A comprehensive water-saving and wastewater discharge treatment system for power plants

Abstract

This invention provides a comprehensive water-saving and wastewater discharge treatment system for power plants. The circulating water discharge treatment subsystem includes a chemical softening unit for receiving and softening a homogeneous mixture of circulating water discharge and wastewater from a chemical water treatment system, producing softened effluent and calcium-based solid particles. The produced calcium-based solid particles are transported to the desulfurization system as a desulfurizing agent. A desalination unit desalinates the softened effluent, producing reusable freshwater and high-salinity reverse osmosis concentrate. The reverse osmosis concentrate is connected to the power plant's desulfurization system to provide process makeup water. The end-of-pipe wastewater treatment subsystem includes a bypass flue gas evaporator for introducing desulfurization wastewater from the desulfurization system and evaporating and solidifying it using high-temperature flue gas. In this invention, the calcium-based solid particles are directly transported to the desulfurization system as a desulfurizing agent. The reverse osmosis concentrate produced by the desalination unit of the circulating water discharge treatment subsystem is directly sent to the desulfurization system as process makeup water, achieving resource recovery and reuse of the main wastewater volume.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, and in particular to a comprehensive treatment system for water conservation and wastewater discharge in power plants. Background Technology

[0002] Thermal power plants are major consumers of industrial water and wastewater. Statistics show that a single 600MW coal-fired power unit can consume tens of thousands of tons of water daily, correspondingly generating a large amount of industrial wastewater with complex composition and varying quality. Based on their source and water quality characteristics, this wastewater can be broadly categorized as follows: First, wastewater from the circulating cooling water system, accounting for over 70% of the total plant wastewater, is characterized by high hardness, moderate salinity, and high levels of organic matter and microorganisms; second, wastewater from the chemical water treatment system, including concentrated water from the reverse osmosis unit, acid and alkali regeneration wastewater generated during ion exchange resin regeneration, and backwash water from the ultrafiltration unit, etc. This portion of wastewater exhibits significant quality fluctuations and complex composition; third, regeneration wastewater from the condensate polishing system; and fourth, desulfurization wastewater from the wet flue gas desulfurization system, which is the most complex, heavily polluted, and difficult-to-treat end-of-pipe wastewater from the power plant.

[0003] Existing power plants are required to gradually achieve wastewater classification, cascade utilization, and near-zero discharge. Achieving zero wastewater discharge from the entire plant has become an inevitable requirement for the survival and development of the thermal power generation industry.

[0004] However, current zero-discharge projects for power plant wastewater still face several prominent technical challenges: Firstly, the chemical softening process of circulating water effluent generates a large amount of difficult-to-dispose chemical sludge. The hardness (calcium and magnesium ions) of circulating water effluent is typically high, with a total hardness reaching 10-20 mmol / L. Before entering the membrane desalination system, it must be softened to prevent scaling on the reverse osmosis membrane surface. Currently, the commonly used chemical softening methods are lime softening or lime-soda ash softening, which involves adding calcium hydroxide (Ca(OH)2) and / or sodium carbonate (Na2CO3) to the water, causing calcium and magnesium ions to precipitate as calcium carbonate (CaCO3) and magnesium hydroxide (Mg(OH)3), respectively. However, this method produces a very large amount of chemical sludge with a high water content (usually exceeding 95%), making dewatering difficult. Furthermore, the sludge contains heavy metals, organic matter, and other impurities, resulting in high disposal costs and significant environmental risks. While ion exchange softening does not produce sludge, it generates a large volume of regeneration wastewater and consumes a significant amount of regeneration reagents, leading to persistently high operating costs. Finding an alternative technology that can soften wastewater efficiently without producing large amounts of sludge has become an important issue in the field of circulating water wastewater treatment.

[0005] Secondly, there is a lack of effective coordination between the circulating water wastewater treatment system and the desulfurization system. After membrane concentration treatment, the circulating water wastewater produces approximately 20%-30% (based on the influent) of reverse osmosis concentrate. This concentrate has a salt content 3-4 times that of the influent and a conductivity of tens of thousands of μS / cm. Direct discharge of this concentrate does not meet the zero-discharge requirement; returning it to the upstream end to mix with the raw water for further treatment will cause salt to continuously accumulate within the system, ultimately leading to irreversible fouling and failure of the membrane system. Although theoretically, the reverse osmosis concentrate can be sent to the desulfurization system as process makeup water—because the desulfurization system has low requirements for makeup water quality, and high-salt water can even be beneficial to the desulfurization reaction to some extent—in practice, the circulating water treatment system and the desulfurization wastewater treatment system are often designed independently, lacking integrated water balance and material flow matching at the design level. This results in the reverse osmosis concentrate not being reliably and stably absorbed by the desulfurization system.

[0006] Thirdly, zero-discharge treatment systems for desulfurization wastewater involve large investments and high operating costs. Desulfurization wastewater has extremely high salt content (TDS can reach 30,000-60,000 mg / L), chloride ion concentrations can reach thousands to tens of thousands of mg / L, and it also contains various heavy metals (such as mercury, cadmium, lead, arsenic, etc.), making it the most difficult end-of-pipe wastewater to treat in power plants. Currently, the mainstream zero-discharge technology for desulfurization wastewater includes pretreatment + evaporation crystallization. Although the technology is mature, the equipment investment is often tens of millions of yuan, and the steam and electricity consumption during operation is enormous, with treatment costs reaching tens to hundreds of yuan per ton of water. Furthermore, the mixed salts produced by evaporation crystallization are hazardous waste, making disposal difficult and expensive. While using flue gas spray evaporation technology to replace traditional evaporation crystallizers can save investment, directly spraying wastewater into the main flue carries the risk of incomplete evaporation, potentially leading to salt accumulation, scaling, and corrosion on the flue's inner walls, and even affecting the normal operation of the dust collector and desulfurization system.

[0007] Fourth, the calcium-based solid products generated during the circulating water softening process have not been utilized as resources. Even if calcium ions are separated from the water in solid form using certain methods, the resulting solid substances are often treated as waste, lacking a systematic design path for direct utilization as byproducts.

[0008] Therefore, developing a comprehensive water-saving and wastewater discharge treatment system for power plants that can simultaneously overcome the above-mentioned technical defects—avoiding the generation of large amounts of difficult-to-dispose chemical sludge, achieving efficient desalination and reuse of circulating water discharge, establishing a synergistic linkage mechanism between circulating water discharge, desulfurization system, and end-of-pipe wastewater treatment, and realizing the resource utilization of by-products—has become an urgent technical issue to be addressed in this field. Summary of the Invention

[0009] The purpose of this invention is to provide a comprehensive treatment system for water conservation and wastewater discharge in power plants, in order to solve the problems existing in the prior art, such as the generation of a large amount of chemical sludge that is difficult to dispose of during the chemical softening process of circulating water discharge, the isolation and lack of coordination between the circulating water discharge treatment and desulfurization wastewater treatment systems leading to difficulties in the disposal of reverse osmosis concentrate, and the inability to effectively utilize the solid products of circulating water softening.

