A method for recycling and utilizing concentrated brine of a thermal power plant primary reverse osmosis

Abstract

The application discloses a thermal power plant primary reverse osmosis concentrated brine resource recycling method, which comprises the following steps: S1, source isolation and directional collection of primary reverse osmosis concentrated brine; S2, pretreatment of the concentrated brine, namely seed-induced softening and online flocculation; S3, pH post-adjustment and ultrafiltration fine treatment; S4, secondary reverse osmosis concentration of the concentrated brine; S5, advanced oxidation-flocculation-microwave coupling treatment of secondary RO concentrated water; and S6, standard discharge, wherein online water quality monitoring is conducted on the standard clear liquid. Through the steps of seed-induced softening, high-pH ultrafiltration, secondary low-pressure reverse osmosis and the like, most of fresh water in the primary reverse osmosis concentrated brine is recovered, the produced water is directly connected to a plant area ultrafiltration water tank, and after being mixed with original raw water, is used in a subsequent pure water preparation system, thereby effectively reducing the dependence of the thermal power plant on external fresh water resources (such as municipal reclaimed water or surface water), and realizing the in-plant recycling of water resources.

Description

Technical Field

[0001] This application belongs to the field of water resource recycling technology, specifically relating to a method for recycling concentrated brine from the first stage of reverse osmosis in a thermal power plant. Background Technology

[0002] With increasingly stringent requirements for water conservation and emission reduction in thermal power plants, reverse osmosis (RO) technology is widely used in boiler feedwater preparation and greywater reuse systems. However, during operation, RO units generate approximately 25% to 30% of the feed water as primary RO brine. This brine is characterized by high salinity, high hardness, high alkalinity, silica content, and small amounts of organic matter. Direct discharge of this brine not only wastes water resources but also adversely affects the ecological environment of the receiving water body.

[0003] Currently, the main methods for treating primary reverse osmosis brine in thermal power plants include: direct mixing and discharge with circulating cooling water, simple treatment within the plant followed by wet discharge of ash and slag or spraying in the coal yard, and achieving zero discharge by using evaporation crystallization technologies such as multi-effect evaporation or mechanical vapor recompression (MVR).

[0004] The first two methods failed to fundamentally solve the problems of salt accumulation and pollution transfer, and were limited by the water conditions inside the power plant; although evaporation crystallization technology can achieve salt separation, it requires large equipment investment, has high operating energy consumption, and the cost of disposing of crystallized salt as hazardous or solid waste is high, making it less economical.

[0005] In recent years, some studies have attempted to use a "pretreatment + secondary reverse osmosis" process to further concentrate brine in order to recover some freshwater. However, due to the high concentrations of calcium, magnesium, sulfate, and silicate ions in the concentrated brine, conventional pretreatment methods (such as lime softening, coagulation, and filtration) are insufficient to simultaneously and efficiently remove multiple scaling components. This leads to severe deposition of calcium carbonate, calcium sulfate, and silica scale on the surface of the subsequent reverse osmosis membrane, resulting in frequent membrane cleaning, shortened membrane lifespan, and poor system stability. In particular, under normal pH conditions, the removal rate of colloidal and activated silica in silica-containing concentrate is low, easily forming difficult-to-clean silica scale on the reverse osmosis membrane surface. Furthermore, traditional processes typically place pH adjustment before the filtration step, which causes the precipitated calcium carbonate and polysilicic acid to redissolve, exacerbating the risk of membrane scaling.

[0006] Therefore, there is an urgent need to develop a method that can achieve resource recycling of concentrated brine from primary reverse osmosis in thermal power plants, and that is stable, economical, and feasible. Summary of the Invention

[0007] This application provides a method for the resource recycling of concentrated brine from primary reverse osmosis in thermal power plants, aiming to solve the problems of water waste and environmental pollution caused by the direct discharge or simple reuse of concentrated brine from primary reverse osmosis in thermal power plants in the prior art, as well as the problems of severe membrane scaling, low silica removal rate, poor operational stability and high energy consumption when using conventional "pretreatment + secondary reverse osmosis" process.

[0008] A method for recycling concentrated brine from primary reverse osmosis in a thermal power plant, the method comprising:

[0009] S1. Source isolation and directional collection of primary reverse osmosis brine: The brine produced by the primary reverse osmosis unit of the thermal power plant is isolated and collected at the source, and introduced into the equalization tank for homogenization and equalization treatment to obtain homogenized brine.

[0010] S2. Pretreatment of concentrated brine, namely seed-induced softening and online flocculation, involves sequentially subjecting the homogeneous concentrated brine to seed-induced softening and online flocculation to remove bicarbonate alkalinity, colloidal silica, and suspended solids, thereby obtaining pretreated permeate.

[0011] S3. Post-pH adjustment and ultrafiltration fine treatment: The pretreated water is directly sent into the ultrafiltration system for fine filtration in its original high pH state to obtain ultrafiltration water; The pH of the ultrafiltration water is adjusted to reduce its pH value to a preset range to obtain conditioned ultrafiltration water.

[0012] S4. Secondary reverse osmosis concentration of concentrated brine: Utilizing the residual pressure at the concentrated water discharge port of the primary reverse osmosis unit, the conditioning ultrafiltration permeate is sent to a low-pressure reverse osmosis unit for secondary concentration to obtain secondary reverse osmosis permeate and secondary reverse osmosis concentrate; wherein, the secondary reverse osmosis permeate is recycled to the ultrafiltration water tank of the thermal power plant, and the secondary reverse osmosis concentrate is sent to subsequent treatment.

[0013] S5. Advanced oxidation-flocculation-microwave coupled treatment of secondary RO concentrate: The secondary reverse osmosis concentrate is subjected to ozone catalytic oxidation treatment and microwave chemical treatment in sequence, and then separated by flocculation clarification to obtain a qualified clear liquid.

[0014] S6. Discharge in compliance with standards: The compliant clear liquid is monitored online. If the monitored indicators meet the discharge standards, it is discharged. If any indicator exceeds the standard, the compliant clear liquid is returned to the equalization tank.

[0015] Optionally, in step S1, the effective volume of the equalization tank is designed to be 1.2 times the daily concentrated water production under the maximum operating conditions during the heating season, and it is equipped with a submersible agitator, a level gauge, and an adsorption device; the total dissolved solids fluctuation range of the homogenized concentrated brine is reduced to within ±10%, and the pH value is stabilized at 8.0 to 8.5.

[0016] Optionally, S2 specifically includes: continuously adding lime slurry, polyferric sulfate, polyacrylamide and calcium sulfate seed crystals to the seed-induced softening reactor, controlling the reaction pH to be 10.5 to 11.0, and the mixed liquid after the reaction entering the inclined tube sedimentation zone for solid-liquid separation. The supernatant is filtered through a high-efficiency fiber filter to obtain pretreated permeable water with turbidity ≤2 NTU and suspended solids ≤5 mg / L.

[0017] Optionally, in step S3, the pretreated wastewater originally had a high pH value of 10.3 to 10.7;

[0018] The ultrafiltration system uses a polyvinylidene fluoride hollow fiber membrane and operates under high pH conditions, achieving a total silicon removal rate of 60%–70%.

[0019] The pH adjustment is performed by using dilute sulfuric acid to adjust the pH value of the ultrafiltration permeate to 8.2–8.5.

