High-salinity wastewater treatment system based on low-temperature multi-effect evaporation and thermal vapor recompression

Abstract

This invention relates to a high-salinity wastewater treatment system based on low-temperature multi-effect evaporation and thermal steam recompression, and pertains to the field of wastewater treatment technology. It includes a saline wastewater inlet pipeline, the outlet of which is connected to a first low-temperature multi-effect evaporation system. The pure water outlet pipeline of the first low-temperature multi-effect evaporation system is connected to a boiler feedwater pipeline. The high-salinity concentrated water outlet pipeline of the first low-temperature multi-effect evaporation system is connected to a nanofiltration unit via a resin softening unit. The pure water outlet pipeline of a second low-temperature multi-effect evaporation system is also connected to the boiler feedwater pipeline, and the high-salinity concentrated water outlet pipeline of the second low-temperature multi-effect evaporation system is connected to a sodium chloride evaporation and crystallization unit. This invention addresses the problem in traditional technologies where high-pressure membrane modules are sensitive to influent water quality, requiring complex enhanced pretreatment processes such as coagulation sedimentation, advanced oxidation, and ultrafiltration, making them unsuitable for industrial wastewater with varying compositions and resulting in high operating costs.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a high-salinity wastewater treatment system based on low-temperature multi-effect evaporation and thermal steam recompression. Background Technology

[0002] Currently, with the continuous expansion of industrial production scale, the output of industrial wastewater, such as high-salinity wastewater, high-concentration organic wastewater, circulating cooling wastewater, reverse osmosis concentrate, coal chemical wastewater, and power plant desulfurization wastewater, is increasing year by year. This type of wastewater is characterized by high salt content, high hardness, high silicon content, numerous corrosive ions, complex composition, and poor biodegradability. It is recognized in the domestic and international water treatment field as a typical wastewater that is difficult to treat, has high operating costs, and is difficult to operate stably. For a long time, traditional treatment processes have mainly relied on biological treatment, deep filtration, and conventional membrane separation. However, under conditions of high salt, high hardness, and high organic matter, these processes generally suffer from low treatment efficiency, unstable operation, severe membrane fouling, high reagent consumption, and persistently high operating costs.

[0003] like Figure 3 As shown, the existing membrane concentration technology for high-salinity wastewater has gradually revealed its shortcomings with use, mainly in the following aspects: First, high-pressure membrane modules are sensitive to the quality of the influent water and require complex enhanced pretreatment processes, such as coagulation sedimentation, advanced oxidation, and ultrafiltration. This results in high operating costs and makes them unsuitable for industrial wastewater with varying compositions.

[0004] Secondly, calcium, magnesium, silicon, and suspended solids in high-salinity wastewater are prone to deposit on the membrane surface, causing rapid decline in membrane flux, requiring frequent chemical cleaning, resulting in short lifespan and high replacement costs.

[0005] Third, existing membrane modules require high-pressure operation, such as high-pressure membrane modules with an osmotic pressure of 10-15 MPa, which results in large investment in energy recovery devices, expensive equipment, and limited overall economic efficiency.

[0006] In conclusion, the existing technology obviously has inconveniences and defects in practical use, so it is necessary to improve it. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a high-salt wastewater treatment system based on low-temperature multi-effect evaporation and thermal steam recompression. This system solves the problem that traditional high-pressure membrane modules are sensitive to influent water quality and require complex enhanced pretreatment processes, such as coagulation sedimentation, advanced oxidation, and ultrafiltration, which are difficult to adapt to industrial wastewater with varying compositions, resulting in high operating costs.

