Method and system for treating desulfurization wastewater of power plant

Abstract

The invention relates to a power plant desulfurization wastewater treatment method and system.The treatment method comprises the steps that desulfurization wastewater is mechanically filtered through a bag filter, and pretreated wastewater with the turbidity smaller than or equal to 5 NTU is obtained; adding modified activated carbon or a chelating resin adsorbent into the pretreated wastewater, and adsorbing heavy metal ions; the pretreated wastewater is introduced into a multi-stage membrane separation system for water-salt separation, and strong brine and recyclable fresh water are obtained; introducing the strong brine into a forced circulation evaporation crystallizer for evaporation and concentration to obtain inorganic salt crystals. Through a synergistic process of mechanical filtration, multi-stage membrane separation, evaporative crystallization and heavy metal adsorption, suspended solids, heavy metals and excessive salts in the high-salinity wastewater are efficiently removed, the separation purity and recovery rate of resources such as gypsum and sodium chloride are improved, the energy consumption of evaporative crystallization and the treatment cost are reduced, and the method is suitable for industrial production. The requirements of pollution treatment, cost control and resource recovery are effectively balanced, and the economic bottleneck in the prior art is broken through.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, specifically to a method and system for treating desulfurization wastewater from power plants. Background Technology

[0002] In the flue gas desulfurization process of coal-fired power plants, the limestone-gypsum wet desulfurization process generates a large amount of high-salinity wastewater, characterized by high total dissolved solids concentration, excessive levels of heavy metal ions and sulfates, and frequent fluctuations in water quality. Current mainstream treatment processes face a technical and economic bottleneck in resource recovery: on the one hand, the recoverable resources in the wastewater, such as gypsum, sodium chloride, and sodium sulfate, are difficult to achieve on a large scale due to low separation efficiency and high purification costs; on the other hand, the economic benefits of evaporation and crystallization treatment of high-salinity wastewater cannot cover the treatment costs.

[0003] Existing technologies struggle to balance the demands of pollution control, cost control, and resource recovery in the resource recycling process. Therefore, there is an urgent need to develop a more mature method and system for treating power plant desulfurization wastewater, and to overcome the technical and economic bottlenecks through process innovation. Summary of the Invention

[0004] The purpose of this invention is to provide a method and system for treating desulfurization wastewater from power plants, in order to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, a first aspect of the present invention provides a method for treating desulfurization wastewater from power plants, the method comprising: The desulfurization wastewater was mechanically filtered using a bag filter to obtain pretreated wastewater; the turbidity of the pretreated wastewater was ≤5 NTU. Modified activated carbon or chelating resin adsorbent is added to the pretreated wastewater to adsorb heavy metal ions; the amount of adsorbent used is 1.2-1.5 times the molar amount of the heavy metal ions. The pretreated wastewater is passed into a multi-stage membrane separation system consisting of at least two reverse osmosis membranes for water-salt separation to obtain concentrated brine and reusable fresh water; the total dissolved solids concentration of the concentrated brine and the reusable fresh water is 2-3 times that of the desulfurization wastewater. The concentrated brine is introduced into a forced circulation evaporator crystallizer for evaporation and concentration to obtain inorganic salt crystals.

[0006] Optionally, the pore size of the bag filter is 20-50 μm, and the flow rate of the mechanical filtration is controlled to be 0.5-1.0 m / h.

[0007] Optionally, the total dissolved solids concentration of the fresh water is ≤1000 mg / L.

[0008] Optionally, the heating steam temperature of the forced circulation evaporator crystallizer is controlled at 70-90°C, so that the concentrated brine is evaporated and concentrated at 60-80°C.

[0009] Optionally, the temperature difference between the heating steam and the concentrated brine is controlled at 20-30°C, and the total dissolved solids concentration of the concentrated brine is ≤150000mg / L. Simultaneously, by adding seed crystals and controlling supersaturation, the crystallization and separation of inorganic salts with a purity ≥95% is achieved. When the purity of inorganic salts is detected to be ≥98%, the crystal slurry discharge program is started, and crystal grading is achieved through a hydrocyclone. The evaporation rate during the evaporation and concentration process satisfies: ; In the formula, This is the temperature influence coefficient. This is the salt concentration inhibition coefficient. To address the temperature difference between the heating steam and the concentrated brine, This represents the total dissolved solids concentration in concentrated brine.

