A system and method for recycling flue gas condensate wastewater and desulfurization wastewater

Abstract

This invention discloses a system and method for recycling flue gas condensate wastewater and desulfurization wastewater. The system includes a pretreatment system, a concentration system, and a crystallization system arranged sequentially. The pretreatment system includes a desulfurization wastewater pretreatment device, a condensate wastewater pretreatment device, and a condensate reverse osmosis treatment device. The concentration system uses a total thermal air preheater, which is equipped with an upper sprayer, an upper water evaporation coil, an air cap, a lower sprayer, and a lower water evaporation coil arranged sequentially from top to bottom. The crystallization system includes a sodium sulfate crystallizer and a sodium chloride crystallizer. Before concentration, the system pretreats the desulfurization wastewater and flue gas condensate wastewater, effectively removing calcium and magnesium ions, heavy metal ions, etc., from them. The resulting crystalline salt is almost free of impurities, achieving complete resource recovery and utilization of both condensate wastewater and desulfurization wastewater, resulting in zero discharge.

Description

Technical Field

[0001] This invention relates to the field of boiler energy conservation and environmental protection technology, specifically to a system and method for recycling flue gas condensate wastewater and desulfurization wastewater. Background Technology

[0002] With the strengthening of national policies on energy conservation and environmental protection, waste heat from coal-fired boiler flue gas, especially the waste heat from wet flue gas at around 50°C after desulfurization, has become a hot area for waste heat recovery. Since the flue gas after desulfurization is already wet-saturated, a large amount of condensate wastewater will be generated whether waste heat is extracted through direct contact heat exchange via spraying or through shell and tube heat exchangers.

[0003] Although the flue gas has been purified by spraying desulfurization slurry from the desulfurization tower, it still contains some soluble gases such as sulfur dioxide, as well as particulate matter or soluble salts such as limestone and gypsum. In other words, the condensate wastewater generated during the flue gas waste heat recovery process still contains a large number of harmful ions. It cannot be directly reused in the production process, and its discharge into the environment would cause pollution. Therefore, how to treat the condensate wastewater generated during flue gas waste heat recovery has become an unresolved issue in the flue gas waste heat recovery process.

[0004] In addition, the desulfurization process of flue gas from coal-fired boilers also generates a large amount of desulfurization wastewater. This wastewater also presents environmental problems: it contains high concentrations of ions, making it unusable for reuse in the process, and direct discharge into the environment causes serious pollution. Although evaporation crystallization processes such as MVR have been proposed to treat desulfurization wastewater and achieve zero discharge requirements, there are two main drawbacks: firstly, they require a large amount of energy, resulting in high treatment costs; secondly, they cannot separate the ions in the wastewater, so the final crystalline salt is classified as hazardous waste, lacking resource value and still causing environmental pollution. Summary of the Invention

[0005] In view of the composition characteristics of condensate wastewater generated from waste heat recovery of flue gas from coal-fired boilers and the composition characteristics of desulfurization wastewater, this invention provides a system and method for recycling flue gas condensate wastewater and desulfurization wastewater, which can simultaneously achieve zero-emission resource recycling of flue gas condensate wastewater and desulfurization wastewater.

[0006] The technical solution of the present invention is as follows:

[0007] In a first aspect of the present invention, a system for recycling flue gas condensate wastewater and desulfurization wastewater is provided, comprising a pretreatment system, a concentration system, and a crystallization system arranged sequentially; wherein, the pretreatment system includes a desulfurization wastewater pretreatment device, a condensate wastewater pretreatment device, and a condensate reverse osmosis treatment device, the concentration system employs a total thermal air preheater, and the total thermal air preheater is arranged from top to bottom as follows: an upper sprayer, an upper water evaporation coil, an air cap, a lower sprayer, and a lower water evaporation coil; the crystallization system includes a sodium sulfate crystallizer and a sodium chloride crystallizer.

