A high-salinity wastewater zero-emission system based on natural cold energy dual-mode operation and a method of using the same

Abstract

This invention provides a zero-discharge system for high-salinity wastewater based on dual-mode operation using natural cooling energy and its usage method. The system includes a pre-concentration unit, a day / night dual-mode downflow tower, a crystallization tank, and an intelligent pump-pipe interlocking unit. This invention achieves "day / night dual-mode" operation through intelligent switching of fluid pipelines: during the day, the downflow tower operates in internal circulation, acting as a gas-liquid mass transfer device to evaporate the primary concentrate to a sub-saturated state and then unidirectionally overflows for storage; at night, a three-way valve switches to a large circulation mode, where the downflow tower acts as a forced convection radiator, introducing natural cold air to rapidly cool the concentrate. This invention utilizes the time difference effect of the crystallization induction period to achieve spatial separation of cooling and crystallization, supplemented by an online concentration closed-loop interlocking mechanism, effectively overcoming the technical challenge of scaling during evaporation in salt systems with temperature-changing precipitation characteristics. This constructs a high-salinity wastewater zero-discharge treatment technology route with extremely low energy consumption and a purely physical mechanism.

Description

Technical Field

[0001] This invention relates to the fields of environmental protection and high-salinity wastewater treatment technology, and more specifically, to a zero-discharge system for high-salinity wastewater based on dual-mode operation of natural cooling energy and its usage method. Background Technology

[0002] In zero-discharge wastewater treatment in industries such as coal chemical and dyeing, efficient salt separation and crystallization of salt systems with temperature-sensitive precipitation characteristics (such as sodium sulfate and sodium carbonate) has long been a key challenge for the engineering community. Current mainstream processes often employ reverse osmosis pre-concentration combined with mechanical vapor recompression (MVR) and other thermal evaporation methods. However, because the solubility of these salts is extremely sensitive to temperature, highly concentrated solutions are prone to localized supersaturation on the high-temperature heat exchange surfaces of traditional metal falling film evaporators, leading to scaling. Hardened scale not only causes a sharp drop in system heat transfer efficiency and frequent shutdowns for cleaning, but the traditional thermal crystallization process also consumes a significant amount of electrical and steam energy.

[0003] Therefore, there is an urgent need for a low-cost, high-efficiency anti-scaling zero-discharge system for high-salt wastewater. Summary of the Invention

[0004] In view of the shortcomings of existing technologies, this invention utilizes the excellent dry and hot sunshine and the dramatic diurnal temperature range in arid regions as free natural heat and cold sources to provide a high-salt wastewater zero-discharge system based on natural cold energy dual-mode operation and its usage method.

[0005] The high-salt wastewater zero-discharge system based on natural cooling energy dual-mode operation of the present invention effectively overcomes the risk of scaling inside the equipment by utilizing the time difference effect of the "crystallization induction period", and is particularly suitable for salt systems with temperature-varying precipitation characteristics.

[0006] Specifically, the high-salinity wastewater zero-discharge system based on natural cooling energy dual-mode operation of the present invention includes a pre-concentration unit, a day / night dual-mode downflow tower, a crystallization tank, and an intelligent pump-pipe interlocking unit. The pre-concentration unit includes a high-pressure RO component. The day / night dual-mode downflow tower has a flexible anti-scaling packing array suspended inside. The flexible anti-scaling packing array is made of at least one of polytetrafluoroethylene (PTFE) fiber, polyvinylidene fluoride (PVDF) fiber, polypropylene (PP) fiber, or a composite woven fabric of the above materials. The crystallization tank is independently and separately located from the day / night dual-mode downflow tower. The intelligent pump-pipe interlocking unit includes a feed water pump, a main circulation pump, and a mother liquor return pump. The feed water pump is connected between the pre-concentration unit and the day / night dual-mode downflow tower.

[0007] Furthermore, the pre-concentration unit also includes a freshwater collection tank connected to the permeate outlet of the high-pressure RO component; the bottom of the day and night dual-mode flow reduction tower is provided with an internal water collection trough and a variable frequency forced blower; the crystallization tank is equipped with an online concentration monitor, which is electrically connected to the feed water pump and the main circulation pump respectively, and is configured to automatically interlock and adjust the variable frequency speed of the feed water pump and the main circulation pump according to a preset concentration threshold.