[0010] Optionally, the membrane flux calculation of the multi-stage membrane separation system follows the fluid transport equation: ; In the formula, For membrane flux, The water permeability coefficient of the membrane module, The operating pressure difference across the membrane, This represents the osmotic pressure difference. The multi-stage membrane separation system adopts a two-stage structure. The operating pressure of the first-stage RO membrane is 1.0-1.2 MPa, and the operating pressure of the second-stage RO membrane is dynamically adjusted based on the osmotic pressure of the first-stage concentrate, satisfying a pressure recursion relationship: ; In the formula, For the first Membrane operating pressure, This is the pressure compensation coefficient. For the first The osmotic pressure difference between the feed water side and the concentrate side.

[0011] Optionally, the mechanical filtration includes two stages of filtration: the first stage uses a bag filter with a pore size of 50 μm for coarse filtration to remove large particulate impurities, and the second stage uses a bag filter with a pore size of 20 μm for fine filtration to remove colloids and fine particles.

[0012] Optionally, the bag filter is equipped with a backwashing device and a differential pressure sensor. When the differential pressure sensor detects a pressure drop ≥0.1MPa, the backwashing device is activated, and the backwashing water flow rate is 10%-15% of the treatment capacity. The treatment capacity is the flow rate of desulfurized wastewater processed per unit time when the bag filter is operating normally.

[0013] Optionally, when adding the modified activated carbon or chelating resin adsorbent: under weakly alkaline conditions of pH=6-8, the modified activated carbon or chelating resin adsorbent is mixed with the pretreated wastewater in a stirred reaction tank. The adsorption time is controlled by a kinetic equation, and the change rate of heavy metal concentration is detected in real time. When the change rate of heavy metal concentration is less than 5% for two consecutive tests, the adsorption reaction is determined to have reached equilibrium, and the stirring of the modified activated carbon or chelating resin adsorbent and the pretreated wastewater is stopped. The dynamic equation is: ; In the formula, for Adsorption amount at any time To balance the adsorption amount, is the adsorption rate constant.

[0014] A second aspect of the present invention provides a treatment system for desulfurization wastewater from power plants, the system applying the treatment method provided in the first aspect of the present invention, the system comprising: The mechanical filtration module is used to mechanically filter desulfurization wastewater using a bag filter with a pore size of 20-50μm. The multi-stage membrane separation system module is used to pass mechanically filtered desulfurization wastewater into a separation system consisting of at least two stages of reverse osmosis membranes. Water and salt separation is achieved through gradient pressure drive, generating concentrated brine with a total dissolved solids concentration of 2-3 times that of the desulfurization wastewater and reusable freshwater. The evaporation and concentration module is used to introduce concentrated brine into the forced circulation evaporation crystallizer and control the heating steam temperature to 70-90℃, so that the concentrated brine is evaporated and concentrated at 60-80℃. The dosing module is used to add modified activated carbon or chelating resin adsorbent to the desulfurization wastewater after mechanical filtration.

[0015] Optionally, the mechanical filtration module specifically includes: A mixing unit is used to mix the modified activated carbon or chelating resin adsorbent with pretreated wastewater in a stirred reaction tank under weakly alkaline conditions of pH=6-8. The first control unit is used to control the adsorption time through a kinetic equation; The detection unit is used to detect the rate of change in heavy metal concentration in real time. The determination unit is used to determine that the adsorption reaction has reached equilibrium when the change rate of heavy metal concentration is less than 5% in two consecutive tests, and to stop the stirring of the modified activated carbon or chelating resin adsorbent with the pretreated wastewater.

[0016] Optionally, the evaporation and concentration module specifically includes: The second control unit is used to achieve high-purity inorganic salt crystallization by controlling the temperature difference between the heating steam and the concentrated brine and the total dissolved solids concentration of the concentrated brine. The crystal slurry discharge program unit is used to start the crystal slurry discharge program when the purity of inorganic salt is detected to be ≥98%, and to achieve crystal classification through a hydrocyclone.

[0017] Through the above technical solutions, the power plant desulfurization wastewater treatment method and system provided by the present invention, through the synergistic process of mechanical filtration, multi-stage membrane separation, evaporation crystallization and heavy metal adsorption, efficiently removes suspended solids, heavy metals and excess salt in high-salt wastewater, improves the separation purity and recovery rate of resources such as gypsum and sodium chloride, reduces evaporation crystallization energy consumption and treatment costs, effectively balances the needs of pollution control, cost control and resource recovery, breaks through the economic bottleneck of existing technologies, and achieves the standard treatment and resource utilization of desulfurization wastewater.

