A desert saline water green energy desalination hydrogen production system

Abstract

The application discloses a kind of desert saline water green hydrogen production system of brine, including water pretreatment unit, adaptive desalination unit, ultra-pure water preparation unit, electrolytic hydrogen production unit, concentrated brine closed-loop processing unit, renewable energy power supply unit, three-stage water storage unit and control unit.Three-stage water storage unit includes raw water regulating tank, desalination water storage tank and ultra-pure water storage tank;Adaptive desalination unit includes electric dialysis reverse branch and nanofiltration-brackish water reverse osmosis branch, and the operation path is selected by switching valve group.Concentrated brine closed-loop processing unit includes membrane distillation device and closed solar crystallization device, and the cooling heat exchange loop of electrolytic hydrogen production unit is connected with the heat exchange of membrane distillation device, and the membrane distillation water backflow is utilized, concentrated liquid enters closed solar crystallization device, and crystallization mother liquor backflow processing is carried out.The application is suitable for green hydrogen production under the condition of inland desert saline water, can improve the adaptability of saline water, stabilize electrolytic water supply, and reduce the liquid discharge of concentrated brine.

Description

Technical Field

[0001] This invention application relates to the field of environmental technology, specifically to a desert saline-alkali water green energy desalination and hydrogen production system. Background Technology

[0002] With the large-scale development of renewable energy sources such as wind power and photovoltaics, the production of green hydrogen through water electrolysis using renewable energy has become an important technological direction for new energy consumption, industrial carbon reduction, and transportation fuel substitution. Northwest my country has vast areas of deserts, Gobi, and saline-alkali land, rich in solar and wind energy resources, possessing the energy and land conditions for constructing green hydrogen projects. However, these regions suffer from a scarcity of freshwater resources. Available water sources are mostly saline-alkali groundwater, shallow brackish water, or water from the edges of salt lakes, typically characterized by high salinity, high alkalinity, high hardness, and high sulfate, silicon, and sediment content, making them unsuitable for direct use in hydrogen electrolysis.

[0003] Existing green hydrogen production systems typically use municipal freshwater, imported freshwater, or conventional pure water equipment to supply water to the electrolyzers. In coastal areas, seawater desalination can also provide water for electrolysis. However, in inland desert areas, directly applying conventional reverse osmosis desalination processes can easily lead to problems such as membrane scaling, increased pressure differential, decreased flux, and frequent cleaning due to the high content of calcium and magnesium ions, sulfates, carbonates, and silicates in the saline water. This can ultimately affect the continuous operation of the electrolytic hydrogen production system.

[0004] On the other hand, inland areas lack the conditions for discharging concentrated brine from seawater desalination into the sea. Direct discharge of concentrated brine from conventional desalination systems could lead to soil salinization, groundwater pollution, and the spread of salt dust. Using only ordinary evaporation ponds also presents problems such as low evaporation efficiency, high leakage risk, and difficulty in further disposing of the mother liquor. Therefore, the preparation of green hydrogen in inland desert scenarios requires not only solving the problem of ultrapure water supply for electrolysis but also addressing the issues of closed-loop reduction and end-of-pipe treatment of concentrated brine.

[0005] Furthermore, the output power of wind and solar power fluctuates, while the electrolysis hydrogen production unit has high requirements for influent water quality, water supply continuity, and operating temperature. In existing systems, the water production unit, electrolysis hydrogen production unit, and concentrated brine treatment unit typically operate independently, lacking coordinated control based on raw water quality, water storage level, renewable energy output power, and electrolyzer thermal status. This can easily lead to problems such as mismatch between water production and hydrogen production loads, frequent start-ups and shutdowns of the electrolyzer, increased burden on energy storage batteries, and curtailment of renewable energy.

[0006] Therefore, it is necessary to provide a green energy desalination hydrogen production and concentrated brine closed-loop treatment system suitable for desert saline water conditions. This system can select a suitable desalination path according to the quality of the saline water, stably produce ultrapure water for electrolytic hydrogen production, and use the waste heat from electrolytic hydrogen production to concentrate the concentrated brine through membrane distillation. Then, the concentrated brine is treated in a closed loop through closed solar crystallization and mother liquor reflux. Summary of the Invention

[0007] To address or partially address the problems existing in related technologies, this invention provides a desert saline-alkali water green energy desalination and hydrogen production system and a concentrated brine closed-loop treatment system, comprising a water intake pretreatment unit, an adaptive desalination unit, an ultrapure water preparation unit, an electrolysis hydrogen production unit, a concentrated brine closed-loop treatment unit, a renewable energy power supply unit, a three-stage water storage unit, and a control unit; the three-stage water storage unit includes a raw water regulating tank, a desalinated water storage tank, and an ultrapure water storage tank, and the water intake pretreatment unit, raw water regulating tank, adaptive desalination unit, desalinated water storage tank, ultrapure water preparation unit, ultrapure water storage tank, and electrolysis hydrogen production unit are sequentially connected; the adaptive desalination unit includes an electrodialysis reverse branch and a nanofiltration-brackish water reverse branch. Both the permeate branch and the brine branch are connected to the inlet pipe of the adaptive desalination unit via switching valve groups. The brine closed-loop treatment unit includes a membrane distillation device and a closed-loop solar crystallization device. The inlet of the membrane distillation device is connected to the brine end of the adaptive desalination unit, the product water end is connected back to the desalination water storage tank or the ultrapure water preparation unit, and the concentrate end is connected to the closed-loop solar crystallization device. The cooling heat exchange circuit of the electrolytic hydrogen production unit is connected to the hot end of the membrane distillation device for heat exchange. The renewable energy power supply unit supplies power to the adaptive desalination unit, the ultrapure water preparation unit, the electrolytic hydrogen production unit, and the brine closed-loop treatment unit. The control unit is used to adjust the desalination path, water production load, hydrogen production load, and brine concentration load.

[0008] Furthermore, the water intake pretreatment unit includes a water intake pump, a sand remover, an automatic backwash filter, a softening and hardening device, and an ultrafiltration device connected in sequence; the softening and hardening device is one or more combinations of an electrochemical induced crystallization reactor, a particle bed crystallization softener, and a chemical precipitation softener, used to reduce the calcium and magnesium hardness and the content of easily scale-forming components in saline-alkali water.

[0009] Furthermore, the product water end of the electrodialysis reverse branch is connected to the desalinated water storage tank through the first product water valve, and is connected to the inlet end of the nanofiltration-brackish water reverse osmosis branch through the second product water valve, so that the electrodialysis reverse branch can operate independently or as a pre-desalination unit of the nanofiltration-brackish water reverse osmosis branch.

