Desulfurization wastewater zero discharge system based on water balance

Abstract

The invention provides a desulfurization wastewater zero discharge system based on water balance. The amount of water entering the desulfurization system during operation of the desulfurization system is larger than the amount of water required by normal operation of desulfurization, and clarified water after desulfurization filtrate is clarified through operation of the desulfurization water balance system replaces process water to wash a demister and enters a slurry dehydration system for use, so that the amount of water entering the desulfurization system from the outside of the desulfurization system is reduced, and normal operation of the desulfurization system is maintained. When excessive harmful ions in the slurry of the desulfurization system endanger normal operation of desulfurization, the desulfurization system discharges filtrate of the desulfurization system in a large proportion at one time into a wastewater zero discharge system for treatment. By adopting the technical scheme of the invention, the problems of high wastewater zero discharge cost and large water treatment amount in boiler operation are solved; and the wastewater zero discharge water treatment amount is reduced with relatively low construction cost and operation cost.

Description

Technical Field

[0001] The invention relates to the field of boiler energy-saving and environmental protection equipment, and more specifically to a desulfurization wastewater zero-discharge system based on water balance. Background Art

[0002] Thermal power is a major water and water user, accounting for 20% of the total industrial water consumption. From the perspective of economic operation and environmental protection, it is of great significance to save water for power generation, increase the reuse rate of circulating water, and achieve "zero discharge" of wastewater from thermal power plants. Desulfurization wastewater is mainly the discharge water from the absorption tower during the wet desulfurization of boiler flue gas in thermal power plants (limestone / gypsum method). It is quite different from the wastewater generated by other systems in the power plant and is the water body with the most complex water quality and the most serious pollution in the water system of thermal power plants. Desulfurization wastewater contains high concentrations of suspended solids, high chloride ions, high salt content, and high concentrations of heavy metals, which are extremely polluting to the environment. Therefore, zero discharge of desulfurization wastewater is imperative. 1. Characteristics of desulfurization wastewater quality The composition and content of pollutants in desulfurization wastewater are related to many factors such as coal type, desulfurization process and operation mode, amount of incoming smoke, limestone quality, gypsum dehydration effect, ammonia escape rate, etc. Its main characteristics are:

[0003] (1) It is weakly acidic, with a pH value of 4-6.5; (2) The suspended solids are high, generally between 6000-15000 mg / L, but the particles are fine, and the main components are dust and desulfurization products (calcium sulfate and calcium sulfite); (3) It contains soluble chlorides, fluorides, nitrates, etc., with a total dissolved solids (TDS) between 25000-60000 mg / L, of which the Cl- content is generally between 5000-20000 mg / L; (4) It contains heavy metal ions such as Hg, Pb, Ni, As, Cd, Cr, etc., and is a type of wastewater that is difficult to treat in power plants.

[0004] 2. Current status of zero discharge of desulfurization wastewater

[0005] At present, the desulfurization wastewater treatment of power plants generally adopts the acid-base neutralization triple-tank treatment method, which uses chemicals to adjust the pH to neutrality and flocculate to remove suspended matter. This process treats the solid particles in the desulfurization wastewater, but does not treat the soluble ions in the water. The wastewater still contains a lot of Cl-, SO42-, Ca2+, and Mg2+.

[0006] At present, there are three process technologies for zero emission of desulfurization wastewater in operation in China: pretreatment + evaporation + crystallization technology, triple box + resin softening + reverse osmosis + forward osmosis + evaporation crystallization, double alkali method + double membrane method + flue evaporation.

[0007] Existing zero-emission technologies for desulfurized wastewater mostly adopt the process of "pretreatment unit + reduction and concentration unit + solidification unit". The designs of each unit complement each other, aiming to meet the process boundary condition requirements of their respective systems and achieve the stable and reliable operation of the entire zero-emission system. The pretreatment unit mainly removes hardness ions and heavy metals in the water body to meet the design requirements of the subsequent reduction and concentration unit. Currently, the secondary softening precipitation method is mainly used, and at the same time, depending on different water qualities, heavy metal removers and filtration devices are supplemented. The design of the reduction and concentration unit determines the output requirements of the reduction and concentration unit according to the water volume of the subsequent solidification unit, mainly including two treatment processes: membrane concentration and thermal evaporation. Considering the overall economy and maturity, the membrane method is mostly used in the market to concentrate and reduce the wastewater. After membrane concentration, the salt content of the wastewater can reach 8-12%. The "solidification unit" is the key in the "zero-emission" system of desulfurized wastewater. According to different treatment degrees, it is mainly divided into two types: resource utilization of crystalline salts and non-resource utilization. For the treatment method of resource utilization of crystalline salts, higher environmental protection requirements are mostly put forward for newly built projects approved after 2016. This treatment method requires the wastewater to be softened to a certain extent or even completely softened before the subsequent membrane method or thermal method for salt separation and concentration and drying treatment processes. The cost of softening agents is high, and old power plants can hardly bear this economic burden. Because the hardness of desulfurized wastewater is as high as 20,000 to 30,000 ppm and the water quality fluctuates greatly, the consumption of chemicals for hardness removal alone has reached 30 to 80 yuan per ton of wastewater.

