A method of desalination of seawater

Abstract

The present application relates to the technical field, especially to a seawater desalination method, comprising using water vapor generated by a multi-stage flash module and water vapor generated by a forced circulation module to preheat seawater liquid into the multi-stage flash module; using a multi-stage flash unit to multi-stage flash the preheated seawater, to obtain water vapor and concentrated concentrated brine; using water vapor generated by the forced circulation module to preheat the concentrated concentrated brine and input the preheated concentrated concentrated brine into a crystallization module; using the forced circulation module to apply negative pressure to the crystallization module, so that the concentrated concentrated brine realizes brine separation below 100 DEG C. The use of the forced circulation evaporator and the subsequent steam to heat the flash water reduces the overall energy consumption, realizes zero discharge of waste water and waste gas; the use of the sunlight modulation technology improves the solar energy utilization rate, and compared with mechanical forced circulation, can greatly reduce the power consumption and reduce the overall energy consumption.

Description

TECHNICAL FIELD

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

[0002] The multi-stage flash evaporation seawater desalination technology is to heat raw seawater to a certain temperature and then introduce it into a flash evaporation chamber. Since 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 will rapidly partially gasify when it enters the flash evaporation chamber due to overheating, thereby reducing the temperature of the hot brine. The condensed steam is the required fresh water. The concentrated seawater is introduced into the subsequent flash evaporation chambers to reduce the pressure stage by stage, so that it flash evaporates and then condenses 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, one feasible solution 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 solution 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 combined with a forced steam discharge device (for example, a flash evaporation process), and has the 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. However, the use of secondary energy sources or solar energy in seawater desalination still has the following defects:

[0005] On the one hand, 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, resulting in low energy utilization efficiency of secondary energy sources;

[0006] On the other hand, the main ways of utilizing solar energy are 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, which is the main energy band of solar radiation, by 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 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 purpose of the present application is mainly achieved by the following technical solutions:

[0010] The present application provides a seawater desalination method, comprising:

[0011] The seawater or concentrated brine is input into the multi-stage flash evaporation module, and water vapor and concentrated brine are output; and the concentrated brine output by each stage of the flash evaporation unit is input into the next stage of the flash evaporation unit as the input water;

[0012] The concentrated brine output by the multi-stage flash evaporation module is input into the crystallization module for further concentration, and water vapor is obtained; the water vapor is input into the forced circulation module for condensation to obtain fresh water;

[0013] The negative pressure generated by the forced circulation module provides a negative pressure environment for the inside of the crystallization module, promoting the flow of water vapor to the forced circulation module.

[0014] Preferably, the seawater desalination method comprises:

[0015] Step 1, using the water vapor generated by the multi-stage flash evaporation module and the water vapor generated by the forced circulation module to preheat the seawater input into the multi-stage flash evaporation module;

[0016] Step 2, using the multi-stage flash evaporation unit to multi-stage flash evaporate the preheated seawater to obtain water vapor and concentrated brine;

[0017] Step 3, using the water vapor generated by the forced circulation module to preheat the concentrated brine and input the preheated concentrated brine into the crystallization module;

[0018] Step 4, using the forced circulation module to apply negative pressure to the crystallization module, so that the concentrated brine is separated at a temperature below 100 DEG C.

[0019] Preferably, the forced circulation module generates negative pressure by physical method; preferably, the forced circulation module comprises a vacuum pump or a water absorption medium; preferably, the forced circulation module comprises a water absorption medium, which generates negative pressure by absorbing water vapor, and provides a negative pressure environment above the liquid surface of the crystallization module; 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.

[0020] Preferably,

[0021] Step 4 of applying negative pressure to the crystallization module comprises:

[0022] S401: The water absorption medium in the adsorption unit combines with water vapor in the crystallization module, and negative pressure is generated;

[0023] 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;

[0024] S403: The regenerated water vapor further enters the water vapor condensation unit and is condensed for recovery.

[0025] Preferably, the water absorption medium is an inorganic lithium salt, preferably one or more of lithium halide, lithium sulfate salt, lithium phosphate salt, preferably one or more of lithium chloride, lithium bromide, lithium iodide, lithium sulfate, lithium dihydrogen phosphate.

[0026] Preferably, the heat source of the heating device is a solid, liquid or gas with a temperature greater than 100°C, or the heating device is a solar spectrum modulation device that outputs radiation with a wavelength in the range of 750nm to 900nm at a proportion of 80% to 95% after modulation processing.

[0027] Preferably, the water absorption medium enters the desorption unit after being absorbed to a water content of 0.55 to 0.7, and the water absorption medium enters the adsorption unit after being dried to 0.45 to 0.55.

[0028] Preferably,

[0029] The seawater desalination method comprises:

[0030] S101: The water vapor generated by the multi-stage flash evaporation module is heat-exchanged through a steam cooling device and a seawater inlet pipeline to achieve heat exchange;

[0031] S102: The cooling pipeline of the condensation heat exchange device in the adsorption unit and the water vapor condensation unit is connected, and the cooling liquid transfers heat in the water vapor condensation unit to the adsorption unit through heat exchange to provide heat for the water absorption process of the water absorption medium;

[0032] S103: The cooling liquid pipeline of the condensation heat exchange device and the seawater inlet pipeline of the multi-stage flash evaporation module are heat-exchanged through a second heat exchanger to increase the seawater inlet temperature of the multi-stage flash evaporation module and reduce the energy consumption of the multi-stage flash evaporation module.

[0033] Preferably, the seawater inlet temperature of the multi-stage flash evaporation module in step 1 is preheated to 90°C to 100°C, and the mass concentration of the concentrated brine in step 2 is 7% to 9%.

[0034] Preferably, the concentrated brine temperature in step 3 is preheated to 70°C to 90°C.

[0035] Compared with the prior art, the present application can at least achieve one of the following beneficial effects:

[0036] (1) The present application combines a forced circulation evaporator with a multi-stage flash evaporation, and the forced circulation evaporator realizes water and salt resource utilization of the flash concentrated brine, solves the pollution of the direct discharge of the flash concentrated brine to the environment, and simultaneously utilizes the forced circulation evaporator and the subsequent steam to heat the flash water, thereby reducing the overall energy consumption and realizing zero discharge of waste water and waste gas.

[0037] (2) The present application uses the water absorption medium to absorb water vapor to generate negative pressure, and provides a negative pressure environment above the liquid surface of the crystallization module instead of mechanical forced circulation; the water absorption medium is heated after water absorption 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; the water absorption medium can be heated after water absorption, and the heating medium can be waste heat, gas or liquid or renewable solar energy, so that the low-grade heat in the waste heat can be fully utilized, and the electric energy consumption can be greatly reduced compared with the mechanical forced circulation, thereby achieving the purpose of energy saving.

[0038] (3) The present application uses a solar spectrum modulation device to directly heat the water absorption medium after absorbing sunlight, and the absorber in the solar spectrum modulation device realizes high-efficiency absorption of solar radiation with a wavelength of 400nm-800nm, and the modulator can obtain radiation with a wavelength of 750nm-900nm after modulating the solar radiation, thereby realizing high-efficiency direct heating of the water absorption medium in the desorption unit, and improving the defect that the existing technology directly uses sunlight to heat water and salt-containing water solution with low efficiency.

