A method and system for reducing and treating steel production wastewater

Abstract

The application relates to the technical field of steel industry wastewater treatment, in particular to a method and system for reducing and treating steel production wastewater, which comprises a water quality adjusting tank, a circulating water supplementing pump, a low-temperature multi-effect evaporator, a fluorine removing device, a flue gas online heat taking device, a flash evaporation device and the like. The comprehensive wastewater of a steel enterprise and flue gas waste heat are taken as resources, the comprehensive wastewater is subjected to circulating concentration and fluorine removing treatment, a small amount of concentrated water is continuously discharged after being concentrated to a certain multiple, and is sent to existing solid waste resources (steel slag) of the steel enterprise for complete treatment. Steam flashed by the waste heat is condensed in the heat exchange pipe, and is collected and sent to various users, and can also be used as water of the flue gas online heat taking device. Through the combination of the evaporator concentration, the flue gas waste heat recovery and the solid waste treatment, the waste heat and the wastewater reuse are realized, the goal of waste making waste is achieved, and the salt balance problem of the water system of the steel production wastewater of the steel enterprise is solved.

Description

Technical Field

[0001] This application relates to the field of wastewater treatment technology in the iron and steel industry, and in particular to a method and system for reducing and disposing of wastewater from steel production. Background Technology

[0002] my country's annual steel production exceeds 1 billion tons. Although the water consumption per ton of steel has dropped to below 3 tons, the entire industry still discharges approximately 600 million tons of wastewater annually. This type of wastewater has high calcium and magnesium hardness, conductivity of 2000–4000 μS / cm, and Cl... - It can reach 1000 mg / L and contains F. - SO4 2- Containing trace amounts of heavy metals, the traditional "neutralization-coagulation-sedimentation-filtration" process can only meet emission standards, with a reuse rate of less than 30%, and generates a large amount of chemical sludge with a water content of over 75%, resulting in high storage costs. If reverse osmosis deep desalination is adopted, it requires high-pressure operation above 5MPa, frequent membrane replacement, and a comprehensive cost of over 4 yuan per ton of water. The concentrate accounts for 20-30% and still needs to be evaporated and crystallized, resulting in extremely high investment costs that steel companies cannot afford. Summary of the Invention

[0003] This application provides a method and system for reducing and disposing of wastewater from steel production, in order to solve the following technical problem: how to achieve salt balance in the water system of wastewater from steel production in steel enterprises. In a first aspect, embodiments of this application provide a method for reducing and disposing of steel production wastewater, including: S1. The steel production wastewater is homogenized to obtain homogenized comprehensive wastewater with an electrical conductivity of 2500μS / cm~3000μS / cm; S2. Reduce the absolute pressure of the evaporator to below 15 kPa; S3. Recover the waste heat of flue gas from the pelletizing, sintering and hot blast furnace processes, use the waste heat of the flue gas to heat the demineralized water to 70 ℃~95 ℃ to obtain waste heat hot water, and perform negative pressure flash evaporation on the waste heat hot water to generate saturated steam. S4. The saturated steam is introduced into the first-effect heat exchange tube of the evaporator, causing the saturated steam to condense and release heat on the inner wall surface of the heat exchange tube; and the homogeneous wastewater is sprayed onto the outer wall surface of the heat exchange tube, causing the homogeneous wastewater to form a liquid film on the outer wall surface of the heat exchange tube and absorb the latent heat of condensation released by the saturated steam, causing part of the homogeneous wastewater to vaporize to form secondary steam and leaving behind concentrated brine. S5. Remove fluoride ions from the concentrated brine to obtain defluorinated concentrated brine; S6. The defluorinated brine and the homogenized integrated wastewater are mixed at a volume flow rate of 1:1 to 1:5 and then sprayed onto the outer wall surface of the heat exchange tube to form a circulating evaporation loop. Repeat steps S1 to S6 until the salt content of the concentrated brine reaches 5 to 10 times the initial salt content of the homogeneous integrated wastewater. Then, continuously discharge high-concentration brine, accounting for 5% to 10% of the total influent volume of the homogeneous integrated wastewater, and send the high-concentration brine to the steel slag treatment process. Use the residual heat of the steel slag in the steel slag treatment process to solidify the high-concentration brine, thereby achieving zero discharge and disposal of the high-concentration brine.

[0004] Optionally, the high-concentration brine is disposed of in the steel slag treatment process as follows: The high-concentration brine is atomized and sprayed onto the surface of the molten steel slag in the steel slag treatment process. The sensible heat of the molten steel slag causes the water in the high-concentration brine to evaporate, the salt to solidify, and the salt to be encapsulated in the glass phase of the molten steel slag, forming a non-toxic inert solid solution.

[0005] Optionally, the negative pressure flash evaporation includes pressure reduction, expansion and vapor-liquid separation in sequence, and the absolute pressure of the negative pressure flash evaporation decreases step by step, with the first-level absolute pressure being 25 kPa to 35 kPa.

[0006] Optionally, the spray density of both the initial spray and the subsequent spray is 0.6 m³. 3 / (m·h)~0.8 m 3 / (m·h).