[0008] Furthermore, the intelligent pump-pipe interlocking unit also includes a three-way control valve; the inlet of the main circulation pump is connected to the water collection trough inside the tower and the crystallization tank respectively through the three-way control valve, and its outlet is connected to the water distributor at the top of the day and night dual-mode flow reduction tower; the inlet of the mother liquor reflux pump is connected to the crystallization tank, and its outlet is connected to the reflux pipeline of the pre-concentration unit; the system also includes a heat source heat exchange unit, which includes a heat source heat exchanger disposed between the pre-concentration unit and the feed water pump; the side wall of the water collection trough inside the tower is provided with a one-way overflow weir, and the outlet of the one-way overflow weir is connected to the crystallization tank through a pipeline.

[0009] Furthermore, the three-way control valve is configured to perform day and night dual-mode flow path switching: in the daytime evaporation and concentration mode, it connects the water collection tank in the tower with the main circulation pump to form a self-circulation; in the nighttime forced cooling mode, it connects the crystallization pool with the main circulation pump to form a large circulation, so that the day and night dual-mode flow reduction tower operates as a forced convection radiator.

[0010] Furthermore, the system also includes a solar photovoltaic array, with a frequency conversion forced blower electrically connected to the solar photovoltaic array. It is configured to be directly driven by photovoltaics in daytime evaporation and concentration mode, and to switch to mains power or energy storage power supply in nighttime forced cooling mode to introduce natural cold air into the tower.

[0011] Furthermore, the high-salt wastewater is a salt system with temperature-dependent precipitation characteristics, and the solute in the salt system is selected from at least one of sodium sulfate, sodium carbonate, potassium nitrate, or magnesium sulfate.

[0012] This invention also provides a method for using the high-salinity wastewater zero-discharge system based on dual-mode operation of natural cooling energy as described above, comprising the following steps: Step S1, Front-end pre-concentration: High-salt wastewater enters the pre-concentration unit, where the high-pressure RO component generates demineralized water which is then discharged into the freshwater collection tank for reuse, producing a primary high-salt concentrate with a mass concentration of 8%-10%. Step S2, Daytime Evaporation and Concentration Mode: Switch the three-way control valve to allow the main circulation pump to draw fluid from the bottom water collection tank inside the tower and pump it into the water distributor at the top of the day and night dual-mode downflow tower, forming a self-circulation within the tower; the primary high-salt concentrate is pumped into the water distributor at the top of the day and night dual-mode downflow tower by the feed water pump, forming a liquid film on the surface of the flexible anti-scaling packing array and flowing downwards; the variable frequency forced blower introduces air for evaporation and concentration; when the concentrate in the bottom water collection tank inside the tower reaches a subsaturated state, it overflows through the one-way overflow weir into the crystallization tank for storage; Step S3, Nighttime Forced Cooling Mode: Turn off the feed water pump; switch the three-way control valve to allow the main circulation pump to draw high-heat concentrated water from the crystallization tank and pump it into the water distributor at the top of the day and night dual-mode flow reduction tower to form a large circulation; the variable frequency forced blower introduces cold air for forced convection heat transfer; the cooled fluid leaves the day and night dual-mode flow reduction tower and falls into the crystallization tank, where crystals of the target salt precipitate. Step S4, Morning Salt Recirculation Mode: Collect the crystals at the bottom of the crystallization tank, and pump the remaining low-temperature mother liquor to the front end of the system for processing by the mother liquor reflux pump.

[0013] Furthermore, in step S2, the primary high-salt concentrate before entering the day-night dual-mode downflow tower is preheated to 40°C-50°C by the heat source heat exchanger and then pumped into the water distributor at the top of the day-night dual-mode downflow tower by the feed water pump; the mass concentration threshold of the subsaturated state is set to 22%-25%.

