A coal-fired power plant desulfurization wastewater zero discharge treatment system and method

Abstract

The application provides a coal-fired power plant desulfurization wastewater zero discharge treatment system and method. The coal-fired power plant desulfurization wastewater zero discharge treatment system comprises a pretreatment unit, a waste heat preheating unit, a negative pressure flash evaporation concentration unit and a steam atomization evaporation crystallization unit, and the pretreatment unit, the waste heat preheating unit, the negative pressure flash evaporation concentration unit and the steam atomization evaporation crystallization unit are sequentially communicated through pipelines.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, and in particular to a zero-discharge treatment system and method for desulfurization wastewater from coal-fired power plants. Background Technology

[0002] Limestone-gypsum wet flue gas desulfurization (FGD) is currently the most widely used desulfurization process in coal-fired power plants. This process generates a certain amount of desulfurization wastewater, which contains high concentrations of suspended solids, calcium and magnesium hardness ions, chloride ions, and total dissolved solids. Direct discharge of this wastewater would cause serious water pollution. With increasingly stringent water pollution discharge standards in the thermal power industry, zero discharge of desulfurization wastewater has become an essential requirement for the environmental retrofitting of existing coal-fired power plants.

[0003] Currently, commonly used zero-discharge technologies for desulfurization wastewater can be mainly divided into three categories: The first category is the traditional evaporation crystallization process, represented by MVR evaporation crystallization. Although it can achieve zero discharge, it has high equipment investment, high operating energy consumption, and many operational failures, placing a heavy burden on enterprises. The second category is the main flue spray evaporation process, which directly atomizes and sprays desulfurization wastewater into the boiler's main flue, utilizing the waste heat of the flue gas to evaporate the moisture. Although this process has lower investment, it is prone to nozzle clogging, flue fouling, and reduced dust collector efficiency, resulting in poor long-term operational stability. The third category is the bypass flue evaporation process, which solves some of the problems of the main flue process, but has low waste heat utilization rate, insufficient concentration ratio, which can seriously affect boiler efficiency, and the scaling problem is difficult to eradicate.

[0004] For flash concentration processes, existing technologies mostly employ high-temperature, high-pressure flash evaporation or multi-stage high-temperature flash evaporation. This not only results in high energy consumption but also a significant decrease in calcium sulfate solubility under high-temperature conditions, rapid scaling, short equipment maintenance cycles, and poor operational stability. Currently, there is no process scheme that couples 80℃ low-temperature heating, -60KPa negative pressure flash concentration, and external steam-assisted heating for atomization evaporation and crystallization, making it impossible to simultaneously achieve low energy consumption, low scaling, and stable zero emissions. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a zero-discharge treatment system and method for desulfurization wastewater from coal-fired power plants, which addresses the shortcomings of the prior art.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: a zero-discharge treatment system for desulfurization wastewater from a coal-fired power plant, comprising: a pretreatment unit, a waste heat preheating unit, a negative pressure flash evaporation concentration unit, and a steam atomization evaporation crystallization unit, wherein the pretreatment unit, the waste heat preheating unit, the negative pressure flash evaporation concentration unit, and the steam atomization evaporation crystallization unit are connected sequentially through pipelines.

[0007] The beneficial effects of adopting the technical solution of this invention are that, through the integrated coupling of the pretreatment unit, the negative pressure flash concentration unit, and the steam atomization evaporation crystallization unit, wastewater hardening removal, volume reduction and concentration, and atomization crystallization salt production can be completed sequentially, with no wastewater discharge throughout the entire process; condensate can be recycled and reused, and crystallized salt residue is collected and disposed of uniformly, fully meeting the environmental protection requirements for zero discharge of power plant desulfurization wastewater. The equipment has a high degree of integration and strong adaptability. It achieves low energy consumption, low scaling, and stable zero discharge.

[0008] Furthermore, the pretreatment unit includes: a regulating tank, a dosing device for adding sodium hydroxide, sodium carbonate and PAM reagents into the regulating tank, and a sludge conveying pump. The waste heat preheating unit, the dosing device and the sludge conveying pump are all connected to the regulating tank through pipelines. The sludge conveying pump is connected to a sludge treatment device through a pipeline. The sludge treatment device is connected to the regulating tank through a pipeline. The regulating tank is connected to a desulfurization wastewater raw liquid pipeline through a pipeline.

[0009] The beneficial effects of adopting the above-mentioned further technical solution are that the dosing device is used to add sodium hydroxide, sodium carbonate, and PAM reagents into the equalization tank to perform homogenization, chemical hardening removal, flocculation, and sedimentation treatment on the desulfurization wastewater, effectively removing calcium and magnesium hardness ions from the wastewater and reducing the effluent hardness to below 50 mg / L. The sludge generated by sedimentation is sent to an external sludge dewatering machine for dewatering via a sludge transfer pump, and the dewatered filtrate is returned to the equalization tank for recycling, avoiding material waste.

[0010] Furthermore, the waste heat preheating unit includes: a tubular heat exchanger for heating wastewater to 78℃-82℃ and a wastewater transfer pump. The pretreatment unit is connected to the tubular heat exchanger via a pipeline, and the wastewater transfer pump is installed on the pipeline between the pretreatment unit and the tubular heat exchanger. The condensate outlet of the tubular heat exchanger is connected to a power plant recycled water tank via a pipeline.

[0011] The beneficial effects of adopting the above-mentioned further technical solution are that by setting up a tubular heat exchanger, the waste heat from the secondary steam generated by the evaporation and crystallization unit can be recovered to preheat the original wastewater, realizing the cascade recycling of waste heat. The entire set of equipment only needs to supplement a small amount of low-pressure steam to meet the operating requirements, eliminating the need for high-temperature heating equipment and significantly reducing equipment operating energy consumption and maintenance costs. The pretreated effluent after treatment in the regulating tank is sent to the tubular heat exchanger via a wastewater transfer pump, where it is preheated using the waste heat from the secondary steam generated by the downstream evaporation tower, stably raising the wastewater temperature to 80°C. After heat exchange, the secondary steam condenses into clean condensate, which is sent to the recycled water tank for recycling, achieving efficient waste heat recovery.

[0012] Furthermore, the negative pressure flash evaporation concentration unit includes: a flash furnace, a vacuum pump for stabilizing the negative pressure inside the flash furnace at -55KPa to -65KPa, a steam heat exchanger, and a concentration circulation pump. The waste heat preheating unit, the vacuum pump, and the concentration circulation pump are all connected to the flash furnace via pipelines. The steam heat exchanger is installed on the pipeline between the flash furnace and the concentration circulation pump, and its two ends are connected to the vacuum pump and the power plant recycled water tank via pipelines, respectively. The bottom of the flash furnace is provided with an online scale removal and flushing port, which is connected to an online flushing structure via a pipeline. The online flushing structure is connected to the pretreatment unit via a pipeline.