[0039] (4) The present application uses a solar spectrum modulation device to modulate the absorbed sunlight into a radiation frequency corresponding to the optimal power generation efficiency of a crystalline silicon photovoltaic module, and the absorber in the solar spectrum modulation device realizes high-efficiency absorption of solar radiation with a wavelength of 400nm-800nm, and the modulator can obtain radiation with a wavelength of 400nm-600nm after modulating the solar radiation, thereby realizing high-efficiency utilization of solar radiation by the crystalline silicon photovoltaic module; at the same time, the seawater inlet of the seawater desalination system cools the crystalline silicon photovoltaic module, prevents the photovoltaic module from overheating, and helps to improve the power generation efficiency, thereby improving the defect that the existing technology uses sunlight to utilize energy of the crystalline silicon photovoltaic module with low efficiency.

[0040] (5) The present application sets a condenser in front of the solar spectrum modulation device, improves the unit energy density, reduces the defect that the traditional solar energy equipment occupies a large area, and at the same time, the seawater inlet of the seawater desalination system cools the crystalline silicon photovoltaic module, so that the photovoltaic module still maintains a high power generation efficiency even under high condensing multiple.

[0041] The above technical solutions can be combined with each other in the present application to achieve more preferred combination solutions. Other features and advantages of the present application will be described in the subsequent description, and some advantages will become apparent from the description, or will be understood by implementing the present application. The purposes and other advantages of the present application can be achieved and obtained through the specific embodiments and the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0042] 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:

[0043] Figure 1 Process flow chart of seawater desalination system in one embodiment of the present application;

[0044] Figure 2 Process flow chart of seawater desalination system in another embodiment of the present application;

[0045] Figure 3 Structure schematic diagram of absorber in another embodiment of the present application;

[0046] Figure 4 Structure schematic diagram of first modulator in another embodiment of the present application;

[0047] Figure 5 Structure schematic diagram of second modulator in another embodiment of the present application.

[0048] Reference signs

[0049] Multi-stage flash module 001; crystallization module 002; forced circulation module 003; photovoltaic power generation unit 004;

[0050] 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;

[0051] 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

[0052] 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, and together with the description, illustrate the principles of the application, but are not intended to limit the scope of the application.

[0053] To solve the problems of high crystallization temperature, high energy consumption and difficult utilization of water vapor resources in the existing seawater desalination technology, the present application introduces a negative pressure environment into the last stage crystallizer of the multi-stage flash seawater system, reduces the concentration and separation temperature of the crystallization module, and evaporates water in the concentrated brine at a lower temperature to realize brine separation, thereby greatly reducing the energy consumption.

[0054] The present application proposes a feasible solution: using mechanical compression forced circulation technology to act as the last stage crystallizer of the multi-stage flash seawater system, using a vacuum pump to cooperate with heating to realize brine separation of the multi-stage flash concentrated brine, and recovering water and salt resources and 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.

[0055] In view of the above-mentioned defects, the mechanical compression forced circulation system is further optimized: the water vapor is absorbed by the water absorption medium 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.

[0056] It should be noted that the water absorption medium after water absorption can be a solid, gas or liquid with waste heat or renewable energy such as solar energy, and the low-grade heat in the waste heat or solar energy can be used to heat the water absorption medium after water absorption to obtain dehydrated water absorption medium, realize the circulation of the water absorption medium, and reduce the electric energy consumption of the mechanical compression forced circulation represented by the vacuum pump.

[0057] 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.

[0058] It should be noted that the water or salt water has the highest spectral absorption rate between 750nm and 900nm, which can reach more than 90%; and the water or salt water has less than 10% of the visible light (especially blue-violet light) in the wavelength of 400nm-740nm in the sunlight, and the light radiation in the wavelength is difficult to directly heat the water or salt water, thereby resulting in low energy utilization efficiency of the sunlight directly used for heating the water or salt water.

[0059] It should be noted that part of the equipment in the seawater desalination system is electrically driven, and the electric energy is still necessary for the seawater desalination system, and another aspect of reducing the energy consumption of the seawater desalination system is to reduce the demand of the seawater desalination system for external power supply, and to widely introduce the electric energy converted from the renewable energy such as solar energy. The biggest problem of the solar power generation (for example, photovoltaic power generation) at present is that the solar energy density is low, and the occupied area is large; although the light collecting equipment can improve the energy density and reduce the occupied area, the light collecting device greatly increases the light receiving surface temperature of the solar power generation equipment after light collecting, on the one hand, the solar power generation equipment (for example, photovoltaic crystalline silicon assembly) has an optimal power generation temperature range, and the power generation efficiency is rapidly reduced when the temperature exceeds the range; on the other hand, limited by the material itself, the energy utilization efficiency is difficult to greatly improve, and the theoretical maximum power generation efficiency of the mass-produced photovoltaic equipment (for example, photovoltaic crystalline silicon assembly) 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.

[0060] In order to solve the problems of low energy density, large occupied area and low energy utilization efficiency of the sunlight directly heating seawater and photovoltaic power generation in the prior art, on the one hand, the light collecting device is used to collect and focus the sunlight radiation in a larger area to the seawater heating or photovoltaic power generation area before the sunlight directly heats the seawater and the photovoltaic power generation; on the other hand, in view of the problem that the surface temperature of the photovoltaic power generation assembly is too high after light collecting, which affects the power generation efficiency, the seawater at the inlet end of the seawater desalination system is used for cooling the photovoltaic power generation assembly, and the seawater at the inlet end is preheated; 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 in the wavelength, thereby improving the utilization rate of the crystalline silicon for the sunlight.

[0061] It should be noted that the photovoltaic power generation principle of the crystalline silicon is quantum absorption principle: when the light irradiates the surface of the silicon crystal, part of the photons is absorbed by the silicon material, the energy of the photons is transmitted to the silicon atoms, and the electrons are transferred,

[0062] The free electrons are gathered on both sides of the P-N junction to generate a potential difference. Photons with energy lower than 1.13 eV cannot be absorbed by the crystalline silicon to generate electricity, and the part of the energy of the photons that can be absorbed is dissipated in the form of heat, so the photon energy / frequency / wavelength used for crystalline silicon power generation needs to be in a suitable range.

[0063] In one aspect, the application provides a seawater desalination method, comprising:

[0064] The seawater or concentrated brine is input into the flash evaporation unit, and water vapor and concentrated brine are output; and the concentrated brine output by each stage of the flash evaporation unit is used as the input water of the next stage of the flash evaporation unit;

[0065] The concentrated brine output by the final stage of the multi-stage flash evaporation module is input into the crystallization module for further concentration to obtain water vapor, and the water vapor is input into the forced circulation module for condensation to obtain fresh water;

[0066] The negative pressure generated by the forced circulation module provides a negative pressure environment for the inside of the crystallization module, promoting the flow of water vapor to the forced circulation module.

[0067] Specifically, the method comprises the following steps:

[0068] Step 1: using the water vapor generated by the multi-stage flash evaporation module and the water vapor generated by the forced circulation module to preheat the seawater inlet of the multi-stage flash evaporation module;

[0069] Step 2: using the multi-stage flash evaporation unit to multi-stage flash evaporate the preheated seawater to obtain water vapor and concentrated brine;

[0070] Step 3: using the water vapor generated by the forced circulation module to preheat the concentrated brine and inputting the preheated concentrated brine into the crystallization module;

[0071] Step 4: using the forced circulation module to apply negative pressure to the crystallization module to realize the separation of the concentrated brine at a temperature lower than 100°C.

[0072] It can be understood that the above steps describe the normal operation stage of the seawater desalination system, and the modules do not generate water vapor at the start-up stage of the seawater desalination system, so they cannot play a preheating role; the start-up stage needs to rely on.

