Photo-thermal material, preparation method thereof and solar multi-effect flash evaporation seawater desalination system

Abstract

According to the photo-thermal material, the preparation method of the photo-thermal material and the solar multi-effect flash evaporation seawater desalination system, the prepared photo-thermal material is simple in method and high in practicability, and the light absorption capacity of graphite can be doubled; a high-temperature fused salt storage tank is arranged behind the first-stage flash tank and the second-stage flash tank to heat steam generated in the flash tanks and is used for driving a steam turbine to generate power, and then the system is driven to operate; the arranged photo-thermal heat accumulator absorbs solar heat in the daytime to perform primary preheating on seawater, and the solar heat is directly absorbed and stored in the heat accumulator in the process, so that the heat transfer step is reduced, and the solar energy utilization rate is effectively improved; seawater is preheated in multiple stages, the temperature of the seawater and the temperature of steam are increased stage by stage in a multi-stage heating mode, and the heat utilization efficiency is maximized.

Description

Technical Field

[0001] The present invention belongs to the technical field related to solar desalination, and in particular relates to a photothermal material and a preparation method thereof and a solar multi-effect flash evaporation 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 for production and life needs to be produced by freshwater equipment. At present, the freshwater equipment commonly used on islands mostly uses reverse osmosis freshwater technology, which is costly and complex. In addition, the freshwater system that relies on seawater evaporation has a huge cost of using power grid electricity. In order to save costs, it is necessary to generate heat by itself or rely on other processes. Inland, this multi-effect flash freshwater system relies on a process that can generate water vapor. Desalination of seawater is achieved with the help of the heat of water vapor.

[0004] Desalination is the only water resource development technology that is not affected by climate and can directly provide fresh water for human life and production. In the long run, desalination is the fundamental way and direction to solve the problem of insufficient water resources on islands. However, islands far from the coast have a single energy model and limited energy supply, mainly relying on diesel generators for power generation. Even if there are power plants on the islands, the power supply is not very sufficient.

[0005] The inventors found that energy storage equipment will also become the future energy hub during the energy transition period. New high-performance heat storage materials are also a current research hotspot. Reasonable arrangement of multi-level phase change heat storage technology can not only solve the intermittent problem of solar energy, but also effectively improve the energy utilization rate of solar desalination systems. There are almost no processes that can produce water vapor on the island, so the multi-effect flash desalination technology can only be used in combination with renewable energy systems. How to reasonably arrange the system structure to reduce dependence on diesel power generation and improve the energy utilization rate of the system is the difficulty and focus.

[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 to solve the problems of high operating costs, additional electricity input and low energy utilization of existing island freshwater systems and maximize energy utilization efficiency are the problems that need to be solved at present. Summary of the invention

[0007] In order to overcome the deficiencies of the above-mentioned prior art, the present invention provides a photothermal material and 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 solution:

[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 taken to obtain a Mxene colloidal solution;

[0011] Adding graphite and dopamine hydrochloride into 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 subjected to low temperature drying 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 photothermal material preparation method as described above.

[0015] In a third aspect, the present invention provides a solar multi-effect flash evaporation seawater desalination system, comprising: a photothermal heat accumulator, wherein the photothermal heat accumulator is 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 primary flash tank, a medium-temperature molten salt storage tank and a secondary flash tank which are sequentially connected to the photothermal heat storage device 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 an oil pipeline;

[0018] The steam generated by the primary flash tank and the secondary flash tank enters the high-temperature molten salt storage tank, and the high-temperature molten salt storage tank 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 primary flash tank and the secondary flash tank to heat the steam generated in the flash tank, which is used to drive the steam turbine to generate electricity and further drive the system to operate; the arranged photothermal heat accumulator absorbs solar energy heat during the day to perform primary preheating of seawater. This process directly absorbs solar energy heat and stores it in the heat accumulator, which reduces the heat transfer steps and effectively improves the utilization rate of solar energy; 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.