[0010] This invention provides a comprehensive treatment system for water conservation and wastewater discharge in power plants, including a circulating water discharge treatment subsystem and an end-of-pipe wastewater treatment subsystem; The circulating water wastewater treatment subsystem includes: A chemical softening unit is used to receive and soften a homogeneous mixture of circulating water discharge and wastewater from a chemical water treatment system, and to produce softened effluent and calcium-based solid particles; the calcium-based solid particles produced in the chemical softening unit are transported to a desulfurization system as a desulfurizing agent; The desalination unit is used to desalinate the softened effluent, producing reusable freshwater and high-salinity reverse osmosis concentrate, respectively; the reverse osmosis concentrate outlet is connected to the power plant's desulfurization system through a pipeline to provide process water for the desulfurization system; The end-of-pipe wastewater treatment subsystem includes a bypass flue gas evaporator, which is used to introduce desulfurization wastewater from the desulfurization system and use high-temperature flue gas to evaporate and solidify it.

[0011] Furthermore, the chemical softening unit includes a chemical crystallization circulating granulation fluidized bed; The circulating water wastewater treatment subsystem also includes: The wastewater buffer tank is used to collect and homogenize the circulating wastewater and the wastewater from the chemical water treatment system; the chemical crystallization circulating granulation fluidized bed is fluidly connected to the outlet of the wastewater buffer tank, and is used to chemically crystallize and soften the homogenized wastewater by adding alkaline agents and seed crystals, and then discharge the crystal particles. The clarifier is connected to the outlet fluid of the chemical crystallization circulating granulation fluidized bed and is used to treat the softened wastewater by coagulation and sedimentation. The clear water tank is fluidly connected to the outlet of the clarifier.

[0012] Furthermore, the chemical crystallization circulating granulation fluidized bed is provided with a water distribution zone, a drug distribution zone, a granulation zone and a clear water zone from bottom to top, and is equipped with a seed crystal addition and particle discharge device to allow calcium ions in the water to crystallize on the seed crystal surface to form recyclable calcium carbonate particles.

[0013] Furthermore, the chemical crystallization circulating granulation fluidized bed is equipped with a circulation pipeline for returning a portion of the clean water to the inlet end to adjust the inlet flow rate and pH conditions.

[0014] Furthermore, the desalination unit includes an ultrafiltration unit and a reverse osmosis unit connected in sequence; The ultrafiltration unit is fluidly connected to the outlet of the clear water tank and is used to perform precision filtration and ultrafiltration treatment on the water effluent from the clear water tank, and output ultrafiltration product water. The reverse osmosis unit is fluidly connected to the outlet of the filter and is used to desalinate the ultrafiltration permeate, outputting reverse osmosis permeate and reverse osmosis concentrate. The reverse osmosis permeate is reused in the power plant's circulating water system and / or chemical water treatment system, and the reverse osmosis concentrate is transported to the power plant's desulfurization system.

[0015] Furthermore, the end-of-pipe wastewater treatment subsystem also includes a rotary atomizer, which is installed inside the bypass flue gas evaporator to atomize the desulfurization wastewater entering the evaporator into droplets, and use the heat of the high-temperature flue gas to evaporate the droplets.

[0016] Furthermore, the end-of-pipe wastewater treatment subsystem also includes a flue gas intake pipeline for drawing high-temperature flue gas from the flue before the power plant air preheater to the bypass flue gas evaporator; the flue gas outlet of the bypass flue gas evaporator is connected to the outlet flue of the air preheater so that the water vapor generated by evaporation enters the subsequent treatment equipment along with the flue gas.

[0017] Furthermore, the end-of-pipe wastewater treatment subsystem also includes a positive pressure pneumatic ash conveying device located at the bottom of the evaporator, used to convey the salt-containing dust generated by evaporation to the ash hopper of the electrostatic precipitator.

[0018] Furthermore, the end-of-pipe wastewater treatment subsystem also includes an automatic cleaning system, which is used to flush the wastewater delivery pipeline of the rotary atomizer with industrial water when the device is shut down or malfunctions.

[0019] Furthermore, the wastewater buffer tank is used to collect reverse osmosis concentrate, regenerated wastewater, ultrafiltration backwash water, circulating water discharge, and fine treatment regenerated wastewater generated by the power plant's chemical water treatment system and to homogenize them.

[0020] The beneficial effects of the technical solution of this invention are as follows: (1) The use of chemical crystallization granulation softening instead of traditional lime causticization softening produces not chemical sludge with high water content and a large number of impurities, but calcium carbonate crystal particles with low water content, high purity, and large particle size. The calcium-based solid particles are directly transported to the desulfurization system as a desulfurizing agent. The limestone-gypsum wet desulfurization process in coal-fired power plants itself requires a large amount of limestone (calcium carbonate) as a desulfurization absorbent. The calcium carbonate particles produced by the chemical softening unit serve as a supplement to the desulfurizing agent, replacing part of the purchased limestone. This achieves waste resource utilization and cross-unit collaborative utilization, resulting in significant economic and environmental benefits.

[0021] (2) The reverse osmosis concentrate produced by the desalination unit of the circulating water wastewater treatment subsystem is directly sent to the desulfurization system as process makeup water, and the calcium-based solid particles produced by the chemical softening unit are sent to the desulfurization system as desulfurizing agents. This avoids the accumulation of salt in the circulation, reduces the industrial water consumption of the desulfurization system, and realizes the resource utilization of wastewater treatment byproducts within the system. The desulfurization system connects the circulating water wastewater treatment and the end-of-pipe wastewater treatment into a complete system for the coordinated utilization of materials and energy, which greatly improves the systematicness and synergy of water use throughout the plant.

[0022] (3) The circulating water discharge, which accounts for the largest volume of wastewater in the plant, is treated by chemical softening, ultrafiltration and reverse osmosis. The resulting water is of excellent quality and can be reused in the circulating water system and chemical water treatment system, realizing the resource reuse of the main wastewater volume. The reverse osmosis concentrate is sent to the desulfurization system for disposal. Finally, a small amount of end-of-pipe desulfurization wastewater is completely solidified through the bypass flue gas evaporator. The corresponding solids are sent to the ash hopper of the electrostatic precipitator, realizing the classified treatment, cascade utilization and final zero discharge of all wastewater in the plant.

[0023] (4) Unlike the existing technology that directly sprays wastewater into the main flue for evaporation, this invention sets up an independent bypass evaporator. High-temperature flue gas is taken from before the air preheater, evaporated in the evaporator, and then returned to the flue after the air preheater. This ensures complete evaporation of wastewater under controllable conditions, eliminating problems such as flue gas ash accumulation, scaling, and low-temperature corrosion caused by incomplete evaporation. Furthermore, the symmetrical intake and return of flue gas from before and after the air preheater will not adversely affect the balance of the boiler flue gas system, ensuring continuous and stable operation of the main unit. Attached Figure Description

[0024] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0025] Figure 1 This is an overall process flow diagram of the integrated treatment system for water conservation and wastewater discharge in a power plant, as described in this embodiment of the invention.

[0026] Figure 2 for Figure 1 Detailed process flow diagram of the wastewater treatment subsystem of the medium-circulation water system.

[0027] Figure 3 This is a process flow diagram of the end-of-pipe wastewater treatment subsystem in an embodiment of the present invention.