[0010] Furthermore, the system is equipped with a water quality detection component, which includes a conductivity detector and / or a total dissolved solids detector for obtaining the total dissolved solids content of saline-alkali water, and includes a hardness detector, a silicon content detector, a sulfate detector, and a pollution index detection component; optionally, the water quality detection component also includes a pH detector and / or a turbidity detector; the control unit selects one of the following operating modes—a first operating mode, a second operating mode, and a third operating mode—based on the detection results of the water quality detection component, wherein the first operating mode is that the saline-alkali water enters the electrodialysis reverse branch, the second operating mode is that the saline-alkali water enters the nanofiltration-brackish water reverse osmosis branch, and the third operating mode is that the saline-alkali water first enters the electrodialysis reverse branch and then enters the nanofiltration-brackish water reverse osmosis branch.

[0011] Furthermore, the control unit is configured to: set a first salinity threshold and a second salinity threshold, wherein the second salinity threshold is higher than the first salinity threshold; and set corresponding first scaling thresholds and second scaling thresholds for hardness, silicon content, sulfate content and pollution index respectively, wherein each second scaling threshold is higher than the corresponding first scaling threshold. When the total dissolved solids content of the saline-alkali water is lower than the first salinity threshold, and the hardness, silicon content, sulfate content and pollution index are all lower than their respective first scaling thresholds, the control system enters the first operating mode. When the total dissolved solids content of the saline-alkali water is not lower than the first salinity threshold and is lower than the second salinity threshold, and the hardness, silicon content, sulfate content and pollution index are all lower than their respective first scaling thresholds, the control system enters the second operating mode. When the total dissolved solids content of the saline-alkali water is lower than the second salinity threshold, and at least one of the hardness, silicon content, sulfate content and pollution index is not lower than its corresponding first scaling threshold and is lower than its corresponding second scaling threshold, the control system enters the third operating mode. When the total dissolved solids content of the saline water is not lower than the second salinity threshold, or when at least one of the hardness, silicon content, sulfate content, and fouling index is not lower than its corresponding second scaling threshold, the control system enters the third operating mode and reduces the recovery rate of the nanofiltration-brine reverse osmosis branch while increasing the flow rate of concentrated brine entering the membrane distillation unit.

[0012] Furthermore, the ultrapure water preparation unit includes a two-stage reverse osmosis unit, an electro-deionization unit, a polishing mixed bed unit, an ultraviolet treatment unit, and a terminal filtration unit connected in sequence. The outlet water pipeline of the ultrapure water preparation unit is equipped with a conductivity detector and a reflux valve. When the conductivity of the outlet water is higher than the set value of the hydrogen electrolysis inlet water, the control unit controls the reflux valve to open, so that the unqualified outlet water flows back to the desalination water storage tank or the inlet of the ultrapure water preparation unit.

[0013] Furthermore, the ultrapure water preparation unit includes a two-stage reverse osmosis unit, an electro-deionization unit, a polishing mixed bed unit, an ultraviolet treatment unit, and a terminal filtration unit connected in sequence. The outlet water pipeline of the ultrapure water preparation unit is equipped with a conductivity detector and a reflux valve. When the conductivity of the outlet water is higher than the set value of the hydrogen electrolysis inlet water, the control unit controls the reflux valve to open, so that the unqualified outlet water flows back to the desalination water storage tank or the inlet of the ultrapure water preparation unit.

[0014] Furthermore, the raw water regulating tank, desalinated water storage tank, and ultrapure water storage tank are all equipped with liquid level detection components; the effective volume of the ultrapure water storage tank is not less than the water intake required for the electrolytic hydrogen production unit to operate at rated power for 2 hours; the control unit is configured to: increase the operating load of the adaptive desalination unit and the ultrapure water production unit when the renewable energy output power is higher than the first power threshold and the desalinated water storage tank or the ultrapure water storage tank has not reached the high liquid level; and reduce or stop the operating load of the adaptive desalination unit when the renewable energy output power is lower than the second power threshold, and supply water to the electrolytic hydrogen production unit from the ultrapure water storage tank.

[0015] Furthermore, the renewable energy power supply unit includes a photovoltaic power generation device, a wind power generation device, an energy storage battery, a DC bus, and an energy management device; the adaptive desalination unit, the ultrapure water preparation unit, the electrolytic hydrogen production unit, and the membrane distillation device are all connected to the DC bus through a conversion device; the energy management device allocates renewable energy output power according to the priority of ultrapure water quality assurance, hydrogen production load maintenance, desalination water storage, concentrated brine concentration, and energy storage battery charging and discharging.

[0016] Furthermore, the cooling heat exchange circuit of the electrolytic hydrogen production unit includes an electrolytic cell coolant outlet, a three-way regulating valve, a first heat exchange branch, and a second heat dissipation branch; the first heat exchange branch is connected to the hot end of the membrane distillation device via a heat exchanger, and the second heat dissipation branch is connected to a heat dissipation device; the control unit adjusts the opening of the three-way regulating valve according to the electrolytic cell coolant outlet temperature and the membrane distillation device hot end inlet temperature, so as to supply heat to the membrane distillation device while ensuring the electrolytic cell operating temperature.

[0017] Furthermore, the concentrated brine closed-loop treatment unit also includes a concentrated brine storage tank, and the closed solar crystallization device includes a seepage-proof crystallization pool, a light-transmitting and heat-insulating cover, a dehumidification channel, a salt scraping mechanism, and a mother liquor return pipeline; the mother liquor return pipeline is connected to the inlet of the membrane distillation device or the concentrated brine storage tank; the concentrated brine closed-loop treatment unit does not have a concentrated brine liquid discharge port that is directly connected to the external environment, the concentrate produced by the membrane distillation device enters the closed solar crystallization device for evaporation and crystallization, and the remaining mother liquor after crystallization is returned to the membrane distillation device or the concentrated brine storage tank for further processing via the mother liquor return pipeline.

[0018] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit the scope of this application.

[0019] Beneficial technical effects of the present invention: First, this invention connects water pretreatment, adaptive desalination, ultrapure water preparation, electrolytic hydrogen production, waste heat membrane distillation, and closed solar crystallization into a continuous system, enabling desert saline water to be converted into ultrapure water for electrolytic hydrogen production after graded treatment, avoiding the problems of chlorine precipitation, electrode corrosion, membrane fouling, and scaling caused by direct electrolysis of saline water.

[0020] Secondly, this invention sets up an electrodialysis reverse osmosis branch and a nanofiltration-brackish water reverse osmosis branch, and achieves individual or combined operation through switching valve groups. The control unit selects the desalination path based on the salinity, hardness, silica content, sulfate content, and pollution index of the saline water, so that low-salt, low-risk water preferentially enters the electrodialysis reverse osmosis branch, medium-risk water is treated by a combination of electrodialysis reverse osmosis and nanofiltration-brackish water reverse osmosis, and high-salt or high-scaling-risk water has a reduced reverse osmosis recovery rate and an increased load on the concentrated brine post-treatment, thereby improving the system's adaptability to complex saline water quality.