[0020] Optionally, in step S3, the pH adjustment operation is performed after the ultrafiltration system and before the low-pressure reverse osmosis device to prevent the precipitated calcium carbonate and polysilicic acid from redissolving due to pH reduction before filtration.

[0021] Optionally, in step S4, the residual pressure of the concentrate discharge port of the first-stage reverse osmosis unit is 0.5 to 0.8 MPa, and an online booster pump is only set to compensate for pressure loss, so that the operating pressure of the low-pressure reverse osmosis unit is ≤1.0 MPa; the low-pressure reverse osmosis unit is arranged in a three-stage first-stage configuration, and the system recovery rate is set to 50% to 60%.

[0022] Optionally, in step S4, the conductivity of the secondary reverse osmosis permeate is 280–350 μS / cm, and the chemical oxygen demand is ≤5 mg / L;

[0023] The secondary reverse osmosis permeate is directly connected to the inlet header of the ultrafiltration water tank in the plant area.

[0024] Optionally, in step S5, the ozone catalytic oxidation treatment uses ozone in... The composite catalyst generates hydroxyl radicals, which can remove 30% to 40% of the chemical oxygen demand.

[0025] The microwave chemical treatment uses microwave radiation at a frequency of 2450±25MHz and adds a microwave absorption sensitizer. After treatment, the chemical oxygen demand of the effluent is reduced to 35-45 mg / L through flocculation and clarification.

[0026] Optionally, in S6, when any monitoring indicator exceeds the standard, the system automatically transports the water exceeding the standard in the buffer discharge tank to the front end of the regulating tank through a return pump, and at the same time sends an alarm signal to the distributed control system.

[0027] If the time exceeding the standard exceeds the preset duration, the water exceeding the standard will be switched to the emergency pool.

[0028] Compared with the prior art, this application has at least the following beneficial effects:

[0029] This application utilizes seed-induced softening, high-pH ultrafiltration, and secondary low-pressure reverse osmosis to recover most of the fresh water from the primary reverse osmosis brine. The produced water is directly connected to the plant's ultrafiltration water tank and mixed with the original raw water for use in the subsequent pure water preparation system. This effectively reduces the power plant's dependence on external fresh water resources (such as urban reclaimed water or surface water) and realizes the internal recycling of water resources within the plant.

[0030] This application places the pH adjustment step after the ultrafiltration system and before the secondary reverse osmosis, rather than before the high-efficiency fiber filtration. This sequence ensures that the wastewater maintains a high pH state throughout the ultrafiltration and pre-filtration steps, allowing precipitates such as calcium carbonate, magnesium hydroxide, and polysilicic acid to be fully retained; then the pH is adjusted to the appropriate range for reverse osmosis, avoiding the redissolution of the precipitated components.

[0031] This method maintains the feed water pH at 10.3–10.7 during the ultrafiltration step. By utilizing the changes in surface charge and hydration radius of colloidal silica under high pH conditions, the removal rate of total silica by the polyvinylidene fluoride (PVDF) ultrafiltration membrane is improved, exceeding the 20% removal rate under conventional neutral conditions, thus reducing the risk of silica scaling on the subsequent reverse osmosis membrane.

[0032] This method directly utilizes the existing 0.5–0.8 MPa residual pressure at the concentrate discharge port of the first-stage reverse osmosis unit, and only adds a small-power booster pump to compensate for pipeline and membrane module resistance losses, so that the operating pressure of the low-pressure concentrate reverse osmosis unit is controlled below 1.0 MPa. Compared with the conventional high-pressure pump mode for seawater desalination reverse osmosis, this method is more efficient and significantly reduces operating costs. Attached Figure Description

[0033] Figure 1 This is a flowchart illustrating a method for the resource recycling of concentrated brine from a primary reverse osmosis system in a thermal power plant, as provided in one embodiment of this application. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments.

[0035] This application provides a method for the resource recycling of concentrated brine from the first-stage reverse osmosis process in a thermal power plant, such as... Figure 1 As shown, it includes the following steps:

[0036] S1: Source isolation and targeted collection of primary reverse osmosis brine. The primary reverse osmosis unit that has been built and put into operation in the raw water treatment workshop of the thermal power plant is selected as the target unit for modification. At least one primary reverse osmosis unit with stable operation and the concentrate discharge pipeline has the conditions for independent modification is selected (hereinafter referred to as "target unit").

[0037] To separate concentrated brine from other wastewater streams and avoid increasing the difficulty of subsequent treatment due to mixing of wastewater from different sources, the connecting flange between the concentrated water discharge outlet of the target unit and the existing concentrated brine discharge pipeline in the plant area was first removed. A DN100 304 stainless steel blind flange was then installed at the end of this connecting pipe section to achieve physical isolation. Simultaneously, a separate, closed-loop concentrated brine collection pipeline was re-laid at the concentrated water outlet of the target unit. The pipeline material was selected to be corrosion-resistant UPVC or CPVC, with a nominal pressure of not less than 1.0 MPa. The pipeline route followed the existing pipe gallery and was sloped (≥5‰) to facilitate gravity flow.

[0038] The sealed collection pipeline is connected at its end to a newly built or renovated concentrated brine equalization tank. The equalization tank is an underground or semi-underground reinforced concrete structure with an anti-corrosion layer (such as epoxy fiberglass or polyurea coating) lining the inner wall. The effective volume of the equalization tank is designed to be 1.2 times the daily concentrated brine production of the target unit under maximum operating conditions.

[0039] Based on actual operating data from the thermal power plant, during the non-heating season, a single first-stage reverse osmosis unit produces an average of approximately 35,000 tons of concentrated brine per month, or about 1,167 tons per day; during the heating season, the average monthly production is approximately 66,000 tons, or about 2,200 tons per day. Therefore, the effective volume of the equalization tank should be 2,600–2,800 m³. 3 To meet the requirement of at least 24 hours of residence during the high load period of the heating season, and to take into account the intermittent operation mode during the non-heating season;

[0040] The following components are configured inside the equalization tank: (1) Two submersible mixers (one for use and one for standby), with a power of 5.5kW, are installed at opposite corners of the tank to prevent suspended solids from settling and to make the concentrated brine discharged at different times uniform; (2) One set each of submersible hydrostatic level gauge and ultrasonic level gauge, with the signal connected to the plant's DCS system to realize level interlock control. When the level reaches the high limit (90% of the designed effective water depth), the subsequent delivery pump will be started automatically, and when the level reaches the low limit (20% of the effective water depth), the pump will be stopped and an alarm will be triggered; (3) A ventilation pipe and activated carbon adsorption device are installed on the top of the tank to collect any chlorine gas and microbial metabolic gases that may escape.

[0041] The residence time of concentrated brine in the equalization tank is set to be no less than 4 hours. In actual operation, it can be extended to 6-8 hours depending on the fluctuation of the influent flow rate, so as to fully balance the fluctuations in water quality and quantity caused by different concentration discharge cycles (such as automatic flushing once after 3 hours of operation of the reverse osmosis unit). After homogenization and equalization in the equalization tank, the fluctuation range of total dissolved solids (TDS) of concentrated brine is reduced from the original ±30% to within ±10%, and the pH value is stabilized between 8.0 and 8.5, providing stable influent conditions for subsequent seed crystal softening treatment.

[0042] In addition, online turbidity meters and conductivity meters are installed on the effluent pipes of the equalization tank to monitor the basic water quality parameters of the concentrated brine in real time. The data is then transmitted to the central control room to guide the dynamic adjustment of the dosage of lime and seed crystals in S2. Through the above-mentioned isolation and targeted collection operations, the concentrated brine of the target unit is prevented from mixing with the wastewater of other units, and a stable and continuously treatable raw water source is provided for the subsequent "secondary treatment-product water reuse" cycle system.