[0018] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0019] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings: Figure 1 This is the main flow chart of the power plant desulfurization wastewater treatment method of the present invention; Figure 2 This is a flowchart of the process of evaporating and concentrating concentrated brine at 60-80℃ in the treatment method of power plant desulfurization wastewater of the present invention; Figure 3 This is a flowchart of the process of adding modified activated carbon or chelating resin adsorbent to the mechanically filtered desulfurization wastewater in the power plant desulfurization wastewater treatment method of the present invention. Figure 4 This is the main structural diagram of the power plant desulfurization wastewater treatment system of the present invention; Figure 5 This is a structural block diagram of the mechanical filtration module in the power plant desulfurization wastewater treatment system of the present invention; Figure 6 This is a structural block diagram of the evaporation and concentration module in the power plant desulfurization wastewater treatment system of the present invention. Detailed Implementation

[0020] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0021] The first aspect of this invention provides a method for treating desulfurization wastewater from power plants, such as... Figure 1 As shown, the processing method includes: Step S100: The desulfurization wastewater is mechanically filtered using a bag filter with a pore size of 20-50 μm. The flow rate of the mechanical filtration is controlled at 0.5-1.0 m / h to remove suspended solids with a particle size greater than 50 μm, resulting in pretreated wastewater. The turbidity of the pretreated wastewater is ≤5 NTU. Step S200: Modified activated carbon or chelating resin adsorbent is added to the pretreated wastewater to selectively adsorb heavy metal ions based on the principle of ion exchange and complexation reaction. The amount of adsorbent used is 1.2-1.5 times the molar amount of the heavy metal ions. Step S300: The pretreated wastewater is fed into a multi-stage membrane separation system consisting of at least two reverse osmosis membranes for water-salt separation. Water-salt separation is achieved by gradient pressure drive to obtain concentrated brine and reusable freshwater. The total dissolved solids concentration of the concentrated brine and the reusable freshwater is 2-3 times that of the desulfurization wastewater. The total dissolved solids concentration of the freshwater is ≤1000mg / L. Step S400: The concentrated brine is introduced into a forced circulation evaporator crystallizer for evaporation and concentration. The heating steam temperature is controlled at 70-90℃, and the concentrated brine is evaporated and concentrated at 60-80℃. Through the addition of seed crystals and control of supersaturation, inorganic salt crystallization and separation with a purity of ≥95% is achieved.

[0022] This invention is based on the pretreatment approach of traditional water treatment, employing a 20-50μm bag filter and controlling the flow rate at 0.5-1.0m / h to remove suspended solids with a particle size >50μm. This avoids clogging of subsequent reverse osmosis membrane modules by suspended solids, reduces the risk of membrane fouling, ensures long-term stable operation of the membrane system, and controls turbidity to ≤5NTU, providing qualified feed water quality for membrane separation. Highly efficient water-salt separation is achieved through gradient pressure driven by at least two stages of reverse osmosis membranes. Addressing the issue of insufficient desalination rate in high-salt wastewater treatment with single-stage reverse osmosis, the two-stage design can concentrate the total dissolved solids (TDS) of the concentrated brine to 2-3 times that of desulfurization wastewater, while producing reusable freshwater with TDS ≤1000mg / L, meeting wastewater discharge standards and achieving water resource recycling. To address the high salt content of the concentrated brine, a forced circulation evaporator crystallizer is used, controlling the heating steam temperature at 70-90℃, allowing the wastewater to evaporate at 60-80℃. The choice of this temperature range stems from a consideration of balancing energy consumption and crystallization efficiency: lower temperatures reduce heat consumption while avoiding salt decomposition or equipment corrosion caused by high temperatures. Through seed crystal addition and supersaturation control, the purity of the inorganic salt is ensured to be ≥95%, enabling the recycling of salt resources. Based on the principles of ion exchange and complexation reactions in materials chemistry, this study targets Hg in wastewater... 2+ Cd 2+ Pb 2+ For heavy metal ions, modified activated carbon or chelating resin is selected as the adsorbent. The amount of adsorbent added is 1.2-1.5 times the molar amount of heavy metal ions. This is based on experience with over-adsorption in actual engineering, which can compensate for the efficiency loss caused by adsorbent saturation and ensure deep removal of heavy metals.

[0023] According to the present invention, optionally, such as Figure 2 As shown, when adding the modified activated carbon or chelating resin adsorbent: Step S301: Under weakly alkaline conditions of pH=6-8, the adsorbent and pretreated wastewater are mixed in a stirred reaction tank. Step S302: Control the adsorption time using kinetic equations: ; In the formula, for The adsorption capacity is measured in real time by an online metal detector, which monitors and calculates the ion concentration in the desulfurization wastewater. To balance the adsorption capacity, it was determined beforehand through isothermal adsorption experiments. The adsorption rate constant is denoted by . Step S303: Real-time detection of the rate of change in heavy metal concentration; Step S304: When the change rate of heavy metal concentration is less than 5% in two consecutive tests, it is determined that the adsorption reaction has reached equilibrium, and the stirring of the modified activated carbon or chelating resin adsorbent with the pretreated wastewater is stopped.

