A seawater desalination system and a seawater desalination method

Abstract

The present application relates to the technical field, especially to a kind of seawater desalination system and seawater desalination method, which combines forced circulation evaporator with multi-stage flash evaporation, and the forced circulation evaporator realizes water and salt resource utilization for flash evaporation concentrated brine;At the same time, low-grade heat or solar energy is used as the steam separation power in the forced circulation evaporator, and solar light modulation technology is used to improve the utilization rate of solar energy, which can greatly reduce the power consumption compared with mechanical forced circulation, reduce the overall energy consumption, solve the environmental pollution caused by direct discharge of flash evaporation concentrated brine, and achieve zero discharge of waste water and waste gas.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field, and particularly relates to a seawater desalination system and a seawater desalination method. BACKGROUND

[0002] The multi-stage flash evaporation seawater desalination technology is to introduce the raw seawater into a flash evaporation chamber after being heated to a certain temperature, and because the pressure in the flash evaporation chamber is controlled to be lower than the saturated steam pressure corresponding to the temperature of the hot brine, the hot brine is rapidly partially gasified after entering the flash evaporation chamber due to overheating, so that the temperature of the hot brine is reduced, and the produced steam is condensed to obtain the required fresh water. The concentrated seawater is introduced into each flash evaporation chamber in turn to reduce the pressure and make it flash evaporate, and then condensed to obtain fresh water.

[0003] The product of the multi-stage flash evaporation seawater desalination technology is fresh water and concentrated brine with extremely high salt content. For the treatment of concentrated brine, a feasible scheme in the prior art is to discharge the concentrated brine into seawater. The salt content of the concentrated brine is much higher than that of seawater, and direct discharge will cause serious harm to the ecological environment of seawater and is increasingly inconsistent with environmental protection requirements. A common scheme in the prior art is to use a high-temperature evaporation crystallization method to obtain crystalline salt from the concentrated brine of seawater desalination. This method needs to be matched with a forced steam discharge device (such as a flash evaporation process), and has defects of high crystallization temperature, high energy consumption, and difficulty in utilizing the separated water vapor resources.

[0004] In order to meet the huge energy consumption of seawater desalination, the prior art has appeared to use secondary energy sources such as industrial waste heat or renewable energy sources such as solar energy to partially replace electric energy, but the secondary energy sources or solar energy used for seawater desalination still has the following defects:

[0005] On the one hand, the secondary energy sources cannot directly provide power for steam discharge, and often need to be converted into electric energy to further provide power for steam discharge, so the energy utilization efficiency of the secondary energy sources is low.

[0006] On the other hand, the main way of using solar energy is photovoltaic power generation and solar thermal utilization. The energy utilization rate of photovoltaic power generation is low, and the large occupied area restricts its further promotion. The solar thermal utilization has a low absorption rate of visible light band, which is the main energy band of solar radiation, to water or salt-containing water, and has a low heat utilization rate and a low heating rate when heating water directly, which restricts its further promotion.

[0007] The prior art needs a seawater desalination system and method that can reduce the consumption of electric energy and improve the low energy utilization efficiency of secondary energy sources or solar energy in seawater desalination. SUMMARY

[0008] In view of the above analysis, the present application aims to provide a seawater desalination system and a seawater desalination method to solve at least one of the technical problems of high power consumption of the existing seawater desalination system and low energy utilization efficiency of secondary energy or solar energy in seawater desalination.

[0009] The present application mainly aims to achieve the above-mentioned purposes by the following technical solutions.

[0010] The present application provides a seawater desalination system, comprising a multi-stage flash evaporation module, a crystallization module and a forced circulation module.

[0011] The concentrated brine of the multi-stage flash evaporation module is communicated with the crystallization module, and the water vapor exhaust of the crystallization module is communicated with the forced circulation module.

[0012] The concentrated brine of the multi-stage flash evaporation module is separated to obtain water vapor in the crystallization module, and enters the forced circulation module under the action of negative pressure provided by the forced circulation module.

[0013] Preferably, the forced circulation module comprises a vacuum pump or a water absorption medium; the water vapor volatilized from the crystallization module is sucked by the negative pressure of the vacuum pump or absorbed by the water absorption medium to provide a negative pressure environment for the inside of the crystallization module, thereby promoting the flow of water vapor to the forced circulation module; the forced circulation module further comprises a water vapor condensation unit, and the water vapor flowing into the forced circulation module is condensed and collected in the water vapor condensation unit.

[0014] Preferably, the forced circulation module further comprises an adsorption unit, a desorption unit and a water absorption medium pump; the adsorption unit is communicated with the crystallization module through a gas path; the adsorption unit and the desorption unit are communicated through two one-way pipelines, at least one of which is provided with a water absorption medium pump; the desorption unit is provided with a heating device and is communicated with the water vapor condensation unit through a gas path.

[0015] Preferably, the heat source of the heating device is a solid, liquid or gas with a temperature greater than 100℃, and the heating mode of the desorption unit can be external surrounding or built-in heat exchanger heating.

[0016] Preferably, the heating device is a solar spectrum modulation device, and the proportion of the wavelength of the output radiation after the modulation treatment of the solar spectrum modulation device is 80% to 95% in the range of 750nm to 900nm.

[0017] Preferably, the solar spectrum modulation device comprises:

[0018] An absorber; the absorber is a double-layer grating structure, comprising a photocatalyst layer, a Si grating layer and a first grating hole penetrating both in sequence according to the light incidence direction;

[0019] The first modulator is arranged on the backlight side of the absorber and comprises a Ti grating layer, a SiO2 grating layer, a CrF3 grating layer and a second grating hole penetrating through the three layers, which are arranged in sequence from the near to the far direction relative to the absorber.

[0020] Preferably, the photocatalyst layer comprises any one of TiO2, ZnO and ZrO2.

[0021] Preferably, the aperture of the first grating hole is 4-12 microns, and / or the first grating hole is provided with a plurality of holes, and the porosity of the projection surface of the absorber is 83-92%.

[0022] Preferably, the first modulator comprises:

[0023] a CrF3 grating layer;

[0024] a SiO2 grating layer formed on the top of the CrF3 grating layer;

[0025] a Ti grating layer formed on the top of the SiO2 grating layer;

[0026] The Ti grating layer, the SiO2 grating layer and the CrF3 grating layer are all provided with through holes penetrating through the top and the bottom of each grating layer, and the through holes of adjacent grating layers are communicated to form the second grating hole.

[0027] A seawater desalination method using the seawater desalination system.

[0028] Compared with the prior art, the present application can achieve at least one of the following beneficial effects:

[0029] (1) The present application combines a forced circulation evaporator with a multi-stage flash evaporation, the forced circulation evaporator realizes water and salt resource utilization of the flash evaporation concentrated brine, solves the pollution of the direct discharge of the flash evaporation concentrated brine to the environment, and at the same time, the forced circulation evaporator and the subsequent steam are used to heat the flash evaporation feed water, which reduces the overall energy consumption and realizes zero discharge of waste water and waste gas.

[0030] (2) The present application generates negative pressure by absorbing water vapor through the water absorption medium, provides a negative pressure environment above the liquid surface of the crystallization module instead of mechanical forced circulation, heats the water absorption medium after water absorption to obtain regenerated water absorption medium and regenerated water vapor, further circulates the water absorption medium, and condenses the water vapor to obtain fresh water; the heating of the water absorption medium after water absorption can be solid, gas or liquid with waste heat or renewable solar energy, the low-grade heat in the waste heat can be fully utilized, the electric energy consumption can be greatly reduced compared with mechanical forced circulation, and the energy saving purpose is achieved.

[0031] (3) The present application utilizes the solar spectrum modulation device to directly heat the water-absorbing medium after absorbing the sunlight, and the absorber therein realizes high-efficiency absorption of the solar radiation with a wavelength of 400-800 nm, and the modulator can obtain the radiation with a wavelength of 750-900 nm after modulating the solar radiation through the solar spectrum modulation device, thereby realizing high-efficiency direct heating of the water-absorbing medium in the desorption unit and improving the defect of low heating efficiency of the existing technology in which the sunlight is directly used for heating water and salt-containing water solution.

[0032] (4) The present application utilizes the solar spectrum modulation device to modulate the absorbed sunlight into the radiation frequency corresponding to the optimal power generation efficiency of the crystalline silicon photovoltaic module, and the absorber therein realizes high-efficiency absorption of the solar radiation with a wavelength of 400-800 nm, and the modulator can obtain the radiation with a wavelength of 400-600 nm after modulating the solar radiation through the solar spectrum modulation device, thereby realizing high-efficiency utilization of the solar radiation by the crystalline silicon photovoltaic module; at the same time, the seawater inlet of the seawater desalination system is used to cool the crystalline silicon photovoltaic module to prevent overheating of the photovoltaic module, which helps to improve the power generation efficiency and improve the defect of low energy utilization efficiency of the existing technology in which the sunlight is used for the crystalline silicon photovoltaic module.

[0033] (5) The present application sets a condenser in front of the solar spectrum modulation device, thereby improving the unit energy density and reducing the defect of large area occupied by the traditional solar energy equipment, and at the same time, the seawater inlet of the seawater desalination system is used to cool the crystalline silicon photovoltaic module, so that the photovoltaic module still maintains a high power generation efficiency even under high condensing multiple.