[0008] To address the above problems, the present invention provides the following technical solution: A high-salt wastewater treatment system based on low-temperature multi-effect evaporation and thermal steam recompression includes a saline wastewater inlet pipeline, the outlet end of which is connected to a low-temperature multi-effect evaporation system. The pure water outlet pipeline of the low-temperature multi-effect evaporation system is connected to the boiler feed water pipeline. The high-salt concentrated water outlet pipeline of the low-temperature multi-effect evaporation system is connected to a nanofiltration unit through a resin softening unit. The nanofiltration unit is connected to a sodium chloride crystallization pipeline and a sodium sulfate crystallization pipeline, respectively. The sodium chloride crystallization pipeline is connected to a second low-temperature multi-effect evaporation system. The pure water outlet pipeline of the second low-temperature multi-effect evaporation system is connected to the boiler feed water pipeline. The high-salt concentrated water outlet pipeline of the second low-temperature multi-effect evaporation system is connected to the sodium chloride evaporation crystallization unit. The sodium sulfate crystallization pipeline is connected to the sodium sulfate freeze crystallization unit via the sodium sulfate evaporation crystallization unit.

[0009] As an optimized solution, both the first and second low-temperature multi-effect evaporation systems include a steam ejector. The steam outlet of the steam ejector is connected to a first-effect evaporator, a second-effect evaporator, and a final-effect evaporator connected in series. The exhaust steam outlet of the final-effect evaporator is connected to the steam inlet of the steam ejector through a recovery pipeline.

[0010] As an optimized solution, the secondary steam outlet of the first-effect evaporator is connected to the heat source end of the second-effect evaporator, and the secondary steam outlet of the second-effect evaporator is connected to the heat source end of the last-effect evaporator.

[0011] As an optimized solution, the exhaust steam outlet of the final-effect evaporator is also connected to a condenser.

[0012] As an optimized solution, the saline wastewater inlet pipeline is connected to the inlet of the first-effect evaporator, the second-effect evaporator, and the final-effect evaporator through the condenser.

[0013] As an optimized solution, the condensate outlet of the final-effect evaporator and the condensate outlet of the condenser are both connected to the pure water outlet pipeline of the product.

[0014] As an optimized solution, the concentrated water outlets of the first-effect evaporator, the second-effect evaporator, and the last-effect evaporator are all connected to the high-salt concentrated water outlet pipeline.

[0015] As an optimized solution, a product water preheater is connected to the pure water outlet pipeline, and the saline wastewater inlet pipeline is connected to the product water preheater.

[0016] As an optimized solution, a brine preheater is connected to the high-salt concentrated water outlet pipeline, and the saline wastewater inlet pipeline is connected to the brine preheater.

[0017] As an optimized solution, the steam inlet of the steam ejector is also connected to waste heat steam.

[0018] Compared with the prior art, the beneficial effects of the present invention are: This invention employs a coupled low-temperature multi-effect evaporation and thermal steam recompression process to replace the traditional high-pressure membrane treatment process. It eliminates the need for pretreatment of high-salt wastewater, such as complex and enhanced pretreatment processes like coagulation sedimentation, advanced oxidation, and multi-stage filtration, and directly meets the feed requirements. This significantly shortens the process flow, reduces equipment investment, and substantially lowers reagent consumption and operating costs. It is also more adaptable to complex and variable industrial wastewater. This invention employs thermal separation, eliminating problems such as membrane module fouling, scaling, and flux decline. It avoids the efficiency reduction caused by the deposition of calcium, magnesium, silicon, and suspended solids on the membrane surface, eliminating the need for frequent chemical cleaning, extending the continuous operation cycle of the equipment, reducing maintenance workload and membrane module replacement costs, and completely solving the problems of membrane fouling, scaling, and flux decline. This system operates under low temperature, low pressure, and negative pressure conditions, eliminating the need for 10-15MPa high-pressure operation. It eliminates the need for expensive equipment such as high-pressure pumps and energy recovery devices, reducing equipment costs and power load. The system is more stable and its overall economic efficiency is significantly better than traditional membrane processes, achieving complete elimination of high-pressure operating conditions and greatly reducing equipment investment and energy consumption. The system uses waste heat / waste heat steam from enterprises as the driving heat source. It recovers the exhaust steam from the last effect through a steam jet (TVC) and recycles it in stages to match the pipeline pressure. It has high thermal energy utilization rate and high water production ratio, further reducing operating costs and making full use of waste heat steam. It has high thermal energy utilization rate and outstanding energy saving effect. The system adopts a low-temperature multi-effect evaporation and distillation process, producing high-quality distilled water that can be directly used as boiler feedwater after simple fine treatment, realizing the resource utilization of wastewater, improving the enterprise's water reuse rate, and helping to achieve near-zero emissions. The system achieves efficient separation and recovery of sodium chloride and sodium sulfate salts through a combination of nanofiltration, resin softening, evaporation crystallization, and freeze crystallization processes, reducing solid waste generation and achieving the dual benefits of resource recovery and environmental compliance. It realizes the resource-based separation of salts and has significant environmental benefits. The secondary steam generated by the previous stage evaporator is directly used as the heat source for the next stage evaporator, realizing the cascade utilization of thermal energy; at the same time, the waste heat of the exhaust steam of the last-effect evaporator is used to preheat the saline wastewater through the condenser; and the waste heat of the product pure water and high-salt concentrated water is used to preheat the saline wastewater through the product water preheater and the concentrated brine preheater, so that the thermal energy in the system is maximized for recovery and recycling, significantly reducing energy consumption and solving the problems of insufficient thermal energy recovery and high operating costs of traditional equipment. Attached Figure Description