[0024] It should be understood that most heavy metal ions readily form hydroxide precipitates under weakly alkaline conditions, which synergistically enhance adsorption efficiency through ion exchange and complexation reactions with the adsorbent. If the pH is too high (>8), precipitates such as Mg(OH)2 may form, covering the active sites of the adsorbent. Conversely, a pH that is too low (<6) will inhibit the complexation reaction. Therefore, a weakly alkaline condition with a pH of 6-8 is the optimal choice for balancing reaction efficiency and avoiding interference. The stirred reaction tank is designed based on the principle of mass transfer enhancement: stirring ensures sufficient contact between the adsorbent and wastewater, reducing mass transfer resistance, accelerating the diffusion of heavy metal ions to the adsorbent surface, and increasing the adsorption rate. The kinetic equation is applied to determine the concentration change rate. When the heavy metal concentration change rate is less than 5% after two consecutive measurements, the reaction is considered balanced, avoiding reagent waste due to over-adsorption while ensuring complete adsorption. By precisely controlling the adsorption conditions and endpoint, the effectiveness of adsorbent dosing is ensured, reducing adsorbent consumption costs.

[0025] According to the present invention, optionally, such as Figure 3 As shown, when the concentrated brine is evaporated and concentrated at 60-80℃: Step S401: By controlling the temperature difference between the heating steam and the concentrated brine to be 20-30℃, and the total dissolved solids concentration of the concentrated brine to be ≤150000mg / L, high-purity inorganic salt, i.e., sodium chloride crystallization, is achieved. The evaporation rate satisfies: ; In the formula, This is the temperature influence coefficient. This is the salt concentration inhibition coefficient. To address the temperature difference between the heating steam and the desulfurization wastewater, This represents the total dissolved solids concentration in concentrated brine. Step S402: When the sodium chloride purity is detected to be ≥98%, start the crystal slurry discharge program and achieve crystal classification through a hydrocyclone; This invention controls the temperature difference between the heating steam and the desulfurization wastewater to 20-30℃. If the difference is too small, the heat transfer rate is low, resulting in insufficient evaporation efficiency; if it is too large, local overheating causes rapid precipitation of salts on the heating surface, forming hard scale that is difficult to remove. An evaporation temperature range of 60-80℃ is suitable for utilizing low-grade waste heat from power plants while avoiding abnormal fluctuations in salt solubility at high temperatures, ensuring a stable crystallization process. For high-purity sodium chloride crystallization: when the TDS is too high, sulfate co-precipitation is likely, reducing product purity; by adjusting the temperature influence coefficient and salt concentration inhibition coefficient, the evaporation rate can be precisely controlled, avoiding impurity encapsulation caused by a sudden increase in supersaturation. When the sodium chloride purity is ≥98%, the crystal slurry discharge procedure is initiated. Hydrocyclone classification separates crystals of different particle sizes, ensuring uniform product particle size, reducing energy consumption and scaling risk during evaporation and crystallization, and improving the economics of resource recovery.

[0026] According to the present invention, optionally, the membrane flux calculation of the multi-stage membrane separation system follows the fluid transport equation: ; In the formula, For membrane flux, The water permeability coefficient of the membrane module, The operating pressure difference across the membrane, This represents the osmotic pressure difference. The multi-stage membrane separation system adopts a two-stage structure. The operating pressure of the first-stage RO membrane is 1.0-1.2 MPa, and the operating pressure of the second-stage RO membrane is dynamically adjusted based on the osmotic pressure of the first-stage concentrate, satisfying a pressure recursion relationship: ; In the formula, For the first The membrane operating pressure is collected in real time by a pressure sensor. The pressure compensation factor is determined by the salt rejection rate of the upstream membrane and the degree of fouling of the membrane element. For the first The osmotic pressure difference between the feed water side and the concentrate side is monitored and calculated in real time using a conductivity meter.

