A low-temperature concentrated brine flash crystallization apparatus and method with self-generated steam replenishment and enhanced foaming

Abstract

This invention provides a low-temperature concentrated brine flash crystallization device and method with self-generated steam foaming enhancement, belonging to the technical field of zero liquid discharge of high-salt wastewater and concentrated brine evaporation crystallization. It includes a concentrated brine storage tank, a pre-filter, a feed pump, a waste heat exchanger, a pressure stabilizing buffer tank, a foaming device, a steam return pipe, a foaming regulating valve, a check valve, a mixer, a large-diameter flash nozzle, a low-pressure flash crystallization chamber, a demister, a condenser, a pressure regulating device, a distilled water collection tank, a brine slurry outlet, a brine separator, a salt crystal collector, a mother liquor circulation pump, and a mother liquor return pipe. This invention solves the problems of insufficient nucleation during low-superheat flash evaporation, inadequate atomization of large-diameter nozzles, easy clogging of small-diameter nozzles, high energy consumption at the end of concentrated brine crystallization, and insufficient stability of continuous system operation in existing technologies.

Description

Technical Field

[0001] This invention relates to the field of zero liquid discharge of high-salt wastewater and concentrated brine evaporation and crystallization technology, and in particular to a low-temperature concentrated brine flash evaporation and crystallization device and method with self-generated steam replenishment and enhancement. Background Technology

[0002] High-salinity wastewater is widely generated in processes such as coal chemical industry, petrochemical industry, metallurgy, electroplating, pharmaceutical industry, printing and dyeing, concentrated wastewater from seawater desalination, landfill leachate treatment, and industrial circulating water discharge. This type of wastewater typically contains high concentrations of chloride ions, sulfate ions, sodium ions, calcium and magnesium ions, and other inorganic salts. If high-salinity wastewater is discharged directly without proper treatment, it can easily cause water mineralization, soil salinization, and long-term pollution of the receiving environment. With increasingly stringent environmental protection requirements and stricter water resource constraints, the treatment goals for high-salinity wastewater are gradually shifting from simply meeting discharge standards to achieving high reuse rates, low risk of external discharge, and zero liquid discharge. Zero-liquid-discharge processes typically include pretreatment, membrane concentration, thermal concentration, and terminal crystallization and solidification. Among these, the terminal crystallization and solidification stage, due to its high brine concentration, high risk of scaling, and high energy consumption, is a crucial factor limiting the engineering-scale promotion of zero-liquid-discharge for high-salinity wastewater.

[0003] Existing membrane concentration technologies, such as reverse osmosis, nanofiltration, electrodialysis, and membrane distillation, are suitable for concentrating brine within a certain concentration range. However, when the brine concentration increases and approaches saturation or supersaturation, membrane methods are typically limited by issues such as increased osmotic pressure, membrane fouling, membrane scaling, and frequent membrane cleaning, making it difficult to directly achieve salt crystal precipitation and solid-liquid separation. Therefore, the concentrated brine after membrane concentration usually still needs to undergo end-of-pipe solidification treatment using thermal or crystallization processes. Traditional thermal crystallization technologies such as mechanical vapor recompression evaporation, forced circulation evaporation, and multi-effect evaporation can handle high-concentration brine, but they typically suffer from high equipment investment, system complexity, easy scaling on heat exchange surfaces, and high maintenance costs. Especially when the concentrated brine is close to saturation or supersaturation, salt crystals easily precipitate on heat exchange surfaces, pipes, and valves, leading to decreased heat transfer efficiency or even blockage. However, for near-saturated or supersaturated concentrated brine, there is a clear contradiction between nozzle orifice diameter, atomization effect, and clogging risk: small-diameter nozzles, while beneficial for liquid breakup, are prone to clogging due to salt crystals, suspended solids, or localized salt precipitation; large-diameter nozzles, while beneficial for improving anti-clogging capabilities, suffer from insufficient jet breakup capacity under low temperature and low superheat conditions, easily leading to a decrease in flash evaporation rate and reduced salt crystal precipitation efficiency. Spray evaporation and flash spray technologies can enhance water evaporation by increasing the gas-liquid contact area. Traditional high-pressure atomization, centrifugal atomization, or airflow atomization typically rely on external mechanical energy, high pressure differential, or high-speed airflow to achieve liquid breakup. To obtain smaller droplets, nozzle orifices are often small, with some high-pressure atomization nozzles even having orifices smaller than 1 mm. For high-salinity wastewater, small-diameter nozzles are highly susceptible to clogging due to salt precipitation, crystal particles, suspended solids, or localized concentration. Low-temperature flash spray crystallization technology driven by low-grade industrial waste heat can heat concentrated brine to a relatively low temperature before spraying it into a low-pressure flash evaporation space, causing water evaporation and promoting salt crystallization. This technology has the potential to utilize low-temperature waste heat, reduce high-grade energy consumption, and minimize scaling on heat exchange surfaces. However, under low-temperature and low-superheat conditions, there are insufficient nucleation sites within the concentrated brine, and conventional low-temperature flash spray evaporation is prone to problems such as delayed liquid column breakup, insufficient atomization, decreased evaporation rate, and insufficient crystallization efficiency. Therefore, there is an urgent need for a device and method that can stably achieve flash atomization, evaporation concentration, and crystallization of concentrated brine under low-temperature, low-superheat, and large-diameter nozzle conditions, while also considering low energy consumption, anti-clogging, and high-efficiency crystallization. Summary of the Invention