[0034] In the present application, the above technical solutions can be combined with each other to realize more preferred combination solutions. Other features and advantages of the present application will be described in the subsequent specification, and some advantages will become apparent from the specification, or will be understood by implementing the present application. The purposes and other advantages of the present application can be realized and obtained through the contents specifically indicated in the specification, examples and drawings. BRIEF DESCRIPTION OF DRAWINGS

[0035] The accompanying drawings are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the principles of the application. In the drawings:

[0036] Figure 1 The process flow chart of the seawater desalination system in one embodiment of the present application;

[0037] Figure 2 The process flow chart of the seawater desalination system in another embodiment of the present application;

[0038] Figure 3 The structure schematic diagram of the absorber in another embodiment of the present application;

[0039] Figure 4 Fig. 1 is a schematic diagram of a first modulator structure in another embodiment of the present application;

[0040] Figure 5 Fig. 2 is a schematic diagram of a second modulator structure in another embodiment of the present application.

[0041] Reference numerals

[0042] Multi-stage flash module 001; crystallization module 002; forced circulation module 003; photovoltaic power generation unit 004;

[0043] Steam cooling device 1; flash unit 2; seawater pump 3; first heat exchanger 4; product water pump 5; second heat exchanger 6; brine pump 7; brine separation device 8; circulating water pump 9; forced circulation evaporator 10; adsorption unit 11; desorption unit 12; regenerator 13; water absorption medium pump 14; water vapor condensation unit 15; absorber 16; first modulator 17; first shield 18; condenser 19; energy storage unit 20; second modulator 21; photovoltaic power generation unit 22; second shield 24; electric heater 26; third cooler 27;

[0044] Photocatalyst layer 1601; Si grating layer 1602; first grating hole 1603; Ti grating layer 1701; SiO2 grating layer 1702; CrF3 grating layer 1703; second grating hole 1704; Ag grating layer 2101; SiC grating layer 2102; MgO grating layer 2103; third grating hole 2104. DETAILED DESCRIPTION

[0045] The preferred embodiments of the present application will be described in detail below with reference to the drawings, which form a part of this application. The drawings, together with the description, are used to explain the principles of the application and to enable the practice of the application by those skilled in the art.

[0046] To solve the problems of high crystallization temperature, high energy consumption and difficult utilization of water vapor resources in the crystallization separation of concentrated brine in the prior art, the present application introduces a negative pressure environment into the last-stage crystallizer of a multi-stage flash seawater system, reduces the concentrated separation temperature of the crystallization module 002, and evaporates water in the concentrated brine at a lower temperature to realize brine separation, thereby greatly reducing the energy consumption.

[0047] The present application proposes a feasible solution: using mechanical compression forced circulation technology to act as the last-stage crystallizer of a multi-stage flash seawater system, using a vacuum pump in combination with heating to realize brine separation of the multi-stage flash concentrated brine, and recovering water and salt resources and the latent heat of water vapor during crystallization; the shortcoming is that the mechanical compression forced circulation needs an electric vacuum pump to provide an additional negative pressure condition, consumes additional electric energy, and has further optimization space for energy consumption.

[0048] In view of the above defects, the mechanical compression type forced circulation system is further optimized: the water absorption medium absorbs water vapor to generate negative pressure, and a negative pressure environment is provided above the liquid surface of the crystallization module; the water absorption medium after water absorption is heated to obtain regenerated water absorption medium and regenerated water vapor, the water absorption medium is further circulated, and the water vapor is condensed to obtain fresh water.

[0049] It should be noted that the water absorption medium after water absorption can be heated by solid, gas or liquid with waste heat or by using renewable energy such as solar energy, and the low-grade heat in the waste heat or the solar energy can be used to heat the water absorption medium after water absorption to obtain dehydrated water absorption medium, so that the water absorption medium is circulated, and the mechanical compression type forced circulation represented by the vacuum pump can greatly reduce the power consumption.

[0050] In order to solve the problems of low energy absorption rate and low energy utilization efficiency of direct heating of solar energy in seawater desalination in the prior art, the seawater desalination system of the present application adopts a solar spectrum modulation device to modulate the input sunlight, mainly outputting light radiation with a wavelength of 750nm-900nm, and water or aqueous solution has the highest absorption rate for light radiation in this wavelength range, thereby realizing efficient direct heating of water or salt-containing water by light radiation.

[0051] It should be noted that water or salt-containing water has the highest spectral absorption rate for light with a wavelength of 750nm-900nm, which can be more than 90%; and water or salt-containing water has less than 10% absorption for visible light with a wavelength of 400nm-740nm (especially blue-violet light) in sunlight, so light radiation in this wavelength range cannot directly heat water or salt-containing water, resulting in low energy utilization efficiency of sunlight for heating water or salt-containing water.

[0052] It should be noted that some equipment in the seawater desalination system is electrically driven, and electricity is still a necessary energy source for the seawater desalination system. Another aspect of reducing the energy consumption of the seawater desalination system is to reduce the demand for external power supply of the seawater desalination system and widely introduce electricity converted from renewable energy such as solar energy. The biggest problem of solar power generation (such as photovoltaic power generation) at present is the low energy density of solar energy and the large area occupied; although the use of concentrating equipment can improve the energy density and reduce the area occupied, the light receiving surface temperature of the solar power generation equipment is greatly increased after concentration by the concentrating device, on the one hand, solar power generation equipment (such as photovoltaic crystalline silicon components) has an optimal power generation temperature range, and the power generation efficiency decreases rapidly when the temperature exceeds the range; on the other hand, due to the limitation of the material itself, the energy utilization efficiency is difficult to be greatly improved, and the theoretical maximum power generation efficiency of mass-produced photovoltaic equipment (such as photovoltaic crystalline silicon components) is ≤30%, and most of the light energy is lost in the form of heat; in addition, the high temperature puts forward higher requirements for the service life and stability of the solar power generation equipment, which restricts the application of photovoltaic power generation in the seawater desalination system.

[0053] In order to solve the problems of low energy density, large occupation area and low energy utilization efficiency of the existing solar direct seawater heating and photovoltaic power generation in seawater desalination, on the one hand, the present application collects and focuses the sunlight radiation of a larger area to the seawater heating or photovoltaic power generation area through a light collecting device before the solar direct seawater heating and photovoltaic power generation; on the other hand, in view of the problem that the surface temperature of the photovoltaic power generation component after light focusing is too high to affect the power generation efficiency, the present application uses the seawater at the inlet end of the seawater desalination system for cooling the photovoltaic power generation component, and at the same time, preheats the seawater at the inlet end; in addition, the seawater desalination system adopts another solar spectrum modulation device to modulate the input sunlight, mainly outputting light radiation between 400nm and 600nm, and the crystalline silicon-based power generation equipment has the highest absorption rate for the light radiation of this wave band, thereby improving the utilization rate of crystalline silicon for sunlight.

[0054] It should be noted that the principle of photovoltaic power generation of crystalline silicon is quantum absorption principle: when light irradiates the surface of the silicon crystal, part of the photons is absorbed by the silicon material, the energy of the photons is transferred to the silicon atoms, the electrons are transferred, become free electrons, and are gathered on both sides of the P-N junction, generating a potential difference; the photons with energy lower than 1.13eV cannot be absorbed by the crystalline silicon to generate electricity, and the part of the photons with energy higher than 1.13eV can be absorbed in the form of heat, so the energy / frequency / wavelength of the photons for crystalline silicon power generation needs to have a suitable range.

[0055] The present application provides a seawater desalination system, as shown in Figure 1 、 Figure 2 The present application provides a seawater desalination system, as shown in

[0056] The concentrated brine of the multi-stage flash evaporation module 001 is separated to obtain water vapor in the crystallization module 002, and enters the forced circulation module 003 under the action of negative pressure provided by the forced circulation module 003.

[0057] Specifically, the multi-stage flash evaporation module 001 comprises a plurality of serially connected flash evaporation units 2, the flash evaporation units 2 input seawater or concentrated brine, and output water vapor and concentrated brine; the concentrated brine output by each flash evaporation unit 2 is used as the input water of the next flash evaporation unit 2;

[0058] The concentrated brine output by the multi-stage flash evaporation module 001 enters the crystallization module 002 for further concentration, and then water vapor and crystallized brine are obtained, and the water vapor enters the forced circulation module 003 for condensation to obtain fresh water;

[0059] The forced circulation module 003 generates negative pressure to provide a negative pressure environment inside the crystallization module 002, and promotes the flow of water vapor to the forced circulation module 003.

[0060] Specifically, the crystallized brine is separated by brine separation to obtain salt crystals and crystallized separation water.

[0061] Preferably, the water vapor flashed out by the flash unit 2 and the seawater inlet of the multi-stage flash module 001 are subjected to heat exchange treatment.

[0062] The multi-stage flash module 001 further comprises a steam cooling device 1, and the water vapor flashed out by the flash unit 2 and the seawater inlet of the multi-stage flash module 001 are subjected to heat exchange treatment in the steam cooling device 1.

