Deep purification system for steel coking wastewater and operation process of deep purification system

Abstract

The invention provides a steel coking wastewater deep purification system and an operation process thereof, and relates to the technical field of industrial wastewater treatment.The system comprises a pretreatment adjusting unit, an electric flocculation purification unit, a solid-liquid separation unit and a molecular sieve adsorption unit which are sequentially connected in the wastewater flow direction; the pretreatment adjusting unit is used for homogenizing the wastewater and adjusting the pH value to 5.5-7.0; the electric flocculation purification unit is used for synergistically purifying fluoride, silicon and calcium ions in the wastewater; the solid-liquid separation unit is used for separating flocs and clear liquid generated by electric flocculation; the molecular sieve adsorption unit is used for deeply removing calcium and silicon in the clear liquid. The technical problem that scaling ions in the high-concentration brine are difficult to deeply remove is solved, and the technical effects that the calcium ion concentration of effluent water is lower than 20 mg / L, the silicon dioxide concentration of the effluent water is lower than 50 mg / L, and the fluorine ion concentration of the effluent water is lower than 5 mg / L are achieved.

Description

Technical Field

[0001] This invention relates to the technical field of industrial wastewater treatment, and in particular to a deep purification system for steel coking wastewater and its operating process. Background Technology

[0002] The large amount of wastewater generated during the steel coking process hinders the industry's green development. This wastewater contains toxic organic compounds such as phenols, cyanides, and ammonia nitrogen, as well as high concentrations of inorganic salts. If not treated properly, it will cause serious and lasting pollution to the water environment. Achieving near-zero wastewater discharge is not only the bottom line for the survival of enterprises, but also a social responsibility that they must fulfill.

[0003] In wastewater reuse and "zero discharge" processes, membrane technologies such as reverse osmosis produce high-concentration brine, which is the ultimate bottleneck of the entire treatment system. The core problem with this concentrated brine is that it is rich in scale-forming ions such as fluoride, silicon, and calcium ions. In subsequent deep treatment units such as evaporation and crystallization, it is very easy to form dense hard scale such as calcium fluoride and calcium silicate, which seriously clogs equipment pipes, causing the system to shut down frequently for cleaning, energy consumption to increase dramatically, and even unable to operate stably, thus affecting the achievement of the "zero discharge" goal.

[0004] Existing technologies have significant limitations in the deep purification of high-concentration brine: Chemical precipitation method: The traditional lime method has limited effect on defluoridation, the effluent is difficult to meet the standards, and a large amount of sludge is generated. At the same time, it introduces excessive calcium ions, which increases the risk of calcium scale formation. Single electrocoagulation method: Although it can effectively remove fluoride and some colloidal silica, it is not capable of removing dissolved active silica and it is difficult to reduce the calcium ion concentration to a low level. The effluent water quality cannot meet the influent requirements of subsequent high-end membranes or evaporators. Adsorption / ion exchange method: Special resins or adsorbents are expensive, easily poisoned and ineffective due to organic pollution, require frequent regeneration, are complex to operate and maintain, and generate secondary wastewater.

[0005] In summary, the steel and coking industry urgently needs to develop a new purification technology that can synergistically, deeply, and economically remove fluorine, silicon, and calcium, ensuring the stable operation of the final "zero emission" system.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] One of the objectives of this invention is to provide a deep purification system for steel coking wastewater, which can solve the technical problem of the difficulty in deep removal of scaling ions in high-concentration brine, and can achieve the technical effect of calcium ion concentration below 20 mg / L, silica concentration below 50 mg / L and fluoride ion concentration below 5 mg / L in the effluent.

[0008] The second objective of this invention is to provide an operating process for a deep purification system for steel coking wastewater, which has advantages such as high efficiency, low operating cost and high degree of automation, providing reliable technical support for zero discharge of steel coking wastewater.

[0009] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, a deep purification system for steel coking wastewater includes a pretreatment conditioning unit, an electrocoagulation purification unit, a solid-liquid separation unit, and a molecular sieve adsorption unit connected sequentially along the wastewater flow direction. The pretreatment adjustment unit is used to homogenize the wastewater and adjust the pH to 5.5-7.0; The electrocoagulation purification unit is used to synergistically purify fluoride, silicon and calcium ions in wastewater. The solid-liquid separation unit is used to separate the flocs and clear liquid generated by electrocoagulation; The molecular sieve adsorption unit is used to remove calcium and silicon from the solution.

[0010] Furthermore, the pretreatment adjustment unit is equipped with an online pH monitor and an automatic dosing device.

[0011] Furthermore, the electrocoagulation purification unit includes an electrocoagulation reactor.