[0014] Furthermore, in step S2, the anti-scaling closed-loop control logic is executed: when the online concentration monitor detects that the concentration in the crystallization tank is close to the upper limit of the set threshold, the speed of the feed water pump is automatically increased to inject low-concentration raw liquid for system dilution, and the flow rate of the main circulation pump is simultaneously increased to increase the liquid film scouring load on the surface of the flexible anti-scaling packing array.

[0015] Furthermore, in step S3, the operating flow rate of the main circulation pump is configured such that the hydraulic residence time of the fluid on the flexible anti-scaling packing array is lower than the crystallization induction period of the salt under the current temperature drop. The crystallization induction period is determined by laser scattering or conductivity catastrophe method, i.e., the time interval from when the supersaturated solution reaches the target temperature to when crystal nuclei are detected; the hydraulic residence time of the fluid on the packing layer is controlled to be 3-5 s, and must be less than 1 / 6 of the crystallization induction period of the salt under the current temperature drop conditions.

[0016] This invention employs a day-night intelligent switching method for fluid pipelines, combined with the time difference effect of the "crystallization induction period," to achieve zero-discharge treatment of high-salt wastewater with temperature-changing precipitation characteristics. Through the flexible linkage between the system's "daytime mass transfer evaporation" and "nighttime heat transfer cooling" modes, along with the coordination of dual-pump closed-loop control, absolute separation of cooling and crystallization in physical space is achieved. This results in excellent scale prevention performance, low operating energy consumption, compatibility with multiple salt types, and deep compatibility with natural environmental characteristics.

[0017] Compared with existing technologies, this invention utilizes the time difference effect of the crystallization induction period to achieve spatial separation of cooling and crystallization, and supplements it with an online concentration closed-loop interlocking mechanism. This effectively overcomes the technical challenge of scaling during the evaporation process in salt systems with temperature-changing precipitation characteristics, and constructs a zero-discharge technology route for high-salt wastewater treatment with extremely low energy consumption and an all-physical mechanism. Specifically, the beneficial effects of this invention are as follows: 1. Effectively inhibits scaling and avoids crusting on heat exchange surfaces: Utilizing the characteristics of the induction period, the high-concentration liquid undergoes only forced cooling and heat transfer in the day and night dual-mode downflow tower, without significant crystal nucleation growth. The precipitation process occurs entirely in the crystallization pool with extremely slow flow rate, significantly reducing the scaling risk of the downflow equipment. 2. Intelligent closed-loop interlock to prevent local dry burning: By regulating the global concentration through the feed water pump and maintaining the local liquid film through the main circulation pump, the dynamic adjustment of the system concentration and the forced coverage of the liquid film are realized, which effectively prevents local oversaturation and scaling caused by evaporation. 3. Wide applicability to multiple operating conditions: The system is not only suitable for sodium sulfate, but also has excellent compatibility with salts with temperature-sensitive precipitation characteristics such as sodium carbonate, potassium nitrate, and magnesium sulfate, thus broadening the application scenarios of industrial zero emission. 4. Extremely low energy consumption: It abandons the traditional thermal evaporation crystallization approach and deeply integrates the dry hot air, cool night air and solar photovoltaics from nature, eliminating the need for high-pressure steam and expensive compression refrigeration equipment, thus significantly reducing the system's operating costs. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the high-salinity wastewater zero-discharge system based on dual-mode operation of natural cooling energy provided in Example 1; Figure 2 This is a schematic diagram of the daytime evaporation and concentration mode of the high-salt wastewater zero-discharge system based on natural cold energy dual-mode operation in Example 2; Figure 3 This is a schematic diagram of the flow direction of the forced cooling mode at night for the high-salt wastewater zero-discharge system based on natural cooling energy dual-mode operation in Example 2; Figure 4 This is a schematic diagram comparing the solubility-temperature relationship of typical temperature-sensitive salts and temperature-insensitive salts in Example 5. Attached reference numerals: 1. High-pressure RO module; 2. Freshwater collection tank; 3. Feed water pump; 4. Day and night dual-mode flow reduction tower; 5. Flexible anti-scaling packing array; 6. Variable frequency forced blower; 7. Inner tower water collection trough; 8. One-way overflow weir; 9. Crystallization tank; 10. Online concentration monitor; 11. Main circulation pump; 12. Three-way control valve; 13. Mother liquor return pump; 14. Solar photovoltaic array; 15. Heat source heat exchanger. Detailed Implementation

[0019] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0020] The technical solution of the present invention will be further explained below with reference to implementation examples.