[0063] Specifically, each flash unit 2 in the multi-stage flash module 001 independently undergoes a "pressurized heating-depressurized flashing" process: the flash unit 2 is pressurized to more than one atmosphere, and the salt-containing water inside the flash unit 2 is heated to more than 100°C, and the salt-containing water does not boil under the pressure; the pressure is reduced, the salt-containing water boils, and part of the steam carries a large amount of latent heat of vaporization, completing the depressurized flashing and realizing the separation of water and salt-containing water; at the same time, the concentrated salt-containing water after flashing is used as the inlet liquid of the next stage of flash unit, wherein the inlet liquid of the first stage of flash unit is seawater, and the salt-containing water discharged from the last stage of flash unit is used as the concentrated brine output by the multi-stage flash module 001; at the same time, the water vapor flashed out enters the steam cooling device 1 and is condensed into fresh water, which is collected and utilized.

[0064] Specifically, the forced circulation module 003 generates negative pressure by a physical method.

[0065] Specifically, the forced circulation module 003 comprises a vacuum pump or a water absorption medium.

[0066] Specifically, the negative pressure suction by the vacuum pump provides a negative pressure environment inside the crystallization module 002, and promotes the flow of water vapor to the forced circulation module 003.

[0067] Specifically, the water absorption medium absorbs the water vapor evaporated from the crystallization module 002 to provide a negative pressure environment above the liquid level of the crystallization module 002, and promotes the flow of water vapor to the forced circulation module 003; by heating the water absorption medium after water absorption, regenerated water vapor is obtained, and the water vapor is further condensed to obtain fresh water.

[0068] Specifically, the forced circulation module 003 comprises a water vapor condensing unit 15. The water vapor condensing unit 15 condenses the regenerated water vapor obtained by heating and decomposing the water vapor sucked by the vacuum pump or the water absorption medium to obtain fresh water.

[0069] Specifically, to complete the circulation of the water absorption medium, the forced circulation module 003 further comprises an adsorption unit 11, a desorption unit 12 and a water absorption medium pump 14; the adsorption unit 11 is in gas communication with the crystallization module 002; the adsorption unit 11 and the desorption unit 12 are in communication through two one-way pipelines, at least one of which is provided with the water absorption medium pump 14; the desorption unit 12 is provided with a heating device and is in gas communication with a water vapor condensation unit 15.

[0070] Specifically, the water absorption medium in the adsorption unit 11 combines with the water vapor in the crystallization module 002 and generates negative pressure, which reduces the saturated vapor pressure of the surface of the concentrated brine in the crystallization module 002, so that the water in the concentrated brine boils below 100℃, and the separation of the brine is completed; the water absorption medium that has completed water absorption is forced to circulate to the desorption unit 12, and the water absorption medium completes dehydration under the action of the heating device, generating a low-water-content regenerated water absorption medium solution and regenerated water vapor, realizing the regeneration of the water absorption medium, which returns to the adsorption unit 11 through the water absorption medium pump 14, and the regenerated water vapor further enters the water vapor condensation unit 15 for condensation and recovery.

[0071] Preferably, only one of the one-way pipelines is provided with the water absorption medium pump 14, and the water absorption medium that has completed water absorption enters the desorption unit 12 from the adsorption unit 11 under the action of gravity, and after completing dehydration in the desorption unit 12, returns to the adsorption unit 11 through the water absorption medium pump 14.

[0072] Preferably, the water absorption medium that has completed water absorption and the regenerated water absorption medium solution are subjected to at least one heat recovery treatment.

[0073] Specifically, the water absorption medium that has completed water absorption and the regenerated water absorption medium solution that circulates to the adsorption unit 11 are subjected to heat exchange in a heat recovery device, which increases the temperature of the water absorption medium entering the desorption unit 12 and reduces the energy consumption of the heating device.

[0074] In a feasible implementation, as shown in Figure 1 the heating device of the desorption unit 12 can be externally surrounded or internally provided with a heat exchanger.

[0075] It can be understood that the heat source with a temperature greater than 100℃ can heat the water absorption medium to promote the volatilization of water therein and complete the dehydration of the water absorption medium.

[0076] Preferably, the heating device is a tubular heat exchanger that internally heats the water absorption medium.

[0077] It can be understood that waste heat is heat generated in industrial production and is difficult to be completely recovered, and is a low-grade energy source compared with electric energy that can be efficiently used; the present application uses waste heat to replace the electric energy consumed by a vacuum pump, which has the significance of energy saving, consumption reduction and cost reduction.

[0078] In another possible implementation, as shown in FIG. 1, the heating device of the desorption unit 12 can be a solar spectrum modulation device, which can directly heat the water-absorbing medium in the desorption unit 12 after modulating the solar radiation, wherein the solar spectrum modulation device modulates the sunlight radiation, and the proportion of the wavelength of the modulated sunlight radiation is 80% to 95% in the range of 750 nm to 900 nm. Figure 2

[0079] Specifically, the solar spectrum modulation device for directly heating the water-absorbing medium in the desorption unit 12 includes:

[0080] The absorber 16 is a double-layer grating structure, which includes, in sequence according to the direction of light incidence, a photocatalyst layer, a Si grating layer 1602, and a first grating hole 1603 penetrating through the two layers.

[0081] The first modulator 17 is arranged on the back side of the absorber 16, and includes, in sequence according to the direction from near to far relative to the absorber 16, a Ti grating layer 1701, a SiO2 grating layer 1702, a CrF3 grating layer 1703, and a second grating hole 1704 penetrating through the three layers.

[0082] The first modulator 17 modulates the sunlight radiation with a frequency of 750 nm to 900 nm, which can efficiently heat water or salt-containing water.

[0083] For example, the first modulator 17 and the water-absorbing medium are sealed and isolated by using high-transmittance materials such as glass, to prevent the water from affecting the modulation, and the sunlight radiation output by the first modulator 17 is transmitted through the high-transmittance material to directly heat the water-absorbing medium.

[0084] It should be noted that the second grating hole 1704 of the first modulator 17 receives the light radiation emitted by the first grating hole 1603 of the absorber 16, which is mainly infrared radiation, and the penetration ability of the infrared radiation is much stronger than that of ultraviolet and visible light, so the second grating hole 1704 and the first grating hole 1603 do not need to be connected in the light path. In order to reduce the radiation loss of the absorber 16, the first modulator 17 is arranged close to the absorber 16, and direct contact between the two is not a necessary requirement.

[0085] Preferably, the contact area between the first modulator 17 and the absorber 16 is designed to be heat-insulated, to further reduce the radiation loss of the absorber 16.

[0086] ​The prior art does not have a modulation structure with good absorption rate of solar radiation and optimal modulation frequency required for water heating. Compared with the prior art, the present application sets an absorber+modulator structure, uses the absorber to efficiently absorb almost the full spectrum of 400nm-800nm of sunlight, and further uses a specially designed modulator to convert the radiation emitted by the absorber into a 750nm-900nm solar radiation frequency band that is most beneficial to the absorption of water and aqueous solution, thereby improving the energy utilization efficiency of sunlight directly used for water and salt-containing aqueous solution heating.

[0087] Specifically, the photocatalyst layer 1601 includes any one of TiO2, ZnO, and ZrO2.

[0088] Specifically, the ratio of the thickness of the Si grating layer 1602 to the thickness of the photocatalyst layer 1601 in the absorber 16 is 1:0.5-3.

[0089] Specifically, the thickness of the Si grating layer 1602 in the absorber 16 is 0.9-1.8um, the thickness of the photocatalyst layer 1601 is 1.0-2.5um, and the aperture of the first grating hole 1603 is 4-12um.

[0090] It should be noted that when the sunlight radiation is incident on the top TiO2 grating, plasmonic resonance effect can be excited, the aperture of the grating can adjust the excited waveband, and the bottom Si grating together plays a waveguide role to excite a kind of Farber cavity resonance effect, so that the light wave oscillates between the gratings, thereby an absorption peak appears, the solar radiation absorption rate is improved, and the absorption rate can reach 80%-95%, realizing high-efficiency absorption. When the aperture of the first grating hole 1603 is 4-12um, an absorption peak can be generated at 400-800nm under the resonance effect, and almost the full spectrum of solar energy can be utilized.

[0091] Preferably, the first grating hole 1603 is provided with a plurality of holes, and the porosity of the absorber projection surface is 83%-92%. The porosity is helpful to improve the unit plane absorption efficiency. If the porosity is too large, the hole density is high, which affects the resonance effect of the first grating hole 1603, and the absorption rate decreases instead. Meanwhile, if the hole density is too high, the preparation difficulty is greatly increased.

[0092] Specifically, the first modulator 17 includes:

[0093] a CrF3 grating layer 1703;

[0094] a SiO2 grating layer 1702 formed on the top of the CrF3 grating layer 1703;

[0095] a Ti grating layer 1701 formed on the top of the SiO2 grating layer 1702;

[0096] The Ti grating layer 1701, the SiO2 grating layer 1702, and the CrF3 grating layer 1703 are each provided with a through hole penetrating through the top and the bottom thereof, and the through holes of the adjacent grating layers are communicated to form the second grating hole 1704.

[0097] Specifically, the thickness ratio of the CrF3 grating layer 1703, the SiO2 grating layer 1702, and the Ti grating layer 1701 is 1:0.01-200:0.01-200.

[0098] Specifically, the thickness of the CrF3 grating layer is 1.5-300 microns, the thickness of the SiO2 grating layer 1702 is 3-300 microns, and the thickness of the Ti grating layer 1701 is 1.8-300 microns.