[0012] Furthermore, the electrode spacing of the electrocoagulation reactor is 10mm-20mm; Preferably, the operating current density of the electrocoagulation reactor is 10 mA / cm². 2 -25mA / cm 2 The hydraulic retention time is 15-30 minutes.

[0013] Furthermore, the solid-liquid separation unit includes a dissolved air flotation machine.

[0014] Furthermore, the dissolved air flotation machine has a dissolved air pressure of 0.3MPa-0.5MPa and a reflux ratio of 20%-30%. Preferably, the hydraulic residence time of the dissolved air flotation machine is 15-25 minutes.

[0015] Furthermore, the molecular sieve adsorption unit includes a molecular sieve adsorption tower; Preferably, the molecular sieve adsorption tower is filled with special molecular sieve filter media; Preferably, the lower layer of the molecular sieve adsorption tower is filled with Na-type clinoptilolite, and the upper layer is filled with high-silica Y-type molecular sieve.

[0016] Furthermore, the system also includes piping connecting the units and its control system; Preferably, the control system is based on a PID control algorithm and adjusts the dosage of the dosing device according to the pH value feedback signal of the effluent from the pretreatment adjustment unit to make the pH 5.5-7.0. Preferably, the control system is based on a predictive model. Based on the effluent quality of the molecular sieve adsorption unit, the breakthrough time is predicted and a regeneration or switching procedure is automatically triggered.

[0017] Secondly, an operating process of any of the above-mentioned systems includes the following steps: Wastewater is passed into a pretreatment conditioning unit for homogenization and pH adjustment to 5.5-7.0, and then into an electrocoagulation purification unit for electrochemical purification, which synergistically removes fluoride, silicon, and calcium ions from the wastewater. The electrocoagulated effluent enters a solid-liquid separation unit for solid-liquid separation to obtain a clear liquid. The clear liquid is then passed into a molecular sieve adsorption unit for deep removal of calcium and silicon, resulting in compliant wastewater.

[0018] Furthermore, the calcium ion concentration of the compliant wastewater is less than 20 mg / L, the silica concentration is less than 50 mg / L, and the fluoride ion concentration is less than 5 mg / L.

[0019] Compared with the prior art, the present invention has at least the following beneficial effects: The deep purification system for steel coking wastewater provided by this invention achieves functional complementarity and synergistic effect through the innovative coupling of electrocoagulation and molecular sieve. Electrocoagulation, as a pre-treatment unit, can efficiently remove most of the fluoride and silicon and initially reduce calcium, thus "lightening the load" for the subsequent molecular sieve. The molecular sieve can then accurately and deeply remove residual pollutants. With the synergistic cooperation of each unit, the technical problem of the difficulty in deeply removing scaling ions in high-concentration brine is solved. Not only is the effluent quality of the system excellent, but it can also stably achieve the stringent indicators of calcium ion concentration below 20 mg / L, silica concentration below 50 mg / L, and fluoride ion concentration below 5 mg / L, completely avoiding the scaling risk of subsequent membrane and thermal desalination systems.

[0020] The operating process of the deep purification system for steel coking wastewater provided by this invention has the advantages of synergistic efficiency, low operating cost and high degree of automation, providing reliable technical support for zero discharge of steel coking wastewater. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 A flowchart of the operation of a deep purification system for steel coking wastewater provided in one embodiment of the present invention; Figure 2 This is an equipment operation diagram of a deep purification system for steel coking wastewater provided in one embodiment of the present invention. Detailed Implementation

[0023] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] According to a first aspect of the present invention, a deep purification system for steel coking wastewater is provided, comprising a pretreatment conditioning unit, an electrocoagulation purification unit, a solid-liquid separation unit, and a molecular sieve adsorption unit connected sequentially along the wastewater flow direction; The pretreatment conditioning unit is used to homogenize the wastewater and adjust the pH to 5.5-7.0; The electrocoagulation purification unit is used to synergistically purify fluoride, silicon and calcium ions in wastewater; The solid-liquid separation unit is used to separate the flocs and clear liquid generated by electrocoagulation; Molecular sieve adsorption units are used to remove calcium and silicon from the solution.

[0025] The system of this invention couples electrocoagulation with molecular sieve technology to construct a series system of "electrochemical synergistic purification + physical adsorption fine treatment". Electrocoagulation, as a pre-treatment unit, efficiently removes most of the fluorine and silicon and initially reduces calcium, while molecular sieve, as a back-end unit, achieves deep removal of residual calcium and silicon. The two complement each other and thoroughly remove a variety of pollutants.

