Desulfurization wastewater grading and salt resource utilization system and method

Abstract

The present disclosure provides a desulfurization wastewater grading salt resource system and method, which belongs to the field of coal-fired power plant wastewater treatment and resource technology. The system comprises: a pretreatment unit for chemical precipitation and solid-liquid separation of desulfurization wastewater, outputting waste liquid and mixed precipitate containing Mg(OH)2 and CaSO4; a precipitate grading utilization unit connected with the pretreatment unit, for sequentially separating Mg(OH)2 precipitate and CaSO4 precipitate from the mixed precipitate, respectively as raw materials for preparing high-strength ceramic beads and roadbed materials; a membrane concentration and crystallization unit connected with the pretreatment unit, for sequentially performing nanofiltration, deep concentration and evaporation crystallization on the waste liquid, respectively producing Na2SO4 and NaCl industrial salt. The present disclosure realizes the full-component resource utilization of magnesium, calcium, sulfate and chloride ions in desulfurization wastewater by combining grading precipitation with grading utilization, solves the problems of difficult disposal of solid waste and low purity of separated salt in traditional processes, and realizes zero discharge and high-value utilization of desulfurization wastewater.

Description

Technical Field

[0001] This disclosure belongs to the field of wastewater treatment and resource utilization technology of coal-fired power plants, specifically relating to a graded and desalinated resource utilization system and method for desulfurization wastewater. Background Technology

[0002] Desulfurization wastewater generated during wet flue gas desulfurization in coal-fired power plants is characterized by high salt content, high suspended solids, high hardness, and heavy metal enrichment, making it one of the most difficult wastewaters to treat in power plants. With the increasingly stringent "Water Pollution Prevention and Control Action Plan" and local environmental protection requirements, zero discharge of desulfurization wastewater has become an inevitable requirement for the green transformation of the power industry.

[0003] Currently, the mainstream technical routes for zero discharge of desulfurization wastewater include the "pretreatment + membrane concentration + evaporation crystallization" process and the "flue gas waste heat evaporation" process. Pretreatment typically uses chemical precipitation to remove hardness ions such as magnesium and calcium ions. However, in traditional processes, the precipitated products are often disposed of as mixed solid waste without proper classification and utilization, resulting in resource waste and secondary pollution. For example, desulfurization wastewater has high magnesium and calcium ion content, and the Mg(OH)2 and CaSO4 mixture formed after precipitation lacks high-value applications and is usually directly landfilled.

[0004] On the other hand, the mixed salt obtained in the evaporation and crystallization process has low purity and high impurities, making it difficult to sell directly as industrial salt, and further salt separation and purification are required. Existing salt separation technologies mostly adopt nanofiltration + evaporation and crystallization, but for desulfurization wastewater with high chlorine and high sulfate content, the deep treatment of the concentrate and permeate after nanofiltration still has problems such as high energy consumption and unstable purity of crystallized salt.

[0005] Therefore, developing a process technology that can achieve graded resource recovery of all components of desulfurization wastewater, including magnesium, calcium, sulfate, and chloride ions, while producing high-purity industrial salt, has significant engineering application value and environmental and economic benefits. Summary of the Invention

[0006] This disclosure aims to at least solve one of the technical problems existing in the prior art, and to provide a system and method for graded and desalinated resource utilization of desulfurization wastewater.

[0007] A first aspect of this disclosure provides a system for the graded and desalinated resource recovery of desulfurization wastewater, the system comprising: The pretreatment unit is used to perform chemical precipitation and solid-liquid separation on the desulfurization wastewater discharged from the desulfurization wastewater system, forming a solution rich in Na. + and Cl - The waste liquid and the mixed precipitate containing Mg(OH)2 and CaSO4; The precipitation and classification utilization unit is connected to the precipitate output end of the pretreatment unit and is used to receive the mixed precipitate and sequentially separate Mg(OH)2 precipitate and CaSO4 precipitate. The membrane concentration and crystallization unit is connected to the waste liquid output end of the pretreatment unit to receive the waste liquid and sequentially pass it through nanofiltration, deep concentration and evaporation crystallization processes to produce Na2SO4 and NaCl industrial salts.

[0008] Optionally, the preprocessing unit includes: The chemical precipitation module is used to add precipitant to desulfurization wastewater, so that magnesium ions and calcium ions in the wastewater are converted into Mg(OH)2 and CaSO4 precipitates, respectively. The solid-liquid separation module, connected to the outlet of the chemical precipitation module, is used to perform solid-liquid separation on the mixture after chemical precipitation, obtaining a mixed precipitate containing Mg(OH)2 and CaSO4, as well as a precipitate rich in Na after most of the magnesium and calcium ions have been removed. + and Cl - Waste liquid.

[0009] Optionally, the precipitation classification and utilization unit includes: The first separation module is connected to the precipitate output end of the solid-liquid separation module in the pretreatment unit. It is used to preferentially separate the Mg(OH)2 precipitate from the mixed precipitate by utilizing the difference in solubility or density between Mg(OH)2 and CaSO4, and then transport it to the high-strength ceramsite preparation section. The second separation module is connected to the outlet of the first separation module and is used to separate the remaining CaSO4 precipitate and transport it to the roadbed material preparation section.