[0021] Third, this invention forms a three-stage water storage structure consisting of a raw water regulating tank, a desalinated water storage tank, and an ultrapure water storage tank, creating a water volume buffer between water intake, desalination, ultrapure water preparation, and hydrogen electrolysis. When renewable energy output is high, the system can increase the water production load and store desalinated and ultrapure water; when renewable energy output is low, the desalination load can be reduced, and the ultrapure water storage tank can continue to supply water to the hydrogen electrolysis unit, thereby reducing frequent start-ups and shutdowns of the electrolyzer and reducing dependence on the capacity of the energy storage battery.

[0022] Fourth, this invention incorporates conductivity detection and a reflux valve in the ultrapure water preparation unit. When the conductivity of the ultrapure water effluent exceeds the set value for the hydrogen electrolysis inlet, the substandard effluent is refluxed back to the desalination water storage tank or the inlet of the ultrapure water preparation unit. This prevents abnormal water quality from entering the electrolyzer, which helps protect the electrolytic membrane, electrodes, and catalyst layer, and improves the operational stability of the hydrogen production unit.

[0023] Fifth, this invention connects the cooling heat exchange circuit of the electrolytic hydrogen production unit to the hot end of the membrane distillation device, enabling the low-grade waste heat generated during the operation of the electrolyzer to be used for concentrated brine membrane distillation. Compared to independent electrically heated membrane distillation, this invention reduces the external heat requirements during the concentrated brine concentration process and improves the overall energy utilization efficiency of the system.

[0024] Sixth, the concentrated brine closed-loop treatment unit of the present invention includes a membrane distillation unit and a closed-loop solar crystallization unit. The permeate from the membrane distillation is recycled, the concentrate from the membrane distillation enters the closed-loop solar crystallization unit, and the mother liquor from crystallization is returned to the concentrated brine storage tank or the membrane distillation unit for further treatment. This structure does not have a concentrated brine liquid discharge outlet that is directly connected to the external environment, making it more suitable for inland desert areas without access to the sea.

[0025] Seventh, the closed solar crystallization device of the present invention is equipped with a seepage-proof crystallization pool, a light-transmitting heat-insulating cover, a dehumidification channel, a salt scraping mechanism and a mother liquor return pipeline, which can reduce the problems of leakage, wind and sand entry, salt dust diffusion and mother liquor retention that exist in ordinary open-air evaporation pools, and facilitate the centralized collection and subsequent disposal of solid salt or salt mud.

[0026] Eighth, this invention comprehensively collects parameters such as water quality, liquid level, renewable energy output power, electrolyzer coolant temperature, and membrane distillation hot end temperature through the control unit, and performs linkage adjustment on the desalination path, water production load, hydrogen production load, and concentrated brine load, so that the system can maintain relatively stable operation under the conditions of fluctuating desert saline water quality and fluctuating wind and solar power. Attached Figure Description

[0027] Figure 1 This is a flowchart of one embodiment of the present invention. Detailed Implementation

[0028] The alternative embodiments of this application will now be described in more detail with reference to the accompanying drawings. While alternative embodiments of this application are shown in the drawings, it should be understood that this application can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to make this application more thorough and complete, and to fully convey the scope of this application to those skilled in the art.

[0029] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0030] The present invention will now be described in detail with reference to the accompanying drawings, as follows: This invention provides a desert saline-alkali water green energy desalination and hydrogen production system and a concentrated brine closed-loop treatment system, including a water intake pretreatment unit, an adaptive desalination unit, an ultrapure water preparation unit, an electrolysis hydrogen production unit, a concentrated brine closed-loop treatment unit, a renewable energy power supply unit, a three-stage water storage unit, and a control unit. The three-stage water storage unit includes a raw water regulating tank, a desalinated water storage tank, and an ultrapure water storage tank, which are sequentially connected. The adaptive desalination unit includes an electrodialysis reverse osmosis branch and a nanofiltration-brackish water reverse osmosis branch, both of which are connected via… The switching valve group is connected to the inlet pipeline of the adaptive desalination unit; the concentrated brine closed-loop treatment unit includes a membrane distillation device and a closed solar crystallization device. The inlet end of the membrane distillation device is connected to the concentrated brine end of the adaptive desalination unit, the product water end is connected back to the desalination water storage tank or the ultrapure water preparation unit, and the concentrate end is connected to the closed solar crystallization device; the cooling heat exchange circuit of the electrolytic hydrogen production unit is connected to the hot end of the membrane distillation device for heat exchange; the renewable energy power supply unit supplies power to the adaptive desalination unit, the ultrapure water preparation unit, the electrolytic hydrogen production unit, and the concentrated brine closed-loop treatment unit; the control unit is used to adjust the desalination path, water production load, hydrogen production load, and concentrated brine concentration load.

[0031] In one embodiment of this invention, the water pretreatment unit includes a water intake pump, a sand remover, an automatic backwash filter, a softening and hardening device, and an ultrafiltration device connected in sequence. The softening and hardening device is one or more combinations of an electrochemically induced crystallization reactor, a granular bed crystallization softener, and a chemical dosing precipitation softener, used to reduce the calcium and magnesium hardness and the content of easily scale-forming components in saline-alkali water. Desert saline-alkali water often contains silt, hardness, silica, and sulfates, which can easily cause scaling or fouling if directly introduced into a membrane system. Through sand removal, filtration, softening, and ultrafiltration staged treatment, the operational burden on subsequent electrodialysis, nanofiltration, reverse osmosis, and EDI units can be reduced.

[0032] In one embodiment of this invention, the product water end of the electrodialysis reverse osmosis branch is connected to the desalinated water storage tank through a first product water valve, and is connected to the inlet end of the nanofiltration-brackish water reverse osmosis branch through a second product water valve, so that the electrodialysis reverse osmosis branch can operate independently or as a pre-desalination unit of the nanofiltration-brackish water reverse osmosis branch.

[0033] The electrodialysis reverse osmosis branch can produce water independently under low salinity conditions, or it can pre-desalinate under medium to high salinity conditions before entering the nanofiltration-brine reverse osmosis branch, thereby reducing the salinity of the reverse osmosis feed water and the risk of scaling on the concentrate side.

[0034] In one embodiment of this invention, the system includes a water quality detection component, comprising a conductivity detector and / or a total dissolved solids detector for obtaining the total dissolved solids content of saline-alkali water, and further including a hardness detector, a silica content detector, a sulfate detector, and a fouling index detection component. Optionally, the water quality detection component also includes a pH detector and / or a turbidity detector. The control unit selects one of three operating modes—a first operating mode, a second operating mode, and a third operating mode—based on the detection results of the water quality detection component. In the first operating mode, the saline-alkali water enters the electrodialysis reverse branch; in the second operating mode, the saline-alkali water enters the nanofiltration-brackish water reverse osmosis branch; and in the third operating mode, the saline-alkali water first enters the electrodialysis reverse branch and then the nanofiltration-brackish water reverse osmosis branch. Conductivity reflects salinity, hardness, silica, sulfate, and pH reflect scaling risk, and turbidity and fouling index reflect membrane fouling risk. The system selects different desalination paths based on these parameters to avoid long-term high-load operation of a fixed process under complex saline-alkali water conditions.