[0026] In summary, the system of this invention, through the coordinated efforts of all units, solves the technical problem of the difficulty in deep removal of scaling ions in high-concentration brine. Not only does the system produce excellent effluent quality, but it can also stably achieve stringent indicators such as calcium ion concentration below 20 mg / L, silica concentration below 50 mg / L, and fluoride ion concentration below 5 mg / L, thus completely avoiding the scaling risks of subsequent membrane and thermal desalination systems.

[0027] In a preferred embodiment, the pretreatment adjustment unit may be equipped with an online pH monitor and an automatic dosing device.

[0028] The pretreatment and conditioning unit is the primary and crucial link for the efficient and stable operation of the entire system. The pretreatment and conditioning unit can equalize the fluctuating influent water quality through the conditioning tank, providing stable influent conditions for subsequent treatment units. The pretreatment and conditioning unit can use an automatic dosing device to precisely control the pH of the wastewater to the range of 5.5-7.0, preferably to the range of 6.0-6.5, laying a vital physicochemical foundation for achieving efficient purification in the subsequent process.

[0029] In this invention, the electrocoagulation purification unit utilizes electrochemical principles to generate highly efficient multifunctional flocculants in situ through the electro-dissolution effect of soluble aluminum anodes, thereby achieving synergistic purification of fluorides, silicon (SiO2), and calcium ions in wastewater.

[0030] Electrocoagulation purification units include, but are not limited to, electrocoagulation reactors.

[0031] The main body of the electrocoagulation reactor can be a corrosion-resistant tank (such as PP, PVC or fiberglass), equipped with an inlet, an outlet and a sludge discharge outlet. Aluminum plates (AA) or aluminum alloy plates can be used as soluble anodes and cathodes (this is the best balance choice based on the cost, toxicity and flocculation efficiency of aluminum and its hydrolysis products). The plates can be arranged in a multi-group parallel plate-frame structure with parallel arrangement between the plates to ensure uniform current density distribution.

[0032] Maintaining a stable pH value in the influent of the electrocoagulation reactor within the range of 5.5-7.0 ensures that the aluminum hydrolysis products are in their most active form.

[0033] In a preferred embodiment, the electrode spacing of the electrocoagulation reactor can be 10mm-20mm, with typical but non-limiting spacings such as 10mm, 12mm, 14mm, 16mm, 18mm, and 20mm, which helps to reduce solution resistance and save energy.

[0034] When direct current is applied to the electrocoagulation reactor, a crucial electrochemical dissolution reaction occurs at the anode, continuously and stably releasing Al, the precursor flocculant, into the wastewater. 3+ Simultaneously, a hydrogen evolution reaction occurs at the cathode, producing OH-. - Diffusion into the bulk solution, reacting with Al 3+ When they meet, they trigger a series of hydrolysis and polymerization reactions, ultimately producing amorphous Al(OH)3 colloids and substances such as Al8(OH). 20 4+ Highly polymerized, strongly positively charged polymeric aluminum hydroxyl ions. These newly formed, highly active aluminum hydrolysis products constitute the physicochemical basis for the synergistic removal of pollutants; for the removal of fluorides, the main process is the formation of... The removal of calcium ions is achieved by promoting the formation of calcium fluoride and calcium silicate precipitates, which are then co-precipitated on the surface of the flocs. For the removal of silicon, the specific complexation between aluminum hydroxyl and silanol hydroxyl groups forms Si-O-Al bonds and is fixed thereon. At the same time, colloidal silicon is captured through charge neutralization and entrapment. For the initial removal of calcium ions, the formation of calcium fluoride and calcium silicate precipitates is promoted and co-precipitated on the surface of the flocs.

[0035] In a preferred embodiment, the operating current density of the electrocoagulation reactor can be 10 mA / cm². 2 -25mA / cm 2 Its typical, but not limiting, density is, for example, 10 mA / cm³. 2 15mA / cm 2 20mA / cm 2 25mA / cm 2 The hydraulic residence time can be 15 min to 30 min, with typical but non-limiting times being 15 min, 20 min, 25 min, and 30 min.

[0036] In this invention, the solid-liquid separation unit is the key link between the preceding and following steps. The solid-liquid separation unit completely separates the composite flocs loaded with pollutants such as fluorine, silicon, and calcium generated by the electrocoagulation purification unit from the water, providing clear influent with extremely low suspended solids content (usually required to be <10mg / L) for the subsequent molecular sieve adsorption unit. This effectively prevents the micropore channels of the molecular sieve from being blocked, ensuring that the entire system can operate stably for a long period of time.

[0037] In a preferred embodiment, the solid-liquid separation unit includes, but is not limited to, a dissolved air flotation machine.