[0008] In some embodiments of the present invention, both the desulfurization wastewater pretreatment device and the condensate wastewater pretreatment device employ sedimentation tanks, wherein the desulfurization wastewater pretreatment device employs a two-stage sedimentation tank, and the condensate wastewater pretreatment device employs a single-stage sedimentation tank.

[0009] In some embodiments of the present invention, the upper water-spraying evaporation coil and the lower water-spraying evaporation coil are connected in series, and the inlet of the upper water-spraying evaporation coil is connected to the flue gas waste hot water inlet.

[0010] In some embodiments of the present invention, the wastewater outlet of the pretreatment wastewater system is connected to the lower section of the total thermal air preheater. The wastewater outlet of the lower section of the total thermal air preheater is connected to the lower section sprayer via a concentrate circulation pump. The wastewater outlet of the lower section of the total thermal air preheater is also connected to the upper section sprayer via a concentrate circulation pump and a regulating valve.

[0011] In some embodiments of the present invention, a concentrated air inlet is provided in the lower section of the total heat air preheater, and a steam outlet is provided in the top of the total heat air preheater. The steam outlet is connected to the boiler combustion air interface via a pipeline.

[0012] In some embodiments of the present invention, the concentrated liquid outlet of the total heat air preheater is connected to the sprayer inside the sodium sulfate crystallizer, and the mother liquor outlet of the sodium sulfate crystallizer is connected to the sprayer inside the sodium chloride crystallizer via a mother liquor pump.

[0013] In some embodiments of the present invention, the coil inlet in the sodium chloride crystallizer is connected to the flue gas waste hot water inlet, and the coil outlet is connected to the inlet of the lower section water spray evaporation coil in the total heat air preheater.

[0014] In some embodiments of the present invention, the crystallization system further includes a filter, a refrigerator, and a crystallization blower connected in sequence, wherein the crystallization blower is connected in sequence via pipelines to a sodium sulfate crystallizer, a sodium chloride crystallizer, and the upper section of a total heat air preheater.

[0015] In a second aspect of the present invention, a method for recycling flue gas condensate wastewater and desulfurization wastewater is provided, comprising the following steps:

[0016] After the pretreated desulfurization wastewater and condensate wastewater are combined, they enter the total heat air preheater for concentration. The concentration process uses waste hot water from the flue gas as a heat source, and the hot and humid air discharged from the upper section of the total heat air preheater is sent to the boiler system as combustion air.

[0017] The concentrated solution first enters a sodium sulfate crystallizer for further concentration and crystallization to obtain sodium sulfate decahydrate crystals, and then enters a sodium chloride crystallizer to obtain sodium chloride crystals.

[0018] In some embodiments of the present invention, during the pretreatment process, desulfurization wastewater is treated by adding Ca(OH)2 lime slurry to adjust the pH value of the wastewater and precipitate magnesium ions, fluoride ions, and iron ions. Then, organic sulfides are added to precipitate mercury ions, followed by the addition of Na2CO3 to remove calcium ions. Finally, sulfuric acid or hydrochloric acid is added to the clear liquid to adjust the pH value to neutral. Calcium and magnesium ions are removed from condensation wastewater by adding Na2CO3.

[0019] One or more technical solutions of the present invention have the following beneficial effects:

[0020] (1) The system provided by the present invention can simultaneously treat and recycle desulfurization wastewater and flue gas condensation wastewater. Before concentration, the desulfurization wastewater and flue gas condensation wastewater are pretreated respectively, which can effectively remove calcium and magnesium ions, heavy metal ions and the like from the desulfurization wastewater and flue gas condensation wastewater. The final crystalline salt is almost free of impurities. All condensation wastewater and desulfurization wastewater are recycled and reused, achieving zero discharge.

