Zero-discharge treatment system and method for desulfurization wastewater from thermal power plants

Abstract

This application discloses a zero-discharge treatment system and method for desulfurization wastewater from thermal power plants. The system includes: a water quality monitoring unit for real-time acquisition of water quality parameters of the desulfurization wastewater; a pretreatment unit; a membrane concentration and reduction unit for separating the wastewater into freshwater and concentrated water using a reverse osmosis membrane module; a diversion control unit for outputting diversion commands and the water quality parameters of the diverted concentrated water; a high-temperature flue gas evaporation module for spraying and evaporating the concentrated water using high-temperature flue gas; a low-temperature waste heat evaporation module for evaporating and concentrating the concentrated water using low-grade waste heat; and a control unit. This application uses a closed-loop system composed of the water quality monitoring unit and the control unit to dynamically adjust the pretreatment reagent dosage, membrane concentration load, and evaporation diversion strategy. Especially in the membrane concentration stage, the minimum effective dosage of scale inhibitor is calculated in real-time based on the Langerile saturation index and the Steve-Davis stability index, combined with transmembrane pressure difference feedback correction, to achieve adaptive optimization of the scale inhibitor and ensure the long-term stable operation of the membrane system.

Description

Technical Field

[0001] This application belongs to the field of wastewater treatment technology for thermal power plants, specifically relating to a zero-discharge treatment system and method for desulfurization wastewater from thermal power plants. Background Technology

[0002] Limestone-gypsum wet desulfurization is the mainstream desulfurization process in thermal power plants, but the desulfurization wastewater it produces has a complex composition, containing high salt, high chlorine, high hardness, and heavy metals, making it difficult to treat. The traditional "three-stage" chemical precipitation method can remove heavy metals and suspended solids, but it cannot effectively remove dissolved salts and chloride ions, making it difficult to achieve wastewater reuse and zero discharge.

[0003] Existing zero-emission technologies mostly adopt the "pretreatment + membrane concentration + evaporation crystallization" route, but they have the following shortcomings:

[0004] High energy consumption and cost: Evaporation and crystallization largely depend on steam-driven processes, leaving room for optimization of operating costs.

[0005] Poor water quality adaptability: The wastewater quality fluctuates greatly, the system lacks self-adaptive adjustment capabilities, which can easily lead to inaccurate dosing of chemicals, membrane scaling and clogging, and unstable evaporation operation.

[0006] The conflict between concentrated wastewater treatment and resource utilization is prominent: if high-salt concentrated wastewater enters high-temperature flue gas for evaporation, it can easily cause excessive chloride ions in fly ash, affecting the utilization of building materials; if low-temperature evaporation is used, the efficiency is low and there are problems with the treatment of crystallized salts, making it difficult to balance all operating conditions.

[0007] Low system integration: The units operate in series, lacking global data interaction and collaborative control, resulting in poor overall stability and making it difficult to achieve the goal of zero emissions in the long term. Summary of the Invention

[0008] This application provides a zero-discharge treatment system and method for desulfurization wastewater from thermal power plants, aiming to solve the problems of high energy consumption and cost, poor water quality adaptability, prominent contradiction between concentrated wastewater treatment and resource utilization, and low system integration in existing technologies.

[0009] Firstly, a zero-discharge treatment system for desulfurization wastewater from thermal power plants, the system comprising:

[0010] A water quality monitoring unit is installed at the inlet end of the desulfurization wastewater conveying pipeline to collect water quality parameters of the desulfurization wastewater in real time. The water quality parameters include chloride ion mass concentration, total dissolved solids value, pH value, calcium ion concentration, magnesium ion concentration and flow rate data.

[0011] The pretreatment unit is connected to the output of the water quality monitoring unit and is used to receive data on calcium ion concentration, magnesium ion concentration, sulfate concentration and pH value uploaded by the water quality monitoring unit. Based on the data, calcium hydroxide and sodium carbonate are dynamically added to soften the desulfurization wastewater and output finely filtered water.

[0012] The membrane concentration and reduction unit is connected to the output of the pretreatment unit and is used to receive the finely filtered water, separate it into fresh water and concentrated water through the reverse osmosis membrane module, and output the water quality parameters and water quantity data of the concentrated water.

[0013] The diversion control unit is connected to the concentrate output terminal of the membrane concentration and reduction unit. It is used to receive the water quality parameters and water volume data of the concentrate, dynamically determine the diversion destination of the concentrate based on the data, and output the diversion command and the water quality parameters of the concentrate after diversion.

[0014] The high-temperature flue gas evaporation module is connected to the concentrate output terminal of the diversion control unit. It is used to receive the diverted concentrate and the chloride ion concentration data of the concentrate transmitted by the diversion control unit, and to spray the concentrate with high-temperature flue gas.

[0015] The low-temperature waste heat evaporation module is connected to the concentrate output terminal of the diversion control unit. It is used to receive the diverted concentrate and the total dissolved solids concentration data of the concentrate transmitted by the diversion control unit, and to evaporate and concentrate the concentrate using low-grade waste heat.

[0016] The control unit establishes bidirectional data communication links with the water quality monitoring unit, pretreatment unit, membrane concentration and reduction unit, diversion control unit, high-temperature flue gas evaporation module, and low-temperature waste heat evaporation module, respectively, to receive online monitoring data and operating status parameters of each unit in real time, and to send adjustment commands to the actuators of each unit.

[0017] Optionally, the water quality monitoring unit includes an online chloride ion selective electrode, a conductivity sensor, a pH meter, an online calcium and magnesium ion analyzer, and an electromagnetic flow meter;

[0018] The water quality data collected by the water quality monitoring unit is transmitted to the data acquisition module of the control unit in the form of analog or digital signals.

[0019] The control unit determines the salinity level of the wastewater based on the chloride ion concentration and total dissolved solids value, dynamically adjusts the dosage of calcium hydroxide and sodium carbonate in the pretreatment unit in conjunction with the calcium and magnesium ion concentration, and predicts and schedules the influent load of the membrane concentration and reduction unit based on the flow data.

[0020] Optionally, the pretreatment unit includes a primary softening reaction tank, a secondary softening reaction tank, a flocculation sedimentation tank, and a sludge dewatering device; the primary softening reaction tank receives desulfurization wastewater, and the control unit calculates the initial dosage of calcium hydroxide based on the magnesium ion concentration and sulfate concentration fed back by the water quality monitoring unit, and adds calcium hydroxide suspension through a variable frequency dosing pump;

[0021] The effluent from the primary softening reaction tank flows by gravity into the secondary softening reaction tank. The control unit calculates the amount of sodium carbonate to be added based on the initial calcium ion concentration and the remaining calcium ion concentration after the primary reaction, and adds sodium carbonate solution through a dosing pump.

[0022] The effluent from the secondary softening reaction tank enters the flocculation sedimentation tank, and the supernatant overflows into the intermediate water tank. After pH adjustment, it enters the sand filtration-ultrafiltration fine filtration unit. The turbidity and sludge density index of the ultrafiltration effluent meet the influent requirements of the membrane concentration and reduction unit.

[0023] Optionally, the membrane concentration and reduction unit includes a security filter, a high-pressure pump, a reverse osmosis membrane stack, an energy recovery device, a freshwater collection tank, and a concentrate buffer tank.

[0024] The freshwater produced by the reverse osmosis membrane stack enters the freshwater collection tank, and the concentrated water produced enters the concentrated water buffer tank.

[0025] The concentrate buffer tank is equipped with an online conductivity meter and a chloride ion selective electrode to monitor the total dissolved solids concentration and chloride ion concentration of the concentrate in real time, and transmit the data to the diversion control unit.

[0026] The control unit dynamically adjusts the high-pressure pump frequency and the opening of the concentrate discharge valve based on the influent conductivity, temperature, and sludge density index values ​​uploaded by the pretreatment unit, combined with the real-time operating data of the membrane stack, to control the system recovery rate.

[0027] Optionally, the diversion control unit includes a concentrate delivery pump, a diversion regulating valve group, a diversion control cabinet, and online water quality monitoring instruments;

[0028] The diversion control cabinet is embedded with a diversion judgment logic module. The diversion judgment logic module receives the total dissolved solids concentration and chloride ion concentration data of the concentrate in real time. Combined with the boiler load, air preheater inlet flue gas temperature and low-temperature economizer inlet water temperature parameters obtained from the unit's distributed control system, the module comprehensively judges the diversion destination of the concentrate.

[0029] When the total dissolved solids concentration of the concentrate is less than 7.0% and the chloride ion concentration is less than 15 g / L, the concentrate should be preferentially distributed to the high-temperature flue gas evaporation module.

[0030] When the total dissolved solids concentration of the concentrate reaches 7.0% or above, or the chloride ion concentration reaches 15 g / L or above, the concentrate will be distributed to the low-temperature waste heat evaporation module.

[0031] The diversion control unit uploads the diversion decision results and real-time flow data to the historical database of the control unit, and transmits the water quality parameters of the diverted concentrate to the control systems of the high-temperature flue gas evaporation module and the low-temperature waste heat evaporation module, respectively.

[0032] Secondly, a method for zero-discharge treatment of desulfurization wastewater from thermal power plants, implemented using the aforementioned zero-discharge treatment system for desulfurization wastewater from thermal power plants, includes the following steps:

[0033] S1. Water quality monitoring and data acquisition: The control unit collects the water quality parameters of the desulfurization wastewater entering the zero-discharge treatment system in real time through the water quality monitoring unit. The water quality parameters include chloride ion mass concentration, total dissolved solids value, pH value, calcium ion concentration, magnesium ion concentration and flow rate data.

[0034] S2. Pretreatment: The control unit dynamically adds calcium hydroxide and sodium carbonate reagents based on the calcium ion concentration, magnesium ion concentration, sulfate concentration and pH value data uploaded from the water quality monitoring steps to perform secondary sedimentation and softening treatment on the desulfurization wastewater and output finely filtered water.

[0035] S3. Membrane concentration and reduction: The finely filtered water produced in the pretreatment step is concentrated through a reverse osmosis seawater desalination membrane module and separated into fresh water and concentrated water. The water quality parameters and water volume data of the concentrated water are output.

[0036] S4. Diversion Judgment: The control unit dynamically determines the diversion destination of the concentrate based on the total dissolved solids concentration and chloride ion concentration of the concentrate output from the membrane concentration and reduction step, combined with the current boiler load and air preheater inlet flue gas temperature obtained from the unit's distributed control system, and outputs the diversion command and the concentrate quality parameters after diversion.

[0037] S5. High-temperature flue gas evaporation: The concentrated water allocated to the high-temperature flue gas evaporation module in the diversion judgment step is atomized by a rotary atomizer and sprayed into the bypass flue gas evaporation tower for evaporation using high-temperature flue gas.

[0038] S6. Low-temperature waste heat evaporation: The concentrated water allocated to the low-temperature waste heat evaporation module in the diversion judgment step is introduced into the evaporation tank and uses the power plant's circulating cooling water drainage or turbine exhaust steam as a heat source for natural evaporation.

[0039] S7. Data feedback and parameter adjustment: The control unit uses the detection data of the chloride ion content of fly ash at the outlet of the high-temperature flue gas evaporation module as a feedback parameter to dynamically adjust the flow rate of concentrated water entering the high-temperature flue gas evaporation module; and uses the evaporation water volume data of the low-temperature waste heat evaporation module as a feedback parameter to dynamically adjust the hot water flow rate of the heat exchanger and the air volume of the fan.

[0040] S8, System-level Coordination and Adaptive Optimization: The control unit periodically analyzes historical data of system operation and iteratively updates the optimal setpoints of each control parameter through a built-in adaptive optimization model.