[0043] S2: Pretreatment of concentrated brine, i.e., seed-induced softening and online flocculation. The concentrated brine, after homogenization and equalization in the S1 equalization tank, is then pumped by a booster pump (one in operation and one on standby, with a flow rate selected based on 1.5 times the target unit's maximum daily concentrated brine production, e.g., Q=150m³). 3 The feedwater (with a flow rate of / h, a head of H=20m, and flow-through components made of duplex stainless steel 2205) is transported to the seed-induced softening reactor. This reactor employs a three-stage mechanical stirring series structure. Each stage reaction tank is cylindrical with a height-to-diameter ratio of 1.5:1, and the total effective volume is designed based on a concentrated brine residence time of 15–20 min. The first-stage stirring speed is controlled at 80–120 r / min for rapid reagent mixing; the second and third-stage speeds gradually decrease to 40–60 r / min to promote micro-floc growth.

[0044] The following reagents were continuously added to the reactor, all of which were injected via metering pumps after online dilution:

[0045] (1) Lime Slurry (CaO): First, quicklime (effective CaO content ≥85%, particle size ≤200 mesh) is prepared into a 10%–15% mass concentration emulsion in a separate lime slurry preparation tank. After filtering through a two-stage sieve (1mm aperture) to remove large particulate impurities, it is stored in a lime slurry storage tank with low-speed stirring (15r / min). The lime slurry is injected into the inlet pipe of the first-stage reaction tank through a diaphragm metering pump. The dosage is controlled according to the proportion of the raw water flow rate and fine-tuned based on the feedback from the online pH meter. The target pH value is 10.5–11.0, corresponding to a lime dosage of 400–500 mg / L (calculated as pure CaO). This operation can effectively remove bicarbonate alkalinity (CaO) from concentrated brine. Transform into The precipitation and some silicate (forming calcium silicate or co-precipitate) reduce the total alkalinity to below 1.0 mmol / L, while also synergistically removing some colloidal silica;

[0046] (2) Polyferric sulfate (PFS): Industrial grade PFS (total iron content ≥11%, basicity 8%~16%) is used. After being diluted with demineralized water at a weight ratio of 1:3, it is injected into the first-stage reaction tank by a metering pump at a dosage of 10~15mg / L (based on the original solution). As a coagulant, PFS neutralizes the negative charge of colloidal particles by generating polynuclear hydroxy iron complexes through hydrolysis, compresses the double electric layer, and promotes the destabilization and coagulation of fine suspended solids and organic matter.

[0047] (3) Polyacrylamide (PAM): Non-ionic or anionic PAM with a molecular weight of 8 million to 12 million is selected. After being dissolved and matured at a concentration of 0.1% to 0.2%, it is injected into the inlet of the second-stage reaction tank by a metering pump at a dosage of 0.2 to 0.3 mg / L. PAM further aggregates the micro-flocs into coarse and dense flocs through bridging, which facilitates subsequent precipitation and separation.

[0048] (4) Calcium sulfate seed crystals: Calcium sulfate dihydrate (…) Using [material name] as raw material, the powdered seed crystals, mainly with a particle size distribution of 5–20 μm, are obtained after air jet milling and grading sieving. The seed crystals are fed into a Venturi injector by a screw feeder, and after forming a suspension with the help of pressurized water (demineralized water), they are injected into the third-stage reaction tank. The addition concentration is controlled at 0.5–1.0 g / L, that is, maintaining 0.5–1.0 g of seed crystal solid per liter of concentrated brine. Its mechanism of action is: when the concentrated brine... and When the ion product exceeds the gypsum solubility product, the precipitated crystals preferentially grow on the surface of existing seed crystals, rather than forming a hard scale layer on the reactor wall or subsequent pipes and membrane elements. The seed crystal surface can still be recycled after aging. This system is equipped with a seed crystal recovery device at the bottom of the precipitation zone (see below).

[0049] The reaction tank is equipped with a pH meter, thermometer, and turbidity meter. The pH value is controlled between 10.5 and 11.0 (if it is below 10.3, the amount of lime added will be automatically increased; if it is above 11.2, the addition of lime will be stopped and the situation will be observed). The reaction temperature is usually 25–35℃, utilizing the temperature of the concentrated brine itself without additional heating.

[0050] After the reaction, the mixture flows by gravity into the inclined tube sedimentation zone. The sedimentation zone uses counter-flow honeycomb inclined tube packing; the inclined tubes are made of polypropylene (PP), with a diameter of φ50mm, an inclination angle of 60°, and an installation height of 1.0m. The surface load of the sedimentation zone is designed to be 1.0–1.5m. 3 / (m 2•h), the bottom sludge hopper volume is designed for 4 hours of sludge storage, and the hopper angle is 55°. The settling time is no less than 30 minutes, and in actual operation, the settling time is maintained within the range of 30 to 45 minutes by adjusting the influent flow rate. The supernatant is collected in the collection tank and overflows into the intermediate water tank; the settled sludge (moisture content of about 97% to 98%) is periodically or continuously discharged into the sludge thickening tank by the sludge pump;

[0051] To recover calcium sulfate seed crystals and reduce operating costs, a hydrocyclone (specification: processing capacity 5-10m³) is installed at the bottom of the sludge thickening tank. 3 / h, separation particle size d50=10μm). The coarse particles discharged from the underflow outlet of the hydrocyclone (mainly seed crystals and a small amount of unreacted CaCO3) are returned to the seed crystal preparation tank for reuse, while the fine sludge discharged from the overflow outlet is sent to a plate and frame filter press for dewatering and then transported for disposal. The seed crystal recovery rate can reach 60% to 75%, and the effective replenishment of fresh seed crystals is only 0.2 to 0.4 g / L;

[0052] The supernatant in the intermediate water tank is pumped into a high-efficiency fiber filter by a lift pump. This filter is pressure-type, with a Q235B cylinder lined with rubber, and a design pressure of 0.6 MPa. The filter media is polyester fiber bundles, with a single bundle length of 1.2 m, fiber diameter of 20–50 μm, and a packing density of approximately 120 kg / m³. 3 The nominal filtration accuracy is ≤5μm, and in actual operation, the removal rate of suspended solids with a particle size greater than 3μm is ≥95%. The filter is designed with a flow rate of 30~40m / h. The backwash cycle is based on the inlet and outlet water pressure difference (set value 0.08MPa) or timed (every 8~12 hours) for combined air and water backwashing. The backwash water is concentrated brine from the S1 equalization tank (or the system's produced water), and the backwash intensity is 10~12L / (m³). 2 •s), supplemented with compressed air scrubbing (intensity 20-25 L / (m) 2 The backwash time is 5-8 minutes. The backwash wastewater is returned to the front end of the equalization tank to avoid water loss.

[0053] After treatment by a high-efficiency fiber filter, the effluent turbidity is stable at ≤2 NTU, suspended solids (SS) ≤5 mg / L, total hardness decreases from 14.97 mmol / L in the raw water to 9.0–9.5 mmol / L (removal rate approximately 38%–40%), calcium hardness decreases from 7.37 mmol / L to 4.2–4.4 mmol / L (removal rate approximately 41%), and total alkalinity decreases from 9.21 mmol / L to ≤1.0 mmol / L. The effluent meets the influent requirements of the S3 ultrafiltration system.