[0021] (2) The system provided by the present invention makes full use of the low-grade flue gas waste heat (hot water) to achieve the concentration, crystallization and salt separation of flue gas condensation wastewater and desulfurization wastewater, realize zero wastewater discharge and resource recovery of crystallized salt. While achieving zero wastewater discharge, the high-temperature and high-humidity steam generated in the total heat air preheater is also sent to the boiler system as combustion air. At the same time, the boiler combustion air supply temperature is increased, which will also reduce boiler fuel consumption and increase energy-saving benefits.

[0022] (3) The system provided by the present invention is equipped with a chiller and a crystallization blower. The crystallization blower is connected to the sodium sulfate crystallizer. In winter, the crystallization blower directly draws ambient air. In summer, when the ambient temperature is high, the chiller in front of the blower inlet is started to cool down the air, ensuring that the air temperature sent into the sodium sulfate crystallizer can meet the requirements of sodium sulfate crystallization and improving the crystallization efficiency of sodium sulfate.

[0023] (4) The system provided by the present invention sets the upper section coil and the lower section coil in the total heat air preheater in series, and sets the coil in the sodium chloride crystallizer and the lower section coil in the total heat air preheater in series, thereby realizing the cascade utilization of waste hot water from flue gas and effectively improving energy utilization efficiency. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of the flue gas condensation wastewater and desulfurization wastewater recycling system of the present invention.

[0025] In the diagram: 1. Boiler combustion air inlet; 2. Desulfurization wastewater pretreatment device; 3. Condensate wastewater reverse osmosis device; 4. Concentrate regulating valve; 5. Air cap; 6. Upper section of total heat air preheater; 7. Upper section sprayer; 8. Upper section water evaporation zone; 9. Concentrate pump; 10. Tail liquid pump; 11. Sodium chloride crystallizer; 12. Sodium chloride crystallization water evaporation zone; 13. Sodium chloride crystallization sprayer; 14. Flue gas waste water inlet; 15. Sodium chloride crystal clarifier; 16. Sodium chloride crystal outlet; 17. Glauber's salt crystal outlet; 18. Mother liquor pump. 19. Sodium sulfate crystallizer; 20. Sodium sulfate crystallizer sprayer; 21. Glauber's salt clarifier; 22. Lower section of total heat air preheater; 23. Lower section water evaporation zone; 24. Lower section sprayer; 25. Concentrated liquid circulation pump; 26. Crystallization blower; 27. Concentrating blower; 28. Refrigeration unit; 29. ​​Filter; 30. Crystallization air inlet; 31. Concentrating air inlet; 32. Flue gas waste water outlet; 33. Condensed wastewater clear water outlet; 34. Condensed wastewater inlet; 35. Condensed wastewater pretreatment device; 36. Desulfurization wastewater inlet. Detailed Implementation

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0027] Example 1

[0028] In a typical embodiment of the present invention, such as Figure 1 As shown, a system for recycling flue gas condensate wastewater and desulfurization wastewater is proposed, comprising a pretreatment system, a concentration system, and a crystallization system arranged sequentially. The pretreatment system includes a desulfurization wastewater pretreatment device 2, a condensate wastewater pretreatment device 35, and a condensate reverse osmosis treatment device 3. Both the desulfurization wastewater pretreatment device 2 and the condensate wastewater pretreatment device 35 employ sedimentation tanks. The desulfurization wastewater pretreatment device is connected to the desulfurization wastewater inlet 36 and employs a two-stage sedimentation tank to remove heavy metal ions from the desulfurization wastewater. The condensate wastewater pretreatment device is connected to the condensate wastewater inlet 34 and employs a single-stage sedimentation tank to remove calcium and magnesium ions from the condensate wastewater. The condensate reverse osmosis treatment device further treats the condensate wastewater to obtain clean water and concentrated water. The clean water is reused in the boiler system or used as industrial water in the plant area, while the concentrated water is sent to subsequent processes for concentration.

