Coal-fired flue gas wet desulphurization wastewater advanced treatment process system

Abstract

The invention provides a coal-fired flue gas wet desulphurization wastewater advanced treatment process system, which comprises: a pretreatment unit, which is used for receiving coal-fired flue gas desulphurization wastewater and wastewater generated by a system subsequent unit, and removing large particle impurities; the membrane treatment unit is communicated with the pretreatment unit and is used for carrying out desalination and salt separation treatment on the pretreated wastewater to generate concentrated water containing high-concentration sodium chloride; the electrolytic treatment unit is communicated with the membrane treatment unit and is used for receiving the concentrated water containing the high-concentration sodium chloride and removing chloride ions in the concentrated water through electrolytic reaction; the sludge treatment unit is communicated with the pretreatment unit and the membrane treatment unit and is used for collecting and treating sludge generated by the system; the wastewater backflow unit is communicated with all the units and used for collecting emptying wastewater, flushing wastewater and filtrate generated by all the units and enabling the collected wastewater to flow back to the pretreatment unit, wastewater treatment is not affected by large fluctuation of unit peak regulation wastewater quantity, the desulfurization wastewater treatment desalination rate is high, the Cl <-> removal effect is good, and wastewater zero discharge can be achieved.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology containing high salt and high chlorine, and in particular to a deep treatment process system for wet desulfurization wastewater from coal-fired flue gas. Background Technology

[0002] With the national advocacy for "zero discharge" of wastewater, desulfurization wastewater has become a limiting factor for coal-fired power plants in achieving this goal. Currently, most coal-fired power plants simply treat desulfurization wastewater using a "three-compartment" process before reusing it in the slurry preparation tank or desulfurization absorption tower. A smaller number use a "three-compartment" process with added membrane treatment, then spray the concentrated water into the flue or use evaporation and crystallization to achieve "zero discharge" of desulfurization wastewater. However, the "three-compartment" process is not suitable for treating solid impurities, heavy metals, and chloride ions in desulfurization wastewater. - Limited removal efficiency and high chloride ion concentration in the concentrate from membrane treatment can lead to corrosion of flue gas ducts and desulfurization equipment, deterioration of desulfurization slurry quality, and consequently, reduced desulfurization efficiency. Furthermore, peak load adjustments and fluctuations in wastewater volume due to unit peak shaving can cause significant instability or malfunctions in the wastewater treatment system.

[0003] Therefore, in order to achieve "zero discharge" of wastewater without affecting the desulfurization efficiency of the system, it is urgent to develop a stable deep treatment system for desulfurization wastewater. Summary of the Invention

[0004] This invention provides a desulfurization wastewater deep treatment system with a reasonable structural design that can operate stably without being affected by the unit's peak shaving, in order to overcome the problems existing in the existing related technologies and to truly achieve "zero discharge" of desulfurization wastewater.

[0005] A deep treatment process system for wet desulfurization wastewater from coal-fired flue gas includes: The pretreatment unit is used to receive wastewater from the desulfurization of coal-fired flue gas and wastewater generated by subsequent units of the system, and to remove large particulate impurities. The membrane treatment unit, connected to the pretreatment unit, is used to desalinate and separate salts from the pretreated wastewater, producing concentrated water with a high concentration of sodium chloride. The electrolysis treatment unit, connected to the membrane treatment unit, is used to receive the wastewater after membrane treatment and remove chloride ions from it through an electrolysis reaction; The sludge treatment unit, connected to the pretreatment unit and the membrane treatment unit, is used to collect and treat the sludge generated by the system. The wastewater recirculation unit is connected to the above-mentioned units and is used to collect the venting wastewater, rinsing wastewater and filtrate generated by each unit, and recirculate the collected wastewater back to the pretreatment unit.

[0006] Preferably, the pretreatment unit includes an equalization tank, a primary sedimentation tank, a chemical dosing and aeration mixing tank, a flocculation reaction tank, a secondary sedimentation tank, and a water storage tank connected in sequence.