[0099] It can be understood that the reason why the output modulated light radiation is concentrated between 750 nm and 900 nm is that the silicon-based grating has a thermal modulation characteristic. The central wavelength of the silicon-based grating is related to the temperature of the silicon grating. Through the heat transfer of the absorber 16, the temperature of the silicon-based grating changes, and the central wavelength of the output spectrum changes at the same time. The Ti metal will also produce a localized surface plasmon resonance at the same time. The CrF3, SiO2, and Ti grating together form a resonant cavity, and the radiation energy is concentrated in the range of 750 nm-900 nm.

[0100] Specifically, the area of the first modulator is m 2 The flow rate of the water-absorbing medium to be heated is m 3 The ratio of m

[0101] Preferably, the first modulator is also provided with a heat-conducting framework that diverges from the central area near the absorber to the side far from the absorber, for uniformly conducting and diverging the sunlight absorbed by the absorber to each area of the first modulator, so as to avoid the rapid heat conduction of the spectral modulator under high heat flux density, and to prevent the local accumulation of heat.

[0102] Preferably, the second grating hole 1704 is provided with a plurality of holes, and the porosity is 83%-92%. A low porosity will reduce the energy density generated by the modulation, while a high porosity will help to improve the unit planar absorption efficiency. However, if the porosity is too high, the hole density will affect the resonance effect of the first grating hole 1603, and the absorption rate will decrease. In addition, poor heat conduction will cause local high-temperature accumulation. At the same time, a too high hole density will greatly increase the difficulty of preparation.

[0103] In a feasible implementation, the seawater desalination system is also provided with a photovoltaic power generation unit 004 for providing electric energy for the seawater desalination system.

[0104] Specifically, the photovoltaic power generation unit 004 includes:

[0105] absorber 16, same as the absorber 16 in the solar spectrum modulation device for directly heating the water-absorbing medium in the desorption unit 12;

[0106] The second modulator comprises, in sequence from near to far relative to the absorber 16, an Ag grating layer 2101, a SiC grating layer 2102, a MgO grating layer 2103, and a third grating hole 2104 penetrating through the three layers;

[0107] The photovoltaic power generation unit 22 generates electricity by receiving the sunlight radiation modulated by the second modulator;

[0108] The energy storage unit 20 stores the electricity generated by the photovoltaic power generation unit 22 and supplies power to the seawater desalination system in the absence of light.

[0109] Specifically, the second modulator comprises:

[0110] The MgO grating layer 2103;

[0111] The SiC grating layer 2102 is formed on the top of the MgO grating layer 2103;

[0112] The Ag grating layer 2101 is formed on the top of the SiC grating layer 2102;

[0113] The Ag grating layer 2101, the SiC grating layer 2102, and the MgO grating layer 2103 are each provided with a through hole penetrating through the top and the bottom thereof, and the through holes of adjacent grating layers are communicated to form the third grating hole 2104.

[0114] Specifically, the third grating hole 2104 is provided with a plurality of holes with a diameter of 4 μm to 12 μm and a porosity of 83% to 92%.

[0115] Specifically, the thickness ratio of each layer of the MgO grating layer 2103, the SiC grating layer 2102, and the Ag grating layer 2101 in the second modulator is 1:0.08-200:0.05-200.

[0116] Specifically, the thickness of the MgO grating layer 2103 is 1.5 μm to 300 μm, the thickness of the SiC grating layer 2102 is 2.5 μm to 300 μm, and the thickness of the Ag grating layer 2101 is 1.5 μm to 300 μm.

[0117] It should be noted that the central wavelength of the SiC grating layer 2102 is related to the temperature of the silicon grating. Through heat transfer of the absorber 16, the temperature of the SiC grating layer 2102 changes, and the output spectrum central wavelength changes at the same time. The MgO grating layer 2103 and the Ag grating layer 2101 will simultaneously produce localized surface plasmon resonance. Under the action of the grating resonant cavity, radiation energy concentrated in 400 nm to 600 nm is generated.

[0118] It should be noted that the third grating hole 2104 of the second modulator receives the light radiation emitted by the first grating hole 1603 of the absorber 16, which is mainly infrared radiation, and the penetration ability of which is much stronger than that of ultraviolet and visible light. Therefore, the third grating hole 2104 and the first grating hole 1603 do not need to be connected in the light path. In order to reduce the radiation loss of the absorber 16, the second modulator is arranged close to the absorber 16, and direct contact between the two is not a necessary requirement.

[0119] Preferably, the contact area between the second modulator and the absorber 16 is designed to be heat-insulating, further reducing the radiation loss of the absorber 16.

[0120] There is no modulation structure in the prior art that has a good absorption rate of solar radiation and can meet the optimal modulation frequency required for crystalline silicon power generation. Compared with the prior art, the present application sets up an absorber + modulator structure, uses the absorber 16 to absorb sunlight efficiently, and further uses a specially designed modulator to convert the radiation emitted by the absorber 16 into a 400nm-600nm solar radiation frequency band that is most beneficial to crystalline silicon power generation, thereby improving the energy utilization efficiency of sunlight directly used for crystalline silicon power generation.

[0121] Preferably, the second modulator is also provided with a heat-conducting framework that diverges from the central area on the side close to the absorber to the side far from the absorber 16, for uniformly conducting and diverging the sunlight absorbed by the absorber to each area of the second modulator, avoiding the rapid heat conduction of the spectral modulator under high heat flux density, and causing local heat accumulation.

[0122] Specifically, the material of the heat-conducting framework in the first modulator and the second modulator includes one or more of copper and aluminum.

[0123] Specifically, the solar spectrum modulation device for directly heating the water-absorbing medium in the desorption unit and the photovoltaic power generation unit 004 further comprises a condenser, which is used to focus sunlight and project it on the solar spectrum modulation device, thereby improving the output power of the solar spectrum modulation device.

[0124] Specifically, the condenser can be a butterfly type or a groove type condenser, and the condensing multiple is 2-50.

[0125] Specifically, the first modulator 17 is further provided with a first shield 18 for adjusting the light intensity between the condenser 19 and the absorber 16; and the second modulator is further provided with a second shield 24 for adjusting the light intensity between the condenser 19 and the absorber 16.

[0126] Specifically, the photovoltaic power generation unit 004 further comprises a third cooler 27 for cooling the photovoltaic power generation unit 22, and the third cooler 27 is in communication with the seawater inlet pipeline of the multi-stage flash module 001,

[0127] Compared with the prior art, the seawater inlet of the multi-stage flash evaporation module 001 absorbs the waste heat of the photovoltaic power generation unit 22 in the third cooler 27 to dissipate the heat energy, thereby reducing the temperature of the photovoltaic power generation unit 22, which helps to keep the photovoltaic power generation unit 22 at a good power generation efficiency, and helps to preheat the multi-stage flash evaporation module 001, thereby reducing the energy consumption of the system.

[0128] Specifically, the water-absorbing medium can be an inorganic lithium salt.

[0129] Preferably, the inorganic lithium salt is one or more of lithium halide, lithium sulfate salt, lithium phosphate salt.

[0130] Preferably, the inorganic lithium salt is one or more of lithium chloride, lithium bromide, lithium iodide, lithium sulfate, lithium dihydrogen phosphate.

[0131] Specifically, the crystallization module 002 comprises a forced circulation evaporator 10 and a brine separation device 8; the concentrated brine generated by the multi-stage flash evaporation module 001 enters the forced circulation evaporator 10, and the concentrated brine is further dehydrated in the forced circulation evaporator 10 to generate crystallized brine; the crystallized brine is separated by the brine separation device 8 to obtain salt crystals and crystallized separation water; and the crystallized separation water flows back to the forced circulation evaporator 10.

[0132] Specifically, the inlet of the forced circulation evaporator 10 also comprises seawater, which is used to dilute the brine when the concentration of the brine in the forced circulation evaporator 10 is too high.

[0133] Preferably, the condensation heat exchange device is arranged in the adsorption unit 11 and the water vapor condensation unit 15, and the condensation heat exchange devices of the two are communicated; the cooling liquid in the condensation heat exchange device and the inlet of the forced circulation evaporator 10 are subjected to at least one heat exchange treatment; the inlet of the forced circulation evaporator 10 is used to cool the water vapor in the water vapor condensation unit 15; the cooling pipelines of the condensation heat exchange devices in the adsorption unit 11 and the water vapor condensation unit 15 are communicated, and the cooling liquid transfers heat in the water vapor condensation unit 15 to the adsorption unit 11 through heat exchange, thereby providing heat for the water-absorbing process of the water-absorbing medium.

[0134] Specifically, the cooling liquid pipeline of the condensation heat exchange device and the inlet pipeline of the forced circulation evaporator 10 are subjected to heat exchange through the first heat exchanger 4, thereby increasing the temperature of the inlet of the forced circulation evaporator 10 and reducing the energy consumption of the forced circulation evaporator 10.

[0135] Specifically, the seawater inlet of the multi-stage flash evaporation module 001 and the cooling liquid in the condensation heat exchange device are subjected to at least one heat exchange treatment.

[0136] Specifically, the cooling liquid pipeline of the condensation heat exchange device and the seawater inlet pipeline of the multi-stage flash evaporation module 001 are subjected to heat exchange through the second heat exchanger 6, thereby increasing the temperature of the seawater inlet of the multi-stage flash evaporation module 001 and reducing the energy consumption of the multi-stage flash evaporation module 001.

[0137] Specifically, the seawater inlet of the multi-stage flash module 001 is selected by the cooling liquid of the steam cooling device 1, and the seawater inlet is heated while the water vapor is condensed, thereby reducing the energy consumption of the multi-stage flash module 001.