[0021] Example 1 This embodiment provides a zero-discharge system for high-salinity wastewater based on dual-mode operation of natural cooling energy. This embodiment uses wastewater with sodium sulfate as the solute as the treatment target.

[0022] like Figure 1 As shown, the high-salt wastewater zero-discharge system based on natural cold energy dual-mode operation in this embodiment forms a multifunctional closed loop in terms of physical connection. The system includes a pre-concentration unit, a day and night dual-mode flow reduction tower 4, a crystallization tank 9, an intelligent pump pipe interlocking unit, and a solar photovoltaic array 14.

[0023] The pre-concentration unit includes a high-pressure RO component 1, which has a concentration ratio of 3-5 times. The product water outlet of the high-pressure RO component 1 is connected to the fresh water collection tank 2, and its concentrate outlet is connected to the water distributor at the top of the day and night dual-mode downflow tower 4 after passing through the heat source heat exchanger 15 and the feed water pump 3.

[0024] The day / night dual-mode flow reduction tower 4 has a flexible anti-scaling packing array 5 suspended inside. The flexible anti-scaling packing array 5 is made of polytetrafluoroethylene (PTFE) fiber. The bottom of the tower has an internal water collection tank 7 and a variable frequency forced blower 6. The side wall has a one-way overflow weir 8, which is connected to a side-mounted crystallization tank 9 via a gravity pipeline (the crystallization tank 9 is independently set up beside the day / night dual-mode flow reduction tower 4). The two inlets of the key flow path switching component, the three-way control valve 12, are connected to the internal water collection tank 7 and the crystallization tank 9, respectively. Its outlet is connected to the main circulation pump 11, which pumps the fluid back to the top of the day / night dual-mode flow reduction tower 4.

[0025] The crystallization tank 9 is equipped with an online concentration monitor 10, which is electrically connected to the feed water pump 3 and the main circulation pump 11 respectively. It is configured to automatically interlock and adjust the variable frequency speed of the feed water pump 3 and the main circulation pump 11 according to the preset concentration threshold.

[0026] The intelligent pump-pipe interlocking unit includes a feed water pump 3, a main circulation pump 11, a mother liquor reflux pump 13, and a three-way control valve 12. The feed water pump 3 is connected between the pre-concentration unit and the day / night dual-mode flow reduction tower 4. The inlet of the mother liquor reflux pump 13 is connected to the crystallization tank 9, and its outlet is connected to the reflux pipeline of the pre-concentration unit. The inlet of the mother liquor reflux pump 13 extends into the supernatant area of ​​the crystallization tank 9, and its outlet is connected back to the front-end raw water tank of the high-pressure RO component 1 to achieve material balance of the entire system.

[0027] The three-way control valve 12 is configured to perform day and night dual-mode flow path switching: in the daytime evaporation and concentration mode, it connects the water collection tank 7 inside the tower with the main circulation pump 11 to form a self-circulation; in the nighttime forced cooling mode, it connects the crystallization pool 9 with the main circulation pump 11 to form a large circulation, so that the day and night dual-mode flow reduction tower 4 operates as a forced convection radiator.

[0028] The variable frequency forced blower 6 is electrically connected to the solar photovoltaic array 14 and is configured to be directly driven by photovoltaics in the daytime evaporation and concentration mode, and to switch to mains power or energy storage power supply in the nighttime forced cooling mode to introduce natural cold air into the tower.

[0029] Example 2 This embodiment provides a method for using the high-salinity wastewater zero-discharge system based on natural cooling energy dual-mode operation as described in Embodiment 1, including the following steps: Step S1, Front-end Pre-concentration: Sodium sulfate wastewater with an initial mass concentration of 3% enters the pre-concentration unit, where it undergoes membrane separation by the high-pressure RO component 1 under a high pressure of 120 bar, producing desalinated water that is discharged into the freshwater collection tank 2 for reuse. The concentrate produces a primary high-salt concentrate with a mass concentration of 10%.