[0008] Inlet and outlet water of the desulfurization system during operation

[0009] Currently, the waste liquid discharged from the zero-emission system of boiler desulfurized wastewater is mainly the filtrate pumped out from the filtrate water tank and enters the wastewater treatment system for treatment. During the operation of the boiler desulfurization system, there are two ways to supplement and discharge the slurry in the absorption tower: (1) The limestone slurry of the desulfurization system is continuously supplemented into the desulfurization absorption tower, and at the same time, the gypsum discharge pump continuously discharges the gypsum slurry outward to maintain the liquid level of the absorption tower within the design range; (2) According to the desulfurization effect, pH value and the liquid level height of the absorption tower, the limestone slurry supplemented into the absorption tower and the discharged gypsum slurry are determined to keep the liquid level height of the absorption tower within the design range, which is an intermittent operation.

[0010] For a 600,000-kilowatt unit, the diameter of the absorption tower is generally 16 meters, the liquid level height is about 14 meters, and the total slurry in the absorption tower is approximately 2,800 cubic meters. When the desulfurization tower of a 600,000-kilowatt unit is operating normally, the flue gas carries away dozens of tons of water vapor per hour (according to the data in Nie Pengfei's paper "Calculation and Analysis of Water Consumption of Wet Flue Gas Desulfurization Devices for 600MW Units", it is 114 tons per hour, and the wastewater discharge is 3.098 tons per hour). As the water vapor evaporates in the absorption tower, the harmful ions in the slurry continuously concentrate. When the harmful ions are excessive and cause the deterioration of the absorption tower slurry, the slurry in the absorption tower needs to be replaced, and a large amount of desulfurization wastewater needs to be discharged during the slurry replacement. With the deep peak shaving of thermal power units in the thermal power industry, when the boiler is operating at low load, the flushing water volume of the demister in the absorption tower, the equipment cooling water volume, etc. are greater than the water volume carried away by the flue gas, and the amount of water that needs to be discharged to the wastewater treatment system due to the imbalance of the desulfurization water system is even greater. During the operation of the power plant, in the operation of the desulfurization water system, the water generated during denitrification, wet electrostatic precipitation, and ash removal is often discharged into the desulfurization water system. Therefore, the zero discharge of desulfurization wastewater is actually the zero discharge of the overall water system of desulfurization, denitrification, wet electrostatic precipitation, and ash removal water.

[0011] 4 Main reasons for the long-term operation of the existing zero discharge of desulfurization water system

[0012] The main reasons for the long-term operation of the zero discharge system of wastewater in most desulfurization systems are as follows: (1) The equipment cooling water of the desulfurization system, the vacuum pump seal cooling water during the operation of the dehydration system, the filter cake flushing water, the filter cloth regeneration flushing water, the demister flushing water in the desulfurization tower, etc. enter the desulfurization system. These water volumes are greater than the water volume carried away by the flue gas in the desulfurization absorption tower, resulting in the discharge water volume of the desulfurization water system being less than the inflow water volume. When the content of harmful ions and impurities in the desulfurization water system is relatively low, the excess water must be discharged through the operation of the zero discharge system of wastewater. (2) Due to technical reasons, in the operating zero discharge system of desulfurization wastewater, when the chloride ions and other substances in the desulfurization system exceed the standard and need to be discharged, continuous treatment and discharge of wastewater are required to ensure the qualification of the slurry. The above reasons lead to various deficiencies in the current zero discharge process system of desulfurization wastewater, such as large treatment water volume, high treatment unit price, high construction cost, etc., and it cannot meet the requirements of green environmental protection, energy conservation, etc.