[0010] Optionally, the membrane concentration and crystallization unit includes: The nanofiltration module, whose input is connected to the waste liquid output of the pretreatment unit, is used to separate monovalent and divalent ions in the waste liquid, producing Na+ enriched ions. + and Cl - Nanofiltration permeate, and SO4 enrichment 2- Nanofiltration concentrate; A deep concentration module is connected to the permeate output end of the nanofiltration module and is used to deeply concentrate the nanofiltration permeate using high-rate reverse osmosis (HFRO) and / or electrodialysis (ED) to obtain a high-concentration NaCl solution. An evaporation crystallization module is connected to the concentrate output end of the nanofiltration module and the solution output end of the deep concentration module, respectively, and is used to evaporate and crystallize the nanofiltration concentrate to produce Na2SO4 industrial salt, and to evaporate and crystallize the high-concentration NaCl solution to produce NaCl industrial salt.

[0011] Optionally, the deep concentration module includes a high-rate reverse osmosis unit and an electrodialysis unit arranged in series or parallel; wherein, The high-rate reverse osmosis device is used to concentrate the nanofiltration permeate to a first preset concentration of NaCl solution, and the electrodialysis device is used to further concentrate the NaCl solution to a second preset concentration.

[0012] Optionally, the system further includes: An online water quality monitoring unit is installed at the inlet and outlet of the pretreatment unit and the membrane concentration and crystallization unit to acquire key water quality parameters of desulfurization wastewater, intermediate products and final products in real time. The key water quality parameters include conductivity, hardness, ion concentration and turbidity. The data fusion control unit is connected to the online water quality monitoring unit, the pretreatment unit, the sedimentation and grading utilization unit, and the membrane concentration and crystallization unit, respectively. It is used to dynamically adjust the amount of precipitant added to the pretreatment unit, the operating pressure, operating cycle, and evaporation temperature of the membrane concentration and crystallization unit according to the key water quality parameters, so as to optimize the salt separation efficiency and product purity.

[0013] Optionally, the data fusion control unit integrates a salt separation resource utilization process model, which is configured as follows: Using the key water quality parameters as input features, and the preset yields and purity of Mg(OH)2 precipitate, CaSO4 precipitate, Na2SO4 and NaCl industrial salt as constraints, the optimal dosage of reagents in the pretreatment unit, the optimal operating pressure of the nanofiltration module, and the optimal evaporation temperature of the evaporation crystallization module are calculated by an optimization algorithm.

[0014] Optionally, the data fusion control unit integrates a salt fractionation resource recovery process model, which is further configured as follows: Based on the signals fed back by the online pH meter and magnesium ion sensor, the dosage of alkaline precipitant is dynamically adjusted using a proportional-integral-differential algorithm to maintain the pH value within the target range of 10.5 to 11.5; based on the real-time concentration read by the online sulfate sensor, the dosage of calcium source precipitant is dynamically adjusted according to the stoichiometric ratio to ensure that the sulfate concentration in the effluent is below the preset threshold.

[0015] Optionally, the data fusion control unit integrates a salt separation resource utilization process model, which is further configured as follows: The system collects real-time data on the influent flow rate, pre-membrane pressure, and temperature parameters of the nanofiltration module. When the permeate flow rate decreases, temperature compensation is performed first. If the decrease is not caused by temperature factors, the operating frequency of the high-pressure pump is gradually increased in increments not exceeding 2% of the current frequency. The system continuously calculates the transmembrane pressure difference. When the transmembrane pressure difference increases by more than 35% compared to the initial operating value and persists for more than 30 minutes, it is determined that physical flushing is required. The permeate valve is closed, and the concentrate discharge valve is opened to flush the membrane surface at a high flow rate. If the transmembrane pressure difference decreases by less than 10% after physical flushing, it is determined that irreversible fouling occurs. A chemical cleaning warning signal is sent to the operation and maintenance system, and the permeate diversion valve is automatically adjusted to return the inferior permeate to the pretreatment unit.

[0016] Optionally, the data fusion control unit integrates a salt fractionation resource recovery process model, which is further configured as follows: Based on the concentrate concentration feedback from the online conductivity meter and chloride ion sensor, the opening of the reflux valve of the high-ratio reverse osmosis unit is dynamically adjusted to increase the net pressure on the membrane surface from 8 MPa to 10 MPa. When the NaCl mass concentration of the concentrate reaches 12%, the electrodialysis unit is automatically started in series with it, and the DC voltage of the electrodialysis unit is adjusted to stabilize the NaCl mass concentration of the final effluent within the range of 18% to 25%.

[0017] Optionally, the data fusion control unit integrates a salt fractionation resource recovery process model, which is further configured as follows: The main regulating parameters are the steam inlet pressure of the first effect and the vacuum degree of the last effect. By adjusting the opening of the drive steam valve and the pumping speed of the vacuum pump in the last effect, the temperature difference between the effects of the multi-effect evaporator is maintained between 8°C and 12°C. When the density meter reading in the crystallizer reaches the target value and the liquid level reaches the high limit, the discharge pump is turned on to discharge the concentrate. After the density drops back to the lower limit, the discharge valve is closed. Based on the online analysis results of the purity of the product salt, the evaporation temperature is gradually adjusted in a range not exceeding ±5°C to keep the purity of the produced industrial salt stable at above 98%.