[0019] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0020] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a flow chart of the saline wastewater treatment process of the present invention; Figure 3 This is a flow chart of a current technology for treating saline wastewater.

[0021] In the diagram: 1-Steam ejector; 2-First-effect evaporator; 3-Second-effect evaporator; 4-Final-effect evaporator; 5-Condenser; 6-Product water preheater; 7-Concentrated brine preheater; 8-Product pure water outlet pipeline; 9-High-salt concentrated water outlet pipeline; 10-Saline wastewater inlet pipeline; 11-Waste heat steam; 12-Recovery pipeline. Detailed Implementation

[0022] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0023] like Figure 1 and Figure 2 As shown, a high-salt wastewater treatment system based on low-temperature multi-effect evaporation and thermal steam recompression includes a saline wastewater inlet pipeline 10, and a low-temperature multi-effect evaporation system is connected to the outlet end of the saline wastewater inlet pipeline 10. The pure water outlet pipeline 8 of the low-temperature multi-effect evaporation system can be connected to the boiler feed water pipeline through a mixed bed or EDI unit. The high-salt concentrated water outlet pipeline 9 of the low-temperature multi-effect evaporation system is connected to a nanofiltration unit through a resin softening unit. The nanofiltration unit is connected to a sodium chloride crystallization pipeline and a sodium sulfate crystallization pipeline respectively. The sodium chloride crystallization pipeline is connected to a low-temperature multi-effect evaporation system II. The pure water outlet pipeline 8 of the low-temperature multi-effect evaporation system II is connected to the boiler feed water pipeline, and the high-salt concentrated water outlet pipeline 9 of the low-temperature multi-effect evaporation system II is connected to the sodium chloride evaporation crystallization unit. The sodium sulfate crystallization pipeline is connected to the sodium sulfate freeze crystallization unit via the sodium sulfate evaporation crystallization unit.

[0024] Both the low-temperature multi-effect evaporation system one and the low-temperature multi-effect evaporation system two include a steam ejector 1. The steam outlet of the steam ejector 1 is connected to a first-effect evaporator 2, a second-effect evaporator 3, and a final-effect evaporator 4 connected in series. The exhaust steam outlet of the final-effect evaporator 4 is connected to the steam inlet of the steam ejector 1 through a recovery pipeline 12.

[0025] The secondary steam outlet of the first-effect evaporator 2 is connected to the heat source end of the second-effect evaporator 3, and the secondary steam outlet of the second-effect evaporator 3 is connected to the heat source end of the last-effect evaporator 4.

[0026] The exhaust steam outlet of the final-effect evaporator 4 is also connected to a condenser 5.