[0028] 100 - Circulating water and wastewater treatment subsystem; 101 - Wastewater buffer tank; 102 - Wastewater lift pump; 103 - Chemical crystallization circulating granulation fluidized bed; 1031 - Water distribution zone; 1032 - Chemical distribution zone; 1033 - Granulation zone; 1034 - Clear water zone; 1035 - Fluidized zone; 1036 - Separation zone; 1037 - Seedling tube; 1038 - Particle discharge tube; 104 - Steel clarifier; 105 - Clear water tank; 106 - Filter feed pump; 107 - Fiber filter; 108 - Self-cleaning filter; 109 - Ultrafiltration unit; 110 - Ultrafiltration product water tank; 111 - Reverse osmosis feed pump; 112 - Security filter; 113 - Reverse osmosis high-pressure pump; 114 - Reverse osmosis unit; 115 - Freshwater tank; 116 - Freshwater pump; 117 - Recycled water tank; 200 - End-of-pipe wastewater treatment subsystem; 201 - Spray water tank; 202 - Spray water pump; 203 - Bypass flue gas evaporator; 2031 - Positive pressure pneumatic ash conveying device; 204 - Automatic cleaning system; 300 - Desulfurization system. Detailed Implementation

[0029] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0031] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. Furthermore, the terms "installed," "connected," and "linked" should be interpreted broadly; for example, they may refer to a fixed connection, a detachable connection, or an integral connection; they may refer to a mechanical connection or an electrical connection; they may refer to a direct connection or an indirect connection through an intermediate medium; and they may refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0032] Example This embodiment uses a 2×350MW supercritical wet-cooled coal-fired power plant (hereinafter referred to as the "example power plant") as an example of a comprehensive water-saving and wastewater treatment renovation project to illustrate the specific implementation of the present invention.

[0033] The basic information of the example power plant is as follows: The construction scale consists of 2×350MW supercritical wet-cooled coal-fired heating units, equipped with supercritical parameter variable-voltage direct-flow boilers, circulating cooling systems, electrostatic precipitators, pneumatic dry ash removal, dry slag discharge, and limestone-gypsum wet flue gas desulfurization (one boiler, one tower arrangement). The main source of production water is treated municipal sewage, with tap water as a backup water source.

[0034] (I) Wastewater sources and overall system architecture of the entire plant like Figure 1 As shown in the figure, this embodiment provides a comprehensive treatment system for water conservation and wastewater discharge in power plants, including a circulating water discharge wastewater treatment subsystem 100 and an end-of-pipe wastewater treatment subsystem 200.

[0035] The circulating water discharge wastewater treatment subsystem 100 and the end-of-pipe wastewater treatment subsystem 200 of this system are not two independent and parallel treatment units, but are closely linked through the power plant's desulfurization system 300. Specifically: The first associated pathway (resource utilization of calcium-based solid particles): The chemical softening unit in the circulating water wastewater treatment subsystem 100 produces calcium-based solid particles—namely, calcium carbonate (CaCO3) crystal particles. These calcium-based solid particles are transported by a conveying device through pipelines or mechanical means to the limestone slurry preparation system of the desulfurization system 300 or directly added to the desulfurization absorption tower as an absorbent for the desulfurization reaction, replacing part of the purchased limestone. Specifically, in this embodiment, the calcium carbonate particles discharged from the chemical crystallization circulating granulation fluidized bed 103 enter the particle collection device, where moisture is filtered out and the particles are transported off-site in solid form. They can be directly processed together with the power plant limestone or used as a desulfurizing agent.

[0036] The second associated path (cascade utilization of reverse osmosis concentrate): The desalination unit in the circulating water wastewater treatment subsystem 100 produces high-salinity reverse osmosis concentrate. This concentrate is piped to the process water tank of the desulfurization system 300 and used as makeup water for the desulfurization tower, replacing part of the industrial fresh water. Specifically, in this embodiment, the concentrate discharge pressure of the reverse osmosis unit 114 is approximately 1.1 MPa, the pipeline length from the chemical water treatment workshop to the process water tank of the desulfurization wastewater workshop is approximately 330 meters, and the friction resistance is approximately 0.3 MPa. Therefore, the concentrate from the reverse osmosis unit utilizes the concentrate pipeline of the chemical water treatment system and ultimately flows to the process water tank of the desulfurization wastewater system.

[0037] Through the material input via the two aforementioned paths, and the absorption of SO2 from the flue gas within the desulfurization system itself, the desulfurization system 300 ultimately produces desulfurization wastewater with complex composition and high salt content. The inlet of the end-of-pipe wastewater treatment subsystem 200 is connected to the wastewater outlet of the desulfurization system 300, receiving the desulfurization wastewater and evaporating and solidifying it through a bypass flue gas evaporator. The resulting solid waste is then sent to the electrostatic precipitator ash hopper for final disposal.

[0038] Thus, the circulating water discharge wastewater treatment subsystem 100, the desulfurization system 300, and the terminal wastewater treatment subsystem 200 are connected by two material links: "calcium-based solid particles are used as desulfurizing agents" and "reverse osmosis concentrate is used as desulfurization makeup water". They form a complete, interconnected wastewater cascade utilization and zero-discharge closed-loop system, and the three constitute an organic whole.

[0039] (ii) Circulating water discharge and wastewater treatment subsystem like Figure 2 As shown, the circulating water wastewater treatment subsystem 100 is the first major component of this system, used to treat the main low-salinity wastewater of the power plant, separating it into reusable freshwater, calcium-based solid particles that can be recycled, and high-salinity concentrated water that needs to be disposed of.

[0040] 1. Wastewater sources and collection The circulating water wastewater treatment subsystem 100 is designed with five water sources: reverse osmosis (RO) concentrate from the chemical water treatment workshop, mixed bed regeneration wastewater from the chemical water treatment workshop, ultrafiltration backwash water from the chemical water treatment workshop, circulating water wastewater, and fine treatment regeneration wastewater. The wastewater from the three streams of the chemical water treatment workshop is collected through the workshop's drainage ditch and sent to Wastewater Buffer Tank 101 (an existing chemical wastewater tank of the power plant, consisting of two tanks, each with an effective volume of V=200m³, totaling 400m³, requiring restorative renovation, including but not limited to dredging and restoration of the anti-corrosion layer). The circulating water discharge is connected to Wastewater Buffer Tank 101 via a newly constructed pipeline, and the refined treatment and regeneration wastewater is connected to the chemical water treatment workshop's drainage ditch and flows into Wastewater Buffer Tank 101. In Wastewater Buffer Tank 101, the five streams of wastewater undergo homogenization and mixing, buffering and balancing fluctuations in water volume and quality.

[0041] Wastewater buffer tank 101 is equipped with an ultrasonic level gauge capable of transmitting 4-20mA signals to monitor the water level both locally and remotely.

[0042] 2. Raw water lifting and transportation Wastewater buffer tank 101 is equipped with two wastewater lift pumps 102 (one in operation and one on standby). These are horizontal centrifugal pumps with a rated flow rate Q = 200 m³ / h, a head H = 30 m, and a motor power N = 55 kW, controlled by frequency converter. The wastewater lift pumps 102 transport the homogenized wastewater from the wastewater buffer tank 101 to the chemical crystallization circulating granulation fluidized bed 103.