[0007] Preferably, an agitator is installed at the bottom of the equalization tank, and the bottom of the tank is sloped from the inlet to the outlet. Sludge discharge pipes are installed at the bottom of the equalization tank, primary sedimentation tank, and secondary sedimentation tank. The chemical dosing aeration mixing tank and the flocculation reaction tank are integrated, and an aeration device is installed at the bottom of the chemical dosing aeration mixing tank.

[0008] Preferably, the membrane treatment unit includes an ultrafiltration subsystem, a nanofiltration subsystem, and a reverse osmosis subsystem; the outlet of the ultrafiltration subsystem is connected to the inlet of the nanofiltration subsystem, and the outlet of the nanofiltration subsystem is connected to the inlet of the reverse osmosis subsystem.

[0009] Preferably, the ultrafiltration subsystem includes a connected ultrafiltration dosing tank and an ultrafiltration device; The nanofiltration subsystem includes a nanofiltration dosing tank, a nanofiltration pressurization pump, and a nanofiltration device connected in sequence. The reverse osmosis subsystem includes a reverse osmosis security filter, a reverse osmosis booster pump, a reverse osmosis unit, a clear water tank, and a reverse osmosis concentrate tank; Both ultrafiltration and nanofiltration dosing tanks are equipped with stirring devices to facilitate thorough mixing of water and chemicals.

[0010] Preferably, the electrolysis treatment unit includes an electrolytic cell, an absorber, a dryer, and an H2 storage tank; the absorber is connected to the anode region of the electrolytic cell; the dryer is connected to the cathode region of the electrolytic cell; and the H2 storage tank is connected to the outlet of the dryer.

[0011] Two units are installed for both nanofiltration pressurization pump and reverse osmosis pressurization pump, one for use and one for backup.

[0012] Preferably, the cathode region and the anode region of the electrolytic cell are separated by a cation exchange membrane.

[0013] Preferably, the upper outlet of the anode area is connected to the bottom of the cathode area via a pipe, and a check valve is installed on the pipe. An electrolytic water outlet is set at the upper part of the cathode area and connected to the clear water tank. A water supply outlet is set at the bottom of the cathode area and connected to the water outlet pipe of the anode area. An electric valve is installed on the water supply pipe. The anode zone of the electrolytic cell is connected to the absorber via a pipe. The absorber stores NaOH solution to absorb the Cl2 generated in the anode zone of the electrolytic cell. The cathode area of ​​the electrolytic cell is connected to a dryer via a pipe to dry the H2 generated in the cathode area of ​​the electrolytic cell; the dryer is connected to an H2 storage tank via a pipe to collect and store the H2 generated in the cathode area of ​​the electrolytic cell.

[0014] Preferably, vent pipes are installed at the bottom of the dosing aeration and mixing tank, flocculation reaction tank, water storage tank, ultrafiltration dosing tank, nanofiltration dosing tank, nanofiltration permeate tank, reverse osmosis concentrate tank, and electrolytic cell.

[0015] Preferably, the sludge treatment unit includes a sludge homogenizing tank, a sludge thickening tank, and a sludge dewatering machine connected in sequence; The sludge homogenizing tank receives sludge discharged from the pretreatment unit and the membrane treatment unit, and the sludge homogenizing tank is equipped with a stirring device. The sludge thickening tank is equipped with a sludge inlet and a water outlet at the top. The sludge inlet is connected to the sludge homogenizing tank through a pipe, and the supernatant is returned to the wastewater collection tank through the water outlet. The sludge discharge pipe at the bottom is connected to the sludge dewatering machine. After the thickened sludge is dewatered, the sludge cake is transported out, and the filtrate is returned to the wastewater collection tank.

[0016] Preferably, the supernatant outlet of the sludge thickening tank and the filtrate outlet of the sludge dewatering machine are both connected to the wastewater return unit.