[0027] The saline wastewater enters the pipeline 10 and is connected to the inlet of the first-effect evaporator 2, the second-effect evaporator 3 and the last-effect evaporator 4 respectively through the condenser 5.

[0028] The condensate outlet of the final-effect evaporator 4 and the condensate outlet of the condenser 5 are both connected to the product pure water outlet pipeline 8.

[0029] The concentrated water outlets of the first-effect evaporator 2, the second-effect evaporator 3, and the last-effect evaporator 4 are all connected to the high-salt concentrated water outlet pipeline 9.

[0030] The pure water outlet pipeline 8 is connected to the product water preheater 6, and the saline wastewater inlet pipeline 10 is connected to the product water preheater 6.

[0031] A brine preheater 7 is connected to the high-salt concentrated water outlet pipeline 9, and the saline wastewater inlet pipeline 10 is connected to the brine preheater 7.

[0032] The steam inlet of steam ejector 1 is also connected to waste heat steam 11.

[0033] The working principle of this device is as follows: This invention employs a coupled low-temperature multi-effect evaporation and thermal steam recompression process to replace the traditional high-pressure membrane treatment process. It eliminates the need for pretreatment of high-salinity wastewater, such as complex enhanced pretreatment processes like coagulation sedimentation, advanced oxidation, and multi-stage filtration. The feed requirements can be directly met through simple hardening treatment, significantly shortening the process flow, reducing equipment investment, and substantially lowering reagent consumption and operating costs. It is also more adaptable to complex and variable industrial wastewater. This invention employs thermal separation, eliminating problems such as membrane module fouling, scaling, and flux decline. It avoids the efficiency reduction caused by the deposition of calcium, magnesium, silicon, and suspended solids on the membrane surface, eliminating the need for frequent chemical cleaning, extending the continuous operation cycle of the equipment, reducing maintenance workload and membrane module replacement costs, and completely solving the problems of membrane fouling, scaling, and flux decline. This system operates under low temperature, low pressure, and negative pressure conditions, eliminating the need for 10-15MPa high-pressure operation. It eliminates the need for expensive equipment such as high-pressure pumps and energy recovery devices, reducing equipment costs and power load. The system is more stable and its overall economic efficiency is significantly better than traditional membrane processes, achieving complete elimination of high-pressure operating conditions and greatly reducing equipment investment and energy consumption. The system uses the enterprise's waste heat / waste heat steam as the driving heat source. It recovers the final-effect exhaust steam through the steam ejector 1 (TVC) and recycles it in stages to match the pipeline pressure. It has high thermal energy utilization rate and high water production ratio, further reducing operating costs and making full use of waste heat steam 11. It has high thermal energy utilization rate and outstanding energy saving effect. The system adopts a low-temperature multi-effect evaporation and distillation process to produce high-quality distilled water with high water quality (TDS≤10mg / L), which can meet various reuse needs and can be directly used as boiler feedwater, realizing the resource utilization of wastewater, improving the enterprise's water reuse rate, and helping to achieve near-zero emissions. The system achieves efficient separation and recovery of sodium chloride and sodium sulfate salts through a combination of nanofiltration, resin softening, evaporation crystallization, and freeze crystallization processes, reducing solid waste generation and achieving the dual benefits of resource recovery and environmental compliance. It realizes the resource-based separation of salts and has significant environmental benefits. The secondary steam generated by the previous stage evaporator is directly used as the heat source for the next stage evaporator, realizing the cascade utilization of thermal energy; at the same time, the waste heat of the exhaust steam of the last-effect evaporator 4 is used to preheat the saline wastewater through the condenser 5; and the waste heat of the product pure water and high-salt concentrated water is used to preheat the saline wastewater through the product water preheater 6 and the concentrated brine preheater 7, so that the thermal energy in the system is maximized for recovery and recycling, significantly reducing energy consumption and solving the problems of insufficient thermal energy recovery and high operating costs of traditional equipment.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A high-salinity wastewater treatment system based on low-temperature multi-effect evaporation and thermal steam recompression, characterized in that: Includes a saline wastewater inlet pipeline (10), the outlet end of which is connected to a low-temperature multi-effect evaporation system; The product pure water outlet pipeline (8) of the low-temperature multi-effect evaporation system is connected to the boiler feed water pipeline. The high-salt concentrated water outlet pipeline (9) of the low-temperature multi-effect evaporation system is connected to a nanofiltration unit through a resin softening unit. The nanofiltration unit is connected to a sodium chloride crystallization pipeline and a sodium sulfate crystallization pipeline, respectively. The sodium chloride crystallization pipeline is connected to a low-temperature multi-effect evaporation system II. The product pure water outlet pipeline (8) of the low-temperature multi-effect evaporation system II is connected to the boiler feed water pipeline. The high-salt concentrated water outlet pipeline (9) of the low-temperature multi-effect evaporation system II is connected to the sodium chloride evaporation crystallization unit. The sodium sulfate crystallization pipeline is connected to the sodium sulfate freeze crystallization unit via the sodium sulfate evaporation crystallization unit.