[0013] The beneficial effects of adopting the above-mentioned further technical solution are that the vacuum pump is installed at the top of the flash furnace to maintain the negative pressure environment inside the furnace. A circulation loop is formed at the bottom of the flash furnace through a concentration circulation pump. Low-temperature negative pressure suppresses scaling, resulting in strong equipment stability: the equipment structure, employing 80℃ low-temperature preheating combined with -60KPa precise negative pressure flash evaporation, significantly improves the solubility of easily scaling salts such as calcium sulfate compared to traditional high-temperature flash evaporation equipment, slowing down the scaling rate inside the equipment. The flash furnace is equipped with a periodic online flushing structure, effectively extending the equipment maintenance cycle and solving the problems of easy scaling and frequent failures in traditional equipment. Wastewater preheated by the tubular heat exchanger is sent to the flash furnace, where a -60KPa negative pressure environment is maintained by the vacuum pump, allowing the 80℃ wastewater to be rapidly flash-evaporated and reduced in volume; the concentration circulation pump enables wastewater circulation flash evaporation, stably controlling the wastewater concentration ratio at 4-5 times; a scale discharge flushing port is set at the bottom of the flash furnace, allowing online flushing every 7 days, with the flushing water flowing back to the regulating tank, effectively preventing salt deposition and equipment blockage. The steam extracted by the vacuum pump recovers its heat through a steam heat exchanger, and the condensate is then recycled.

[0014] Furthermore, the steam atomization evaporation crystallization unit includes: a drying evaporation tower, a dual-fluid spray gun, and an exhaust fan. The drying evaporation tower is a double-layered sleeve structure with an insulation layer. The dual-fluid spray gun and the exhaust fan are both installed at the top of the drying evaporation tower and are connected to the drying evaporation tower. The negative pressure flash evaporation concentration unit is connected to the dual-fluid spray gun, and the exhaust fan is connected to the waste heat preheating unit through a pipeline. The bottom of the drying evaporation tower is provided with a crystallized salt residue collection and discharge structure.

[0015] The beneficial effects of adopting the above-mentioned further technical solution are that the spray gun has a good anti-clogging effect and is suitable for long-term continuous operation. The double-layered sleeve-type spray gun with an arc-shaped flow guide channel allows the low-pressure steam on the outer side to form a tangential rotating high-speed airflow. This not only provides secondary heating to the atomized wastewater droplets, ensuring complete vaporization of the water, but also continuously purifies the outer wall of the nozzle, preventing nozzle crystallization and clogging at the source. This eliminates the need for frequent disassembly and replacement of equipment parts, significantly improving the continuous operational stability of the entire system. The concentrated high-salt wastewater is fed into the double-layered sleeve-type spray gun at the top of the evaporation tower. The inner tube of the spray gun transports the concentrated wastewater, atomizing it into fine droplets with an average particle size of 65μm. The outer tube is filled with 0.5MPa low-pressure saturated steam, which forms a rotating airflow through a 25° arc-shaped flow guide channel, heating the droplets from all directions, causing the water to vaporize instantly and the salt to crystallize. The vaporized steam is returned to the tubular heat exchanger to preheat the original wastewater solution. The crystallized salt residue falls to the bottom of the evaporation tower for unified collection and disposal. The condensate can be directly reused in the power plant's production system. The drying evaporation tower requires insulation and has a double-layered sleeve structure. The outer layer recovers steam and any condensate, while the inner layer recovers salt crystal particles.

[0016] Furthermore, the dual-fluid spray gun includes an inner tube and an outer tube. The outer tube is sleeved on the outside of the inner tube. The inner tube is connected to the negative pressure flash evaporation concentration unit through a pipeline. The outer tube is connected to a steam pipeline with a steam pressure range of 0.3MPa-0.6MPa through a pipeline. The outlet end of the outer tube is provided with multiple arc-shaped guide channels with a radial angle range of 20°-40°.

[0017] The beneficial effects of adopting the above-mentioned further technical solution are that the spray gun has a good anti-clogging effect and is suitable for long-term continuous operation. The double-layered sleeve-type spray gun with an arc-shaped flow guide channel allows the low-pressure steam on the outer side to form a tangential rotating high-speed airflow. This not only provides secondary heating to the atomized wastewater droplets, ensuring complete vaporization of the water, but also continuously purifies the outer wall of the nozzle, preventing nozzle crystallization and clogging at the source. This eliminates the need for frequent disassembly and replacement of equipment parts, significantly improving the continuous operational stability of the entire system. The concentrated high-salt wastewater is fed into the double-layered sleeve-type spray gun at the top of the evaporation tower. The inner tube of the spray gun transports the concentrated wastewater, atomizing it into fine droplets with an average particle size of 65μm. The outer tube is filled with 0.5MPa low-pressure saturated steam, which forms a rotating airflow through a 25° arc-shaped flow guide channel, heating the droplets from all directions, causing the water to vaporize instantly and the salt to crystallize. The vaporized steam is returned to the tubular heat exchanger to preheat the original wastewater solution. The crystallized salt residue falls to the bottom of the evaporation tower for unified collection and disposal. The condensate can be directly reused in the power plant's production system. The double-layer sleeve spray gun includes an inner tube and an outer tube. The inner tube transports concentrated desulfurization wastewater, and the outer tube transports low-pressure heating steam. The outlet end of the outer tube is provided with several arc-shaped guide channels with a radial angle of 20°-40°. The steam forms an airflow that rotates along the outer wall of the nozzle through the guide channels.

[0018] Furthermore, the present invention also provides a method for zero-discharge treatment of desulfurization wastewater from coal-fired power plants. Based on the above-mentioned zero-discharge treatment system for desulfurization wastewater from coal-fired power plants, the method includes: S1, pre-treating the desulfurization wastewater to remove hardness through a pre-treatment unit; S2, preheating the pre-treated effluent with waste heat through a waste heat preheating unit; S3, concentrating the preheated desulfurization wastewater under negative pressure flash evaporation through a negative pressure flash concentration unit; and S4, performing steam coupling atomization evaporation crystallization on the concentrated desulfurization wastewater through a steam atomization evaporation crystallization unit.

[0019] The beneficial effects of adopting the technical solution of this invention are that, through the integrated coupling of the pretreatment unit, the negative pressure flash concentration unit, and the steam atomization evaporation crystallization unit, wastewater hardening removal, volume reduction and concentration, and atomization crystallization salt production can be completed sequentially, with no wastewater discharge throughout the entire process; condensate can be recycled and reused, and crystallized salt residue is collected and disposed of uniformly, fully meeting the environmental protection requirements for zero discharge of power plant desulfurization wastewater. The equipment has a high degree of integration and strong adaptability. It achieves low energy consumption, low scaling, and stable zero discharge.

[0020] Further, step S1 includes: S11, homogenizing and equalizing the desulfurization wastewater through a regulating tank; S12, adding sodium hydroxide, sodium carbonate, and PAM reagent to the regulating tank through a dosing device to chemically soften the desulfurization wastewater and remove calcium and magnesium hardness ions, and obtaining pretreated effluent through flocculation sedimentation and filtration; step S2 includes: S21, transporting the pretreated effluent to a tubular heat exchanger through a wastewater transfer pump; S22, preheating the wastewater to 78℃-82℃ with secondary steam generated by a steam atomization evaporation crystallization unit; and recycling the clean condensate obtained after the secondary steam releases heat and condenses.

[0021] The beneficial effects of adopting the above-mentioned further technical solution are that the original desulfurization wastewater is passed into a regulating tank for homogenization and flow equalization, and sodium hydroxide and sodium carbonate are added for chemical softening to remove calcium and magnesium hardness ions. After flocculation, sedimentation, and filtration, pretreated effluent is obtained. A tubular heat exchanger is installed to recover the waste heat from the secondary steam generated by the evaporation and crystallization unit to preheat the original wastewater, achieving a cascaded recycling of waste heat. The entire system only requires a small amount of low-pressure steam to meet operating requirements, eliminating the need for high-temperature heating equipment and significantly reducing equipment operating energy consumption and maintenance costs.