[0007] Secondly, embodiments of this application provide a steel production wastewater reduction and disposal system, which includes, in sequence along the material flow direction: Water quality equalization tank, which is equipped with a steel production wastewater inlet and a homogenized integrated wastewater outlet; A circulating water supply pump, wherein the inlet of the circulating water supply pump is connected to the homogenized integrated sewage outlet of the water quality regulating tank, and the outlet of the circulating water supply pump is connected to the spray inlet of the evaporator; The evaporator is provided with a spray inlet, a steam inlet, a secondary steam outlet, a concentrated brine outlet, and a product water outlet; A defluorination device, wherein the inlet of the defluorination device is connected to the concentrated brine outlet of the evaporator, and the outlet of the defluorination device is connected to the inlet of the circulating water pump; A flue gas online heat extraction device, wherein the flue gas online heat extraction device is provided with a flue gas inlet, a demineralized water inlet, and a waste heat hot water outlet; A flash evaporator, wherein the hot water inlet of the flash evaporator is connected to the waste heat hot water outlet of the flue gas online heat extraction device, and the steam outlet of the flash evaporator is connected to the steam inlet of the evaporator; A vacuum pump, which is connected to the vapor phase space of the evaporator, is used to reduce the absolute pressure of the final stage of the evaporator to below 15 kPa. The steel slag treatment process interface is connected to the high-concentration brine discharge valve of the evaporator, and is used to introduce high-concentration brine into the steel slag treatment process for solidification and disposal.

[0008] Optionally, the evaporator is a horizontal tube falling film evaporator with no less than three effects, each effect is equipped with a concentrated brine collection tank, and the concentrated brine collection tank of the last effect is connected to the interface of the steel slag treatment process through a high concentrated brine discharge valve.

[0009] Optionally, the flue gas online heat extraction device is a corrosion-resistant finned tube heat exchanger.

[0010] Optionally, the defluorination device is a fluidized bed crystallization reactor, in which natural mineral powder with a particle size of 40-60 mesh is added to form fluoride particles with a diameter of 1-3 mm, and the fluidized bed crystallization reactor is provided with a fluoride particle discharge port.

[0011] Optionally, the system further includes a water reuse network, the inlet of which is connected to the water outlet of the evaporator, and the outlet of which is connected to the water supply ports of the ironmaking, steelmaking, hot rolling and cold rolling processes, respectively, so as to realize the reuse of water throughout the plant.

[0012] Optionally, the system further includes a seawater cooling circuit, wherein the cooling seawater inlet of the seawater cooling circuit is connected to the cooling side inlet of the last-effect condenser of the evaporator, and the warm water outlet of the seawater cooling circuit is connected to the inlet of the thermal seawater desalination device for recovering the low-temperature waste heat discharged from the last-effect condenser.

[0013] The technical solutions provided in this application have the following advantages compared with the prior art: The wastewater reduction and disposal method and system provided in this application are simple to operate and have low operating costs. The method utilizes the combined wastewater and flue gas waste heat from steel enterprises as resources. The combined wastewater undergoes cyclic concentration and defluorination treatment. After concentration to a certain factor, a small amount of concentrated water is continuously discharged and sent to the existing solid waste resources (steel slag) of the steel enterprise for complete disposal. The steam generated from the waste heat flash condenses in the heat exchange tubes and is collected and sent to various users, or it can be used as water for online flue gas heat recovery devices. By combining evaporator concentration, flue gas waste heat recovery, and solid waste disposal, the method achieves the goal of waste heat and wastewater reuse, turning waste into waste, and solves the salt balance problem of the water system for steel production wastewater in steel enterprises. Attached Figure Description

[0014] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of a steel production wastewater reduction and disposal system provided in an embodiment of this application; wherein, 1-Water quality equalization tank 2-Circulating water supply pump 3-Evaporator 4-Online flue gas heat exchange device 5-Defluorination device 6-Flash Evaporation Unit 7-Vacuum Pump Detailed Implementation To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0017] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0018] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Furthermore, in the description of this application, terms such as "comprising" and "including" mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than one" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0019] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0020] In a first aspect, embodiments of this application provide a method for reducing and disposing of steel production wastewater, including: S1. The steel production wastewater is homogenized to obtain homogenized comprehensive wastewater with an electrical conductivity of 2500 μS / cm to 3000 μS / cm; S2. Reduce the absolute pressure of the final stage of the evaporator to below 15 kPa; S3. Recover the waste heat of flue gas from the pelletizing, sintering and hot blast furnace processes, use the waste heat of the flue gas to heat the demineralized water to 70 ℃~95 ℃ to obtain waste heat hot water, and perform negative pressure flash evaporation on the waste heat hot water to generate saturated steam. S4. The saturated steam is introduced into the first-effect heat exchange tube of the evaporator, causing the saturated steam to condense and release heat on the inner wall surface of the heat exchange tube; and the homogeneous wastewater is sprayed onto the outer wall surface of the heat exchange tube, causing the homogeneous wastewater to form a liquid film on the outer wall surface of the heat exchange tube and absorb the latent heat of condensation released by the saturated steam, causing part of the homogeneous wastewater to vaporize to form secondary steam and leaving behind concentrated brine. S5. Remove fluoride ions from the concentrated brine to obtain defluorinated concentrated brine; S6. The defluorinated brine and the homogenized integrated wastewater are mixed at a volume flow rate of 1:1 to 1:5 and then sprayed onto the outer wall surface of the heat exchange tube to form a circulating evaporation loop. Repeat steps S1 to S6 until the salt content of the concentrated brine reaches 5 to 10 times the initial salt content of the homogeneous integrated wastewater. Then, continuously discharge high-concentration brine, accounting for 5% to 10% of the total influent volume of the homogeneous integrated wastewater, and send the high-concentration brine to the steel slag treatment process. Use the residual heat of the steel slag in the steel slag treatment process to solidify the high-concentration brine, thereby achieving zero discharge and disposal of the high-concentration brine.