[0035] In one embodiment of this invention application, a first salinity threshold and a second salinity threshold are set, and the second salinity threshold is higher than the first salinity threshold; and corresponding first scaling thresholds and second scaling thresholds are set for hardness, silicon content, sulfate content and pollution index, respectively, and each second scaling threshold is higher than the corresponding first scaling threshold. When the total dissolved solids content of the saline-alkali water is lower than the first salinity threshold, and the hardness, silicon content, sulfate content and pollution index are all lower than their respective first scaling thresholds, the control system enters the first operating mode. When the total dissolved solids content of the saline-alkali water is not lower than the first salinity threshold and is lower than the second salinity threshold, and the hardness, silicon content, sulfate content and pollution index are all lower than their respective first scaling thresholds, the control system enters the second operating mode. When the total dissolved solids content of the saline-alkali water is lower than the second salinity threshold, and at least one of the hardness, silicon content, sulfate content and pollution index is not lower than its corresponding first scaling threshold and is lower than its corresponding second scaling threshold, the control system enters the third operating mode. When the total dissolved solids content of the saline-alkali water is not lower than the second salinity threshold, or when at least one of the following—hardness, silica content, sulfate content, and fouling index—is not lower than its corresponding second scaling threshold, the control system enters the third operating mode. This mode reduces the recovery rate of the nanofiltration-brackish water reverse osmosis branch while increasing the flow rate of concentrated brine entering the membrane distillation unit. Low-salt, low-risk water is preferentially processed via electrodialysis reverse osmosis; medium-risk water uses a combined route; and high-salt or high-scaling-risk water has its reverse osmosis recovery rate reduced, with high-concentration tasks assigned to the membrane distillation and crystallization units to minimize scaling on the reverse osmosis concentrate side.

[0036] In one embodiment of this invention, the ultrapure water preparation unit includes a two-stage reverse osmosis unit, an electro-deionization unit, a polishing mixed bed unit, an ultraviolet treatment unit, and a terminal filtration unit connected in sequence. The outlet water pipeline of the ultrapure water preparation unit is equipped with a conductivity detector and a reflux valve. When the outlet water conductivity is higher than the set value for the hydrogen electrolysis inlet water, the control unit controls the reflux valve to open, allowing the substandard outlet water to flow back to the desalination water storage tank or the inlet of the ultrapure water preparation unit. Electrolyzers, especially PEM electrolyzers, have high requirements for inlet water conductivity and particle cleanliness. Through multi-stage ultrapure water treatment and the reflux of substandard water, it is possible to prevent abnormal water quality from directly entering the electrolyzer, reducing the risk of electrode, membrane, and catalyst layer contamination.

[0037] In one embodiment of this invention, the raw water regulating tank, desalinated water storage tank, and ultrapure water storage tank are all equipped with liquid level detection components; the effective volume of the ultrapure water storage tank is not less than the water intake required for the electrolytic hydrogen production unit to operate at rated power for 2 hours; the control unit is configured to: increase the operating load of the adaptive desalination unit and the ultrapure water production unit when the renewable energy output power is higher than a first power threshold and the desalinated water storage tank or the ultrapure water storage tank has not reached a high liquid level; and reduce or stop the operating load of the adaptive desalination unit when the renewable energy output power is lower than a second power threshold, and supply water to the electrolytic hydrogen production unit from the ultrapure water storage tank. The water tank is not only a liquid storage container but also plays a role in peak shaving and valley filling. More water is produced and stored when green electricity is abundant, and less water is produced or stopped when green electricity is insufficient, with the ultrapure water storage tank maintaining the water supply to the electrolyzer, thereby reducing the start-up and shutdown of the electrolyzer and the dependence on large-capacity batteries.

[0038] In one embodiment of this invention, the renewable energy power supply unit includes a photovoltaic power generation device, a wind power generation device, an energy storage battery, a DC bus, and an energy management device. The adaptive desalination unit, ultrapure water preparation unit, electrolytic hydrogen production unit, and membrane distillation device are all connected to the DC bus via a conversion device. The energy management device allocates renewable energy output power according to the priority of ultrapure water quality assurance, hydrogen production load maintenance, desalinated water storage, concentrated brine concentration, and energy storage battery charging and discharging. By forming a unified energy supply platform consisting of photovoltaic, wind power, energy storage battery, and DC bus, multi-stage conversion losses can be reduced, and water production, hydrogen production, and concentrated brine concentration can be prioritized, making the system more suitable for desert scenarios with significant wind and solar fluctuations.

[0039] In one embodiment of this invention, the cooling heat exchange circuit of the electrolytic hydrogen production unit includes an electrolyzer coolant outlet, a three-way regulating valve, a first heat exchange branch, and a second heat dissipation branch. The first heat exchange branch is connected to the hot end of the membrane distillation device via a heat exchanger, and the second heat dissipation branch is connected to a heat dissipation device. The control unit adjusts the opening of the three-way regulating valve according to the electrolyzer coolant outlet temperature and the membrane distillation device hot end inlet temperature to supply heat to the membrane distillation device while ensuring the electrolyzer's operating temperature. The heat from the electrolyzer coolant is preferentially supplied to the membrane distillation hot end for concentrated brine. When excessive waste heat is supplied or the electrolyzer requires enhanced heat dissipation, the three-way regulating valve directs some coolant to the heat dissipation branch to ensure that waste heat utilization does not affect the electrolyzer's safe temperature control.

[0040] In one embodiment of this invention, the closed-loop brine treatment unit further includes a brine storage tank, and the closed-loop solar crystallization device includes a seepage-proof crystallization pool, a light-transmitting and heat-insulating cover, a dehumidification channel, a salt scraping mechanism, and a mother liquor return pipeline. The mother liquor return pipeline is connected to the inlet of the membrane distillation unit or the brine storage tank. The closed-loop brine treatment unit does not have a brine liquid discharge port directly connected to the external environment. The concentrate produced by the membrane distillation unit enters the closed-loop solar crystallization device for evaporation and crystallization. After crystallization, the remaining mother liquor is returned to the membrane distillation unit or the brine storage tank for further processing via the mother liquor return pipeline. The seepage-proof crystallization pool prevents brine leakage, the light-transmitting and heat-insulating cover enhances solar evaporation, the dehumidification channel discharges water vapor, the salt scraping mechanism facilitates the discharge of solid salt, and the mother liquor return pipeline prevents the direct discharge of high-concentration mother liquor. This structure is suitable for inland desert areas without access to the sea.