[0022] Further, step S3 includes: S31, sending the preheated desulfurization wastewater into a flash furnace; S32, maintaining the negative pressure range inside the flash furnace at -55KPa to 65KPa using a vacuum pump; S33, recovering and utilizing the secondary steam generated from the flash vaporization of some water through a steam heat exchanger; S34, discharging the unvaporized concentrated wastewater through the flash furnace to obtain concentrated desulfurization wastewater; Step S4 includes: S41, sending the concentrated desulfurization wastewater into a dual-fluid spray gun; S42, conveying and atomizing the concentrated desulfurization wastewater through the inner side of the dual-fluid spray gun, and introducing steam through the outer side of the dual-fluid spray gun to reheat the atomized droplets, so that the water in the droplets is completely vaporized and the salt crystallizes out; the water vapor is condensed and recovered, and the crystallized salt residue is discharged and disposed of uniformly.

[0023] The beneficial effects of adopting the above-mentioned further technical solutions are as follows: The equipment structure, employing 80℃ low-temperature preheating combined with -60KPa precise negative pressure flash evaporation, significantly improves the solubility of easily scale-forming salts such as calcium sulfate compared to traditional high-temperature flash evaporation equipment, slowing down the rate of internal scaling. Simultaneously, the flash furnace is equipped with a periodic online flushing structure, effectively extending the equipment maintenance cycle and solving the problems of easy scaling and frequent malfunctions in traditional equipment. The use of a double-layered sleeve-type spray gun with an arc-shaped flow guide channel allows the low-pressure steam on the outer side to form a tangential rotating high-speed airflow. This not only provides secondary heating to the atomized wastewater droplets, ensuring complete vaporization of the water, but also continuously purifies the outer wall of the nozzle, preventing nozzle crystallization and clogging at the source. This eliminates the need for frequent disassembly and replacement of equipment parts, significantly improving the continuous operational stability of the entire system.

[0024] Furthermore, for operating conditions with high water volume and low concentration requirements, in step S22, the wastewater is preheated to 82°C using a tubular heat exchanger; in step S32, a vacuum pump maintains the negative pressure inside the flash furnace at -55 kPa. For operating conditions with high concentration and low water volume, in step S22, the wastewater is preheated to 78°C using a tubular heat exchanger; in step S32, a vacuum pump maintains the negative pressure inside the flash furnace at -65 kPa. For operating conditions with no requirements for water volume or concentration, in step S22, the wastewater is preheated to 80°C using a tubular heat exchanger; in step S32, a vacuum pump maintains the negative pressure inside the flash furnace at -60 kPa. In step S12... After dewatering the sludge generated by flocculation and sedimentation, the filtrate is returned to the regulating tank for reprocessing; in step S3, the bottom of the flash furnace is periodically flushed online, and the flushing water is discharged into the regulating tank for reprocessing, with a concentration ratio of 4-6 times; step S42 includes: steam forming an airflow rotating along the outer wall of the nozzle through the guide channel, and the concentrated desulfurization wastewater is atomized to form droplets with a particle size ≤90μm; the steam pressure is 0.3MPa-0.6MPa; the steam and condensate are recovered through the outer layer of the drying evaporation tower, and the salt crystal particles are recovered through the inside of the drying evaporation tower; the condensed water is reused in the power plant desulfurization system or boiler feedwater system, and the crystallized salt slag is sent to the power plant ash field for unified disposal.

[0025] The beneficial effects of adopting the above-mentioned further technical solutions are as follows: the vacuum pump maintains the negative pressure inside the flash furnace at -55 kPa, and the tubular heat exchanger preheats the wastewater to 82°C, achieving a wastewater concentration ratio of up to 4.2 times, which is suitable for power plant operating conditions with high water volume and low concentration requirements. The vacuum pump maintains the negative pressure inside the flash furnace at -65 kPa, and the tubular heat exchanger preheats the wastewater to 78°C, achieving a wastewater concentration ratio of up to 5.8 times, suitable for operating conditions with high concentration and low water volume, demonstrating wide equipment adaptability. The equipment structure employing 80°C low-temperature preheating combined with -60 kPa precise negative pressure flash evaporation significantly improves the solubility of easily scale-forming salts such as calcium sulfate compared to traditional high-temperature flash evaporation equipment, slowing down the rate of internal scaling. Simultaneously, the flash furnace is equipped with a periodic online flushing structure, effectively extending the equipment maintenance cycle and solving the problems of easy scaling and frequent malfunctions in traditional equipment.

[0026] The advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is one of the structural schematic diagrams of a zero-discharge treatment system for desulfurization wastewater from a coal-fired power plant provided in an embodiment of the present invention.

[0029] Figure 2 This is the second schematic diagram of the zero-discharge treatment system for desulfurization wastewater from a coal-fired power plant provided in an embodiment of the present invention.

[0030] The following are the reference numerals: 1. Regulating tank; 2. Dosing device; 3. Sludge transfer pump; 4. Tubular heat exchanger; 5. Flash furnace; 6. Vacuum pump; 7. Steam heat exchanger; 8. Concentrating circulation pump; 9. Drying evaporation tower; 10. Two-fluid spray gun; 11. Exhaust fan; 12. Wastewater transfer pump. Detailed Implementation

[0031] The principles and features of the present invention are described below with reference to the accompanying drawings. The embodiments described are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0032] 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 some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0033] Therefore, the following detailed description of the embodiments of the 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. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0034] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0035] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper", "lower", "horizontal", "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the invention is usually placed during use, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0036] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0037] like Figure 1 and Figure 2 As shown in the figure, an embodiment of the present invention provides a zero-discharge treatment system for desulfurization wastewater from a coal-fired power plant, comprising: a pretreatment unit, a waste heat preheating unit, a negative pressure flash evaporation concentration unit, and a steam atomization evaporation crystallization unit, wherein the pretreatment unit, the waste heat preheating unit, the negative pressure flash evaporation concentration unit, and the steam atomization evaporation crystallization unit are connected sequentially through pipelines.

[0038] The beneficial effects of adopting the technical solution of this invention are that, through the integrated coupling of the pretreatment unit, the negative pressure flash concentration unit, and the steam atomization evaporation crystallization unit, wastewater hardening removal, volume reduction and concentration, and atomization crystallization salt production can be completed sequentially, with no wastewater discharge throughout the entire process; condensate can be recycled and reused, and crystallized salt residue is collected and disposed of uniformly, fully meeting the environmental protection requirements for zero discharge of power plant desulfurization wastewater. The equipment has a high degree of integration and strong adaptability. It achieves low energy consumption, low scaling, and stable zero discharge.

[0039] like Figure 1 and Figure 2 As shown, the pretreatment unit further includes: a regulating tank 1, a dosing device 2 for adding sodium hydroxide, sodium carbonate and PAM reagents into the regulating tank 1, and a sludge transfer pump 3. The waste heat preheating unit, the dosing device 2 and the sludge transfer pump 3 are all connected to the regulating tank 1 through pipelines. The sludge transfer pump 3 is connected to a sludge treatment device through a pipeline. The sludge treatment device is connected to the regulating tank 1 through a pipeline. The regulating tank 1 is connected to a desulfurization wastewater raw liquid pipeline through a pipeline.

[0040] The beneficial effects of adopting the above-mentioned further technical solution are that the dosing device is used to add sodium hydroxide, sodium carbonate, and PAM reagents into the equalization tank to perform homogenization, chemical hardening removal, flocculation, and sedimentation treatment on the desulfurization wastewater, effectively removing calcium and magnesium hardness ions from the wastewater and reducing the effluent hardness to below 50 mg / L. The sludge generated by sedimentation is sent to an external sludge dewatering machine for dewatering via a sludge transfer pump, and the dewatered filtrate is returned to the equalization tank for recycling, avoiding material waste.