[0004] The purpose of this invention is to provide a low-temperature concentrated brine flash crystallization device and method with self-generated steam replenishment and enhancement, which solves the problems of insufficient nucleation at low superheat flash evaporation, insufficient atomization of large-diameter nozzles, easy clogging of small-diameter nozzles, high energy consumption at the end of concentrated brine crystallization, and insufficient stability of continuous system operation in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A low-temperature concentrated brine flash crystallization device with self-generated steam foam replenishment enhancement includes a concentrated brine storage tank, a pre-filter, a feed pump, a waste heat exchanger, a pressure stabilizing buffer tank, a foam replenisher, a steam reflux pipe, a foam replenishment regulating valve, a check valve, a mixer, a large-diameter flash nozzle, a low-pressure flash crystallization chamber, a demister, a condenser, a pressure regulating device, a distilled water collection tank, a brine slurry outlet, a brine separator, a salt crystal collector, a mother liquor circulation pump, and a mother liquor reflux pipe.

[0006] The outlet of the concentrated brine storage tank is connected to the inlet of the pre-filter; the outlet of the pre-filter is connected to the inlet of the feed pump; the outlet of the feed pump is connected to the inlet of the waste heat exchanger; the outlet of the waste heat exchanger is connected to the inlet of the pressure stabilizing buffer tank; the outlet of the pressure stabilizing buffer tank is connected to the inlet of the bubbler; the outlet of the bubbler is connected to the inlet of the mixer; the outlet of the mixer is connected to the inlet of the large-diameter flash nozzle; the outlet of the large-diameter flash nozzle is connected to the low-pressure flash crystallization chamber; the gas phase outlet of the low-pressure flash crystallization chamber is connected to the inlet of the demister via a steam pipe; one end of the steam return pipe is connected to the middle of the steam pipe; the steam return pipe... The other end is connected to the steam inlet of the foam replenisher. A foam replenishing regulating valve and a check valve are sequentially installed on the steam return pipe. The outlet of the demister is connected to the inlet of the condenser. The liquid outlet of the condenser is connected to the distilled water collection tank. The pressure regulating device is connected to the gas side outlet of the condenser and regulates the pressure of the low-pressure flash crystallization chamber through the condenser and steam pipeline. A salt slurry outlet is provided at the bottom of the low-pressure flash crystallization chamber. The salt slurry outlet is connected to the brine separator. The solid outlet of the brine separator is connected to the salt crystal collector. The mother liquor outlet of the brine separator is connected to the inlet of the concentrated brine storage tank through the mother liquor return pipe. A mother liquor circulation pump is installed on the mother liquor return pipe.

[0007] Furthermore, the bubble replenisher is a Venturi bubble replenisher, which includes an inlet constriction section, a throat, a diffuser section, and a negative pressure suction port. The inlet constriction section is located at one end of the bubble replenisher, the diffuser section is located at the other end of the bubble replenisher, the throat is located between the inlet constriction section and the diffuser section, and the negative pressure suction port is located at the top of the throat. The negative pressure suction port serves as the steam inlet of the bubble replenisher and is connected to the steam return pipe.

[0008] Furthermore, the ratio of the throat diameter to the inlet pipe diameter of the bubble replenisher is 0.45 to 0.65, the liquid flow velocity in the throat of the bubble replenisher is 4 m / s to 12 m / s, and the local pressure drop formed by the bubble replenisher is 10 kPa to 50 kPa.

[0009] Furthermore, the outlet diameter of the large-diameter flash nozzle is 6mm to 20mm, and the outlet flow velocity of the large-diameter flash nozzle is 4m / s to 12m / s.

[0010] Furthermore, the low-pressure flash crystallization chamber is used to provide a flash environment with a pressure lower than that at the inlet of the large-diameter flash nozzle, and the absolute pressure of the low-pressure flash crystallization chamber is 10 kPa to 50 kPa; the effective superheat of the concentrated brine before entering the large-diameter flash nozzle is 5°C to 15°C.

[0011] A method for using a low-temperature concentrated brine flash crystallization device with self-generated steam replenishment and enhanced foaming includes the following steps: S1. Start-up status: During the start-up phase, the concentrated brine storage tank is first filled with concentrated brine to be treated, and the feed pump and pressure regulating device are started to bring the low-pressure flash crystallization chamber to the set pressure. With the foam replenishment regulating valve closed or slightly open, the heated concentrated brine enters the low-pressure flash crystallization chamber through the large-diameter flash nozzle and generates initial self-generated steam. When the pressure, flow rate or temperature of the self-generated steam in the low-pressure flash crystallization chamber reaches the set conditions, the foam replenishment regulating valve is gradually opened to allow the self-generated steam to enter the foam replenisher through the steam return pipe.

[0012] S2. Pretreatment of concentrated brine: The concentrated brine to be treated enters the concentrated brine storage tank and passes through a pre-filter to remove large particulate suspended matter.

[0013] S3. Heating concentrated brine: The feed pump sends the concentrated brine into the waste heat exchanger, which uses industrial low-grade waste heat to heat the concentrated brine to the set temperature. The concentrated brine can be heated to 40℃~95℃.

[0014] S4. Allow the heated concentrated brine to flow through the bubble replenisher: The bubble replenisher creates a local low-pressure zone as the concentrated brine flows through it.

[0015] S5. Self-generated steam is drawn from the middle of the steam pipeline and introduced into the bubbler under pressure difference through the steam return pipe.