[0073] Specifically, the preheating of the seawater inlet of the multi-stage flash evaporation module in step 1 comprises:

[0074] S101: The water vapor generated by the multi-stage flash evaporation module exchanges heat through the steam cooling device and the seawater inlet pipeline;

[0075] S102: The condensing heat exchange device is arranged in the adsorption unit and the water vapor condensing unit, the cooling pipeline of the condensing heat exchange device in the adsorption unit and the water vapor condensing unit is communicated, and the cooling liquid transfers heat in the water vapor condensing unit to the adsorption unit through heat exchange, so as to provide heat for the water absorption process of the water absorption medium;

[0076] S103: The cooling liquid pipeline of the condensing heat exchange device and the seawater inlet pipeline of the multi-stage flash evaporation module pass through the second heat exchanger for heat exchange, so as to increase the seawater inlet temperature of the multi-stage flash evaporation module and reduce the energy consumption of the multi-stage flash evaporation module.

[0077] Specifically, in step 1, the seawater inlet temperature of the multi-stage flash evaporation module is preheated to 90-100℃, and the reason is that the temperature of the circulating water in the heater is matched, the heat exchange temperature difference is reduced, and the energy loss is reduced.

[0078] Specifically, in step 2, the mass concentration of the concentrated brine 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.

[0079] Specifically, in step 3, the concentrated brine temperature is preheated to 70-90℃, and the reason is that the temperature is matched with the heater, and at the same time, the forced circulation evaporator has a suitable superheat degree, which can reduce the heat exchange loss, and at the same time, enough steam is generated to reduce the circulating concentrated water volume.

[0080] Specifically, in step 4, negative pressure is applied to the crystallization module, including:

[0081] The negative pressure generated by the forced circulation module provides a negative pressure environment for the inside of the crystallization module, and promotes the flow of water vapor to the forced circulation module.

[0082] Specifically, the forced circulation module generates negative pressure through a physical method.

[0083] Specifically, the forced circulation module includes a vacuum pump or a water absorption medium; the vacuum pump is communicated with the crystallization module to provide a negative pressure environment for the inside of the crystallization module

[0084] Preferably, the forced circulation module includes a water absorption medium, which generates negative pressure by absorbing water vapor to provide 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.

[0085] Specifically, the water absorption medium can be an inorganic lithium salt.

[0086] Preferably, the inorganic lithium salt is one or more of lithium halide, lithium sulfate salt, and lithium phosphate salt.

[0087] Preferably, the inorganic lithium salt is one or more of lithium chloride, lithium bromide, lithium iodide, lithium sulfate, and lithium dihydrogen phosphate.

[0088] Specifically, the water absorption medium is absorbed to a water content of 0.55-0.7 and then enters the desorption unit; the water absorption medium is dried to 0.45-0.55 and then enters the adsorption unit from the desorption unit.

[0089] Specifically, the amount of water absorption medium m 3 The ratio of the seawater flow m 3 / h is 0.3-0.55.

[0090] Specifically, a negative pressure is applied to the crystallization module in step 4, including the following steps:

[0091] S401: The water absorption medium in the adsorption unit combines with water vapor in the crystallization module, and a negative pressure is generated;

[0092] 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, generating a low-water-content regenerated water absorption medium solution and regenerated water vapor;

[0093] S403: The regenerated water vapor further enters the water vapor condensation unit and is recovered by condensation.

[0094] Specifically, in step 402, when the heating device uses 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.

[0095] Specifically, in step 402, when the heating device uses a solar spectrum modulation device, solar radiation can be concentrated by a condenser and then modulated 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.

[0096] Specifically, in step 4, salt water separation is achieved, including the following steps:

[0097] S411: The concentrated salt water produced 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;

[0098] S412: The crystalline salt water enters the salt water separation device to separate and obtain crystalline salt and crystalline separation water.

[0099] Specifically, the crystalline separation water can be returned to the forced circulation evaporator, and compared with the prior art, the overall production process has no solid waste and exhaust gas emission, achieving zero emission of exhaust gas, wastewater and waste solids.

[0100] Specifically, the working temperature in the forced circulation evaporator is 60-70°C, and the vacuum degree is 19-32 kPa.

[0101] Specifically, the above-mentioned seawater desalination method further comprises the steps of generating electricity by using a photovoltaic power generation unit and preheating the seawater inlet of the multi-stage flash evaporation module 001:

[0102] d1: generating electricity by focusing solar radiation on the photovoltaic power generation unit through a condenser;

[0103] d2: preheating the seawater inlet of the multi-stage flash evaporation module by cooling the photovoltaic power generation unit with the third cooler.

[0104] On the other hand, the present application provides a seawater desalination system for the above-mentioned seawater desalination method, as shown in Figure 1 、 Figure 2 which comprises a multi-stage flash evaporation module 001, a crystallization module 002, and a forced circulation module 003.

[0105] 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.

[0106] The concentrated brine output by the multi-stage flash evaporation module 001 finally enters the crystallization module 002 for further concentration to obtain water vapor and crystallized brine, and the water vapor enters the forced circulation module 003 for condensation to obtain fresh water.

[0107] 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.

[0108] Specifically, the crystallized brine is separated to obtain salt crystals and crystallized separation water.

[0109] Preferably, the water vapor flashed out by the flash evaporation unit 2 and the seawater inlet of the multi-stage flash evaporation module 001 are subjected to heat exchange treatment.

[0110] The multi-stage flash evaporation module 001 further comprises a steam cooling device 1, and the water vapor flashed out by the flash evaporation unit 2 and the seawater inlet of the multi-stage flash evaporation module 001 are subjected to heat exchange treatment in the steam cooling device 1.

[0111] Specifically, each flash unit 2 in the multi-stage flash module 001 independently performs a "pressurized heating-depressurized flashing" process: the flash unit 2 is pressurized to more than one atmosphere, 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, part of the steam carries a large amount of latent heat, the depressurized flashing is completed, the water and the salt-containing water are separated; at the same time, the concentrated salt-containing water after the flashing is used as the liquid into the next stage of the flash unit, wherein the liquid into the first stage of the flash unit is seawater, and the salt-containing water discharged from the last stage of the flash unit is used as the concentrated salt water output by the multi-stage flash module 001; at the same time, the steam after the flashing enters the steam cooling device 1 and is condensed into fresh water, which is collected and utilized.

[0112] Specifically, the forced circulation module 003 generates negative pressure by a physical method.

[0113] Specifically, the forced circulation module 003 comprises a vacuum pump or a water absorption medium.

[0114] 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.

[0115] 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 promote 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.

[0116] 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.

[0117] Specifically, in order 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 communication with the gas path of the crystallization module 002; the adsorption unit 11 and the desorption unit 12 are in communication through two one-way pipelines, at least one one-way pipeline is provided with the water absorption medium pump 14; the desorption unit 12 is provided with a heating device and is in communication with the gas path of the water vapor condensing unit 15.

[0118] Specifically, the water-absorbing medium in the adsorption unit 11 combines with 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°C, and the brine separation is completed; the water-absorbing medium that has completed water absorption is forced to circulate to the desorption unit 12, and the water-absorbing medium completes dehydration under the action of the heating device, generates a low-water-content regenerated water-absorbing medium solution and regenerated water vapor, and realizes regeneration of the water-absorbing medium, which returns to the adsorption unit 11 through the water-absorbing medium pump 14, and the regenerated water vapor further enters the water vapor condensing unit 15 and is recovered.