[0021] S1 homogenizes the steel production wastewater to obtain electrical conductivity values ​​of 2500 μS / cm, 2501 μS / cm, 2502 μS / cm, 2503 μS / cm, 2504 μS / cm, 2505 μS / cm, 2506 μS / cm, 2507 μS / cm, 2508 μS / cm, 2509 μS / cm, 2510 μS / cm…2990 μS / cm, 2991 μS / cm, 2992 μS / cm, 2993 μS / cm, 2994 μS / cm, 2995 μS / cm, 2996 μS / cm, 2997 μS / cm, 2998 μS / cm, 2999 μS / cm, and 3000 μS / cm. This homogeneous wastewater, with concentrations of μS / cm, eliminates peak pollutant concentrations caused by fluctuations in water quality during ironmaking, steelmaking, hot rolling, and cold rolling processes. This stabilizes the ionic strength of the inlet water to the subsequent evaporator within the range of 2500 μS / cm to 3000 μS / cm, thereby inhibiting the heterogeneous nucleation rate of calcium carbonate and calcium sulfate on the outer wall of the heat exchange tubes. This extends the scaling induction period on the outer wall of the heat exchange tubes to ≥720 h, ensuring a continuous water recovery rate of ≥90% for the evaporator. S2 reduces the absolute pressure of the evaporator to below 15 kPa, 14 kPa, 13 kPa, 12 kPa, 11 kPa, 10 kPa, 9 kPa, 8 kPa, 7 kPa, 6 kPa, 5 kPa, 4 kPa, and 3 kPa, thereby lowering the boiling point of the homogeneous wastewater on the outer wall surface of the heat exchange tube to 55 ℃~45 ℃. This causes the homogeneous wastewater to undergo phase change vaporization when a falling film forms on the outer wall surface of the first-effect heat exchange tube of the evaporator, thus extracting water from the homogeneous wastewater at low temperature to form secondary steam. This avoids the loss of water from CaSO4·2H2O crystal hydrate due to high-temperature evaporation, which would lead to the formation of a hard CaSO4 scale layer. This maintains the heat flux on the outer wall surface of the heat exchange tube ≥1.8 kW·m-2, thereby continuously producing secondary steam and leaving behind concentrated brine. S3 recovers waste heat from the pelletizing process, sintering process, and hot blast furnace process. This waste heat is used to heat demineralized water to temperatures of 70℃, 71℃, 72℃, 73℃, 74℃, 75℃, 76℃, 77℃, 78℃, 79℃, 80℃, 81℃, 82℃, 83℃, 84℃, 85℃, 86℃, 87℃, 88℃, 89℃, 90℃, 91℃, 92℃, 93℃, 94℃, and 95℃. Waste heat water is obtained by evaporating at ℃, and then the waste heat water is subjected to negative pressure flash evaporation, thereby converting the sensible heat in the waste heat water into the latent heat of saturated steam. In this way, the low-grade waste heat inside the steel enterprise replaces the steam from the external high-pressure boiler, thereby reducing the steam heat source cost of the evaporator to 15 yuan / t of produced water. This reduces the overall operating cost of the steel production wastewater reduction and disposal method by ≥35%, thereby improving the economic efficiency of steel production wastewater reuse. S4 introduces saturated steam into the first-effect heat exchange tube of the evaporator, causing the saturated steam to condense and release heat on the inner wall surface of the heat exchange tube; and sprays homogeneous wastewater onto the outer wall surface of the heat exchange tube, causing the homogeneous wastewater to form a liquid film on the outer wall surface of the heat exchange tube and absorb the latent heat of condensation released by the saturated steam, causing part of the homogeneous wastewater to vaporize and form secondary steam, leaving behind concentrated brine, thereby removing water from the homogeneous wastewater in the form of secondary steam, and increasing the salt concentration in the concentrated brine to 1.2 times the initial salt content, thus completing the first concentration and reduction. S5 removes fluoride ions from concentrated brine to obtain defluorinated concentrated brine, thereby reducing the F- concentration from ≤50 mg / L to ≤5 mg / L, and thus preventing F- from being released. - In the subsequent cyclic evaporation process, it reacts with Ca. 2+ Mg 2+ CaF2 and MgF2 precipitates are formed and deposited on the outer wall surface of the heat exchange tubes, thereby maintaining the cleanliness of the outer wall surface of the heat exchange tubes and ensuring that the water recovery rate of the evaporator is ≥90% during long-term operation. S6 mixes the defluoridated brine with homogenized wastewater at volumetric flow rates of 1:1, 1:2, 1:3, 1:4, 1:5, etc., and then sprays it again onto the outer wall of the heat exchange tube to form a circulating evaporation loop. This dilutes the concentrated salt in the defluoridated brine to 1.1 times the initial salt content, thereby making the evaporation load of each effect of the evaporator uniform. This prevents premature crystallization of the end effect due to salt oversaturation, allowing the circulating evaporation loop to continue operating until the salt content of the brine reaches 5, 6, 7, 8, 9, 10 times, etc., the initial salt content of the homogenized wastewater. Repeat steps S1 to S6 until the salt content of the concentrated brine reaches 5, 6, 7, 8, 9, and 10 times the initial salt content of the homogeneous wastewater. Then, continuously discharge high-concentration brine, accounting for 5%, 6%, 7%, 8%, 9%, and 10% of the total influent volume of the homogeneous wastewater. Send the high-concentration brine to the steel slag treatment process, where the residual heat of the steel slag solidifies the high-concentration brine. This evaporates the water in the high-concentration brine and encapsulates the salt in the molten steel slag glass phase, forming a non-toxic inert solid solution. This causes the NaCl, Na2SO4, CaCl2, MgCl2, and KCl salts in the high-concentration brine to lose their water solubility, thereby achieving zero discharge and disposal of steel production wastewater. This results in a steel production wastewater reuse rate of ≥90% and a high-concentration brine discharge of ≤10%, ultimately solving the technical problem of "how to improve the reuse rate of steel production wastewater and achieve zero discharge".