[0013] 5 Slurry clarification experiment

[0014] The main reason why the filtrate water from the vacuum dewatering machine cannot be directly reused is that the filtrate water contains a large amount of impurities, which will cause scaling at the demister and other places, affecting the use effect and service life. We found through experiments that the slurry taken out from the desulfurization absorption tower or the slurry in the filtrate water tank is basically clarified after standing for 4 - 8 hours, and the upper layer of the slurry is as clear as tap water after standing for 24 hours. According to the experimental results, it is proved that the clarified aqueous solution of the slurry by physical standing clarification method can be used for the flushing of the demister in the desulfurization tower and the dehydration system, reducing the water volume entering the desulfurization system and solving the balance problem of the desulfurization water system. Summary of the Invention

[0015] In view of the phenomenon that the existing desulfurized wastewater zero - discharge technology needs to treat a large amount of desulfurized wastewater, resulting in a substantial increase in the operating cost of the power plant. The present invention provides a desulfurized wastewater zero - discharge system based on water balance.

[0016] The basic principle of the present invention: The desulfurized wastewater zero - discharge system based on water balance includes a desulfurization equipment system, a desulfurization water balance system, a wastewater zero - discharge system, and a DCS control system. When the desulfurization equipment system operates and the harmful ions in the desulfurization slurry do not exceed the standard, the desulfurization water balance system mainly operates. When the harmful ions and impurities in the desulfurization slurry exceed the standard, the water system balance system and the wastewater zero - discharge system operate simultaneously. By discharging a large amount of slurry at large intervals and in a short time, the harmful ions are discharged and the stable operation of the desulfurization equipment system is maintained. This system reduces the total amount of wastewater treatment, and the operating cost is less than that of other systems.

[0017] 1. Water system balance part

[0018] The biggest feature of the desulfurized wastewater zero - discharge system based on water balance compared with the current technology: (1). The physical clarification process route is adopted for the desulfurization water system balance. No chemical reagents need to be added for treatment during normal use, and the operating cost is low. (2). The flushing water of the absorber demister is the root cause of the difficult control of the water balance in the desulfurization system. Using the clarified filtrate water to flush the demister and the gypsum dewatering machine can reduce the total amount of water entering the desulfurization system from the outside, and the water balance of the entire desulfurization system can be maintained.

[0019] Physical clarification stage: The slurry discharged from the desulfurization absorber is dehydrated and enters the filtrate water tank. The water pump in the filtrate water tank discharges the filtrate water into the clarified water tank. The filtrate water is clarified in the clarified water tank for about 24 hours. The filtrate water is divided into clarified water and the bottom sediment layer. (When necessary during operation, some agents can be added to accelerate clarification.)

[0020] Discharge of clarified water: The clarified water passes through the clarified water discharge port, is filtered and enters the clarified water storage tank. The water in the clarified water tank is filtered and then pressurized by a water pump and enters the demister pipeline to wash the demister and enter the dewatering system for use, greatly reducing the amount of process water entering, thereby maintaining the water balance of the system. The original demister flushing water system is connected in an inter - standby manner through valves.

[0021] Discharge of the bottom sediment layer: When the upper clarified water level in the clarified water tank drops to the upper limit of the lowest level of the stirrer in the clarified water tank, the stirrer is started to stir the sediment layer in the clarified water tank into a turbid liquid. The bottom drain port of the clarified water tank is opened to discharge the turbid liquid, and the discharged suspension enters the dewatering machine for dehydration.

[0022] The process water originally used for the demister flushing water is mainly used for filter cake flushing water and a small amount is used for demister flushing, reducing the amount of water entering from outside the desulfurization system.

[0023] 2. A zero-emission desulfurization wastewater system that operates with large intermittent discharges of slurry and then undergoes evaporation treatment in multiple ways

[0024] This process system is used in a double-tower double-zone desulfurization system or a double-zone desulfurization system in the absorber tower flue. By activating the emergency quenching spray in the low-PH absorber tower (flue desulfurization zone) (lowering the flue gas temperature to avoid damage to the spray layer and demister due to high temperature), all the slurry in the low-PH absorber tower (flue desulfurization zone) is discharged, and the low-PH absorber tower (flue desulfurization zone) is filled with fresh limestone tank slurry; then all the slurry in the high-PH absorber tower is discharged. The slurries discharged from the high- and low-PH desulfurization zones enter the wastewater treatment system after dehydration. The two independent slurry discharges in the double-zone desulfurization system reduce the concentration of harmful ions in the desulfurization system slurry to the lowest level, and the total amount of water discharged to the wastewater treatment system is the least. The double-tower double-zone desulfurization system or the double-zone desulfurization system in the absorber tower flue is the best operation mode for reducing the desulfurization wastewater discharge volume.

[0025] Currently, most desulfurization systems in China are single-tower desulfurization systems. In a single-tower desulfurization system, only when operating at low load and burning low-sulfur coal can the absorber tower only discharge slurry externally without replenishing limestone slurry. About 10% or more of the slurry in the absorber tower is discharged at one time. After the slurry discharge is completed, limestone slurry is added to the absorber tower. The calculation of the decrease in the concentration of harmful ions in the absorber tower slurry is as follows:

[0026] When 10% of the absorber tower slurry is discharged for the first time, the harmful ions in the absorber tower slurry drop to 90%.