[0017] Preferably, the wastewater return unit includes a wastewater collection tank, which collects the wastewater generated after treatment by each unit, and the wastewater is finally returned to the equalization tank for further treatment via a feedwater pump.

[0018] This invention achieves the following beneficial effects: It regulates and controls fluctuations in water volume and quality caused by unit peak shaving in a regulating tank; removes COD, ammonia nitrogen, large particles, suspended solids, and some heavy metal precipitates and colloids from wastewater through primary sedimentation, aeration, flocculation, and sedimentation; performs desalination and purification treatment through a membrane treatment device; removes chloride ions from the concentrated water generated by the membrane treatment device through electrolysis; collects and recirculates filtrate and flushing wastewater back to the front-end regulating tank for further treatment; and processes, dries, and stores the generated gas for reuse. This invention is unaffected by large fluctuations in wastewater volume caused by unit peak shaving, achieves high desalination rates in desulfurization wastewater treatment, and reduces chloride ions. - It has a good removal effect and can achieve "zero discharge" of wastewater.

[0019] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings.

[0020] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0021] To more clearly illustrate the embodiments of the present invention, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 This is a flowchart of a deep treatment process system for wet desulfurization wastewater from coal-fired flue gas in an embodiment of the present invention.

[0022] Figure 2 This is a schematic diagram of an electrolytic cell in a deep treatment process system for wet desulfurization wastewater from coal-fired flue gas according to an embodiment of the present invention. In the diagram: equalization tank (1); lift pump (2); primary sedimentation tank (3); chemical dosing and aeration mixing tank (4); flocculation reaction tank (5); secondary sedimentation tank (6); water storage tank (7); feed pump (8); ultrafiltration dosing tank (9); ultrafiltration device (10); nanofiltration dosing tank (11); nanofiltration pressurizing pump (12); nanofiltration device (13); nanofiltration permeate tank (14); reverse osmosis security filter (15); reverse osmosis pressurizing pump (16); reverse osmosis device (17); clear water tank (18); reverse osmosis concentrate tank (19); electrolytic cell (20); absorber (21); dryer (22); H2 storage tank (23); sludge homogenizing tank (24); sludge thickening tank (25); sludge dewatering machine (26); wastewater collection tank (27); cation exchange membrane (28); check valve (29); electric valve (30). Detailed Implementation

[0023] To make the objectives, features, and advantages of this invention more apparent and understandable, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. The following embodiments are explanations of the invention, but the invention is not limited to the following embodiments.

[0024] In one embodiment, such as Figure 1 As shown, a deep treatment process system for wet desulfurization wastewater from coal-fired flue gas includes: The pretreatment unit is used to receive wastewater from the desulfurization of coal-fired flue gas and wastewater generated by subsequent units of the system, and to remove large particulate impurities. The membrane treatment unit, connected to the pretreatment unit, is used to desalinate and separate salts from the pretreated wastewater, producing concentrated water with a high concentration of sodium chloride. The electrolysis treatment unit, connected to the membrane treatment unit, is used to receive the wastewater after membrane treatment and remove chloride ions from it through an electrolysis reaction; The sludge treatment unit, connected to the pretreatment unit and the membrane treatment unit, is used to collect and treat the sludge generated by the system. The wastewater recirculation unit is connected to the above-mentioned units and is used to collect the venting wastewater, rinsing wastewater and filtrate generated by each unit, and recirculate the collected wastewater back to the pretreatment unit.

[0025] The working principle and beneficial effects of the above technical solution are as follows: it is not affected by large fluctuations in the peak-shaving wastewater volume of the unit; it has a high desalination rate in desulfurization wastewater treatment; and it contains Cl... - It has a good removal effect and can achieve "zero discharge" of wastewater.