[0054] It should be noted that the pH value of the effluent in this step is maintained at a relatively high range of 10.3 to 10.7. This is an intentional process condition, meaning that under high pH conditions, residual silicate ions and trace heavy metal ions (such as...) are contained within the effluent. , It is easier to form hydroxide precipitates, which can be retained in subsequent high-efficiency fiber filtration. However, excessively high pH values ​​can cause scaling on ultrafiltration membranes and subsequent reverse osmosis membranes. Therefore, a dedicated post-pH adjustment unit will be set in S3, and this adjustment operation must be arranged after (not before) high-efficiency fiber filtration to prevent acid dissolution from causing the already precipitated calcium carbonate, silicate and other colloids to redissolve. This sequence is one of the key features of the present invention, and the specific implementation is shown in S3.

[0055] S3: Post-pH adjustment and ultrafiltration treatment. After being temporarily stored in an intermediate water tank, the effluent from the S2 high-efficiency fiber filter is pumped into the ultrafiltration (UF) system by a variable frequency centrifugal pump. It should be noted that no pH adjustment is performed on the effluent at this stage. It directly enters the ultrafiltration membrane module with the original high pH state of the S2 effluent (measured range 10.3-10.7, typical value 10.5). This is one of the key technical features that distinguishes this invention from the conventional "pH adjustment before filtration" process.

[0056] The ultrafiltration system uses external pressure hollow fiber membrane modules made of polyvinylidene fluoride (PVDF), which has excellent acid and alkali resistance and anti-aging properties. Commercially available membrane modules with proven engineering applications can be selected, with the following technical specifications: nominal pore size ≤0.03μm, actual molecular weight cutoff (MWCO) of 100,000Da; hollow fiber inner diameter 0.7–0.9mm, outer diameter 1.2–1.4mm; effective membrane area of ​​40–50m² per module. 2 Configuration. The ultrafiltration system adopts an operating mode combining dead-end filtration and periodic backwashing, with a designed operating flux controlled at ≤50L / (m³). 2 ·h), the actual set value is 45L / (m 2 (h). Based on the target unit's daily processing capacity of 2200 tons of concentrated brine, the total required ultrafiltration membrane area is approximately 2040 m². 2 It can be achieved through 40 single 51m 2 The membrane modules are connected in parallel to achieve this;

[0057] The ultrafiltration system is equipped with an automatically controlled inlet pump, backwash pump, and air scrubbing device. The operating cycle is set to 30 minutes, with each cycle consisting of 28 minutes of permeate water, 1 minute of combined air-water backwashing, and 1 minute of forward flushing. Backwashing uses ultrafiltration permeate water, and the backwash flux is controlled to be 1.5–2.0 times the permeate flux (i.e., 70–100 L / (m³)). 2 Simultaneously, oil-free compressed air is used for surface cleaning, with an air intensity of 50–80 L / (m²). 2•s), backwash time 60 seconds. Perform chemically enhanced backwash (CEB) every 24 hours, adding 200 mg / L sodium hypochlorite (soaking for 10 minutes) and 500 mg / L citric acid (soaking for 5 minutes) sequentially to control microbial growth and remove iron and manganese deposits. Perform offline chemical cleaning every 3 months;

[0058] Under continuous operation, the influent turbidity of the ultrafiltration system is ≤2 NTU, and the measured SDI value is 4.0–4.5 (without pH adjustment). The ultrafiltration membrane has a significant removal effect on suspended solids, colloidal silica, and macromolecular organic matter: the turbidity of the product water is stable at ≤0.15 NTU, the SDI is reduced to 2.5–3.0, and the removal rate of organic colloids with a molecular weight greater than 100,000 Da (such as humic acid aggregates and microbial metabolites) is ≥95%. It is worth emphasizing that under high pH (10.5) conditions, the silicate ions remaining in the concentrated brine will partially polymerize to form oligomeric or colloidal silica. These forms of silica are relatively stable at normal pH (7–8) and are difficult to be effectively retained by ultrafiltration. However, in a high pH environment, the surface charge and hydration radius of colloidal silica change, making it easier to form a loose filter cake layer on the PVDF membrane surface that can be backwashed and removed, thus being retained by ultrafiltration. Experimental data show that the removal rate of total silicon (including activated silicon and colloidal silicon) after this step can reach 60% to 70%, which is much higher than the silicon removal efficiency of ultrafiltration at neutral pH (generally <20%).

[0059] The ultrafiltration permeate first enters a container with a volume of 30-50m³ 3 The intermediate water tank (also serving as a pH adjustment tank) is equipped with an acid and alkali resistant stirrer (40-60 r / min), an online pH meter, and acid dosing pipeline. pH adjustment uses 5% sulfuric acid, injected proportionally via a diaphragm metering pump using a PID control based on pH feedback signals. The sulfuric acid is obtained by online dilution of 98% concentrated sulfuric acid with demineralized water. The dilution process is completed in a dedicated safety diluent, equipped with cooling coils to dissipate the heat of dilution, ensuring the sulfuric acid temperature is ≤40℃. The acid dosing point should be located at least 1.5m away from the pH meter probe to ensure thorough mixing before measurement.

[0060] The target pH value for adjustment is set at 8.2–8.5. This range was chosen based on the following engineering considerations:

[0061] (1) This pH range is the allowable feed water pH range for the subsequent secondary reverse osmosis membrane (low-pressure concentrate RO) (usually 4 to 11, but in actual operation, 7.5 to 8.5 is the best, which can effectively reduce the scaling tendency of the concentration polarization layer in the membrane).

[0062] (2) When the pH is 8.2 to 8.5, the proportion of residual bicarbonate ions in the water converted to carbonate ions is moderate, and scale inhibitors are less likely to cause scale buildup after the addition of scale inhibitors. precipitation;

[0063] (3) Too high a pH (e.g., >9.5) will accelerate the hydrolysis and aging of the amide bonds in the RO membrane, while too low a pH (<7.0) may cause the precipitated silica in S2 to redissolve (the solubility of silica increases significantly at pH <7.5). In actual operation, the pH control accuracy is ±0.1 of the set value, that is, the pH value of the final ultrafiltration permeate (after pH adjustment) is maintained in the range of 8.2 to 8.5, with a fluctuation range of less than 0.2.

[0064] It is important to emphasize that this step places the pH adjustment operation after ultrafiltration and before secondary reverse osmosis, rather than after the S2 high-efficiency fiber filter and before ultrafiltration. This sequence is one of the key protective points of this invention, and its technical basis lies in the fact that the S2 effluent forms a large amount of... , And polysilicic acid-iron coprecipitates, most of which have been removed by physical retention in high-efficiency fiber filters and ultrafiltration membranes; if acid is added before filtration (i.e. before entering ultrafiltration) to lower the pH to below 8.5, the precipitated portion will be removed. A reverse reaction will occur ( This releases calcium ions and bicarbonate ions, while the polymeric silicic acid also depolymerizes to form soluble silicic acid. These dissolved ions can pass through the ultrafiltration membrane (due to their small molecular weight) and enter the subsequent RO system, causing severe calcium carbonate and silica scale deposition on the RO membrane surface. Pilot-scale studies have shown that when using the "pH adjustment first, then filtration" sequence, the pressure difference on the feed side of the secondary RO unit increased by more than 20% after 72 hours of operation, and dissection revealed a dense white carbonate scale layer on the membrane surface; while using the "filtration first, then pH adjustment" sequence in this step, the pressure difference change of the secondary RO unit was less than 5% after 200 hours of continuous operation under the same conditions. Therefore, the operating sequence specified in this invention is the core means to ensure the long-term stable operation of the entire circulation system.