[0138] Specifically, the steam cooling device 1 is provided with a plurality of

[0139] Optionally, the steam cooling device 1 is provided in one-to-one correspondence with the flash unit 2, and the water vapor of the flash unit 2 is collected as fresh water after being cooled by the steam cooling device 1.

[0140] Specifically, the water vapor outlet of the flash unit 2 is connected with the first inlet of the steam cooling device 1 to enter the first heat exchange chamber, and the seawater inlet pipeline of the multi-stage flash module 001 is connected with the second inlet of the steam cooling device 1 to enter the second heat exchange chamber; the first heat exchange chamber and the second heat exchange chamber are not communicated, and the water vapor and the seawater inlet are heat-exchanged through the contact surface of the two chambers.

[0141] On the other hand, the present application provides a preparation method of a solar full-spectrum absorber 16 used in the above-mentioned seawater desalination system, which can achieve 80%~95% absorption rate to 400nm to 800nm solar radiation, including the following steps:

[0142] a1: using chemical vapor deposition to prepare a double-layer composite structure with a photocatalyst layer 1601 and a Si grating layer 1602;

[0143] a2: using photoresist to spin-coat on the top or bottom of the double-layer composite structure to prepare a template with a target shape;

[0144] a3: based on the template, dry etching the double-layer composite structure to obtain the absorber 16 with a first grating hole 1603.

[0145] On the other hand, the present application provides a preparation method of a light modulator used in the above-mentioned seawater desalination system, which can convert the solar radiation absorbed by the above-mentioned absorber 16 into radiation with a wavelength mainly of 750nm-900nm, including the following steps:

[0146] b1: using chemical vapor deposition to prepare a three-layer composite structure with a CrF3 layer, a SiO2 layer and a Ti layer arranged in sequence;

[0147] b2: using photoresist to spin-coat on the top or bottom of the three-layer composite structure to prepare a template with a target shape;

[0148] b3: based on the template, dry etching the three-layer composite structure to obtain the light modulator with a second grating hole 1704 and a heat-conducting skeleton filling hole;

[0149] b4: filling the heat-conducting skeleton filling hole with a high-thermal-conductivity material to obtain a final product.

[0150] In another aspect, the present application provides a method for preparing a light modulator for the above-mentioned seawater desalination system, which can convert the solar radiation absorbed by the above-mentioned absorber 16 into radiation with a wavelength mainly between 400 nm and 600 nm, comprising the following steps:

[0151] c1: preparing a three-layer composite structure with sequentially arranged MgO layer, SiC layer and Ag layer by chemical vapor deposition;

[0152] c2: preparing a template with a target shape by spin-coating a photoresist on the top or bottom of the three-layer composite structure;

[0153] c3: obtaining a light modulator with third grating holes and heat-conducting skeleton filling holes by dry etching the three-layer composite structure based on the template;

[0154] c4: filling the heat-conducting skeleton filling hole with a high-thermal-conductivity material to obtain a final product.

[0155] Specifically, the above-mentioned chemical vapor deposition, photoresist and dry etching all adopt methods or products disclosed in the prior art, which are not particularly limited in the present application.

[0156] It should be noted that when the heat-conducting skeleton filling hole is inclined relative to the top and bottom surfaces of the composite structure, the etching angle of the dry etching is adjusted to realize the etching and forming of the heat-conducting skeleton filling hole.

[0157] In another aspect, the present application provides a seawater desalination method using the above-mentioned seawater desalination system, comprising the following steps:

[0158] Step 1: using the water vapor generated by the multi-stage flash module and the water vapor generated by the forced circulation module to preheat the seawater inlet of the multi-stage flash module;

[0159] Step 2: using the multi-stage flash unit to multi-stage flash the preheated seawater to obtain water vapor and concentrated concentrated brine;

[0160] Step 3: using the water vapor generated by the forced circulation module to preheat the concentrated concentrated brine and inputting the preheated concentrated concentrated brine into the crystallization module;

[0161] Step 4: using the forced circulation module to apply negative pressure to the crystallization module, so that the concentrated concentrated brine is separated into brine at a temperature lower than 100℃.

[0162] It can be understood that the above-mentioned steps describe the normal operation stage of the seawater desalination system, and the modules do not generate water vapor during the start-up stage of the seawater desalination system, so they cannot play a preheating role; during the start-up stage, the.

[0163] Specifically, the seawater inlet of the multi-stage flash evaporation module in step 1 is preheated, including:

[0164] S101: The water vapor generated by the multi-stage flash evaporation module exchanges heat through the steam cooling device and the seawater inlet pipeline;

[0165] S102: The condensation heat exchange device is arranged in the adsorption unit and the water vapor condensation unit, the cooling pipelines of the condensation heat exchange devices in the adsorption unit and the water vapor condensation unit are communicated, and the cooling liquid transfers heat from the water vapor condensation unit to the adsorption unit through heat exchange, thereby providing heat for the water absorption process of the water absorption medium;

[0166] S103: The cooling liquid pipeline of the condensation heat exchange device and the seawater inlet pipeline of the multi-stage flash evaporation module exchange heat through the second heat exchanger 6, thereby increasing the seawater inlet temperature of the multi-stage flash evaporation module and reducing the energy consumption of the multi-stage flash evaporation module.

[0167] Specifically, the seawater inlet temperature of the multi-stage flash evaporation module in step 1 is preheated to 90-100℃, and the reason is that the temperature is matched with the circulating water in the heater, thereby reducing the heat exchange temperature difference and energy loss.

[0168] Specifically, the concentration of the concentrated brine in step 2 is 7%-9%, and it should be noted that after the seawater inlet temperature is preheated to 90-100℃, the seawater is concentrated to 7%-9% at most through flash evaporation.

[0169] Specifically, the concentrated brine temperature in step 3 is preheated to 70-90℃, and the reason is that the temperature is matched with the heater temperature, while ensuring that the forced circulation evaporator has a suitable superheat degree, which can reduce the heat exchange loss, while generating sufficient steam to reduce the circulating concentrated water volume.

[0170] Specifically, step 4 applies negative pressure to the crystallization module, including:

[0171] The forced circulation module generates negative pressure to provide a negative pressure environment for the inside of the crystallization module, and promotes the flow of water vapor to the forced circulation module.

[0172] Specifically, the forced circulation module generates negative pressure through a physical method.

[0173] Specifically, the forced circulation module includes a vacuum pump or a water absorption medium.

[0174] Preferably, the forced circulation module includes a water absorption medium, which generates negative pressure by absorbing water vapor, thereby providing a negative pressure environment above the liquid surface of the crystallization module; and by heating the water absorption medium after water absorption, regenerated water vapor is obtained, and the water vapor is further condensed to obtain fresh water.

[0175] Specifically, the water absorption medium can be an inorganic lithium salt.

[0176] Preferably, the inorganic lithium salt is one or more of lithium halide, lithium sulfate salt, lithium phosphate salt.

[0177] Preferably, the inorganic lithium salt is one or more of lithium chloride, lithium bromide, lithium iodide, lithium sulfate, lithium dihydrogen phosphate.

[0178] Specifically, the water absorption medium enters the desorption unit after the water content is 0.55-0.7; and the water absorption medium enters the adsorption unit after being dried to 0.45-0.55 in the desorption unit.

[0179] Specifically, the amount of water absorption medium m 3 The ratio of the seawater flow rate m 3 / h is 0.3-0.55.

[0180] Specifically, the negative pressure is applied to the crystallization module in step 4, including the following steps:

[0181] S401: The water absorption medium in the adsorption unit combines with the water vapor in the crystallization module, and a negative pressure is generated;

[0182] S402: The water absorption medium that has completed water absorption is forced to circulate to the desorption unit, and the water absorption medium completes dehydration under the action of the heating device to generate a low-water-content regenerated water absorption medium solution and regenerated water vapor;

[0183] S403: The regenerated water vapor further enters the water vapor condensation unit and is recovered by condensation.

[0184] Specifically, when the heating device in step 402 uses a solid, liquid or gas containing waste heat to heat and dehydrate the water absorption medium, an external surrounding or built-in heat exchanger is used to heat the desorption unit.

[0185] Specifically, when the heating device in step 402 uses a solar spectrum modulation device, solar radiation can be concentrated by a condenser, and then modulated and processed by the solar spectrum modulation device to obtain solar light with a radiation frequency of 400-800 nm, which is used to directly heat the water absorption medium in the desorption unit.

[0186] Specifically, the salt water separation in step 4 includes the following steps:

[0187] S411: The concentrated salt water generated by the multi-stage flash evaporation module enters the forced circulation evaporator, and the concentrated salt water is further dehydrated in the forced circulation evaporator to generate crystalline salt water;

[0188] S412: The crystalline salt water enters the salt water separation device to separate and obtain crystalline salt and crystalline separation water.

[0189] Specifically, the crystalline separation water can be returned to the forced circulation evaporator, and compared with the prior art, the overall production process does not produce solid waste and exhaust gas, achieving zero emission of exhaust gas, wastewater and solid waste.

[0190] Specifically, the working temperature in the forced circulation evaporator is 60-70℃, and the vacuum degree is 19-32 kPa.

[0191] Specifically, the seawater desalination method further comprises the steps of generating electricity by using a photovoltaic power generation unit and preheating seawater into the multi-stage flash evaporation module 001.