[0026] In one embodiment, such as Figure 1 As shown, the pretreatment unit includes an equalization tank 1, a primary sedimentation tank 3, a chemical dosing and aeration mixing tank 4, a flocculation reaction tank 5, a secondary sedimentation tank 6, and a water storage tank 7 connected in sequence. A stirrer is installed at the bottom of the equalization tank, and a slope of 0.05 is set from the inlet to the outlet. An emptying and sludge discharge pipe is installed at the lowest point of the slope, which is the bottom of the equalization tank outlet, to facilitate the emptying and cleaning of the equalization tank. The blades of the stirrer installed at the bottom are 10-15cm away from the bottom of the tank to facilitate water mixing. The bottom of the equalization tank 1, primary sedimentation tank 3 and secondary sedimentation tank 6 are equipped with sludge discharge pipes; the chemical dosing aeration and mixing tank 4 and the flocculation reaction tank 5 are integrated, and the bottom of the chemical dosing aeration and mixing tank 4 is equipped with an aeration device. The working principle and beneficial effects of the above technical solution are as follows: To cope with fluctuations in the amount of peak-shaving wastewater generated by the unit, an equalization tank is designed to regulate the water volume. The primary sedimentation tank can initially remove large particles and suspended solids from the wastewater, preventing them from affecting the operation of subsequent aeration equipment. After the wastewater undergoes flocculation, smaller particles and suspended solids in the secondary sedimentation tank increase in size due to flocculation, and some heavy metals in the wastewater are removed through sedimentation or colloidal flocculation. Furthermore, sludge discharge pipes are installed at the bottom of the primary and secondary sedimentation tanks. The sludge discharged from these tanks, along with the sludge generated by the equalization tank and ultrafiltration / nanofiltration devices, flows into the sludge homogenization tank. Alternatively, depending on the specific site conditions, the sludge generated by these devices can be discharged into the sludge homogenization tank through different pipelines.

[0027] The chemical dosing aeration and mixing tank and the flocculation reaction tank are integrated. The bottom of the chemical dosing aeration and mixing tank is equipped with aeration devices, such as aeration discs or aeration pipes, designed to remove COD and ammonia nitrogen from the wastewater. Calcium hydroxide solution and flocculant are added to the aeration tank, mixed through aeration and mixing, and then introduced into the flocculation reaction tank for flocculation. An online pH meter needs to be installed in the flocculation reaction zone to monitor the pH value of the wastewater.

[0028] The bottom of the chemical dosing aeration and mixing tank, flocculation reaction tank, water storage tank, ultrafiltration dosing tank, nanofiltration dosing tank, nanofiltration permeate tank, reverse osmosis concentrate tank, and electrolytic cell are all equipped with vent pipes to facilitate equipment inspection and maintenance, and to allow the vented wastewater to enter the wastewater collection tank.

[0029] In one embodiment, such as Figure 1 As shown, the membrane treatment unit includes an ultrafiltration subsystem, a nanofiltration subsystem, and a reverse osmosis subsystem; the outlet of the ultrafiltration subsystem is connected to the inlet of the nanofiltration subsystem, and the outlet of the nanofiltration subsystem is connected to the inlet of the reverse osmosis subsystem. The ultrafiltration subsystem includes a connected ultrafiltration dosing tank 9 and an ultrafiltration device 10; The nanofiltration subsystem includes a nanofiltration dosing tank 11, a nanofiltration pressurization pump 12, and a nanofiltration device 13 connected in sequence. The reverse osmosis subsystem includes a reverse osmosis security filter 15, a reverse osmosis booster pump 16, a reverse osmosis unit 17, a clear water tank 18, and a reverse osmosis concentrate tank 19; The ultrafiltration dosing tank 9 and the nanofiltration dosing tank 11 are equipped with stirring devices to facilitate thorough mixing of water and chemicals. The working principle and beneficial effects of the above technical solution are as follows: An ultrafiltration dosing tank is set at the front end of the ultrafiltration device. The ultrafiltration dosing tank is equipped with a stirring device to facilitate thorough mixing of the chemicals and water. Sodium hydroxide and sodium carbonate are added to the ultrafiltration dosing tank. Sodium hydroxide is reserved. If the pH of the water effluent from the storage tank does not meet the design requirements, sodium hydroxide will continue to be added. Sodium carbonate needs to be added continuously. The dosage can be adjusted according to the calcium hardness of the influent. After the wastewater undergoes the chemical reaction, calcium ions react to form calcium carbonate. Then, the generated calcium carbonate and some heavy metal ions are filtered out by ultrafiltration. The ultrafiltration permeate enters the nanofiltration dosing tank.