[0041] Optionally, in S1, the water quality monitoring unit is located between the outlet pipe of the triplex treatment system and the inlet pipe of the clear water tank, and continuously monitors the water quality parameters of the wastewater through an online chloride ion selective electrode, a conductivity sensor, a pH meter, an online calcium and magnesium ion analyzer and an electromagnetic flow meter.

[0042] Each monitoring instrument completes data acquisition every 5 to 10 minutes, and the data is transmitted to the data acquisition module of the control unit in the form of analog or digital signals.

[0043] The control unit performs sliding window averaging filtering on the collected data. When the chloride ion concentration exceeds 15 g / L or the total dissolved solids exceed 35 g / L, the control unit issues a water quality anomaly warning and triggers the high-salt diversion logic in the subsequent diversion judgment step.

[0044] Optionally, S2 includes: a primary softening reaction tank receiving desulfurization wastewater, a control unit calculating the initial dosage of calcium hydroxide slurry based on magnesium ion concentration and sulfate concentration, and adding calcium hydroxide suspension via a variable frequency dosing pump;

[0045] The control unit dynamically adjusts the amount of calcium hydroxide supplementation based on the data from the online calcium and magnesium analyzer at the outlet of the primary reaction tank. When the magnesium ion removal rate reaches more than 95% and the sulfate concentration drops below 2.5 g / L, the control unit monitors the upward trend of calcium ion concentration. When the calcium ion concentration exceeds 1.8 g / L, the primary dosing is stopped.

[0046] The primary softened effluent flows by gravity into the secondary softening reaction tank. The control unit calculates the sodium carbonate dosage based on the initial calcium ion concentration and the remaining calcium ion concentration after the primary reaction, and adds sodium carbonate solution through a dosing pump. The calcium ion concentration in the effluent after the reaction is controlled below 0.15 g / L.

[0047] The softened water from the secondary stage enters the flocculation sedimentation tank, where polyacrylamide is added to promote flocculation and sedimentation. The supernatant overflows into the intermediate water tank and, after pH adjustment, enters the sand filtration-ultrafiltration fine filtration unit. The turbidity of the ultrafiltration effluent is controlled below 0.2 NTU, and the sludge density index is less than 4.

[0048] Optionally, in step S3, the membrane concentration and reduction step is equipped with a scale inhibitor dosing device. The control unit calculates the Langerier saturation index and the Steve-Davis stability index based on the calcium ion concentration, sulfate concentration, carbonate concentration and concentration factor in the influent. When the Langerier saturation index is greater than 0 or the Steve-Davis stability index is less than 6.0, the minimum effective dosage of scale inhibitor is determined according to the calculation model and continuously added to the high-pressure pump inlet pipe through a metering pump.

[0049] The freshwater produced by the membrane stack enters the freshwater collection tank and is then pumped to the desulfurization process water tank for reuse via a freshwater transfer pump.

[0050] The concentrate produced by the membrane stack enters the concentrate buffer tank, which is equipped with an online conductivity meter and a chloride ion selective electrode to monitor the concentrate water quality parameters in real time and transmit them to the diversion control unit.

[0051] Optionally, in S4, the diversion judgment logic is executed as follows: when the total dissolved solids concentration of the concentrate is less than 7.0% and the chloride ion concentration is less than 15g / L, the control unit allocates the concentrate to the high-temperature flue gas evaporation module;

[0052] When the total dissolved solids concentration of the concentrate reaches 7.0% or higher, or the chloride ion concentration reaches 15 g / L or higher, the control unit will distribute the concentrate to the low-temperature waste heat evaporation module.

[0053] When the unit load is below 60% or the flue gas temperature at the air preheater inlet is below 320℃, the control unit automatically lowers the inlet water threshold of the high-temperature flue gas evaporation module from 7.0% to 6.5%.

[0054] When water quality parameters fluctuate at the threshold boundary, the control unit continuously monitors for 15 minutes and takes the moving average. If the average value continues to exceed the threshold boundary for more than 10 minutes, a switching operation is performed.

[0055] The control unit uploads the diversion decision results and real-time flow data to the historical database, and transmits the water quality parameters of the diverted concentrate to the control systems of the high-temperature flue gas evaporation module and the low-temperature waste heat evaporation module respectively.

[0056] Compared with the prior art, this application has at least the following beneficial effects:

[0057] This application utilizes a closed-loop system comprised of a water quality monitoring unit and a control unit to dynamically adjust pretreatment reagent dosage, membrane concentration load, and evaporation diversion strategy. Particularly in the membrane concentration stage, the minimum effective dosage of scale inhibitor is calculated in real-time based on the Langerile Saturation Index (LSI) and the Stevie-Davis Stability Index (SDSI). Combined with transmembrane pressure differential feedback correction, adaptive optimization of the scale inhibitor is achieved, ensuring the long-term stable operation of the membrane system.

[0058] This application establishes a dual-mode system of "high-temperature flue gas evaporation + low-temperature waste heat evaporation." The diversion control unit dynamically determines the diversion destination based on parameters such as concentrated wastewater TDS, chloride ion concentration, unit load, and flue gas temperature: low-salt concentrated wastewater preferentially enters high-temperature flue gas evaporation, efficiently utilizing flue gas waste heat and controlling fly ash quality; high-salt concentrated wastewater automatically switches to low-temperature waste heat evaporation, utilizing low-grade waste heat from circulating water or exhaust steam for deep concentration and crystallization. This achieves "quality-based diversion and tiered utilization," effectively resolving the contradiction between high-salt concentrated wastewater treatment and by-product resource utilization.

[0059] The high-temperature module utilizes 300-360℃ flue gas for direct spray evaporation, while the low-temperature module utilizes 20-40℃ circulating cooling water drainage or turbine exhaust steam for ambient temperature evaporation. This maximizes the utilization of the power plant's own waste heat resources, significantly reduces dependence on external steam or electricity, and substantially reduces operating energy consumption. Attached Figure Description

[0060] Figure 1 A schematic diagram of the module connections of a zero-discharge treatment system for desulfurization wastewater from a thermal power plant provided in one embodiment of this application;

[0061] Figure 2 This is a schematic flowchart of a zero-discharge treatment method for desulfurization wastewater from a thermal power plant, provided in one embodiment of this application. Detailed Implementation

[0062] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments.

[0063] The zero-discharge treatment system for desulfurization wastewater from thermal power plants provided in this application is as follows: Figure 1 As shown, the system includes:

[0064] Water quality monitoring unit, pretreatment unit, membrane concentration and volume reduction unit, diversion control unit, high-temperature flue gas evaporation module, low-temperature waste heat evaporation module, control unit;

[0065] The water quality monitoring unit is located at the inlet of the desulfurization wastewater conveying pipeline, specifically between the effluent pipeline of the triplex treatment system and the inlet pipeline of the clear water tank. It is used to collect real-time water quality parameters of the desulfurization wastewater entering the zero-discharge treatment system. This unit includes an online chloride ion selective electrode, a conductivity sensor, a pH meter, an online calcium and magnesium ion analyzer, and an electromagnetic flowmeter. These are used to continuously monitor the wastewater's chloride ion concentration, total dissolved solids (TDS) value, pH value, calcium and magnesium ion concentrations, as well as instantaneous and cumulative flow rates. All monitoring instruments are made of corrosion-resistant materials and are equipped with automatic cleaning and periodic calibration modules to ensure long-term operational stability and data accuracy.

[0066] The collected water quality data is transmitted to the data acquisition and processing module of the control unit in the form of 4-20mA analog signals or Modbus RTU digital signals. The control unit determines the salinity level of the wastewater based on the chloride ion concentration and TDS value, and dynamically adjusts the dosage of calcium hydroxide and sodium carbonate in the pretreatment unit in combination with the calcium and magnesium ion concentration; at the same time, it predicts and schedules the influent load of the subsequent membrane concentration and reduction unit based on the flow data. In addition, when the chloride ion concentration exceeds the preset threshold (e.g., 15g / L) or the TDS exceeds 35g / L, the control unit issues an early warning and triggers the high-salinity diversion logic of the diversion control unit, preferentially guiding the wastewater to the low-temperature waste heat evaporation module to avoid the risk of scaling and corrosion caused by high-salinity wastewater entering the membrane system or high-temperature flue gas system.

[0067] The pretreatment unit is connected to the output of the water quality monitoring unit to receive desulfurization wastewater temporarily stored in the clear water tank. Based on the calcium ion concentration, magnesium ion concentration, sulfate concentration, and pH value data uploaded by the water quality monitoring unit, calcium hydroxide and sodium carbonate are dynamically added to remove scale-forming ions such as calcium, magnesium, and sulfate from the wastewater. This unit includes a primary softening reaction tank, a secondary softening reaction tank, a flocculation sedimentation tank, and a sludge dewatering device. The tanks are connected via overflow or pipelines, and a stirring device is installed to ensure thorough mixing of the chemicals and wastewater.

[0068] The primary softening reactor receives desulfurization wastewater from the clear water tank. The pH value within the reactor is monitored in real-time using an online pH meter. Based on the magnesium ion and sulfate concentrations reported by the water quality monitoring unit, the control unit calculates the initial dosage of calcium hydroxide slurry and continuously adds a 10% (w / w) calcium hydroxide suspension to the primary softening reactor via a variable frequency dosing pump. During the reaction, magnesium ions precipitate as magnesium hydroxide, and some sulfate ions precipitate as calcium sulfate. The control unit dynamically adjusts the supplementary calcium hydroxide dosage based on data from the online calcium and magnesium analyzer at the primary reactor outlet, ensuring a magnesium ion removal rate of over 95%, while simultaneously controlling the sulfate concentration to below 2.5 g / L. The control unit also monitors the upward trend of calcium ion concentration, stopping primary dosing when the calcium ion concentration exceeds a preset threshold (e.g., 1.8 g / L) to prevent excessive calcium ions from increasing subsequent sodium carbonate consumption.

[0069] The effluent from the primary softening reactor flows by gravity into the secondary softening reactor. The control unit calculates the sodium carbonate dosage based on the initial calcium ion concentration fed back from the water quality monitoring unit and the remaining calcium ion concentration after the primary reaction. A 10% sodium carbonate solution is then added to the reactor via a separate dosing pump. The sodium carbonate reacts with the calcium ions in the wastewater to form calcium carbonate precipitate, and the calcium ion concentration in the effluent after the reaction is controlled below 0.15 g / L. The secondary softening reactor is equipped with an online turbidity meter and pH meter. When the turbidity abnormally increases, the flocculant dosing device is automatically triggered to add polyacrylamide to promote the flocculation and sedimentation of fine particles.

[0070] The effluent from the secondary softening reaction tank enters the flocculation sedimentation tank, where inclined tube packing is installed to enhance the sedimentation effect. The supernatant overflows into the intermediate water tank, and the sludge settled at the bottom (mainly calcium carbonate, magnesium hydroxide and a small amount of calcium sulfate) is transported to the sludge dewatering device for pressure filtration through a sludge pump. The sludge cake after pressure filtration is transported off-site for disposal, and the filtrate is returned to the inlet of the primary softening reaction tank for reprocessing.

[0071] After the intermediate water tank effluent is adjusted to neutral by a pH adjustment device, it enters the sand filtration-ultrafiltration unit. The sand filter is used to remove suspended particles, and the ultrafiltration membrane module is used to remove colloids and microorganisms with a particle size greater than 0.02μm. The turbidity of the ultrafiltration effluent is controlled below 0.2NTU, and the sludge density index (SDI) is less than 4, meeting the feed water requirements of the subsequent membrane concentration and reduction unit. The ultrafiltration system is equipped with automatic backwashing and chemical cleaning functions, and the backwashing cycle is automatically adjusted according to changes in transmembrane pressure difference.