[0192] d1: generating electricity by focusing solar radiation on the photovoltaic power generation unit through a condenser;

[0193] d2: preheating seawater into the multi-stage flash evaporation module by cooling the photovoltaic power generation unit with the third cooler.

[0194] In order to further illustrate the progress of the present application, the following examples and comparative examples are provided:

[0195] Example 1

[0196] This embodiment discloses a seawater desalination system, as shown in the figure, comprising a multi-stage flash evaporation module 001, a crystallization module 002, and a forced circulation module 003. Figure 1

[0197] The multi-stage flash evaporation module 001 comprises a plurality of flash evaporation units 2 connected in series, which input seawater or concentrated brine and output water vapor and concentrated brine; the concentrated brine output by each flash evaporation unit 2 is used as the input water of the next flash evaporation unit 2.

[0198] The concentrated brine enters the crystallization module 002 for further concentration to obtain water vapor and crystallized brine, the water vapor enters the forced circulation module 003 for condensation to obtain fresh water, and the crystallized brine is separated by brine separation to obtain salt crystals and crystallized separation water.

[0199] The forced circulation module 003 generates negative pressure to provide a negative pressure environment inside the crystallization module 002, promoting the flow of water vapor to the forced circulation module 003.

[0200] The forced circulation module 003 comprises an adsorption unit 11, a desorption unit 12, and a water vapor condensation unit 15; the water vapor condensation unit 15 heats and decomposes the water vapor or water absorption medium sucked by the vacuum pump to obtain regenerated water vapor for condensation to obtain fresh water.

[0201] The desorption unit 12 is connected with a heating device, and the desorption unit 12 is heated by the built-in coil.

[0202] The forced circulation module 003 contains a water absorption medium, which absorbs water vapor to generate negative pressure and provides a negative pressure environment above the liquid level of the crystallization module 002; the water absorption medium is heated after water absorption to obtain regenerated water vapor, and the water vapor is further condensed to obtain fresh water.

[0203] ​The water absorption medium which has completed water absorption enters the pipeline of the desorption unit 12, and the regenerated water absorption medium solution circulates to the pipeline of the adsorption unit 11 through a heat exchanger 13 to exchange heat, thereby increasing the temperature of the water absorption medium entering the desorption unit 12 and reducing the energy consumption of the external heating device.

[0204] The heat source of the heating device is a high-temperature steam of 130 DEG C of a chemical industry, and the heating device adopts a tubular heat exchanger to internally heat the water absorption medium; and the water absorption medium is lithium bromide.

[0205] The crystallization module 002 comprises a forced circulation evaporator 10 and a brine separation device 8; the concentrated brine generated by the multi-stage flash evaporation module 001 enters the forced circulation evaporator 10, and the concentrated brine is further dehydrated in the forced circulation evaporator 10 to generate crystallized brine; the crystallized brine is separated by the brine separation device 8 to obtain salt crystals and crystallized separation water; and the crystallized separation water flows back to the forced circulation evaporator 10.

[0206] The condensing heat exchange device is arranged in the adsorption unit 11 and the water vapor condensing unit 15, and the condensing heat exchange devices of the two are communicated; the cooling liquid in the condensing heat exchange device and the liquid inlet of the forced circulation evaporator 10 are subjected to one heat exchange treatment.

[0207] The cooling pipelines of the condensing heat exchange devices in the adsorption unit 11 and the water vapor condensing unit 15 are communicated, and the cooling liquid transfers the heat in the water vapor condensing unit 15 to the adsorption unit 11 through heat exchange, thereby providing heat for the water absorption process of the water absorption medium.

[0208] The cooling liquid pipeline of the condensing heat exchange device and the liquid inlet pipeline of the forced circulation evaporator 10 are subjected to heat exchange through the first heat exchanger 4, thereby increasing the temperature of the liquid inlet of the forced circulation evaporator 10 and reducing the energy consumption of the forced circulation evaporator 10.

[0209] Specifically, the seawater liquid inlet of the multi-stage flash evaporation module 001 and the cooling liquid in the condensing heat exchange device are subjected to one heat exchange treatment.

[0210] The flashed water vapor and the seawater liquid inlet of the multi-stage flash evaporation module 001 are subjected to heat exchange treatment.

[0211] The steam cooling devices 1 are arranged in series and the number of the steam cooling devices 1 is the same as that of the flash evaporation units 2.

[0212] Embodiment 2

[0213] The embodiment discloses a seawater desalination system, as shown in Figure 2 The heating device heat source is changed to a solar spectrum modulation device for directly heating water and salt-containing water compared with the heating device heat source of embodiment 1.

[0214] Embodiment 3

[0215] The embodiment discloses a seawater desalination system, as shown in Figure 2As shown in Figure 2, compared with Example 1, the crystalline silicon photovoltaic power generation unit is added for power supply of the seawater desalination system, and an electric heating device is arranged in the desorption unit, so that the electric energy in the energy storage unit can be used to heat and dehydrate the water-absorbing medium.

[0216] Example 4

[0217] This example discloses a seawater desalination system, in which the forced circulation module 003 of Example 1 is replaced by a vacuum pump.

[0218] Example 5

[0219] This example discloses a solar spectrum modulation device for directly heating water and salt-containing water, which is used in Example 2, as shown in Figure 3, and comprises: Figure 2 、 Figure 3 、 Figure 4 As shown in Figure 3, the solar spectrum modulation device comprises:

[0220] The absorber 16 is a double-layer grating structure, which comprises, in sequence according to the incident direction of light, a photocatalyst layer 1601, a Si grating layer 1602, and a first grating hole 1603 penetrating through the two layers.

[0221] The first modulator 17 is arranged on the side away from the light of the absorber 16, and comprises, in sequence from the side close to the absorber 16 to the side away from the absorber 16, a Ti grating layer 1701, a SiO2 grating layer 1702, a CrF3 grating layer 1703, and a second grating hole 1704 penetrating through the three layers.

[0222] The photocatalyst layer 1601 is TiO2; the Si grating layer 1602 in the absorber 16 has a thickness of 0.9 μm, the photocatalyst layer 1601 has a thickness of 1.0 μm, the first grating hole 1603 has an aperture of 4 μm, and the absorber 16 has a porosity of 83%.

[0223] The CrF3 grating layer 1703 has a thickness of 1.5 μm, the SiO2 grating layer 1702 has a thickness of 3 μm, the Ti grating layer 1701 has a thickness of 1.8 μm, and the second grating hole 1704 has a porosity of 83%.

[0224] The condenser 19 is a butterfly condenser 19, and the condensing multiple is 10.

[0225] The first modulator 17 is further provided with a heat-conducting framework, which diverges from the central area on the side close to the absorber 16 to the side away from the absorber 16, and is used to uniformly conduct and diverge the sunlight absorbed by the absorber 16 to each area of the first modulator 17, so as to avoid the rapid heat conduction of the spectrum modulator under high heat flux density, and to avoid the local accumulation of heat due to the non-uniform temperature of the spectrum modulator.

[0226] The absorber 16 has a measured absorption rate of 85% or more for 400-800 nm solar radiation, and the first modulator 17 has an output radiation ratio of 88% or more in the wavelength range of 750-900 nm.

[0227] Embodiment 6

[0228] This embodiment discloses a solar spectrum modulation device for directly heating water and salt-containing water, as shown in Figure 2 、 Figure 3 、 Figure 4 , which comprises:

[0229] The absorber 16 is a double-layer grating structure, comprising a photocatalyst layer 1601, a Si grating layer 1602, and a first grating hole 1603 penetrating both, arranged in sequence according to the incident direction of light.

[0230] The first modulator 17 is arranged on the back side of the absorber 16, comprising a Ti grating layer 1701, a SiO2 grating layer 1702, a CrF3 grating layer 1703, and a second grating hole 1704 penetrating all three, arranged in sequence from near to far relative to the absorber 16.

[0231] The photocatalyst layer 1601 is ZnO; the Si grating layer 1602 in the absorber 16 has a thickness of 1.8 μm, the photocatalyst layer 1601 has a thickness of 2.5 μm, and the first grating hole 1603 has a hole diameter of 12 μm; the porosity of the absorber 16 is 92%.

[0232] The CrF3 grating layer 1703 has a thickness of 300 μm, the SiO2 grating layer 1702 has a thickness of 300 μm, the Ti grating layer 1701 has a thickness of 300 μm; the second grating hole 1704 has a porosity of 92%.

[0233] The condenser 19 is a groove condenser 19, and the condensing multiple 20.

[0234] The first modulator 17 is also provided with a heat-conducting framework, which diverges from the central area on the side near the absorber 16 to the side far from the absorber 16, for uniformly conducting and diverging the sunlight absorbed by the absorber 16 to each area of the first modulator 17, avoiding the rapid heat conduction of the spectrum modulator under high heat flux density, resulting in local accumulation of heat. (The drawing in the specification is not shown)

[0235] The absorber 16 has a measured absorption rate of 62% for 400-800 nm solar radiation, and the first modulator 17 has an output radiation ratio of 87% in the wavelength range of 750-900 nm.