[0119] Preferably, only one one-way pipeline is provided with the water-absorbing medium pump 14, and the water-absorbing medium that has completed water absorption enters the desorption unit 12 under the action of gravity, and returns to the adsorption unit 11 through the water-absorbing medium pump 14 after completing dehydration in the desorption unit 12.

[0120] Preferably, the water-absorbing medium that has completed water absorption and the regenerated water-absorbing medium solution are subjected to at least one heat recovery treatment.

[0121] Specifically, the water-absorbing medium that has completed water absorption and the regenerated water-absorbing medium solution circulating to the adsorption unit 11 pipeline are subjected to heat exchange in the heat exchanger, so as to increase the temperature of the water-absorbing medium entering the desorption unit 12 and reduce the energy consumption of the heating device.

[0122] In a feasible implementation mode, as shown in Figure 1 the heating device of the desorption unit 12 can be externally surrounded or internally provided with a heat exchanger.

[0123] It can be understood that the temperature of the heat source should be greater than 100°C to heat the water-absorbing medium and promote the volatilization of water therein, so as to complete dehydration of the water-absorbing medium.

[0124] Preferably, the heating device is a tubular heat exchanger for internal heating of the water-absorbing medium.

[0125] 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 which can be used efficiently; the present application uses waste heat to replace the electric energy consumed by the vacuum pump, which has the significance of energy saving, consumption reduction and cost reduction.

[0126] In another feasible implementation mode, as shown in Figure 2 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 and processing solar radiation, wherein the proportion of the wavelength of the solar radiation after the modulation and processing of the solar spectrum modulation device is 80% to 95% in the range of 750nm to 900nm.

[0127] Specifically, the solar spectrum modulation device for directly heating the water absorption medium in the desorption unit 12 comprises:

[0128] The absorber 16 is a double-layer grating structure comprising a photocatalyst layer, 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;

[0129] The first modulator 17 is arranged on the back side of the absorber 16 and comprises 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;

[0130] The first modulator 17 modulates the output frequency of the solar radiation to 750nm-900nm, which can efficiently heat water or salt-containing water.

[0131] Exemplarily, the first modulator 17 is sealed and isolated from the water absorption medium by using high-transmittance materials such as glass, to prevent the influence of water on the modulation, and the solar radiation output after the modulation of the first modulator 17 is directly heated to the water absorption medium through the high-transmittance material.

[0132] 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 mostly infrared radiation, and its penetration ability 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.

[0133] Preferably, the contact area between the first modulator 17 and the absorber 16 is designed to be heat-insulating, further reducing the radiation loss of the absorber 16.

[0134] 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 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 solar radiation of 400nm-800nm, and further uses a specially designed modulator to convert the radiation emitted by the absorber into a solar radiation frequency band of 750nm-900nm, which is most beneficial to the absorption of water and aqueous solution, thereby improving the energy utilization efficiency of solar light directly used for water and salt-containing water solution heating.

[0135] Specifically, the photocatalyst layer 1601 comprises any one of TiO2, ZnO and ZrO2.

[0136] 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.

[0137] Specifically, the thickness of the Si grating layer 1602 in the absorber 16 is 0.9-1.8 μm, the thickness of the photocatalyst layer 1601 is 1.0-2.5 μm, and the aperture of the first grating hole 1603 is 4-12 μm.

[0138] It should be noted that the plasmonic resonance effect can be excited when the sunlight is incident on the top TiO2 grating, 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 light absorption rate is improved, and the absorption rate can reach 80%-95%, thereby realizing high-efficiency absorption. When the aperture of the first grating hole 1603 is 4-12 μm, an absorption peak can be generated at 400-800 nm under the resonance effect, and almost full-spectrum energy of the sunlight can be utilized.

[0139] Preferably, the first grating hole 1603 is provided with a plurality of holes, and the porosity of the projection surface of the absorber is 83%-92%. The porosity is helpful to improve the unit planar 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. Meanwhile, if the hole density is too high, the preparation difficulty is greatly increased.

[0140] Specifically, the first modulator 17 comprises:

[0141] a CrF3 grating layer 1703;

[0142] a SiO2 grating layer 1702 formed on the top of the CrF3 grating layer 1703;

[0143] a Ti grating layer 1701 formed on the top of the SiO2 grating layer 1702;

[0144] 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 adjacent grating layers are communicated to form the second grating hole 1704.

[0145] Specifically, the ratio of the thickness of the CrF3 grating layer 1703, the thickness of the SiO2 grating layer 1702, and the thickness of the Ti grating layer 1701 is 1:0.01-200:0.01-200.

[0146] Specifically, the thickness of the CrF3 grating layer is 1.5-300 μm, the thickness of the SiO2 grating layer 1702 is 3-300 μm, and the thickness of the Ti grating layer 1701 is 1.8-300 μm.

[0147] It can be understood that the reason why the modulator can realize the output modulation of the light radiation emission energy concentrated between 750nm-900nm 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 produces a localized surface plasmon resonance at the same time, and the CrF3, SiO2, Ti grating together form a resonant cavity to produce radiation energy concentrated in 750nm-900nm.

[0148] Specifically, the first modulator has an area m 2 The flow rate m 3 The ratio of h to m is 0.3-0.5:1.

[0149] Preferably, the first modulator is also provided with a heat-conducting framework, which is divergent from the central area on the side close to 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 produce local heat accumulation.

[0150] Preferably, the second grating hole 1704 is provided with a plurality of holes, and the porosity is 83%-92%. The porosity is low, and the energy density generated by the modulation will decrease; the porosity is large, which helps to improve the unit planar 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. If the heat conduction is not good, local high temperature accumulation will be produced. At the same time, if the hole density is too high, the preparation difficulty will be greatly increased.

[0151] In a feasible implementation manner, the seawater desalination system is also provided with a photovoltaic power generation unit 004 for providing electric energy for the seawater desalination system.

[0152] Specifically, the photovoltaic power generation unit 004 comprises:

[0153] The absorber 16 is the same as the absorber 16 in the solar spectrum modulation device for directly heating the water-absorbing medium in the desorption unit 12;

[0154] 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;

[0155] The photovoltaic power generation unit 22 receives the sunlight radiation modulated by the second modulator to generate electricity;

[0156] 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.

[0157] Specifically, the second modulator comprises:

[0158] MgO grating layer 2103;

[0159] SiC grating layer 2102: formed on the top of MgO grating layer 2103;

[0160] Ag grating layer 2101: formed on the top of SiC grating layer 2102;

[0161] Ag grating layer 2101, SiC grating layer 2102, MgO grating layer 2103 are provided with through holes penetrating through the top and bottom thereof, and the through holes of adjacent grating layers are communicated to form the third grating hole 2104.

[0162] Specifically, the third grating hole 2104 is provided with a plurality of holes with a diameter of 4-12 μm and a porosity of 83-92%.

[0163] Specifically, the thickness ratio of each layer of MgO grating layer 2103, SiC grating layer 2102 and Ag grating layer 2101 in the second modulator is 1:0.08-200:0.05-200.

[0164] Specifically, the thickness of MgO grating layer 2103 is 1.5-300 μm, the thickness of SiC grating layer 2102 is 2.5-300 μm, and the thickness of Ag grating layer 2101 is 1.5-300 μm.

[0165] It should be noted that the center wavelength of SiC grating layer 2102 is related to the temperature of the silicon grating, and the temperature of SiC grating layer 2102 changes through the heat transfer of absorber 16, and the output spectrum center wavelength also changes, and MgO grating layer 2103 and Ag grating layer 2101 will simultaneously produce localized surface plasmon resonance, and under the action of grating resonant cavity, concentrated radiation energy of 400-600 nm is produced.