[0072] The control unit acquires raw water quality data uploaded by the water quality monitoring unit, online instrument data from each tank in the pretreatment unit, and the operating frequency of the dosing pumps in real time through the data acquisition module. Based on the built-in dosing model, it dynamically adjusts the dosage of chemicals to achieve closed-loop control of the softening process. When the raw water quality fluctuates beyond the treatment capacity of the softening unit, the control unit automatically adjusts the influent flow to the pretreatment unit or issues an early warning signal to guide the operators to intervene.

[0073] The membrane concentration and reduction unit is connected to the output of the pretreatment unit, specifically located at the rear end of the sand filtration-ultrafiltration fine filtration device. It receives the desulfurization wastewater after softening and fine filtration, and separates it into freshwater and concentrated water using a reverse osmosis seawater desalination membrane module, achieving wastewater volume reduction and salt concentration. This unit includes a security filter, a high-pressure pump, a reverse osmosis membrane stack, an energy recovery device, a freshwater collection tank, and a concentrated water buffer tank. All equipment is connected via corrosion-resistant high-pressure pipelines and is equipped with online monitoring instruments for pressure, flow rate, conductivity, pH value, and oxidation-reduction potential.

[0074] The finely filtered water from the pretreatment unit first enters a security filter with a filter precision set to 5μm. This filter is used to intercept trace particles that may be carried in the ultrafiltration water, preventing mechanical damage to the membrane elements from the high-pressure water flow. A low-pressure switch is installed at the outlet of the security filter; when the inlet water pressure falls below a set value (e.g., 0.1MPa), the pump automatically stops to prevent the high-pressure pump from running dry. The wastewater after security filtration enters the inlet of the high-pressure pump. The high-pressure pump uses frequency conversion control, adjusting its speed based on real-time feedback of the membrane stack inlet flow and pressure to maintain the membrane stack inlet pressure within a set range (typically 5.0–7.0MPa), meeting the operational requirements of the seawater desalination membrane module.

[0075] The reverse osmosis membrane stack uses fouling-resistant seawater desalination membrane elements, with an effective membrane area of ​​no less than 37m² per element. 2 The desalination rate is no less than 99.5%. The membrane stack is designed in a two-stage configuration, with the concentrate from the first stage entering the second stage for further concentration to improve the system recovery rate. An electrically operated slow-opening valve and pressure buffer device are installed at the membrane stack inlet to prevent water hammer impact on the membrane elements caused by the high-pressure pump starting. A permeate flow meter and conductivity meter are installed on the desalination side of the membrane stack for real-time monitoring of desalination production and quality; a concentrate flow meter and conductivity meter are installed on the concentrate side for monitoring the concentration ratio and salinity.

[0076] Based on the influent conductivity, temperature, and SDI value uploaded by the pretreatment unit, combined with real-time operating data of the membrane stack, the control unit dynamically adjusts the high-pressure pump frequency and the concentrate discharge valve opening to maintain the system recovery rate within the range of 60% ± 3%. When the influent temperature is below 15℃, the control unit automatically increases the high-pressure pump frequency to compensate for the decrease in permeate flux caused by the drop in water temperature; when the influent SDI value exceeds 3.5, the control unit issues a warning signal, prompting the pretreatment unit to adjust operating parameters or start the chemical cleaning program of the ultrafiltration system in advance.

[0077] To prevent membrane element scaling and microbial contamination, this unit is equipped with a scale inhibitor dosing device and a non-oxidizing bactericide dosing device. The scale inhibitor dosage is calculated based on the concentrations of calcium ions, sulfate ions, and carbonate ions in the feed water and is continuously added to the high-pressure pump inlet pipe via a metering pump, with the concentration controlled within the range of 2–5 mg / L. The bactericide is added intermittently, with the dosing cycle linked to the ultrafiltration system's backwashing cycle to prevent microbial growth on the membrane surface. Furthermore, an online oxidation-reduction potential meter is installed at the membrane stack inlet; when the oxidation-reduction potential exceeds 350 mV, the bactericide dosing automatically stops to prevent residual oxidant from oxidizing the membrane elements.

[0078] Furthermore, the control system of the membrane concentration and reduction unit incorporates a dynamic antiscalant dosing calculation module. This module is connected to the data output terminal of the pretreatment unit and the online analysis instrument at the membrane stack inlet. It is used to receive parameters such as calcium ion concentration, sulfate concentration, carbonate concentration, total dissolved solids, pH value and temperature in the inlet water in real time. Combined with the preset concentration factor of the membrane stack and the actual recovery rate, it calculates the Langerier saturation index and the Steve-Davis stability index to determine the minimum effective dosage of antiscalant, avoiding waste of reagents and membrane fouling caused by excessive dosage.

[0079] Specifically, before or during membrane stack startup, the control unit reads the calcium ion concentration, sulfate concentration, and carbonate concentration data at the outlet of the secondary softening reactor in the pretreatment unit at set intervals (e.g., 15 minutes). Simultaneously, it reads data from the online pH meter, temperature sensor, and conductivity meter at the membrane stack inlet, using these as input parameters for the calculation model. Based on the membrane stack's preset recovery target (60%) and the current actual recovery rate, the calculation module determines the concentration factor of each ion on the concentrate side of the membrane stack, and then calculates the Langrillly Saturation Index (LSI) and the Stevie-Davis Stability Index (SDSI) on the concentrate side.

[0080] The Langerile Indices (LSI) are calculated based on the actual pH value, saturated pH value, and temperature correction factor of the influent. When the LSI value is greater than 0, it indicates that calcium carbonate has a tendency to scale. For every 0.5 unit increase in the LSI value, the basic dosage of scale inhibitor should be increased by a set ratio (e.g., 20%). The Steve Davis Stability Index (SDSI) is calculated based on the calcium ion concentration, sulfate concentration, total dissolved solids (TDSI), and temperature of the influent. When the SDSI value is less than 6.0, it indicates that calcium sulfate has a tendency to scale. For every 0.5 unit decrease in the SDSI value, the basic dosage of scale inhibitor should be increased by a set ratio (e.g., 15%).

[0081] The calculation module integrates the evaluation results of LSI and SDSI, selects the higher of the two as the minimum effective dosage of scale inhibitor under the current operating conditions, and controls the frequency of the metering pump via a 4-20mA signal to continuously add the scale inhibitor (usually a phosphorus-containing small molecule polymer or polycarboxylic acid compound) into the high-pressure pump inlet pipe. Simultaneously, the calculation module compares the theoretical calculation value with the actual transmembrane pressure difference change rate and permeate flow rate decline rate during operation. When the actual pressure difference rise rate exceeds a preset threshold (e.g., 0.05 bar / day), the control unit automatically determines that the scale inhibitor dosage is insufficient and increases the dosage in step increments (e.g., 5%) based on the calculated value until the pressure difference rise rate returns to the normal range. Conversely, when the pressure difference change rate is consistently below the threshold and no scaling products are detected on the concentrate side, the control unit gradually decreases the dosage to the calculated value, achieving adaptive optimization of the scale inhibitor dosage.

[0082] Furthermore, when the effluent quality of the pretreatment unit experiences a sudden change (such as a sudden increase in calcium ion concentration exceeding 20%), the control unit automatically triggers a feedforward compensation mechanism for the scale inhibitor dosage, adding a safety margin (e.g., 10%–15%) to the calculated value. Once the influent quality stabilizes, the system gradually returns to the calculated value. The input parameters, intermediate calculation results, and final dosage data of the calculation module are all recorded in the control unit's historical database for operational trend analysis and maintenance early warning.

[0083] The freshwater produced by the reverse osmosis membrane stack (conductivity ≤600μS / cm, total dissolved solids ≤300mg / L) enters the freshwater collection tank and is then pumped to the desulfurization process water tank via a freshwater transfer pump to serve as supplementary water for the desulfurization system, replacing part of the fresh water intake. The freshwater collection tank is equipped with a level control system; when the level reaches the high limit, it automatically adjusts the high-pressure pump frequency or triggers the system's reduced-flow operation mode.

[0084] The concentrate produced by the reverse osmosis membrane stack (total dissolved solids concentration approximately 4.5%–7.0%, chloride ion concentration approximately 10–15 g / L) enters the concentrate buffer tank. The concentrate buffer tank is equipped with an online conductivity meter, chloride ion selective electrode, and level gauge to monitor the concentrate's water quality parameters and flow rate data in real time, and transmits the data to the diversion control unit. Based on the concentrate's total dissolved solids concentration, chloride ion concentration, and temperature data, combined with the current unit load status and flue gas temperature parameters, the diversion control unit dynamically determines the allocation ratio of the concentrate to the high-temperature flue gas evaporation module or the low-temperature waste heat evaporation module.

[0085] The membrane concentration and depletion unit is equipped with an automatic shutdown protection and chemical cleaning system. When the high-pressure pump outlet pressure exceeds 8.0 MPa, the concentrate flow rate is lower than the set value, or the permeate quality deteriorates (conductivity exceeds 1000 μS / cm), the control unit automatically executes the shutdown procedure, shuts down the high-pressure pump, and opens the electric slow-closing valve. The chemical cleaning system is equipped with an independent cleaning water tank and cleaning pump. When the intermembrane pressure difference of the membrane stack increases by 15% from the initial value or the permeate flow rate decreases by 10%, the control unit prompts the operator to perform chemical cleaning. The cleaning solution can be selected as acidic (for inorganic scale) or alkaline (for organic matter and microorganisms) depending on the type of contaminant. The cleaning process adopts a segmented circulation method, and the cleaning waste liquid is returned to the inlet of the pretreatment unit for reprocessing.

[0086] The diversion control unit is located between the concentrate buffer tank and the high-temperature flue gas evaporation module and the low-temperature waste heat evaporation module in the membrane concentration and depletion unit. It receives the concentrate output from the concentrate buffer tank and dynamically diverts it to the high-temperature flue gas evaporation module or the low-temperature waste heat evaporation module based on the total dissolved solids concentration, chloride ion concentration, current unit load status, and flue gas temperature parameters. This unit includes a concentrate transfer pump, a diversion regulating valve group, a diversion control cabinet, and online water quality monitoring instruments. All equipment is connected via corrosion-resistant pipes, and pressure, flow rate, and water quality online monitoring points are installed.

[0087] An online conductivity meter and chloride ion selective electrode are installed in the concentrate buffer tank to continuously monitor the total dissolved solids concentration and chloride ion concentration of the concentrate. The data is transmitted in real time as digital signals to the data acquisition module of the diversion control cabinet. The diversion control cabinet has an embedded diversion judgment logic module, which compares the real-time water quality data with the preset diversion threshold and combines it with parameters such as the current boiler load, air preheater inlet flue gas temperature, and low-temperature economizer inlet water temperature obtained from the unit's distributed control system to comprehensively determine the diversion destination of the concentrate.

[0088] The specific logic for the diversion judgment is as follows: When the total dissolved solids concentration of the concentrate is below 7.0% and the chloride ion concentration is below 15 g / L, the diversion control unit prioritizes allocating the concentrate to the high-temperature flue gas evaporation module. At this time, the control cabinet outputs a command to open the high-temperature side diversion regulating valve and simultaneously close the low-temperature side diversion regulating valve. The concentrate is then pressurized by the delivery pump and sent to the atomizing spray gun of the high-temperature flue gas evaporation module. This judgment is based on the tolerance analysis of the high-temperature flue gas evaporation module to the influent water quality: when the total dissolved solids concentration is below 7.0%, the wastewater evaporates completely after atomization, and the increase in chloride ion content of fly ash due to residual salt is controlled within 0.05%, which does not affect the comprehensive utilization of fly ash; when the chloride ion concentration is below 15 g / L, the risk of chloride ion corrosion to the equipment during the evaporation process is within a controllable range.