[0038] Because the electrocoagulation products have a moderate density and may contain fine hydrogen bubbles, they can be efficiently separated using a dissolved air flotation machine.

[0039] The working principle of a dissolved air flotation (DAF) system is to pressurize a portion of the flotation effluent and dissolve air into it, forming saturated dissolved air water. Then, a large number of 20-50 micrometer microbubbles are generated in the contact chamber via a release device. These bubbles efficiently adhere to the floc particles in the electrocoagulation effluent, forming a "bubble-floc" composite. Its overall density is much less than water, causing it to quickly float to the surface under buoyancy, forming a scum layer, which is then removed by a scraper. The clear water is discharged from the bottom of the tank. Compared to traditional inclined plate sedimentation tanks, DAF offers faster separation speeds, higher efficiency, and a more compact tank structure. It is particularly effective at treating lightweight flocs containing microbubbles, consistently ensuring that the suspended solids in the effluent are below 5 mg / L.

[0040] In a preferred embodiment, the dissolved air flotation machine can have a dissolved air pressure of 0.3 MPa-0.5 MPa, with typical but non-limiting pressures such as 0.3 MPa, 0.4 MPa, and 0.5 MPa, and a reflux ratio of 20%-30%, with typical but non-limiting reflux ratios such as 20%, 22%, 24%, 26%, 28%, and 30%.

[0041] In a preferred embodiment, the hydraulic residence time of the dissolved air flotation unit can be 15 min to 25 min, with typical but non-limiting times being, for example, 15 min, 20 min, and 25 min.

[0042] In this invention, the molecular sieve adsorption unit serves as the final refining unit. This unit can utilize the unique properties of special molecular sieves to deeply remove residual calcium ions and dissolved silicon that are difficult to completely remove by the preceding units through a synergistic mechanism of highly selective ion exchange and precise physical adsorption.

[0043] In this invention, the molecular sieve adsorption unit includes, but is not limited to, a molecular sieve adsorption tower.

[0044] In a preferred embodiment, the molecular sieve adsorption tower is filled with special molecular sieve filter media. The lower layer of the molecular sieve adsorption tower can be filled with Na-type clinoptilolite, and the upper layer can be filled with high-silica Y-type molecular sieve.

[0045] The molecular sieve adsorption tower adopts a double-layer composite packing structure with a lower layer of zeolite and an upper layer of high-silica Y-type molecular sieve, achieving deep calcium and silicon removal simultaneously in one tower.

[0046] For deep removal of calcium, the molecular sieve adsorption tower uses Na-type clinoptilolite, which utilizes its crystal structure to specifically select for divalent calcium ions, resulting in a highly efficient ion exchange reaction that firmly fixes the calcium ions in the channels. For deep removal of silicon, it relies on the huge specific surface area and uniform pore size of hydrophobic molecular sieves such as high-silica Y-type sieves, which adsorb active silica molecules (H4SiO4) in water through strong van der Waals forces, and achieve a molecular-scale sieving effect with its precise pore size.

[0047] Clear influent after solid-liquid separation passes through an adsorption tower filled with molecular sieves at an empty tower flow rate of 3BV / h-8BV / h. During this process, calcium and silicon are deeply removed. When the concentration of calcium or silicon in the effluent approaches the breakthrough threshold, the saturated molecular sieve needs to be regenerated.

[0048] In this invention, Na-type clinoptilolite can be eluted and regenerated using a high-concentration sodium chloride solution (5%-10%) (Ca(Zeo)2 + 2Na). + →2Na-Zeo+Ca 2+The adsorption capacity is greatly restored by using hot dilute sodium hydroxide solution (1%-2%) to dissolve and desorb the adsorbed silicon (SiO2 (adsorbed state) + 2NaOH → Na2SiO3 + H2O), thus greatly restoring the adsorption capacity.

[0049] Through efficient adsorption-regeneration operation, the molecular sieve adsorption unit can stably ensure the Ca content in the final effluent. 2+ With concentrations below 20 mg / L and SiO2 concentrations below 50 mg / L, it can provide absolutely safe feed water for subsequent evaporation crystallization or membrane systems, completely solving the problem that restricts the stable operation of zero-discharge systems.

[0050] The permeate water, after deep purification by molecular sieves, can be collected in a permeate tank. This tank not only homogenizes the water quality and buffers the flow rate, but also provides a short-term, stable supply of compliant water to the downstream system during the regeneration of the molecular sieve tower. Key monitoring instruments such as online calcium ion analyzers and silicon meters can be installed on the permeate pipeline to perform real-time, continuous final checks on the effluent, ensuring the Ca content is within acceptable limits. 2+ If the concentration is below 20 mg / L or the SiO2 concentration is below 50 mg / L, any exceeding of the limit will immediately trigger an alarm.