[0030] Step S2, Daytime Evaporation Concentration Mode: (e.g.) Figure 2As shown, under this operating condition, the three-way control valve 12 switches to connect the water collection tank 7 inside the tower with the main circulation pump 11, and the main circulation pump 11 maintains a high-frequency self-circulation of the fluid inside the tower. The main circulation pump 11 draws fluid from the water collection tank 7 inside the tower and pumps it into the water distributor at the top of the day and night dual-mode downflow tower 4 to form a self-circulation inside the tower; the primary high-salt concentrate produced by the pre-concentration at the front end is preheated to 45°C by the heat exchanger 15 using low-grade waste heat from the plant area, and then pumped into the water distributor at the top of the day and night dual-mode downflow tower 4 by the feed water pump 3, forming a liquid film on the surface of the flexible anti-scaling packing array 5 and flowing downwards; the variable frequency forced blower 6, driven by the solar photovoltaic array 14, introduces dry and hot air from the outside, causing the water in the liquid film to evaporate rapidly. As concentration proceeds, the fluid concentration in the water collection tank 7 inside the tower gradually increases. When the concentrate concentration in the water collection tank 7 inside the tower reaches the subsaturation critical point of 25%, the excess fluid overflows through the one-way overflow weir 8 and is temporarily stored in the crystallization tank 9. At this time, the system is equipped with an automatic anti-scaling adjustment program: the online concentration monitor 10 monitors in real time. Once the concentration approaches the saturation line of 26%, the system automatically increases the speed of the feed water pump 3 to introduce the above-mentioned primary high-salt concentrate, and simultaneously increases the speed of the main circulation pump 11 to 120% of the rated flow. The large hydraulic load is used to flush the surface of the flexible anti-scaling packing array 5 to prevent local oversaturation dry spots from appearing.

[0031] Step S3, Nighttime Forced Cooling Mode: (e.g.) Figure 3As shown, after nightfall, the system stops feeding and preheating, and shuts down the feed water pump 3; the three-way control valve 12 is switched so that the main circulation pump 11 draws 25% of the high-heat concentrate stored in the crystallization tank 9 and pumps it into the water distributor at the top of the day-night dual-mode downflow tower 4; at this time, the variable frequency forced blower 6 introduces natural cold air (typical temperature 10℃) at full power; the fluid undergoes forced heat transfer on the surface of the flexible anti-scaling packing array 5, and the temperature drops instantly from 45℃ to below 10℃, and the fluid enters an extremely supersaturated metastable state. Because the flow rate setting of the main circulation pump 11 in the system configuration makes the residence time of the fluid on the flexible anti-scaling packing array 5 in the tower (t1=5s) strictly less than the crystallization induction period of the target salt at this temperature drop (t2>30s), the fluid only completes heat exchange in the day-night dual-mode downflow tower 4 without precipitation, successfully delaying the crystallization precipitation to occur in the crystallization tank 9 where the flow rate is extremely slow. The crystallization induction period was determined by laser scattering or conductivity catastrophe method. The determination method and supersaturation correlation model were referenced from Mullin JW's "Crystallization" (4th edition, Butterworth-Heinemann, 2001), Kashchiev D.'s "Nucleation: Basic Theory with Applications" (Butterworth-Heinemann, 2000), and Chen Jianxin et al.'s "Determination and Correlation of Crystallization Induction Period of Sodium Sulfate Solution" (Journal of Chemical Industry and Engineering, 2015, 66(5): 1678-1685).

[0032] Step S4, Morning Salt Discharge and Recirculation Mode: After continuous cooling circulation, a large amount of target salt crystals accumulate at the bottom of crystallization tank 9. Salt discharge is carried out in the morning, and the separated low-temperature mother liquor (concentration approximately 9%) is pumped back to the front end of the system by mother liquor recirculation pump 13 to re-enter the circulation.