[0089] When the total dissolved solids concentration (TDS) of the concentrate reaches 7.0% or higher, or the chloride ion concentration reaches 15 g / L or higher, the diversion control unit automatically distributes the concentrate to the low-temperature waste heat evaporation module. The control cabinet outputs a command to open the low-temperature side diversion regulating valve and close the high-temperature side diversion regulating valve. The concentrate is then pressurized by the transfer pump and sent to the inlet of the heat exchanger of the low-temperature waste heat evaporation module. This judgment is based on the requirements for fly ash quality protection: after high TDS wastewater enters the high-temperature flue gas evaporation module, the residual salt content increases significantly, which may cause the chloride ion mass fraction of fly ash to exceed 0.30%, affecting the application of fly ash in prestressed concrete; high chloride ion concentration wastewater exacerbates the risk of equipment corrosion during high-temperature evaporation, and chloride ions may form corrosive products such as ammonium chloride in the flue gas system;

[0090] The diversion control unit incorporates a buffer transition logic during switching. When water quality parameters approach threshold boundaries (e.g., total dissolved solids concentration fluctuating between 6.8% and 7.2%), the diversion control cabinet does not immediately execute the switch. Instead, it continuously monitors for 15 minutes and takes a moving average. If the average value consistently exceeds the threshold boundary for more than 10 minutes, the switching operation is executed to avoid frequent switching of the diversion valve due to instantaneous fluctuations in water quality. During the switching process, the control cabinet employs a pre-open, post-close timing control strategy: first, the target-side diversion regulating valve is gradually opened; then, after the pressure in the target-side pipeline stabilizes, the original-side diversion regulating valve is gradually closed. The switching time is controlled within the range of 30 to 60 seconds to ensure stable outlet pressure of the concentrate delivery pump and avoid water hammer impact.

[0091] The diversion control unit also features an emergency diversion mode. When the high-temperature flue gas evaporation module is shut down due to equipment failure or maintenance, the control cabinet automatically diverts all concentrate to the low-temperature waste heat evaporation module. When the low-temperature waste heat evaporation module is shut down, the control cabinet automatically diverts the concentrate to the high-temperature side, provided that the concentrate quality meets the inlet requirements of the high-temperature flue gas evaporation module. When both evaporation modules fail to operate normally, the diversion control unit automatically shuts down the concentrate delivery pump and issues an alarm signal, while simultaneously instructing the membrane concentration and reduction unit to reduce the recovery rate or enter standby mode.

[0092] The diversion control unit uploads the diversion decision results and real-time flow data to the historical database of the control unit. Simultaneously, it transmits the diverted concentrate water quality parameters (total dissolved solids concentration, chloride ion concentration, temperature, and flow rate) to the control systems of the high-temperature flue gas evaporation module and the low-temperature waste heat evaporation module, respectively. These parameters are used as feedforward parameters by downstream modules when adjusting atomization particle size, flue gas extraction rate, heat exchange area, or circulation flow rate. After receiving the concentrate chloride ion concentration data from the diversion control unit, the high-temperature flue gas evaporation module dynamically adjusts the gas-liquid ratio of the atomizing nozzle to control the atomization particle size within the range of 50–80 μm. Higher chloride ion concentrations result in smaller atomization particle sizes, shortening evaporation time and reducing the risk of wall adhesion. Similarly, after receiving the concentrate total dissolved solids concentration data, the low-temperature waste heat evaporation module dynamically adjusts the circulating water pump frequency and fan volume. Higher total dissolved solids concentrations result in correspondingly higher circulation flow rate and air volume, maintaining a stable evaporation rate.

[0093] The high-temperature flue gas evaporation module is connected to the concentrated water output terminal of the diversion control unit and is located between the main flue before the boiler air preheater inlet and the main flue before the dust collector inlet. It receives the concentrated water distributed by the diversion control unit and uses the high-temperature flue gas before the air preheater inlet to spray and evaporate the concentrated water. The residual salts after evaporation enter the dust removal system with the flue gas and are captured by fly ash. The water vapor generated by evaporation enters the desulfurization tower with the flue gas after passing through the dust collector. After condensation in the desulfurization tower, it indirectly supplements the desulfurization process water. This module includes a bypass flue, a spray drying tower, a rotary atomizer, a gas distributor, a flue gas damper system, and supporting measuring instruments and control systems.

[0094] The bypass flue is led out from the main flue before the air preheater inlet. The connection point is located on the straight section of the air preheater inlet flue, avoiding bends and support locations to ensure stable flue gas flow. The high-temperature flue gas first enters the upper part of the spray drying tower through the inlet electric regulating damper, where it undergoes heat and mass transfer with the atomized wastewater droplets. Then, it returns from the lower outlet of the spray drying tower to the main flue between the air preheater and the dust collector via the outlet electric switch damper. The inlet regulating damper adopts a single-axis double-damper structure, with an electrically driven regulating mechanism to control the amount of flue gas entering the spray drying tower. The outlet damper is a switch type, used to isolate the bypass flue when the system is shut down. The damper blades are made of Q235-A material, and the elastic seals are made of 316L stainless steel to adapt to the high-temperature flue gas environment. The sealing air for the damper is drawn from the air supplied by the boiler blower to prevent high-temperature flue gas leakage.

[0095] The spray drying tower is a vertical cylindrical structure made of Q345 steel. Its dimensions are designed based on the maximum wastewater treatment capacity (6.0 m³ / h), inlet flue gas temperature (330–360℃), outlet flue gas temperature (120–140℃), and atomized droplet evaporation time. A maintenance room and lifting device are provided at the top of the tower for easy maintenance and replacement of the rotating atomizer. The tower is lined with a wear-resistant inner lining, designed to withstand temperatures above 300℃, to prevent erosion and wear from high-speed flue gas. The pressure loss of the spray drying tower is controlled below 550 Pa, ensuring that the overall pressure loss of the bypass flue system does not exceed 850 Pa, thus reducing the negative pressure impact on the main boiler flue system.

[0096] The rotary atomizer is the core equipment of the high-temperature flue gas evaporation module, located at the center of the top of the spray drying tower. It consists of a motor, gearbox, atomizing disc, and flow-through components. The motor dynamically adjusts the rotation speed of the atomizing disc based on the concentrate flow rate, chloride ion concentration, and flue gas temperature parameters transmitted from the diversion control unit, atomizing the concentrate into fine droplets with a diameter of 20–60 μm. The atomizing disc is designed with a diameter of 210 mm and is made of Hastelloy alloy to resist corrosion and abrasion from high-salt wastewater. During atomizer operation, the concentrate supplied by the diversion control unit is pumped to a high-level feed tank and flows by gravity into the rotary atomizer. Under centrifugal force, it expands into a thin film and breaks down into droplets. The atomizer is equipped with a circulating cooling water system to cool the heat generated by high-speed rotation. The cooling water is taken from the power plant's circulating water system, and the return water is returned to the circulating water system, without increasing water consumption. The atomizer is also equipped with a compressed air sealing system to prevent flue gas and dust from entering the atomizer bearing area.

[0097] The gas distributor, constructed of 304 stainless steel, is located at the flue gas inlet at the top of the spray drying tower. It is used to evenly distribute the high-temperature flue gas entering the tower, promoting effective mixing of the flue gas and atomized droplets. The gas distributor features an annular blade structure with an adjustable blade angle. The optimal blade angle is determined during system commissioning based on the flue gas flow rate and atomized droplet size distribution, creating a rotating, upward airflow within the tower. This prolongs the residence time of the atomized droplets and improves evaporation efficiency. The pressure loss of the gas distributor is controlled below 200 Pa to avoid significantly impacting the overall resistance of the bypass flue system.

[0098] The control unit dynamically adjusts the rotation speed of the rotary atomizer and the opening of the inlet flue gas regulating baffle based on the concentrated water flow rate and chloride ion concentration data transmitted from the diversion control unit, combined with real-time feedback of the inlet and outlet flue gas temperatures of the spray drying tower. When the concentrated water chloride ion concentration is high (e.g., 12–15 g / L), the control unit increases the atomizer rotation speed to control the atomized particle size within the range of 20–40 μm, shortening the droplet evaporation time and preventing high-salt droplets from adhering to the inner wall of the tower. When the concentrated water chloride ion concentration is low (e.g., below 10 g / L), the control unit appropriately reduces the atomizer rotation speed to control the atomized particle size within the range of 40–60 μm, reducing atomizer energy consumption. The control unit calculates the required theoretical flue gas volume based on the inlet flue gas temperature and concentrated water flow rate, and controls the actual extracted flue gas volume within the set range by adjusting the inlet baffle opening, ensuring that the outlet flue gas temperature of the spray drying tower is basically consistent with the flue gas temperature in the main flue before the dust collector inlet (temperature difference controlled within ±5℃), reducing the impact on the operation of the subsequent dust removal system.

[0099] During the operation of the high-temperature flue gas evaporation module, the control unit collects real-time data on the inlet and outlet flue gas temperatures, the temperature distribution on the inner wall of the spray drying tower, the pressure difference between the inlet and outlet flue gas, and the atomizer operating parameters. When the inner wall temperature is lower than a set threshold (e.g., 100℃) or when an abnormally low point appears in the inner wall temperature distribution (difference exceeding 15℃), the control unit determines that there is a risk of droplet adhesion to the wall. It automatically increases the opening of the inlet flue gas regulating damper to increase the flue gas volume, or increases the atomizer speed to reduce the atomized particle size, until the inner wall temperature returns to a safe range. When the outlet flue gas temperature is lower than 100℃, the control unit automatically reduces the concentrate feed rate or decreases the atomizer speed to prevent excessive cooling of the flue gas inside the tower, which could lead to water vapor condensation.

[0100] The residual salts after evaporation adhere to the surface of dust particles in the flue gas and are collected by the dust collector through the outlet flue, mixing into the fly ash. The control unit periodically acquires the chloride ion mass fraction detection data of the fly ash (manual input or online monitoring). When the chloride ion mass fraction exceeds 0.30%, the control unit automatically reduces the processing water volume of the high-temperature flue gas evaporation module, allocates the excess concentrated water to the low-temperature waste heat evaporation module for treatment, and dynamically adjusts the concentrated water treatment load of the high-temperature flue gas evaporation module according to the changing trend of the chloride ion content of the fly ash, ensuring that the fly ash quality meets the comprehensive utilization requirements of GB / T50146—2014 "Technical Specification for Application of Fly Ash in Concrete".

[0101] A dust hopper and pneumatic conveying system are installed at the bottom of the spray drying tower to collect the small amount of dry dust settling inside the tower. The dust hopper is equipped with a level gauge; when the dust level in the hopper reaches the high limit, the pneumatic conveying system automatically activates to transport the dry dust to the dust silo, preventing dust accumulation in the dust hopper from affecting the airflow distribution within the tower. The compressed air for the pneumatic conveying system is taken from the plant's compressed air system, and the conveying pipeline is equipped with wear-resistant elbows and an automatic unclogging device to prevent dry dust from accumulating and clogging the pipeline.