[0236] Embodiment 7

[0237] This embodiment discloses a solar spectrum modulation device for directly heating water and salt-containing water, as shown in Figure 2、 Figure 3 、 Figure 4 As shown in the figure, it comprises:

[0238] The absorber 16 is a double-layer grating structure, comprising a photocatalyst layer 1601, a Si grating layer 1602 and a first grating hole 1603 penetrating through the two layers, arranged in sequence according to the incident direction of light;

[0239] The first modulator 17 is arranged on the back side of the absorber 16, comprising a Ti grating layer 1701, a SiO2 grating layer 1702, a CrF3 grating layer 1703 and a second grating hole 1704 penetrating through the three layers, arranged in sequence from near to far relative to the absorber 16.

[0240] The photocatalyst layer 1601 is ZrO2; the thickness of the Si grating layer 1602 in the absorber 16 is 1.5 μm, the thickness of the photocatalyst layer 1601 is 2.0 μm, and the aperture of the first grating hole 1603 is 8 μm; the porosity of the absorber 16 is 88%.

[0241] The thickness of the CrF3 grating layer 1703 is 100 μm, the thickness of the SiO2 grating layer 1702 is 100 μm, the thickness of the Ti grating layer 1701 is 200 μm; the porosity of the second grating hole 1704 is 89%.

[0242] The condenser 19 is a groove condenser 19, and the condensing multiple is 30.

[0243] The first modulator 17 is also provided with a heat-conducting framework, which diverges from the central area on the side close to the absorber 16 to the side far from the absorber 16, for uniformly conducting and diverging the sunlight absorbed by the absorber 16 to each area of the first modulator 17, so as to avoid the rapid heat conduction of the spectral modulator under high heat flux density, and the local accumulation of heat, which causes the temperature to be uniform.

[0244] It is measured that the absorber 16 has a 71% absorption rate for 400 nm to 800 nm sunlight radiation, and the output radiation of the first modulator 17 accounts for 95% in the wavelength range of 750 nm to 900 nm.

[0245] In the embodiments 6 and 7, the photocatalyst layer is selected to be ZnO and ZrO2 instead of TiO2 in the embodiment 5, and the absorber has a certain decrease in absorption rate.

[0246] Embodiment 8

[0247] The embodiment discloses a crystalline silicon photovoltaic power generation unit, which is used in the embodiment 3, as shown in the figure, comprising: Figure 2 、 Figure 3 、 Figure 5 As shown in the figure, it comprises:

[0248] The absorber 16 is a double-layer grating structure, which comprises a photocatalyst layer 1601, a Si grating layer 1602 and a first grating hole 1603 penetrating through the two layers in sequence according to the incident direction of light;

[0249] The second modulator comprises an Ag grating layer 2101, a SiC grating layer 2102, an MgO grating layer 2103 and a third grating hole 2104 penetrating through the three layers in sequence from the near to the far direction relative to the absorber 16;

[0250] The photovoltaic power generation unit 22 is a crystalline silicon photovoltaic module.

[0251] The energy storage unit 20 is a battery pack.

[0252] The photocatalyst layer 1601 is TiO2; the thickness of the Si grating layer 1602 in the absorber 16 is 0.9 μm, the thickness of the photocatalyst layer 1601 is 1.0 μm, the aperture of the first grating hole 1603 is 4 μm; and the porosity of the absorber 16 is 83%.

[0253] The third grating hole 2104 is provided with a plurality of holes with an aperture of 4 μm and a porosity of 83%; the thickness of the MgO grating layer 2103 is 1.5 μm, the thickness of the SiC grating layer 2102 is 2.5 μm, and the thickness of the Ag grating layer 2101 is 1.5 μm.

[0254] A condenser 19 is further provided, which is a groove condenser 19 with a condensing multiple of 30.

[0255] The second modulator is further provided with a heat-conducting framework, which is divergent from the central area of the side close to the absorber 16 to the side far from the absorber 16, and is used for uniformly conducting and diverging the sunlight absorbed by the absorber 16 to each area of the second modulator, so as to avoid the local accumulation of heat under the condition of high heat flux density and the rapid heat conduction of the spectral modulator to produce a uniform temperature.

[0256] It is measured that the absorber 16 has an absorption rate of 85% for the sunlight radiation of 400 nm to 800 nm, and the proportion of the output radiation of the second modulator in the wavelength range of 400 nm to 600 nm is 84%.

[0257] Embodiment 9

[0258] The embodiment discloses a crystalline silicon photovoltaic power generation unit 004, which comprises: Figure 2 、 Figure 3 、 Figure 5 as shown in the drawings, comprising:

[0259] The absorber 16 is a double-layer grating structure, which comprises a photocatalyst layer 1601, a Si grating layer 1602 and a first grating hole 1603 penetrating through the two layers in sequence according to the incident direction of light;

[0260] The second modulator comprises, in sequence from the near to the far direction relative to the absorber 16, an Ag grating layer 2101, an SiC grating layer 2102, an MgO grating layer 2103, and a third grating hole 2104 penetrating through the three layers;

[0261] The photovoltaic power generation unit 22 is a crystalline silicon photovoltaic module.

[0262] The energy storage unit 20 is a battery pack.

[0263] The photocatalyst layer 1601 is TiO2; the Si grating layer 1602 in the absorber 16 has a thickness of 1.8 μm, the photocatalyst layer 1601 has a thickness of 2.5 μm, and the first grating hole 1603 has a hole diameter of 12 μm; and the absorber 16 has a porosity of 92%.

[0264] The third grating hole 2104 is provided with a plurality of holes, each having a hole diameter of 12 μm and a porosity of 83%; the MgO grating layer 2103 has a thickness of 300 μm, the SiC grating layer 2102 has a thickness of 300 μm, and the Ag grating layer 2101 has a thickness of 300 μm.

[0265] The concentrator 19 is also provided, and the concentrator 19 is a groove-type concentrator 19 with a concentration ratio of 10.

[0266] The second modulator is also provided with a heat-conducting framework that diverges from the central area on the side close to the absorber 16 to the side far from the absorber 16, and is used to uniformly conduct and diverge the sunlight absorbed by the absorber 16 to each area of the second modulator, so as to avoid the rapid heat conduction of the spectral modulator under high heat flux density, and to prevent the local accumulation of heat.

[0267] It is measured that the absorber 16 has a solar radiation absorption rate of 88% for 400 nm to 800 nm, and the second modulator has an output radiation proportion of 87% in the wavelength range of 400 nm to 600 nm.

[0268] Embodiment 10

[0269] The embodiment discloses a crystalline silicon photovoltaic power generation unit 004, as shown in Figure 2 、 Figure 3 、 Figure 5 The embodiment discloses a crystalline silicon photovoltaic power generation unit 004, as shown in

[0270] The absorber 16 is a double-layer grating structure, comprising, in sequence from the light incidence direction, a photocatalyst layer 1601, an Si grating layer 1602, and a first grating hole 1603 penetrating through the two layers.

[0271] The second modulator comprises, in sequence from the near to the far direction relative to the absorber 16, an Ag grating layer 2101, an SiC grating layer 2102, an MgO grating layer 2103, and a third grating hole 2104 penetrating through the three layers.

[0272] The photocatalyst layer 1601 is TiO2; the Si grating layer 1602 in the absorber 16 has a thickness of 1.5 μm, the photocatalyst layer 1601 has a thickness of 2.0 μm, and the first grating hole 1603 has an aperture of 8 μm; the absorber 16 has a porosity of 88%.

[0273] The third grating hole 2104 is provided with a plurality of holes, each having an aperture of 8 μm and a porosity of 90%; the MgO grating layer 2103 has a thickness of 200 μm, the SiC grating layer 2102 has a thickness of 200 μm, and the Ag grating layer 2101 has a thickness of 180 μm.

[0274] A condenser 19 is further provided, which is a trough-shaped condenser 19, and the condensing multiple is 20.

[0275] The second modulator is further provided with a heat-conducting framework that diverges from the central area on the side close to the absorber 16 to the side far from the absorber 16, and is used to evenly conduct and diverge the sunlight absorbed by the absorber 16 to each area of the second modulator, so as to avoid the rapid heat conduction of the spectral modulator under high heat flux density, and the local accumulation of heat.

[0276] It is measured that the absorber 16 has a solar radiation absorption rate of 92% for 400 nm to 800 nm, and the second modulator output radiation accounts for 93% in the wavelength range of 400 nm to 600 nm.

[0277] The absorber absorption rate test in Examples 5-10 is calculated by removing the reflected energy of the illumination surface of the absorber from the solar radiation energy per unit area; the wavelength range of the output radiation of the first modulator and the second modulator is measured by using a spectrum analyzer.

[0278] Conclusion:

[0279] The absorber prepared in Examples 5-10 has a solar radiation absorption rate of 62% to 92% for 400 nm to 800 nm, and the absorber with TiO2 as the photocatalyst layer has a solar radiation absorption rate of 85% to 92% for 400 nm to 800 nm;

[0280] The first modulator output radiation accounts for 87% to 95% in the wavelength range of 750 nm to 900 nm;

[0281] The second modulator output radiation accounts for 84% to 93% in the wavelength range of 400 nm to 600 nm.