[0018] A second aspect of this disclosure provides a method for graded and desalinated resource recovery of desulfurization wastewater based on the above-mentioned system, the method comprising: Chemical precipitation and solid-liquid separation are performed on the desulfurization wastewater discharged from the desulfurization wastewater system to form a solution rich in Na. + and Cl - The waste liquid and mixed precipitate containing Mg(OH)2 and CaSO4; The Mg(OH)2 precipitate and CaSO4 precipitate separated from the mixed precipitate are used as raw materials for the preparation of high-strength ceramsite and roadbed materials, respectively, and are then graded and utilized. The waste liquid is subjected to nanofiltration, deep concentration and evaporation crystallization in sequence to produce Na2SO4 and NaCl industrial salts respectively.

[0019] Optionally, the chemical precipitation and solid-liquid separation of the desulfurization wastewater includes: Add an alkaline precipitant to the desulfurization wastewater and adjust the pH value to 10.5-11.5 to precipitate magnesium ions in the form of Mg(OH)2. Add calcium source precipitant to desulfurization wastewater to precipitate sulfate ions in the form of CaSO4; The precipitated mixture was subjected to solid-liquid separation by pressure filtration or centrifugation to obtain a mixed precipitate containing Mg(OH)2 and CaSO4, as well as a precipitate rich in Na. + and Cl - Waste liquid.

[0020] Optionally, the step of sequentially subjecting the waste liquid to nanofiltration, deep concentration, and evaporation crystallization includes: The operating pressure of the nanofiltration process is controlled at 2.0-4.0 MPa to allow monovalent Na+ ions to pass through. + and Cl - Through nanofiltration membranes, divalent ions SO42- 2- It is trapped, forming a permeate rich in NaCl and a concentrate rich in Na2SO4. The NaCl-rich permeate was concentrated to a NaCl mass concentration of 8%-12% using a high-rate reverse osmosis process, and then further concentrated to a NaCl mass concentration of 18%-25% using an electrodialysis process. The Na2SO4-rich concentrate is evaporated and crystallized to produce anhydrous Na2SO4 industrial salt. The highly concentrated NaCl solution is evaporated and crystallized to produce high-purity NaCl industrial salt.

[0021] The present disclosure presents a graded and desalinated resource recovery system and method for desulfurization wastewater, which has the following advantages over existing technologies: First, this disclosure combines graded sedimentation with graded utilization to sequentially separate the mixed precipitate generated from traditional desulfurization wastewater pretreatment into Mg(OH)2 and CaSO4, which are then used to prepare high-strength ceramsite and roadbed materials, respectively. This achieves high-value utilization of solid waste and avoids secondary pollution and resource waste caused by landfilling.

[0022] Second, this disclosure adopts a membrane-based salt separation route of nanofiltration + deep concentration + evaporation crystallization. Targeting the characteristics of high chlorine and high sulfate in desulfurization wastewater, nanofiltration achieves efficient separation of monovalent and divalent ions. Then, deep concentration is achieved through a series of high-rate reverse osmosis and electrodialysis, which significantly reduces the energy consumption of evaporation crystallization. At the same time, high-purity Na2SO4 and NaCl industrial salts are obtained, meeting industrial-grade product standards.

[0023] Third, by setting up an online water quality monitoring unit and a data fusion control unit, and combining them with a process optimization model, this disclosure can dynamically adjust the dosage of reagents and operating parameters according to the fluctuations in the desulfurization wastewater quality, ensuring the long-term stable operation of the system and producing resource-based products that meet the requirements, thus having significant environmental and economic benefits. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the desulfurization wastewater graded and desalinated resource recovery system of Embodiment 1 of this disclosure; Figure 2 This is a flowchart of the desulfurization wastewater classification and desalination resource utilization method of Embodiment 3 of this disclosure. Detailed Implementation

[0025] To enable those skilled in the art to better understand the technical solutions of this disclosure, the disclosure will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] Example 1 like Figure 1 As shown in the figure, this embodiment provides a desulfurization wastewater classification and salt resource utilization system, which includes: a pretreatment unit 100, a sedimentation and classification utilization unit 200, a membrane concentration and crystallization unit 300, an online water quality monitoring unit 400, and a data fusion control unit 500.

[0027] Furthermore, such as Figure 1 As shown, the pretreatment unit 100 includes a chemical precipitation module 110 and a solid-liquid separation module 120. The chemical precipitation module 110 is a reaction vessel equipped with a stirrer, its inlet connected to the outlet of the desulfurization wastewater pipeline of the desulfurization wastewater system. The chemical precipitation module 110 is equipped with a pH meter and a dosing device for adding alkaline precipitants (such as sodium hydroxide or lime slurry) and calcium source precipitants (such as calcium chloride or lime). Based on the alkaline precipitant and adjusting the pH to 10.5-11.5, magnesium and calcium ions in the wastewater are converted into Mg(OH)2 precipitate, and sulfate ions are precipitated into CaSO4 precipitate based on the calcium source precipitant. Next, the solid-liquid separation module 120 uses a plate and frame filter press, its inlet connected to the outlet of the chemical precipitation module 110, for solid-liquid separation of the precipitated mixed slurry, obtaining mixed precipitate (mainly composed of Mg(OH)2 and CaSO4) and waste liquid (rich in Na). +Cl - (and a small amount of residual ions).

