flash evaporation seawater desalination system according to claim 5, characterized in that: Reflecting mirrors are arranged around the outside of the photothermal heat storage device.

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