[0102] The high-temperature flue gas evaporation module is equipped with automatic shutdown protection and flushing procedures. Before system shutdown, the concentrated water feed is stopped, and high-temperature flue gas is continuously purged for 5-10 minutes to ensure complete evaporation of residual droplets in the tower before closing the inlet flue gas damper. After shutdown, the cleaning water system is started to flush the rotary atomizer to prevent residual wastewater from drying and clogging the atomizing disc nozzles. The cleaning water is taken from the power plant's industrial water system, and the flushing waste liquid is returned to the pretreatment unit inlet for reprocessing. When starting the system, the inlet flue gas damper is opened first to allow high-temperature flue gas preheating spray drying tower to be introduced. After the temperature inside the tower rises to above 200°C, the rotary atomizer is started and concentrated water is introduced to ensure that wastewater droplets can evaporate in time after entering the tower, avoiding wall adhesion problems during cold start-up.

[0103] The low-temperature waste heat evaporation module is connected to the concentrated water output terminal of the diversion control unit and is installed at an available location in the power plant's circulating cooling water drainage system or turbine exhaust steam system. It receives high-salt concentrated water distributed by the diversion control unit and uses low-grade waste heat from power plant circulating cooling water drainage or turbine exhaust steam as a heat source. Under normal temperature and pressure conditions, the concentrated water undergoes natural evaporation. After evaporation, the concentrated water reaches a supersaturated state and precipitates crystallized salt. The crystallized salt enters a salt separation unit for separation and collection. The water vapor generated during evaporation is either discharged into the atmosphere or recovered by a condensation device. This module includes a heat source extraction system, a heat exchange system, an evaporation system, a salt separation system, and supporting measuring instruments and control systems.

[0104] The heat source extraction system selects its access point based on the power plant's waste heat resources. When using circulating cooling water drainage as the heat source, the water intake point is located at the condenser outlet circulating water siphon well or circulating water drainage pipeline. The intake pipeline is equipped with an electric butterfly valve and a Y-type filter. A circulating hot water pump pumps the warm drainage water at approximately 20–40°C to the heat exchange system. When using turbine exhaust steam as the heat source, the steam intake point is located at the turbine low-pressure cylinder exhaust pipeline. The intake pipeline is equipped with an electric shut-off valve and a desuperheating and pressure reducing device to adjust the exhaust steam parameters to a safe range suitable for heat exchanger operation. A temperature sensor and flow meter are installed at the outlet of the heat source extraction system to monitor temperature and flow changes on the heat source side, and the data is transmitted to the control unit in real time.

[0105] The heat exchange system employs shell-and-tube or plate heat exchangers to achieve heat transfer between the heat source medium and the concentrated wastewater from desulfurization. The heat source side of the heat exchanger is supplied with circulating cooling water or turbine exhaust steam, while the wastewater side is supplied with concentrated wastewater from the diversion control unit. The heat exchanger is made of titanium or duplex stainless steel to resist the corrosive effects of the high-salt concentrated wastewater. A circulating water pump is installed on the wastewater side of the heat exchanger to continuously pump the concentrated wastewater from the evaporation system into the heat exchanger for heating before returning it to the evaporation system, forming a circulating heating loop. A bypass regulating valve is installed on the heat source side of the heat exchanger. The control unit adjusts the opening of the bypass valve according to the heating temperature required by the evaporation system to control the flow rate of the heat source entering the heat exchanger, keeping the temperature of the heated concentrated wastewater within a set range (typically 35–45°C, with a maximum of 50°C). Temperature and pressure sensors are installed at the inlet and outlet of the heat exchanger. When the temperature difference between the wastewater side and the heat source side falls below a set value (e.g., 2°C), the control unit determines that the heat exchanger is scaled or clogged and automatically triggers an online cleaning program.

[0106] The evaporation system employs an enhanced natural evaporation tank or evaporation tower structure to achieve the evaporation and concentration of heated concentrate. The evaporation tank is designed as a rectangular or circular reinforced concrete structure with an anti-corrosion lining. The lining material is made of vinyl ester resin glass flakes or polyurea elastomer to resist corrosion and penetration by high-salt wastewater. A concentrate circulation zone and a crystallization sedimentation zone are located at the bottom of the evaporation tank. The circulation zone uses a forced circulation pump to send the concentrate to a heat exchanger for heating before returning it to the evaporation tank, forming a circulating heating and evaporation loop.

[0107] An enhanced evaporation device is installed at the top of the evaporation tank, including multiple sets of high-efficiency atomizing nozzles and cross-flow fans. The atomizing nozzles atomize the circulating concentrated water into fine droplets (approximately 100–300 μm in diameter), and the fans force air across the atomization area, accelerating mass and heat transfer between the droplets and the air, thus improving evaporation efficiency. A demister is installed at the top of the evaporation tank to prevent fine droplets from escaping with the airflow and causing environmental pollution. Inside the evaporation tank, level gauges, thermometers, conductivity meters, and densitometers are installed to monitor the liquid level, temperature, salinity, and solution density in real time. The data is transmitted to the control unit in digital signal form.

[0108] The salt separation system is located in the crystallization settling zone of the evaporation tank to collect and separate the crystalline salt that precipitates after reaching a supersaturated state. A conical salt collection hopper is installed at the bottom of the crystallization settling zone. The precipitated crystalline salt settles to the bottom of the hopper under gravity and is then transported to the salt separation unit via a salt discharge pump or screw conveyor. The salt separation unit uses a horizontal screw centrifuge or plate and frame filter press to separate the crystalline salt slurry into crystalline salt solids and a separation liquid. The crystalline salt solids are washed, dried, and collected, and can be used for industrial salt resource utilization or landfill disposal according to environmental protection requirements. The separation liquid is returned to the evaporation tank for further evaporation and concentration, achieving complete zero discharge of wastewater. The salt separation system is equipped with an online moisture content detector. When the moisture content of the crystalline salt exceeds a set value (e.g., 10%), the control unit automatically adjusts the centrifuge speed or the filter press feed pressure until the moisture content returns to the acceptable range.

[0109] The control unit comprehensively regulates system operation based on multiple parameters (including concentrate TDS concentration, chloride ion content, flow rate data, as well as evaporator level, temperature, and ambient meteorological conditions). Specifically, for high-salinity concentrate (TDS 7%–10%), the system raises the heating temperature to 45–50°C and correspondingly increases the circulation flow rate and fan air volume to ensure evaporation efficiency while avoiding scaling risks; while for low-salinity concentrate (TDS 4%–7%), the system optimizes and reduces heat source input and air volume to minimize energy consumption while maintaining necessary evaporation efficiency.

[0110] The control unit monitors the solution density and conductivity in the evaporation tank in real time. When the solution density reaches a set threshold (e.g., 1.20–1.25 g / cm³), the control unit will detect the solution. 3 When the concentration or conductivity reaches a set threshold (e.g., 150–180 mS / cm), the system determines that the concentrate has reached a supersaturated state and automatically starts the salt separation system to perform salt discharge. During the salt discharge process, the control unit dynamically adjusts the operating frequency of the salt discharge pump according to the rate of change of density and conductivity, maintaining the concentration of the solution in the evaporation tank within the optimal crystallization range. This prevents a large amount of crystallized salt from depositing and hardening at the bottom of the tank due to untimely salt discharge, or from excessive salt discharge causing a decrease in the concentration in the evaporation tank and affecting the evaporation efficiency.

[0111] The system establishes a dynamic balance mechanism between evaporation capacity and processing load. The control unit calculates the actual evaporation volume of the low-temperature waste heat evaporation module in real time (based on liquid level changes and flow rate differences) and feeds the data back to the diversion control and membrane concentration system as a basis for adjusting operating parameters.

[0112] When the efficiency of the low-temperature evaporation module decreased (evaporation rate <0.8m³), it was detected that... 3When the system automatically performs load redistribution (per hour), it gradually reduces the amount of concentrate allocated to the low-temperature module while increasing the processing ratio of the high-temperature flue gas evaporation module. This dynamic balancing strategy ensures that even when the performance of a single module fluctuates, the overall system can maintain a stable and efficient concentrate treatment capacity.

[0113] The low-temperature waste heat evaporation module is equipped with an automatic shutdown protection and cleaning system. Before system shutdown, the concentrated water feed is stopped, the heat source extraction system valve is closed, and the evaporation system continues to circulate for 30-60 minutes to allow the solution temperature in the evaporation tank to drop to ambient temperature before stopping the circulation pump and fan. After shutdown, the cleaning system is activated to perform online cleaning of the heat exchanger wastewater side. The cleaning solution uses a low-concentration hydrochloric acid or citric acid solution to remove any calcium carbonate or calcium sulfate scale that may form on the heat exchanger surface. The cleaning wastewater is returned to the pretreatment unit inlet for reprocessing. An emptying pipe and a flushing water pipe are installed at the bottom of the evaporation tank. The evaporation tank is periodically emptied and the bottom is flushed to remove the mud and crystalline salt residue deposited at the bottom. The flushing wastewater is treated by the salt separation system and then returned to the evaporation tank.

[0114] The control unit serves as the central control hub of the system. It establishes bidirectional data communication links with the water quality monitoring unit, pretreatment unit, membrane concentration and reduction unit, diversion control unit, high-temperature flue gas evaporation module, and low-temperature waste heat evaporation module, respectively. This allows it to receive real-time online monitoring data and operating status parameters from each unit, and, based on preset control algorithms and dynamic optimization models, send adjustment commands to the actuators of each unit, achieving coordinated control and adaptive optimization throughout the entire system process. The control unit adopts a distributed control system architecture, consisting of a main control server, data acquisition module, logic operation module, command output module, and human-machine interface. All modules are connected via redundant industrial Ethernet to ensure system reliability.

[0115] The data acquisition module of the control unit acquires data in real time from the water quality monitoring unit, including chloride ion concentration, total dissolved solids concentration, calcium and magnesium ion concentration, pH value, and flow rate. It also acquires data from the pretreatment unit, including pH value, turbidity, liquid level, and dosing pump operating frequency in each reaction tank. Furthermore, it acquires data from the membrane concentration and reduction unit, including influent conductivity, temperature, SDI value, membrane stack pressure, permeate conductivity, concentrate conductivity, and recovery rate. The module also acquires data from the diversion control unit, including total dissolved solids concentration, chloride ion concentration, diversion valve opening, and concentrate distribution flow rate. Finally, it acquires data from the high-temperature flue gas evaporation module, including air preheater inlet flue gas temperature, spray dryer inlet and outlet flue gas temperatures, tower inner wall temperature distribution, atomizer speed, inlet baffle opening, and fly ash chloride ion content. Finally, it acquires data from the low-temperature waste heat evaporation module, including heat source temperature, heat exchanger inlet and outlet temperatures, evaporation tank liquid level, solution temperature, conductivity, density, ambient temperature, ambient humidity, wind speed, and crystallization salt moisture content. All collected data is filtered and outlier removed by the data acquisition module and then stored in the historical database for use by the logic operation module.

[0116] The control unit integrates a multi-layered intelligent algorithm system to achieve end-to-end optimization from basic control to advanced decision-making. Among them, the feedforward control algorithm is responsible for dealing with predictable changes such as water quality fluctuations; the feedback control algorithm ensures that the system quickly returns to the set operating conditions after disturbances; the fuzzy logic judgment algorithm handles uncertainties such as boundary conditions; and the adaptive optimization algorithm continuously learns from operating data and dynamically adjusts control parameters to achieve long-term optimized operation of the system.