[0033] Measurements showed that when the diurnal temperature range of the external temperature is 35℃, the daytime evaporation rate per unit area of ​​packing material can reach 2.8 kg / (m²). 2 (h); Simultaneously, thanks to the spatial separation mechanism of "fluid residence time < crystallization induction period" under forced cooling conditions at night, no obvious hard salt scale adhesion was observed in the flexible anti-scaling packing array 5 during 30 days of continuous operation. The crystals produced by the crystallization tank 9 have a purity of over 98%, achieving zero discharge and reuse of wastewater and resource utilization of salts.

[0034] Example 3 This embodiment refers to Embodiment 2. The difference between this embodiment and Embodiment 2 is that the primary high-salt concentrate produced by the pre-concentration at the front end of S2 is preheated to 35°C by the heat source heat exchanger 15 using low-grade waste heat from the plant area.

[0035] Measurements showed that when the diurnal temperature range of the external temperature was 25℃, the daytime evaporation rate per unit area of ​​packing material could reach 2.5 kg / (m²).2 ·h).

[0036] Example 4 This embodiment refers to Embodiment 2. The difference between this embodiment and Embodiment 2 is that the primary high-salt concentrate produced by the pre-concentration at the front end of S2 is preheated to 40°C by the heat source heat exchanger 15 using low-grade waste heat from the plant area.

[0037] Measurements showed that when the diurnal temperature range of the external temperature is 30℃, the daytime evaporation rate per unit area of ​​packing material can reach 2.6 kg / (m²). 2 ·h).

[0038] Example 5 This embodiment determined the solubility of sodium sulfate, sodium carbonate, potassium nitrate, and sodium chloride at different temperatures, such as Figure 4 As shown, Figure 4 A schematic diagram comparing the solubility-temperature relationship of typical temperature-sensitive salts (such as sodium sulfate, sodium carbonate, and potassium nitrate) and temperature-insensitive salts (such as sodium chloride) is shown. The solubility of the temperature-sensitive salt system (sodium sulfate, sodium carbonate, and potassium nitrate), which is the focus of this invention, decreases sharply with decreasing temperature. Based on the temperature-sensitive precipitation characteristics of salts, this invention achieves spatial decoupling between the high-temperature evaporation zone and the low-temperature crystallization zone by setting up an independent but switchable flow path water collection tank 7 and a crystallization tank 9 within the tower.

[0039] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A zero-discharge system for high-salinity wastewater based on dual-mode operation using natural cooling energy, characterized in that, The system includes a pre-concentration unit, a day and night dual-mode downflow tower (4), a crystallization tank (9), and an intelligent pump-pipe interlocking unit; the pre-concentration unit includes a high-pressure RO component (1); the day and night dual-mode downflow tower (4) has a flexible anti-scaling packing array (5) suspended inside; the crystallization tank (9) and the day and night dual-mode downflow tower (4) are set up independently and side by side; the intelligent pump-pipe interlocking unit includes a feed water pump (3), a main circulation pump (11), and a mother liquor return pump (13); the feed water pump (3) is connected between the pre-concentration unit and the day and night dual-mode downflow tower (4); The day and night dual-mode flow reduction tower (4) is provided with an internal water collection trough (7) and a variable frequency forced blower (6) at the bottom; the crystallization pool (9) is provided with an online concentration monitor (10), which is electrically connected to the feed water pump (3) and the main circulation pump (11) respectively. The intelligent pump pipe interlocking unit also includes a three-way control valve (12); the inlet of the main circulation pump (11) is connected to the water collection trough (7) in the tower and the crystallization tank (9) respectively through the three-way control valve (12), and its outlet is connected to the water distributor at the top of the day and night dual-mode flow reduction tower (4); the inlet of the mother liquor reflux pump (13) is connected to the crystallization tank (9), and its outlet is connected to the reflux pipeline of the pre-concentration unit; The three-way control valve (12) is configured to perform day and night dual-mode flow path switching: in the daytime evaporation and concentration mode, the water collection tank (7) inside the tower is connected to the main circulation pump (11) to form a self-circulation; in the nighttime forced cooling mode, the crystallization pool (9) is connected to the main circulation pump (11) to form a large circulation, so that the day and night dual-mode flow reduction tower (4) can operate as a forced convection radiator.