[0041] like Figure 1 and Figure 2 As shown, the waste heat preheating unit further includes: a tubular heat exchanger 4 for heating wastewater to 78℃-82℃ and a wastewater transfer pump 12. The pretreatment unit is connected to the tubular heat exchanger 4 through a pipeline, and the wastewater transfer pump 12 is installed on the pipeline between the pretreatment unit and the tubular heat exchanger 4. The condensate outlet of the tubular heat exchanger 4 is connected to a power plant recycled water tank through a pipeline.

[0042] The beneficial effects of adopting the above-mentioned further technical solution are that by setting up a tubular heat exchanger, the waste heat from the secondary steam generated by the evaporation and crystallization unit can be recovered to preheat the original wastewater, realizing the cascade recycling of waste heat. The entire set of equipment only needs to supplement a small amount of low-pressure steam to meet the operating requirements, eliminating the need for high-temperature heating equipment and significantly reducing equipment operating energy consumption and maintenance costs. The pretreated effluent after treatment in the regulating tank is sent to the tubular heat exchanger via a wastewater transfer pump, where it is preheated using the waste heat from the secondary steam generated by the downstream evaporation tower, stably raising the wastewater temperature to 80°C. After heat exchange, the secondary steam condenses into clean condensate, which is sent to the recycled water tank for recycling, achieving efficient waste heat recovery.

[0043] like Figure 1 and Figure 2 As shown, the negative pressure flash evaporation concentration unit further includes: a flash furnace 5, a vacuum pump 6 for stabilizing the negative pressure inside the flash furnace 5 at -55KPa to -65KPa, a steam heat exchanger 7, and a concentration circulation pump 8. The waste heat preheating unit, the vacuum pump 6, and the concentration circulation pump 8 are all connected to the flash furnace 5 through pipelines. The steam heat exchanger 7 is installed on the pipeline between the flash furnace 5 and the concentration circulation pump 8. The two ends of the steam heat exchanger 7 are respectively connected to the vacuum pump 6 and the power plant recycled water tank through pipelines. The bottom of the flash furnace 5 is provided with an online scale removal and flushing port. The online scale removal and flushing port is connected to an online flushing structure through a pipeline. The online flushing structure is connected to the pretreatment unit through a pipeline.

[0044] The beneficial effects of adopting the above-mentioned further technical solution are that the vacuum pump is installed at the top of the flash furnace to maintain the negative pressure environment inside the furnace. A circulation loop is formed at the bottom of the flash furnace through a concentration circulation pump. Low-temperature negative pressure suppresses scaling, resulting in strong equipment stability: the equipment structure, employing 80℃ low-temperature preheating combined with -60KPa precise negative pressure flash evaporation, significantly improves the solubility of easily scaling salts such as calcium sulfate compared to traditional high-temperature flash evaporation equipment, slowing down the scaling rate inside the equipment. The flash furnace is equipped with a periodic online flushing structure, effectively extending the equipment maintenance cycle and solving the problems of easy scaling and frequent failures in traditional equipment. Wastewater preheated by the tubular heat exchanger is sent to the flash furnace, where a -60KPa negative pressure environment is maintained by the vacuum pump, allowing the 80℃ wastewater to be rapidly flash-evaporated and reduced in volume; the concentration circulation pump enables wastewater circulation flash evaporation, stably controlling the wastewater concentration ratio at 4-5 times; a scale discharge flushing port is set at the bottom of the flash furnace, allowing online flushing every 7 days, with the flushing water flowing back to the regulating tank, effectively preventing salt deposition and equipment blockage. The steam extracted by the vacuum pump recovers its heat through a steam heat exchanger, and the condensate is then recycled.

[0045] like Figure 1 and Figure 2 As shown, the steam atomization evaporation crystallization unit further includes: a drying evaporation tower 9, a dual-fluid spray gun 10, and an exhaust fan 11. The drying evaporation tower 9 is a double-layer sleeve structure with an insulation layer. The dual-fluid spray gun 10 and the exhaust fan 11 are both installed on the top of the drying evaporation tower 9 and are connected to the drying evaporation tower 9. The negative pressure flash evaporation concentration unit is connected to the dual-fluid spray gun 10, and the exhaust fan 11 is connected to the waste heat preheating unit through a pipeline. The bottom of the drying evaporation tower 9 is provided with a crystallized salt residue collection and discharge structure.

[0046] The beneficial effects of adopting the above-mentioned further technical solution are that the spray gun has a good anti-clogging effect and is suitable for long-term continuous operation. The double-layered sleeve-type spray gun with an arc-shaped flow guide channel allows the low-pressure steam on the outer side to form a tangential rotating high-speed airflow. This not only provides secondary heating to the atomized wastewater droplets, ensuring complete vaporization of the water, but also continuously purifies the outer wall of the nozzle, preventing nozzle crystallization and clogging at the source. This eliminates the need for frequent disassembly and replacement of equipment parts, significantly improving the continuous operational stability of the entire system. The concentrated high-salt wastewater is fed into the double-layered sleeve-type spray gun at the top of the evaporation tower. The inner tube of the spray gun transports the concentrated wastewater, atomizing it into fine droplets with an average particle size of 65μm. The outer tube is filled with 0.5MPa low-pressure saturated steam, which forms a rotating airflow through a 25° arc-shaped flow guide channel, heating the droplets from all directions, causing the water to vaporize instantly and the salt to crystallize. The vaporized steam is returned to the tubular heat exchanger to preheat the original wastewater solution. The crystallized salt residue falls to the bottom of the evaporation tower for unified collection and disposal. The condensate can be directly reused in the power plant's production system. The drying evaporation tower requires insulation and has a double-layered sleeve structure. The outer layer recovers steam and any condensate, while the inner layer recovers salt crystal particles.

[0047] like Figure 1 and Figure 2 As shown, the dual-fluid spray gun 10 further includes an inner tube and an outer tube. The outer tube is sleeved on the outside of the inner tube. The inner tube is connected to the negative pressure flash evaporation concentration unit through a pipeline. The outer tube is connected to a steam pipeline with a steam pressure range of 0.3MPa-0.6MPa through a pipeline. The outlet end of the outer tube is provided with multiple arc-shaped guide channels with a radial angle range of 20°-40°.

[0048] The beneficial effects of adopting the above-mentioned further technical solution are that the spray gun has a good anti-clogging effect and is suitable for long-term continuous operation. The double-layered sleeve-type spray gun with an arc-shaped flow guide channel allows the low-pressure steam on the outer side to form a tangential rotating high-speed airflow. This not only provides secondary heating to the atomized wastewater droplets, ensuring complete vaporization of the water, but also continuously purifies the outer wall of the nozzle, preventing nozzle crystallization and clogging at the source. This eliminates the need for frequent disassembly and replacement of equipment parts, significantly improving the continuous operational stability of the entire system. The concentrated high-salt wastewater is fed into the double-layered sleeve-type spray gun at the top of the evaporation tower. The inner tube of the spray gun transports the concentrated wastewater, atomizing it into fine droplets with an average particle size of 65μm. The outer tube is filled with 0.5MPa low-pressure saturated steam, which forms a rotating airflow through a 25° arc-shaped flow guide channel, heating the droplets from all directions, causing the water to vaporize instantly and the salt to crystallize. The vaporized steam is returned to the tubular heat exchanger to preheat the original wastewater solution. The crystallized salt residue falls to the bottom of the evaporation tower for unified collection and disposal. The condensate can be directly reused in the power plant's production system. The double-layer sleeve spray gun includes an inner tube and an outer tube. The inner tube transports concentrated desulfurization wastewater, and the outer tube transports low-pressure heating steam. The outlet end of the outer tube is provided with several arc-shaped guide channels with a radial angle of 20°-40°. The steam forms an airflow that rotates along the outer wall of the nozzle through the guide channels.