[0043] The start and stop of the wastewater lift pump 102 are interlocked with the liquid level of the wastewater buffer tank 101 and the start and stop status of the chemical crystallization circulating granulation fluidized bed 103: the lift pump stops when the water level in the wastewater buffer tank 101 is low or the chemical crystallization circulating granulation fluidized bed 103 is stopped; the lift pump starts when the water level in the wastewater buffer tank 101 is high and the chemical crystallization circulating granulation fluidized bed 103 is running. The wastewater lift pump 102 adopts frequency conversion control to achieve precise matching with the processing capacity of the subsequent softening unit. A flow meter and pressure transmitter are installed on the outlet pipe of the wastewater lift pump 102 to monitor the water flow rate and pressure entering the chemical crystallization circulating granulation fluidized bed 103.

[0044] 3. Chemical softening unit – chemical crystallization circulating granulation fluidized bed The chemical crystallization circulating granulation fluidized bed 103 is the core equipment of this subsystem for achieving chemical softening, with a rated treatment capacity of 180 m³ / h, and one unit is installed. Its working principle and technical characteristics are: it adopts chemical crystallization granulation softening technology, that is, adding seed crystals and alkaline agents (sodium hydroxide, sodium carbonate) to the water to be treated, so that the calcium ions (Ca²⁺, Ca²⁺, and Ca²⁺) in the water... + ) and carbonate ions (CO3²) -A chemical reaction occurs to produce calcium carbonate (CaCO3), which crystallizes and precipitates in a controlled manner on the seed crystal surface, unlike the random precipitation that forms amorphous sludge in traditional lime softening methods. As calcium carbonate continuously adheres to and deposits on the seed crystal surface, the seed crystal particles gradually grow, eventually forming large particles with a considerable diameter (up to several millimeters). Under gravity, these particles settle to the bottom of the fluidized bed and are discharged at regular intervals. After discharge, the particles enter a particle collection device, where water is filtered out before being transported off-site. The discharged filtrate flows through a drainage ditch to the recycling water tank 117.

[0045] like Figure 2 As shown, the chemical crystallization circulating granulation fluidized bed 103 has, from bottom to top, a water distribution zone 1031, a drug distribution zone 1032, a granulation zone 1033, and a clear water zone 1034. The area near the bottom of the cylinder is the fluidization zone 1035, the area near the top is the separation zone 1036, and the area between the cylinders is the settling zone. The fluidization zone 1035 is connected to the seed crystal addition pipe 1037, and the seed crystals circulate between the fluidization zone 1035, the separation zone 1036, and the settling zone. The fluidization zone 1035 is also connected to the particle discharge pipe 1038, and the particles formed by chemical crystallization circulating granulation settle to the bottom in the fluidization zone 1035 and are finally discharged from the particle discharge pipe 1038.

[0046] The effluent pipe of the chemical crystallization circulating granulation fluidized bed 103 is equipped with an acid inlet for adding hydrochloric acid to adjust the pH value of the effluent to a range suitable for subsequent coagulation, clarification, and membrane treatment. The effluent header of the chemical crystallization circulating granulation fluidized bed 103 is equipped with a pressure transmitter that outputs a 4-20mA DC standard signal.

[0047] The operating target of this softening unit is a water treatment capacity of not less than 180 m³ / h, with an effluent Ca² content of 1 / 2. + The concentration is no more than 2 mmol / L to meet the feed water requirements of the subsequent membrane desalination unit. At the same time, the generated calcium carbonate crystal particles have high purity and low water content, and can be directly sent to the desulfurization system 300 as a desulfurizing agent to realize the resource recycling of solid products.

[0048] 4. Coagulation and Settling Unit – Steel Settler The effluent from the chemical crystallization circulating granulation fluidized bed 103 flows by gravity into the steel clarifier 104 for coagulation and sedimentation treatment. The steel clarifier 104 has a rated treatment capacity of 180 m³ / h and is installed in one unit.

[0049] The design features of the steel clarifier 104 include: an upward flow velocity in the clear water zone not exceeding 1.2 mm / s; and the addition of inclined plates (inclined tubes) in the clear water zone to increase the sedimentation area, allowing flocs to gradually settle down on the inclined tube wall surface during the upward flow of clear water, thus improving the mud-water separation effect. Coagulants and flocculants are added to the inlet zone of the steel clarifier 104. In this embodiment, the coagulant is polyferric sulfate (transport concentration 40%, preparation concentration 20%), and the flocculant is polyacrylamide (PAM) (solid powder, preparation concentration 0.1%). After the reagents and the water to be treated are thoroughly mixed and reacted through mechanical stirring, larger floc particles are formed, achieving efficient sedimentation and separation in the inclined plate zone. The target turbidity of the effluent from the steel clarifier 104 is not greater than 5 NTU.

[0050] The steel clarifier 104 is equipped with two sludge pumps (one in operation and one on standby). The sludge pumps are slurry pumps with a single unit flow rate Q = 15 m³ / h, head H = 20 m, motor power N = 7.5 kW, and frequency converter control. The sludge pumps have both sludge circulation and sludge discharge functions: during normal operation, a portion of the sludge is circulated back to the inlet of the steel clarifier to maintain a certain sludge concentration in the tank, which helps improve coagulation and sedimentation efficiency; excess sludge is transported through pipelines to the plant's reclaimed water treatment system for unified treatment.

[0051] The steel clarifier 104 is equipped with a turbidity meter and a pH meter on its outlet header, which outputs a 4-20mA DC standard signal for online monitoring of the effluent quality, providing a reference for the operation of subsequent treatment units.

[0052] 5. Clear water storage system The effluent from the steel clarifier 104, after pH adjustment, enters the clear water tank 105. Clear water tank 105 is an underground reinforced concrete structure with an effective volume V=300m³, and consists of one unit. Clear water tank 105 is equipped with an ultrasonic level gauge capable of transmitting 4-20mA signals remotely for local and remote monitoring of the water level. Clear water tank 105 provides an intermediate buffer for subsequent filtration and membrane treatment units, balancing water flow fluctuations.

[0053] 6. Fiber Filter Unit The clean water in the clear water tank 105 is boosted and pressurized by the filter feed pump 106 before entering the fiber filter 107. The filter feed pump 106 is a horizontal centrifugal pump, with a total of two units (one in operation and one on standby). Each pump has a rated flow rate Q = 125 m³ / h, a head H = 52 m, a motor power N = 30 kW, and is frequency converter controlled. The start and stop of the filter feed pump 106 are interlocked with the liquid level in the clear water tank 105.

[0054] Fiber filter 107 is a precision filtration device preceding the membrane treatment stage in this subsystem. It is used to further remove fine suspended particles and colloids from the water, protecting the subsequent ultrafiltration and reverse osmosis membranes. Two high-efficiency fiber filters are installed, one in operation and one on standby. Each filter has a capacity of Q = 125 m³ / h, a filtration accuracy of 2-5 microns, a filtration rate of 30-40 m / h, and a self-consumption rate of approximately 2%. Fiber filters have advantages such as large specific surface area, low filtration resistance, high filtration accuracy, and strong contaminant removal capacity, making them superior to traditional quartz sand filters or multi-media filters.

[0055] The fiber filter 107 is equipped with a flow meter on its inlet header, outputting a 4-20mA DC standard signal. Each fiber filter has a local pressure gauge on its inlet and outlet pipes to monitor the pressure difference and determine if backwashing is necessary. The fiber filter 107 is equipped with a turbidity meter on its outlet header, outputting a 4-20mA DC standard signal.