[0041] For clarity, the following examples will be used to provide a detailed description.

[0042] Example 1 This embodiment uses desert saline-alkali groundwater as the treatment target. The raw water is first taken from a saline-alkali groundwater well, allowed to stand to remove large particles of sediment, and then sent to a raw water tank for later use. The typical water quality of the raw water is: pH about 9.2, TDS about 12.0 g / L, total hardness about 1000 mg / L, SiO2 content about 50 mg / L (calculated as CaCO3), SO4²⁻ content about 1600 mg / L, and SDI about 4.5.

[0043] Before starting the experiment, check that all storage tanks, pipelines, valves, pump sets, sensors, and control cabinets are in normal working order. Connect the level gauges of the raw water regulating tank, desalinated water storage tank, and ultrapure water storage tank to the control unit, and install the conductivity, pH, hardness, silicon content, sulfate content, and contamination index detection components on the inlet pipeline of the adaptive desalination unit.

[0044] The water intake pump is started to send raw water into the pretreatment unit. The raw water passes sequentially through a sand separator, an automatic backwash filter, an electrochemically induced crystallization softening device, and an ultrafiltration device. The sand separator mainly removes sand particles from the water, the automatic backwash filter intercepts suspended solids, the softening device reduces calcium and magnesium hardness, and the ultrafiltration device further removes colloids and fine particles. The pretreated water then enters the raw water conditioning tank.

[0045] The adaptive desalination unit was then activated. The control unit first read the TDS, hardness, SiO2, SO4²⁻, and SDI of the raw water. In the experiment, the first salinity threshold was set to 5.0 g / L, and the second salinity threshold was set to 15.0 g / L; the first hardness threshold was set to 600 mg / L, and the second hardness threshold was set to 1200 mg / L; the first SiO2 threshold was set to 40 mg / L, and the second hardness threshold was set to 60 mg / L; the first SO4²⁻ threshold was set to 1000 mg / L, and the second hardness threshold was set to 2000 mg / L; and the first SDI threshold was set to 4.0, and the second SDI threshold was set to 5.0.

[0046] Based on the water quality described above, the control unit selects the combined desalination mode. First, the inlet valve of the electrodialysis reverse branch is opened, allowing the pretreated saline water to enter the electrodialysis reverse branch for pre-desalination; simultaneously, the first product water valve directly connecting the electrodialysis reverse branch to the desalinated water storage tank is closed, and the second product water valve connecting to the nanofiltration-brackish water reverse osmosis branch is opened, allowing the effluent from the electrodialysis reverse branch to continue entering the nanofiltration-brackish water reverse osmosis branch.

[0047] After the nanofiltration-brackish water reverse osmosis branch is started, the nanofiltration module first removes some divalent ions and easily scale-forming components, and then the brackish water reverse osmosis module performs deep desalination. The desalinated water produced by this branch enters the desalinated water storage tank, and the concentrated brine produced enters the concentrated brine temporary storage tank. If the pressure differential of the reverse osmosis branch increases during operation, the control unit reduces the reverse osmosis recovery rate and increases the flow rate of concentrated brine entering the membrane distillation unit.

[0048] Once the desalinated water storage tank reaches the set level, the ultrapure water preparation unit is started. The desalinated water sequentially enters the secondary reverse osmosis unit, the electro-deionization unit, the polishing mixed bed unit, the ultraviolet treatment unit, and the terminal filtration unit. The upper limit for the effluent conductivity of the ultrapure water preparation unit is set to 0.8 μS / cm. If the effluent conductivity exceeds this set value, the control unit opens the reflux valve, allowing that portion of the water to flow back to the desalinated water storage tank or the inlet of the ultrapure water preparation unit; if the effluent conductivity meets the requirements, it enters the ultrapure water storage tank.

[0049] Once the ultrapure water storage tank reaches the start-up level, the electrolysis hydrogen production unit is activated. Ultrapure water is fed into the electrolyzer from the ultrapure water storage tank, and the renewable energy power supply unit supplies power to the electrolysis hydrogen production unit via a DC bus. The hydrogen produced by electrolysis is separated into gas and liquid and dried before entering the hydrogen storage device, while the oxygen enters the oxygen collection pipeline or reuse pipeline.

[0050] When the electrolysis hydrogen production unit is running, the cooling heat exchange circuit is activated simultaneously. Coolant flows from the electrolyzer's coolant outlet and enters a three-way regulating valve. One path of the three-way regulating valve connects to the membrane distillation heat exchanger, and the other path connects to the heat dissipation device. When the membrane distillation unit requires heating, the control unit increases the opening of the branch leading to the membrane distillation heat exchanger, allowing residual heat from the electrolyzer to be transferred to the hot end of the membrane distillation unit. When the electrolyzer temperature is too high, the control unit increases the opening of the heat dissipation branch to ensure stable electrolyzer temperature.

[0051] The membrane distillation unit is then started. The concentrated brine in the brine storage tank is pumped into the membrane distillation unit, with the hot end temperature set at approximately 60°C and the cold end temperature at approximately 25°C. The membrane distillation permeate is returned to the desalination water storage tank or the inlet of the ultrapure water preparation unit, while the membrane distillation concentrate enters the closed-loop solar crystallization unit.

[0052] The closed-loop solar crystallization unit consists of a seepage-proof crystallization tank, a light-transmitting and heat-insulating cover, a dehumidification channel, a salt scraping mechanism, and a mother liquor return pipeline. After the membrane distillation concentrate enters the seepage-proof crystallization tank, it continues to evaporate and crystallize under solar irradiation and ventilation. The solid salt or salt sludge formed by crystallization is periodically discharged by the salt scraping mechanism, and the incompletely crystallized mother liquor is returned to the concentrated brine storage tank or the inlet of the membrane distillation unit for further treatment through the mother liquor return pipeline.

[0053] During operation, the control unit continuously monitors the liquid levels of the raw water regulating tank, desalinated water storage tank, and ultrapure water storage tank. When the renewable energy output power is high and the desalinated water storage tank or ultrapure water storage tank has not reached a high liquid level, the load of the adaptive desalination unit and ultrapure water preparation unit is increased; when the renewable energy output power is low, the operation of the adaptive desalination unit is reduced or stopped, and the ultrapure water storage tank continues to supply water to the electrolysis hydrogen production unit.

[0054] If any abnormality occurs during operation, handle it as follows: If the pollution index of the pretreated effluent exceeds the limit, stop feeding water into the desalination unit and start backwashing; if the conductivity of the ultrapure water exceeds the limit, close the inlet valve of the electrolyzer and open the reflux valve; if the liquid level in the ultrapure water storage tank is too low, reduce the load of the electrolysis hydrogen production unit; if the temperature of the coolant in the electrolyzer is too high, increase the flow rate of the heat dissipation branch; if the mother liquor level in the closed solar crystallization unit is too high, stop feeding liquid and temporarily store or reflux the concentrate.