[0051] To meet the inlet water requirements of subsequent high-end equipment, trace amounts of sodium hypochlorite can be added for disinfection, effectively preventing the growth of microorganisms in subsequent membrane systems or evaporators. The purified water that fully meets all the standards can be safely and stably pumped by the product water transfer pump to the downstream disc tube reverse osmosis (DTRO) system for final concentration or directly into the evaporator crystallizer.

[0052] In this invention, the system also includes pipelines connecting the various units and its control system.

[0053] In a preferred embodiment, the control system can be based on a PID control algorithm to adjust the dosage of the dosing device according to the pH value feedback signal of the effluent from the pretreatment adjustment unit, so that the pH is 5.5-7.0.

[0054] In the preprocessing stage, the system employs a "feedforward-feedback" composite control algorithm: through a PID algorithm (such as... The dosage is dynamically adjusted based on the real-time pH value, and feedforward compensation is performed based on historical data of the influent pH to take action in advance to offset water quality fluctuations and ensure that the inlet pH of the electrocoagulation unit is stable within the optimal range; the PID algorithm ensures that the electrocoagulation purification unit obtains influent with extremely stable pH, which is the basis for the efficient conduct of subsequent chemical reactions.

[0055] In PID algorithm The deviation value is the difference between the set value and the measured value at time t. The proportional gain determines the strength of the control action's response to the current deviation. When the pH suddenly deviates from the set value (e.g., a pH increase caused by a dosing pump malfunction), the proportional term will immediately generate a strong correction signal, commanding the dosing pump (e.g., an acid pump) to rapidly increase the dosage to suppress the expansion of the deviation. The larger the value, the faster the response, but an excessively large value may cause system oscillation; The integral term represents the accumulation (integration) of deviations over all past times, used to eliminate steady-state error. If only proportional control is used, pH may eventually stabilize at 6.3 (instead of 6.2), with a very small static deviation. The integral term will continue to accumulate due to this persistent small deviation, gradually increasing the control effect until the pH is accurately "pushed back" to 6.2. The differential term represents the rate of change of the deviation, i.e. how fast the deviation changes. It has a "predictive" control function. If the pH is dropping rapidly, the differential term will generate a reverse control function in advance (such as reducing the amount of acid pump added) to prevent the pH from "overshooting" and falling below the set value. The output of the controller, after PID calculation, is finally sent to the actuator (acid / alkali metering pump) as a control signal. This signal determines the speed or stroke frequency of the metering pump, thereby achieving precise and stable pH adjustment.

[0056] In a preferred embodiment, the control system can be based on a predictive model. Based on the effluent quality of the molecular sieve adsorption unit, the breakthrough time is predicted and the regeneration or switching program is automatically triggered.

[0057] For the critical molecular sieve adsorption unit, the control system introduces an innovative algorithm: a "predictive model based on dynamic adsorption capacity." This model monitors the effluent concentration in real time using an online calcium / silicon meter and integrates historical adsorption data to dynamically calculate the remaining working capacity of the adsorption tower and the predicted breakthrough time. When the remaining operating time is predicted to be below the threshold, the system can issue an early warning or automatically switch to the backup tower and start the regeneration program, changing passive response to active management, fundamentally eliminating the risk of excessive effluent quality, and significantly reducing operating costs by precisely controlling the timing and dosage of regeneration.

[0058] In the prediction model To predict breakthrough time, the system predicts how many hours the current molecular sieve adsorption tower can operate stably before its effluent concentration exceeds the allowable value. Given the remaining adsorption capacity of the adsorption tower, how many grams of pollutants can the molecular sieve inside the tower still adsorb? The concentration of pollutants in the influent, specifically Ca in the wastewater entering the molecular sieve adsorption tower. 2 +Or the concentration of SiO2; the higher the concentration, the faster the adsorption tower is "consumed," and the longer the breakthrough time. The shorter it is; The system's processing flow rate is the water flow rate through the adsorption tower. The higher the flow rate, the greater the total amount of pollutants delivered to the adsorption tower per unit time. The more (the more) that penetrates time The shorter it is.

[0059] According to a second aspect of the present invention, an operating process for the system described in any one of the preceding claims is provided, comprising the following steps: Wastewater is passed into a pretreatment conditioning unit for homogenization and pH adjustment to 5.5-7.0, and then into an electrocoagulation purification unit for electrochemical purification, which synergistically removes fluoride, silicon, and calcium ions from the wastewater. The electrocoagulated effluent enters a solid-liquid separation unit for solid-liquid separation to obtain a clear liquid. The clear liquid is then passed into a molecular sieve adsorption unit for deep removal of calcium and silicon, resulting in compliant wastewater.