[0022] In some embodiments, the high-concentration brine is disposed of in the steel slag treatment process in the following manner: The high-concentration brine is atomized and sprayed onto the surface of the molten steel slag in the steel slag treatment process. The sensible heat of the molten steel slag causes the water in the high-concentration brine to evaporate, the salt to solidify, and the salt to be encapsulated in the glass phase of the molten steel slag, forming a non-toxic inert solid solution.

[0023] High-concentration brine is atomized and sprayed onto the surface of molten steel slag in the steel slag treatment process. The sensible heat of the molten steel slag causes the water in the high-concentration brine to evaporate instantly. This causes the NaCl, Na2SO4, CaCl2, MgCl2, and KCl salts in the high-concentration brine to solidify and encapsulate rapidly within the glassy phase of the molten steel slag, forming a non-toxic, inert solid solution. This renders the high-concentration brine insoluble in water, achieving zero discharge and disposal of the high-concentration brine. This ensures that the steel production wastewater reuse rate is ≥90% and the high-concentration brine discharge is ≤10%, ultimately solving the technical problem of "how to improve the reuse rate of steel production wastewater and achieve zero discharge".

[0024] In some embodiments, the negative pressure flash evaporation sequentially includes pressure reduction, expansion and vapor-liquid separation, and the absolute pressure of the negative pressure flash evaporation decreases step by step, with the first-level absolute pressure being 25 kPa to 35 kPa.

[0025] The negative pressure flash evaporation process sequentially includes pressure reduction, expansion, and vapor-liquid separation. The absolute pressure of the negative pressure flash evaporation decreases progressively, with the first-stage absolute pressures being 25 kPa, 26 kPa, 27 kPa, 28 kPa, 29 kPa, 30 kPa, 31 kPa, 32 kPa, 33 kPa, 34 kPa, and 35 kPa, respectively. This progressively releases the sensible heat from the waste hot water, resulting in a progressively decreasing boiling point in each expansion chamber. This ensures that the waste hot water maintains a superheat of ≥5 °C in the final expansion chamber, guaranteeing a saturated steam dryness fraction ≥98% at the outlet of the final expansion chamber. Consequently, the water droplet mass fraction carried by the saturated steam entering the first-effect heat exchange tube of the evaporator is ≤2%, preventing the formation of a liquid film thermal resistance on the inner wall of the heat exchange tube and maintaining a condensation heat transfer coefficient ≥6 kW·m². -2 ·K -1 This ensures that the evaporator water recovery rate is ≥90%, ultimately solving the technical problem of "how to improve the reuse rate of steel production wastewater and achieve zero discharge".

[0026] In some embodiments, the spray density of both the initial spray and the subsequent spray is 0.6 m. 3 / (m·h)~0.8 m 3 / (m·h).

[0027] The spray density for both the initial spray and the subsequent re-spray is 0.61 m³. 3 / (m·h)、0.62 m3 / (m·h)、0.63 m 3 / (m·h)、0.64m3 / (m·h)、0.65 m3 / (m·h)、0.66 m3 / (m·h)、0.67 m3 / (m·h)、0.68 m3 / (m·h)、0.69 m3 / (m·h)、0.70 m3 / (m·h)、0.71 m3 / (m·h)、0.72 m3 / (m·h), 0.73 m3 / (m·h), 0.74 m3 / (m·h), 0.75 m3 / (m·h), 0.76 m3 / (m·h), 0.77 m3 / (m·h), 0.78 m3 / (m·h), 0.79 m3 / (m·h), 0.80 The concentration of water in the heat exchanger is measured in m³ / (m·h), which ensures that a continuous falling film forms on the outer surface of the heat exchanger tubes, thereby maintaining the temperature difference between the water in the falling film and the saturated steam on the inner wall of the heat exchanger tubes at ≥10 °C, thus ensuring that the evaporation flux on the falling film surface is ≥0.02 kg·m³. -2 ·s -1 This allows for the efficient conversion of water in homogeneous wastewater into secondary steam, resulting in a water recovery rate of ≥90%, ultimately solving the technical problem of "how to improve the reuse rate of steel production wastewater and achieve zero discharge".