[0049] The regulating tank 1 is connected to desulfurization wastewater, and an integrated wastewater treatment device is installed inside the regulating tank 1.

[0050] Furthermore, the present invention also provides a method for zero-discharge treatment of desulfurization wastewater from coal-fired power plants. Based on the above-mentioned zero-discharge treatment system for desulfurization wastewater from coal-fired power plants, the method includes: S1, pre-treating the desulfurization wastewater to remove hardness through a pre-treatment unit; S2, preheating the pre-treated effluent with waste heat through a waste heat preheating unit; S3, concentrating the preheated desulfurization wastewater under negative pressure flash evaporation through a negative pressure flash concentration unit; and S4, performing steam coupling atomization evaporation crystallization on the concentrated desulfurization wastewater through a steam atomization evaporation crystallization unit.

[0051] The beneficial effects of adopting the technical solution of this invention are that, through the integrated coupling of the pretreatment unit, the negative pressure flash concentration unit, and the steam atomization evaporation crystallization unit, wastewater hardening removal, volume reduction and concentration, and atomization crystallization salt production can be completed sequentially, with no wastewater discharge throughout the entire process; condensate can be recycled and reused, and crystallized salt residue is collected and disposed of uniformly, fully meeting the environmental protection requirements for zero discharge of power plant desulfurization wastewater. The equipment has a high degree of integration and strong adaptability. It achieves low energy consumption, low scaling, and stable zero discharge.

[0052] Further, step S1 includes: S11, homogenizing and equalizing the desulfurization wastewater through equalization tank 1; S12, adding sodium hydroxide, sodium carbonate and PAM reagent to equalization tank 1 through dosing device 2 to chemically soften the desulfurization wastewater and remove calcium and magnesium hardness ions, and obtaining pretreated effluent through flocculation sedimentation and filtration; step S2 includes: S21, transporting the pretreated effluent to tubular heat exchanger 4 through wastewater transfer pump 12; S22, preheating the wastewater temperature to 78℃-82℃ through secondary steam generated by steam atomization evaporation crystallization unit; and recycling the clean condensate obtained after the secondary steam releases heat and condenses.

[0053] The beneficial effects of adopting the above-mentioned further technical solution are that the original desulfurization wastewater is passed into a regulating tank for homogenization and flow equalization, and sodium hydroxide and sodium carbonate are added for chemical softening to remove calcium and magnesium hardness ions. After flocculation, sedimentation, and filtration, pretreated effluent is obtained. A tubular heat exchanger is installed to recover the waste heat from the secondary steam generated by the evaporation and crystallization unit to preheat the original wastewater, achieving a cascaded recycling of waste heat. The entire system only requires a small amount of low-pressure steam to meet operating requirements, eliminating the need for high-temperature heating equipment and significantly reducing equipment operating energy consumption and maintenance costs.

[0054] Further, step S3 includes: S31, sending the preheated desulfurization wastewater into flash furnace 5; S32, maintaining the negative pressure range inside flash furnace 5 at -55KPa to 65KPa using vacuum pump 6; S33, recovering and utilizing the secondary steam generated by flash vaporization of some water through steam heat exchanger 7; S34, discharging the unvaporized concentrated wastewater through flash furnace 5 to obtain concentrated desulfurization wastewater; Step S4 includes: S41, sending the concentrated desulfurization wastewater into dual-fluid spray gun 10; S42, conveying and atomizing the concentrated desulfurization wastewater through the inside of dual-fluid spray gun 10, and introducing steam through the outside of dual-fluid spray gun 10 to reheat the atomized droplets, so that the water in the droplets is completely vaporized and the salt crystallizes out; the water vapor is condensed and recovered, and the crystallized salt residue is discharged and disposed of uniformly.

[0055] The beneficial effects of adopting the above-mentioned further technical solutions are as follows: The equipment structure, employing 80℃ low-temperature preheating combined with -60KPa precise negative pressure flash evaporation, significantly improves the solubility of easily scale-forming salts such as calcium sulfate compared to traditional high-temperature flash evaporation equipment, slowing down the rate of internal scaling. Simultaneously, the flash furnace is equipped with a periodic online flushing structure, effectively extending the equipment maintenance cycle and solving the problems of easy scaling and frequent malfunctions in traditional equipment. The use of a double-layered sleeve-type spray gun with an arc-shaped flow guide channel allows the low-pressure steam on the outer side to form a tangential rotating high-speed airflow. This not only provides secondary heating to the atomized wastewater droplets, ensuring complete vaporization of the water, but also continuously purifies the outer wall of the nozzle, preventing nozzle crystallization and clogging at the source. This eliminates the need for frequent disassembly and replacement of equipment parts, significantly improving the continuous operational stability of the entire system.

[0056] Furthermore, for operating conditions with high water volume and low concentration requirements, in step S22, the wastewater is preheated to 82°C using the tubular heat exchanger 4, and in step S32, the vacuum pump 6 maintains the negative pressure inside the flash furnace 5 at -55 kPa; for operating conditions with high concentration and low water volume, in step S22, the wastewater is preheated to 78°C using the tubular heat exchanger 4, and in step S32, the vacuum pump 6 maintains the negative pressure inside the flash furnace 5 at -65 kPa; for operating conditions with no requirements for water volume or concentration, in step S22, the wastewater is preheated to 80°C using the tubular heat exchanger 4, and in step S32, the vacuum pump 6 maintains the negative pressure inside the flash furnace 5 at -60 kPa; Step S12 In step S3, after the sludge generated by flocculation and sedimentation is dewatered, the filtrate is returned to the regulating tank 1 for reprocessing; in step S42, the bottom of the flash furnace 5 is periodically flushed online, and the flushing water is discharged into the regulating tank 1 for reprocessing, with a concentration ratio of 4-6 times; step S52 includes: steam is formed into an airflow rotating along the outer wall of the nozzle through the guide channel, and the concentrated desulfurization wastewater is atomized to form droplets with a particle size ≤90μm; the steam pressure is 0.3MPa-0.6MPa; the steam and condensate are recovered through the outer layer of the drying evaporation tower 9, and the salt crystal particles are recovered through the interior of the drying evaporation tower 9; the condensed water is reused in the power plant desulfurization system or boiler feedwater system, and the crystallized salt slag is sent to the power plant ash field for unified disposal.

[0057] The beneficial effects of adopting the above-mentioned further technical solutions are as follows: the vacuum pump maintains the negative pressure inside the flash furnace at -55 kPa, and the tubular heat exchanger preheats the wastewater to 82°C, achieving a wastewater concentration ratio of up to 4.2 times, which is suitable for power plant operating conditions with high water volume and low concentration requirements. The vacuum pump maintains the negative pressure inside the flash furnace at -65 kPa, and the tubular heat exchanger preheats the wastewater to 78°C, achieving a wastewater concentration ratio of up to 5.8 times, suitable for operating conditions with high concentration and low water volume, demonstrating wide equipment adaptability. The equipment structure employing 80°C low-temperature preheating combined with -60 kPa precise negative pressure flash evaporation significantly improves the solubility of easily scale-forming salts such as calcium sulfate compared to traditional high-temperature flash evaporation equipment, slowing down the rate of internal scaling. Simultaneously, the flash furnace is equipped with a periodic online flushing structure, effectively extending the equipment maintenance cycle and solving the problems of easy scaling and frequent malfunctions in traditional equipment.