[0016] S6. To form steam bubbles or steam nuclei in the bubbler: The volume fraction of steam bubbles or steam nuclei in the concentrated brine before entering the large-diameter flash nozzle can be controlled to be 0.1% to 20%; or the ratio of the volume flow rate of the self-generated steam to the volume flow rate of the concentrated brine in the steam return pipe can be controlled to be 0.001 to 0.20.

[0017] S7. The concentrated brine containing steam bubbles or steam nuclei is injected into the low-pressure flash crystallization chamber through a large-diameter flash nozzle. The outlet flow rate of the large-diameter flash nozzle is controlled to be 4m / s to 12m / s.

[0018] S8. Allow steam bubbles or steam nuclei to grow under reduced pressure conditions in a low-pressure flash crystallization chamber to induce the concentrated brine to break up, flash evaporate, and precipitate salt crystals.

[0019] S9. The water vapor generated by flash evaporation is condensed and recovered.

[0020] S10. Separate the precipitated salt crystals and mother liquor: The separated mother liquor can be returned to the step before or during the concentrated brine heating step, mixed with the newly added concentrated brine, and then processed.

[0021] Advantages of this invention: 1. Since the steam return pipe introduces the self-generated steam generated in the low-pressure flash crystallization chamber into the bubble replenisher under the action of pressure difference, the present invention can pre-place steam bubbles or steam nuclei in the concentrated brine before the inlet of the large-diameter flash nozzle. The steam bubbles or steam nuclei can serve as flash nucleation sites, alleviating the problem of insufficient nucleation under low superheat conditions.

[0022] 2. Since the pre-placed steam bubbles or steam nuclei can grow rapidly as the pressure decreases after entering the low-pressure flash crystallization chamber, the present invention can use the expansion of bubbles to induce the breakage of liquid columns, liquid films or droplets, so that large-diameter nozzles can still have good flash breakage and evaporation effects under low temperature and low superheat conditions.

[0023] 3. Since the outlet diameter of the large-diameter flash nozzle is greater than 5mm, the present invention can reduce the risk of nozzle blockage caused by salting out of concentrated brine, crystal particles, suspended matter or local crystallization, thereby improving the stability of continuous operation under crystal-containing or high-salt conditions.

[0024] 4. Since the present invention uses self-generated water vapor as the bubble replenishing medium, rather than a large amount of external air, it can reduce the possibility of non-condensable gases such as air entering the condensation system, which is beneficial to maintaining the condensation heat exchange efficiency and the pressure stability of the low-pressure flash crystallization chamber.

[0025] 5. Since the atomization enhancement mechanism of the present invention mainly relies on the self-generated steam negative pressure return, the pre-positioning of the steam core in front of the nozzle, and the growth of bubbles in a low-pressure environment, rather than simply relying on the shearing or compressed air source of the high-pressure small-diameter nozzle, it is beneficial to reduce the dependence on high-pressure pumps, compressed air or high-grade energy, and is easy to couple with industrial low-grade waste heat.

[0026] 6. Since the present invention can be equipped with a foam replenishment regulating valve, a check valve, and a mother liquor reflux, the system can maintain operational stability by adjusting the foam replenishment amount, reflux flow rate, or flushing operation when starting up, stopping, when salinity rises abnormally, when pipeline pressure difference is abnormal, or when the risk of salt slurry deposition increases. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the device of the present invention; Figure 2 This is a schematic diagram showing the connection relationship between the bubble replenisher and the steam return pipe in this invention; Figure 3 This is a schematic diagram showing the connection relationship between the bubble replenisher, the mixer, and the large-diameter flash nozzle in this invention; Figure 4This is a schematic diagram of the self-generated steam replenishment and enhanced flash crushing mechanism of the present invention; In the diagram: 1. Concentrated brine storage tank; 2. Pre-filter; 3. Feed pump; 4. Waste heat exchanger; 5. Pressure stabilizing buffer tank; 6. Foaming device; 61. Inlet contraction section; 62. Throat; 63. Diffusion section; 64. Negative pressure suction port; 7. Steam return pipe; 8. Foaming regulating valve; 9. Check valve; 10. Mixer; 11. Large-diameter flash nozzle; 12. Low-pressure flash crystallization chamber; 13. Demister; 14. Condenser; 15. Pressure regulating device; 16. Distilled water collection tank; 17. Brine outlet; 18. Brine separator; 19. Salt crystal collector; 20. Mother liquor circulation pump; 21. Mother liquor return pipe. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention.

[0029] like Figure 1 As shown, a low-temperature concentrated brine flash crystallization device with self-generated steam foam replenishment includes a concentrated brine storage tank 1, a pre-filter 2, a feed pump 3, a waste heat exchanger 4, a pressure stabilizing buffer tank 5, a foam replenisher 6, a steam return pipe 7, a foam replenishment regulating valve 8, a check valve 9, a mixer 10, a large-diameter flash nozzle 11, a low-pressure flash crystallization chamber 12, a demister 13, a condenser 14, a pressure regulating device 15, a distilled water collection tank 16, a brine slurry outlet 17, a brine separator 18, a salt crystal collector 19, a mother liquor circulation pump 20, and a mother liquor return pipe 21.