[0029] The concentration system employs a total heat air preheater, which includes an upper section 6 and a lower section 22. The upper section 6 consists of an upper sprayer 7, a water evaporation zone 8, and an air cap 5. An upper water evaporation coil is installed in the upper water evaporation zone 8. The lower section 22 consists of a lower sprayer 24 and a lower water evaporation zone 23. A lower water evaporation coil is installed in the lower water evaporation zone 23. The upper and lower water evaporation coils are connected in series. The inlet of the upper water evaporation coil is connected to the flue gas waste heat inlet 14, and the flue gas waste heat outlet 32 ​​of the lower water evaporation coil is connected to the flue gas waste heat recovery system.

[0030] A wastewater inlet is provided on the total heat air preheater, which is connected to the wastewater outlet of the pretreatment wastewater system. The wastewater outlet of the lower section of the total heat air preheater is connected to the lower section sprayer 24 via a concentrate circulation pump 25. The wastewater outlet of the lower section of the total heat air preheater is also connected to the upper section sprayer 7 via a concentrate circulation pump 25 and a concentrate regulating valve 4. A concentration air inlet 31 is provided in the lower section of the total heat air preheater, which supplies air into the total heat air preheater via a concentration blower. A steam outlet is provided at the top of the total heat air preheater, which is connected to the boiler combustion air interface 1 via a pipeline.

[0031] The crystallization system includes a sodium sulfate crystallizer 19 and a sodium chloride crystallizer 11. The sodium sulfate crystallizer 19 is equipped with a sodium sulfate crystallization sprayer 20, and a sodium sulfate clarification tank 21 is provided at the bottom of the sodium sulfate crystallizer 19. A sodium sulfate crystal outlet 17 is provided at the bottom of the sodium sulfate clarification tank 21. The sodium chloride crystallizer 11 is equipped with a sodium chloride crystallization water evaporation zone 12 and a sodium chloride crystallization sprayer 13 at the top. A sodium chloride crystallization water evaporation coil is provided in the sodium chloride crystallizer 12. A sodium chloride crystal clarification tank 15 is provided at the bottom of the sodium chloride crystallizer 11. A sodium chloride crystallization outlet 16 is provided at the bottom of the sodium chloride crystallizer 15.

[0032] The concentrated liquid outlet of the total heat air preheater is connected to the sodium chloride crystallizer sprayer 13 in the sodium sulfate crystallizer 19 via the concentrated liquid pump 9. The mother liquor outlet of the sodium sulfate crystallizer 19 is connected to the sodium chloride crystallizer sprayer 13 in the sodium chloride crystallizer 11 via the mother liquor pump 18. The inlet of the sodium chloride crystallizer water evaporation coil is connected to the flue gas waste hot water inlet 14, and the coil outlet is connected to the inlet of the lower section water evaporation coil in the total heat air preheater.

[0033] Furthermore, the crystallization system also includes a crystallization air inlet 30, a filter 29, a refrigeration unit 28, and a crystallization blower 26 connected in sequence. The crystallization blower 26 is connected in sequence via pipelines to a sodium sulfate crystallizer 19, a sodium chloride crystallizer 11, and the upper section 6 of the total heat air preheater.

[0034] The condensate wastewater generated by the flue gas waste heat recovery system mainly contains ions. Cl- , Na + Ca 2+ And small amounts of potassium ions, magnesium ions, Very small amounts of iron ions, etc., must be removed because calcium and magnesium ions easily form scale during the concentration process, affecting equipment operation and subsequent processes.

[0035] Furthermore, Na₂CO₃ is used as a calcium and magnesium removal agent to treat the condensate wastewater. Calcium and magnesium ions are removed by precipitation with CaCO₃, MgCO₃, and Mg(OH)₂. The resulting clarified condensate wastewater is then sent to a reverse osmosis system. The purified water obtained from reverse osmosis is reused in the boiler system or used as industrial water in the plant area, while the concentrated water is sent to subsequent processes for concentration. After the above treatment, the main ions in the condensate wastewater are... Cl - Na + .