[0028] It should be noted that the dosing device in this embodiment can be a dosing pump.

[0029] Furthermore, such as Figure 1 As shown, the sedimentation and fractionation utilization unit 200 includes a first separation module 210 and a second separation module 220. The inlet of the first separation module 210 is connected to the sediment output end of the solid-liquid separation module, and this first separation module is a hydrocyclone, utilizing the density difference between Mg(OH)₂ and CaSO₄ (Mg(OH)₂ density is approximately 2.36 g / cm³). 3 The density of CaSO4 is approximately 2.96 g / cm³. 3 Under hydraulic action, the lighter Mg(OH)2 precipitate is separated from the top overflow and sent to the high-strength ceramsite preparation section. Simultaneously, the underflow from the first separation module 210 is a slurry enriched with CaSO4. Next, the inlet of the second separation module 220 is connected to the outlet of the first separation module, and this second separation module is a centrifuge used to further dewater the underflow slurry to obtain CaSO4 precipitate, which is then transported to the roadbed material preparation section.

[0030] This embodiment adds an independent precipitation and classification utilization unit, which performs classification and separation based on the differences in solubility and density of Mg(OH)2 and CaSO4 precipitates, and uses the two products in building materials fields such as high-strength ceramsite and roadbed materials, to realize high-value cross-industry utilization of solid waste.

[0031] Furthermore, such as Figure 1 As shown, the membrane concentration and crystallization unit 300 includes a nanofiltration module 310, a deep concentration module 320, and an evaporation crystallization module 330. The inlet of the nanofiltration module 310 is connected to the waste liquid output of the solid-liquid separation module 120, and the permeate outlet of the nanofiltration module 310 is connected to the deep concentration module 320. This nanofiltration module uses a spiral wound nanofiltration membrane assembly and operates at a pressure of 2.0-4.0 MPa, preferably 2.5 MPa. Under this pressure condition, Na... + and Cl - SO4 passes through a nanofiltration membrane. 2-The permeate is trapped, forming a NaCl-rich permeate and a Na2SO4-rich concentrate. Next, the inlet of the deep concentration module 320 is connected to the permeate output of the nanofiltration module 310, used to deeply concentrate the nanofiltration permeate to obtain a high-concentration NaCl solution. Furthermore, the evaporation and crystallization module 330 is connected to both the concentrate output of the nanofiltration module 310 and the solution output of the deep concentration module 320. This evaporation and crystallization module 330 is used to evaporate and crystallize the nanofiltration concentrate to produce Na2SO4 industrial salt, and to evaporate and crystallize the high-concentration NaCl solution to produce NaCl industrial salt.

[0032] In some preferred embodiments, the deep concentration module 320 of this embodiment further includes a high-rate reverse osmosis unit (HFRO, operating pressure 8-10 MPa) and an electrodialysis unit (ED) connected in series. The high-rate reverse osmosis unit is used to concentrate the nanofiltration permeate to a first preset concentration of NaCl solution, and the electrodialysis unit is used to further concentrate the NaCl solution to a second preset concentration.

[0033] It should be noted that the first preset concentration can be 8%-12%, and the second preset concentration is 18%-25%. That is to say, the NaCl solution needs to be concentrated to a mass concentration of more than 20%.

[0034] In some preferred embodiments, the evaporation crystallization module includes a sodium sulfate evaporator and a sodium chloride evaporator, which are used to receive nanofiltration concentrate and a deeply concentrated NaCl solution, respectively, and produce anhydrous Na2SO4 and NaCl industrial salts through multi-effect evaporation or mechanical vapor recompression evaporation.

[0035] Furthermore, such as Figure 1 As shown, the online water quality monitoring unit 400 is connected to the inlet and / or outlet of the pretreatment unit 100 and the membrane concentration and crystallization unit 300, and is used to obtain real-time data on desulfurization wastewater and intermediate products (rich in Na). + and Cl - The key water quality parameters of the waste liquid and mixed precipitates containing Mg(OH)2 and CaSO4, and the final products (Mg(OH)2 precipitate, CaSO4 precipitate, Na2SO4 and NaCl industrial salt) include pH, conductivity, suspended solids concentration, hardness, total dissolved solids (TDS), ion concentration, chemical oxygen demand (COD) and turbidity.

[0036] For example, the above-mentioned online water quality monitoring unit is connected to the inlet of the chemical precipitation module, the outlet of the solid-liquid separation module, the inlet of the nanofiltration module, and the outlet of the evaporation crystallization module.

[0037] It should be noted that the online water quality monitoring unit in this embodiment includes an online conductivity meter, a hardness meter, and an ion-selective electrode installed at locations such as the desulfurization wastewater inlet, the pretreatment unit outlet, and the nanofiltration permeate outlet, to collect water quality data in real time.

[0038] Furthermore, such as Figure 1 As shown, the data fusion control unit 500 is connected to the online water quality monitoring unit 400, the pretreatment unit 100, the sedimentation and grading utilization unit 200, and the membrane concentration and crystallization unit 300, respectively. It is used to dynamically adjust the reagent dosage, operating pressure, and membrane cleaning triggering conditions of the pretreatment unit 100, the sedimentation and grading utilization unit 200, and the membrane concentration and crystallization unit 300, as well as the evaporation temperature and concentrate discharge cycle of the evaporation and crystallization unit, according to the key water quality parameters.