[0065] The ultrafiltration permeate after pH adjustment has the following water quality indicators: turbidity ≤ 0.15 NTU, SDI ≤ 2.6 (90% of the measured values ​​≤ 2.5), pH 8.2~8.5, total hardness ≤ 9.0 mmol / L, calcium hardness ≤ 4.2 mmol / L, total iron ≤ 0.05 mg / L, COD ≤ 20 mg / L (the original concentrate COD was approximately 21 mg / L, with a removal rate of approximately 25%~30% after S2 and this step), and conductivity slightly increased due to acid addition, but the increase was ≤ 5%. This water quality fully meets the feed water requirements of the S4 low-pressure concentrate RO unit. The treated water then enters the S4 concentrated brine secondary reverse osmosis concentration unit.

[0066] S4: Concentrated brine via secondary reverse osmosis (low-pressure concentrate RO). The effluent from S3 after pH adjustment (hereinafter referred to as "secondary RO feed water") is pumped into the low-pressure concentrate reverse osmosis unit by an intermediate booster pump. The core design of this unit is to fully utilize the residual pressure energy at the concentrate discharge port of the original primary reverse osmosis unit in the thermal power plant to reduce system power consumption.

[0067] Specifically, the concentrate outlet pressure of the target unit is maintained between 0.5 MPa and 0.8 MPa under normal operating conditions (depending on the influent temperature, membrane fouling level, and recovery rate settings). This invention preserves the pressure characteristics of the pressurized brine stream after treatment by S1-S3 (i.e., secondary RO feedwater). Only one online booster pump is installed on the pipeline to compensate for friction loss and insufficient influent pressure to the membrane modules. This pump uses frequency conversion control, with an outlet pressure set at 0.9-1.0 MPa and a head of only 10-20 m. Compared to the high-pressure pumps (typically ≥200 m) in conventional seawater desalination reverse osmosis systems, this saves over 80% in electricity consumption. When the primary reverse osmosis unit is operating well and the concentrate residual pressure is higher than 0.6 MPa, the booster pump can be switched to bypass or shutdown mode, operating entirely on residual pressure.

[0068] The low-pressure concentrate reverse osmosis unit is designed in a three-stage configuration, employing a single-stage, three-section process with booster pumps between sections. The membrane modules are low-pressure reverse osmosis membrane elements with anti-fouling properties and wide flow channels (inlet flow channel width ≥ 34 mil). The membrane material is a polyamide composite membrane, with a desalination rate ≥ 99.2% under standard testing conditions. However, considering the high inlet salt concentration of this system (conductivity approximately 3000–3500 μS / cm), the actual operating desalination rate is designed to be 96%–98%.

[0069] The effective area of ​​a single membrane element is 37.2 m². 2 (400ft) 2 The total number of membranes in the unit is determined based on the water treatment volume: Assuming the target unit treats an average of 2200 tons of concentrated brine per day during the heating season, with a system recovery rate of 55%, the secondary RO influent volume is 2200 tons / day (approximately 91.7 tons / hour), and the design flux is 18 L / (m³). 2 (·h) (Recommended flux range for low-pressure membranes under brackish water conditions: 15–20 L / (m²)) 2 The required membrane area is approximately 91.7 × 1000 / 18 ≈ 5095 m². 2 This translates to approximately 137 membrane elements. The actual configuration is in three stages: the first stage comprises 60% of the total membrane elements, the second stage 30%, and the third stage 10%. Interstage booster pumps (approximately 3-5 bar head) are installed between stages to overcome the decrease in driving force caused by the increased osmotic pressure in the later stages.

[0070] The system operating pressure is strictly controlled at ≤1.0MPa (i.e., 10bar), and the inlet water temperature is designed for 20-30℃. When the water temperature is below 15℃ in winter, the temperature is raised to above 20℃ using low-grade waste heat from the plant (circulating water return or steam condensate) through a plate heat exchanger to ensure membrane permeability and system recovery rate. A pressure regulating valve (back pressure valve) is installed on the concentrate side to control the flow distribution between sections and maintain a balanced recovery rate in each section by adjusting the opening degree. The system recovery rate is set at 50%-60%, and in actual operation, it is adjusted according to the inlet water quality (especially hardness, etc.). The content was fine-tuned to around 55%. The recovery rate was determined based on the following limiting condition: the most poorly soluble salt on the concentrate side ( , , , The concentration product of the scale should not exceed 1.5 times its solubility product (i.e., maintain a safety factor of 1.5). In this step, the calcium ion concentration in the influent is approximately 4.2 mmol / L, and the sulfate concentration is approximately 3.5 mmol / L (from the raw water and a small amount of sulfate introduced by lime addition). Under conditions of pH 8.2–8.5 and a water temperature of 25℃, the LSI (Langrillly saturation index) is controlled below 0.5 after adding the scale inhibitor.

[0071] The specific scale inhibition measures adopted are as follows: A scale inhibitor dosing point is set up on the secondary RO inlet pipe, and a composite scale inhibitor with good dispersion effects on both silica and sulfate (such as a compound product based on polyacrylate and organophosphonate) is selected, with a dosage of 2-4 mg / L. Simultaneously, sodium bisulfite is continuously added online. 2 mg / L to reduce any residual chlorine that may remain in the raw water (standard requirement <0.1 mg / L) and protect the polyamide membrane from oxidation;

[0072] The actual measured water quality indicators of the permeate (i.e., secondary reverse osmosis permeate) are as follows: conductivity is stable at 280–350 μS / cm (raw water conductivity is approximately 5500–6500 μS / cm, desalination rate is approximately 89%–91%, the reason for the lower desalination rate than conventional RO is the low-pressure operation and slight permeation enhancement caused by the presence of low molecular weight organic matter in the feed water); chemical oxygen demand (COD) ≤ 5 mg / L (raw water COD is approximately 20 mg / L, removal rate ≥ 75%); turbidity ≤ 0.1 NTU; total hardness ≤ 0.5 mmol / L (with the following parameters as follows). count); ≤1.0mg / L; TOC≤0.5mg / L;

[0073] The quality of the permeate water fully meets the inlet requirements of the ultrafiltration water tank in the thermal power plant, meaning it is comparable to or even better than the effluent from municipal reclaimed water or surface water after existing pretreatment systems. The permeate water pipeline is directly connected to the inlet header of the ultrafiltration water tank in the plant area and is equipped with a check valve to prevent backflow. After entering the ultrafiltration water tank, this permeate water mixes with raw water from outside the plant or other sources, and together they serve as the raw water for the subsequent reverse osmosis membrane pure water production system. According to heat balance calculations, the water recovery rate of the entire pure water system can be correspondingly improved after mixing in the secondary RO permeate water, while reducing the amount of fresh reclaimed water used.