[0028] Figure 1 This is a schematic diagram of a steel production wastewater reduction and disposal system provided in an embodiment of this application, as shown below. Figure 1 As shown: Secondly, embodiments of this application provide a steel production wastewater reduction and disposal system, which includes, in sequence along the material flow direction: Water quality equalization tank 1, wherein the water quality equalization tank 1 is provided with a steel production wastewater inlet and a homogenized integrated wastewater outlet; The circulating water supply pump 2 has its inlet connected to the homogenized integrated sewage outlet of the water quality regulating tank 1, and its outlet connected to the spray inlet of the evaporator 3. The evaporator 3 is provided with a spray inlet, a steam inlet, a secondary steam outlet, a concentrated brine outlet, and a product water outlet; The defluorination device 5 has its inlet connected to the concentrated brine outlet of the evaporator 3, and its outlet connected to the inlet of the circulating water pump 2. The flue gas online heat extraction device 4 is provided with a flue gas inlet, a demineralized water inlet, and a waste heat hot water outlet. The flash evaporator 6 has a hot water inlet connected to the waste heat hot water outlet of the flue gas online heat extraction device 4, and a steam outlet connected to the steam inlet of the evaporator 3. Vacuum pump 7, which is connected to the gas phase space of evaporator 3, is used to reduce the absolute pressure of evaporator 3 to below 15 kPa; The steel slag treatment process interface is connected to the high-concentration brine discharge valve of the evaporator 3, and is used to introduce high-concentration brine into the steel slag treatment process for solidification and disposal.

[0029] The water quality equalization tank 1 is equipped with a steel production wastewater inlet and a homogenized comprehensive wastewater outlet, thereby collecting and homogenizing the steel production wastewater discharged from the ironmaking, steelmaking, hot rolling and cold rolling processes, and thus stabilizing the conductivity of the homogenized comprehensive wastewater at 2500μS / cm~3000μS / cm, thereby eliminating the fluctuation of the inlet water quality of the subsequent evaporator 3. The inlet of the circulating water pump 2 is connected to the outlet of the homogeneous integrated sewage in the water quality equalization tank 1, and the outlet of the circulating water pump 2 is connected to the spray inlet of the evaporator 3, so that the homogeneous integrated sewage is delivered to the evaporator 3 at a spray density of 0.6 m3 / (m·h) to 0.8 m3 / (m·h), thereby ensuring continuous falling film evaporation. Evaporator 3 is equipped with a spray inlet, a steam inlet, a secondary steam outlet, a concentrated brine outlet, and a product water outlet, thereby removing water from the homogenized wastewater in the form of secondary steam, and increasing the salt concentration in the concentrated brine to 1.2 times the initial salt content, thus completing the first concentration and reduction. The inlet of the defluorination device 5 is connected to the concentrated brine outlet of the evaporator 3, and the outlet of the defluorination device 5 is connected to the inlet of the circulating water pump 2, thereby removing F from the concentrated brine. - The concentration was reduced from ≤50 mg / L to ≤5 mg / L, thereby avoiding F - CaF2 and MgF2 precipitates are formed in the circulating evaporation loop, thereby maintaining the cleanliness of the outer wall surface of the heat exchange tube and ensuring a product water recovery rate of ≥90%. The flue gas online heat recovery device 4 is equipped with a flue gas inlet, a demineralized water inlet, and a waste heat hot water outlet, thereby recovering the waste heat of flue gas from the pelletizing, sintering, and hot blast furnace processes, and then heating the demineralized water to 70 ℃~95 ℃ to obtain waste heat hot water, thus replacing external steam with internal waste heat of the steel enterprise; The hot water inlet of the flash evaporator 6 is connected to the waste heat hot water outlet of the flue gas online heat extraction device 4, and the steam outlet of the flash evaporator 6 is connected to the steam inlet of the evaporator 3, thereby converting the waste heat hot water into saturated steam, which in turn provides a heat source for the evaporator 3, thereby reducing operating costs by ≥35%; Vacuum pump 7 is connected to the gas phase space of evaporator 3, and is used to reduce the absolute pressure of evaporator 3 to below 15 kPa, thereby reducing the boiling point of homogenized wastewater to 55 ℃~45 ℃, thus achieving low-temperature evaporation, avoiding scaling of heat exchange tubes, and ensuring a water recovery rate of ≥90%; The interface of the steel slag treatment process is connected to the high-concentration brine discharge valve of evaporator 3, which is used to introduce the high-concentration brine into the steel slag treatment process. The high-concentration brine is solidified by the sensible heat of the molten steel slag, thereby forming a non-toxic inert solid solution. This achieves zero discharge and disposal of the high-concentration brine, and makes the steel production wastewater reuse rate ≥90% and the high-concentration brine discharge ≤10%. Ultimately, it solves the technical problem of "how to improve the reuse rate of steel production wastewater and achieve zero discharge".

[0030] In some embodiments, the evaporator 3 is a horizontal tube falling film evaporator 3 with no less than three effects, each effect is provided with a concentrated brine collection tank, and the concentrated brine collection tank of the last effect is connected to the interface of the steel slag treatment process through a high concentrated brine discharge valve.

[0031] Evaporator 3 is a horizontal tube falling film evaporator with no less than three effects. Each effect is equipped with a concentrated brine collection tank, which is connected by a weir plate. The concentrated brine from the first effect overflows through the weir plate to the concentrated brine collection tank of the second effect, and so on, until it is collected in the concentrated brine collection tank of the last effect. The concentrated brine collection tank of the last effect is connected to the interface of the steel slag treatment process through a high-concentration brine discharge valve, so that the salt content of the concentrated brine in the last effect is accurately 5, 6, 7, 8, 9, 10 times the initial salt content of the homogeneous wastewater, etc., thereby ensuring that the volume fraction of high-concentration brine discharge is ≤10% of the total influent volume of homogeneous wastewater, thereby reducing the heat load of the steel slag treatment process and achieving zero discharge and disposal of high-concentration brine. This ultimately solves the technical problem of "how to improve the reuse rate of steel production wastewater and achieve zero discharge".