[0117] The system employs a proactive and coordinated control strategy, analyzing real-time water quality data (chloride ion concentration, TDS value) and system operating parameters (recovery rate, concentrate production) to accurately predict concentrate quality changes within 1-2 hours. When the system predicts that concentrate salinity will exceed the standard (TDS>7.0% or Cl>15g / L), it automatically implements a dual adjustment mechanism: firstly, it appropriately reduces the membrane system recovery rate (e.g., from 60% to 55%) to reduce the generation of high-salinity concentrate; secondly, it optimizes the diversion ratio in advance, increasing the treatment ratio of the low-temperature waste heat evaporation module. This predictive control effectively protects the high-temperature flue gas evaporation module, ensuring that fly ash quality is not affected by high-salinity wastewater.

[0118] The logic operation module executes the diversion control optimization algorithm. The module reads the total dissolved solids (TDS) and chloride ion concentration of the concentrate from the diversion control unit in real time, and combines this with the current boiler load and air preheater inlet flue gas temperature obtained from the unit's distributed control system to calculate the dynamic correction coefficient for the diversion threshold. When the unit load is below 60% or the air preheater inlet flue gas temperature is below 320℃, the module automatically lowers the inlet water threshold of the high-temperature flue gas evaporation module from a TDS of 7.0% to 6.5%, allocating the excess concentrate to the low-temperature waste heat evaporation module to ensure the evaporation effect of the high-temperature flue gas evaporation module under low-load conditions. The module also uses the detection data of fly ash chloride ion content as a feedback parameter for diversion control. When the fly ash chloride ion mass fraction exceeds 0.28%, the module gradually reduces the concentrate allocation ratio of the high-temperature flue gas evaporation module until the fly ash chloride ion content falls below 0.25%.

[0119] The logic operation module executes the coordinated control algorithm of the high-temperature flue gas evaporation module. Based on the concentrate flow rate and chloride ion concentration transmitted to the high-temperature flue gas evaporation module from the diversion control unit, and combined with the inlet flue gas temperature of the spray drying tower, the module calculates the required atomizer speed and inlet flue gas damper opening. The concentrate chloride ion concentration and inlet flue gas temperature jointly determine the target range of atomized particle size: when the chloride ion concentration is higher than 12 g / L or the inlet flue gas temperature is lower than 330℃, the module sets the target atomized particle size to 20–40 μm and correspondingly increases the atomizer speed to 13000–14000 r / min; when the chloride ion concentration is lower than 10 g / L and the inlet flue gas temperature is higher than 350℃, the module sets the target atomized particle size to 40–60 μm and reduces the atomizer speed to 11000–12000 r / min, reducing energy consumption while ensuring evaporation effect. The module calculates the required theoretical flue gas volume based on the concentrate flow rate and inlet flue gas temperature. By adjusting the opening of the inlet damper, it controls the actual extracted flue gas volume within ±5% of the calculated value. It also monitors the difference between the flue gas temperature at the outlet of the spray drying tower and the flue gas temperature at the inlet of the dust collector. When the difference exceeds ±5℃, the module automatically corrects the flue gas volume setting value.

[0120] The logic operation module executes the coordination control algorithm of the low-temperature waste heat evaporation module. Based on the total dissolved solids concentration and flow rate of the concentrate transmitted to the low-temperature waste heat evaporation module from the diversion control unit, and combined with the real-time solution density, conductivity, temperature, and ambient meteorological conditions in the evaporation tank, the module calculates the required heat source flow rate, circulation flow rate, and fan airflow. The module has a built-in evaporation rate prediction model that predicts the theoretical evaporation rate under current operating conditions based on ambient temperature, humidity, wind speed, and solution temperature. When the actual evaporation rate is lower than 80% of the theoretical value, the module gradually increases the heat source flow rate and fan airflow to raise the solution temperature to the set upper limit (45-50℃) until the evaporation rate returns to the normal range. Based on the rate of change of solution density and conductivity in the evaporation tank, the module dynamically adjusts the salt discharge frequency and amount of the salt separation system. When the density increase rate exceeds 0.01 g / cm³ / h, the module initiates the salt discharge operation in advance to prevent excessive solution supersaturation from causing a large amount of crystalline salt to deposit at the bottom of the tank.

[0121] The logic operation module executes an adaptive optimization algorithm. The module periodically (e.g., weekly) analyzes historical system data, including energy consumption data, reagent consumption data, equipment runtime, and maintenance records for each unit. It iteratively updates the optimal settings for each control parameter using a built-in optimization model. For example, based on the historical data showing the correlation between scale inhibitor dosage and membrane stack pressure rise rate under different water quality conditions, the module optimizes the correction coefficient of the scale inhibitor dosage model; based on the historical data showing the correlation between different atomized particle sizes and tower inner wall temperature distribution, it optimizes the matching curve between atomizer rotation speed and concentrated chloride ion concentration; and based on the historical data showing the correlation between evaporation rate and fan energy consumption under different environmental conditions, it optimizes the operating strategy of the low-temperature waste heat evaporation module.

[0122] The control unit's command output module converts the adjustment commands generated by the logic operation module into control signals recognizable by the actuators, and outputs them to the execution devices of each unit via 4-20mA signals or digital communication protocols. The command output module adopts a closed-loop verification mechanism. After each command is issued, it monitors the feedback signals of the actuators (such as valve opening feedback, frequency converter frequency feedback). When the deviation between the feedback value and the command value exceeds a set threshold (such as ±5%), the module automatically repeats the command or issues a fault alarm.

[0123] The human-machine interface (HMI) of the control unit is located in the central control room. It uses a graphical user interface to display the system flowchart, operating parameters of each unit, equipment status, historical trend curves, and alarm information in real time. Operators can manually intervene in system operating parameters, set the allowable adjustment range for each control module, and view historical data and operating reports through the interface. The HMI features multi-level access control to ensure operational security.

[0124] The control unit is equipped with system-level safety interlock protection logic. When any critical parameter of any component exceeds the safety threshold, the module automatically executes preset protection actions. When the inner wall temperature of the high-temperature flue gas evaporation module remains below 80°C for more than 2 minutes, the module automatically stops the concentrate feed and initiates the purging procedure; when the liquid level in the evaporation tank of the low-temperature waste heat evaporation module exceeds the high limit or falls below the low limit, the module automatically adjusts the concentrate distribution rate of the diversion control unit; when the outlet pressure of the high-pressure pump of the membrane concentration and reduction unit exceeds 8.5 MPa, the module automatically stops the pump and closes the inlet valve; when a serious fault occurs in any part of the entire system, the module automatically executes the system-level safety shutdown procedure and sends a fault diagnosis report to the host computer system.

[0125] In one embodiment, a method for zero-discharge treatment of desulfurization wastewater from a thermal power plant is provided, implemented using the aforementioned zero-discharge treatment system for desulfurization wastewater from a thermal power plant, as shown in the attached figure. Figure 2 As shown, the method includes the following steps:

[0126] S1. Water Quality Monitoring and Data Acquisition: The control unit collects real-time water quality parameters of the desulfurization wastewater entering the zero-discharge treatment system through the water quality monitoring unit. The water quality monitoring unit is located between the effluent pipe of the three-tank treatment system and the influent pipe of the clear water tank. It continuously monitors the chloride ion mass concentration, total dissolved solids value, pH value, calcium and magnesium ion mass concentrations, instantaneous flow rate, and cumulative flow rate of the wastewater through an online chloride ion selective electrode, conductivity sensor, pH meter, online calcium and magnesium ion analyzer, and electromagnetic flow meter.

[0127] Each monitoring instrument completes data acquisition every 5-10 minutes, transmitting the data to the control unit's data acquisition module in the form of a 4-20mA analog signal or a Modbus RTU digital signal. The control unit performs sliding window averaging filtering on the acquired data, with the window width dynamically adjusted according to the parameter change rate to suppress sensor noise and transient disturbances. The acquired raw data and filtered data are stored together in the historical database for subsequent steps. When the chloride ion concentration exceeds 15g / L or the total dissolved solids exceed 35g / L, the control unit issues a water quality anomaly warning, triggering the high-salinity diversion logic in the subsequent diversion judgment step.

[0128] S2. Pretreatment: Based on the calcium ion concentration, magnesium ion concentration, sulfate concentration, and pH value data uploaded from the water quality monitoring steps, the control unit dynamically adds calcium hydroxide and sodium carbonate reagents to perform secondary precipitation and softening treatment on the desulfurization wastewater. The primary softening reaction tank receives desulfurization wastewater from the clear water tank. The control unit calculates the initial dosage of calcium hydroxide slurry based on the magnesium ion concentration and sulfate concentration, and continuously adds a 10% (w / w) calcium hydroxide suspension to the tank via a variable frequency dosing pump. During the reaction, magnesium ions precipitate out as magnesium hydroxide, and sulfate ions partially precipitate out as calcium sulfate.

[0129] The control unit dynamically adjusts the calcium hydroxide supplementation dosage based on data from the online calcium and magnesium analyzer at the outlet of the primary reaction tank. When the magnesium ion removal rate reaches over 95% and the sulfate concentration drops below 2.5 g / L, the control unit monitors the upward trend of the calcium ion concentration. Primary dosing is stopped when the calcium ion concentration exceeds 1.8 g / L. The primary softened effluent flows by gravity into the secondary softening reaction tank. The control unit calculates the sodium carbonate dosage based on the initial calcium ion concentration and the remaining calcium ion concentration after the primary reaction. A 10% sodium carbonate solution is added to the tank via an independent dosing pump. After the reaction, the calcium ion concentration in the effluent is controlled below 0.15 g / L, and the magnesium ion concentration is controlled below 0.6 g / L.

[0130] The softened effluent from the secondary treatment enters the flocculation sedimentation tank, where polyacrylamide is added to promote the flocculation and sedimentation of fine particles. The supernatant overflows into the intermediate water tank, where it is adjusted to neutral by a pH adjustment device before entering the sand filtration-ultrafiltration fine filtration unit. The sand filter traps suspended particles, while the ultrafiltration membrane module removes colloids and microorganisms with a particle size greater than 0.02 μm. The turbidity of the ultrafiltration effluent is controlled below 0.2 NTU, and the sludge density index is less than 4, meeting the feed water requirements for subsequent membrane concentration and reduction steps. The control unit automatically adjusts the backwashing frequency based on changes in the transmembrane pressure difference of the ultrafiltration system. When the transmembrane pressure difference increases by more than 15% from the initial value, the chemical cleaning program is initiated.

[0131] S3. Membrane Concentration and Reduction: The finely filtered water produced in the pretreatment step is concentrated through a reverse osmosis seawater desalination membrane module to achieve volume reduction and salt concentration of the wastewater. The finely filtered water first enters a 5μm security filter to remove trace particulate matter, and then is pressurized to 5.0-7.0MPa by a variable frequency high-pressure pump before entering the reverse osmosis membrane stack;

[0132] The membrane stack uses antifouling seawater desalination membrane elements, arranged in a two-stage configuration. The concentrate from the first stage enters the second stage for further concentration, with the system recovery rate controlled within 60% ± 3%. The control unit dynamically adjusts the high-pressure pump frequency and concentrate discharge valve opening based on the influent conductivity, temperature, and sludge density index values ​​uploaded from the pretreatment steps, combined with real-time membrane stack operating data. When the influent temperature is below 15℃, the high-pressure pump frequency is automatically increased to compensate for the decrease in permeate flux; when the influent sludge density index exceeds 3.5, a warning signal is issued to prompt the pretreatment unit to adjust operating parameters. The membrane concentration and reduction step is equipped with an antiscalant dosing device. The control unit calculates the Langerier saturation index and the Steve-Davis stability index based on the calcium ion concentration, sulfate concentration, carbonate concentration, and concentration factor in the influent. When the Langerier saturation index is greater than 0 or the Steve-Davis stability index is less than 6.0, the minimum effective dosage of antiscalant is determined according to the calculation model and continuously added to the high-pressure pump inlet pipe via a metering pump.