[0027] This invention is based on a segmented concentration technique, employing a two-stage reverse osmosis membrane structure. Traditional single-stage reverse osmosis membranes, when treating high-concentration wastewater, are prone to a sharp drop in membrane flux due to excessively high osmotic pressure. The two-stage structure, however, reduces the feed salt concentration to the secondary membrane through pre-desalination in the first stage, followed by deep concentration in the secondary membrane, alleviating the operating pressure on the single-stage membrane. The first-stage RO membrane's operating pressure setting of 1.0-1.2 MPa is based on a balance between the pressure resistance and desalination efficiency of conventional reverse osmosis membranes: too low a pressure results in insufficient desalination, while too high a pressure accelerates membrane aging. The dynamic pressure adjustment mechanism of the secondary RO membrane is designed to address the characteristic that the osmotic pressure of concentrated brine increases with the concentration factor. It uses a pressure recursion relationship to match osmotic pressure changes in real time, preventing a decrease in permeate rate due to insufficient pressure. The pressure compensation coefficient is determined by the salt rejection rate and fouling level of the preceding membrane, based on the dynamic correction requirements for membrane performance degradation in engineering practice: when membrane fouling worsens or the rejection rate decreases, the compensation coefficient is increased to ensure the effective driving pressure of the secondary membrane. The conductivity meter monitors the osmotic pressure difference in real time, enabling precise pressure regulation, avoiding the lag of manual operation, and improving the membrane system's adaptability to water quality fluctuations.

[0028] According to the present invention, optionally, the mechanical filtration includes two stages of filtration: the first stage uses a bag filter with a pore size of 50 μm for coarse filtration to remove large particulate impurities, and the second stage uses a bag filter with a pore size of 20 μm for fine filtration to remove colloids and fine particles.

[0029] According to the present invention, optionally, the bag filter is equipped with a backwashing device and a differential pressure sensor. When the differential pressure sensor detects a pressure drop ≥0.1MPa, the backwashing device is activated, and the backwashing water flow rate is 10%-15% of the treatment capacity. The treatment capacity is the flow rate of desulfurized wastewater treated per unit time when the bag filter is operating normally.

[0030] The first stage of this invention uses a 50μm pore size bag filter for coarse filtration, primarily removing large-particle impurities such as unreacted limestone particles and gypsum crystals from the desulfurization process. If these impurities enter subsequent systems, they can easily cause pipe blockage or membrane surface scratches. The second stage uses a 20μm pore size bag filter for fine filtration, focusing on colloidal particles and fine particulates. These substances are the main causes of membrane fouling, and fine filtration can significantly reduce the risk of irreversible membrane fouling. The filtration flow rate is controlled at 0.5-1.0 m / h, based on the principle of filtration kinetics: too high a flow rate causes impurities to penetrate the filter media, while too low a flow rate reduces treatment efficiency. This range is the optimal choice balancing filtration effect and treatment capacity. Addressing the common problem of "filter cake buildup" in long-term filtration systems, a backwashing device is installed. When the pressure difference ≥ 0.1 MPa (indicating significant filter media blockage), backwashing is automatically initiated. The backwash water flow rate is 10%-15% of the treatment capacity, effectively removing the filter cake while avoiding water waste.

[0031] A second aspect of the present invention provides a treatment system for desulfurization wastewater from power plants. The system applies the treatment method provided in the first aspect of the present invention. As shown in the figure, the system includes: Mechanical filtration module 100 is used to mechanically filter desulfurization wastewater using a bag filter with a pore size of 20-50μm; The multi-stage membrane separation system module 200 is used to pass mechanically filtered desulfurization wastewater into a separation system consisting of at least two stages of reverse osmosis membranes. Water and salt separation is achieved through gradient pressure drive, generating concentrated brine with a total dissolved solids concentration of 2-3 times that of the desulfurization wastewater and reusable freshwater. The evaporation and concentration module 300 is used to introduce concentrated brine into the forced circulation evaporation crystallizer and control the heating steam temperature to 70-90℃, so that the concentrated brine is evaporated and concentrated at 60-80℃. The dosing module 400 is used to add modified activated carbon or chelating resin adsorbent to desulfurization wastewater after mechanical filtration.

[0032] The mechanical filtration module 100 of this invention uses a bag filter with a pore size of 20-50μm to mechanically filter desulfurization wastewater. The multi-stage membrane separation system module 200 passes the mechanically filtered desulfurization wastewater into a multi-stage membrane separation system composed of at least two stages of reverse osmosis membranes. Water and salt separation is achieved through gradient pressure drive, generating concentrated brine with a total dissolved solids concentration of 2-3 times that of the desulfurization wastewater and reusable fresh water. The concentrated brine is introduced into a forced circulation evaporation crystallizer. The evaporation concentration module 300 controls the heating steam temperature to 70-90℃, so that the concentrated brine is evaporated and concentrated at 60-80℃. The addition module 400 adds modified activated carbon or chelating resin adsorbent to the mechanically filtered desulfurization wastewater.