2. The high-salinity wastewater zero-discharge system based on natural cooling energy dual-mode operation according to claim 1, characterized in that, The pre-concentration unit also includes a freshwater collection tank (2) connected to the product outlet of the high-pressure RO component (1).

3. The high-salinity wastewater zero-discharge system based on natural cooling energy dual-mode operation according to claim 2, characterized in that, The system also includes a heat source heat exchange unit, which includes a heat source heat exchanger (15) disposed between the pre-concentration unit and the feed water pump (3); the side wall of the water collection bottom tank (7) in the tower is provided with a one-way overflow weir (8), and the outlet of the one-way overflow weir (8) is connected to the crystallization tank (9) through a pipeline.

4. The high-salinity wastewater zero-discharge system based on natural cooling energy dual-mode operation according to claim 2, characterized in that, The system also includes a solar photovoltaic array (14), and the variable frequency forced blower (6) is electrically connected to the solar photovoltaic array (14) and configured to accept direct photovoltaic drive in daytime evaporation and concentration mode and switch to mains power or energy storage power supply in nighttime forced cooling mode.

5. The high-salinity wastewater zero-discharge system based on natural cooling energy dual-mode operation according to claim 1, characterized in that, The high-salinity wastewater is a salt system with temperature-dependent precipitation characteristics, and the solute in the salt system is selected from at least one of sodium sulfate, sodium carbonate, potassium nitrate, or magnesium sulfate.

6. The method of using the high-salinity wastewater zero-discharge system based on natural cooling energy dual-mode operation as described in claim 1, characterized in that, Includes the following steps: Step S1, Front-end pre-concentration: High-salt wastewater enters the pre-concentration unit, and the high-pressure RO component (1) generates desalinated water which is discharged into the freshwater collection tank (2) for reuse, producing a primary high-salt concentrate with a mass concentration of 8%-10%. Step S2, Daytime Evaporation and Concentration Mode: Switch the three-way control valve (12) so that the main circulation pump (11) draws the fluid from the water collection tank (7) in the tower and pumps it into the water distributor at the top of the day and night dual-mode downflow tower (4) to form a self-circulation in the tower; the primary high-salt concentrate is pumped into the water distributor at the top of the day and night dual-mode downflow tower (4) by the feed water pump (3) and forms a liquid film on the surface of the flexible anti-scaling packing array (5) and flows downward; the variable frequency forced blower (6) introduces air for evaporation and concentration; when the concentrate in the water collection tank (7) in the tower reaches a subsaturated state, it overflows into the crystallization tank (9) through the one-way overflow weir (8) for storage; Step S3, Nighttime Forced Cooling Mode: Turn off the feed water pump (3); switch the three-way control valve (12) so that the main circulation pump (11) draws the hot concentrated water in the crystallization tank (9) and pumps it into the water distributor at the top of the day and night dual-mode flow tower (4) to form a large circulation; the variable frequency forced blower (6) introduces cold air for forced convection heat transfer; the cooled fluid leaves the day and night dual-mode flow tower (4) and falls into the crystallization tank (9), and crystals of the target salt are precipitated in the tank; Step S4, Morning Salt Recirculation Mode: Collect the crystals at the bottom of the crystallization tank (9), and pump the remaining low-temperature mother liquor to the front end of the system for processing by the mother liquor reflux pump (13).

7. The method according to claim 6, characterized in that, In step S2, the primary high-salt concentrate before entering the day and night dual-mode downflow tower (4) is preheated to 40°C-50°C by the heat source heat exchanger (15) and then pumped into the water distributor at the top of the day and night dual-mode downflow tower (4) by the feed water pump (3); the mass concentration threshold of the subsaturated state is set to 22%-25%.

8. The method according to claim 6, characterized in that, In step S3, the operating flow rate of the main circulation pump (11) is configured such that the hydraulic residence time of the fluid on the flexible anti-scaling packing array (5) is lower than the crystallization induction period of the salt at the current temperature drop.

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