[0058] This invention belongs to the field of industrial wastewater treatment technology, specifically relating to a zero-discharge treatment system for desulfurization wastewater from coal-fired power plants. It is suitable for the harmless and resource-oriented zero-discharge treatment of high-salt, high-hardness desulfurization wastewater generated by limestone-gypsum wet desulfurization processes. The purpose of this invention is to address the shortcomings of existing zero-discharge desulfurization wastewater treatment equipment, such as high energy consumption, easy scaling, easy nozzle clogging, poor operational stability, and low waste heat utilization. This invention provides a zero-discharge treatment system for desulfurization wastewater from coal-fired power plants, which is an 80℃ negative pressure flash evaporation coupled with steam atomization evaporation system. This solves the technical problems of high maintenance costs, unstable operating conditions, and poor zero-discharge treatment effect of existing equipment.

[0059] The present invention provides a zero-discharge treatment system for desulfurization wastewater from a coal-fired power plant, which can be a zero-discharge treatment system for desulfurization wastewater using 80°C negative pressure flash evaporation coupled with steam atomization evaporation. It includes a pretreatment unit, a waste heat preheating unit, a negative pressure flash evaporation concentration unit, and a steam atomization evaporation crystallization unit connected in sequence.

[0060] The pretreatment unit includes a regulating tank 1, a dosing device 2, and a sludge conveying pump 3. The outlet of the dosing device 2 is connected to the inside of the regulating tank 1. The bottom of the regulating tank 1 is connected to the feed end of an external sludge dewatering machine through the sludge conveying pump 3. The regulating tank 1 is connected to the desulfurization wastewater raw liquid pipeline, and the overflow port is connected to the waste heat preheating unit.

[0061] The waste heat preheating unit includes a wastewater transfer pump 12 and a tubular heat exchanger 4. The outlet of the regulating tank 1 is connected to the wastewater inlet of the tubular heat exchanger 4 through the wastewater transfer pump 12.

[0062] The negative pressure flash evaporation concentration unit includes a flash furnace 5, a vacuum pump 6, and a concentration circulation pump 8. The wastewater outlet of the tubular heat exchanger 4 is connected to the feed end of the flash furnace 5. The vacuum pump 6 is installed on the top of the flash furnace 5 and is used to maintain the negative pressure environment inside the furnace. The bottom of the flash furnace 5 forms a circulation loop through the concentration circulation pump 8. An online scale removal and flushing port is provided at the bottom of the flash furnace 5.

[0063] The steam atomization evaporation crystallization unit includes a drying evaporation tower 9, a double-layered sleeve-type spray gun (dual-fluid spray gun 10), and an exhaust fan 11. The concentrated water outlet of the flash furnace 5 is connected to the double-layered sleeve-type spray gun (dual-fluid spray gun 10) at the top of the drying evaporation tower 9. The double-layered sleeve-type spray gun (dual-fluid spray gun 10) includes an inner tube and an outer tube nested inside and outside. The inner tube is connected to the concentrated wastewater pipeline, and the outer tube is connected to the low-pressure steam pipeline. The outlet end of the outer tube is uniformly provided with several arc-shaped guide channels with a radial angle of 20°-40°. The secondary steam outlet of the drying evaporation tower 9 is connected to the steam inlet of the tubular heat exchanger 4. The exhaust fan 11 is installed at the top of the drying evaporation tower 9.

[0064] Furthermore, the vacuum pump 6 is adapted to maintain the negative pressure inside the flash furnace 5 at a stable range of -55KPa to -65KPa, with the optimal negative pressure setting being -60KPa.

[0065] Furthermore, the waste heat preheating temperature of the tubular heat exchanger 4 is adapted to the wastewater temperature rise to 78℃-82℃, with the optimal preheating temperature set at 80℃.

[0066] Furthermore, the atomized particle size of the inner tube outlet of the double-layer sleeve spray gun (dual fluid spray gun 10) is ≤90μm, and the low-pressure saturated steam pressure connected to the outer tube is 0.4MPa-0.6MPa.

[0067] Furthermore, the wastewater concentration ratio of flash furnace 5 is adapted to 4-6 times, and flash furnace 5 is equipped with a 7-day cycle automatic online flushing structure.

[0068] Furthermore, the condensate outlet of the tubular heat exchanger 4 is connected to the power plant's recycled water tank, and a crystalline salt residue collection and discharge structure is installed at the bottom of the drying evaporation tower 9.

[0069] 1. Low energy consumption and high waste heat utilization rate: The present invention is equipped with a tubular heat exchanger, which can recover the waste heat of the secondary steam generated by the evaporation and crystallization unit to preheat the original wastewater, realize the cascade recycling of waste heat, and the whole set of equipment only needs to supplement a small amount of low-pressure steam to meet the working conditions. There is no need for high-temperature heating equipment, which greatly reduces the energy consumption and maintenance costs of the equipment.

[0070] 2. Low-temperature negative pressure suppression for strong equipment stability: This invention adopts an equipment structure of 80℃ low-temperature preheating combined with -60KPa precise negative pressure flash evaporation. Compared with traditional high-temperature flash evaporation equipment, it can significantly improve the solubility of easily scale-forming salts such as calcium sulfate and slow down the scaling rate inside the equipment. At the same time, the flash furnace is equipped with a periodic online flushing structure, which effectively extends the equipment maintenance cycle and solves the problems of easy scaling and frequent failures of traditional equipment.

[0071] 3. Excellent anti-clogging effect of the spray gun, suitable for long-term continuous operation: The present invention adopts a double-layer sleeve spray gun with an arc-shaped flow guide channel. The low-pressure steam on the outside can form a tangential rotating high-speed airflow, which can not only reheat the atomized wastewater droplets to ensure complete vaporization of water, but also continuously blow the outer wall of the nozzle, thus avoiding nozzle crystallization and clogging from the root. There is no need to frequently disassemble and replace equipment parts, which greatly improves the continuous operation stability of the entire system.

[0072] 4. Integrated design for zero emissions throughout the process: This invention integrates a pretreatment unit, a negative pressure flash concentration unit, and a steam atomization evaporation crystallization unit, which can sequentially complete wastewater hardening removal, volume reduction and concentration, and atomization crystallization for salt production, with no wastewater discharge throughout the process; condensate can be recycled and reused, and crystallized salt residue is collected and disposed of in a unified manner, fully meeting the environmental protection requirements for zero discharge of desulfurization wastewater from power plants. The equipment has a high degree of integration and strong adaptability.

[0073] Example See Figure 1 This invention provides a zero-discharge treatment system for desulfurization wastewater from a coal-fired power plant. It includes a regulating tank 1, a dosing device 2, a sludge transfer pump 3 (pretreatment step); a wastewater transfer pump 12, a tubular heat exchanger 4 (waste heat preheating step); a flash furnace 5, a vacuum pump 6, a steam heat exchanger 7, a concentration circulation pump 8 (negative pressure flash concentration step); a drying evaporation tower 9, a two-fluid spray gun 10, and a drying fan 11 (atomization evaporation crystallization step).