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

[0023] The accompanying drawings in the specification, 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 This is a schematic diagram of the overall structure of a solar multi-effect flash evaporation seawater desalination system in Embodiment 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 The temperature change curve of the material prepared in Example 1 of the present invention under light;

[0028] In the figure, 1. Photothermal 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. Photothermal heat storage material; 14. Aerogel glass. DETAILED DESCRIPTION

[0029] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those 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 specific embodiments only and are not intended to be limiting of exemplary embodiments according to the present invention.

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

[0032] Embodiment 1

[0033] The present 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, and stirring in a water bath at 35-40°C for 48 hours, and then centrifuging the mixed solution for multiple times, washing the precipitate with water, and centrifuging and changing water for multiple times until the upper liquid turns dark green, stopping the water change, and centrifuging again for 3-4 times, and then ultrasonicating in an ice bath for 30min-1h, and taking the upper black solution as the Mxene colloidal solution.

[0034] Dopamine hydrochloride and graphite EG in a mass ratio of 1:3 are added to a solution of anhydrous ethanol and deionized water in a volume ratio of 1:3, and the pH of the mixed solution is adjusted to 8.5 with ammonia water. The mixture is stirred at 35-45°C for 24 hours, and the solid matter is 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 min-1 h and then dried in a low-temperature vacuum environment to obtain the EG modified with PDA and Mxene.

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

[0037] The phase change material can be organic, inorganic or hydrated salt phase change material between 50-70° C. As an implementation method, the phase change material of this embodiment uses 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 is 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 water bath at 40 ° C for 48 hours, and then the mixed solution is centrifuged several times, and the precipitate is washed with water, and the water is changed by centrifugation several times until the upper liquid turns dark green, and the water is stopped, and the water is changed again by centrifugation 3-4 times, and then ultrasonicated in an ice bath for 30 minutes, and the upper black solution is taken as the Mxene colloidal solution.

[0040] Dopamine hydrochloride and EG in a mass ratio of 1:3 are added to anhydrous ethanol and deionized water solution in a volume ratio of 1:3, and the pH of the mixed solution is adjusted to 8.5 with ammonia water. The mixture is stirred at 40°C for 24 hours, and the solid matter is 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 the PDA-modified EG, placed in a vacuum environment for 30 min and then dried in a low-temperature vacuum environment to obtain the PDA- and Mxene-modified EG.

[0042] Finally, the phase change material, the thickener carboxymethyl cellulose CMC, and the nucleating agent disodium hydrogen phosphate dodecahydrate DHPD are mixed together, and the photothermal material is prepared 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 blending and vacuum impregnation with unmodified EG. Its light absorption performance is 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. When the time reaches the temperature mutation position, the phase change ends at the dotted line position in the figure. From the perspective of phase change time, the material with 7ml Mxene has the shortest phase change time and the best photothermal performance. The pure SAT material cannot phase change under light. The phase change time of the material of the unmodified EG and SAT composite in the comparative example is very long, and the photothermal performance is poor.

[0046] Embodiment 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 desalination system proposed in this embodiment includes: a photothermal 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 cyclically 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 sequence through oil pipelines;

[0050] The steam generated by the primary flash tank 5 and the secondary 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 exhausted by 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 is a seawater flow route, a steam route is a steam flow route, and an oil route is a heat transfer oil flow route.

[0052] Water route: The concentrated brine is discharged through the photothermal heat storage tank 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 heat transfer 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, one end of the photothermal heat storage device 1 is connected to the pretreated seawater, and the other end is connected to the shell-and-tube gas-liquid heat exchanger 3; the photothermal heat storage device 1 is filled with photothermal materials, and multiple rows of vertical serpentine coils 12 are arranged, and the seawater enters and exits from the lower side of the serpentine coils 12 and flows out from the upper side, and is encapsulated with aerogel glass 14 on the outermost side. Reflectors are arranged around the photothermal heat storage device 1 to concentrate and reflect sunlight to the surrounding surfaces of the photothermal heat storage device 1. Among them, the aerogel glass 14 can achieve good thermal insulation performance and has a light transmittance of more than 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 arranged 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, and the water level valve is closed after the fresh water is discharged.