[0036] The desulfurization wastewater from the desulfurization process mainly contains ions Cl - F - Na + Ca 2+ Mg 2+ K + Zn 2+ Hg 2+ Cu 2+ F 3+ And chromium ions, cadmium ions, manganese ions, etc. Heavy metal ions and F - It is not only highly toxic, but also very harmful to subsequent processing procedures, so it must be removed.

[0037] Furthermore, Ca(OH)2 lime slurry is added to the desulfurization wastewater to adjust the pH value to around 9, precipitating most of the heavy metal ions, magnesium ions, fluoride ions, and iron ions. Then, organic sulfides such as sodium thiosulfate are added to precipitate Hg. 2+ Since calcium ions can still cause scaling in subsequent processes, Na2CO3 needs to be added to the clear solution to remove calcium ions. Finally, sulfuric acid or hydrochloric acid is added to the clear solution to adjust the pH to around 7.

[0038] The main ions in the desulfurization wastewater after the above treatment are Cl - Na + .

[0039] The condensate concentrate obtained through reverse osmosis, along with the treated desulfurization wastewater, is combined and enters the concentration process. The concentration process uses combustion air heating and humidification. The waste water from the flue gas waste heat recovery system first enters the coil in the upper section of the total heat air preheater's water evaporation zone to heat the concentrate, and then enters the coil in the lower section of the total heat air preheater's water evaporation zone before returning to the flue gas waste heat recovery system.

[0040] Furthermore, the condensate wastewater concentrate and the treated desulfurization wastewater enter the lower section water collection pan of the total heat air preheater. The concentrate is then pumped by a concentrate circulation pump to the lower section sprayer, where it is sprayed into the water evaporation zone. In the water evaporation zone, the concentrate absorbs heat from the residual hot water in the coils, evaporating and concentrating. The concentration blower then sends ambient air into the lower section of the total heat air preheater, where it is heated and humidified in the water evaporation zone. The air, carrying the water vapor evaporated from the concentrate, passes through the air hood and enters the upper section of the total heat air preheater.

[0041] Furthermore, the concentrated water from the lower section of the total heat air preheater enters the upper section sprayer of the total heat air preheater through the concentrated liquid regulating valve, and then passes through the upper section water spray evaporation zone for further concentration and evaporation. The resulting concentrated liquid is discharged into the sodium sulfate crystallizer by the concentrated liquid pump. The air from the lower section of the total heat air preheater is heated and humidified through the water spray evaporation zone and discharged from the top of the total heat air preheater to enter the boiler system.

[0042] Evaporation and concentration via a total heat air preheater Basically, all of them can be converted into

[0043] Furthermore, within the sodium sulfate crystallizer, the concentrated liquid from the upper section of the total heat preheater enters the sprayer, and is then cooled by cold air supplied by the crystallization blower. The solubility of sodium sulfate in water decreases as temperature decreases. Therefore, as the concentrated liquid temperature decreases, sodium sulfate decahydrate crystals (sodium sulfate) will precipitate. The concentrated liquid then enters the sodium sulfate clarification tank, where sodium sulfate and mother liquor are separated. The sodium sulfate is washed and sold as a product, while the mother liquor pump sends the separated mother liquor to the sodium chloride crystallizer.

[0044] Furthermore, within the sodium chloride crystallizer, the mother liquor is sprayed from the top sprayer into the evaporation zone, where it is further concentrated and evaporated under the heating effect of waste hot water from the flue gas. Since the solubility of sodium chloride changes little with temperature, and the mother liquor from the sodium sulfate crystallizer is at a lower temperature, sodium chloride will precipitate first during the heating and evaporation process in the evaporation zone. The mother liquor from which sodium chloride crystals precipitate enters the sodium chloride clarification tank, where sodium chloride and tailings are separated. The sodium chloride crystals are washed and sold as refined industrial salt, while the tailings are pumped to the sodium sulfate crystallizer for further separation of sodium sulfate.