[0074] like Figure 1 and Figure 2 As shown in the figure, the present invention provides a zero-discharge treatment system for desulfurization wastewater from a coal-fired power plant, which includes a pretreatment unit, a waste heat preheating unit, a negative pressure flash evaporation concentration unit, and a steam atomization evaporation crystallization unit. Each unit is connected in sequence by pipelines to form an integrated zero-discharge treatment equipment system for desulfurization wastewater.

[0075] The pretreatment unit includes a regulating tank 1, a dosing device 2, and a sludge transfer pump 3. The dosing device 2 adds sodium hydroxide, sodium carbonate, and PAM to the regulating tank 1 to homogenize, chemically remove hardness, and perform flocculation and sedimentation treatment on the desulfurization wastewater, effectively removing calcium and magnesium hardness ions from the wastewater and reducing the effluent hardness to below 50 mg / L. The sludge generated by sedimentation is sent to an external sludge dewatering machine for dewatering via the sludge transfer pump 3. The dewatered filtrate is returned to the regulating tank 1 for recycling, avoiding material waste.

[0076] The waste heat preheating unit includes a wastewater transfer pump 12 and a tubular heat exchanger 4. The pretreated effluent from the regulating tank 1 is sent to the tubular heat exchanger 4 via the wastewater transfer pump 12. The waste heat from the secondary steam generated by the downstream evaporator tower 9 is used for preheating, which stably raises the wastewater temperature to 80°C. After the secondary steam heats up, it is condensed into clean condensate and sent to the recycled water tank for reuse, thus achieving efficient waste heat recovery.

[0077] The negative pressure flash evaporation concentration unit includes a flash furnace 5, a vacuum pump 6, a steam heat exchanger 7, and a concentration circulation pump 8. Wastewater preheated by the tubular heat exchanger 4 is sent to the flash furnace 5. The vacuum pump 6 maintains a negative pressure environment of -60 kPa inside the furnace, enabling rapid flash evaporation and volume reduction of the 80°C wastewater. The concentration circulation pump 8 achieves wastewater circulation flash evaporation, stably controlling the wastewater concentration ratio at 4-5 times. A scale discharge and flushing port is installed at the bottom of the flash furnace 5, which is flushed online every 7 days. The flushing water is returned to the regulating tank 1, effectively preventing salt deposits from clogging the equipment. The steam extracted by the vacuum pump 6 recovers heat through the steam heat exchanger 7, and the condensate is recycled.

[0078] The steam atomization evaporation crystallization unit includes an evaporation tower 9, a double-layered pipe spray gun (dual-fluid spray gun 10), and a drying fan 11. The concentrated high-salt wastewater is sent to the double-layered pipe spray gun (dual-fluid spray gun 10) at the top of the evaporation tower 9. The inner tube of the spray gun transports the concentrated wastewater and atomizes it into fine droplets with an average particle size of 65μm. The outer tube is filled with 0.5MPa low-pressure saturated steam. The steam forms a rotating airflow through a 25° arc-shaped guide channel, which heats the droplets from all directions, causing the water to vaporize instantly and the salt to crystallize and precipitate. The vaporized water vapor is returned to the tubular heat exchanger 4 to preheat the wastewater. The crystallized salt residue falls to the bottom of the evaporation tower 9 for unified collection and disposal. The condensate can be directly reused in the power plant production system.

[0079] In another embodiment, the vacuum pump 6 maintains the negative pressure in the flash furnace at -55 kPa, and the tubular heat exchanger 4 preheats the wastewater to 82°C, achieving a wastewater concentration ratio of up to 4.2 times, which can be adapted to power plant operating conditions with high water volume and low concentration requirements.

[0080] In the third embodiment, the vacuum pump 6 maintains the negative pressure in the flash furnace at -65KPa, and the tubular heat exchanger 4 preheats the wastewater to 78°C. The wastewater concentration ratio can reach 5.8 times, which is suitable for high concentration and low water volume operating conditions, and the equipment has wide adaptability.

[0081] This invention provides a method for zero-discharge treatment of desulfurization wastewater from coal-fired power plants, specifically a method for zero-discharge treatment of desulfurization wastewater using 80℃ negative pressure flash evaporation coupled with steam atomization evaporation. The method includes the following steps: Step S1: Pretreatment for hardness removal: The original desulfurization wastewater is passed into a regulating tank 1 for homogenization and equalization. Sodium hydroxide and sodium carbonate are added for chemical softening to remove calcium and magnesium hardness ions. After flocculation, sedimentation, and filtration, pretreated effluent is obtained. Step S2: Waste heat preheating: The pretreated effluent is passed into a tubular heat exchanger 4, where secondary steam generated by the subsequent steam-coupled atomization evaporation crystallization unit is used for preheating, raising the wastewater temperature to 78℃-82℃. The secondary steam is then released and condensed to obtain clean water. Condensate recycling; Step S3: Negative pressure flash concentration: The preheated desulfurization wastewater is sent into flash furnace 5, maintaining the negative pressure inside flash furnace 5 at -55KPa to -65KPa. The secondary steam generated by the flash vaporization of some water is sent to the heat exchanger for recycling. The unvaporized concentrated wastewater is discharged from the bottom of the flash furnace to obtain concentrated desulfurization wastewater; Step S4: Steam coupled atomization evaporation crystallization: The concentrated desulfurization wastewater is sent into a double-layer sleeve spray gun. The concentrated desulfurization wastewater is transported and atomized inside the spray gun, and low-pressure steam is introduced outside the spray gun to reheat the atomized droplets, so that the water in the droplets is completely vaporized and the salt crystallizes out; the water vapor is condensed and recovered, and the crystallized salt residue is discharged and disposed of uniformly.

[0082] In step S2, the wastewater temperature is preheated to 80°C.

[0083] In step S3, the negative pressure inside the flash furnace is maintained at -60 kPa.

[0084] In step S1, after the sludge produced by flocculation and sedimentation is dewatered, the filtrate is returned to the equalization tank for reprocessing.

[0085] In step S3, the bottom of the flash furnace is periodically flushed online, and the flushing water is discharged into the regulating tank for reprocessing.

[0086] In step S4, the double-layer sleeve spray gun includes an inner tube and an outer tube. The inner tube transports concentrated desulfurization wastewater, and the outer tube transports low-pressure heating steam. The outlet end of the outer tube is provided with several arc-shaped guide channels with a radial angle of 20°-40°. The steam forms an airflow that rotates along the outer wall of the nozzle through the guide channels.

[0087] In step S4, the concentrated desulfurization wastewater is atomized to form fine droplets with a particle size ≤90μm.

[0088] In step S4, the pressure of the low-pressure steam is 0.3MPa-0.6MPa.

[0089] In step S3, the concentration ratio is 4-6 times.

[0090] In step S4, the condensed water is reused in the power plant's desulfurization system or boiler feedwater system, and the crystallized salt slag is sent to the power plant's ash disposal site for unified treatment.

[0091] In step S4, the drying evaporator 9 requires insulation and has a double-layered sleeve structure. The outer layer recovers steam and any condensate, while the inner layer recovers salt crystal particles.

[0092] 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.

Claims

1. A zero-discharge treatment system for desulfurization wastewater from a coal-fired power plant, characterized in that, include: The pretreatment unit, the waste heat preheating unit, the negative pressure flash evaporation concentration unit, and the steam atomization evaporation crystallization unit are connected sequentially through pipelines.