[0030] The nanofiltration unit is equipped with a nanofiltration dosing tank and a nanofiltration pressurization pump at the front end. The effluent from the ultrafiltration system mainly contains NaCl and Na2SO4. Therefore, nanofiltration is used to further desalinate the effluent from the ultrafiltration system. To further reduce the Na2SO4 content and improve the NaCl purity, a nanofiltration dosing tank is installed at the front end of the nanofiltration unit. BaCl2 is mainly added. After being stirred and mixed evenly by the stirring device in the nanofiltration dosing tank, Na2SO4 in the water reacts with BaCl2 to form BaSO4 precipitate and NaCl. Under the action of the nanofiltration pressurization pump, the permeate containing NaCl enters the nanofiltration permeate tank, while the concentrated water containing BaSO4 precipitate and a small amount of heavy metal ions is discharged into the sludge equalization tank, thereby further improving the NaCl purity in the water.

[0031] A reverse osmosis (RO) pre-filter and a RO booster pump are installed at the front end of the RO unit. The RO pre-filter effectively prevents 0.5-10μm particles, colloids, and microorganisms from entering the RO unit and causing physical damage or fouling to the RO membrane, thereby extending the membrane's lifespan. The RO booster pump provides sufficient pressure to the RO unit. Water from the nanofiltration permeate tank enters the RO unit through the RO booster pump, where NaCl is retained in the RO concentrate. The RO permeate is stored in the clear water tank for later use, while the concentrate with high NaCl concentration is stored in the RO concentrate tank for electrolytic dechlorination treatment in the electrolytic cell. If necessary, a Cl2 filter can be installed in the RO concentrate tank. - Online monitoring instrument and stirrer, and setting up dilute HCl dosing, if Cl in the reverse osmosis concentrate... - When the concentration is too low or the pH is unfavorable for electrolysis, additional dilute HCl is added to maintain the Cl- concentration in the reverse osmosis concentrate. - Stabilize the concentration or adjust the pH of the reverse osmosis concentrate to further improve the stability of electrolysis.

[0032] Install three-way valves on the inlet and outlet pipes of the ultrafiltration unit, nanofiltration unit, and reverse osmosis unit. During backwashing, close the product water outlet valve and the inlet water valve to prevent backwash wastewater from entering downstream and upstream equipment and causing pollution. Finally, discharge the backwash wastewater into the wastewater collection tank.

[0033] In one embodiment, the pretreatment unit may be further equipped with a booster pump 2, and the membrane treatment unit may be further equipped with a feed water pump 8. Two booster pumps 2 and two feed water pumps 8 are provided, one for use and one for standby.

[0034] The working principle and beneficial effects of the above technical solution are as follows: the booster pump 2 is set after the equalization tank 1 and is connected to the equalization tank 1 and the primary sedimentation tank 3 in sequence. When the equalization tank is set at the lowest elevation, the desulfurization wastewater flows into the equalization tank by gravity and is then pumped into the subsequent equipment for treatment by the booster pump.

[0035] The feed water pump 8 is located between the pretreatment unit and the ultrafiltration subsystem, connecting the pretreatment unit and the membrane treatment unit. The ultrafiltration subsystem uses power to stably transport the pretreated wastewater to the ultrafiltration dosing tank 9, meeting the basic requirements of membrane treatment for inlet water pressure and flow rate.