[0055] In this embodiment, the concentrated brine closed-loop treatment unit does not have a concentrated brine liquid discharge port that is directly connected to the external environment. Membrane distillation permeate is reused, crystallization mother liquor is refluxed, and solid salt or salt mud is discharged centrally.

[0056] Experimental Example 1: Comparison of Adaptive Desalination and Fixed Reverse Osmosis Desalination Experimental Objective The purpose of this invention is to verify whether the adaptive desalination route of "electrodialysis reverse pre-desalination + nanofiltration - brackish water reverse osmosis" can reduce the risk of membrane fouling and improve the desalination recovery rate and operational stability.

[0057] test raw water Desert saline-alkali groundwater was used as the raw water, and was uniformly added to the raw water tank and stirred evenly. The raw water had a pH of 9.2, a TDS of 12.0 g / L, a total hardness of 1000 mg / L, a SiO2 content of 50 mg / L (calculated as CaCO3), a SO4²⁻ content of 1600 mg / L, and an SDI of 4.5.

[0058] Experimental grouping Two sets of devices are set up.

[0059] The example group uses the system of the present invention. After pretreatment, the raw water first enters the electrodialysis reverse branch for pre-desalination, and then enters the nanofiltration-brackish water reverse osmosis branch for deep desalination.

[0060] Comparative Example 1 uses a fixed nanofiltration-brackish water reverse osmosis process. The raw water is directly introduced into the nanofiltration-brackish water reverse osmosis branch after the same pretreatment. No electrodialysis reverse pre-desalination is set up, and the desalination path is not switched according to the water quality.

[0061] Test Procedure First, the pretreatment systems of both sets of devices are cleaned until the effluent is stable, and then they are connected to the same raw water tank. Both sets pass through a sand separator, an automatic backwash filter, a softening and hardening removal device, and an ultrafiltration device in sequence to ensure that the pretreatment conditions entering the desalination section are consistent.

[0062] After the example group is started, the control unit reads the TDS, hardness, SiO2, SO4²⁻, and SDI of the feed water. Since the water quality is within the medium scaling risk range, the control unit opens the inlet valve of the electrodialysis reverse osmosis branch and the second product water valve leading to the nanofiltration-brackish water reverse osmosis branch, allowing the raw water to be pre-desalinated via the electrodialysis reverse osmosis branch before entering the nanofiltration-brackish water reverse osmosis branch. The initial recovery rate of the nanofiltration-brackish water reverse osmosis branch is set to 70%, and is automatically adjusted downwards during operation based on the pressure difference on the concentrate side.

[0063] After startup, Comparative Example 1 directly sends the pretreated effluent into the fixed nanofiltration-brackish water reverse osmosis branch, with the initial recovery rate also set at 70%. During operation, no desalination path switching is performed; it operates only under conventional pressure and flow control.

[0064] Both sets of feed water flow rates were set to 80 L / h and operated continuously for 72 hours. Feed water pressure, concentrate pressure, permeate conductivity, permeate flow rate, and membrane module pressure differential were recorded every 6 hours. After operation, the average recovery rate of the desalination section, unit permeate power consumption, membrane pressure differential rise rate, and standardized flux retention rate were calculated.

[0065] Test results Desalination permeate conductivity (μS / cm) 310±24 360±31 Desalination recovery rate / % 73.6±1.3 66.1±1.5 Desalination section power consumption / kWh / m³ 1.62±0.08 1.90±0.10 Membrane pressure differential rise rate / kPa / h 0.42±0.05 1.21±0.12 Standardized flux after 72 hours 0.94±0.02 0.81±0.03 Number of chemical cleanings 0 1 Results Explanation Under the same raw water and pretreatment conditions, the example group pre-desalinated the water through an electrodialysis reverse branch before it entered the nanofiltration-brackish water reverse osmosis branch, reducing the feed water salinity and the risk of scaling on the concentrate side of the downstream pressure membrane system. Compared with the fixed reverse osmosis route, the example group showed higher recovery rate, slower membrane pressure differential rise, and better flux retention after 72 hours of operation.

[0066] Experimental Example 2: Comparison of Three-Stage Water Storage Scheduling and Real-Time Water Supply Hydrogen Production Experimental Objective The study aims to verify whether the three-stage water storage unit, consisting of a raw water regulating tank, a desalinated water storage tank, and an ultrapure water storage tank, can buffer the fluctuations in renewable energy and reduce the start-up and shutdown of electrolyzers and the curtailment of electricity.

[0067] Test conditions Both units employ a 10kW electrolysis hydrogen production unit, with a 10kWh battery capacity for energy storage. Renewable energy is supplied by a programmable DC power supply simulating photovoltaic and wind power output, with a 72-hour power curve set, and a total input power of 600kWh.

[0068] Experimental grouping The example group uses the system of the present invention, which includes a raw water regulating tank, a desalinated water storage tank and an ultrapure water storage tank, and the control unit adjusts the water production load and hydrogen production load according to the tank liquid level and the output power of renewable energy.

[0069] Comparative Example 2 employs a real-time water supply method for hydrogen production, using only a conventional small-capacity pure water buffer tank, without the coordinated operation of raw water regulating tanks, desalinated water storage tanks, and ultrapure water storage tanks. The pure water preparation unit operates in real-time according to the electrolyzer load.

[0070] Test Procedure Before the experiment began, two sets of electrolytic hydrogen production units, pure water preparation units, and energy storage batteries were connected to the same renewable energy simulation system. In Example 2, the liquid levels of the raw water regulating tank, desalinated water storage tank, and ultrapure water storage tank were preset to about 50%; in Comparative Example 2, only the conventional pure water buffer tank was replenished to the normal start-up liquid level.

[0071] Initiate a 72-hour wind and solar power simulation curve. In the example group, when the renewable energy output power is higher than the set value and the desalination water storage tank or ultrapure water storage tank has not reached the high liquid level, increase the load of the adaptive desalination unit and ultrapure water preparation unit; when the renewable energy output power decreases, reduce or stop the water production load, and the ultrapure water storage tank continues to supply the electrolyzer.

[0072] In Comparative Example 2, when the output power of renewable energy increases, the electrolyzer and the pure water preparation unit simultaneously increase their loads; when the output power decreases or the pure water buffer tank level is insufficient, the electrolyzer reduces its load or shuts down.

[0073] During the test, the following data were recorded: new energy input power, electrolyzer power consumption, battery charge and discharge, abandoned power, cumulative electrolyzer operating time, number of start-ups and shutdowns, hydrogen production, and number of low liquid level alarms.