[0030] The outlet of the concentrated brine storage tank 1 is connected to the inlet of the pre-filter 2, the outlet of the pre-filter 2 is connected to the inlet of the feed pump 3, the outlet of the feed pump 3 is connected to the inlet of the waste heat exchanger 4, the outlet of the waste heat exchanger 4 is connected to the inlet of the pressure stabilizing buffer tank 5, the outlet of the pressure stabilizing buffer tank 5 is connected to the inlet of the bubble replenisher 6, the outlet of the bubble replenisher 6 is connected to the inlet of the mixer 10, and the outlet of the mixer 10 is connected to the inlet of the large-diameter flash nozzle 11. The mixer 10 is used to further disperse the self-generated steam in the concentrated brine, improving the uniformity of the gas-liquid two-phase flow before entering the large-diameter flash nozzle 11. The mixer 10 can be at least one of the following: a vortex mixer, a static mixer, a spiral guide mixer, a tangential inflow mixer, a baffle mixer, and a porous dispersion mixer. The outlet of the large-diameter flash nozzle 11 is connected to the low-pressure flash crystallization chamber 12. The gas phase outlet of the low-pressure flash crystallization chamber 12 is connected to the inlet of the demister 13 via a steam pipe. The demister 13 is used to intercept droplets, salt spray, or micro-crystals entrained in water vapor. The demister 13 is a wire mesh demister, a baffle plate demister, a cyclone demister, or a combined demister structure. One end of the steam return pipe 7 is connected to the middle of the steam pipe, and the other end of the steam return pipe 7 is connected to the steam inlet of the bubble replenisher 6. It is used to introduce self-generated steam into the concentrated brine pipeline, so that the self-generated steam forms steam bubbles or steam nuclei in the concentrated brine. A bubble replenishment regulating valve 8 and a check valve 9 are sequentially installed on the steam return pipe 7. The bubble replenishment regulating valve 8 is used to regulate the flow rate of self-generated steam entering the bubble replenisher 6, and the check valve 9 is used to prevent concentrated brine from flowing back into the steam return pipe 7. The outlet of the demister 13 is connected to the inlet of the condenser 14, which is used to condense the water vapor generated by flash evaporation into distilled water. The condenser 14 can be a plate condenser, shell-and-tube condenser, spray condenser, direct contact condenser, or other condensation device. The liquid outlet of the condenser 14 is connected to the distilled water collection tank 16. The pressure regulating device 15 is connected to the gas-side outlet of the condenser 14 and regulates the pressure of the low-pressure flash crystallization chamber 12 through the condenser 14 and the steam pipeline. The pressure regulating device 15 can be a vacuum pump, a steam ejector, a condensation vacuum combination device, a pressure regulating valve, or a combination thereof. A salt slurry outlet 17 is provided at the bottom of the low-pressure flash crystallization chamber 12. The salt slurry outlet 17 is connected to the brine separator 18. The solid outlet of the brine separator 18 is connected to the salt crystal collector 19. The mother liquor outlet of the brine separator 18 is connected to the inlet of the concentrated brine storage tank 1 through the mother liquor return pipe 21. A mother liquor circulation pump 20 is provided on the mother liquor return pipe 21. The salt slurry generated at the bottom of the low-pressure flash crystallization chamber 12 enters the brine separator 18 through the salt slurry outlet 17. The brine separator 18 is used to separate the precipitated salt crystals from the mother liquor. The brine separator 18 is a settling separator, a hydrocyclone separator, a centrifuge, a filter, a baffle plate separator, a scraper-type crystallization and salt discharge device, or a combination thereof.After separation, the salt crystals enter the salt crystal collector 19. The separated mother liquor is returned to the concentrated brine storage tank 1 or the inlet of the waste heat exchanger 4 via the mother liquor circulation pump 20 and the mother liquor return pipe 21, and then mixed with the newly added concentrated brine for further processing.

[0031] In a preferred embodiment of the present invention, the bubble replenisher 6 is a negative pressure bubble replenisher. When concentrated brine flows through the bubble replenisher 6, a local low-pressure zone is formed inside the bubble replenisher 6. The pressure in this local low-pressure zone is lower than the gas phase pressure at the self-generated steam outlet, causing the self-generated steam to enter the bubble replenisher 6 through the steam return pipe 7 under the action of the pressure difference.

[0032] As a preferred embodiment of the present invention, such as Figure 2 and Figure 3 As shown, the bubble replenisher 6 is a Venturi bubble replenisher. The bubble replenisher 6 includes an inlet constriction section 61, a throat 62, a diffuser section 63, and a negative pressure suction port 64. The inlet constriction section 61 is located at one end of the bubble replenisher 6, the diffuser section 63 is located at the other end of the bubble replenisher 6, the throat 62 is located between the inlet constriction section 61 and the diffuser section 63, and the negative pressure suction port 64 is located at the top of the throat 62. The negative pressure suction port 64 serves as the steam inlet of the bubble replenisher 6 and is connected to the steam return pipe 7.

[0033] In a preferred embodiment of the present invention, the ratio of the diameter of the throat 62 of the bubble replenisher 6 to the diameter of the inlet pipe is 0.45 to 0.65, the liquid flow velocity of the throat 62 of the bubble replenisher 6 is 4 m / s to 12 m / s, and the local pressure drop formed by the bubble replenisher 6 is 10 kPa to 50 kPa.

[0034] In a preferred embodiment of the present invention, the bubble replenisher 6 is an ejector, an ejector pump, a swirling negative pressure bubble replenisher, a microporous steam injector, a mechanical gas mixer, or other gas-liquid mixing device capable of introducing self-generated steam into the concentrated brine pipeline and forming steam bubbles or steam nuclei.