[0036] Both can be installed at their respective locations or not, depending on the actual process layout, reducing construction difficulty; the booster pump can also be used in conjunction with the regulating tank to cope with water volume fluctuations for peak shaving of the unit.

[0037] In one embodiment, such as Figure 1 and Figure 2 As shown, the cathode region and anode region of the electrolytic cell 20 are separated by a cation exchange membrane 28; The upper outlet of the anode area is connected to the bottom of the cathode area through a pipe, and a check valve 29 is installed on the pipe. An electrolytic water outlet is set at the upper part of the cathode area and connected to the clear water tank through a pipe. A water supply outlet is set at the bottom of the cathode area and connected to the water outlet pipe of the anode area. An electric valve 30 is installed on the water supply pipe. The anode region of electrolytic cell 20 is connected to absorber 21 via a pipe. The absorber 21 stores NaOH solution to absorb Cl2 generated in the anode region of electrolytic cell 20. The cathode region of the electrolytic cell 20 is connected to the dryer 22 via a pipe for drying the H2 generated in the cathode region of the electrolytic cell 20; the dryer 22 is connected to the H2 storage tank 23 via a pipe for collecting and storing the H2 generated in the cathode region of the electrolytic cell 20.

[0038] The working principle and beneficial effects of the above technical solution are as follows: the cathode area and anode area of ​​the electrolytic cell are separated by a cation exchange membrane to prevent OH from entering the cell during operation. -The water moves to the anode and reacts with the Cl2 generated at the anode, increasing the residual chlorine content in the purified water. The upper outlet of the anode zone is connected to the bottom of the cathode zone, facilitating the flow of electrolyzed water from the upper anode zone into the cathode zone by gravity. During operation, reverse osmosis concentrate containing high concentrations of NaCl enters from the bottom of the anode zone, and the electrolyzed water is discharged from the upper end of the anode zone into the bottom of the cathode zone as cathode replenishment water. Finally, the purified water from electrolysis is discharged from the upper part of the cathode zone into the clear water tank for storage and reuse. In addition, during initial startup, due to the effect of the intermediate diaphragm, the water in the cathode zone is relatively low, so a cathode replenishment inlet is provided, which is connected to the pipeline from the anode zone to the cathode zone. The anode zone of the electrolytic cell is connected to the absorber via a pipeline. The absorber stores NaOH solution to absorb the Cl2 generated in the anode zone of the electrolytic cell, preventing the Cl2 generated at the anode from entering the environment and polluting the environment and harming human health. A purified water inlet is located at the bottom of the cathode zone of the electrolytic cell, and a drain outlet is located at the top to discharge water containing high concentrations of OH-. - The alkaline solution is used to dry the H2 generated in the cathode area of ​​the electrolytic cell, which is connected to the drying chamber via a pipeline. The dried H2 is then stored in an H2 storage tank connected to the drying chamber for reuse; the H2 storage tank must be equipped with a pressure gauge.

[0039] In one embodiment, such as Figure 1 As shown, the sludge treatment unit includes a sludge homogenizing tank 24, a sludge thickening tank 25, and a sludge dewatering machine 26 connected in sequence. The sludge homogenizing tank 24 receives sludge discharged from the pretreatment unit and the membrane treatment unit, and the sludge homogenizing tank 24 is equipped with a stirring device. The upper end of the sludge thickening tank 25 is equipped with a sludge inlet and a water outlet. The sludge inlet is connected to the sludge homogenizing tank through a pipe, and the supernatant is returned to the wastewater collection tank 27 through the water outlet. The bottom is equipped with a sludge discharge pipe connected to the sludge dewatering machine 26. After the thickened sludge is dewatered, the sludge cake is transported out, and the filtrate is returned to the wastewater collection tank 27. The wastewater return unit includes a wastewater collection tank 27, which collects the wastewater generated after treatment by each unit. The wastewater is then returned to the equalization tank 1 for further treatment via a feedwater pump.