[0074] Test results Renewable energy input power / kWh 600.0 600.0 New energy consumption rate / % 89.4 76.2 Wasted electricity / kWh 63.6 142.7 Total battery charge / discharge volume / kWh 106.2 174.5 Cumulative running time of electrolytic cell / h 68.1 55.4 Electrolytic cell start-up and shutdown times 2 8 Hydrogen production per 72 hours / kg 8.82 7.36 Number of times ultrapure water low level alarm 0 5 Results Explanation The example group partially decouples the water production and hydrogen production processes through a three-stage water storage unit. When green electricity is abundant, desalinated water and ultrapure water are prepared and stored in advance. When green electricity is insufficient, the ultrapure water storage tank maintains the operation of the electrolyzer. Compared with real-time water supply for hydrogen production, the example group exhibits lower power waste, less battery cycle load, and significantly fewer electrolyzer start-ups and shutdowns.

[0075] Experimental Example 3: Comparison of Electrolytic Waste Heat Film Distillation and Closed-Circuit Crystallization Treatment Experimental Objective The study aimed to verify whether the waste heat from hydrogen production via electrolysis could be used for membrane distillation to concentrate brine, and whether this, combined with closed-loop solar crystallization and mother liquor reflux, could reduce external heating energy consumption and decrease the discharge of liquid concentrated brine.

[0076] Test materials The concentrated brine produced in the desalination section of Comparative Experiment 1 was used as the feed water for membrane distillation. After adjustment and thorough mixing, the TDS of the concentrated brine was 60 g / L. 480 L of concentrated brine was taken from each group for membrane distillation experiments.

[0077] Experimental grouping The system of the present invention is used in the example group. The hot end of the membrane distillation device is connected to the cooling heat exchange circuit of the electrolytic hydrogen production unit through a heat exchanger, and the waste heat of the electrolytic cell is used preferentially for heating. The membrane distillation concentrate enters the closed solar crystallization device, and the crystallization mother liquor is returned to the concentrated brine temporary storage tank.

[0078] Comparative Example 3 uses the same membrane distillation device, but does not connect to the cooling heat exchange circuit of the electrolysis hydrogen production unit, and uses independent electric heating to maintain the hot end temperature; the membrane distillation concentrate enters a regular open-air evaporation tank, without a light-transmitting heat insulation cover, a salt scraping mechanism, or a mother liquor return pipeline.

[0079] Test Procedure First, rinse both sets of membrane distillation units with clean water, then replace the pipelines with concentrated brine. The membrane areas of both sets of membrane distillation units should be kept consistent, the hot-end temperature should be set to 60℃, the cold-end temperature should be set to 25℃, and the concentrated brine circulation flow rate should be kept consistent.

[0080] In the example group, the cooling heat exchange circuit of the electrolytic hydrogen production unit is started, and the three-way valve is adjusted so that part of the coolant enters the membrane distillation heat exchange branch and supplies heat to the hot end of the membrane distillation through the heat exchanger; when the temperature of the hot end is insufficient, a small amount of electric auxiliary heating is used to make up for the temperature.

[0081] Comparative Example 3: Start the independent electric heater to maintain the hot end of the membrane distillation at the same temperature.

[0082] Both membrane distillation systems were run continuously for 72 hours, and the following parameters were recorded: membrane distillation product water output, product water conductivity, concentrate volume, concentrate TDS, external electric heating power consumption, and membrane flux.

[0083] After membrane distillation, 160L of each of the two concentrates was taken and fed into the crystallization section. In Example 3, the concentrate was fed into a closed solar crystallization device, which included a seepage-proof crystallization tank, a light-transmitting and heat-insulating cover, a dehumidification channel, a salt scraping mechanism, and a mother liquor return pipeline. In Comparative Example 3, the concentrate was fed into a conventional open-air evaporation tank. Both crystallization areas were 3 m², and the system operated continuously for 10 days, recording the evaporation volume, dry weight of the crystallized salt, volume of remaining mother liquor, and liquid discharge.

[0084] Test results Membrane distillation stage MD inlet water volume / L 480 480 MD influent TDS / g / L 60.0 60.0 Average membrane flux / L / m²·h 7.10±0.65 7.28±0.61 MD permeate volume / L 315 318 MD product water conductivity / μS / cm 24±6 23±5 MD concentrate volume / L 165 162 MD concentrate TDS / g / L 174 178 External electric heating power consumption / kWh / m³ water production 4.2 39.5 Waste heat supply as a percentage of heating capacity / % 82.7 0 Crystallization stage Volume of concentrate entering the crystallization section / L 160 160 Salt mass entering the crystallization section / kg 27.8 28.5 10-day evaporation rate (L) 143 129 Dry weight of crystalline salt / kg 20.9 16.8 Remaining mother liquor volume / L 17 31 Remaining mother liquor TDS / g / L Approximately 408 Approximately 377 Is the mother liquor refluxing? yes no Liquid discharge rate / L 0 31 Results Explanation The two membrane distillation groups produced similar amounts and quality of water, but the example group used the waste heat from the electrolytic cell cooling as the main heat source, and the power consumption for external electric heating was significantly lower than that of Comparative Example 3. After entering the crystallization stage, the example group used a closed-loop solar crystallization system and mother liquor reflux to allow the remaining high-concentration mother liquor to continue to be returned to the system for treatment, without forming liquid concentrated brine for discharge; Comparative Example 3 used a conventional evaporation tank, and the remaining mother liquor needed to be discharged or disposed of separately.

[0085] The various embodiments of this invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A closed-loop system for desalination and hydrogen production from saline-alkali water in desert areas, characterized in that: The system includes a water intake pretreatment unit, an adaptive desalination unit, an ultrapure water preparation unit, an electrolytic hydrogen production unit, a concentrated brine closed-loop treatment unit, a renewable energy power supply unit, a three-stage water storage unit, and a control unit. The three-stage water storage unit comprises a raw water regulating tank, a desalinated water storage tank, and an ultrapure water storage tank, which are sequentially connected. The adaptive desalination unit includes an electrodialysis reverse osmosis branch and a nanofiltration-brackish water reverse osmosis branch, both connected to the inlet water of the adaptive desalination unit via switching valve groups. The pipelines are connected; the concentrated brine closed-loop treatment unit includes a membrane distillation device and a closed solar crystallization device. The inlet of the membrane distillation device is connected to the concentrated brine end of the adaptive desalination unit, the product water end is connected back to the desalination water storage tank or the ultrapure water preparation unit, and the concentrate end is connected to the closed solar crystallization device; the cooling heat exchange circuit of the electrolytic hydrogen production unit is connected to the hot end of the membrane distillation device for heat exchange; the renewable energy power supply unit supplies power to the adaptive desalination unit, the ultrapure water preparation unit, the electrolytic hydrogen production unit, and the concentrated brine closed-loop treatment unit; the control unit is used to adjust the desalination path, water production load, hydrogen production load, and concentrated brine concentration load.