[0056] The fiber filter 107 is equipped with a backwashing system and backwashing fans. Two horizontal centrifugal pumps are used for backwashing, one in operation and one on standby. Each pump has a flow rate Q = 70 m³ / h, a head H = 15 m, and a motor power N = 11 kW. Two Roots blowers are used for backwashing, one in operation and one on standby. Each blower has a flow rate Q = 11.4 m³ / min, an exhaust pressure P = 0.06 MPa, and a motor power N = 30 kW. When the pressure difference between the inlet and outlet water of the fiber filter reaches a set value or a set operating time is reached, the backwashing program is automatically started for backwashing and regeneration.

[0057] 7. Ultrafiltration Unit The effluent from fiber filter 107 enters self-cleaning filter 108 to further protect the subsequent ultrafiltration membrane module. Self-cleaning filter 108 is a mesh-type self-cleaning filter with a filtration accuracy of 100μm, a design pressure of 1.0MPa, and a motor power of N=0.37kW. According to the design documents, a total of two self-cleaning filters are installed, one of which utilizes existing equipment from the existing chemical water treatment system.

[0058] Ultrafiltration unit 109 uses a pressure-type hollow fiber ultrafiltration membrane module. One new ultrafiltration unit is added, with a rated treatment capacity of Q=110 m³ / h. An existing ultrafiltration unit in the chemical water treatment system undergoes restorative modifications (including but not limited to the unit frame, system piping, and valves) to meet current water quality and quantity requirements. The control of the modified ultrafiltration unit is also integrated into the decentralized control system of the newly built circulating water and wastewater treatment subsystem.

[0059] The ultrafiltration membrane elements are externally pressurized hollow fiber ultrafiltration membranes, with a membrane area of ​​55.7 m² / element, and a single set is equipped with 36 membrane elements. Considering the raw water quality conditions, the net flux of the ultrafiltration membrane is limited to no more than 50 L / (m²·h). This relatively conservative flux design helps control the membrane fouling rate and extends the chemical cleaning cycle and service life of the membrane elements. Sampling pipes are installed on the product water pipes of the ultrafiltration unit; the number and location of sampling points can effectively diagnose the system's operating status.

[0060] The ultrafiltration system is designed with an average water recovery rate of no less than 90% (after three years of operation), an effluent turbidity of no more than 0.5 NTU, and an effluent SDI index of no more than 3, meeting the influent requirements of the reverse osmosis system.

[0061] The ultrafiltration unit 109 is equipped with two ultrafiltration backwash pumps, one in operation and one on standby. These are horizontal centrifugal pumps with a single unit flow rate Q = 150 m³ / h, head H = 20 m, and motor power N = 22 kW, controlled by frequency converter. The ultrafiltration unit 109 also includes a chemically enhanced backwash system and a chemical cleaning system, with the chemical cleaning system shared with the reverse osmosis unit. The chemical cleaning water tank is made of steel lined with rubber. The ultrafiltration chemical cleaning system has two dosing units: a bactericide unit and a hydrochloric acid unit.

[0062] The ultrafiltration unit 109 can perform online integrity testing of membrane elements to ensure that the effluent water quality meets standards at all times. Each series unit of the ultrafiltration unit 109 can operate individually or simultaneously.

[0063] 8. Ultrafiltration permeate tank The permeate from the ultrafiltration unit 109 enters the ultrafiltration permeate tank 110. The ultrafiltration permeate tank 110 is an underground reinforced concrete structure, consisting of one tank equipped with an ultrasonic level gauge. The ultrafiltration permeate has a dual function: it serves as the feed water source for the subsequent reverse osmosis unit and also as the backwash water source for the ultrafiltration unit during backwashing. This reuse design reduces the need for a separate backwash water tank.

[0064] 9. Desalination Unit – Reverse Osmosis System The ultrafiltration permeate in the ultrafiltration permeate tank 110 is transported to the security filter 112 and the reverse osmosis unit 114 via the reverse osmosis feed pump 111.

[0065] (1) Reverse osmosis feed pump 111 The reverse osmosis feed pump 111 provides a stable feed flow and pressure to the reverse osmosis unit 114. Two horizontal centrifugal pumps are used, one in operation and one on standby. Each pump has a flow rate Q = 100 m³ / h, a head H = 40 m, and a motor power N = 22 kW. The outlet header of the reverse osmosis feed pump 111 is equipped with online instruments such as an ORP (oxidation-reduction potential) meter, a conductivity meter, and a thermometer to monitor the water quality entering the reverse osmosis unit 114.

[0066] (2) Security filter 112 The security filter 112 serves as the final safety barrier before entering the reverse osmosis high-pressure pump and membrane module, and its structure meets the requirements for rapid filter element replacement. In this embodiment, the security filter uses a high-flow-rate pleated filter element with a filtration accuracy of 5μm and a surface filtration velocity of no more than 10m³ / (m²·h). Local pressure gauges are installed at both the inlet and outlet of the security filter 112, and the end caps are connected by flanges.

[0067] (3) Reverse osmosis high-pressure pump 113 and supporting system The reverse osmosis high-pressure pump 113 provides the driving pressure required to overcome osmotic pressure and system resistance for the reverse osmosis membrane elements. It is a horizontal single-stage centrifugal pump, one unit in total, with a flow rate Q = 100 m³ / h, head H = 150 m, motor power N = 110 kW, and frequency conversion control. The outlet of the reverse osmosis high-pressure pump 113 is equipped with an automatic slow-opening device (controlling the valve opening speed) to prevent the membrane modules from being subjected to instantaneous impact from high-pressure water. A manual stainless steel shut-off valve is installed at the outlet of the reverse osmosis high-pressure pump 113. All valves, pipes, and fittings on the high-pressure pump outlet and concentrate side are rated for PN2.5 MPa. The reverse osmosis high-pressure pump 113 uses a corrosion-resistant mechanical seal. Pressure gauges and pressure switches are installed at the inlet and outlet of the reverse osmosis high-pressure pump 113: alarms and pump stop when the inlet water pressure is low, and alarms and pump stop when the outlet water pressure is high, to protect the membrane elements from damage due to operational errors.

[0068] (4) Reverse osmosis unit 114 Reverse osmosis unit 114 is the core equipment of this desalination unit. One new reverse osmosis unit will be added, with a single unit production capacity of Q=75 m³ / h, a recovery rate of 75%, and a desalination rate of not less than 98% (within the first year of operation). An existing reverse osmosis unit in the chemical water treatment system will undergo restorative modifications (including but not limited to the unit frame, system piping, and valves) to meet the current water quality and quantity requirements. The control of the modified reverse osmosis unit will also be integrated into the newly built circulating water and wastewater treatment subsystem.

[0069] The reverse osmosis membrane elements are selected as anti-fouling products to adapt to the complex water quality conditions of circulating water discharge and chemical water treatment system drainage, slowing down the membrane fouling rate caused by organic matter and microorganisms. The reverse osmosis unit can be chemically cleaned in two stages; each stage's feed water, concentrate, and permeate pipes are equipped with sufficient interfaces and valves to form fixed pipeline connections with the cleaning solution inlet and outlet pipes, rather than conventional temporary hose connections, facilitating daily operation and maintenance. A local manual SDI (Soil Degradation Index) meter is installed on the reverse osmosis unit's feed water header. A flow control valve (stabilizing valve) is installed at the reverse osmosis unit's concentrate outlet to control the water recovery rate; the valve configuration consists of one pneumatic valve and one bypass manual valve. A pneumatic discharge valve is installed on the reverse osmosis unit's permeate pipe to protect the membrane elements during start-up, shutdown, and cleaning; check valves and butterfly valves are also provided. The reverse osmosis unit has a programmed start-up and shutdown device that automatically performs a delayed permeate flush after shutdown, using permeate to replace the concentrate in the membrane elements, preventing irreversible membrane fouling caused by the drying and clumping of the concentration polarization layer during shutdown. Sampling points are installed in both the permeate and concentrate pipe systems of the reverse osmosis unit, and are centrally located in columns. The number and location of the sampling points can effectively diagnose and determine the operating status of the system.