[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 desalination system in this embodiment is as follows: the pretreated 20-35°C seawater is preheated to 45-55°C in the photothermal heat accumulator 1, 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-stage 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, and then enters the second-stage flash tank 9, where concentrated brine is discharged at the tail, and the steam generated in the second-stage flash tank 9 converges with the steam generated in the first-stage flash tank 5 and enters the high-temperature molten salt storage tank 6 for heating while restoring the negative pressure state to standard atmospheric pressure, and 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 heat transfer oil and the operation of the vacuum pump in the flash tank, and the excess electric energy is stored.

[0062] During the day, the solar thermal system 2 converts solar energy into heat energy to produce high-temperature heat transfer oil at 400°C. The heat transfer oil stores the heat in 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 reabsorb the heat. Among them, the phase change temperature of the molten salt in the high-temperature molten salt storage tank is 320-380°C, the phase change temperature of the molten salt in the medium-temperature molten salt storage tank is 200-250°C, and the phase change temperature of the molten salt in the low-temperature molten salt storage tank is 110-150°C.

[0063] In this embodiment, a photothermal heat storage device, 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 are sequentially arranged, and the temperature of seawater and steam is gradually increased by multi-stage preheating and multi-stage heating to maximize the heat utilization efficiency.

[0064] In this embodiment, a high-temperature molten salt storage tank is arranged behind the primary flash tank and the secondary 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 energy heat during the day, and is used to perform primary preheating of the pretreated seawater. This process directly absorbs solar energy heat and stores it in the heat storage device, which reduces the heat transfer steps and effectively improves the utilization rate of solar energy.

[0066] In this embodiment, the shell and tube gas-liquid heat exchanger also acts as a fresh water condenser. A fresh water outlet is arranged at the bottom of each steam chamber of the shell and tube gas-liquid heat exchanger. When the fresh water level reaches a certain height, the fresh water valve is opened to collect fresh water, thereby realizing a simpler and more convenient function of fresh water condensation and collection.

[0067] In this embodiment, the pretreated seawater reaches a water 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 implementation mode 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 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 taken to obtain a Mxene colloidal solution; Adding graphite and dopamine hydrochloride into a solution of anhydrous ethanol and deionized water, adjusting the pH value, stirring, and drying to obtain modified graphite; The MXene colloidal solution and the modified graphite are mixed and subjected to low temperature drying to obtain the modified graphite; The modified graphite is mixed with a phase change material to obtain a photothermal material.

2. The method for preparing a photothermal material according to claim 1, characterized in that: 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, characterized in that: The phase change material is sodium acetate trihydrate.

4. The method for preparing a photothermal material according to claim 1, characterized in that: The mass ratio of the dopamine hydrochloride to the graphite is 1:3; the mass ratio of the anhydrous ethanol to the deionized water is 1:

3.

5. The method for preparing a photothermal material according to claim 1, characterized in that: Graphite and dopamine hydrochloride are added to a solution of anhydrous ethanol and deionized water, the pH value is adjusted to 8.5, and the mixture is stirred at 35°C-45°C for 24 hours. After filtering the solid matter, the mixture is vacuum dried at 45°C-50°C to obtain graphite modified with polydopamine.

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

7. A photothermal material obtained by the method for preparing the photothermal material according to any one of claims 1 to 6.

8. A solar multi-effect flash evaporation seawater desalination system, characterized in that: include: A photothermal heat storage device, wherein the photothermal heat storage device is filled with the photothermal material obtained by the preparation method according to any one of claims 1 to 6 or the photothermal material according to claim 7; It also includes: a shell and tube gas-liquid heat exchanger, a low-temperature molten salt storage tank, a primary flash tank, a medium-temperature molten salt storage tank and a secondary flash tank which are sequentially connected to the photothermal heat storage device 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 an oil pipeline; The steam generated by the primary flash tank and the secondary flash tank enters the high-temperature molten salt storage tank, and the high-temperature molten salt storage tank 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.

9. The island solar multi-effect flash desalination system coupled with a power generation device as claimed in claim 8, characterized in that: The photothermal heat storage device comprises aerogel glass, and a serpentine coil and the photothermal material arranged inside the aerogel glass.

10. The island solar multi-effect flash desalination system coupled with a power generation device as claimed in claim 8, characterized in that: Reflecting mirrors are arranged around the outside of the photothermal heat storage device.

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