[0027] When 10% of the absorber tower slurry is discharged for the second time, the harmful ions in the absorber tower slurry drop to 81%.

[0028] When 10% of the absorber tower slurry is discharged for the third time, the harmful ions in the absorber tower slurry drop to 72.9%.

[0029] When 10% of the absorber tower slurry is discharged for the fourth time, the harmful ions in the absorber tower slurry drop to 65.61%.

[0030] When 10% of the absorber tower slurry is discharged for the fifth time, the harmful ions in the absorber tower slurry drop to 59.049%.

[0031] When 10% of the absorber tower slurry is discharged for the sixth time, the harmful ions in the absorber tower slurry drop to 53.1441%.

[0032] Through the above slurry discharge calculation, the efficiency of reducing harmful ions by the single-tower desulfurization system through slurry discharge is lower than that of the double-tower and double-zone desulfurization system. According to the calculations of 15% fixed-ratio slurry discharge and 20% fixed-ratio slurry discharge, a pattern will be found that the greater the proportion of the slurry discharged each time to the total slurry in the absorption tower when replacing the same volume of slurry, the better the effect of removing harmful ions. When the desulfurization system discharges the slurry in the absorption tower, it also discharges all the water in the water balance system into the desulfurization wastewater zero-discharge system, which has a better effect than the fixed-ratio slurry discharge in the absorption tower. The best operating state is to replace all the slurry in the tower each time the absorption tower is shut down, and to intermittently replace a relatively large proportion of the circulating slurry volume in the absorption tower during operation.

[0033] According to the calculations, we designed a desulfurization wastewater zero-discharge combined process system based on the water balance, which features large-interval working slurry discharge and multiple evaporation treatments, reducing the total desulfurization wastewater treatment volume and the operating costs of the power plant. The principle is as follows:

[0034] Increase the water in the water balance system to the highest level, supplement the absorption tower liquid level to a position above the design liquid level and close to the overflow port, stop supplying limestone slurry to the absorption tower and flushing the demister, start the absorption tower gypsum slurry discharge pump, discharge the circulating slurry in the absorption tower to the dehydration system, and the gypsum slurry becomes filtrate after removing gypsum in the dehydration system and enters the filtrate water tank. The filtrate in the filtrate water tank is pressurized by a water pump and enters the clarified water tank, where suspended solids are removed by static settlement to clarify the water. The clarified water passing through the filter to remove debris is discharged into the clarified water storage tank, and the clarified water entering the clarified water storage tank is pressurized by a water pump and enters the following two processes: (1) Enter the acid-base neutralization triple box for softening treatment, and the treated water enters the desulfurization system for reuse or is used as reclaimed water for other purposes; (2) Enter the negative-pressure wastewater evaporator for concentration, the concentrated wastewater solution enters the concentrated wastewater tank, and the distilled water enters the distilled water reuse storage tank. The concentrated wastewater in the concentrated wastewater tank is pressurized by a water pump and then enters the vacuum wastewater evaporator for evaporation respectively, enters the boiler and flue evaporation systems for evaporation, and enters the wastewater triple box for treatment.

[0035] The described desulfurization wastewater zero-discharge system based on water balance includes a desulfurization system, a desulfurization water balance system, a wastewater zero-discharge system, and a DCS control system.

[0036] Furthermore, the described desulfurization system includes a denitrification water system, a wet electrostatic precipitation water system, an ash removal water system, and a desulfurization equipment system.

[0037] Furthermore, the described desulfurization equipment system includes a desulfurization filtrate water tank, an absorption tower, an internal spray layer in the absorption tower, a demister, a quench spray, a stirrer, a gypsum discharge pump, a slurry circulation pump, a limestone slurry tank, a limestone slaking system, a dewatering system, a process water tank, a gypsum buffer tank, a filtrate water tank, a sump pit, an accident slurry tank, a denitration collection water tank, a wet electrostatic precipitator collection water tank, an ash removal water collection tank, a clarified water tank, a clarified water filter, a clarified water storage tank, connecting pipes, water pumps, motors, valves, electric actuators connected to the valves, and pneumatic actuators. The clarified water tank, the clarified water filter, the clarified water storage tank and their affiliated facilities are common equipment for the desulfurization equipment system, the desulfurization water balance system, and the zero wastewater discharge system.