[0060] The system of this invention has the advantages of efficient operation, low operating cost and high degree of automation, providing reliable technical support for zero discharge of steel coking wastewater.

[0061] In a preferred embodiment, the calcium ion concentration of the treated water is less than 20 mg / L, the silica concentration is less than 50 mg / L, and the fluoride ion concentration is less than 5 mg / L.

[0062] The present invention will be further illustrated by the following examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0063] Example 1 A deep purification system for steel coking wastewater includes a pretreatment and conditioning unit, an electrocoagulation purification unit, a solid-liquid separation unit, and a molecular sieve adsorption unit connected sequentially along the wastewater flow direction. The pretreatment conditioning unit is used to homogenize the wastewater and adjust the pH to 5.5-7.0; The pretreatment and conditioning unit homogenizes the fluctuating incoming water through a conditioning tank. It is equipped with an online pH monitor and an automatic dosing device. The pretreatment and conditioning unit uses the automatic dosing device to precisely control the pH of the wastewater to the range of 5.5-7.0. The electrocoagulation purification unit is used to synergistically purify fluoride, silicon and calcium ions in wastewater; The electrocoagulation purification unit uses an electrocoagulation reactor, which utilizes electrochemical principles to generate highly efficient multifunctional flocculants in situ through the electro-dissolution effect of soluble aluminum anodes, thereby synergistically purifying fluorides, silicon (SiO2) and calcium ions in wastewater. The electrode spacing of the electrocoagulation reactor is 15 mm, and the operating current density is 18 mA / cm².2 The hydraulic residence time is 20 minutes; The solid-liquid separation unit is used to separate the flocs and clear liquid generated by electrocoagulation; The solid-liquid separation unit uses a dissolved air flotation machine; The dissolved air flotation unit has a dissolved air pressure of 0.4 MPa, a reflux ratio of 25%, and a hydraulic retention time of 20 min. Molecular sieve adsorption units are used to remove calcium and silicon from the solution. The molecular sieve adsorption unit uses a molecular sieve adsorption tower; The lower layer of the molecular sieve adsorption tower is filled with Na-type clinoptilolite, and the upper layer is filled with high-silica Y-type molecular sieve.

[0064] Example 2 The only difference between this embodiment and Embodiment 1 is that the electrode spacing of the electrocoagulation reactor is 10mm. Everything else is the same as in Example 1.

[0065] Example 3 The only difference between this embodiment and Embodiment 1 is that the electrode spacing of the electrocoagulation reactor is 20mm. Everything else is the same as in Example 1.

[0066] Example 4 The only difference between this embodiment and Embodiment 1 is that the operating current density of the electrocoagulation reactor is 10 mA / cm². 2 ; Everything else is the same as in Example 1.

[0067] Example 5 The only difference between this embodiment and Embodiment 1 is that the operating current density of the electrocoagulation reactor is 25 mA / cm². 2 ; Everything else is the same as in Example 1.

[0068] Example 6 The only difference between this embodiment and Embodiment 1 is that the dissolved air flotation machine has a dissolved air pressure of 0.3 MPa. Everything else is the same as in Example 1.

[0069] Example 7 The only difference between this embodiment and Embodiment 1 is that the dissolved air flotation machine has a dissolved air pressure of 0.5 MPa. Everything else is the same as in Example 1.

[0070] Example 8 The only difference between this embodiment and Embodiment 1 is that the hydraulic residence time of the dissolved air flotation machine is 15 minutes. Everything else is the same as in Example 1.

[0071] Example 9 The only difference between this embodiment and Embodiment 1 is that the hydraulic residence time of the dissolved air flotation machine is 25 minutes. Everything else is the same as in Example 1.