[0045] Furthermore, the crystallization blower delivers ambient air to the sodium sulfate crystallizer, then from there into the sodium chloride crystallizer, and finally into the upper section of the total heat air preheater. The waste hot water evaporated from the sodium chloride crystallizer then enters the lower section coil of the total heat air preheater. In summer, when the ambient temperature is high, the chiller at the inlet of the crystallization blower is activated to lower the ambient air temperature to below 20°C, ensuring the sodium sulfate crystallizer operates normally and stably.

[0046] Furthermore, the hot, humid air discharged from the upper section of the total heat air preheater is sent to the boiler system as combustion air. Because the temperature is higher than the ambient temperature, especially in winter, it also provides energy-saving benefits for the boiler.

[0047] Example 2

[0048] In a typical embodiment of the present invention, a method for recycling flue gas condensate wastewater and desulfurization wastewater is proposed, comprising the following steps:

[0049] After the pretreated desulfurization wastewater and condensate wastewater are combined, they enter the total heat air preheater for concentration. The concentration process uses waste hot water from the flue gas as a heat source, and the hot and humid air discharged from the upper section of the total heat air preheater is sent to the boiler system as combustion air.

[0050] The concentrated solution first enters a sodium sulfate crystallizer for further concentration and crystallization to obtain sodium sulfate decahydrate crystals, and then enters a sodium chloride crystallizer to obtain sodium chloride crystals.

[0051] Furthermore, during the pretreatment process, the desulfurization wastewater is treated by adding lime slurry to adjust the pH value and precipitate magnesium, fluoride, and iron ions. Then, organic sulfides are added to precipitate mercury ions, followed by the addition of calcium ions. Finally, sulfuric acid or hydrochloric acid is added to the clear liquid to adjust the pH value to neutral. The coagulation wastewater is treated by adding calcium and magnesium ions to remove them.

[0052] The preferred embodiment of the present invention will be described below using a 130t / h high-pressure fluidized bed boiler from a certain factory as an example.

[0053] The flue gas temperature at the air preheater outlet is 140℃, and the flue gas volumetric flow rate is approximately 178,000 Nm³. 3 The flue gas mass flow rate is approximately 244 t / h, and the boiler combustion air flow rate is approximately 160,000 Nm³ / h. 3 The flue gas temperature at the desulfurization outlet is 49℃, and limestone calcium desulfurization is used. Waste heat is recovered from the desulfurization outlet flue gas, reducing the temperature to approximately 25℃, recovering approximately 15.2MW of waste heat and generating approximately 20t / h of condensate wastewater. The desulfurization system slurry makeup water volume is approximately 7t / h, and the desulfurization wastewater volume is approximately 1t / h.

[0054] The 20t / h condensate wastewater from the flue gas waste heat recovery system is tested for calcium and magnesium ion content. Based on this, an appropriate amount of sodium carbonate is added to ensure that most of the calcium and magnesium ions precipitate. The wastewater is then sent to the condensate wastewater pretreatment system for stirring and sedimentation. The resulting clarified liquid is sent to the reverse osmosis treatment system for further treatment. The reverse osmosis produces approximately 6t / h of concentrate and approximately 14t / h of purified water. The purified water is reused for process water within the plant, while the concentrate is sent to the lower section of the total heat air preheater.

[0055] Approximately 1 t / h of desulfurization wastewater is sent to the desulfurization wastewater pretreatment system. Impurity ions are precipitated by adding agents such as calcium hydroxide and sodium thiosulfate. Then, sodium carbonate is added to the clear liquid to precipitate calcium ions. After that, sulfuric acid or hydrochloric acid is added to adjust the pH value to below 9. The liquid is then combined with the concentrated condensate wastewater and sent to the lower section of the total heat air preheater.