[0038] Furthermore, in the described desulfurization system, the water in the filtrate water tank enters the limestone slaking system as needed through the control of the filtrate water pump valve group. Part of the filtrate is used to prepare the limestone slurry, and the prepared limestone slurry enters the desulfurization system for desulfurization circulation; the other part of the filtrate enters the desulfurization water balance system and the zero wastewater discharge system.

[0039] Furthermore, the described desulfurization water balance system includes: a process water tank, a process water tank water pump valve pipeline group, a filtrate water tank filter, a clarified water filter, a filtrate water pump valve pipeline group, a clarified water tank, a clarified water storage tank, a clarified water pump valve pipeline group, a clarified water tank sediment layer slurry discharge pipeline valve group, a clarified water pipeline, a clarified water storage tank, a clarified water pump valve pipeline group, a clarified water switching valve pipeline group, and connecting pipes.

[0040] Furthermore, the described filtrate water filter is a multi-layer sand filter that can be regenerated, or other filtering equipment.

[0041] Furthermore, the described filtrate clarified water tank consists of two independent tanks. Each tank is equipped with a stirrer, a liquid level gauge, an external flap-type liquid level display instrument, and a transparent window through which the impurity content and liquid transparency of the liquid can be clearly observed.

[0042] Furthermore, the filtrate clarified water tank body can be an open or closed container. The container material is made of metal welding or non-metallic anti-corrosion materials. If the box body is made of metal materials, it needs to have anti-corrosion ability or be subjected to anti-corrosion treatment.

[0043] Furthermore, the described clarified water filter is a multi-layer sand filter that can be regenerated, or other filtering equipment.

[0044] Furthermore, the described clarified water pump valve pipeline group discharges the clarified water to the absorption tower for demister flushing, enters the dewatering system for internal circulation as needed, or enters the wastewater triple box for wastewater treatment and enters the desulfurization wastewater zero discharge system.

[0045] Furthermore, the material of the clarified water storage tank container is made of metal welding or non-metal anti-corrosion material. If the box body is made of metal material, it needs to have anti-corrosion ability, or the metal material needs to be treated with anti-corrosion.

[0046] Furthermore, the clarified water storage tank is equipped with a stirrer, a liquid level gauge, an external flap type liquid level display instrument, and a transparent window through which the impurity content and liquid transparency of the liquid can be clearly observed.

[0047] Furthermore, the zero-discharge system for desulfurized wastewater includes a clarified water tank, a clarified water storage tank, a clarified water storage tank water pump valve pipeline group, a wastewater triple box, a negative pressure wastewater evaporator, a vacuum wastewater evaporator, a concentrated wastewater tank, a boiler and a flue evaporator, a solid storage room for calcium chloride, etc., and heat exchangers from the flue, cooling tower, steam exhaust of the steam turbine, and boiler. 、 Distilled water reuse storage tank.

[0048] Furthermore, the wastewater concentrated in the negative pressure wastewater evaporation container is pressurized by a water pump and sprayed into the boiler and flue for evaporation and crystallization as needed, enters the acid-base neutralization triple box for softening treatment, and enters the vacuum wastewater evaporator for evaporation and crystallization for resource utilization.

[0049] Furthermore, the concentrated aqueous solution evaporated by the boiler and flue is pressurized by a water pump and sprayed into the atomization evaporation before the electrostatic precipitator (bag filter). The crystallized particles are collected by the dust collector and enter the ash hopper. The solids after evaporation are cleaned regularly.

[0050] Furthermore, the acid-base neutralization triple box conducts softening treatment, and the water treated by softening is reused or enters other systems.

[0051] Furthermore, the heat for evaporating wastewater in the negative pressure wastewater evaporation container and the vacuum wastewater evaporator comes from the heat of the flue, cooling tower, steam exhaust of the steam turbine, and boiler. (The vacuum degree is 5000 Pa. Water can evaporate normally at 33 °C.)

[0052] Furthermore, the negative pressure wastewater evaporation container is a multi-effect evaporation to improve the multiple use of thermal energy.

[0053] Furthermore, the vacuum wastewater evaporator is a multi-effect evaporation to improve the multiple use of thermal energy.

[0054] Furthermore, all the valve pipeline groups and connecting pipelines are made of metal materials, non-metal materials with anti-corrosion ability, or ordinary metal materials lined with rubber, plastic, or porcelain.

[0055] Furthermore, for the measurement system, the measurement system is connected to the DCS centralized control system.

[0056] The further described DCS centralized control system conducts centralized control by measuring and sensing signals of system measurement water pumps, valves, motors, water tank level gauges, etc.; the water pumps, valves, and motors all have local and remote control functions.