[0072] Example 10 This embodiment describes the operating process of the system in Embodiments 1-9. (See...) Figure 1 and Figure 2 This includes the following steps: (a) Pretreatment and pH adjustment: Steel coking wastewater first enters an effective volume of 15m³ 3 The equalization tank (HRT=3h) was used for 3 hours to equalize the water quality and quantity. The submersible agitator (power 0.75kW) in the tank ran continuously to ensure that the wastewater was mixed evenly. The online pH monitor detects water quality in real time. When the pH value deviates from the set range, the integrated control system immediately starts the automatic dosing program to precisely adjust the pH of the wastewater to the range of 6.0-6.4. (b) Electrocoagulation and synergistic purification: The wastewater, after pH adjustment, is treated at 5m³. 3 A flow rate of / h is pumped into the tubular electrocoagulation reactor. Under the influence of the electric field, the aluminum anode plate continuously dissolves and releases Al. 3+ These Al 3+ Rapid hydrolysis generates Al(OH)3 colloids with strong adsorption and flocculation capabilities, as well as various polymeric aluminum hydroxyl ions; The novel aluminum flocculant achieves synergistic removal of pollutants through three mechanisms, including forming AlF with fluoride ions. x (OH) 3-x Precipitation achieves deep fluoride removal by immobilizing colloidal silicon and active silicon into aluminosilicate complex through adsorption and complexation, which promotes the co-precipitation of calcium ions with fluoride ions and silicate ions to form slightly soluble salts. (c) Solid-liquid separation: The flocs carried by the electrocoagulation effluent are completely separated by the dissolved air flotation device, which efficiently separates the flocs from the clear liquid; The dissolved air flotation device pressurizes and dissolves air into a portion of the flotation effluent to form saturated dissolved air water. Then, a large number of 20-50 micron microbubbles are generated in the contact chamber through the release device. These bubbles adhere efficiently to the floc particles in the electrocoagulation water to form a "bubble-floc" composite. Its overall density is much less than that of water, so it quickly floats to the surface under the action of buoyancy, forming a scum layer, which is then removed by a scum scraper. The clean water is discharged from the bottom of the tank. (d) Molecular sieve adsorption purification: Wastewater flows through the bed from top to bottom. Zeolite reduces the calcium ion concentration to below 15 mg / L through ion exchange reaction. At the same time, the molecular sieve achieves precise sieving and van der Waals adsorption of silica molecules with its uniform nano-sized pores, controlling the silica concentration to below 40 mg / L. When the concentration of calcium ions in the effluent approaches the breakthrough threshold of 15 mg / L, the system automatically switches to the backup adsorption tower and starts the intelligent regeneration program. First, the bed is loosened by hydraulic backwashing at a flow rate of 15 m / h. Then, the zeolite layer is regenerated with 6% sodium chloride solution to restore its ion exchange capacity. Next, the silicon components adsorbed by the molecular sieve are desorbed with 1.5% sodium hydroxide solution at 60℃. After multiple stages of forward washing until the effluent pH is <9 and the conductivity is <1500 μS / cm, the adsorption tower fully recovers its adsorption performance and can be put back into operation.

[0073] Comparative Example 1 The only difference between this comparative example and Example 1 is that the system does not include an electrocoagulation purification unit. Everything else is the same as in Example 1.

[0074] Compared with Example 1, the drawback of this comparative example is that it cannot remove most of the fluorine and silicon and initially reduce calcium through electrocoagulation, which leads to overload of the subsequent molecular sieve adsorption unit, failure of the calcium and silicon concentration in the effluent to meet the standards, and a sharp shortening of the molecular sieve regeneration cycle.

[0075] Comparative Example 2 The only difference between this comparative example and Example 1 is that chemical precipitation is used instead of the electrocoagulation purification unit in the system. Everything else is the same as in Example 1.

[0076] Compared with Example 1, the drawback of this comparative example is that it usually suffers from problems such as large sludge production, high operating costs, and the introduction of new impurity ions, making it difficult to achieve the same level of synergistic removal effect of pollutants.

[0077] Comparative Example 3 The only difference between this comparative example and Example 1 is that the system does not include a solid-liquid separation unit. Everything else is the same as in Example 1.

[0078] Compared with Example 1, the drawback of this comparative example is that, without solid-liquid separation, the flocs generated by electrocoagulation directly enter the molecular sieve adsorption unit, quickly clogging the micropores of the molecular sieve, causing the adsorption tower to fail and the system to be unable to operate normally.

[0079] Comparative Example 4 The only difference between this comparative example and Example 1 is that the molecular sieve adsorption unit is not set in the system. Everything else is the same as in Example 1.

[0080] Compared with Example 1, the drawback of this comparative example is that relying solely on electrocoagulation cannot reduce the concentration of calcium and silicon below the required threshold, and the effluent quality cannot meet the influent requirements of subsequent membrane systems or evaporative crystallizers.

[0081] Comparative Example 5 The only difference between this comparative example and Example 1 is that the molecular sieve adsorption unit is replaced with a common adsorbent (such as activated alumina) or ion exchange resin in the system. Everything else is the same as in Example 1.

[0082] Compared with Example 1, the shortcomings of this comparative example are that the selectivity and adsorption capacity for calcium and silicon are insufficient, the effluent water quality is unstable, and regeneration is difficult and the operating cost is high.