[0133] The freshwater produced by the membrane stack (conductivity ≤600μS / cm) enters the freshwater collection tank and is then pumped to the desulfurization process water tank for reuse. The concentrate produced by the membrane stack (total dissolved solids concentration 4.5%~7.0%, chloride ion concentration 10~15g / L) enters the concentrate buffer tank. The buffer tank is equipped with an online conductivity meter and a chloride ion selective electrode to monitor the concentrate water quality parameters in real time and transmit them to the diversion control unit.

[0134] S4. Diversion Decision: Based on the total dissolved solids (TDS) and chloride ion concentration of the concentrate output from the membrane concentration and reduction step, and combined with the current boiler load and air preheater inlet flue gas temperature obtained from the unit's distributed control system, the control unit dynamically determines the diversion destination of the concentrate. The diversion decision logic is as follows: When the TDS concentration is below 7.0% and the chloride ion concentration is below 15 g / L, the control unit allocates the concentrate to the high-temperature flue gas evaporation module; when the TDS concentration reaches 7.0% or higher, or the chloride ion concentration reaches 15 g / L or higher, the control unit allocates the concentrate to the low-temperature waste heat evaporation module.

[0135] When the unit load is below 60% or the flue gas temperature at the air preheater inlet is below 320℃, the control unit automatically lowers the water inlet threshold of the high-temperature flue gas evaporation module from the total dissolved solids concentration of 7.0% to 6.5%, and distributes the excess concentrate to the low-temperature waste heat evaporation module.

[0136] When water quality parameters fluctuate within the threshold boundary, the control unit continuously monitors for 15 minutes and takes a moving average. If the average value continuously exceeds the threshold boundary for more than 10 minutes, a switching operation is performed. During the switching process, a sequential control strategy of opening first and then closing is adopted. The target-side diversion regulating valve is gradually opened first, and after the pressure in the target-side pipeline stabilizes, the original-side diversion regulating valve is gradually closed. The switching time is controlled within the range of 30 to 60 seconds.

[0137] The control unit uploads the diversion decision results and real-time flow data to the historical database, and transmits the water quality parameters of the diverted concentrate to the control systems of the high-temperature flue gas evaporation module and the low-temperature waste heat evaporation module respectively.

[0138] S5. High-temperature flue gas evaporation: The concentrate allocated to the high-temperature flue gas evaporation module in the diversion judgment step is atomized by a rotary atomizer and sprayed into the bypass flue gas evaporation tower, where it is evaporated using the high-temperature flue gas at 300-360°C before the air preheater inlet. The concentrate is pumped to the high-level feed box by a feed pump and flows by gravity into the rotary atomizer. The atomizer speed is controlled by a gearbox within the range of 11000-14000 r / min, atomizing the concentrate into fine droplets with a diameter of 20-60 μm.

[0139] The control unit dynamically adjusts the atomizer speed and atomized particle size based on the chloride ion concentration of the concentrated water and the flue gas temperature at the air preheater inlet, as transmitted in the diversion judgment step: when the chloride ion concentration is higher than 12 g / L or the inlet flue gas temperature is lower than 330℃, the target atomized particle size is set to 20-40 μm, and the atomizer speed is increased to 13000-14000 r / min; when the chloride ion concentration is lower than 10 g / L and the inlet flue gas temperature is higher than 350℃, the target atomized particle size is set to 40-60 μm, and the atomizer speed is reduced to 11000-12000 r / min.

[0140] The control unit calculates the required theoretical flue gas volume based on the concentrated water flow rate and the inlet flue gas temperature. By adjusting the opening of the regulating damper at the inlet of the bypass flue, the actual extracted flue gas volume is controlled within ±5% of the calculated value, so that the flue gas temperature at the outlet of the spray drying tower is basically the same as the flue gas temperature in the main flue before the dust collector inlet, and the temperature difference is controlled within ±5℃.

[0141] The control unit monitors the temperature distribution inside the spray drying tower in real time. When the temperature inside the tower is below 100℃ or an abnormally low point appears in the temperature distribution (difference exceeding 15℃), it automatically increases the opening of the inlet flue gas damper to increase the flue gas volume or increases the atomizer speed to reduce the atomized particle size until the temperature inside the tower returns to a safe range. The residual salts after evaporation adhere to the surface of dust particles in the flue gas and are collected by the dust collector through the outlet flue, mixing into the fly ash. The water vapor generated by evaporation enters the desulfurization tower after passing through the dust collector with the flue gas, and indirectly supplements the desulfurization process water after condensation in the desulfurization tower. A small amount of dry ash collected in the ash hopper at the bottom of the spray drying tower is periodically transported to the ash silo via a pneumatic ash conveying system.

[0142] S6. Low-Temperature Waste Heat Evaporation: The concentrated water allocated to the low-temperature waste heat evaporation module in the diversion judgment step is introduced into the evaporation tank. It utilizes power plant circulating cooling water drainage or turbine exhaust steam as a heat source for natural evaporation at 15–40°C. The heat source extraction system selects the access point based on the power plant's waste heat resources. When using circulating cooling water drainage as a heat source, the water intake point is located at the condenser outlet circulating water siphon well. A circulating hot water pump pumps the 20–40°C warm drainage water to the heat exchange system. When using turbine exhaust steam as a heat source, the steam intake point is located at the turbine low-pressure cylinder exhaust pipe. After being regulated by a desuperheating and pressure-reducing device, the steam enters the heat exchanger.

[0143] The heat exchanger heats the circulating concentrate in the evaporation tank to 35–45°C. The heated concentrate is then returned to the evaporation tank, forming a circulating heating loop via a circulation pump. Atomizing nozzles and a cross-flow fan are installed at the top of the evaporation tank. The atomizing nozzles atomize the circulating concentrate into 100–300 μm droplets, and the fan forces air across the atomization area to accelerate mass and heat transfer between the droplets and the air.

[0144] The control unit dynamically adjusts the heat source flow rate, circulation flow rate, and fan volume based on the total dissolved solids concentration of the concentrate transmitted in the diversion judgment step, combined with the solution density, conductivity, temperature, and ambient meteorological conditions in the evaporation tank. When the total dissolved solids concentration of the concentrate is high (7%–10%), the concentrate heating temperature is increased to 45–50°C, while the circulation flow rate and fan volume are increased to enhance evaporation efficiency; when the total dissolved solids concentration of the concentrate is low (4%–7%), the heat source flow rate and fan volume are appropriately reduced to save energy.

[0145] The control unit monitors the solution density and conductivity in the evaporation tank in real time. When the solution density reaches 1.20–1.25 g / cm³, the control unit will detect the solution density. 3 When the conductivity reaches 150–180 mS / cm, the concentrate is considered to be supersaturated, and the salt separation system is activated for salt discharge. The precipitated crystallized salt settles into the salt collection hopper in the crystallization settling zone under gravity. The crystallized salt slurry is then transported to a horizontal screw centrifuge or plate and frame filter press via a salt discharge pump to separate into solid crystallized salt and a separation liquid. The solid crystallized salt is washed, dried, and collected for resource utilization, while the separation liquid is returned to the evaporation tank for further evaporation and concentration.

[0146] The control unit dynamically adjusts the operating frequency of the salt discharge pump according to the rate of change of density and conductivity, so as to maintain the concentration of the solution in the evaporation tank within the optimal crystallization range.

[0147] S7. Data feedback and parameter adjustment: The control unit uses the detection data of the chloride ion content of fly ash at the outlet of the high-temperature flue gas evaporation module (sampled and detected every shift) as feedback parameters to dynamically adjust the flow rate of concentrated water entering the high-temperature flue gas evaporation module.

[0148] When the chloride ion mass fraction of fly ash exceeds 0.28%, the control unit gradually reduces the concentrate distribution ratio of the high-temperature flue gas evaporation module, allocating the excess concentrate to the low-temperature waste heat evaporation module for treatment through the diversion control unit, until the chloride ion content of fly ash falls below 0.25%. When the chloride ion mass fraction of fly ash remains below 0.20%, the control unit appropriately increases the processing load of the high-temperature flue gas evaporation module to improve the overall system's operational economy. The control unit uses the evaporation water volume data of the low-temperature waste heat evaporation module (calculated by the change rate of the evaporation tank liquid level and the difference between the inlet and outlet water flow rates) as feedback parameters to dynamically adjust the hot water flow rate of the heat exchanger and the fan air volume.

[0149] When the actual evaporation rate is lower than the design value (e.g., less than 0.8m³), 3 When the actual evaporation rate is higher than the design value and the solution temperature is lower than the set lower limit, the control unit gradually increases the heat source flow rate and the fan air volume to raise the solution temperature to the set upper limit until the evaporation rate returns to the normal range. When the actual evaporation rate is higher than the design value and the solution temperature is lower than the set lower limit, the control unit appropriately reduces the heat source flow rate and the fan air volume to save energy.

[0150] The control unit also feeds back the actual evaporation volume of the low-temperature waste heat evaporation module to the diversion control unit. When the evaporation capacity of the low-temperature waste heat evaporation module is insufficient, the diversion control unit automatically reduces the amount of concentrate allocated to the low-temperature waste heat evaporation module and increases the amount of concentrate allocated to the high-temperature flue gas evaporation module to ensure the dynamic balance of the concentrate treatment load of the entire system.

[0151] S8, System-level Coordination and Adaptive Optimization: The control unit regularly (weekly) analyzes the historical data of the system operation, including energy consumption data, reagent consumption data, equipment runtime and maintenance records of each unit, and iteratively updates the optimal setpoints of each control parameter through the built-in adaptive optimization model.

[0152] The optimization model uses system operating costs (electricity, chemical, and heat consumption) as the objective function and control parameters of each unit as variables. It employs multiple linear regression to calculate the optimal matching relationship for each parameter, automatically updating the correction coefficient for the diversion threshold, the correction factor for the scale inhibitor dosing model, the matching curve between atomizer speed and chloride ion concentration, and the operating strategy table for the low-temperature waste heat evaporation module. The control unit stores the updated control parameters in the logic operation module, and subsequently executes control according to the optimized parameters, achieving continuous improvement in system operating economy. The control unit also monitors key operating indicators of the entire system; when any indicator deviates from the normal operating range, it automatically executes preset safety interlock protection actions to ensure safe and stable system operation.

[0153] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A zero-discharge treatment system for desulfurization wastewater from thermal power plants, characterized in that, The system includes: A water quality monitoring unit is installed at the inlet end of the desulfurization wastewater conveying pipeline to collect water quality parameters of the desulfurization wastewater in real time. The water quality parameters include chloride ion mass concentration, total dissolved solids value, pH value, calcium ion concentration, magnesium ion concentration and flow rate data. The pretreatment unit is connected to the output of the water quality monitoring unit and is used to receive data on calcium ion concentration, magnesium ion concentration, sulfate concentration and pH value uploaded by the water quality monitoring unit. Based on the data, calcium hydroxide and sodium carbonate are dynamically added to soften the desulfurization wastewater and output finely filtered water. The membrane concentration and reduction unit is connected to the output of the pretreatment unit and is used to receive the finely filtered water, separate it into fresh water and concentrated water through the reverse osmosis membrane module, and output the water quality parameters and water quantity data of the concentrated water. The diversion control unit is connected to the concentrate output terminal of the membrane concentration and reduction unit. It is used to receive the water quality parameters and water volume data of the concentrate, dynamically determine the diversion destination of the concentrate based on the data, and output the diversion command and the water quality parameters of the concentrate after diversion. The high-temperature flue gas evaporation module is connected to the concentrate output terminal of the diversion control unit. It is used to receive the diverted concentrate and the chloride ion concentration data of the concentrate transmitted by the diversion control unit, and to spray the concentrate with high-temperature flue gas. The low-temperature waste heat evaporation module is connected to the concentrate output terminal of the diversion control unit. It is used to receive the diverted concentrate and the total dissolved solids concentration data of the concentrate transmitted by the diversion control unit, and to evaporate and concentrate the concentrate using low-grade waste heat. The control unit establishes bidirectional data communication links with the water quality monitoring unit, pretreatment unit, membrane concentration and reduction unit, diversion control unit, high-temperature flue gas evaporation module, and low-temperature waste heat evaporation module, respectively, to receive online monitoring data and operating status parameters of each unit in real time, and to send adjustment commands to the actuators of each unit.