[0057] In summary, the present invention is a desulfurized wastewater zero-discharge system based on water balance. It adopts a wastewater zero-discharge process system that mainly uses physical clarification, internally recycles clarified water to replace part of the process water, discharges slurry intermittently, and does not use treatment chemicals, reducing the wastewater treatment volume, chemical agent volume, and operating cost of the current desulfurized wastewater zero-discharge process system, and reducing environmental pollution. Compared with conventional wastewater zero-discharge technologies, conventional wastewater zero-discharge technologies need to continuously treat wastewater to meet the wastewater zero-discharge required for the water balance of the desulfurization system. Calculated according to the designed wastewater treatment water volume of 20 m 3 / h and 4000 h / y, the water volume is 80000 m 3 / y. Calculated based on the chloride ion content in the industrial water of the power plant at 550 mg / l, it takes about 22 volumes of pure water to be evaporated to enrich to 12000 mg / l. Calculated according to this ratio, the present invention only needs to treat 4000 m of desulfurized wastewater 3 / y, and the operating cost is less than 5%, with great advantages. Description of the Drawings

[0058] Figure 1 It is a block diagram of a desulfurized wastewater zero-discharge system based on water balance according to the present invention.

[0059] Annotation description: 1. Aqueous solution from wet electrostatic precipitator, denitration, and boiler ash removal; 2. Filtrate water tank; 3. Filtrate water pump valve group; 4. Filtrate filter group; 5. Clarified water tank 1; 6. Clarified water tank 2; 7. Clarified water pump valve group; 8. Clarified water filter group; 9. Clarified water storage tank 1; 10. Clarified water storage tank 2; 11. Water pump valve group; 12. Switching valve group; 13. Desulfurization tower; 14. Dewatering system; 15. Heat from flue gas, cooling tower, turbine exhaust, and boiler; 16. Wastewater triple box; 17. Negative pressure wastewater evaporator; 18. Distilled water reuse storage tank; 19. Process water pump valve group; 20. Concentrated wastewater tank; 21. Vacuum wastewater evaporator; 22. Boiler and flue gas evaporation system; 23. Storage room for solid particles such as calcium chloride; 24. Heat from flue gas, cooling tower, turbine exhaust, and boiler; 25. Electrostatic precipitator or bag filter; 26. Process water tank; 27. Desulfurization slurry preparation system; 28. Concentrated wastewater pump valve group. Detailed Embodiments

[0060] Our desulfurized wastewater zero-discharge system based on water balance is applicable to the water systems of boiler desulfurization, denitration, wet electrostatic precipitator, and ash removal water. Refer to Figure 1We will describe the process system solution of the present invention: The aqueous solution from 1 wet electrostatic precipitator, denitrification, and boiler ash removal is discharged into the 2 filtrate water tank through a pipeline; the filtrate generated after the slurry in the absorption tower is dehydrated by the dehydration system enters the 2 filtrate water tank.

[0061] When the desulfurization slurry needs to be prepared in the desulfurization system, the filtrate in the 2 filtrate water tank enters the 27 desulfurization slurry preparation system through the action of the 3 filtrate water pump valve group. The desulfurization slurry prepared in the 27 desulfurization slurry preparation system enters the absorption tower to remove sulfur dioxide and the like in the flue gas; when the horizontal balance system and zero wastewater discharge work need to be carried out, the filtrate in the 2 filtrate water tank first enters the 4 filtrate filter group through the action of the 3 filtrate water pump valve group to remove solid particles in the filtrate. The filtrate after removing solid particles is controlled by the filtrate filter group to first fill one of the clarified water tanks 1 and clarified water tanks 2 with filtrate for physical clarification, and then start injecting filtrate into the other clarified water tank. After 10 - 30 hours of static clarification in the wastewater clarification tank, the filtrate becomes clear and transparent.

[0062] The filtrate in the clarified water tank becomes a clear aqueous solution without suspended particles after about 24 hours of static settlement. The clear aqueous solution in the clarified water tank is controlled by the 7 clarified water pump valve group to first empty one of the clarified water tanks. After the bottom of the emptied clarified water tank is emptied, the filtrate filtered to remove solid particles is injected through the 4 filtrate filter group; after emptying one clarified water tank, the other clarified water tank is emptied through the control of the 7 clarified water pump valve group, and the two clarified water tanks take turns in the above work process.