[0035] In a preferred embodiment of the present invention, the outlet diameter of the large-diameter flash nozzle 11 is greater than 5 mm, and the outlet diameter of the large-diameter flash nozzle 11 is 6 mm to 20 mm. The large-diameter flash nozzle 11 can be a straight-hole nozzle, a tapered nozzle, a tapered-expanding nozzle, a flat-mouth nozzle, an annular nozzle, a multi-hole nozzle, or a slit nozzle. The outlet flow velocity of the large-diameter flash nozzle 11 is 4 m / s to 12 m / s.

[0036] In a preferred embodiment of the present invention, the low-pressure flash crystallization chamber 12 provides a flash environment with a pressure lower than the inlet pressure of the large-diameter flash nozzle 11. The absolute pressure of the low-pressure flash crystallization chamber 12 is 10 kPa to 50 kPa. The effective superheat of the concentrated brine before entering the large-diameter flash nozzle 11 is 5°C to 15°C. In this specification, the effective superheat refers to the difference between the temperature of the concentrated brine before entering the large-diameter flash nozzle 11 and the saturation temperature of the salt solution corresponding to the pressure of the low-pressure flash crystallization chamber 12. For salt-containing systems, due to the boiling point elevation phenomenon of salt solutions, the saturation temperature of the salt solution should be corrected according to the salinity.

[0037] The pressure of the low-pressure flash crystallization chamber 12 can be determined based on the concentrated brine feed temperature, the target effective superheat, and the boiling point elevation of the salt solution, so that the concentrated brine has a flash driving force after entering the low-pressure flash crystallization chamber 12. When the salinity increases, leading to an increase in the boiling point, the flash crushing effect can be maintained by reducing the pressure of the low-pressure flash crystallization chamber 12, increasing the concentrated brine feed temperature, or increasing the amount of self-generated steam for foaming.

[0038] like Figure 4 As shown, concentrated brine containing vapor bubbles or vapor nuclei enters the low-pressure flash crystallization chamber 12 through a large-diameter flash nozzle 11. Due to the decrease in external pressure, the vapor bubbles or vapor nuclei grow rapidly. The expansion effect generated by the bubble growth induces the breakage of the liquid column, liquid film, or droplets, promoting water vaporization. As water evaporates, the concentrated brine further concentrates. When the salt content reaches or exceeds the solubility limit, salt crystals precipitate and form a salt slurry.

[0039] As a preferred embodiment of the present invention, the main operating parameters of the device of the present invention can be set as follows:

[0040] The above parameters are not required to be arbitrarily combined, but should meet the following constraints: the pressure of the low-pressure flash crystallization chamber 12 should be determined according to the feed temperature and the boiling point rise of the salt solution, so that the effective superheat is kept within the set range; the throughput of the large-diameter flash nozzle 11 should be matched with the nozzle outlet diameter, so that the nozzle outlet flow rate is kept within the set range; the pressure of the local low-pressure zone in the bubble replenisher 6 should be lower than the gas phase pressure at the self-generated steam outlet, so as to ensure that the self-generated steam can be introduced into the bubble replenisher 6; the solids content of the salt slurry should be kept within the flowable range to avoid blockage of the salt slurry outlet 17, the inlet of the brine separator 18, or the mother liquor return pipe 21.

[0041] A method for using a low-temperature concentrated brine flash crystallization device with self-generated steam replenishment and enhanced foaming includes the following steps: S1. Start-up status: During the start-up phase, the concentrated brine storage tank 1 is first filled with concentrated brine to be treated, and the feed pump 3 and pressure regulating device 15 are started to make the low-pressure flash crystallization chamber 12 reach the set pressure. With the foam replenishing regulating valve 8 closed or slightly open, the heated concentrated brine enters the low-pressure flash crystallization chamber 12 through the large-diameter flash nozzle 11 and generates initial self-generated steam. When the pressure, flow rate or temperature of the self-generated steam in the low-pressure flash crystallization chamber 12 reaches the set conditions, the foam replenishing regulating valve 8 is gradually opened so that the self-generated steam enters the foam replenisher 6 through the steam return pipe 7.

[0042] S2. Pretreatment of concentrated brine: The concentrated brine to be treated enters the concentrated brine storage tank 1 and passes through the pre-filter 2 to remove large particulate suspended matter.

[0043] S3. Heating concentrated brine: Feed pump 3 sends concentrated brine into waste heat exchanger 4. Waste heat exchanger 4 uses industrial low-grade waste heat to heat concentrated brine to a set temperature. Concentrated brine can be heated to 40℃~95℃.

[0044] S4. Allow the heated concentrated brine to flow through the bubble replenisher 6: The bubble replenisher 6 forms a local low-pressure zone when the concentrated brine flows through it.

[0045] S5. Self-generated steam is drawn from the middle of the steam pipeline and introduced into the bubble replenisher 6 under pressure difference through the steam return pipe 7.

[0046] S6. To form steam bubbles or steam nuclei in the bubbler 6: The volume fraction of steam bubbles or steam nuclei in the concentrated brine before entering the large-diameter flash nozzle 11 can be controlled to be 0.1% to 20%; or the ratio of the volume flow rate of the self-generated steam to the volume flow rate of the concentrated brine in the steam return pipe 7 can be controlled to be 0.001 to 0.20.

[0047] S7. The concentrated brine containing steam bubbles or steam nuclei is injected into the low-pressure flash crystallization chamber 12 through the large-diameter flash nozzle 11. The outlet flow rate of the large-diameter flash nozzle 11 is controlled to be 4m / s to 12m / s.

[0048] S8. Allow steam bubbles or steam nuclei to grow under reduced pressure conditions in the low-pressure flash crystallization chamber 12 to induce the concentrated brine to break up, flash evaporate, and precipitate salt crystals.