[0040] The working principle and beneficial effects of the above technical solution are as follows: the sludge homogenizing tank receives sludge from the equalization tank, primary sedimentation tank, secondary sedimentation tank, ultrafiltration device and nanofiltration device, and the sludge homogenizing tank is equipped with a stirring device so that the sludge can be fully mixed before entering the sludge thickening tank for thickening and volume reduction treatment.

[0041] The sludge thickening tank is equipped with a sludge inlet and a water outlet at the top. The sludge inlet is connected to the sludge homogenizing tank through a pipe, and the supernatant is returned to the wastewater collection tank through the water outlet. The sludge discharge pipe at the bottom is connected to the sludge dewatering machine. After the thickened sludge is dewatered by the dewatering machine, the sludge cake is transported out, and the filtrate is returned to the wastewater collection tank.

[0042] The flushing or venting wastewater from each unit's treated equipment, as well as the filtrate from the sludge dewatering machine, the supernatant from the sludge thickening tank, and the wastewater generated from the flushing of the ultrafiltration unit, nanofiltration unit, reverse osmosis unit, and reverse osmosis security filter, are discharged into the wastewater collection tank. The wastewater is then returned to the equalization tank for further treatment via a feedwater pump, thus achieving "zero discharge" of wastewater.

[0043] Although the present invention has been disclosed above with reference to embodiments, it is not intended to limit the scope of protection of the present invention. Any modifications and refinements made by those skilled in the art without departing from the concept and scope of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A deep treatment process system for wet desulfurization wastewater from coal-fired flue gas, characterized in that, include: The pretreatment unit is used to receive wastewater from the desulfurization of coal-fired flue gas and wastewater generated by subsequent units of the system, and to remove large particulate impurities. The membrane treatment unit, connected to the pretreatment unit, is used to desalinate and separate salts from the pretreated wastewater, producing concentrated water with a high concentration of sodium chloride. The electrolysis unit, connected to the membrane treatment unit, is used to receive concentrated water containing high concentrations of sodium chloride and remove chloride ions from it through an electrolysis reaction; The sludge treatment unit, connected to the pretreatment unit and the membrane treatment unit, is used to collect and treat the sludge generated by the system. The wastewater recirculation unit is connected to the above-mentioned units and is used to collect the venting wastewater, rinsing wastewater and filtrate generated by each unit, and recirculate the collected wastewater back to the pretreatment unit.

2. The deep treatment process system for wet desulfurization wastewater from coal-fired flue gas according to claim 1, characterized in that, The pretreatment unit includes an equalization tank (1), a primary sedimentation tank (3), a chemical dosing and aeration mixing tank (4), a flocculation reaction tank (5), a secondary sedimentation tank (6), and a water storage tank (7) connected in sequence.

3. The deep treatment process system for wet desulfurization wastewater from coal-fired flue gas according to claim 2, characterized in that, A stirrer is installed at the bottom of the equalization tank (1), and the bottom of the tank is sloped from the inlet to the outlet. The equalization tank (1), the primary sedimentation tank (3) and the secondary sedimentation tank (6) are equipped with sludge discharge pipes at the bottom. The chemical dosing aeration stirring tank (4) and the flocculation reaction tank (5) are integrated. An aeration device is installed at the bottom of the chemical dosing aeration stirring tank (4).

4. The deep treatment process system for wet desulfurization wastewater from coal-fired flue gas according to claim 1, characterized in that, The membrane treatment unit includes an ultrafiltration subsystem, a nanofiltration subsystem, and a reverse osmosis subsystem; the outlet of the ultrafiltration subsystem is connected to the inlet of the nanofiltration subsystem, and the outlet of the nanofiltration subsystem is connected to the inlet of the reverse osmosis subsystem.