[0166] 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 region of the absorber 16, which is mainly infrared radiation, and its own penetration ability is much stronger than that of ultraviolet and visible light, so the third grating hole 2104 and the first grating hole 1603 do not need to be connected in optical path, and 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.

[0167] Preferably, the contact area between the second modulator and the absorber 16 is selected to be heat-insulating, further reducing the radiation loss of the absorber 16.

[0168] The prior art does not have a modulation structure with good absorption rate of solar radiation and optimal modulation frequency required for crystalline silicon power generation. Compared with the prior art, the present application sets an absorber + modulator structure, uses the absorber 16 to efficiently absorb sunlight, and further uses a specially designed modulator to convert the radiation emitted by the absorber 16 into a 400nm-600nm solar radiation frequency band most beneficial to crystalline silicon power generation, thereby improving the energy utilization efficiency of sunlight directly used for crystalline silicon power generation.

[0169] Preferably, the second modulator is also provided with a heat-conducting framework diverging from the central area near the absorber to the side far from the absorber 16, for uniformly conducting heat from the sunlight absorbed by the absorber to each area of the second modulator, avoiding local heat accumulation in the spectrum modulator under high heat flux density.

[0170] Specifically, the heat-conducting framework material in the first modulator and the second modulator comprises one or more of copper and aluminum.

[0171] 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 for focusing sunlight and projecting it on the solar spectrum modulation device, thereby improving the output power of the solar spectrum modulation device.

[0172] Specifically, the condenser can be a butterfly condenser or a groove condenser, and the condensing multiple is 2-50.

[0173] Specifically, the first modulator 17 is further provided with a first shield 18 for adjusting light intensity between the condenser 19 and the absorber 16; the second modulator is further provided with a second shield 24 for adjusting light intensity between the condenser 19 and the absorber 16.

[0174] 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 evaporation module 001,

[0175] Compared with the prior art, the seawater inlet of the multi-stage flash evaporation module 001 absorbs the heat energy dissipated by the photovoltaic power generation unit 22 in the third cooler 27, thereby reducing the temperature of the photovoltaic power generation unit 22. On the one hand, it helps to maintain a good power generation efficiency of the photovoltaic power generation unit 22; on the other hand, it helps to preheat the multi-stage flash evaporation module 001, thereby reducing the system energy consumption.

[0176] Specifically, the water-absorbing medium can be an inorganic lithium salt.

[0177] Preferably, the inorganic lithium salt is one or more of lithium halide, lithium sulfate salt, and lithium phosphate salt.

[0178] Preferably, the inorganic lithium salt is one or more of lithium chloride, lithium bromide, lithium iodide, lithium sulfate, lithium dihydrogen phosphate.

[0179] Specifically, the crystallization module 002 comprises a forced circulation evaporator 10 and a brine separation device 8; the concentrated brine produced 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; the crystallized separation water is returned to the forced circulation evaporator 10.

[0180] Specifically, the liquid inlet of the forced circulation evaporator 10 also comprises seawater, which is used to adjust the concentration of the brine in the forced circulation evaporator 10, and dilution is performed when the concentration of the brine in the forced circulation evaporator 10 is too high.

[0181] Preferably, the adsorption unit 11 and the water vapor condensation unit 15 are provided with condensation heat exchange devices, and the condensation heat exchange devices of the two are communicated, the cooling liquid in the condensation heat exchange devices and the liquid inlet of the forced circulation evaporator 10 are subjected to at least one heat exchange treatment; the water vapor in the water vapor condensation unit 15 is cooled by using the liquid inlet of the forced circulation evaporator 10; 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 absorption process of the water absorption medium.

[0182] Specifically, the cooling liquid pipeline of the condensation 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.

[0183] 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.

[0184] 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.

[0185] Specifically, the cooling liquid of the steam cooling device 1 is selected as the seawater inlet of the multi-stage flash evaporation module 001, and the heating of the seawater inlet is completed at the same time as the condensation of the water vapor, thereby reducing the energy consumption of the multi-stage flash evaporation module 001.

[0186] Specifically, the steam cooling device 1 is provided with a plurality of.

[0187] Optionally, the steam cooling device 1 is provided in one-to-one correspondence with the flash evaporation unit 2, and the water vapor of the flash evaporation unit 2 is collected after being cooled by the steam cooling device 1 and then flows together to be collected as fresh water.

[0188] 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; the steam cooling device 1 second inlet of the seawater inlet pipeline of the multi-stage flash module 001 is connected 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 exchanged by the heat exchange surface of the two chambers.

[0189] In another aspect, the application provides a preparation method of a solar full-spectrum absorber, which is used in the above-mentioned seawater desalination system, can achieve 80%~95% absorption rate to 400nm to 800nm solar radiation, and comprises the following steps:

[0190] a1: using chemical vapor deposition to prepare a double-layer composite structure with a photocatalyst layer and a Si grating layer;

[0191] 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;

[0192] a3: based on the template, dry etching the double-layer composite structure to obtain an absorber with a first grating hole.

[0193] In another aspect, the application provides a preparation method of a light modulator, which is used in the above-mentioned seawater desalination system, can convert the solar radiation absorbed by the above-mentioned absorber into radiation with a wavelength mainly of 750nm-900nm, and comprises the following steps:

[0194] 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;

[0195] 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;

[0196] b3: based on the template, dry etching the three-layer composite structure to obtain a light modulator with a second grating hole heat-conducting skeleton filling hole;

[0197] b4: filling the heat-conducting skeleton filling hole with a high-thermal-conductivity material to obtain a final product.

[0198] In another aspect, the application provides a preparation method of a light modulator, which is used in the above-mentioned seawater desalination system, can convert the solar radiation absorbed by the above-mentioned absorber 16 into radiation with a wavelength mainly of 400nm-600nm, and comprises the following steps:

[0199] c1: using chemical vapor deposition to prepare a three-layer composite structure with a MgO layer, a SiC layer and an Ag layer arranged in sequence;

[0200] c2: using photoresist to spin-coat on the top or bottom of the three-layer composite structure to prepare a template with a target shape;

[0201] c3: A light modulator with a third grating hole and a thermally conductive skeleton filling hole is obtained by dry etching of a three-layer composite structure based on a template.

[0202] c4: The thermal conductivity material is used to fill the holes of the thermally conductive skeleton to obtain the final product.

[0203] Specifically, the chemical vapor deposition, photoresist and dry etching described above all use methods or products that have been disclosed in the prior art, and this invention does not impose any particular limitations.

[0204] It should be noted that when the filling holes of the heat-conducting skeleton are tilted relative to the top and bottom surfaces of the composite structure, the existing technology of adjusting the dry etching angle is used to achieve the etching and shaping of the filling holes of the heat-conducting skeleton.

[0205] To further illustrate the advancements of this invention, the following embodiments and comparative examples are provided:

[0206] Example 1

[0207] This embodiment discloses a seawater desalination method, such as Figure 1 As shown, it includes the following steps:

[0208] After being preheated by the steam cooling devices 1 at each stage, the seawater enters the second heat exchanger 6 and is heated to 100°C. Then it enters the multi-stage flash evaporation unit 2 and is concentrated to a concentration of 7%. After that, it enters the first heat exchanger 4 and is heated to 90°C. Then it enters the forced circulation evaporator 10 (the operating temperature of the forced circulation evaporator 10 is 70°C). The concentrated brine and salt particles are separated by the brine separation device 8. The concentrated brine is mixed with the brine flowing out of the final flash evaporation unit 2 by the brine pump 7 before the first heat exchanger 4, making full use of the residual heat of the brine flowing out of the forced circulation evaporator 10.