2. The high-salinity wastewater treatment system based on low-temperature multi-effect evaporation and thermal steam recompression according to claim 1, characterized in that: Both the low-temperature multi-effect evaporation system one and the low-temperature multi-effect evaporation system two include a steam ejector (1). The steam outlet of the steam ejector (1) is connected to a first-effect evaporator (2), a second-effect evaporator (3), and a final-effect evaporator (4) connected in series. The exhaust steam outlet of the final-effect evaporator (4) is connected to the steam inlet of the steam ejector (1) through a recovery pipeline (12).

3. The high-salinity wastewater treatment system based on low-temperature multi-effect evaporation and thermal steam recompression according to claim 2, characterized in that: The secondary steam outlet of the first-effect evaporator (2) is connected to the heat source end of the second-effect evaporator (3), and the secondary steam outlet of the second-effect evaporator (3) is connected to the heat source end of the last-effect evaporator (4).

4. The high-salinity wastewater treatment system based on low-temperature multi-effect evaporation and thermal steam recompression according to claim 2, characterized in that: The exhaust steam outlet of the final-effect evaporator (4) is also connected to a condenser (5).

5. The high-salinity wastewater treatment system based on low-temperature multi-effect evaporation and thermal steam recompression according to claim 4, characterized in that: The saline wastewater inlet pipeline (10) is connected to the inlet of the first-effect evaporator (2), the second-effect evaporator (3), and the last-effect evaporator (4) respectively through the condenser (5).

6. The high-salinity wastewater treatment system based on low-temperature multi-effect evaporation and thermal steam recompression according to claim 4, characterized in that: The condensate outlet of the final-effect evaporator (4) and the condensate outlet of the condenser (5) are connected together to the pure water outlet pipeline (8) of the product.

7. The high-salinity wastewater treatment system based on low-temperature multi-effect evaporation and thermal steam recompression according to claim 2, characterized in that: The concentrated water outlets of the first-effect evaporator (2), the second-effect evaporator (3), and the last-effect evaporator (4) are all connected to the high-salt concentrated water outlet pipeline (9).

8. The high-salinity wastewater treatment system based on low-temperature multi-effect evaporation and thermal steam recompression according to claim 2, characterized in that: The pure water outlet pipeline (8) is connected to a product water preheater (6), and the saline wastewater inlet pipeline (10) is connected to the product water preheater (6).

9. The high-salinity wastewater treatment system based on low-temperature multi-effect evaporation and thermal steam recompression according to claim 7, characterized in that: The high-salt concentrated water outlet pipeline (9) is connected to a concentrated brine preheater (7), and the saline wastewater inlet pipeline (10) is connected to the concentrated brine preheater (7).

10. The high-salinity wastewater treatment system based on low-temperature multi-effect evaporation and thermal steam recompression according to claim 2, characterized in that: The steam inlet of the steam ejector (1) is also connected to waste heat steam (11).

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