[0049] S9. The water vapor generated by flash evaporation is condensed and recovered.

[0050] S10. Separate the precipitated salt crystals and mother liquor: The separated mother liquor can be returned to the step before or during the concentrated brine heating step, mixed with the newly added concentrated brine, and then processed.

[0051] Method Example 1. Treatment of moderately saline concentrated brine: The total salinity of the concentrated brine to be treated is 12 wt%. After being filtered by pre-filter 2, it enters waste heat exchanger 4 and is heated to 60°C. The pressure of the low-pressure flash crystallization chamber 12 is corrected and controlled according to the boiling point rise under this salinity condition, so that the effective superheat of the concentrated brine before entering the large-diameter flash nozzle 11 is maintained at 5°C to 15°C. In one operating mode, the absolute pressure of the low-pressure flash crystallization chamber 12 can be controlled within the range of 15 kPa to 25 kPa, and fine-tuned according to the condensate generation rate, nozzle inlet pressure difference, and foam replenishment status.

[0052] The heated concentrated brine enters the bubbler 6 via the pressure stabilizing buffer tank 5. In this embodiment, the bubbler 6 is a Venturi bubbler, with a throat diameter to inlet pipe diameter ratio of 0.55. By adjusting the bubbler regulating valve 8, the volume fraction of steam bubbles or vapor nuclei in the concentrated brine before entering the large-diameter flash nozzle 11 is maintained at 2%–6%, or the ratio of the self-generated steam volume flow rate to the concentrated brine volume flow rate in the steam return pipe 7 is maintained at 0.01–0.05. The concentrated brine containing steam bubbles or vapor nuclei is sprayed into the low-pressure flash crystallization chamber 12 through the large-diameter flash nozzle 11 with an outlet diameter of 8 mm. After entering the low-pressure flash crystallization chamber 12, the concentrated brine undergoes flash breakage and evaporation concentration. The steam is condensed and recovered by the condenser 14, and the concentrated brine slurry enters the brine separator 18 for solid-liquid separation.

[0053] Under this condition, after the bubble-addition regulating valve 8 is opened, steam bubbles or steam nuclei are formed in the concentrated brine before the nozzle inlet, the complete section of the jet column is shortened, and the breaking start position is closer to the outlet of the large-diameter flash nozzle 11; the spray diffusion range in the low-pressure flash crystallization chamber 12 is larger than when the bubble-addition is closed, the droplet settling area is more dispersed, the amount of condensate produced by the condenser 14 is more stable, and the pressure difference fluctuation at the nozzle inlet is reduced.

[0054] Method Example 2. Treatment of high-salinity concentrated brine: The total salinity of the concentrated brine to be treated is 20 wt%, which is heated to 70°C by the waste heat exchanger 4. The absolute pressure of the low-pressure flash crystallization chamber 12 is corrected and controlled according to the boiling point rise of the 20 wt% concentrated brine, so that the effective superheat of the concentrated brine before entering the large-diameter flash nozzle 11 is maintained at 5°C to 15°C. In one operating mode, the absolute pressure of the low-pressure flash crystallization chamber 12 can be controlled within the range of 20 kPa to 35 kPa, and the boiling point rise caused by the increase in salinity can be adapted by reducing the pressure, increasing the feed temperature, or increasing the self-generated steam replenishment.

[0055] The bubble replenisher 6 employs a Venturi bubble replenisher, with the liquid flow velocity at its throat controlled between 6 m / s and 10 m / s. The volume fraction of steam bubbles or steam nuclei is controlled between 5% and 10%, or the ratio of the volumetric flow rate of self-generated steam in the steam return pipe 7 to the volumetric flow rate of concentrated brine is controlled between 0.03 and 0.08. The concentrated brine containing steam bubbles or steam nuclei is injected into the low-pressure flash crystallization chamber 12 through a large-diameter flash nozzle 11 with an outlet diameter of 10 mm. Due to the large outlet diameter of the large-diameter flash nozzle 11, salt precipitation particles and suspended crystals are less likely to cause nozzle blockage. The concentrated brine is further concentrated and salt crystals precipitate in the low-pressure flash crystallization chamber 12. The brine slurry is separated by the brine separator 18, and the mother liquor is returned to the system inlet for recycling.

[0056] During continuous operation, the large-diameter flash nozzle 11 reduces the probability of blockage caused by salt precipitation particles and suspended crystals, and the steam bubbles or steam nuclei in front of the nozzle inlet can compensate for the problem of insufficient nucleation under high salinity conditions. The system can maintain a relatively stable spray crushing and condensation recovery state. After the salt slurry is discharged through the brine separator 18, the separated mother liquor can continue to be recycled for circulation treatment.

[0057] Method Example 3. Multi-nozzle scale-up processing: In high-volume processing scenarios, multiple large-diameter flash nozzles 11 can be connected in parallel on the top or side wall of the same low-pressure flash crystallization chamber 12. Each large-diameter flash nozzle 11 can be equipped with a bubble replenisher 6 and a bubble replenishment regulating valve 8 upstream, or multiple large-diameter flash nozzles 11 can share a set of steam reflux main pipe and bubble replenishment distribution pipe.

[0058] In one embodiment, the opening of the foaming regulating valve 8 of each branch can be adjusted according to the flow rate of each branch, the nozzle inlet pressure, and the steam return flow rate, so that the volume fraction of steam bubbles or steam nuclei in the concentrated brine upstream of the large-diameter flash nozzles 11 is maintained within a set range. Multiple large-diameter flash nozzles 11 form a spray array, thereby expanding the system's processing capacity.