2. The zero-discharge treatment system for desulfurization wastewater from a coal-fired power plant according to claim 1, characterized in that, The pretreatment unit includes: a regulating tank (1), a dosing device (2) for adding sodium hydroxide, sodium carbonate and PAM reagents into the regulating tank (1), and a sludge transfer pump (3). The waste heat preheating unit, the dosing device (2) and the sludge transfer pump (3) are all connected to the regulating tank (1) through pipelines. The sludge transfer pump (3) is connected to a sludge treatment device through a pipeline. The sludge treatment device is connected to the regulating tank (1) through a pipeline. The regulating tank (1) is connected to a desulfurization wastewater raw liquid pipeline through a pipeline.

3. The zero-discharge treatment system for desulfurization wastewater from a coal-fired power plant according to claim 1, characterized in that, The waste heat preheating unit includes a tubular heat exchanger (4) for heating wastewater to 78℃-82℃ and a wastewater transfer pump (12). The pretreatment unit is connected to the tubular heat exchanger (4) through a pipeline. The wastewater transfer pump (12) is installed on the pipeline between the pretreatment unit and the tubular heat exchanger (4). The condensate outlet of the tubular heat exchanger (4) is connected to a power plant recycled water tank through a pipeline.

4. The zero-discharge treatment system for desulfurization wastewater from a coal-fired power plant according to claim 1, characterized in that, The negative pressure flash evaporation concentration unit includes: a flash furnace (5), a vacuum pump (6) for stabilizing the negative pressure in the flash furnace (5) at -55KPa to -65KPa, a steam heat exchanger (7), and a concentration circulation pump (8). The waste heat preheating unit, the vacuum pump (6), and the concentration circulation pump (8) are all connected to the flash furnace (5) through pipelines. The steam heat exchanger (7) is installed on the pipeline between the flash furnace (5) and the concentration circulation pump (8). The two ends of the steam heat exchanger (7) are connected to the vacuum pump (6) and the power plant recycled water tank through pipelines, respectively. The bottom of the flash furnace (5) is provided with an online scale discharge and flushing port. The online scale discharge and flushing port is connected to an online flushing structure through a pipeline. The online flushing structure is connected to the pretreatment unit through a pipeline.

5. The zero-discharge treatment system for desulfurization wastewater from a coal-fired power plant according to claim 1, characterized in that, The steam atomization evaporation crystallization unit includes: a drying evaporation tower (9), a dual-fluid spray gun (10), and a drying fan (11). The drying evaporation tower (9) is a double-layer sleeve structure with a heat insulation layer. The dual-fluid spray gun (10) and the drying fan (11) are both installed on the top of the drying evaporation tower (9). The dual-fluid spray gun (10) and the drying fan (11) are both connected to the drying evaporation tower (9). The negative pressure flash evaporation concentration unit is connected to the dual-fluid spray gun (10). The drying fan (11) is connected to the waste heat preheating unit through a pipeline. The bottom of the drying evaporation tower (9) is provided with a crystallized salt residue collection and discharge structure.

6. The zero-discharge treatment system for desulfurization wastewater from a coal-fired power plant according to claim 5, characterized in that, The dual-fluid spray gun (10) includes an inner tube and an outer tube. The outer tube is sleeved on the outside of the inner tube. The inner tube is connected to the negative pressure flash evaporation concentration unit through a pipeline. The outer tube is connected to a steam pipeline with a steam pressure range of 0.3MPa-0.6MPa through a pipeline. The outlet end of the outer tube is provided with multiple arc-shaped guide channels with a radial angle range of 20°-40°.

7. A method for zero-discharge treatment of desulfurization wastewater from a coal-fired power plant, characterized in that, Based on the zero-discharge treatment system for desulfurization wastewater from a coal-fired power plant according to any one of claims 1 to 6, the method for zero-discharge treatment of desulfurization wastewater from a coal-fired power plant includes: S1. The desulfurization wastewater is pretreated to remove hardness through a pretreatment unit; S2. The pretreated effluent is preheated with waste heat through a waste heat preheating unit. S3. The preheated desulfurization wastewater is concentrated by negative pressure flash evaporation through a negative pressure flash evaporation concentration unit. S4. The concentrated desulfurization wastewater is subjected to steam coupling atomization evaporation crystallization through a steam atomization crystallization unit.

8. The method for zero-discharge treatment of desulfurization wastewater from a coal-fired power plant according to claim 7, characterized in that, Step S1 includes: S11. Homogenize and equalize the quantity of desulfurization wastewater using the equalization tank (1); S12. Sodium hydroxide, sodium carbonate and PAM are added to the regulating tank (1) through the dosing device (2) to chemically soften the desulfurization wastewater and remove calcium and magnesium hardness ions. The pretreated effluent is obtained by flocculation, sedimentation and filtration. Step S2 includes: S21. The pretreated effluent is transported to the tubular heat exchanger (4) by the wastewater transfer pump (12). S22. The wastewater temperature is raised to 78℃-82℃ by preheating with secondary steam generated by the steam atomization evaporation crystallization unit; the clean condensate obtained after the secondary steam is condensed is recycled.

9. The method for zero-discharge treatment of desulfurization wastewater from a coal-fired power plant according to claim 8, characterized in that, Step S3 includes: S31. Send the preheated desulfurization wastewater into the flash furnace (5). S32. The negative pressure range inside the flash furnace (5) is maintained at -55KPa to 65KPa by the vacuum pump (6); S33. Secondary steam generated by partial water flash vaporization is recovered and utilized through a steam heat exchanger (7); S34. Unvaporized concentrated wastewater is discharged through flash furnace (5) to obtain concentrated desulfurization wastewater; Step S4 includes: S41. Concentrated desulfurization wastewater is fed into a dual-fluid spray gun (10). S42. Concentrated desulfurization wastewater is conveyed and atomized through the inner side of the dual-fluid spray gun (10). Steam is introduced through the outer side of the dual-fluid spray gun (10) to heat the atomized droplets a second time, so that the water in the droplets is completely vaporized and the salt crystallizes out. The water vapor is condensed and recovered, and the crystallized salt residue is discharged and disposed of in a unified manner.

10. A method for zero-discharge treatment of desulfurization wastewater from a coal-fired power plant according to claim 9, characterized in that, For high water volume and low concentration requirements, in step S22, the wastewater is preheated to 82°C using a tubular heat exchanger (4), and in step S32, the negative pressure inside the flash furnace (5) is maintained at -55KPa using a vacuum pump (6); for high concentration and low water volume requirements, in step S22, the wastewater is preheated to 78°C using a tubular heat exchanger (4), and in step S32, the negative pressure inside the flash furnace (5) is maintained at -65KPa using a vacuum pump (6); for conditions with no requirements for water volume or concentration, in step S22, the wastewater is preheated to 80°C using a tubular heat exchanger (4), and in step S32, the negative pressure inside the flash furnace (5) is maintained at -60KPa using a vacuum pump (6); Step S1 In step 2, after the sludge generated by flocculation and sedimentation is dewatered, the filtrate is returned to the regulating tank (1) for reprocessing; in step S3, the bottom of the flash furnace (5) is periodically flushed online, and the flushing water is discharged into the regulating tank (1) for reprocessing, with a concentration ratio of 4-6 times; step S42 includes: steam forms an airflow rotating along the outer wall of the nozzle through the guide channel, and the concentrated desulfurization wastewater is atomized to form droplets with a particle size ≤90μm; the steam pressure is 0.3MPa-0.6MPa; the steam and condensate are recovered through the outer layer of the drying evaporation tower (9), and the salt crystal particles are recovered through the interior of the drying evaporation tower (9); the condensed water is reused in the power plant desulfurization system or boiler feedwater system, and the crystallized salt slag is sent to the power plant ash field for unified disposal.

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