2. The zero-discharge treatment system for desulfurization wastewater from thermal power plants according to claim 1, characterized in that, The water quality monitoring unit includes an online chloride ion selective electrode, a conductivity sensor, a pH meter, an online calcium and magnesium ion analyzer, and an electromagnetic flow meter. The water quality data collected by the water quality monitoring unit is transmitted to the data acquisition module of the control unit in the form of analog or digital signals. The control unit determines the salinity level of the wastewater based on the chloride ion concentration and total dissolved solids value, dynamically adjusts the dosage of calcium hydroxide and sodium carbonate in the pretreatment unit in conjunction with the calcium and magnesium ion concentration, and predicts and schedules the influent load of the membrane concentration and reduction unit based on the flow data.

3. The zero-discharge treatment system for desulfurization wastewater from thermal power plants according to claim 1, characterized in that, The pretreatment unit includes a primary softening reaction tank, a secondary softening reaction tank, a flocculation sedimentation tank, and a sludge dewatering device. The primary softening reaction tank receives desulfurization wastewater. The control unit calculates the initial dosage of calcium hydroxide based on the magnesium ion concentration and sulfate concentration fed back by the water quality monitoring unit, and adds calcium hydroxide suspension through a variable frequency dosing pump. The effluent from the primary softening reaction tank flows by gravity into the secondary softening reaction tank. The control unit calculates the amount of sodium carbonate to be added based on the initial calcium ion concentration and the remaining calcium ion concentration after the primary reaction, and adds sodium carbonate solution through a dosing pump. The effluent from the secondary softening reaction tank enters the flocculation sedimentation tank, and the supernatant overflows into the intermediate water tank. After pH adjustment, it enters the sand filtration-ultrafiltration fine filtration unit. The turbidity and sludge density index of the ultrafiltration effluent meet the influent requirements of the membrane concentration and reduction unit.

4. The zero-discharge treatment system for desulfurization wastewater from thermal power plants according to claim 1, characterized in that, The membrane concentration and reduction unit includes a security filter, a high-pressure pump, a reverse osmosis membrane stack, an energy recovery device, a freshwater collection tank, and a concentrate buffer tank. The freshwater produced by the reverse osmosis membrane stack enters the freshwater collection tank, and the concentrated water produced enters the concentrated water buffer tank. The concentrate buffer tank is equipped with an online conductivity meter and a chloride ion selective electrode to monitor the total dissolved solids concentration and chloride ion concentration of the concentrate in real time, and transmit the data to the diversion control unit. The control unit dynamically adjusts the high-pressure pump frequency and the opening of the concentrate discharge valve based on the influent conductivity, temperature, and sludge density index values ​​uploaded by the pretreatment unit, combined with the real-time operating data of the membrane stack, to control the system recovery rate.

5. The zero-discharge treatment system for desulfurization wastewater from thermal power plants according to claim 1, characterized in that, The diversion control unit includes a concentrate delivery pump, a diversion regulating valve group, a diversion control cabinet, and online water quality monitoring instruments; The diversion control cabinet is embedded with a diversion judgment logic module. The diversion judgment logic module receives the total dissolved solids concentration and chloride ion concentration data of the concentrate in real time. Combined with the boiler load, air preheater inlet flue gas temperature and low-temperature economizer inlet water temperature parameters obtained from the unit's distributed control system, the module comprehensively judges the diversion destination of the concentrate. When the total dissolved solids concentration of the concentrate is less than 7.0% and the chloride ion concentration is less than 15 g / L, the concentrate should be preferentially distributed to the high-temperature flue gas evaporation module. When the total dissolved solids concentration of the concentrate reaches 7.0% or above, or the chloride ion concentration reaches 15 g / L or above, the concentrate will be distributed to the low-temperature waste heat evaporation module. The diversion control unit uploads the diversion decision results and real-time flow data to the historical database of the control unit, and transmits the water quality parameters of the diverted concentrate to the control systems of the high-temperature flue gas evaporation module and the low-temperature waste heat evaporation module, respectively.

6. A method for zero-discharge treatment of desulfurization wastewater from thermal power plants, characterized in that, The method is implemented using the zero-discharge treatment system for desulfurization wastewater from thermal power plants according to any one of claims 1 to 5, and includes the following steps: S1. Water quality monitoring and data acquisition: The control unit collects the water quality parameters of the desulfurization wastewater entering the zero-discharge treatment system in real time through the water quality monitoring unit. The water quality parameters include chloride ion mass concentration, total dissolved solids value, pH value, calcium ion concentration, magnesium ion concentration and flow rate data. S2. Pretreatment: The control unit dynamically adds calcium hydroxide and sodium carbonate reagents based on the calcium ion concentration, magnesium ion concentration, sulfate concentration and pH value data uploaded from the water quality monitoring steps to perform secondary sedimentation and softening treatment on the desulfurization wastewater and output finely filtered water. S3. Membrane concentration and reduction: The finely filtered water produced in the pretreatment step is concentrated through a reverse osmosis seawater desalination membrane module and separated into fresh water and concentrated water. The water quality parameters and water volume data of the concentrated water are output. S4. Diversion Judgment: The control unit dynamically determines the diversion destination of the concentrate based on the total dissolved solids concentration and chloride ion concentration of the concentrate output from the membrane concentration and reduction step, combined with the current boiler load and air preheater inlet flue gas temperature obtained from the unit's distributed control system, and outputs the diversion command and the concentrate quality parameters after diversion. S5. High-temperature flue gas evaporation: The concentrated water allocated to the high-temperature flue gas evaporation module in the diversion judgment step is atomized by a rotary atomizer and sprayed into the bypass flue gas evaporation tower for evaporation using high-temperature flue gas. S6. Low-temperature waste heat evaporation: The concentrated water allocated to the low-temperature waste heat evaporation module in the diversion judgment step is introduced into the evaporation tank and uses the power plant's circulating cooling water drainage or turbine exhaust steam as a heat source for natural evaporation. S7. Data feedback and parameter adjustment: The control unit uses the detection data of the chloride ion content of fly ash at the outlet of the high-temperature flue gas evaporation module as a feedback parameter to dynamically adjust the flow rate of concentrated water entering the high-temperature flue gas evaporation module; and uses the evaporation water volume data of the low-temperature waste heat evaporation module as a feedback parameter to dynamically adjust the hot water flow rate of the heat exchanger and the air volume of the fan. S8, System-level Coordination and Adaptive Optimization: The control unit periodically analyzes historical data of system operation and iteratively updates the optimal setpoints of each control parameter through a built-in adaptive optimization model.

7. The method for zero-discharge treatment of desulfurization wastewater from thermal power plants according to claim 6, characterized in that, In S1, the water quality monitoring unit is set between the effluent pipe of the triplex treatment system and the influent pipe of the clear water tank. It continuously monitors the water quality parameters of the wastewater through an online chloride ion selective electrode, a conductivity sensor, a pH meter, an online calcium and magnesium ion analyzer, and an electromagnetic flow meter. Each monitoring instrument completes data acquisition every 5 to 10 minutes, and the data is transmitted to the data acquisition module of the control unit in the form of analog or digital signals. The control unit performs sliding window averaging filtering on the collected data. When the chloride ion concentration exceeds 15 g / L or the total dissolved solids exceed 35 g / L, the control unit issues a water quality anomaly warning and triggers the high-salt diversion logic in the subsequent diversion judgment step.

8. The method for zero-discharge treatment of desulfurization wastewater from thermal power plants according to claim 6, characterized in that, The S2 includes: a primary softening reaction tank receiving desulfurization wastewater; a control unit calculating the initial dosage of calcium hydroxide slurry based on magnesium ion concentration and sulfate concentration; and adding calcium hydroxide suspension via a variable frequency dosing pump. The control unit dynamically adjusts the amount of calcium hydroxide supplementation based on the data from the online calcium and magnesium analyzer at the outlet of the primary reaction tank. When the magnesium ion removal rate reaches more than 95% and the sulfate concentration drops below 2.5 g / L, the control unit monitors the upward trend of the calcium ion concentration. When the calcium ion concentration exceeds 1.8 g / L, the primary dosing is stopped. The primary softened effluent flows by gravity into the secondary softening reaction tank. The control unit calculates the sodium carbonate dosage based on the initial calcium ion concentration and the remaining calcium ion concentration after the primary reaction, and adds sodium carbonate solution through a dosing pump. The calcium ion concentration in the effluent after the reaction is controlled below 0.15 g / L. The softened water from the secondary stage enters the flocculation sedimentation tank, where polyacrylamide is added to promote flocculation and sedimentation. The supernatant overflows into the intermediate water tank and, after pH adjustment, enters the sand filtration-ultrafiltration fine filtration unit. The turbidity of the ultrafiltration effluent is controlled below 0.2 NTU, and the sludge density index is less than 4.

9. The method for zero-discharge treatment of desulfurization wastewater from thermal power plants according to claim 6, characterized in that, In S3, the membrane concentration and reduction step is equipped with a scale inhibitor dosing device. The control unit calculates the Langerier saturation index and the Steve-Davis stability index based on the calcium ion concentration, sulfate concentration, carbonate concentration and concentration factor in the influent. When the Langerier saturation index is greater than 0 or the Steve-Davis stability index is less than 6.0, the minimum effective dosage of scale inhibitor is determined according to the calculation model and continuously added to the high-pressure pump inlet pipe through the metering pump. The freshwater produced by the membrane stack enters the freshwater collection tank and is then pumped to the desulfurization process water tank for reuse via a freshwater transfer pump. The concentrate produced by the membrane stack enters the concentrate buffer tank, which is equipped with an online conductivity meter and a chloride ion selective electrode to monitor the concentrate water quality parameters in real time and transmit them to the diversion control unit.

10. The method for zero-discharge treatment of desulfurization wastewater from thermal power plants according to claim 6, characterized in that, In S4, the diversion judgment logic is executed as follows: when the total dissolved solids concentration of the concentrate is less than 7.0% and the chloride ion concentration is less than 15g / L, the control unit will allocate the concentrate to the high-temperature flue gas evaporation module. When the total dissolved solids concentration of the concentrate reaches 7.0% or higher, or the chloride ion concentration reaches 15 g / L or higher, the control unit will distribute the concentrate to the low-temperature waste heat evaporation module. When the unit load is below 60% or the flue gas temperature at the air preheater inlet is below 320℃, the control unit automatically lowers the inlet water threshold of the high-temperature flue gas evaporation module from 7.0% to 6.5%. When water quality parameters fluctuate at the threshold boundary, the control unit continuously monitors for 15 minutes and takes the moving average. If the average value continues to exceed the threshold boundary for more than 10 minutes, a switching operation is performed. The control unit uploads the diversion decision results and real-time flow data to the historical database, and transmits the water quality parameters of the diverted concentrate to the control systems of the high-temperature flue gas evaporation module and the low-temperature waste heat evaporation module respectively.

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