[0083] Test case To verify the treatment effect of the systems in Examples 1-9 and Comparative Examples 1-5 on coking wastewater, the system operation process was the same as in Example 10. Based on the detection data of the molecular sieve adsorption tower outlet for a continuous week and every 4 hours, the weekly average value was calculated, and the effluent water quality of each system is shown in Tables 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 and 14.

[0084] The water quality indicators for coking wastewater are as follows:

[0085] Table 1. Effluent water quality of the system in Example 1

[0086] Table 2. Effluent water quality of the system in Example 2

[0087] Table 3. Effluent water quality of the system in Example 3

[0088] Table 4. Effluent water quality of the system in Example 4

[0089] Table 5. Effluent water quality of the system in Example 5

[0090] Table 6. Effluent water quality of the system in Example 6

[0091] Table 7. Effluent water quality of the system in Example 7

[0092] Table 8. Effluent water quality of the system in Example 8

[0093] Table 9. Effluent water quality of the system in Example 9

[0094] Table 10 Effluent water quality of Comparative Example 1 system

[0095] Table 11 Effluent water quality of Comparative Example 2 system

[0096] Table 12 Effluent water quality of Comparative Example 3 system

[0097] Table 13 Effluent water quality of Comparative Example 4 system

[0098] Table 14 Effluent water quality of Comparative Example 5 system

[0099] Therefore, this invention solves the technical problem of the difficulty in deep removal of scaling ions in high-concentration brine, achieving the technical effect of calcium ion concentration below 20 mg / L, silica concentration below 50 mg / L, and fluoride ion concentration below 5 mg / L in the effluent.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A deep purification system for steel coking wastewater, characterized in that, It includes a pretreatment and conditioning unit, an electrocoagulation and purification unit, a solid-liquid separation unit, and a molecular sieve adsorption unit connected sequentially along the wastewater flow direction; The pretreatment adjustment unit is used to homogenize the wastewater and adjust the pH to 5.5-7.0; The electrocoagulation purification unit is used to synergistically purify fluoride, silicon and calcium ions in wastewater. The solid-liquid separation unit is used to separate the flocs and clear liquid generated by electrocoagulation; The molecular sieve adsorption unit is used to remove calcium and silicon from the solution.

2. The system according to claim 1, characterized in that, The pretreatment adjustment unit is equipped with an online pH monitor and an automatic dosing device.

3. The system according to claim 1, characterized in that, The electrocoagulation purification unit includes an electrocoagulation reactor.

4. The system according to claim 3, characterized in that, The electrode spacing of the electrocoagulation reactor is 10mm-20mm; Preferably, the operating current density of the electrocoagulation reactor is 10 mA / cm². 2 -25mA / cm 2 The hydraulic residence time is 15-30 minutes.

5. The system according to claim 1, characterized in that, The solid-liquid separation unit includes a dissolved air flotation machine.

6. The system according to claim 5, characterized in that, The dissolved air flotation machine has a dissolved air pressure of 0.3MPa-0.5MPa and a reflux ratio of 20%-30%. Preferably, the hydraulic residence time of the dissolved air flotation machine is 15-25 minutes.

7. The system according to claim 1, characterized in that, The molecular sieve adsorption unit includes a molecular sieve adsorption tower; Preferably, the molecular sieve adsorption tower is filled with special molecular sieve filter media; Preferably, the lower layer of the molecular sieve adsorption tower is filled with Na-type clinoptilolite, and the upper layer is filled with high-silica Y-type molecular sieve.

8. The system according to any one of claims 1-7, characterized in that, The system also includes pipelines connecting the various units and their control system. Preferably, the control system is based on a PID control algorithm and adjusts the dosage of the dosing device according to the pH value feedback signal of the effluent from the pretreatment adjustment unit to make the pH 5.5-7.

0. Preferably, the control system is based on a predictive model. Based on the effluent quality of the molecular sieve adsorption unit, the breakthrough time is predicted and a regeneration or switching procedure is automatically triggered.

9. An operating process of the system according to any one of claims 1-8, characterized in that, Includes the following steps: Wastewater is passed into a pretreatment conditioning unit for homogenization and pH adjustment to 5.5-7.0, and then into an electrocoagulation purification unit for electrochemical purification, which synergistically removes fluoride, silicon, and calcium ions from the wastewater. The electrocoagulated effluent enters a solid-liquid separation unit for solid-liquid separation to obtain a clear liquid. The clear liquid is then passed into a molecular sieve adsorption unit for deep removal of calcium and silicon, resulting in compliant wastewater.

10. The operating process according to claim 9, characterized in that, The qualified produced water has a calcium ion concentration of less than 20 mg / L, a silica concentration of less than 50 mg / L, and a fluoride ion concentration of less than 5 mg / L.

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