[0039] It should be noted that the data fusion control unit in this embodiment can be an industrial control computer, which is connected to the dosing pump, high-pressure pump, electric valve and other actuators in each sensor and chemical precipitation module.

[0040] It should also be noted that the control unit embeds a salt resource utilization process model. This model is a neural network trained based on historical operating data. In the construction of the neural network, the key water quality parameters are used as input features, and the preset yields and purities of Mg(OH)2 precipitate, CaSO4 precipitate, Na2SO4, and NaCl industrial salts are used as constraints. The optimal dosage of reagents in the pretreatment unit, the optimal operating pressure of the nanofiltration module, and the optimal evaporation temperature of the evaporation crystallization module are calculated through an optimization algorithm. Based on the trained neural network, using real-time key water quality parameters as input, it can directly output the optimal precipitant dosage, nanofiltration operating pressure, and evaporation temperature, and execute these parameters through the PLC to control the pretreatment unit, the precipitation classification and utilization unit, and the membrane concentration and crystallization unit, respectively. The specific control process of the data fusion control unit for the other units is described in detail below.

[0041] 1. Adjustment process of the preprocessing unit For the chemical precipitation module 110, the data fusion control unit 500 dynamically adjusts the frequency of the alkaline precipitant dosing pump based on signals from the online pH meter and magnesium ion sensor using a proportional-integral-derivative algorithm. Specifically, when the pH value is below the set lower limit of 10.5, the control unit gradually increases the dosing pump frequency to raise the pH value back to the target range of 11.0 ± 0.2. When the magnesium ion concentration increases due to fluctuations in the influent water quality, the built-in process model calculates the required additional alkali amount using a feedforward method and adds it to the PID output to ensure that the magnesium ion concentration in the effluent remains consistently below 50 mg / L.

[0042] For the addition of the calcium source precipitant, the data fusion control unit 500, based on the real-time concentration read by the online sulfate sensor, calculates the precipitant according to the stoichiometric ratio of Ca. 2+ :SO4 2- The ratio is 1:1, and an excess coefficient of 1.05 to 1.1 is set to automatically adjust the stroke or frequency of the calcium salt dosing pump. If the sulfate concentration in the effluent is still higher than the threshold, the excess coefficient is gradually increased to 1.2 times until the standard is met.

[0043] The sludge discharge action of the solid-liquid separation module 120 is jointly controlled by a sludge level gauge and an effluent turbidity sensor. When the sludge interface in the sedimentation tank rises to a set high limit, i.e., 80% of the effective height of the tank, the data fusion control unit 500 triggers the sludge discharge valve to open and starts the sludge pump to run for a preset time. When the effluent turbidity sensor detects a sudden increase in turbidity exceeding 10 NTU, it is determined to be a sludge runoff event, and the control unit immediately executes an emergency sludge discharge procedure and simultaneously sends an alarm signal to the decentralized control system.

[0044] 2. Adjustment process of nanofiltration module For the nanofiltration module 310, the data fusion control unit 500 aims to maintain the rated permeate flux by collecting influent flow rate, pre-membrane pressure, and temperature parameters in real time. When the permeate flow rate decreases, the control unit first performs temperature compensation correction. If the decrease is not caused by low temperature, it is determined to be due to membrane fouling or insufficient drive pressure. Subsequently, the operating frequency of the high-pressure pump is gradually increased in increments not exceeding 2% of the current frequency to raise the pre-membrane pressure. If the pre-membrane pressure rises to the rated upper limit of 4.0 MPa and the permeate flow rate still cannot recover, the control unit stops pressurizing and automatically switches to the membrane cleaning judgment logic.

[0045] The data fusion control unit 500 continuously calculates the transmembrane pressure difference, which is the difference between the pressure before and after the membrane. When the transmembrane pressure difference increases by more than 35% compared to the initial operating value and persists for more than 30 minutes, it is determined that physical flushing is required. At this time, the control unit closes the permeate valve and opens the concentrate discharge valve to flush the membrane surface at a high flow rate. If the transmembrane pressure difference decreases by less than 10% after physical flushing, it is further determined to be irreversible fouling. The control unit sends a chemical cleaning warning signal to the operation and maintenance system and automatically adjusts the permeate diversion valve to return the inferior permeate to the pretreatment unit 100 for reprocessing, while reducing the system operating load to avoid damage to the membrane module.

[0046] 3. Adjustment process of the deep concentration module For the high-rate reverse osmosis unit in the deep concentration module 320, the data fusion control unit 500 dynamically adjusts the opening of the high-pressure pump outlet reflux valve based on the concentrate concentration feedback from the online conductivity meter and chloride ion sensor. When the NaCl mass concentration on the high-rate reverse osmosis permeate side increases from 8% to 12%, the control unit gradually closes the reflux valve opening, causing the net pressure on the membrane surface to increase from 8 MPa to 10 MPa, thus overcoming the impact of the increased osmotic pressure.

[0047] When the concentrate concentration reaches 12%, the data fusion control unit 500 automatically determines that the high-rate reverse osmosis device is approaching its operating limit, and then starts the electrodialysis device in series with it, and adjusts the DC voltage of the electrodialysis to control the ion migration rate, so that the NaCl mass concentration of the final effluent is stabilized in the range of 18% to 25%.