[0282] Example 11

[0283] The present embodiment discloses a seawater desalination method, which uses the seawater desalination system described in Example 1, as shown in the figure, comprising the following steps: Figure 1

[0284] ​The seawater is preheated by the steam cooling device 1, and then enters the second heat exchanger 6 to be heated to 100℃, and then enters the multi-stage flash evaporation unit 2 to be concentrated to 7%, and then enters the first heat exchanger 4 to be heated to 90℃, and then enters the forced circulation evaporator 10 (the working temperature of the forced circulation evaporator 10 is 70℃), and then the concentrated brine and salt particles enter the brine separation device 8 for separation, and then the concentrated brine is mixed with the brine flowing out of the last-stage flash evaporation unit 2 in front of the first heat exchanger 4 under the action of the brine pump 7, and the waste heat of the brine flowing out of the forced circulation evaporator 10 is fully utilized.

[0285] The steam generated by the multi-stage flash evaporation unit 2 enters the steam cooling device 1 to be condensed, and at the same time, the seawater entering the steam cooling device 1 is sequentially heated by the waste heat, and finally collected by the product water pump 5.

[0286] The steam generated by the forced circulation evaporator 10 enters the adsorption unit 11 and is mixed with the concentrated lithium bromide solution, and the vacuum effect generated thereby can maintain the vacuum environment required by the forced circulation evaporator 10. The diluted lithium bromide solution enters the desorption unit 12 through the regenerator 13, the desorption unit 12 is connected to a 130℃ steam source, and the lithium bromide solution is dehumidified, and the concentrated lithium bromide solution generated thereby is mixed with the steam generated by the forced circulation evaporator 10 through the regenerator 13 under the action of the water medium pump 14, and the steam generated thereby enters the water vapor condensation unit 15 to be condensed into product water.

[0287] The circulating water system, under the action of the circulating water pump 9, absorbs the heat of the steam in the water vapor condensation unit 15, and then enters the second heat exchanger 6 to heat the seawater preheated by the steam cooling device, and then enters the first heat exchanger 4 to heat the concentrated brine about to enter the forced circulation evaporator 10, and then the circulating water enters the adsorption unit 11 to provide heat for the lithium bromide absorption process, and then the circulating water enters the water vapor condensation unit 15 to complete a cycle. The seawater is preheated by the steam cooling device 1, and then enters the second heat exchanger 6 for secondary preheating.

[0288] Example 12

[0289] The embodiment discloses a seawater desalination method, which uses the seawater desalination system described in Example 2, as shown in the figure, the difference from Example 11 is that the following steps are included: Figure 2

[0290] The desorption unit 12 of Example 11 is connected to a 130℃ steam source to dehumidify the lithium bromide solution, which is replaced by using the solar spectrum modulation device of Example 1 to modulate and process the solar radiation to obtain a wavelength of 400nm-800nm radiation to directly heat the lithium bromide solution.

[0291] Example 13

[0292] ​The present example discloses a seawater desalination method, using the seawater desalination system described in Example 3, the difference from Example 12 is that it further comprises the following steps:

[0293] The photovoltaic power generation unit of Example 8 is used to generate electricity, store electricity, and electrically heat the desorption unit for dehydration.

[0294] Comparative Example 1

[0295] Compared with Example 5, no modulation device is provided for directly heating the water-absorbing medium, and the light-absorbing unit is directly irradiated after being concentrated by the light concentrator, and the rest is the same as Example 5.

[0296] Comparative Example 2

[0297] Compared with Example 8, the photovoltaic power generation unit does not have an absorber and a second modulator, and the photovoltaic power generation unit is directly irradiated after being concentrated by the light concentrator, and the rest is the same as Example 8.

[0298] Comparative Example 3

[0299] Compared with Example 5, the first grating hole aperture is set to 15 μm, and the rest is the same as Example 5. The measured absorption rate of the absorber to 400 nm to 800 nm solar radiation is 76%.

[0300] Comparative Example 4

[0301] Compared with Example 5, the first grating hole aperture is set to 2 μm, and the rest is the same as Example 5. The measured absorption rate of the absorber to 400 nm to 800 nm solar radiation is 69%.

[0302] As can be seen from Comparative Example 5, Comparative Example 3 and Comparative Example 4, the absorption rate of the absorber to 400 nm to 800 nm solar radiation will decrease if the first grating hole aperture is too large or too small.

[0303] Comparative Example 5

[0304] Compared with Example 5, the second grating hole aperture is set to 15 μm, and the rest is the same as Example 5. The first modulator output radiation energy ratio in 750 nm to 900 nm is 84%.

[0305] Comparative Example 6

[0306] Compared with Example 5, the second grating hole aperture is set to 2 μm, and the rest is the same as Example 5. The first modulator output radiation energy ratio in 750 nm to 900 nm is 79%.

[0307] As can be seen from Comparative Example 5, Comparative Example 5 and Comparative Example 6, the first modulator output radiation energy ratio in 750 nm to 900 nm will decrease if the second grating hole aperture is too large or too small.

[0308] Comparative Example 7

[0309] The third grating hole aperture is set to 15 μm, and the rest is the same as in Example 8. The second modulator has a radiation energy percentage of 75% at 400 nm to 600 nm.

[0310] Comparative Example 8

[0311] The third grating hole aperture is set to 2 μm, and the rest is the same as in Example 8. The second modulator has a radiation energy percentage of 83% at 400 nm to 600 nm.

[0312] From Comparative Examples 8, Comparative Example 7 and Comparative Example 8, it can be seen that too large or too small third grating hole apertures will result in a decrease in the radiation energy percentage of the second modulator output radiation at 400 nm to 600 nm. Too small third grating hole apertures will increase the manufacturing difficulty and are less economical.

[0313] Experimental Example 1

[0314] Example 5 and Comparative Example 1 were measured using the seawater desalination system described in Example 2 and the operating method described in Example 12. The 1 m 3 lithium bromide aqueous solution, at 0.25 m 2 Under direct heating of sunlight at the solar focusing area (concentration ratio 10), the time for the water content to decrease from 0.7 to 0.45 was 3 min and 10 min, respectively.

[0315] Test Conclusion: From Comparative Example 5 and Comparative Example 1, it can be seen that the addition of the first modulator can significantly improve the heating efficiency of the water absorbing medium under direct heating of sunlight.

[0316] Experimental Example 2

[0317] Example 8 and Comparative Example 2 were measured using the seawater desalination system described in Example 3 and the operating method described in Example 13. The 0.25 m 2 Under direct heating of sunlight at the solar focusing area (concentration ratio 30), the power generation of the photovoltaic power generation unit was 32.1 KW·h and 8.2 KW·h, respectively, in 24 h (crystalline silicon component power generation efficiency about 20%, actual illumination time 8 h).

[0318] Test Conclusion:

[0319] From Comparative Example 8 and Comparative Example 2, it can be seen that the addition of the second modulator can significantly improve the power generation efficiency of the crystalline silicon photovoltaic component.

[0320] The above description is only the preferred specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any change or replacement within the technical range disclosed by the present application can be easily thought of by those skilled in the art, and should be covered within the protection scope of the present application.

Claims

1. A sea water desalination system, characterized by, The system comprises a multi-stage flash module, a crystallization module, and a forced circulation module. The concentrated brine of the multi-stage flash module is communicated with the crystallization module, and the water vapor of the crystallization module is communicated with the forced circulation module. The concentrated brine of the multi-stage flash module is separated to obtain water vapor in the crystallization module, and enters the forced circulation module under the negative pressure provided by the forced circulation module. The forced circulation module comprises a water absorption medium, which absorbs the water vapor volatilized from the crystallization module to provide a negative pressure environment in the crystallization module, and promotes the flow of the water vapor to the forced circulation module. The water absorption medium is an inorganic lithium salt, and the working temperature in the forced circulation evaporator is 60-70℃, and the vacuum degree is 19-32kPa. The forced circulation module further comprises an adsorption unit, a desorption unit, and a water absorption medium pump. The heating device is a solar spectrum modulation device. The solar spectrum modulation device comprises: An absorber, which is a double-layer grating structure and comprises a photocatalyst layer, a Si grating layer, and first grating holes penetrating through the two layers arranged in sequence according to the incident direction of light; A first modulator arranged on the back side of the absorber and comprising a Ti grating layer, a SiO2 grating layer, a CrF3 grating layer, and second grating holes penetrating through the three layers arranged in sequence from near to far relative to the absorber; The proportion of the output radiation wavelength in the range of 750-900nm after the modulation of the first modulator is 80%-95%.

2. The system for desalination of seawater according to claim 1, characterized in that, The adsorption unit and the crystallization module are communicated through a gas path, and the adsorption unit and the desorption unit are communicated through two one-way pipelines, at least one of which is provided with a water absorption medium pump.

3. The system for desalination of seawater according to claim 1, characterized in that, The photocatalyst layer comprises any one of TiO2, ZnO, and ZrO2.

4. The system for desalination of seawater according to claim 1, characterized in that, The aperture of the first grating hole is 4-12μm.

5. The system for desalination of seawater according to claim 1, characterized in that, The first grating hole is provided with a plurality of holes, and the porosity of the projection surface of the absorber is 83%-92%.

6. The system for desalination of seawater according to claim 1, characterized in that, The first modulator comprises: A CrF3 grating layer; A SiO2 grating layer formed on the top of the CrF3 grating layer; A Ti grating layer formed on the top of the SiO2 grating layer; The Ti grating layer, the SiO2 grating layer, and the CrF3 grating layer are all provided with through holes penetrating through the top and bottom of each grating layer, and the through holes of adjacent grating layers are communicated to form the second grating holes.

7. A method of desalination of sea water, characterized in that, The seawater desalination system of any one of claims 1-6 is used.

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