[0056] A concentrated liquid circulation pump draws concentrated water from the lower section of the total thermal air preheater's water collection pan. Most of it is sent to the sprayer for spraying, while a small portion is sent to the upper section of the total thermal air preheater for spraying via a regulating valve, and then enters the water evaporation zone for heating and concentration. The regulating valve is adjusted according to the density of the concentrated liquid in the upper water collection pan; when the concentration is too low, the valve is closed, and when it is too high, the valve is opened wider.

[0057] Approximately 140,000 m³ of ambient air was drawn in by the concentrator fan. 3 The steam is fed to the lower section of the total heat air preheater at a rate of / h, where it is heated in the water spray evaporation zone. Simultaneously, it carries away the water vapor evaporated from the concentrated water. The steam then passes through the air hood into the upper section of the total heat air preheater, where it carries away the water vapor evaporated from the concentrated water spray zone. The final temperature reaches 40℃ (winter) to 42℃ (summer), and the relative humidity reaches approximately 85%, before entering the boiler's primary and secondary air fan systems.

[0058] The waste hot water (approximately 45℃ in winter and 47℃ in summer), about 320 t / h, obtained from the flue gas waste heat recovery system, is sent to the upper section coil of the total heat air preheater to heat the concentrated water. The temperature drops to 42℃ (winter) - 45℃ (summer), and then enters the lower section water spray zone coil, where the temperature drops to 25℃ (winter) - 35℃ (summer), before returning to the flue gas waste heat recovery system.

[0059] After being heated and concentrated in the lower and upper water spray zones of the total thermal air preheater, the concentrated sodium sulfate solution entering the upper water collection pan of the total thermal air preheater is nearly saturated (temperature between 38℃ (winter) and 42℃ (summer)). It is then pumped to the sodium sulfate crystallizer by the concentrated solution pump for crystallization.

[0060] Inside the sodium sulfate crystallizer, concentrated liquid is sprayed from the top, exchanging heat with the air from the crystallization blower, lowering the temperature to 5℃ (winter) - 20℃ (summer). Because the solubility of sodium sulfate decreases sharply with decreasing temperature in the range of 0-40℃, sodium sulfate crystals (sodium sulfate) will precipitate from the concentrated liquid at this point. Since the solubility of sodium chloride changes less with temperature, a large amount of sodium chloride crystals will not precipitate. The air supplied to the crystallization blower is drawn directly from the ambient air in winter; in summer, when the ambient temperature is higher, a chiller before the blower inlet is activated to cool the air, ensuring that the temperature of the air supplied to the sodium sulfate crystallizer meets the requirements for sodium sulfate crystallization.

[0061] The sodium sulfate crystallizer discharges the mother liquor into the sodium sulfate clarification tank for crystal and mother liquor separation. The separated crystals are washed to remove the mother liquor adhering to them and can be used as Glauber's salt for resource utilization. The mother liquor is then pumped to the sodium chloride crystallizer for spraying.

[0062] Inside the sodium chloride crystallizer, the mother liquor is sprayed into the water-spraying coil, where it is heated and concentrated by residual hot water at 45℃ (winter) - 47℃ (summer). The water vapor is carried away by air from the sodium sulfate crystallizer. Due to the increased temperature, the solubility of sodium sulfate increases, so sodium chloride precipitates first as the water evaporates. The precipitated mother liquor is then discharged into a sodium chloride clarification tank for crystal separation. The separated crystals, after washing to remove adhering mother liquor, can be used as industrial refined salt for resource utilization. The tailings are pumped to the sodium sulfate crystallizer for further sodium sulfate separation until all the tailings have evaporated and crystallized.

[0063] Thus, all condensate wastewater and desulfurization wastewater have been recycled and reused, achieving zero discharge.