[0048] 4. Adjustment process of the evaporation and crystallization unit For the evaporation and crystallization module 330, the data fusion control unit 500 primarily regulates the first-effect inlet steam pressure and the last-effect vacuum degree. By adjusting the opening degree of the drive steam valve and the pumping rate of the last-effect vacuum pump, the control unit maintains the temperature difference between each effect of the multi-effect evaporator between 8°C and 12°C to ensure heat transfer efficiency.

[0049] When the densitometer reading inside the crystallizer reaches the target value of 1.25 g / cm³ 3 When the liquid level reaches the high limit, the data fusion control unit 500 activates the discharge pump to discharge the concentrate. The discharge duration is set to 10 to 30 seconds based on the density decrease rate, until the density drops back to the lower limit of 1.18 g / cm³. 3 Then close the discharge valve.

[0050] The data fusion control unit 500 also fine-tunes the evaporation temperature based on the online analysis results of the product salt purity. When the purity decreases, it is determined that the insufficient supersaturation may lead to excessively fine crystals or co-extrusion of impurities. The control unit gradually increases or decreases the evaporation temperature by no more than ±5°C to optimize the crystallization kinetics and ensure that the purity of the produced industrial salt is stabilized at above 98%.

[0051] 5. Closed-loop control and model optimization All the above adjustments are performed using closed-loop control. The data fusion control unit 500 embeds a process optimization model, which is built based on deep belief networks or digital twin technology. Using historical operating data and real-time water quality parameters as input, it continuously updates the target setpoints of the control parameters. Through this model, the system can adapt to fluctuations in desulfurization wastewater quality and the degradation of equipment performance, achieving long-term stable operation.

[0052] Based on the above structures, the desulfurization wastewater graded and desalinated resource utilization process in this embodiment is as follows: Figure 1 As shown, during system operation in this embodiment, the desulfurization wastewater discharged from the desulfurization wastewater system first enters the chemical precipitation module 110, where alkali is added to adjust the pH to 11.0, magnesium ions precipitate as Mg(OH)2, and an appropriate amount of calcium chloride is added to precipitate sulfate ions as CaSO4. Then, the resulting mixed slurry enters a plate and frame filter press for solid-liquid separation, yielding mixed precipitate and waste liquid. The mixed precipitate enters a hydrocyclone to separate Mg(OH)2 (overflow) and CaSO4 (underflow), while the waste liquid enters a nanofiltration module, forming a NaCl-rich permeate and a Na2SO4-rich concentrate. The permeate (mainly NaCl) is concentrated by HFRO and ED and then evaporated and crystallized to obtain NaCl industrial salt, while the concentrate (mainly Na2SO4) is directly evaporated and crystallized to obtain Na2SO4 industrial salt. Throughout the process, the data fusion control unit dynamically adjusts the operating parameters of the pretreatment unit, the precipitation classification and utilization unit, and the membrane concentration and crystallization unit based on online monitoring data from the online water quality monitoring unit, ensuring that the product salt purity is ≥98%.

[0053] This implementation scheme enables continuous monitoring of desulfurization raw water, pretreatment intermediate liquid, membrane feed / product water / concentrate, crystallization feed / effluent, and the associated water of the final salt production process, allowing for real-time monitoring of water quality at each stage. Based on real-time monitoring data, the system can dynamically and automatically adjust various process operating parameters: for example, it automatically adjusts the dosage of alkaline precipitant and calcium source precipitant according to changes in influent hardness and magnesium and sulfate ion concentrations to ensure precipitation effect; furthermore, it dynamically optimizes the operating pressure of nanofiltration and high-rate reverse osmosis based on membrane influent and effluent conductivity, turbidity, and transmembrane pressure difference, and automatically triggers membrane cleaning procedures based on changes in transmembrane pressure difference to delay membrane fouling; and it matches the optimal evaporation temperature according to the concentrate concentration to ensure crystallization efficiency and salt quality. This system changes the existing technology's reliance on offline manual testing and timed sampling, achieving full-process online monitoring and intelligent closed-loop control.

[0054] Example 2 The difference between this embodiment and Embodiment 1 is that the first separation module 210 of the precipitation classification utilization unit 200 adopts a selective dissolution method. That is, the first separation module is a settling tank. Taking advantage of the characteristic that Mg(OH)2 is easily soluble in acid while CaSO4 is insoluble in dilute acid, dilute hydrochloric acid is slowly added to the mixed precipitate, and the pH is controlled at 6-7, so that Mg(OH)2 dissolves into Mg 2+ The Mg(OH)₂ is introduced into a solution, and then high-purity Mg(OH)₂ is reprecipitated by adding alkali. This method is suitable for applications requiring higher purity of Mg(OH)₂.

[0055] Example 3 This embodiment provides a method for the graded and desalinated resource utilization of desulfurization wastewater based on the above system, such as... Figure 2 As shown, it includes the following steps: S100, graded sedimentation and solid-liquid separation: chemical precipitation and solid-liquid separation are performed on the desulfurization wastewater discharged from the desulfurization wastewater system to form waste liquid rich in Na+ and Cl- and mixed precipitate containing Mg(OH)2 and CaSO4.