[0059] Comparative example of Method Example 1. Treatment of medium-salinity concentrated brine under conditions of no self-generated steam replenishment: Except for closing the foaming regulating valve 8 and preventing the self-generated steam from entering the foaming device 6 through the steam return pipe 7, the salinity of the concentrated brine, the feed temperature, the pressure of the low-pressure flash crystallization chamber 12, the outlet diameter of the large-diameter flash nozzle 11, the nozzle inlet pressure, and the mother liquor return method are all the same as in Method Example 1. The concentrated brine is directly sprayed into the low-pressure flash crystallization chamber 12 through the large-diameter flash nozzle 11.

[0060] Compared with Method Example 1, in the comparative example, since the concentrated brine before the inlet of the large-diameter flash nozzle 11 lacks pre-placed steam bubbles or steam nuclei, the nucleation triggering of the concentrated brine after entering the low-pressure flash crystallization chamber 12 is delayed, the complete section of the spray column is extended, the breakage starting position is moved backward, the spray diffusion range is reduced, the droplet settling area is more concentrated, the condensate generation rate decreases or fluctuations increase, and the nozzle inlet pressure difference is more likely to fluctuate abnormally during high-salt or crystal-containing operation.

[0061] This demonstrates that, under conditions of low superheat and large-diameter nozzles, a synergistic effect exists between the steam bubbles or nuclei formed by the self-generated steam upstream of the nozzle and the low-pressure flash evaporation environment. This synergistic effect differs from traditional enhancement methods that simply increase injection pressure, reduce nozzle orifice diameter, add external air atomization, or add external solid crystal nuclei. It improves the low-temperature flash evaporation fragmentation and crystallization precipitation effects while maintaining the anti-clogging advantage of large-diameter nozzles, reducing the introduction of non-condensable gases, and minimizing the risk of added particles.

[0062] The device of this invention draws the self-generated steam from the low-pressure flash crystallization chamber back to the negative pressure bubble replenisher upstream of the large-diameter flash nozzle via a steam return pipe. Utilizing the localized low-pressure zone formed when concentrated brine flows through the bubble replenisher, the self-generated steam enters the main stream of concentrated brine under pressure differential, and is pre-positioned as steam bubbles or vapor nuclei before the nozzle inlet. When the concentrated brine containing these steam bubbles or vapor nuclei enters the low-pressure flash crystallization chamber through the large-diameter flash nozzle, the steam bubbles or vapor nuclei grow rapidly under reduced pressure, thereby inducing the breakup of liquid columns, liquid films, or droplets, promoting flash evaporation and salt crystal precipitation. Thus, this invention improves the flash breakup effect under low-temperature and low-superheat conditions while maintaining the anti-clogging advantage of the large-diameter nozzle. This invention does not simply rely on increasing the injection pressure, reducing the nozzle orifice diameter, or adding a high-speed airflow to achieve atomization; instead, it uses the negative pressure return of self-generated steam and the pre-positioning of vapor nuclei before the nozzle to make it easier for concentrated brine to undergo bubble growth-driven breakup, vaporization, and crystallization after entering the low-pressure flash environment.

[0063] Compared with the enhancement methods of adding external air or adding external solid crystal nuclei, the present invention uses the system's own water vapor as the foaming medium, which can reduce the possibility of non-condensable gases such as external air entering the condensation system and avoid the introduction of additional solid particles that could cause blockage of nozzles, pipelines or brine separation units. At the same time, since the self-generated steam comes from the low-pressure flash crystallization chamber, the foaming process and the flash evaporation process form an internal circulation, which is beneficial to maintaining the stability of continuous system operation.

[0064] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Therefore, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention also intends to include these modifications and variations.

Claims

1. A low-temperature concentrated brine flash crystallization device with self-generated steam replenishment and enhanced foaming, characterized in that: It includes a concentrated brine storage tank (1), a pre-filter (2), a feed pump (3), a waste heat exchanger (4), a pressure stabilizing buffer tank (5), a foam replenisher (6), a steam return pipe (7), a foam replenishing regulating valve (8), a check valve (9), a mixer (10), a large-diameter flash nozzle (11), a low-pressure flash crystallization chamber (12), a demister (13), a condenser (14), a pressure regulating device (15), a distilled water collection tank (16), a brine outlet (17), a brine separator (18), a salt crystal collector (19), a mother liquor circulation pump (20), and a mother liquor return pipe (21). The outlet of the concentrated brine storage tank (1) is connected to the inlet of the pre-filter (2), the outlet of the pre-filter (2) is connected to the inlet of the feed pump (3), the outlet of the feed pump (3) is connected to the inlet of the waste heat exchanger (4), the outlet of the waste heat exchanger (4) is connected to the inlet of the pressure stabilizing buffer tank (5), the outlet of the pressure stabilizing buffer tank (5) is connected to the inlet of the bubble replenisher (6), the outlet of the bubble replenisher (6) is connected to the inlet of the mixer (10), the outlet of the mixer (10) is connected to the inlet of the large-diameter flash nozzle (11), the outlet of the large-diameter flash nozzle (11) is connected to the low-pressure flash crystallization chamber (12), the gas phase outlet of the low-pressure flash crystallization chamber (12) is connected to the inlet of the demister (13) through a steam pipe, one end of the steam return pipe (7) is connected to the middle of the steam pipe, and the other end of the steam return pipe (7) is connected to the bubble replenisher (6). The steam inlet is connected to the steam return pipe (7), and a foaming regulating valve (8) and a check valve (9) are installed in sequence on the steam return pipe (7). The outlet of the demister (13) is connected to the inlet of the condenser (14). The liquid outlet of the condenser (14) is connected to the distilled water collection tank (16). The pressure regulating device (15) is connected to the gas side outlet of the condenser (14) and the pressure of the low-pressure flash crystallization chamber (12) is regulated through the condenser (14) and the steam pipe. The bottom of the low-pressure flash crystallization chamber (12) is provided with a salt slurry outlet (17). The salt slurry outlet (17) is connected to the brine separator (18). The solid outlet of the brine separator (18) is connected to the salt crystal collector (19). The mother liquor outlet of the brine separator (18) is connected to the inlet of the concentrated brine storage tank (1) through the mother liquor return pipe (21). The mother liquor return pipe (21) is provided with a mother liquor circulation pump (20).