[0070] (5) Drug injection system To ensure the long-term stable operation of the reverse osmosis membrane elements, this system is equipped with a reverse osmosis antiscalant dosing system and a reductant dosing system. The capacity of each chemical solution tank is sufficient to meet the chemical consumption requirements of all equipment for two days and nights, and each is equipped with local and remote level indicators. High and low level alarms are configured in the logic and interlocked with the corresponding pumps. Both the antiscalant and reductant solution tanks are equipped with electric stirring and dissolving devices with speed reducers. The dosing pumps use variable frequency speed control, with an adjustment range of 0-100% of the flow rate, and can also be manually adjusted. A standby pump is provided, and the standby pump automatically switches on.

[0071] (6) Reverse osmosis chemical cleaning system and flushing system The reverse osmosis unit 114 and the ultrafiltration unit 109 share a single chemical cleaning unit. The equipment in the cleaning system is selected with appropriate corrosion resistance levels, and the materials of pipes, valves, etc., are capable of withstanding the corrosion of the cleaning medium. The flushing system includes flushing pumps, pneumatic valves, pipes, etc., providing flushing functionality for the reverse osmosis unit 114. The reverse osmosis flushing pumps are horizontal single-stage centrifugal pumps, with two units in total (one in operation and one on standby). Each pump has a flow rate Q = 100 m³ / h, a head H = 20 m, and a motor power N = 18.5 kW.

[0072] 10. Freshwater storage, transportation, and concentrated wastewater discharge system (1) Freshwater system The permeate from the reverse osmosis unit 114 enters the freshwater tank 115. The freshwater tank 115 is a reinforced concrete structure, with one tank and a submersible level gauge (with high and low level alarm functions) capable of transmitting 4-20mA signals remotely to monitor the water level in the freshwater tank both locally and remotely.

[0073] Freshwater pump 116 is a horizontal single-stage centrifugal pump, with two units in total, one in operation and one on standby. Each pump has a flow rate Q = 100 m³ / h, a head H = 20 m, and a motor power N = 18.5 kW. The outlet header of freshwater pump 116 can be divided into two branches: one to the clarified water tank of the plant's chemical water treatment system, and the other to the plant's circulating water makeup system. The final produced water enters the cooling tower for recycling.

[0074] (2) Concentrate discharge system – leading to the desulfurization system The concentrate produced by the reverse osmosis unit 114 is the key material flow for achieving coordinated operation between the various subsystems in this invention. The discharge pressure of this reverse osmosis concentrate is approximately 1.1 MPa. Utilizing the existing concentrate delivery pipeline of the chemical water treatment system (total length approximately 330 meters, friction resistance approximately 0.3 MPa), it is ultimately sent to the process water tank of the desulfurization system 300 in a pressurized gravity flow manner, serving as process makeup water for the desulfurization tower.

[0075] (3) Wastewater recycling system During operation, the circulating water wastewater treatment subsystem 100 collects backwash wastewater from fiber filters, ultrafiltration backwash wastewater (including backwash wastewater from the reused ultrafiltration unit in the chemical water treatment system), chemical cleaning wastewater from ultrafiltration and reverse osmosis units, workshop floor flushing water, and chemical dosing area flushing wastewater through indoor drainage ditches and is then channeled to the newly built recycling water tank 117. The recycling water tank 117 is equipped with a recycling water pump that returns the collected wastewater to the wastewater buffer tank 101, where it is mixed again with the incoming water before entering the chemical softening unit for further treatment. This constitutes an internal wastewater recycling system, minimizing the system's own water discharge and further improving the overall water recovery efficiency.

[0076] 11. Sludge Disposal from Steel Clarifiers During the operation of the steel clarifier 104, the generated chemical sludge is periodically transported to the plant's reclaimed water treatment system for unified treatment via a sludge discharge pump. Considering the characteristics of the chemical crystallization circulating granulation fluidized bed 103, which involves the addition of crystal seeds and the presence of a small amount of fine particles in the discharged sludge, a wear-resistant and corrosion-resistant slurry pump is selected for the sludge discharge pump.

[0077] (III) End-of-pipe wastewater treatment subsystem like Figure 3 As shown, the end-of-pipe wastewater treatment subsystem 200 is the second main component of this system, used to treat the high-salt wastewater discharged from the desulfurization system 300 and achieve its complete evaporation and solidification.

[0078] The total designed evaporation capacity of this subsystem is 8 m³ / h, employing a high-speed rotary atomization process and a one-unit-one-tower arrangement (i.e., each unit is equipped with a separate evaporator). The designed processing capacity of a single evaporator is no less than 4 m³ / h, and the total designed processing capacity is 2 × 4 m³ / h.

[0079] 1. Desulfurization wastewater inflow and transportation system The desulfurization wastewater generated by the desulfurization system 300 is drawn from the nearest pipeline already laid in the plant to the slag bin and led to the spray water tank 201 set up in this subsystem. The desulfurization wastewater in the spray water tank 201 is pressurized by the spray water pump 202 and then transported to the rotary atomizer of the bypass flue gas evaporator 203.

[0080] Because desulfurization wastewater has extremely high salt content and high concentration of calcium and magnesium ions, it is prone to scaling and crystallization inside the pipes. Therefore, duplex stainless steel is selected as the material for the pipes leading to the evaporator tower, utilizing its excellent resistance to chloride ion pitting and crevice corrosion to ensure long-term reliable operation of the pipes in highly corrosive media. The spray pump 202 is a corrosion-resistant pump type capable of withstanding the high salt and high chloride ion conditions of the desulfurization wastewater.

[0081] To prevent wastewater from accumulating and clogging the pipelines due to crystal precipitation during system shutdowns or malfunctions, an automatic cleaning system 204 is installed in the wastewater delivery pipeline. This automatic cleaning system 204 includes a cleaning water tank (industrial water source) and connecting pipelines. It automatically activates when the system shuts down normally or malfunctions, using industrial water to flush and replace the wastewater delivery pipeline, ensuring unobstructed flow. The industrial water in the cleaning water tank is pressurized by a cleaning water pump and then enters the wastewater pipeline.

[0082] 2. Flue gas extraction system The heat source for the bypass flue gas evaporator 203 comes from the high-temperature flue gas before the boiler air preheater. Specifically, for a single unit, a portion of flue gas is drawn from the outlet of the denitrification reactor and the A-side and B-side flues before the air preheater inlet, resulting in two flue gas paths. The flue gas duct specifications are Ø1220×6mm, and each path is equipped with a manual damper. The two flue gas paths merge into one and enter the evaporator. The main flue gas duct specifications are Ø1220×6mm, and an electrically adjustable damper is installed on the main flue gas duct. The actuator of this electrically adjustable damper is a high-temperature type, which can automatically adjust the flue gas flow rate entering the evaporator based on the flue gas temperature at the evaporator outlet.