[0033] According to the present invention, optionally, such as Figure 5 As shown, the mechanical filtration module 100 specifically includes: Mixing unit 101 is used to mix the modified activated carbon or chelating resin adsorbent with the pretreated wastewater in a stirred reaction tank under weakly alkaline conditions of pH=6-8. The first control unit 102 is used to control the adsorption time through a kinetic equation; Detection unit 103 is used to detect the rate of change of heavy metal concentration in real time; The determination unit 104 is used to determine that the adsorption reaction has reached equilibrium when the change rate of heavy metal concentration is less than 5% in two consecutive tests, and to stop the stirring of the modified activated carbon or chelating resin adsorbent with the pretreated wastewater.

[0034] Under weakly alkaline conditions of pH 6-8, the mixing unit 101 controls the mixing of the adsorbent and desulfurization wastewater in a stirred reaction tank. The first control unit 102 controls the adsorption time through a kinetic equation. The detection unit 103 detects the change rate of heavy metal concentration in real time. When the change rate of heavy metal concentration is less than 5% for two consecutive detections, the judgment unit 104 determines that the adsorption reaction has reached equilibrium and stops the stirring of the adsorbent and the pretreated wastewater.

[0035] According to the present invention, optionally, such as Figure 6 As shown, the evaporation and concentration module 300 specifically includes: The second control unit 301 is used to achieve high-purity inorganic salt crystallization by controlling the temperature difference between the heating steam and the concentrated brine and the total dissolved solids concentration of the concentrated brine. The crystal slurry discharge program unit 302 is used to start the crystal slurry discharge program when the purity of inorganic salt is detected to be ≥98%, and to achieve crystal classification through a hydrocyclone.

[0036] The second control unit 301 of the present invention achieves high-purity sodium chloride crystallization by controlling the temperature difference between the heating steam and the concentrated brine and the total dissolved solids concentration of the concentrated brine. When the sodium chloride purity is detected to be ≥98%, the crystal slurry discharge program unit 302 starts the crystal slurry discharge program and achieves crystal grading through a hydrocyclone.

[0037] This invention provides a method and system for treating desulfurization wastewater from power plants. Based on traditional water treatment pretreatment concepts, it employs a 20-50μm bag filter, controlling the flow rate at 0.5-1.0 m / h to remove suspended solids with a particle size >50μm. This avoids clogging of subsequent reverse osmosis membrane modules by suspended solids, reduces the risk of membrane fouling, ensures long-term stable operation of the membrane system, and controls turbidity to ≤5 NTU, providing qualified feed water quality for membrane separation. Highly efficient water-salt separation is achieved through gradient pressure drive of at least two stages of reverse osmosis membranes. Addressing the issue of insufficient desalination rate in high-salt wastewater treatment with single-stage reverse osmosis, the two-stage design can concentrate the total dissolved solids (TDS) of the brine to 2-3 times that of the desulfurization wastewater, while simultaneously producing reusable freshwater with TDS ≤1000 mg / L, meeting wastewater discharge standards and achieving water resource recycling. To address the high salt content of concentrated brine, a forced circulation evaporation crystallizer is employed, controlling the heating steam temperature at 70-90℃ to evaporate the wastewater at 60-80℃. This temperature range was chosen to balance energy consumption and crystallization efficiency: lower temperatures reduce heat consumption while avoiding salt decomposition or equipment corrosion caused by high temperatures. Through seed crystal addition and supersaturation control, the purity of inorganic salts is ensured to be ≥95%, enabling the recovery and utilization of salt resources. Based on the principles of ion exchange and complexation reactions in materials chemistry, this method is applied to the Hg in the wastewater. 2+ Cd 2+ Pb 2+ For heavy metal ions, modified activated carbon or chelating resin is selected as the adsorbent. The adsorbent dosage is 1.2-1.5 times the molar amount of heavy metal ions, based on experience with over-adsorption in actual engineering. This can compensate for the efficiency loss caused by adsorbent saturation, ensuring deep removal of heavy metals. Through the synergistic process of mechanical filtration, multi-stage membrane separation, evaporation crystallization, and heavy metal adsorption, suspended solids, heavy metals, and excess salt in high-salt wastewater are efficiently removed. This improves the separation purity and recovery rate of resources such as gypsum and sodium chloride, reduces the energy consumption and treatment cost of evaporation crystallization, effectively balances the needs of pollution control, cost control, and resource recovery, breaks through the existing technical and economic bottlenecks, and achieves the standard treatment and resource utilization of desulfurization wastewater.