[0032] In some embodiments, the flue gas online heat extraction device 4 is a corrosion-resistant finned tube heat exchanger.

[0033] The flue gas online heat extraction device 4 is a corrosion-resistant finned tube heat exchanger, which transfers the waste heat of the flue gas to the demineralized water through the finned tube wall, thereby preventing SO2, HCl, and NO from entering the flue gas. x This causes acid dew point corrosion on the heat exchanger tube wall, thus ensuring that the heat exchanger tube wall thickness reduction rate is ≤0.05 mm·a. -1 This extends the service life of the flue gas online heat extraction device 4 by ≥10 years, thereby continuously providing saturated steam to the evaporator 3, ensuring a steel production wastewater reuse rate of ≥90%, and ultimately solving the technical problem of "how to improve the reuse rate of steel production wastewater and achieve zero discharge".

[0034] In some embodiments, the defluorination device 5 is a fluidized bed crystallization reactor, in which natural mineral powder with a particle size of 40 to 60 mesh is added to form fluoride particles with a diameter of 1-3 mm, and the fluidized bed crystallization reactor is provided with a fluoride particle discharge port.

[0035] The defluorination device 5 is a fluidized bed crystallization reactor. Natural mineral powder with particle sizes of 40 mesh, 41 mesh, 42 mesh, 43 mesh, 44 mesh, 45 mesh, 46 mesh, 47 mesh, 48 mesh, 49 mesh, 50 mesh, 51 mesh, 52 mesh, 53 mesh, 54 mesh, 55 mesh, 56 mesh, 57 mesh, 58 mesh, 59 mesh, and 60 mesh is added to the fluidized bed crystallization reactor. The reactor is equipped with a fluoride particle discharge port, thereby removing fluoride from the concentrated brine. - Al on the surface of natural mineral powder 3+ The reaction produces AlF3·3H2O crystals, which in turn cause F to... - Separate from concentrated brine in solid crystal form, thereby reducing the F in the concentrated brine. - The concentration was reduced from ≤50 mg / L to ≤5 mg / L, thereby avoiding F- CaF2 and MgF2 precipitates are formed in the circulating evaporation loop, thereby keeping the outer wall surface of the heat exchange tube clean and ensuring that the water recovery rate is ≥90%, ultimately solving the technical problem of "how to improve the reuse rate of steel production wastewater and achieve zero discharge".

[0036] In some embodiments, the system further includes a water recycling network, the inlet of which is connected to the water outlet of the evaporator 3, and the outlet of which is connected to the water supply ports of the ironmaking, steelmaking, hot rolling and cold rolling processes, respectively, so as to realize the recycling of water throughout the plant.

[0037] The inlet of the permeate water reuse pipeline is connected to the permeate water outlet of evaporator 3. The outlet of the permeate water reuse pipeline is connected to the water supply outlets of the ironmaking process, steelmaking process, hot rolling process, and cold rolling process, respectively. This allows all permeate water with a conductivity ≤100 μs / cm and turbidity ≤0.1 NTU to be reused in various steel production processes, thereby replacing ≥90% of the fresh water supply and reducing the water intake of steel enterprises by ≥10%. This achieves the resource utilization of steel production wastewater and ultimately solves the technical problem of "how to improve the reuse rate of steel production wastewater and achieve zero discharge".

[0038] In some embodiments, the system further includes a seawater cooling circuit, wherein the cooling seawater inlet of the seawater cooling circuit is connected to the cooling side inlet of the last-effect condenser of the evaporator 3, and the warm water outlet of the seawater cooling circuit is connected to the inlet of the thermal seawater desalination device for recovering the low-temperature waste heat discharged from the last-effect condenser.

[0039] The cooling seawater inlet of the seawater cooling circuit is connected to the cooling side inlet of the last-effect condenser of the evaporator 3, and the warm water outlet of the seawater cooling circuit is connected to the inlet of the thermal seawater desalination unit. This allows the low-temperature waste heat discharged from the last-effect condenser to be transferred to the thermal seawater desalination system in the form of warm water, thereby increasing the inlet water temperature of the thermal seawater desalination unit by 3℃~5℃. This reduces the amount of supplementary steam required for the thermal seawater desalination system by ≥5%, thereby improving the overall energy utilization efficiency of the plant by ≥2%, and further reducing the operating energy consumption of the steel production wastewater reduction and disposal system. This ensures that the steel production wastewater reuse rate is ≥90%, ultimately solving the technical problem of "how to improve the reuse rate of steel production wastewater and achieve zero discharge".

[0040] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0041] I. Implementation Examples Example 1 S1 homogenizes the steel production wastewater to obtain homogenized comprehensive wastewater with an electrical conductivity of 2500 μs / cm; S2 reduces the absolute pressure of evaporator 3 to 15 kPa; S3 recovers the waste heat from the flue gas in the pelletizing, sintering and hot blast furnace processes, uses the waste heat to heat the demineralized water to 70°C to obtain waste heat hot water, and performs negative pressure flash evaporation on the waste heat hot water to generate saturated steam; S4 The saturated steam is introduced into the first-effect heat exchange tube of the evaporator 3, so that the saturated steam condenses and releases heat on the inner wall surface of the heat exchange tube; and the homogeneous wastewater is sprayed onto the outer wall surface of the heat exchange tube, so that the homogeneous wastewater forms a liquid film on the outer wall surface of the heat exchange tube and absorbs the latent heat of condensation released by the saturated steam, so that part of the homogeneous wastewater vaporizes to form secondary steam and leaves behind concentrated brine. S5 removes fluoride ions from concentrated brine to obtain defluorinated concentrated brine; S6 mixes the defluorinated brine and homogenized wastewater at a volumetric flow rate of 1:1, and then sprays it onto the outer wall of the heat exchange tube to form a circulating evaporation loop. Repeat steps S1 to S6 until the salt content of the concentrated brine reaches 5 times the initial salt content of the homogenized integrated wastewater. Then, continuously discharge high-concentration brine accounting for 5% of the total influent volume of the homogenized integrated wastewater and send the high-concentration brine to the steel slag treatment process. Use the residual heat of the steel slag in the steel slag treatment process to solidify the high-concentration brine, thereby achieving zero discharge and disposal of the high-concentration brine.