2. The low-temperature concentrated brine flash crystallization device with self-generated steam replenishment and enhanced crystallization according to claim 1, characterized in that: The bubble replenisher (6) is a Venturi bubble replenisher. The bubble replenisher (6) includes an inlet constriction section (61), a throat (62), a diffuser section (63), and a negative pressure suction port (64). The inlet constriction section (61) is located at one end of the bubble replenisher (6), the diffuser section (63) is located at the other end of the bubble replenisher (6), the throat (62) is located between the inlet constriction section (61) and the diffuser section (63), and the negative pressure suction port (64) is located at the top of the throat (62). The negative pressure suction port (64) serves as the steam inlet of the bubble replenisher (6) and is connected to the steam return pipe (7).

3. The low-temperature concentrated brine flash crystallization device with self-generated steam replenishment and enhanced crystallization according to claim 2, characterized in that: The ratio of the diameter of the throat (62) of the bubble replenisher (6) to the diameter of the inlet pipe is 0.45 to 0.65, the liquid flow velocity of the throat (62) of the bubble replenisher (6) is 4 m / s to 12 m / s, and the local pressure drop formed by the bubble replenisher (6) is 10 kPa to 50 kPa.

4. The low-temperature concentrated brine flash crystallization device with self-generated steam replenishment and enhanced crystallization according to claim 3, characterized in that: The outlet diameter of the large-diameter flash nozzle (11) is 6mm to 20mm, and the outlet flow velocity of the large-diameter flash nozzle (11) is 4m / s to 12m / s.

5. The low-temperature concentrated brine flash crystallization device with self-generated steam replenishment and enhanced crystallization according to claim 4, characterized in that: The low-pressure flash crystallization chamber (12) is used to provide a flash environment with a pressure lower than that at the inlet of the large-diameter flash nozzle (11). The absolute pressure of the low-pressure flash crystallization chamber (12) is 10 kPa to 50 kPa. The effective superheat of the concentrated brine before entering the large-diameter flash nozzle (11) is 5°C to 15°C.

6. A method of using a low-temperature concentrated brine flash crystallization device with self-generated steam replenishment and enhancement, characterized in that, Includes the following steps: S1. Start-up state: During the start-up phase, the concentrated brine storage tank (1) is filled with concentrated brine to be treated, and the feed pump (3) and pressure regulating device (15) are started to make the low-pressure flash crystallization chamber (12) reach the set pressure. With the foam replenishing regulating valve (8) closed or slightly open, the heated concentrated brine enters the low-pressure flash crystallization chamber (12) through the large-diameter flash nozzle (11) and generates initial self-generated steam. When the pressure, flow rate or temperature of the self-generated steam in the low-pressure flash crystallization chamber (12) reaches the set conditions, the foam replenishing regulating valve (8) is gradually opened so that the self-generated steam enters the foam replenisher (6) through the steam return pipe (7). S2. Pretreatment of concentrated brine: The concentrated brine to be treated enters the concentrated brine storage tank (1) and passes through the pre-filter (2) to remove large particulate suspended matter; S3. Heating concentrated brine: The feed pump (3) sends the concentrated brine into the waste heat exchanger (4), which uses industrial low-grade waste heat to heat the concentrated brine to the set temperature. The concentrated brine can be heated to 40℃~95℃. S4. The heated concentrated brine flows through the bubble replenisher (6): the bubble replenisher (6) forms a local low-pressure area when the concentrated brine flows through it; S5. Self-generated steam is drawn from the middle of the steam pipe and introduced into the bubbler (6) under pressure difference through the steam return pipe (7). S6. To form steam bubbles or steam nuclei in the bubbler (6): The volume fraction of steam bubbles or steam nuclei in the concentrated brine before entering the large-diameter flash nozzle (11) can be controlled to be 0.1% to 20%; or the ratio of the volume flow rate of the self-generated steam to the volume flow rate of the concentrated brine in the steam return pipe (7) can be controlled to be 0.001 to 0.

20. S7. The concentrated brine containing steam bubbles or steam nuclei is injected into the low-pressure flash crystallization chamber (12) through a large-diameter flash nozzle (11). The outlet flow rate of the large-diameter flash nozzle (11) is controlled to be 4m / s to 12m / s. S8. Allow steam bubbles or steam nuclei to grow under reduced pressure conditions in the low-pressure flash crystallization chamber (12) to induce the concentrated brine to break up, flash evaporate and precipitate salt crystals; S9. Condense and recover the water vapor generated during flash evaporation; S10. Separate the precipitated salt crystals and mother liquor: The separated mother liquor can be returned to the step before or during the concentrated brine heating step, mixed with the newly added concentrated brine, and then processed.

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