[0038] According to the present invention, optionally, in order for the above-described method and system to operate smoothly, the system may include more or fewer components than those described above, or combine certain components, or different components, in addition to the various modules described above. For example, it may include input / output devices, network access devices, buses, processors, and memory.

[0039] According to the present invention, optionally, the processor may be a central processing unit, or it may be other general-purpose processors, digital signal processors, application-specific integrated circuits, off-the-shelf programmable gate arrays or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or any conventional processor, etc. The processor is the control center of the system and connects various parts using various interfaces and lines.

[0040] The present invention will be further illustrated by the following examples, but the present invention is not limited thereto.

[0041] Example This embodiment provides a method for treating desulfurization wastewater from a power plant, the method comprising: Step S1: Use a bag filter with a pore size of 50μm for the first stage of coarse filtration to remove large particulate impurities from the desulfurization wastewater, and use a bag filter with a pore size of 20μm for the second stage of fine filtration to remove colloids and fine particles from the desulfurization wastewater; control the flow rate at 1m / h to obtain pretreated wastewater with a turbidity of 4NTU. Step S2: Add modified activated carbon adsorbent to the pretreated wastewater. Under weakly alkaline conditions (pH=8), mix the adsorbent and the pretreated wastewater in a stirred reaction tank. The amount of adsorbent used is 1.5 times the molar amount of heavy metal ions. Monitor the change rate of heavy metal concentration in real time. When the change rate of heavy metal concentration is less than 5% for two consecutive tests, the adsorption reaction is determined to have reached equilibrium, and the stirring of the modified activated carbon adsorbent and the pretreated wastewater is stopped. Step S3: The pretreated wastewater is passed into a multi-stage membrane separation system consisting of two reverse osmosis membranes for water-salt separation. The operating pressure of the first-stage RO membrane is 1.0 MPa, and the operating pressure of the second-stage RO membrane is 0.8 MPa, yielding concentrated brine and reusable freshwater. The total dissolved solids concentration of the desulfurization wastewater is 70,000 mg / L. The total dissolved solids concentration of the concentrated brine and the reusable freshwater is twice that of the desulfurization wastewater, i.e., 140,000 mg / L. The total dissolved solids concentration of the freshwater is 800 mg / L. Step S4: The concentrated brine is introduced into a forced circulation evaporator crystallizer for evaporation and concentration. The heating steam temperature is controlled at 80°C, and the concentrated brine is evaporated and concentrated at 60°C. The temperature difference between the heating steam and the concentrated brine is controlled at 20°C, and the total dissolved solids concentration of the concentrated brine is 140,000 mg / L. Sodium chloride crystallization with a purity ≥95% is achieved by adding seed crystals and controlling supersaturation. When the purity of sodium chloride is detected to be 98%, the crystal slurry discharge program is started, and crystal classification is achieved by using a hydrocyclone.

[0042] This embodiment utilizes a synergistic process of mechanical filtration, multi-stage membrane separation, evaporation crystallization, and heavy metal adsorption to efficiently remove suspended solids, heavy metals, and excess salt from desulfurization wastewater, thereby improving the separation purity and recovery rate of resources such as sodium chloride.

[0043] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0044] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0045] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for treating desulfurization wastewater from a power plant, characterized in that, The processing method includes: The desulfurization wastewater was mechanically filtered using a bag filter to obtain pretreated wastewater; the turbidity of the pretreated wastewater was ≤5 NTU. Modified activated carbon or chelating resin adsorbent is added to the pretreated wastewater to adsorb heavy metal ions; the amount of adsorbent used is 1.2-1.5 times the molar amount of the heavy metal ions. The pretreated wastewater is passed into a multi-stage membrane separation system consisting of at least two reverse osmosis membranes for water-salt separation to obtain concentrated brine and reusable fresh water; the total dissolved solids concentration of the concentrated brine and the reusable fresh water is 2-3 times that of the desulfurization wastewater. The concentrated brine is introduced into a forced circulation evaporator crystallizer for evaporation and concentration to obtain inorganic salt crystals.

2. The processing method according to claim 1, wherein, The bag filter has a pore size of 20-50 μm, and the flow rate of the mechanical filtration is controlled to be 0.5-1.0 m / h.

3. The processing method according to claim 1, wherein, The total dissolved solids concentration of the freshwater is ≤1000 mg / L; The heating steam temperature of the forced circulation evaporator crystallizer is controlled at 70-90°C, so that the concentrated brine is evaporated and concentrated at 60-80°C.