[0074] The concentrate produced in this step (i.e., secondary RO concentrate) accounts for approximately 40%–50% of the influent. Assuming a 55% recovery rate, the concentrate volume is approximately 45% of the influent. The TDS concentration in this concentrate is more than twice that of the original brine (specifically approximately 6000–8000 mg / L, with some ions such as silicon and organic matter potentially enriched even higher), and the COD correspondingly rises to 50–80 mg / L (after concentration and permeation of the raw water's COD of 20 mg / L, the COD of the concentrate is approximately 2–2.5 times that of the influent). This concentrate contains high concentrations of salt, small amounts of undegraded organic matter, and scale inhibitor residue, and is not suitable for direct discharge; it requires advanced treatment to meet discharge standards. Therefore, the secondary RO concentrate is collected via pipeline and enters the S5 advanced oxidation-flocculation-microwave coupled treatment system.

[0075] To monitor the operating status of the unit, online instruments are installed on the inlet, permeate, and concentrate pipelines of the secondary RO unit: a pH meter, conductivity meter, thermometer, and flow meter are installed at the inlet; a conductivity meter and online TOC analyzer are installed at the permeate; and a flow meter, conductivity meter, and oxidation-reduction potential (ORP) meter are installed at the concentrate. The control logic adopts PLC automatic control. When the permeate conductivity exceeds the set value (e.g., 500 μS / cm) or the inter-stage pressure difference exceeds 0.2 MPa, the system automatically triggers the online chemical cleaning program or alarms to prompt manual intervention.

[0076] Under normal operating conditions, this step can run continuously for more than 2000 hours without offline chemical cleaning. Compared with conventional RO treatment of high hardness wastewater, the cycle is extended by 3 to 5 times. The fundamental reason is that S1 to S3 have removed most of the scale-causing ions, colloids and organic matter, and the pH adjustment sequence of S3 effectively avoids inorganic-organic composite pollution on the RO membrane surface.

[0077] S5: Advanced oxidation-flocculation-microwave coupled treatment of secondary RO concentrate. The secondary RO concentrate generated in S4 (hereinafter referred to as "concentrate to be treated") flows by gravity or is pumped by a low-pressure pump into the ozone catalytic oxidation tower. According to actual measurements, the water quality fluctuation range of this stream is: CODcr 80~120mg / L (typical value 105mg / L), TDS 8000~15000mg / L (typical value 12000mg / L), pH 8.0~8.5. The concentration is approximately 3000–5000 mg / L, and the conductivity is 15–25 mS / cm. Due to the high TDS and chloride ion concentrations, conventional biological treatment is difficult to implement, and hydroxyl radicals are easily quenched by chloride ions during advanced oxidation processes. Therefore, an enhanced treatment process combining catalytic ozone oxidation and microwave chemistry is required, as detailed below:

[0078] The ozone catalytic oxidation tower adopts a vertical steel structure, lined with polytetrafluoroethylene (PTFE) or coated with Hastelloy C-276 anti-corrosion layer. The tower diameter to height ratio is approximately 1:4, and the effective volume is designed based on the flow rate of the concentrate to be treated and a reaction time of 30 minutes. Assuming an average daily concentrate treatment capacity of approximately 1000 tons during the heating season (i.e., S4 concentrate production is approximately 45% of the influent, and secondary RO influent is 2200 tons / day × 45% ≈ 990 tons / day, equivalent to approximately 41.25 tons / hour), the required effective tower volume is ≥20.6 m³. 3 The actual value is 25m. 3 The tower is divided into three parts from bottom to top: a water distribution zone, a catalytic reaction zone, and a water outlet zone.

[0079] The water distribution zone adopts a side-inlet and bottom-outlet system, equipped with microporous titanium plate aeration discs (pore size 10-20μm). Ozone gas is evenly dispersed through the aeration discs and then comes into counter-current contact with the wastewater. Ozone is generated on-site by an oxygen-source ozone generator with a gas purity ≥90%. Ozone production is calculated based on a dosage of 30-50 mg / L and the volume of water to be treated; taking the upper limit of 50 mg / L, the required ozone volume is 41.25 m³. 3 / h×1000L / m 3 ×50mg / L / 1000=2062.5g / h, therefore an ozone generator with a rated output of 3kg / h (with a margin) is selected. The ozone exhaust gas is decomposed by an exhaust gas destroyer (heated catalytic type) and then discharged into the atmosphere.

[0080] Catalytic reaction zone loading The composite catalyst is supported by activated alumina spheres (3-5 mm in diameter, specific surface area ≥ 200 m² / g), and the active component is... The loading rate is 5%–8% (by weight). The catalyst layer height is 2 / 3 of the effective height of the tower, approximately 3.5–4 m, supported by a grid plate and covered with stainless steel wire mesh. The empty tower flow rate of wastewater in the catalyst layer is controlled at 1.5–2.5 m / h, and the contact time is ≥30 min (actually designed as 35 min). Under the action of the catalyst, the efficiency of ozone decomposition to generate hydroxyl radicals (·OH) is increased by 3–5 times, and the Mn(IV) / Mn(III) redox cycle can be continuously catalyzed. For recalcitrant organic compounds in the concentrate, such as long-chain alkanes, benzene series compounds, polycyclic aromatic hydrocarbons, and humic acids, hydroxyl radicals can attack their stable structures such as carbon-carbon double bonds and benzene rings, breaking them into small molecule carboxylic acids, aldehydes, and ketones, making them more biodegradable. The concentration of the raw water was increased from <0.1 to 0.25-0.35, improving its biodegradability (although no subsequent biological treatment tank was installed, the efficiency of microwave chemical treatment was improved).

[0081] The ozone catalytic oxidation tower's operating parameters are controlled via online ORP and COD sensors. When the effluent ORP falls below 600mV, the ozone dosage is automatically increased. The gas-to-water ratio is controlled at 1:3–1:5 (volume ratio), and the residual ozone concentration in the tail gas is ≤0.1mg / L. This step achieves an average COD removal rate of approximately 30%–40%, reducing the effluent COD to 50–80mg / L. Increase to 15-25 mg / L;

[0082] The effluent from the ozone catalytic oxidation tower flows by gravity into the microwave chemical treatment unit. The core equipment of this unit is the microwave reactor, which employs a rectangular or cylindrical resonant cavity. The inner wall is made of polished 304 stainless steel and coated with a Teflon anti-corrosion layer. An external magnetron (industrial grade, frequency 2450±25MHz, single-tube output power 1.5kW) is installed in the cavity. 3–5 magnetrons are configured according to the water volume to be treated, and the total microwave output power is controlled at a power density ≤2kW / m³. 3 Wastewater. Treatment capacity: 41.25 m³ 3 Based on a per-hour calculation, the required total microwave power is ≤82.5kW, and the actual configuration uses six 1.5kW magnetrons (totaling 9kW, with a power density of only 0.22kW / m²). 3 The flow rate is far below the upper limit, indicating that the design can be scaled down or intermittent operation can be used. Here, a conservative design is adopted based on the peak flow rate.

[0083] A more reasonable configuration is to use multiple units in parallel or in batches, but in continuous flow design, low power density and long residence time are used to ensure the effect.

[0084] The reactor is equipped with a meandering flow channel or a spiral guide plate to allow the wastewater to remain in the chamber for 5–10 minutes. A powdered sensitizer (Chemical B) addition point is located at the wastewater inlet. The sensitizer is a composite metal oxide (such as copper-manganese oxide or ferrite) micropowder with a particle size ≤10μm, possessing strong microwave absorption and catalytic capabilities. The sensitizer powder is continuously injected into the pipeline via a screw feeder and a Venturi injector, mixing with water before entering the microwave reactor. The sensitizer dosage is 200–300 mg / L (based on wastewater). Under the action of the microwave field, a "hot spot" effect is formed, promoting the non-thermal catalytic degradation of organic matter. Microwaves can also cause polar organic molecules to oscillate at high frequency, accelerating the bond-breaking process, and simultaneously inactivating residual bacteria and viruses (if present).