[0209] The steam generated by each flash evaporation unit 2 enters the steam cooling device 1 for condensation, while the incoming seawater is gradually heated, and finally collected by the product water pump 5.

[0210] The steam generated by the forced circulation evaporator 10 enters the adsorption unit 11 and mixes with the concentrated lithium bromide solution. The vacuum effect generated maintains the vacuum environment required by the forced circulation evaporator 10. The diluted lithium bromide solution enters the desorption unit 12 via the regenerator 13. The desorption unit 12 is supplied with a 130°C steam source to dehumidify the lithium bromide solution. The resulting concentrated lithium bromide solution, under the action of the water suction pump 14, enters the adsorption unit 11 via the regenerator 13 and mixes with the steam generated by the forced circulation evaporator 10. The resulting steam enters the water vapor condensation unit 15 and condenses into product water.

[0211] The circulating water system, under the action of the circulating water pump 9, enters the second heat exchanger 6 after absorbing the heat of the steam in the water vapor condensing unit 15 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 condensing unit 15 to complete a cycle. After the seawater preheated by the steam cooling device 1 at each stage enters the second heat exchanger 6 for secondary preheating.

[0212] Example 2

[0213] This embodiment discloses a seawater desalination method, as shown in Figure 2 The difference between this embodiment and Example 1 is that it comprises the following steps:

[0214] The desorption unit 12 of Example 1 is connected to a 130℃ steam source to dehumidify the lithium bromide solution, and is replaced by a solar spectrum modulation device to modulate and process solar radiation to obtain a wavelength of 400nm-800nm radiation to directly heat the lithium bromide solution.

[0215] Example 3

[0216] This embodiment discloses a seawater desalination method, which differs from Example 2 in that it further comprises the following steps:

[0217] The desorption unit is electrically heated and dehydrated by using a photovoltaic power generation unit to generate electricity and store electricity.

[0218] Example 4

[0219] This embodiment discloses a seawater desalination system for implementing the seawater desalination method of Example 1, as shown in Figure 1 It comprises a multi-stage flash evaporation module 001, a crystallization module 002, and a forced circulation module 003.

[0220] The multi-stage flash evaporation module 001 comprises a plurality of flash evaporation units 2 connected in series, and the flash evaporation units 2 input seawater or concentrated brine and output water vapor and concentrated concentrated brine; the concentrated concentrated brine output by each stage of flash evaporation units 2 serves as the input water for the next stage of flash evaporation units 2;

[0221] 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 to obtain salt crystals and crystallized separation water;

[0222] The forced circulation module 003 generates negative pressure to provide a negative pressure environment inside the crystallization module 002 to promote the flow of water vapor to the forced circulation module 003.

[0223] The forced circulation module 003 comprises an adsorption unit 11, a desorption unit 12 and a water vapor condensing unit 15. The water vapor condensing unit 15 condenses the water vapor or water absorption medium pumped by the vacuum pump to obtain regenerated water vapor and fresh water.

[0224] The desorption unit 12 is connected with a heating device, and the desorption unit 12 is heated by the built-in coil.

[0225] The forced circulation module 003 contains water absorption medium, which absorbs water vapor to generate negative pressure, and provides a negative pressure environment above the liquid surface 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.

[0226] The water absorption medium that 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 and passes 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.

[0227] The heating device uses 130℃ high-temperature steam as a heat source, and uses a tube heat exchanger to heat the water absorption medium.

[0228] The crystallization module 002 comprises a forced circulation evaporator 10 and a brine separation device 8. The concentrated brine produced 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 crystalline brine. The crystalline brine is separated by the brine separation device 8 to obtain salt crystals and crystalline separation water. The crystalline separation water flows back to the forced circulation evaporator 10.

[0229] The adsorption unit 11 and the water vapor condensing unit 15 are provided with condensing heat exchange devices, and the condensing heat exchange devices of the two are connected. The cooling liquid in the condensing heat exchange devices and the liquid inlet of the forced circulation evaporator 10 are subjected to one heat exchange process.

[0230] The cooling pipelines of the condensing heat exchange devices in the adsorption unit 11 and the water vapor condensing unit 15 are connected, and the cooling liquid transfers 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.

[0231] 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.

[0232] Specifically, the seawater 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 process.

[0233] The water vapor flashed out is subjected to heat exchange with the seawater inlet of the multi-stage flash evaporation module 001.

[0234] The steam cooling device 1 is arranged in series and the number of the flash evaporation units 2 is the same.

[0235] Embodiment 5

[0236] This embodiment discloses a seawater desalination system for the seawater desalination method of embodiment 2, as shown in Figure 2 The heat source of the heating device in embodiment 4 is replaced by a solar spectrum modulation device for directly heating water and salt-containing water.

[0237] Embodiment 6

[0238] This embodiment discloses a seawater desalination system for the seawater desalination method of embodiment 3, as shown in Figure 2 Compared with embodiment 5, a crystalline silicon photovoltaic power generation unit is added to supply power to 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.

[0239] Embodiment 7

[0240] This embodiment discloses a seawater desalination system, in which the forced circulation module 003 of embodiment 5 is replaced by a vacuum pump.

[0241] Embodiment 8

[0242] This embodiment discloses a solar spectrum modulation device for directly heating water and salt-containing water, which is used in embodiment 5, as shown in Figure 2 、 Figure 3 、 Figure 4 The solar spectrum modulation device comprises:

[0243] 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, which are arranged in sequence according to the incident direction of light.

[0244] The first modulator 17 is arranged on the back side of the absorber 16, and comprises 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, which are arranged in sequence from near to far relative to the absorber 16.

[0245] 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, and the aperture of the first grating hole 1603 is 4 μm; the porosity of the absorber 16 is 83%.

[0246] The thickness of the CrF3 grating layer 1703 is 1.5 μm, the thickness of the SiO2 grating layer 1702 is 3 μm, the thickness of the Ti grating layer 1701 is 1.8 μm, and the porosity of the second grating hole 1704 is 83%.

[0247] The concentrator 19 is a butterfly concentrator 19, and the concentration multiple is 10.

[0248] The first modulator 17 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, for uniformly conducting heat from the sunlight absorbed by the absorber 16 to each area of the first modulator 17, avoiding local accumulation of heat under high heat flux density, which causes the spectral modulator to rapidly conduct heat and be uniformly at temperature, thereby generating heat.

[0249] It is measured that the absorber 16 has an absorption rate of 85% or more for sunlight radiation of 400 nm to 800 nm, and the first modulator 17 has an output radiation of 88% or more in the wavelength range of 750 nm to 900 nm.

[0250] Example 9

[0251] This embodiment discloses a solar spectral modulation device for directly heating water and salt-containing water, as shown in Figure 2 、 Figure 3 、 Figure 4 The device comprises:

[0252] The absorber 16 is a double-layer grating structure, comprising, in sequence according to the direction of light incidence, a photocatalyst layer 1601, a Si grating layer 1602, and a first grating hole 1603 penetrating through the two layers.

[0253] The first modulator 17 is arranged on the side far from the light of the absorber 16, and comprises, 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.

[0254] 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, the first grating hole 1603 has an aperture of 12 μm; and the absorber 16 has a porosity of 92%.