[0063] The clarified water discharged by the 7 clarified water pump valve group enters the 8 clarified water filter group. The 8 clarified water filter group filters the clarified water to prevent solid impurity particles from passing through. The 8 clarified water filter group controls the clarified water to enter the 9 clarified water storage tank 1 and the 10 clarified water storage tank 2 for storage according to needs. The clarified water in the 9 clarified water storage tank 1 and the 10 clarified water storage tank 2 has three flow directions through the operation of the 11 water pump valve group: 1. The clarified water enters the 12 switching valve group; 2. The clarified water enters the 17 negative pressure wastewater evaporation container for negative pressure evaporation; 3. The clarified water enters the 16 wastewater triple box for direct wastewater treatment.

[0064] The clarified water enters the 12 switching valve group and enters the desulfurization system to wash the demister in the desulfurization system and wash the filter cake of the dehydrator. The process water in the 26 process water tank in the desulfurization system flows through the control of the 19 process water pump valve group: 1. To the desulfurization slurry dehydrator to meet the need of the desulfurization slurry dehydrator for process water; 2. To the 12 switching valve group to control the cleaning work of the demister through the 12 switching valve. The clarified water enters the 12 switching valve group and enters the desulfurization system to complete the desulfurization water balance.

[0065] The clarified water enters the 16 Wastewater Triple Tank for direct treatment of pharmaceutical wastewater. The treated water is reused or used for other purposes. The 16 Wastewater Triple Tank is a conventional wastewater treatment system in power plants and serves as a backup in this system.

[0066] The clarified water enters the 17 Negative-pressure Wastewater Evaporation Vessel for multi-effect negative-pressure evaporation. The heat for negative-pressure evaporation comes from the heat provided by the flue gas, cooling tower, turbine exhaust steam, and boiler to the negative-pressure wastewater evaporation vessel. The distilled water condensed in the negative-pressure wastewater evaporation vessel is collected and enters the 18 Distilled Water Reuse Storage Tank for reuse.

[0067] The concentrated wastewater after negative-pressure evaporation and concentration in the 17 Negative-pressure Wastewater Evaporation Vessel enters the 20 Concentrated Wastewater Tank for storage. Through the control of the 28 Concentrated Water Wastewater Pump Valve Group, the concentrated wastewater has three flow directions: 1. Enter the 16 Wastewater Triple Tank for wastewater treatment, and the treated water is reused or discharged after meeting the external discharge standards; 2. Enter the 22 Boiler and Flue Gas Evaporation System for evaporation of the concentrated wastewater. The evaporated water vapor is discharged through the chimney, and the remaining waste residue after evaporation is collected by the electrostatic precipitator and bag filter and landfilled or sold together with fly ash; 3. Enter the 21 Vacuum Wastewater Evaporator. The 21 Vacuum Wastewater Evaporator uses the heat from the flue gas, cooling tower, turbine exhaust steam, and boiler for multi-effect vacuum evaporation. The distilled water discharged from the 21 Vacuum Wastewater Evaporator enters the 18 Distilled Water Reuse Storage Tank for storage and reuse. The waste residues such as calcium chloride discharged from the 21 Vacuum Wastewater Evaporator enter the 23 Calcium Chloride and Other Solid Particle Storage Room for temporary storage, and the calcium chloride and other solid particles are landfilled or sold.

[0068] In this embodiment, the preferred pipelines, tanks, etc. have a flushing system to ensure the stable operation of the system through flushing. In this embodiment, the exhaust steam temperature of the steam turbine of the condensing generator set used in the preferred vacuum wastewater evaporation system is about 35 degrees (calculated according to the IAPWS-IF97 water and steam calculation software, water can evaporate normally at a vacuum degree of 5000 Pa and a temperature above 33 degrees. The appropriate evaporation and condensation temperature range is achieved by adjusting the vacuum degree of the vacuum wastewater evaporation system).

[0069] This embodiment preferably further includes a measurement system for all devices in the system. The measurement system is connected to a DCS centralized control system. The DCS centralized control system controls the execution system based on the data measured by the measurement system and external instructions to ensure the stable operation of the system.

[0070] This embodiment preferably further includes a valve and a pump actuator, which are connected to the motor or pneumatic component to ensure the stable operation of the system. The above is only the preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the concept of the present invention belong to the protection scope of the present invention. It should be noted that for those of ordinary skill in the art, several improvements and refinements made without departing from the principle of the present invention should also be regarded as within the protection scope of the present invention.