[0042] Example 2 S1 homogenizes the steel production wastewater to obtain homogenized comprehensive wastewater with an electrical conductivity of 2750 μs / cm; S2 reduces the absolute pressure of evaporator 3 to 10 kPa; S3 recovers the waste heat from the flue gas in the pelletizing, sintering and hot blast furnace processes, uses the waste heat to heat the demineralized water to 82°C to obtain waste heat hot water, and performs negative pressure flash evaporation on the waste heat hot water to generate saturated steam; S4 is the same as in Example 1; S5 is the same as in Example 1; S6 mixes the defluorinated brine with the homogenized wastewater at a volumetric flow rate of 1:3 and then sprays it onto the outer wall of the heat exchange tube to form a circulating evaporation loop. Repeat steps S1 to S6 until the salt content of the concentrated brine reaches 7.5 times the initial salt content of the homogeneous integrated wastewater. Then, continuously discharge high-concentration brine accounting for 7.5% of the total influent volume of the homogeneous integrated wastewater and send the high-concentration brine to the steel slag treatment process. Use the residual heat of the steel slag in the steel slag treatment process to solidify the high-concentration brine, thereby achieving zero discharge and disposal of the high-concentration brine.

[0043] Example 3 S1 homogenizes the steel production wastewater to obtain homogenized comprehensive wastewater with an electrical conductivity of 3000 μs / cm; S2 reduces the absolute pressure of evaporator 3 to 5 kPa; S3 recovers the waste heat from the flue gas in the pelletizing, sintering and hot blast furnace processes, uses the waste heat to heat the demineralized water to 95°C to obtain waste heat hot water, and performs negative pressure flash evaporation on the waste heat hot water to generate saturated steam; S4 is the same as in Example 1; S5 is the same as in Example 1; S6 mixes the defluorinated brine with the homogenized wastewater at a volumetric flow rate of 1:5 and then sprays it onto the outer wall of the heat exchange tube to form a circulating evaporation loop. Repeat steps S1 to S6 until the salt content of the concentrated brine reaches 10 times the initial salt content of the homogenized integrated wastewater. Then, continuously discharge high-concentration brine accounting for 10% of the total influent volume of the homogenized integrated wastewater and send the high-concentration brine to the steel slag treatment process. Use the residual heat of the steel slag in the steel slag treatment process to solidify the high-concentration brine, thereby achieving zero discharge and disposal of the high-concentration brine.

[0044] Example 4 Steps S1 to S6 are exactly the same as in Example 3, the only difference being: The high-concentration brine is disposed of in the steel slag treatment process as follows: the high-concentration brine is atomized and sprayed into the surface of the molten steel slag in the steel slag treatment process at a pressure of 0.1 MPa. The sensible heat of the molten steel slag is used to evaporate the water in the high-concentration brine, solidify the salt and encapsulate it in the glass phase of the molten steel slag to form a non-toxic inert solid solution.

[0045] Example 5 Steps S1 to S6 are exactly the same as in Example 3, the only difference being: The high-concentration brine is disposed of in the steel slag treatment process by atomizing and spraying it into the surface of the molten steel slag at a pressure of 0.3 MPa to form a non-toxic inert solid solution.

[0046] II. Comparative Example Comparative Example 1 (waste heat recovery from flue gas omitted) S1 is the same as in Example 1; S2 is the same as in Example 1; S3 does not recover waste heat from the flue gas in the pelletizing, sintering and hot blast stove processes, and directly uses external 0.5 MPa saturated steam as a heat source; S4~S6 are the same as in Example 1; Repeat steps S1 to S6 until the salt content of the concentrated brine reaches 5 times the initial salt content of the homogenized integrated wastewater. Then, continuously discharge high-concentration brine accounting for 5% of the total influent volume of the homogenized integrated wastewater and send the high-concentration brine to the steel slag treatment process. Use the residual heat of the steel slag in the steel slag treatment process to solidify the high-concentration brine, thereby achieving zero discharge and disposal of the high-concentration brine.

[0047] Comparative Example 2 (Defluorination step omitted) S1 is the same as in Example 1; S2 is the same as in Example 1; S3 is the same as in Example 1; S4 is the same as in Example 1; S5 does not perform the step of removing fluoride ions from concentrated brine, but directly mixes concentrated brine with homogenized integrated wastewater; S6 is the same as in Example 1; Repeat steps S1 to S6 until the heat exchange tube is forced to shut down due to CaF2 scale blockage on the outer wall. Record that the salt content of the concentrated brine at this time is 2.3 times the initial salt content of the homogeneous wastewater. Then, continuously discharge high-concentration brine accounting for 5% of the total influent volume of the homogeneous wastewater and send the high-concentration brine to the steel slag treatment process. Use the residual heat of the steel slag in the steel slag treatment process to solidify the high-concentration brine, achieving zero discharge and disposal of the high-concentration brine.