[0255] 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; and the second grating hole 1704 has a porosity of 92%.

[0256] The concentrator 19 is a groove-type concentrator 19, and the concentration multiple is 20.

[0257] The first modulator 17 is also provided with a heat conduction framework, which is divergent from the central area on 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 first modulator 17, so as to avoid the rapid heat conduction of the spectral modulator under high heat flux density, and to avoid the local accumulation of heat.

[0258] It is measured that the absorptivity of the absorber 16 to the sunlight radiation of 400 nm to 800 nm is 62%, and the proportion of the radiation output by the first modulator 17 in the wavelength range of 750 nm to 900 nm is 87%.

[0259] Embodiment 10

[0260] The embodiment discloses a solar spectrum modulation device for directly heating water and salt-containing water, as shown in Figure 2 、 Figure 3 、 Figure 4 The solar spectrum modulation device comprises an absorber 16, a first modulator 17, a second modulator 18 and a condenser 19.

[0261] The absorber 16 is a double-layer grating structure, and 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.

[0262] The first modulator 17 is arranged on the side far from the light of the absorber 16, and comprises, in sequence according to the direction from the absorber 16 to the first modulator 17, 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.

[0263] The photocatalyst layer 1601 is ZrO2; 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 a hole diameter of 8 μm; and the absorber 16 has a porosity of 88%.

[0264] The CrF3 grating layer 1703 has a thickness of 100 μm, the SiO2 grating layer 1702 has a thickness of 100 μm, the Ti grating layer 1701 has a thickness of 200 μm, and the second grating hole 1704 has a porosity of 89%.

[0265] The condenser 19 is a trough condenser 19, and has a condensing multiple of 30.

[0266] The first modulator 17 is also provided with a heat conduction framework, which is divergent from the central area on 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 first modulator 17, so as to avoid the rapid heat conduction of the spectral modulator under high heat flux density, and to avoid the local accumulation of heat.

[0267] The measured absorption rate of the absorber 16 to the 400nm-800nm solar radiation is 71%, and the output radiation of the first modulator 17 is 95% in the 750nm-900nm wavelength range.

[0268] In the embodiments 9 and 10, the photocatalyst layer is made of ZnO and ZrO2 instead of TiO2 in the embodiment 8, and the absorption rate of the absorber is decreased.

[0269] Embodiment 11

[0270] The embodiment discloses a crystalline silicon photovoltaic power generation unit, which is used in the embodiment 6, and comprises: Figure 2 、 Figure 3 、 Figure 5 as shown in the drawings, and comprises:

[0271] The absorber 16 is a double-layer grating structure, and comprises a photocatalyst layer 1601, a Si grating layer 1602 and a first grating hole 1603 penetrating the two layers, which are arranged in sequence according to the incident direction of light.

[0272] 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 the three layers, which are arranged in sequence from the near to the far of the absorber 16.

[0273] The photovoltaic power generation unit 22 is a crystalline silicon photovoltaic module.

[0274] The energy storage unit 20 is a battery pack.

[0275] The photocatalyst layer 1601 is TiO2; the thickness of the Si grating layer 1602 in the absorber 16 is 0.9μm, the thickness of the photocatalyst layer 1601 is 1.0μm, the aperture of the first grating hole 1603 is 4μm; and the porosity of the absorber 16 is 83%.

[0276] The third grating hole 2104 is provided with a plurality of holes with an aperture of 4μm and a porosity of 83%; the thickness of the MgO grating layer 2103 is 1.5μm, the thickness of the SiC grating layer 2102 is 2.5μm, and the thickness of the Ag grating layer 2101 is 1.5μm.

[0277] The concentrator 19 is also provided, and the groove-type concentrator 19 is selected, and the concentration multiple is 30.

[0278] The second modulator is also provided with a heat-conducting framework, which is divergent from the center 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.

[0279] The measured absorption rate of the absorber 16 to the 400-800 nm sunlight radiation is 85%, and the proportion of the output radiation of the second modulator in the 400-600 nm wavelength range is 84%.

[0280] Embodiment 12

[0281] 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

[0282] 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 light incidence direction;

[0283] 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 arranged in sequence from the near to the far direction relative to the absorber 16;

[0284] The photovoltaic power generation unit 22 is selected from a crystalline silicon photovoltaic module;

[0285] The energy storage unit 20 is selected from a battery pack.

[0286] The photocatalyst layer 1601 is TiO2; the thickness of the Si grating layer 1602 in the absorber 16 is 1.8 μm, the thickness of the photocatalyst layer 1601 is 2.5 μm, the aperture of the first grating hole 1603 is 12 μm; and the porosity of the absorber 16 is 92%.

[0287] The third grating hole 2104 is provided with a plurality of holes with an aperture of 12 μm and a porosity of 83%; the thickness of the MgO grating layer 2103 is 300 μm, the thickness of the SiC grating layer 2102 is 300 μm, and the thickness of the Ag grating layer 2101 is 300 μm.

[0288] The concentrator 19 is also provided, and the groove type concentrator 19 is selected, and the concentration multiple is 10.

[0289] The second modulator is also provided with a heat-conducting framework, which is divergent from the center 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 uniform temperature.

[0290] The measured absorption rate of the absorber 16 to the 400-800 nm sunlight radiation is 85%, and the proportion of the output radiation of the second modulator in the 400-600 nm wavelength range is 84%.

[0291] Embodiment 13

[0292] The embodiment discloses a crystalline silicon photovoltaic power generation unit004, as shown in Figure 2 、 Figure 3 、 Figure 5 The crystalline silicon photovoltaic power generation unit004 comprises the following components.

[0293] 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 the two layers, which are arranged in sequence according to the incident direction of light.

[0294] 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 the three layers, which are arranged in sequence from the near to the far direction relative to the absorber 16.

[0295] 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 a pore size of 8 μm; and the absorber 16 has a porosity of 88%.

[0296] The third grating hole 2104 is provided with a plurality of holes, each having a pore size 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.

[0297] The concentrator 19 is also provided, and the trough-type concentrator 19 is selected, and the concentration multiple is 20.

[0298] The second modulator is also provided with a heat-conducting framework that diverges from the center area on 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 rapid heat conduction of the spectral modulator under high heat flux density, and the local accumulation of heat.

[0299] It is measured that the absorber 16 has a solar radiation absorption rate of 92% for 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 93%.

[0300] The absorber absorption rate test in Embodiments 8-13 is calculated by removing the reflected energy of the illumination surface of the absorber per unit area of solar radiation energy; the wavelength range of the output radiation of the first modulator and the second modulator is measured by using a spectrum analyzer.

[0301] Conclusion:

[0302] Example 8-13 The absorber has an absorption rate of 62% to 92% for 400nm to 800nm solar radiation, and the absorber with TiO2 as the photocatalyst layer has an absorption rate of 85% to 92% for 400nm to 800nm solar radiation;

[0303] The first modulator outputs radiation in the wavelength range of 750nm to 900nm, and the proportion of the radiation energy is 87% to 95%;

[0304] The second modulator outputs radiation in the wavelength range of 400nm to 600nm, and the proportion of the radiation energy is 84% to 93%.

[0305] Comparative Example 1

[0306] Comparative Example 1 does not have a modulating device for directly heating the water-absorbing medium, and the light concentrator is used to directly irradiate the water-absorbing medium of the desorption unit after concentrating, and the rest is the same as Example 8.