[0083] The flue gas from the evaporator outlet is returned to the air preheater outlet flue, which is divided into two branch pipes. The main return flue has a specification of Ø1220×6mm and is equipped with an electrically operated damper (specification Ø1220); the branch flue has a specification of Ø920×6mm, and each branch pipe is equipped with a manually operated damper. The symmetrical design of flue gas intake and return from both sides A and B ensures that the flue gas will not be misaligned or blocked on both sides of the air preheater.

[0084] Under the design conditions, the inlet flue gas temperature of the evaporator is 368℃, and the outlet flue gas temperature is 150℃ (maintained above the corresponding flue gas acid dew point temperature to avoid low-temperature condensation corrosion). The amount of flue gas consumed to treat 4t / h of wastewater is 36284Nm³ / h.

[0085] All flues feature a circular cross-section and an airtight, double-welded structure, with ample external reinforcement to prevent vibration and tremors. The arrangement and shape of flue materials, support structures, and internal components (such as baffles and guide plates) have been optimized to minimize pressure drop in the flue system.

[0086] 3. Bypass flue gas evaporator and rotary atomization system The bypass flue gas evaporator 203 mainly consists of an evaporation tower, a rotary atomizer, a flue gas distributor, a pneumatic ash conveying device 2031, and a steel frame platform.

[0087] (1) Evaporation tower The evaporator tower is a high-efficiency evaporation vessel with an ash hopper at the bottom. The ash hopper cone angle is designed at 60° to ensure that solid particles slide smoothly and are discharged without bridging. The evaporator tower is supported by an independent steel frame structure. The tower body is fixed to the steel frame by sliding supports and limiting devices to compensate for thermal expansion displacement throughout the operation. The steel frame structure itself has sufficient strength, stability, and deformation control capabilities. A platform and stairs are provided on the frame for convenient maintenance and testing. The steel frame columns are supported by independent foundations.

[0088] (2) Rotary atomizer The rotary atomizer is the core equipment of the end-of-pipe wastewater treatment subsystem 200, located at the top center of the evaporation tower. This system uses high-speed rotary atomization, which, compared to conventional nozzle atomization, can achieve a finer and more uniform droplet size distribution and is less prone to clogging.

[0089] The main technical parameters of the rotary atomizer are: rotation speed above 12,000 rpm, continuously adjustable; inlet water flow rate not exceeding 0.6 m / s; inlet water pressure not exceeding 0.2 MPa; maximum spray volume not less than 4 m³ / h. The atomizing disc material of the rotary atomizer meets the requirements for corrosion resistance and wear resistance. The rotary atomizer is a complete set including the atomizer body (including shell, motor, atomizing disc, etc.), mechanical cabinet (including lubrication system and cooling water system), and control cabinet.

[0090] (3) Flue gas distributor The flue gas distributor is located at the flue gas inlet at the top of the evaporation tower. Its main function is to ensure that the hot flue gas entering the evaporation tower from the pipes is evenly distributed along the entire cross-section of the tower, and to fully and effectively mix with the fine wastewater droplets sprayed from the rotary atomizer, so that the moisture evaporates rapidly. At the same time, the structural design of the flue gas distributor can prevent the occurrence of wet wall phenomenon and avoid scale and caking on the inner surface of the tower wall.

[0091] The flue gas distributor consists of three parts: an inlet volute, radial guide vanes, and inner conical guide vanes. The inlet volute guides the flue gas in a swirling manner, while the radial and inner conical guide vanes work together to ensure uniform distribution of the flue gas flow along the circumference and radial direction of the tower, guaranteeing uniform flow field and efficient gas-liquid mixing within the evaporation tower. The flue gas distributor area is equipped with a separate platform and ladder for easy maintenance and replacement of the rotary atomizer.

[0092] Under normal operating conditions, the extremely fine droplets provided by the rotary atomizer come into full contact with the high-temperature flue gas. The water in the droplets evaporates completely in a very short time, while the various salts dissolved in the wastewater precipitate out as fine, dry solid particles. The fly ash mixed in with the flue gas enters the subsequent electrostatic precipitator and is captured and collected. The water vapor generated by evaporation is drawn out from the bottom of the evaporation tower along with the flue gas and enters the air preheater outlet flue.

[0093] 4. Pneumatic ash conveying system Solid materials collected in the ash hopper at the bottom of the evaporator (mainly including salt particles precipitated after the evaporation of desulfurization wastewater and a small amount of fly ash mixed in) are periodically discharged and transported by an independently configured pneumatic ash conveying device 2031. Each evaporator is equipped with one independent positive pressure pneumatic ash conveying device 2031 with a conveying capacity of not less than 2000 kg / h.

[0094] The ash conveying pipeline is made of 16Mn material, with a designed service life of no less than 10 years. The pipeline elbows are ceramic-lined elbows, with a curvature radius 6-10 times the nominal diameter of the pipeline, and a designed service life of no less than 5 years. The conveying endpoint is the ash hopper of the third electric field of the corresponding electrostatic precipitator (above the high material level). The solid matter produced by evaporation is ultimately mixed with a large amount of fly ash and transported off-site from the ash silo for disposal. The compressed air source for pneumatic ash conveying is taken from the existing electrostatic precipitator ash conveying compressed air system in the plant area, eliminating the need for new compressed air preparation equipment.

[0095] (iv) Control System In order to operate the above-mentioned process system efficiently and safely and reduce the workload of operation and maintenance personnel, this embodiment is designed with the goal of unattended operation on site. All daily operation tasks, such as signal acquisition, equipment control, fault diagnosis and key parameter adjustment, are incorporated into the distributed control system for centralized control.

[0096] The circulating water wastewater treatment subsystem 100 is equipped with an independent distributed control system (DCS). A DCS main cabinet, I / O cabinet, one engineering station, and one operator station are installed in the newly built circulating water treatment workshop's electronics room. An additional operator station is located in the plant's central control room and chemical control room. The end-of-pipe wastewater treatment subsystem 200 uses the same DCS equipment as the power plant's main system, with the necessary cards and facilities configured in the unit turbine DCS section.

[0097] The main characteristics of control logic design include: The start and stop of each water pump are interlocked with the liquid levels of the upstream and downstream water tanks or pools to prevent water overflow or pump cavitation during dry running. For pump sets that need to operate continuously, in addition to the liquid level interlock, the inlet and outlet water flow rates are also balanced to avoid frequent start and stop of the process section due to liquid level fluctuations, thus extending the service life of the equipment.

[0098] The dosing rate of the metering pump is automatically proportionally adjusted based on the signal from the inlet header flow meter to ensure accurate and economical dosing. The dosing rate of the chemical softening unit is automatically adjusted based on the inlet flow rate, and the alkaline dosing rate is also closed-loop adjusted based on the online pH monitoring value of the inlet water. The clarifier can automatically discharge sludge according to a set sequence. The filter triggers an automatic backwashing program based on the inlet and outlet water pressure difference or a set operating time. The ultrafiltration unit automatically backwashes periodically; the backwashing cycle and duration can be set and changed on the DCS. The reverse osmosis system monitors comprehensive indicators such as permeate conductivity, inter-stage pressure difference, and cumulative permeate volume. When preset conditions are met, the DCS issues a prompt and guides the operator to perform semi-automatic or automatic chemical cleaning operations.