Claims

1. A desulfurized wastewater zero - discharge system based on water balance, characterized in that: It includes a desulfurization system, a desulfurization water balance system, a zero wastewater discharge system, and a DCS control system. In the zero wastewater discharge system for desulfurization based on water balance, when the desulfurization system is operating normally, the amount of water carried away by the evaporation of flue gas in the desulfurization tower is less than the amount of water entering the desulfurization system, resulting in water imbalance in the desulfurization system. When the harmful impurities in the desulfurization system slurry do not exceed the standard, the water balance system is started to clarify the desulfurized filtrate water. After clarification, the clarified water replaces the process water to wash the demister and replaces the dehydrator wash water for reuse, reducing the process water entering the desulfurization system to maintain the normal operation of the desulfurization system. When the harmful ions and impurities in the desulfurization system slurry endanger the normal operation of the desulfurization system, the zero wastewater discharge system is started to evaporate the wastewater that needs to be discharged from the desulfurization system to remove harmful ions and impurities, maintaining the normal operation of the desulfurization system.

2. The zero-discharge system for desulfurized wastewater based on water balance according to claim 1, wherein: The desulfurization system described above includes a denitrification water system, a wet electrostatic precipitation water system, an ash removal water system, and a desulfurization equipment system.

3. The desulfurization equipment system according to claim 2, characterized in that: The desulfurization equipment system includes a desulfurized filtrate water tank, an absorption tower, an internal spray layer in the absorption tower, a demister, a quench spray, a stirrer, a gypsum discharge pump, a slurry circulation pump, a limestone slurry tank, a limestone pulping system, a dehydration system, a process water tank, a gypsum buffer tank, a filtrate water tank, a sump, an accident slurry tank, a denitrification collection water tank, a wet electrostatic precipitation collection water tank, an ash removal water collection water tank, a clarified water tank, a clarified water filter, a clarified water storage tank, connecting pipes, water pumps, motors, valves, electric actuators connected to the valves, and pneumatic actuators. The clarified water tank, the clarified water filter, the clarified water storage tank and their affiliated facilities belong to the shared equipment of the desulfurization equipment system, the desulfurization water balance system, and the zero wastewater discharge system.

4. The zero-discharge system for desulfurization wastewater based on water balance according to claim 1, wherein: The desulfurization water balance system includes a process water tank, a process water tank water pump valve pipeline group, a filtrate water tank filter, a clarified water filter, a filtrate water pump valve pipeline group, a clarified water tank, a clarified water storage tank, a clarified water pump valve pipeline group, a clarified water tank sediment layer slurry discharge pipeline valve group, a clarified water pipeline, a clarified water storage tank, a clarified water pump valve pipeline group, a clarified water switching valve pipeline group, and connecting pipes.

5. The zero - discharge system for desulfurized wastewater based on water balance according to claim 4, characterized in that: The clarified water tank and the clarified water storage tank are equipped with flap type level gauges, filtrate transparent windows, clarified water tank sediment layer slurry discharge pipeline valve groups, stirrers, and on-line level measuring instruments. The clarified water tank sediment layer slurry discharge pipeline valve group discharges the high-solid content slurry to the dehydration system for dehydration treatment.

6. The zero-discharge system for desulfurized wastewater based on water balance according to claim 1, characterized in that: The described zero liquid discharge system includes: a clarified water tank, a clarified water storage tank, a clarified water storage tank water pump valve pipeline group, a waste water triple tank, a negative pressure waste water evaporator, a vacuum waste water evaporator, a concentrated waste water tank, a boiler and a flue evaporator, a solid storage room for calcium chloride, etc., and heat exchangers from the flue, cooling tower, turbine exhaust, and boiler 、 A distilled water reuse storage tank.

7. The zero wastewater discharge system according to claim 6, characterized in that: For the concentrated wastewater tank, after the concentrated wastewater is pressurized by the water pump valve group, the clarified wastewater is conveyed to the boiler and flue before the dust collector for atomization evaporation as needed, and one way uses the heat of the flue, cooling tower, steam exhaust of the steam turbine, and boiler for vacuum multi-effect evaporation, and one way enters the wastewater triple box for treatment. After the concentrated wastewater is treated by the wastewater triple box, it enters the desulfurization system for continued use and is used as reclaimed water.

8. The zero wastewater discharge system according to claim 6, characterized in that: The negative pressure wastewater evaporator and the vacuum wastewater evaporator are multi-effect evaporators, and the heat used comes from the heat of the flue, cooling tower, steam exhaust of the steam turbine, and boiler.

9. The zero - discharge system for desulfurized wastewater based on water balance according to claim 1, wherein: The boxes, pipelines, and equipment have a heat preservation and tracing system to ensure the normal operation of the equipment.

10. The zero-discharge system for desulfurized wastewater based on water balance according to claim 1, characterized in that: The described DCS system automatically makes interlock judgments on all measured signals of the desulfurized wastewater zero-discharge system based on water balance to control the actions of valves and water pump motors. Meanwhile, the equipment has local and remote control functions.

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