[0064] The embodiments described above provide a detailed explanation of the technical solution of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, or similar substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A flue gas condensation wastewater and desulfurization wastewater recycling system, characterized in that, The system comprises a pretreatment system, a concentration system and a crystallization system arranged in sequence; the pretreatment system comprises a desulfurization wastewater pretreatment device, a condensation wastewater pretreatment device and a condensation water reverse osmosis treatment device; the concentration system adopts a full-heat air preheater; the full-heat air preheater is internally provided with an upper section sprayer, an upper section water-evaporating coil, a hood, a lower section sprayer and a lower section water-evaporating coil arranged in sequence from top to bottom; and the crystallization system comprises a sodium sulfate crystallizer and a sodium chloride crystallizer. The upper section water-evaporating coil and the lower section water-evaporating coil are arranged in series, and the inlet of the upper section water-evaporating coil is connected with the flue gas waste heat water inlet. The wastewater outlet of the pretreatment system is connected with the lower section of the full-heat air preheater; the wastewater outlet of the lower section of the full-heat air preheater is connected with the lower section sprayer through a concentrated liquid circulating pump; and the wastewater outlet of the lower section of the full-heat air preheater is also connected with the upper section sprayer through a concentrated liquid circulating pump and a regulating valve. The coil inlet in the sodium chloride crystallizer is connected with the flue gas waste heat water inlet, and the coil outlet is connected with the inlet of the lower section water-evaporating coil in the full-heat air preheater. The crystallization system further comprises a filter, a refrigerating machine and a crystallization air blower connected in sequence; and the crystallization air blower is connected with the sodium sulfate crystallizer, the sodium chloride crystallizer and the upper section of the full-heat air preheater through pipes in sequence. The concentrated liquid outlet of the full-heat air preheater is connected with the sprayer in the sodium sulfate crystallizer, and the mother liquor outlet of the sodium sulfate crystallizer is connected with the sprayer in the sodium chloride crystallizer through a mother liquor pump.

2. The flue gas condensation wastewater and desulfurization wastewater recycling system according to claim 1, characterized in that, The desulfurization wastewater pretreatment device and the condensation wastewater pretreatment device both adopt a sedimentation tank; the desulfurization wastewater pretreatment device adopts a two-stage sedimentation tank, and the condensation wastewater pretreatment device adopts a one-stage sedimentation tank.

3. The flue gas condensation wastewater and desulfurization wastewater recycling system of claim 1, wherein The lower section of the full-heat air preheater is provided with a concentrated air inlet, the top of the full-heat air preheater is provided with a steam outlet, and the steam outlet is connected with a boiler combustion-supporting air interface through a pipe.

4. A method for recycling flue gas condensate wastewater and desulfurization wastewater, which is implemented by using the system according to any one of claims 1-3, characterized in that, The system comprises the following steps: The pretreated desulfurization wastewater and condensation wastewater are mixed and then enter the full-heat air preheater for concentration; the concentration process adopts flue gas waste heat water as a heat source; and the hot and humid air discharged from the upper section of the full-heat air preheater is sent to a boiler system as combustion-supporting air; The concentrated liquid after concentration firstly enters the sodium sulfate crystallizer for concentration and crystallization to obtain sodium sulfate decahydrate crystals, and then enters the sodium chloride crystallizer to obtain sodium chloride crystals.

5. The flue gas condensation wastewater and desulfurization wastewater recycling method according to claim 4, characterized in that, During the pretreatment process, desulfurization wastewater is added with lime emulsion to adjust the PH value of the wastewater and precipitate magnesium ions, fluorine ions and iron ions, then added with organic sulfide to precipitate mercury ions, and then added with sodium sulfite to remove calcium ions, and finally added with sulfuric acid or hydrochloric acid to adjust the PH value to neutral. sodium sulfite to remove calcium ions, and finally added with sulfuric acid or hydrochloric acid to adjust the PH value to neutral. Coagulation waste water is treated by adding calcium and magnesium ions are removed.

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