[0085] An online temperature sensor and a rapid COD detector are installed at the microwave reactor outlet to ensure that the outlet water temperature rises by no more than 5°C (i.e., from 20-25°C to no more than 30°C), thus preventing excessive energy consumption.

[0086] The microwave-treated effluent enters a flocculation and clarification tank, which is a combination of an inclined tube (plate) sedimentation tank and a horizontal flow sedimentation tank. The front end is a mixing zone, and the rear end is a sedimentation zone. Polyacrylamide (PAM), either anionic or nonionic with a molecular weight of 10 million, is added to the mixing zone as a 0.1% solution, added continuously at a dosage of 0.5 mg / L. The function of PAM is to flocculate the tiny suspended solids (including partially deactivated sensitizer particles, organic flocs, and metal oxides) in the microwave-treated wastewater into larger particles, facilitating sedimentation in the sedimentation zone.

[0087] The surface load of the sedimentation zone is designed to be 0.8–1.0 m. 3 / (m 2 ·h), settling time ≥20min (actually 30min). A sludge hopper and spiral sludge discharge machine are installed at the bottom; the discharged sludge (moisture content approximately 96%–98%) enters the intermediate sludge tank. The supernatant flows by gravity into the buffer discharge tank, ready for S6 compliance discharge testing;

[0088] To recover the sensitizer and reduce operating costs, the sludge from the clarifier is treated. The sludge is pumped by a screw pump into a hydrocyclone assembly (one unit in operation and one on standby, with a single unit processing capacity of 5-10 m³). 3 / h, separation particle size d50=8~10μm). The underflow port (heavy section) of the hydrocyclone yields sensitizer-enriched particles at a concentration of approximately 5%~10% (weight-to-volume ratio), which are returned to the mixing pipe before the microwave reactor inlet for reuse. The return flow rate is controlled at 10%~15% of the influent flow rate. The fine sludge discharged from the overflow port (mainly containing organic residues, calcium carbonate, and other inert solids) enters a plate and frame filter press for dewatering. The filter cake is disposed of as general solid waste, and the filtrate is returned to the equalization tank. Through sludge recirculation, the amount of fresh sensitizer replenished can be reduced from 300mg / L to 150~180mg / L, saving 40%~50%.

[0089] In one specific embodiment, actual operating data shows that the total COD removal rate (relative to the secondary RO concentrate) of this step can reach 55% to 70%. When the influent COD is 100 to 120 mg / L, the effluent COD after flocculation and clarification can be reduced to 35 to 45 mg / L, and SS ≤ 20 mg / L, meeting the requirements of the Class I standard (COD ≤ 60 mg / L, SS ≤ 50 mg / L) of the Integrated Wastewater Discharge Standard (GB8978-1996).

[0090] Furthermore, high TDS does not affect the treatment effect of this step, because microwave chemistry and catalytic ozone are not inhibited by salinity (a significant advantage compared to processes such as Fenton). The clarified liquid after this step enters S6 for final monitoring and discharge or reflux control to meet standards.

[0091] S6: Compliant discharge and intelligent diversion. The supernatant from the S5 flocculation and clarification tank (hereinafter referred to as "drainage") is pumped into the buffer discharge tank by gravity or via a lift pump. The buffer discharge tank adopts an above-ground reinforced concrete structure, with an epoxy fiberglass anti-corrosion coating (thickness ≥2mm) on the inner wall. Its effective volume is designed for a drainage volume of no less than 30 minutes. The S5 treatment capacity is 41.25 m³. 3 Based on a per-hour rate, the effective volume of the buffer discharge pool is taken as 25m³. 3 The pool is divided into two sections: the front section is a monitoring buffer zone, and the rear section is a discharge / recirculation switching zone. An overflow weir and an electric gate valve are installed between the two sections to facilitate isolation and maintenance in case of system failure.

[0092] An online water quality monitoring integrated device is installed within the monitoring buffer zone, including the following sensors (all industrial-grade corrosion-resistant, with a signal output of 4-20mA, and connected to the DCS system):

[0093] pH electrode (glass composite electrode, automatic temperature compensation, range 0~14, accuracy ±0.1).

[0094] COD online analyzer (potassium dichromate method or ultraviolet absorption method, range 0~200mg / L, accuracy ±5%)

[0095] Turbidity / SS detector (infrared scattering method, range 0~100NTU or 0~500mg / L, accuracy ±5%).

[0096] Online ammonia nitrogen analyzer (salicylic acid method or ion-selective electrode method, range 0-50 mg / L, accuracy ±5%).

[0097] Conductivity / TDS sensor (range 0~200mS / cm, accuracy ±1%).

[0098] Each instrument is installed in the still water area of ​​the monitoring pool, and baffles are installed in the water flow path to eliminate air bubbles and flow velocity interference. The sampling frequency is set to once every 5 minutes, and the data is processed by PLC logic to generate "discharge" or "recirculation" commands.

[0099] The discharge standard complies with the Class I standard of the "Integrated Wastewater Discharge Standard" (GB8978-1996). Specific limits are: pH 6-9, COD ≤ 60 mg / L, SS ≤ 50 mg / L, ammonia nitrogen ≤ 8 mg / L, petroleum hydrocarbons ≤ 5 mg / L (if any). While TDS is not mandatory under national standards, it must comply with the indirect discharge limits approved by the local environmental protection department (generally, industrial wastewater pipe networks in industrial parks require TDS ≤ 2000 mg / L or more leniently; the actual effluent TDS of this system is approximately 8000-12000 mg / L, exceeding the requirements for pipe network connection in most industrial parks, therefore this needs special explanation).

[0100] It should be noted that the final concentrated wastewater discharged using the method of this invention still has a relatively high TDS (Total Dissolved Solids). Advanced TDS treatment is not within the scope of this method (because industrial wastewater networks in industrial parks typically allow for higher salinity, or power plants are equipped with facilities for mixing and diluting with other low-salinity water). If local requirements also mandate TDS compliance, nanofiltration or electrodialysis units can be added after S5. However, the core of this method is to ensure that organic and suspended solids indicators such as COD, SS, and ammonia nitrogen meet standards. TDS issues can be resolved through in-plant mixing or by applying for a separate discharge permit. For the sake of rigor, online monitoring in this step still includes conductivity, used for recording and early warning.

[0101] When all monitoring indicators meet the standard limits (and remain stable for at least 10 minutes), the PLC opens the electric valve of the discharge pool and simultaneously starts the discharge pump (one in use and one on standby, made of fluoroplastic or duplex stainless steel) to discharge water into the industrial wastewater network of the park. A check valve and a manual maintenance valve are installed on the discharge pipe, and a sampling port is reserved for manual comparison and verification.

[0102] If any indicator exceeds the standard (e.g., COD suddenly rises to >60mg / L, or pH drift exceeds the 6-9 range), the system immediately executes a reflux operation: the discharge pump stops, and simultaneously the reflux electric valve opens, transferring the excess water from the buffer discharge tank to the front end of the concentrated brine equalization tank described in S1 via the reflux pump (shared with the discharge pump, switched via valve group). A flow meter is installed on the reflux pipeline, and the reflux flow rate is designed to be ≤20% to ensure the equalization tank does not overflow due to excessive instantaneous reflux. Simultaneously, the system sends an alarm signal to the DCS, prompting operators to check the operating parameters from S2 to S5 (such as lime dosage, ozone production, sensitizer concentration, etc.) and take corrective measures.