[0307] Comparative Example 2

[0308] Comparative Example 2 does not have an absorber and a second modulator for the photovoltaic power generation unit, and the light concentrator is used to directly irradiate the photovoltaic power generation unit after concentrating, and the rest is the same as Example 11.

[0309] Comparative Example 3

[0310] Comparative Example 3 has a first grating hole aperture of 15μm, and the rest is the same as Example 8. The measured absorption rate of the absorber for 400nm to 800nm solar radiation is 76%.

[0311] Comparative Example 4

[0312] Comparative Example 4 has a first grating hole aperture of 2μm, and the rest is the same as Example 8. The measured absorption rate of the absorber for 400nm to 800nm solar radiation is 69%.

[0313] Comparative Example 8, Comparative Example 3 and Comparative Example 4 show that the first grating hole aperture is too large or too small, which will cause the absorption rate of the absorber for 400nm to 800nm solar radiation to decrease.

[0314] Comparative Example 5

[0315] Comparative Example 5 has a second grating hole aperture of 15μm, and the rest is the same as Example 8. The first modulator outputs radiation in the wavelength range of 750nm to 900nm, and the proportion of the radiation energy is 84%.

[0316] Comparative Example 6

[0317] Comparative Example 6 has a second grating hole aperture of 2μm, and the rest is the same as Example 8. The first modulator outputs radiation in the wavelength range of 750nm to 900nm, and the proportion of the radiation energy is 79%.

[0318] From Comparative Example 8, Comparative Example 5 and Comparative Example 6, it can be seen that the first modulator output radiation energy ratio at 750nm-900nm decreases when the second grating hole aperture is set too large or too small.

[0319] Comparative Example 7

[0320] Comparing Example 11, the third grating hole aperture is set to 15μm, and the rest is the same as Example 11. The second modulator output radiation energy ratio at 400nm-600nm is 75%.

[0321] Comparative Example 8

[0322] Comparing Example 11, the third grating hole aperture is set to 2μm, and the rest is the same as Example 11. The second modulator output radiation energy ratio at 400nm-600nm is 83%.

[0323] From Comparative Example 11, Comparative Example 7 and Comparative Example 8, it can be seen that the second modulator output radiation energy ratio at 400nm-600nm decreases when the third grating hole aperture is set too large or too small; and the third grating hole aperture is too small, which increases the manufacturing difficulty and is less economical.

[0324] Experimental Example 1

[0325] Comparing Example 8 and Comparative Example 1, the seawater desalination system described in Example 5 and the operation method described in Example 2 are used to measure 1m 3 lithium bromide aqueous solution, and the time for the water content to decrease from 0.7 to 0.45 under direct heating of sunlight focused on an area (concentration ratio 10) is 3min and 10min, respectively. 2

[0326] Test Conclusion: From Comparative Example 8 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.

[0327] Experimental Example 2

[0328] Comparing Example 11 and Comparative Example 2, the seawater desalination system described in Example 6 and the operation method described in Example 3 are used to measure 0.25m 2 lithium bromide aqueous solution, and the time for the water content to decrease from 0.7 to 0.45 under direct heating of sunlight focused on an area (concentration ratio 30) is 3min and 10min, respectively.

[0329] Test Conclusion:

[0330] From Comparative Example 11 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 module. ​

[0331] The above description is only the preferred embodiment of the present application, but the protection scope of the present application is not limited to this. Any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A method of desalination of sea water, characterized in that, The method comprises the following steps: sea water or concentrated brine is input into a multi-stage flash module, water vapor and concentrated brine are output; the concentrated brine output by each stage of the multi-stage flash module is input into the next stage of the multi-stage flash module; the concentrated brine output by the final stage of the multi-stage flash module is input into a crystallization module to obtain water vapor, and the water vapor is input into a forced circulation module to obtain fresh water; the forced circulation module generates negative pressure to provide a negative pressure environment for the crystallization module, so that water vapor flows to the forced circulation module; the forced circulation module generates negative pressure by a physical method; the forced circulation module comprises a water absorption medium, the water absorption medium absorbs water vapor to generate negative pressure, and a negative pressure environment is provided above the liquid level of the crystallization module; the water absorption medium is heated to obtain regenerated water vapor, and the water vapor is further condensed to obtain fresh water; the water absorption medium is an inorganic lithium salt; the working temperature of the forced circulation evaporator is 60-70 DEG C, and the vacuum degree is 19-32 kPa; the heating device is a solar spectrum modulation device, which comprises an absorber and a first modulator arranged on the back side of the absorber; the absorber is a double-layer grating structure, which comprises a photocatalyst layer, a Si grating layer and first grating holes penetrating through the two layers arranged in sequence according to the direction of light incidence; the first modulator comprises a Ti grating layer, a SiO2 grating layer, a CrF3 grating layer and second grating holes penetrating through the three layers arranged in sequence according to the direction from the absorber to the distance from the absorber; the proportion of the wavelength of the solar radiation after the modulation of the solar spectrum modulation device is 80-95% in the range of 750-900 nm.

2. The method of desalination of seawater according to claim 1, characterized in that, The method comprises the following steps: 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 sea water input into the multi-stage flash module; Step 2: using the multi-stage flash unit to multi-stage flash the preheated sea water to obtain water vapor and concentrated brine; Step 3: using the water vapor generated by the forced circulation module to preheat the concentrated brine and input the preheated concentrated brine into the crystallization module; Step 4: using the forced circulation module to apply negative pressure to the crystallization module, so that the concentrated brine is separated at a temperature lower than 100 DEG C.

3. The method according to claim 2, wherein the step 4 of applying negative pressure to the crystallization module comprises: S401: the water absorption medium in the adsorption unit combines with the water vapor in the crystallization module, and negative pressure is generated; S402: the water absorption medium after water absorption is forced to circulate to the desorption unit, and the water absorption medium is dehydrated under the action of the heating device to generate a low-water-content regenerated water absorption medium solution and regenerated water vapor; S403: the regenerated water vapor further enters the water vapor condensing unit to be condensed and recovered. The inorganic lithium salt is one or more of lithium halide, lithium sulfate salt, lithium phosphate salt.

4. The method of desalination of sea water according to claim 3, characterized in that, The inorganic lithium salt is one or more of lithium chloride, lithium bromide, lithium iodide, lithium sulfate and lithium dihydrogen phosphate.

5. The method of desalination of sea water according to claim 4, characterized in that, The water absorption medium is dried to 0.45-0.55 before entering the adsorption unit from the desorption unit.

6. The method of desalination of sea water according to claim 1, characterized in that, The method comprises the following steps:

7. The method of desalination of sea water according to claim 6, characterized in that, ​ S101: The water vapor generated by the multi-stage flash evaporation module is heat-exchanged by a steam cooling device and a seawater inlet pipeline; S102: The cooling pipeline of the condensing heat exchange device in the adsorption unit and the water vapor condensing unit is connected, and the cooling liquid transfers the heat in the water vapor condensing unit to the adsorption unit by heat exchange, thereby providing heat for the water absorption process of the water absorption medium; S103: The cooling liquid pipeline of the condensing heat exchange device and the seawater inlet pipeline of the multi-stage flash evaporation module are heat-exchanged by a second heat exchanger, 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.

8. The method of desalination of sea water according to claim 7, characterized in that, In step 1, the seawater inlet temperature of the multi-stage flash evaporation module is preheated to 90-100℃, and in step 2, the mass concentration of the concentrated brine is 7-9%.

9. The method of desalination of seawater according to any one of claims 1-8, characterized in that, In step 3, the concentrated brine is preheated to 70-90℃.

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