4. The processing method according to claim 3, wherein, The temperature difference between the heating steam and the concentrated brine is controlled at 20-30℃, and the total dissolved solids concentration of the concentrated brine is ≤150000mg / L. Simultaneously, through seed crystal addition and supersaturation control, inorganic salt crystallization separation with a purity ≥95% is achieved. When the inorganic salt purity is detected to be ≥98%, the crystal slurry discharge program is initiated, and crystal grading is achieved through a hydrocyclone. The evaporation rate during the evaporation and concentration process satisfies: ； In the formula, This is the temperature influence coefficient. This is the salt concentration inhibition coefficient. To address the temperature difference between the heating steam and the concentrated brine, This represents the total dissolved solids concentration in concentrated brine.

5. The processing method according to claim 1, wherein, The membrane flux calculation of the multi-stage membrane separation system follows the fluid transport equation: ； In the formula, For membrane flux, The water permeability coefficient of the membrane module, The operating pressure difference across the membrane, This represents the osmotic pressure difference. The multi-stage membrane separation system adopts a two-stage structure. The operating pressure of the first-stage RO membrane is 1.0-1.2 MPa, and the operating pressure of the second-stage RO membrane is dynamically adjusted based on the osmotic pressure of the first-stage concentrate, satisfying a pressure recursion relationship: ； In the formula, For the first Membrane operating pressure, This is the pressure compensation coefficient. For the first The osmotic pressure difference between the feed water side and the concentrate side.

6. The processing method according to claim 1, wherein, The mechanical filtration includes two stages of filtration: the first stage uses a bag filter with a pore size of 50μm for coarse filtration to remove large particulate impurities, and the second stage uses a bag filter with a pore size of 20μm for fine filtration to remove colloids and fine particles. The bag filter is equipped with a backwashing device and a differential pressure sensor. When the differential pressure sensor detects a pressure drop ≥0.1MPa, the backwashing device is activated, and the backwashing water flow rate is 10%-15% of the treatment capacity. The treatment capacity is the flow rate of desulfurized wastewater processed per unit time when the bag filter is operating normally.

7. The processing method according to claim 1, wherein, When adding the modified activated carbon or chelating resin adsorbent: Under weakly alkaline conditions of pH 6-8, the modified activated carbon or chelating resin adsorbent is mixed with the pretreated wastewater in a stirred reaction tank. The adsorption time is controlled by a kinetic equation, and the change rate of heavy metal concentration is monitored in real time. When the change rate of heavy metal concentration is less than 5% for two consecutive tests, the adsorption reaction is determined to have reached equilibrium, and the stirring of the modified activated carbon or chelating resin adsorbent with the pretreated wastewater is stopped. The dynamic equation is: ； In the formula, for Adsorption amount at any time To balance the adsorption amount, is the adsorption rate constant.

8. A treatment system for desulfurization wastewater from a power plant, characterized in that, The system applies the processing method as described in any one of claims 1-7, and the system comprises: The mechanical filtration module is used to mechanically filter desulfurization wastewater using a bag filter with a pore size of 20-50μm. The multi-stage membrane separation system module is used to pass mechanically filtered desulfurization wastewater into a separation system consisting of at least two stages of reverse osmosis membranes. Water and salt separation is achieved through gradient pressure drive, generating concentrated brine with a total dissolved solids concentration of 2-3 times that of the desulfurization wastewater and reusable freshwater. The evaporation and concentration module is used to introduce concentrated brine into the forced circulation evaporation crystallizer and control the heating steam temperature to 70-90℃, so that the concentrated brine is evaporated and concentrated at 60-80℃. The dosing module is used to add modified activated carbon or chelating resin adsorbent to the desulfurization wastewater after mechanical filtration.

9. The processing system according to claim 8, wherein, The mechanical filtration module specifically includes: A mixing unit is used to mix the modified activated carbon or chelating resin adsorbent with pretreated wastewater in a stirred reaction tank under weakly alkaline conditions of pH=6-8. The first control unit is used to control the adsorption time through a kinetic equation; The detection unit is used to detect the rate of change in heavy metal concentration in real time. The determination unit is used to determine that the adsorption reaction has reached equilibrium when the change rate of heavy metal concentration is less than 5% in two consecutive tests, and to stop the stirring of the modified activated carbon or chelating resin adsorbent with the pretreated wastewater.

10. The processing system according to claim 8, wherein, The evaporation and concentration module specifically includes: The second control unit is used to achieve high-purity inorganic salt crystallization by controlling the temperature difference between the heating steam and the concentrated brine and the total dissolved solids concentration of the concentrated brine. The crystal slurry discharge program unit is used to start the crystal slurry discharge program when the purity of inorganic salt is detected to be ≥98%, and to achieve crystal classification through a hydrocyclone.

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