[0099] In the end-of-pipe wastewater treatment subsystem 200, the inlet and outlet flue gas temperatures of the evaporator tower are monitored in real time via thermocouples. An electrically operated regulating damper installed on the flue gas header automatically adjusts according to the outlet flue gas temperature. When the outlet temperature is too low, the damper opening decreases to increase the inlet flue gas flow and heat input; when the outlet temperature is too high, the damper opens further to save flue gas consumption and reduce system resistance. Simultaneously, various protection parameters of the rotary atomizer, such as cold air temperature, cooling water temperature, lubricating oil pressure, bearing temperature, and winding temperature, are integrated into the DCS for protection interlocking and fault tripping logic. When preset interlocking protection conditions are triggered, the DCS automatically stops the spray water pump 202, closes the flue gas extraction system damper, starts the automatic cleaning system 204, and activates the pneumatic ash conveying device to perform ash conveying operations, ensuring the system can safely exit operation under abnormal conditions such as main equipment failure without causing pipeline blockage or ash accumulation.

[0100] (v) Electrical system The circulating water wastewater treatment subsystem 100 will have one 400V low-voltage power distribution unit installed in the newly built circulating water treatment workshop. The calculated power load is Sjs=440kVA, arranged in two sections with reserved space for future connections. Each section will have a single power supply line and adopt a single busbar structure without segmentation. The power supply for the two sections will be taken from the existing power distribution bays of the PC section of the chemical water treatment system (the original power supply bays for the maintenance building and the charging piles), respectively. The loads of these two sections will be rescheduled to be powered by the chemical water MCC and the newly added MCC. The new power distribution unit will include an incoming line cabinet and a feeder cabinet.

[0101] The power supply for the end-of-pipe wastewater treatment subsystem 200 is taken from the denitrification motor control center (MCC) of the corresponding unit. The denitrification MCC is already equipped with a dual power supply switching device. This system draws power from its downstream side and does not require a separate dual power supply switching device. A power cabinet is configured on-site at the evaporator tower, and the load it supports can be controlled locally and remotely.

[0102] All motors are equipped with short-circuit and overload protection. The safety protection logic uses a three-pronged approach—time, sequence, and equipment status—to ensure process reliability and prevent dangers and malfunctions caused by a single signal causing false triggering or failure to operate.

[0103] Electrical equipment and structures are grounded using a composite artificial grounding network with horizontal grounding electrodes as the primary component and vertical grounding electrodes as a secondary component. The grounding resistance is no greater than 4 ohms, and the network is reliably connected to the main grounding network of the entire plant at at least two points. All electrical equipment casings, bases, conductive objects within structures, metal pipes, cable sheaths, and protective conduits are reliably grounded.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A comprehensive treatment system for water conservation and wastewater discharge in power plants, characterized in that, This includes a circulating water discharge and wastewater treatment subsystem and an end-of-pipe wastewater treatment subsystem; The circulating water wastewater treatment subsystem includes: A chemical softening unit is used to receive and soften a homogeneous mixture of circulating water discharge and wastewater from a chemical water treatment system, and to produce softened effluent and calcium-based solid particles; the calcium-based solid particles produced in the chemical softening unit are transported to a desulfurization system as a desulfurizing agent; The desalination unit is used to desalinate the softened effluent, producing reusable freshwater and high-salinity reverse osmosis concentrate, respectively; the reverse osmosis concentrate outlet is connected to the power plant's desulfurization system through a pipeline to provide process water for the desulfurization system; The end-of-pipe wastewater treatment subsystem includes a bypass flue gas evaporator, which is used to introduce desulfurization wastewater from the desulfurization system and use high-temperature flue gas to evaporate and solidify it.

2. The integrated processing system according to claim 1, characterized in that, The chemical softening unit includes a chemical crystallization circulating granulation fluidized bed; The circulating water wastewater treatment subsystem also includes: The wastewater buffer tank is used to collect and homogenize the circulating wastewater and the wastewater from the chemical water treatment system; the chemical crystallization circulating granulation fluidized bed is fluidly connected to the outlet of the wastewater buffer tank, and is used to chemically crystallize and soften the homogenized wastewater by adding alkaline agents and seed crystals, and then discharge the crystal particles. The clarifier is connected to the outlet fluid of the chemical crystallization circulating granulation fluidized bed and is used to treat the softened wastewater by coagulation and sedimentation. The clear water tank is fluidly connected to the outlet of the clarifier.

3. The integrated processing system according to claim 2, characterized in that, The chemical crystallization circulating granulation fluidized bed is equipped with a water distribution zone, a drug distribution zone, a granulation zone and a clear water zone from bottom to top, and is equipped with a seed crystal addition and particle discharge device to allow calcium ions in the water to crystallize on the seed crystal surface to form recyclable calcium carbonate particles.

4. The integrated processing system according to claim 3, characterized in that, The chemical crystallization circulating granulation fluidized bed is equipped with a circulation pipeline for returning a portion of the clean water to the inlet end to adjust the inlet flow rate and pH conditions.

5. The integrated processing system according to claim 2, characterized in that, The desalination unit includes an ultrafiltration unit and a reverse osmosis unit connected in sequence; The ultrafiltration unit is fluidly connected to the outlet of the clear water tank and is used to perform precision filtration and ultrafiltration treatment on the water effluent from the clear water tank, and output ultrafiltration product water. The reverse osmosis unit is fluidly connected to the outlet of the filter and is used to desalinate the ultrafiltration permeate, outputting reverse osmosis permeate and reverse osmosis concentrate. The reverse osmosis permeate is reused in the power plant's circulating water system and / or chemical water treatment system, and the reverse osmosis concentrate is transported to the power plant's desulfurization system.

6. The integrated processing system according to claim 2, characterized in that, The terminal wastewater treatment subsystem also includes a rotary atomizer, which is installed inside the bypass flue gas evaporator to atomize the desulfurization wastewater entering the evaporator into droplets, and use the heat of the high-temperature flue gas to evaporate the droplets.

7. The integrated processing system according to claim 6, characterized in that, The end-of-pipe wastewater treatment subsystem also includes a flue gas intake pipeline for drawing high-temperature flue gas from the flue in front of the power plant air preheater to the bypass flue gas evaporator. The flue gas outlet of the bypass flue gas evaporator is connected to the flue gas outlet of the air preheater so that the water vapor generated by evaporation enters the subsequent treatment equipment along with the flue gas.

8. The integrated processing system according to claim 7, characterized in that, The end-of-pipe wastewater treatment subsystem also includes a positive pressure pneumatic ash conveying device located at the bottom of the evaporator, used to convey the salt-containing dust generated by evaporation to the ash hopper of the electrostatic precipitator.

9. The integrated processing system according to claim 6, characterized in that, The end-of-pipe wastewater treatment subsystem also includes an automatic cleaning system, which is used to flush the wastewater delivery pipeline of the rotary atomizer with industrial water when the device is shut down or malfunctions.

10. The integrated processing system according to claim 9, characterized in that, The wastewater buffer tank is used to collect reverse osmosis concentrate, regenerated wastewater, ultrafiltration backwash water, circulating water discharge, and fine treatment regenerated wastewater generated by the power plant's chemical water treatment system and to homogenize them.

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