[0056] Specifically, an alkaline precipitant is added to the desulfurization wastewater to adjust the pH to 10.5-11.5, causing magnesium ions to precipitate as Mg(OH)₂; then a calcium source precipitant is added to precipitate sulfate ions as CaSO₄. The precipitated mixture is then separated into solid and liquid phases using pressure filtration or centrifugation to obtain a mixed precipitate containing Mg(OH)₂ and CaSO₄, as well as a Na₂-rich precipitate. + and Cl - Waste liquid.

[0057] S200, Precipitation and Classification: Separating Mg(OH)2 precipitate and CaSO4 precipitate from the mixed precipitate.

[0058] Specifically, the mixed precipitate is separated into Mg(OH)2 precipitate and CaSO4 precipitate by hydrocyclone separation or selective dissolution. Mg(OH)2 is transported to the high-strength ceramsite preparation section, and CaSO4 is transported to the roadbed material preparation section.

[0059] In some preferred methods, hydrocyclone separation is employed, utilizing the density difference between Mg(OH)₂ and CaSO₄ (Mg(OH)₂ density is approximately 2.36 g / cm³). 3 The density of CaSO4 is approximately 2.96 g / cm³. 3 Under hydraulic action, the lighter Mg(OH)2 precipitate is separated from the top overflow and sent to the high-strength ceramsite preparation section. At the same time, the underflow of the first separation module 210 is a slurry enriched with CaSO4.

[0060] In other preferred methods, a selective dissolution method is employed, utilizing the property that Mg(OH)₂ is readily soluble in acids while CaSO₄ is insoluble in dilute acids. Dilute hydrochloric acid is slowly added to the mixed precipitate, controlling the pH at 6-7, to dissolve Mg(OH)₂ into Mg. 2+ It enters the solution, and then high-purity Mg(OH)2 is reprecipitated by adding alkali solution.

[0061] S300, Membrane Salt Separation and Deep Concentration: The waste liquid is subjected to nanofiltration, deep concentration and evaporation crystallization in sequence to produce Na2SO4 and NaCl industrial salts.

[0062] Specifically, the waste liquid obtained in step S100 is subjected to nanofiltration treatment, with the operating pressure controlled at 2.0-4.0 MPa, to remove monovalent Na+ ions. + and Cl - Through the nanofiltration membrane, divalent ions SO42-2- The solution is retained, forming a NaCl-rich permeate and a Na2SO4-rich concentrate. High-rate reverse osmosis is used to concentrate the NaCl-rich permeate to a NaCl mass concentration of 8%-12%, followed by electrodialysis to a concentration of 18%-25%. The Na2SO4-rich concentrate is then evaporated and crystallized to produce anhydrous Na2SO4 industrial salt. The highly concentrated NaCl solution is then evaporated and crystallized to produce high-purity NaCl industrial salt.

[0063] It should be noted that during the above process, the conductivity, hardness, and ion concentration of each process node are monitored in real time by an online water quality monitoring unit. The data fusion control unit dynamically adjusts the amount of precipitant added in step S100, the operating pressure of the nanofiltration membrane in step S300, and the temperature and residence time of evaporation and crystallization according to the built-in process model, so that the purity of the product always meets the industrial salt standard.

[0064] This disclosure achieves the full-component resource utilization of desulfurization wastewater through the aforementioned system and method, converting elements such as magnesium, calcium, sulfur, sodium, and chlorine in the wastewater into high-value products or industrial raw materials, thus realizing true zero emissions and a circular economy.

[0065] It is understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of this disclosure, and this disclosure is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of this disclosure, and these modifications and improvements are also considered to be within the scope of protection of this disclosure.

Claims

1. A graded and desalinated resource recovery system for desulfurization wastewater, characterized in that, The system includes: The pretreatment unit is used to perform chemical precipitation and solid-liquid separation on the desulfurization wastewater discharged from the desulfurization wastewater system, forming a solution rich in Na. + and Cl - The waste liquid and the mixed precipitate containing Mg(OH)2 and CaSO4; The precipitation and classification utilization unit is connected to the precipitate output end of the pretreatment unit, and is used to receive the mixed precipitate and sequentially separate Mg(OH)2 precipitate and CaSO4 precipitate. The membrane concentration and crystallization unit is connected to the waste liquid output end of the pretreatment unit to receive the waste liquid and sequentially pass it through nanofiltration, deep concentration and evaporation crystallization processes to produce Na2SO4 and NaCl industrial salts.

2. The system according to claim 1, characterized in that, The preprocessing unit includes: The chemical precipitation module is used to add precipitant to desulfurization wastewater, so that magnesium ions and calcium ions in the wastewater are converted into Mg(OH)2 precipitate and CaSO4 precipitate, respectively. A solid-liquid separation module, connected to the outlet of the chemical precipitation module, is used to perform solid-liquid separation on the mixture after chemical precipitation, obtaining a mixed precipitate containing Mg(OH)2 and CaSO4, as well as a precipitate rich in Na. + and Cl - Waste liquid.