2. The desert saline-alkali water green energy desalination hydrogen production and concentrated brine closed-loop treatment system according to claim 1, characterized in that, The water intake pretreatment unit includes a water intake pump, a sand remover, an automatic backwash filter, a softening and hardening device, and an ultrafiltration device connected in sequence. The softening and hardening device is one or more combinations of an electrochemical induced crystallization reactor, a particle bed crystallization softener, and a chemical precipitation softener, used to reduce the calcium and magnesium hardness and the content of easily scale-forming components in saline-alkali water.

3. The desert saline-alkali water green energy desalination hydrogen production and concentrated brine closed-loop treatment system according to claim 1, characterized in that, The product water end of the electrodialysis reverse osmosis branch is connected to the desalinated water storage tank through the first product water valve, and is connected to the inlet end of the nanofiltration-brackish water reverse osmosis branch through the second product water valve, so that the electrodialysis reverse osmosis branch can operate independently or as a pre-desalination unit of the nanofiltration-brackish water reverse osmosis branch.

4. The desert saline-alkali water green energy desalination hydrogen production and concentrated brine closed-loop treatment system according to claim 1, characterized in that, The system is equipped with a water quality detection component, which includes a conductivity detector and / or a total dissolved solids detector for obtaining the total dissolved solids content of saline-alkali water, and includes a hardness detector, a silicon content detector, a sulfate detector, and a pollution index detection component; optionally, the water quality detection component further includes a pH detector and / or a turbidity detector; The control unit selects one of the following operating modes based on the detection results of the water quality detection component: a first operating mode, a second operating mode, and a third operating mode. The first operating mode is that the saline water enters the electrodialysis reverse branch; the second operating mode is that the saline water enters the nanofiltration-brackish water reverse osmosis branch; and the third operating mode is that the saline water first enters the electrodialysis reverse branch and then enters the nanofiltration-brackish water reverse osmosis branch.

5. The desert saline-alkali water green energy desalination hydrogen production and concentrated brine closed-loop treatment system according to claim 4, characterized in that, A first salinity threshold and a second salinity threshold are set, with the second salinity threshold being higher than the first salinity threshold; and corresponding first scaling thresholds and second scaling thresholds are set for hardness, silicon content, sulfate content and pollution index, with each second scaling threshold being higher than the corresponding first scaling threshold. When the total dissolved solids content of the saline-alkali water is lower than the first salinity threshold, and the hardness, silicon content, sulfate content and pollution index are all lower than their respective first scaling thresholds, the control system enters the first operating mode. When the total dissolved solids content of the saline-alkali water is not lower than the first salinity threshold and is lower than the second salinity threshold, and the hardness, silicon content, sulfate content and pollution index are all lower than their respective first scaling thresholds, the control system enters the second operating mode. When the total dissolved solids content of the saline-alkali water is lower than the second salinity threshold, and at least one of the hardness, silicon content, sulfate content and pollution index is not lower than its corresponding first scaling threshold and is lower than its corresponding second scaling threshold, the control system enters the third operating mode. When the total dissolved solids content of the saline water is not lower than the second salinity threshold, or when at least one of the hardness, silicon content, sulfate content, and fouling index is not lower than its corresponding second scaling threshold, the control system enters the third operating mode and reduces the recovery rate of the nanofiltration-brine reverse osmosis branch while increasing the flow rate of concentrated brine entering the membrane distillation unit.

6. The desert saline-alkali water green energy desalination hydrogen production and concentrated brine closed-loop treatment system according to claim 1, characterized in that, The ultrapure water preparation unit includes a two-stage reverse osmosis unit, an electro-deionization unit, a polishing mixed bed unit, an ultraviolet treatment unit, and a terminal filtration unit connected in sequence. The outlet water pipeline of the ultrapure water preparation unit is equipped with a conductivity detector and a reflux valve. When the conductivity of the outlet water is higher than the set value of the inlet water for electrolysis hydrogen production, the control unit controls the reflux valve to open, so that the unqualified outlet water flows back to the desalination water storage tank or the inlet end of the ultrapure water preparation unit.

7. The desert saline-alkali water green energy desalination hydrogen production and concentrated brine closed-loop treatment system according to claim 1, characterized in that, The raw water regulating tank, desalinated water storage tank, and ultrapure water storage tank are all equipped with liquid level detection components; the effective volume of the ultrapure water storage tank is not less than the water intake required for the electrolytic hydrogen production unit to operate at rated power for 2 hours; the control unit is configured to: increase the operating load of the adaptive desalination unit and the ultrapure water production unit when the renewable energy output power is higher than the first power threshold and the desalinated water storage tank or the ultrapure water storage tank has not reached the high liquid level; and reduce or stop the operating load of the adaptive desalination unit when the renewable energy output power is lower than the second power threshold, and supply water to the electrolytic hydrogen production unit from the ultrapure water storage tank.

8. The desert saline-alkali water green energy desalination hydrogen production and concentrated brine closed-loop treatment system according to claim 1, characterized in that, The renewable energy power supply unit includes a photovoltaic power generation device, a wind power generation device, an energy storage battery, a DC bus, and an energy management device; the adaptive desalination unit, the ultrapure water preparation unit, the electrolytic hydrogen production unit, and the membrane distillation device are all connected to the DC bus through a conversion device; the energy management device allocates renewable energy output power according to the priority of ultrapure water quality assurance, hydrogen production load maintenance, desalination water storage, concentrated brine concentration, and energy storage battery charging and discharging.

9. The desert saline-alkali water green energy desalination hydrogen production and concentrated brine closed-loop treatment system according to claim 1, characterized in that, The cooling and heat exchange circuit of the electrolytic hydrogen production unit includes an electrolytic cell coolant outlet, a three-way regulating valve, a first heat exchange branch, and a second heat dissipation branch. The first heat exchange branch is connected to the hot end of the membrane distillation device via a heat exchanger, and the second heat dissipation branch is connected to a heat dissipation device. The control unit adjusts the opening of the three-way regulating valve according to the electrolytic cell coolant outlet temperature and the membrane distillation device hot end inlet temperature to supply heat to the membrane distillation device while ensuring the electrolytic cell operating temperature.

10. The desert saline-alkali water green energy desalination hydrogen production and concentrated brine closed-loop treatment system according to claim 1, characterized in that, The concentrated brine closed-loop treatment unit also includes a concentrated brine storage tank. The closed-loop solar crystallization device includes a seepage-proof crystallization pool, a light-transmitting and heat-insulating cover, a dehumidification channel, a salt scraping mechanism, and a mother liquor return pipeline. The mother liquor return pipeline is connected to the inlet of the membrane distillation device or the concentrated brine storage tank. The concentrated brine closed-loop treatment unit does not have a concentrated brine liquid discharge port that is directly connected to the external environment. The concentrate produced by the membrane distillation device enters the closed-loop solar crystallization device for evaporation and crystallization. After crystallization, the remaining mother liquor is returned to the membrane distillation device or the concentrated brine storage tank for further processing via the mother liquor return pipeline.

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