[0103] To prevent excessive water from remaining in the buffer tank for an extended period and causing further water quality deterioration, a maximum retention time of 8 hours is set. If the problem persists within 8 hours, the system will automatically transfer the water from the buffer tank to a backup emergency tank (with a volume of not less than 500m³). 3 Once the situation returns to normal, the waste will be returned in batches for further processing. A high liquid level signal in the emergency pool will trigger a system-wide load reduction or shutdown protection mechanism.

[0104] In addition, this step also includes a regular manual sampling and calibration mechanism. Once a week, laboratory personnel collect samples at the emission point and perform comparative analysis according to national standard methods (GB11914-1989 for COD measurement, GB7479-87 for ammonia nitrogen measurement, gravimetric method for SS measurement, etc.) to calibrate the accuracy of the online instruments. Calibration records are archived for future reference.

[0105] Through the aforementioned intelligent diversion and recirculation retreatment mechanism, the method of this invention ensures that the final effluent quality consistently meets the Class I standard requirements of GB8978-1996 under any normal or slightly disturbed operating conditions, achieving environmentally compliant discharge. Furthermore, the water recirculated into S2-S5 has already undergone partial degradation, reducing the required reagents and energy consumption for retreatment and thus not significantly increasing operating costs. Actual operational statistics show that during three months of continuous operation, the system triggered recirculation due to effluent exceeding standards on average once every two weeks, with each recirculation flow not exceeding 5% of the daily treated water volume, resulting in an overall environmental compliance rate of 100%.

[0106] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A method for the resource recycling of concentrated brine from primary reverse osmosis in a thermal power plant, characterized in that, The method includes: S1. Source isolation and directional collection of primary reverse osmosis brine: The brine produced by the primary reverse osmosis unit of the thermal power plant is isolated and collected at the source, and introduced into the equalization tank for homogenization and equalization treatment to obtain homogenized brine. S2. Pretreatment of concentrated brine, namely seed-induced softening and online flocculation, involves sequentially subjecting the homogeneous concentrated brine to seed-induced softening and online flocculation to remove bicarbonate alkalinity, colloidal silica, and suspended solids, thereby obtaining pretreated permeate. S3. Post-pH adjustment and ultrafiltration fine treatment: The pretreated water is directly sent into the ultrafiltration system for fine filtration in its original high pH state to obtain ultrafiltration water; The pH of the ultrafiltration water is adjusted to reduce its pH value to a preset range to obtain conditioned ultrafiltration water. S4. Secondary reverse osmosis concentration of concentrated brine: Utilizing the residual pressure at the concentrated water discharge port of the primary reverse osmosis unit, the conditioning ultrafiltration permeate is sent to a low-pressure reverse osmosis unit for secondary concentration to obtain secondary reverse osmosis permeate and secondary reverse osmosis concentrate; wherein, the secondary reverse osmosis permeate is recycled to the ultrafiltration water tank of the thermal power plant, and the secondary reverse osmosis concentrate is sent to subsequent treatment. S5. Advanced oxidation-flocculation-microwave coupled treatment of secondary RO concentrate: The secondary reverse osmosis concentrate is subjected to ozone catalytic oxidation treatment and microwave chemical treatment in sequence, and then separated by flocculation clarification to obtain a qualified clear liquid. S6. Discharge in compliance with standards: The compliant clear liquid is monitored online. If the monitored indicators meet the discharge standards, it is discharged. If any indicator exceeds the standard, the compliant clear liquid is returned to the equalization tank.

2. The method for resource recycling of concentrated brine from primary reverse osmosis in a thermal power plant according to claim 1, characterized in that, In S1, the effective volume of the regulating tank is designed to be 1.2 times the daily concentrated water production under the maximum operating conditions during the heating season, and it is equipped with a submersible agitator, a level gauge and an adsorption device; the total dissolved solids fluctuation range of the homogenized concentrated brine is reduced to within ±10%, and the pH value is stabilized at 8.0 to 8.

5.

3. The method for resource recycling of primary reverse osmosis concentrated brine from a thermal power plant according to claim 1, characterized in that, S2 specifically includes: continuously adding lime slurry, polyferric sulfate, polyacrylamide and calcium sulfate seed crystals to the seed-induced softening reactor, controlling the reaction pH to be 10.5-11.0, and the mixed liquid after the reaction enters the inclined tube sedimentation zone for solid-liquid separation. The supernatant is filtered through a high-efficiency fiber filter to obtain pretreated permeable water with turbidity ≤2NTU and suspended solids ≤5mg / L.

4. The method for resource recycling of concentrated brine from primary reverse osmosis in a thermal power plant according to claim 1, characterized in that, In step S3, the pretreated water originally had a high pH value of 10.3 to 10.

7. The ultrafiltration system uses a polyvinylidene fluoride hollow fiber membrane and operates under high pH conditions, achieving a total silicon removal rate of 60%–70%. The pH adjustment is performed by using dilute sulfuric acid to adjust the pH value of the ultrafiltration permeate to 8.2–8.

5.

5. The method for resource recycling of concentrated brine from primary reverse osmosis in a thermal power plant according to claim 1, characterized in that, In step S3, the pH adjustment operation is performed after the ultrafiltration system and before the low-pressure reverse osmosis device to prevent the precipitated calcium carbonate and polysilicic acid from redissolving due to pH reduction before filtration.

6. The method for resource recycling of primary reverse osmosis concentrated brine from a thermal power plant according to claim 1, characterized in that, In step S4, the residual pressure of the concentrate discharge port of the first-stage reverse osmosis unit is 0.5 to 0.8 MPa. Only an online booster pump is set to compensate for pressure loss, so that the operating pressure of the low-pressure reverse osmosis unit is ≤1.0 MPa. The low-pressure reverse osmosis unit is arranged in a three-stage first-stage configuration, and the system recovery rate is set to 50% to 60%.

7. The method for resource recycling of concentrated brine from primary reverse osmosis in a thermal power plant according to claim 1, characterized in that, In step S4, the conductivity of the secondary reverse osmosis permeate is 280–350 μS / cm, and the chemical oxygen demand is ≤5 mg / L. The secondary reverse osmosis permeate is directly connected to the inlet header of the ultrafiltration water tank in the plant area.

8. The method for resource recycling of concentrated brine from primary reverse osmosis in a thermal power plant according to claim 1, characterized in that, In step S5, the ozone catalytic oxidation treatment uses ozone in... The composite catalyst generates hydroxyl radicals, which can remove 30% to 40% of the chemical oxygen demand. The microwave chemical treatment uses microwave radiation at a frequency of 2450±25MHz and adds a microwave absorption sensitizer. After treatment, the chemical oxygen demand of the effluent is reduced to 35-45 mg / L through flocculation and clarification.

9. The method for resource recycling of primary reverse osmosis concentrated brine from a thermal power plant according to claim 1, characterized in that, In S6, when any monitoring indicator exceeds the standard, the system automatically transports the water exceeding the standard in the buffer discharge pool to the front end of the regulating pool through the return pump, and at the same time sends an alarm signal to the distributed control system. If the time exceeding the standard exceeds the preset duration, the water exceeding the standard will be switched to the emergency pool.

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