3. The system according to claim 1, characterized in that, The precipitation and fractionation utilization unit includes: The first separation module is connected to the precipitate output end of the pretreatment unit. It is used to preferentially separate the Mg(OH)2 precipitate from the mixed precipitate by utilizing the difference in solubility or density between Mg(OH)2 and CaSO4, and then transport it to the high-strength ceramsite preparation section. The second separation module is connected to the outlet of the first separation module and is used to separate the remaining CaSO4 precipitate in the mixed precipitate and transport it to the roadbed material preparation section.

4. The system according to claim 1, characterized in that, The membrane concentration and crystallization unit includes: The nanofiltration module, connected to the waste liquid output of the pretreatment unit, is used to separate monovalent and divalent ions in the waste liquid, producing Na+ enriched ions. + and Cl - Nanofiltration permeate, and SO4 enrichment 2- Nanofiltration concentrate; A deep concentration module is connected to the permeate output end of the nanofiltration module and is used to deeply concentrate the nanofiltration permeate to obtain a high-concentration NaCl solution. An evaporation crystallization module is connected to the concentrate output end of the nanofiltration module and the solution output end of the deep concentration module, respectively, and is used to evaporate and crystallize the nanofiltration concentrate to produce Na2SO4 industrial salt, and to evaporate and crystallize the high-concentration NaCl solution to produce NaCl industrial salt.

5. The system according to claim 4, characterized in that, The deep concentration module includes a high-rate reverse osmosis unit and an electrodialysis unit connected in series or parallel; wherein... The high-rate reverse osmosis device is used to concentrate the nanofiltration permeate to a NaCl solution of a first preset concentration; The electrodialysis device is used to further concentrate the NaCl solution to a second preset concentration.

6. The system according to claim 1, characterized in that, The system also includes: The online water quality monitoring unit is connected to the inlet and outlet of the pretreatment unit and the membrane concentration and crystallization unit, and is used to obtain real-time data on the desulfurization wastewater rich in Na. + and Cl - Key water quality parameters of waste liquid and mixed precipitates containing Mg(OH)2 and CaSO4, Mg(OH)2 precipitate and CaSO4 precipitate and Na2SO4 and NaCl industrial salt; The key water quality parameters include pH, conductivity, suspended solids concentration, hardness, total dissolved solids, ion concentration, chemical oxygen demand, and turbidity. The data fusion control unit is connected to the online water quality monitoring unit, the pretreatment unit, the sedimentation and grading utilization unit, and the membrane concentration and crystallization unit, respectively. It is used to dynamically adjust the amount of precipitant added to the pretreatment unit, the operating pressure and membrane cleaning triggering conditions of the membrane concentration and crystallization unit, and the evaporation temperature and concentrate discharge cycle of the evaporation and crystallization unit according to the key water quality parameters.

7. The system according to claim 6, characterized in that, The data fusion control unit integrates a salt separation resource recovery process model, which is configured as follows: Using the key water quality parameters as input features, and the preset yields and purity of Mg(OH)2 precipitate, CaSO4 precipitate, Na2SO4 and NaCl industrial salt as constraints, the optimal dosage of reagents in the pretreatment unit, the optimal operating pressure and membrane cleaning triggering conditions of the nanofiltration module, and the evaporation temperature and concentrate discharge cycle of the evaporation crystallization unit are calculated by an optimization algorithm.

8. A method for graded and desalinated resource utilization of desulfurization wastewater based on the system described in any one of claims 1 to 7, characterized in that, The method includes: Chemical precipitation and solid-liquid separation are performed on the desulfurization wastewater discharged from the desulfurization wastewater system to form a solution rich in Na. + and Cl - The waste liquid and mixed precipitate containing Mg(OH)2 and CaSO4; The Mg(OH)2 precipitate and CaSO4 precipitate were separated from the mixed precipitate; The waste liquid is subjected to nanofiltration, deep concentration and evaporation crystallization in sequence to produce Na2SO4 and NaCl industrial salts.

9. The method according to claim 8, characterized in that, The process of chemical precipitation and solid-liquid separation of the desulfurization wastewater discharged from the desulfurization wastewater system includes: Add an alkaline precipitant to the desulfurization wastewater discharged from the desulfurization wastewater system to adjust the pH value to 10.5-11.5, so that magnesium ions precipitate in the form of Mg(OH)2. Add calcium source precipitant to desulfurization wastewater to precipitate sulfate ions in the form of CaSO4; The precipitated mixture was subjected to solid-liquid separation by pressure filtration or centrifugation to obtain a mixed precipitate containing Mg(OH)2 and CaSO4, as well as a precipitate rich in Na. + and Cl - Waste liquid.

10. The method according to claim 8, characterized in that, The waste liquid is subjected to nanofiltration, deep concentration, and evaporation crystallization treatment in sequence, including: Under pressure conditions of 2.0-4.0 MPa, Na... + and Cl - SO4 passes through a nanofiltration membrane. 2- It is trapped, forming a permeate rich in NaCl and a concentrate rich in Na2SO4. The NaCl-rich permeate is concentrated to a NaCl mass concentration of 8%-12% using a high-rate reverse osmosis process, and then further concentrated to a NaCl mass concentration of 18%-25% using an electrodialysis process. The Na2SO4-rich concentrate is evaporated and crystallized to produce anhydrous Na2SO4 industrial salt. The concentrated NaCl solution is evaporated and crystallized to produce high-purity NaCl industrial salt.

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