5. The deep treatment process system for wet desulfurization wastewater from coal-fired flue gas according to claim 4, characterized in that: The ultrafiltration subsystem includes a connected ultrafiltration dosing tank (9) and an ultrafiltration device (10). The nanofiltration subsystem includes a nanofiltration dosing tank (11), a nanofiltration pressurizing pump (12), and a nanofiltration device (13) connected in sequence. The reverse osmosis subsystem includes a reverse osmosis security filter (15), a reverse osmosis booster pump (16), a reverse osmosis unit (17), a clear water tank (18), and a reverse osmosis concentrate tank (19). The ultrafiltration dosing tank (9) and the nanofiltration dosing tank (11) are equipped with stirring devices to facilitate thorough mixing of water and chemicals.

6. The deep treatment process system for wet desulfurization wastewater from coal-fired flue gas according to claim 1, characterized in that, The electrolysis treatment unit includes an electrolytic cell (20), an absorber (21), a dryer (22), and an H2 storage tank (23); the absorber (21) is connected to the anode area of ​​the electrolytic cell (20); the dryer (22) is connected to the cathode area of ​​the electrolytic cell (20); and the H2 storage tank (23) is connected to the outlet of the dryer (22).

7. The deep treatment process system for wet desulfurization wastewater from coal-fired flue gas according to claim 6, characterized in that, The cathode region and anode region of the electrolytic cell (20) are separated by a cation exchange membrane (28); The upper outlet of the anode zone is connected to the bottom of the cathode zone through a pipe, and a check valve (29) is installed on the pipe. An electrolytic water outlet is provided at the top of the cathode area and connected to the clear water tank (18). A water supply outlet is provided at the bottom of the cathode area and connected to the water outlet pipe of the anode area. An electric valve (30) is installed on the water supply pipe. The anode area of ​​the electrolytic cell (20) is connected to the absorber (21) through a pipe. The absorber (21) stores NaOH solution to absorb the Cl2 generated in the anode area of ​​the electrolytic cell (20). The cathode region of the electrolytic cell (20) is connected to the dryer (22) via a pipe for drying the H2 generated in the cathode region of the electrolytic cell (20); the dryer (22) is connected to the H2 storage tank (23) via a pipe for collecting and storing the H2 generated in the cathode region of the electrolytic cell (20).

8. The deep treatment process system for wet desulfurization wastewater from coal-fired flue gas according to any one of claims 2-7, characterized in that, Vent pipes are installed at the bottom of the dosing aeration and mixing tank (4), flocculation reaction tank (5), water storage tank (7), ultrafiltration dosing tank (9), nanofiltration dosing tank (11), nanofiltration permeate tank (14), reverse osmosis concentrate tank (19) and electrolytic cell (20).

9. The deep treatment process system for wet desulfurization wastewater from coal-fired flue gas according to claim 1, characterized in that, The sludge treatment unit includes a sludge homogenizing tank (24), a sludge thickening tank (25), and a sludge dewatering machine (26) connected in sequence. The sludge homogenizer (24) receives sludge discharged from the pretreatment unit and the membrane treatment unit, and the sludge homogenizer (24) is equipped with a stirring device inside; The upper end of the sludge thickening tank (25) is equipped with a sludge inlet and a water outlet. The sludge inlet is connected to the sludge homogenizing tank (24) through a pipe. The supernatant is returned to the wastewater collection tank (27) through the water outlet. The bottom is equipped with a sludge discharge pipe connected to the sludge dewatering machine (26). After the thickened sludge is dewatered by the sludge dewatering machine (26), the sludge cake is transported out and the filtrate is returned to the wastewater collection tank (27).

10. The deep treatment process system for wet desulfurization wastewater from coal-fired flue gas according to claim 9, characterized in that, The supernatant outlet of the sludge thickening tank (25) and the filtrate outlet of the sludge dewatering machine (26) are both connected to the wastewater return unit.

11. The deep treatment process system for wet desulfurization wastewater from coal-fired flue gas according to claim 1, characterized in that, The wastewater return unit includes a wastewater collection tank (27), which collects the wastewater generated after treatment by each unit. The wastewater is then returned to the equalization tank (1) for further treatment via a water supply pump.

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