[0048] III. Results Data Experimental methods: 1. Method for determining the reuse rate of steel production wastewater: 1.1 Install an electromagnetic flow meter at the evaporator product water outlet and continuously record the cumulative product water volume Vproduct water for 24 hours; 1.2 Install an electromagnetic flow meter at the inlet of the water quality equalization tank to simultaneously record the cumulative volume of steel production wastewater V_raw water over 24 hours; 1.3 Calculate the steel production wastewater reuse rate according to formula (1): Steel production wastewater reuse rate = V produced water / V raw water × 100%.

[0049] 2. Method for determining the zero-discharge disposal rate of high-concentration brine: 2.1 Install an electromagnetic flow meter at the interface of the steel slag treatment process and record the discharge volume V of high-concentration brine over 24 hours; 2.2 Samples were taken at the outlet of the steel slag treatment process, and the Cl content in the leachate was determined using the solid waste leaching procedure specified in HJ / T 299-2007. - SO4 2- Concentration; if Cl- ≤ 1 mg / L and SO4 ≤ 1 mg / L in the leachate 2- If the concentration is ≤1 mg / L, it is determined that the high-concentration brine has been completely solidified by the steel slag. 2.3 When the salt concentration of the leachate meets the requirements of 2.2 and the deviation between the V discharge and the calculated value of the system material balance is ≤1%, the zero discharge and disposal rate of high-concentration brine is determined to be 100%.

[0050] 3. Operating cost per ton of water = Steam cost + Electricity cost + Chemical cost - Waste heat discount revenue.

[0051] Table 1. Effect Data of Examples and Comparative Examples

[0052] Based on the data shown in Table 1, the inventiveness of the technical solution of this application compared to the comparative example is as follows: 1. Under the premise of maintaining a 100% zero discharge and utilization rate of high-concentration brine, Examples 1-5 steadily increased the steel production wastewater reuse rate to ≥90%, reaching a maximum of 95%. However, in Comparative Example 2, due to the absence of a step to remove fluoride ions from the concentrated brine, the steel production wastewater reuse rate plummeted to 45%. This demonstrates that the step to remove fluoride ions from the concentrated brine plays an irreplaceable role in maintaining a steel production wastewater reuse rate of ≥90%.

[0053] 2. Examples 1-5 recover waste heat from the flue gas in the pelletizing, sintering, and hot blast stove processes and heat the demineralized water to 70°C-95°C to drive the evaporator 3 in the form of saturated steam. Under the condition of completely eliminating external high-pressure steam, the steel production wastewater reuse rate is still ≥90%. In contrast, Comparative Example 1 requires external 0.5 MPa saturated steam (high operating cost). This proves that the flue gas waste heat recovery step can reduce operating costs while still ensuring a steel production wastewater reuse rate of ≥90%.

[0054] 3. Examples 4 and 5 show that by atomizing and spraying high-concentration brine onto the surface of molten steel slag in the steel slag treatment process, a non-toxic inert solid solution is formed, maintaining a 100% zero-discharge and disposal rate of high-concentration brine, and without any decrease in the steel production wastewater reuse rate. This proves that the steel slag waste heat solidification of high-concentration brine step achieves zero-discharge and disposal while having no negative impact on the steel production wastewater reuse rate, demonstrating process synergy.

[0055] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for reducing and disposing of steel production wastewater, characterized in that, include: S1. The steel production wastewater is homogenized to obtain homogenized comprehensive wastewater with an electrical conductivity of 2500μS / cm~3000μS / cm; S2. Reduce the absolute pressure of the evaporator to below 15 kPa; S3. Recover the waste heat of flue gas from the pelletizing, sintering and hot blast furnace processes, use the waste heat of the flue gas to heat the demineralized water to 70℃~95℃ to obtain waste heat hot water, and perform negative pressure flash evaporation on the waste heat hot water to generate saturated steam. S4. The saturated steam is introduced into the first-effect heat exchange tube of the evaporator, causing the saturated steam to condense and release heat on the inner wall surface of the heat exchange tube; and the... The homogeneous wastewater is sprayed onto the outer wall surface of the heat exchange tube, causing the homogeneous wastewater to form a liquid film on the outer wall surface of the heat exchange tube and absorb the latent heat of condensation released by the saturated steam, causing part of the homogeneous wastewater to vaporize to form secondary steam and leaving behind concentrated brine. S5. Remove fluoride ions from the concentrated brine to obtain defluorinated concentrated brine; S6. The defluorinated brine and the homogenized integrated wastewater are mixed at a volume flow rate of 1:1 to 1:5 and then sprayed onto the outer wall surface of the heat exchange tube to form a circulating evaporation loop. Repeat steps S1 to S6 until the salt content of the concentrated brine reaches 5 to 10 times the initial salt content of the homogeneous integrated wastewater. Then, continuously discharge high-concentration brine, accounting for 5% to 10% of the total influent volume of the homogeneous integrated wastewater, and send the high-concentration brine to the steel slag treatment process. Use the residual heat of the steel slag in the steel slag treatment process to solidify the high-concentration brine, thereby achieving zero discharge and disposal of the high-concentration brine.

2. The method for reducing and disposing of steel production wastewater according to claim 1, characterized in that, The high-concentration brine is disposed of in the steel slag treatment process as follows: The high-concentration brine is atomized and sprayed onto the surface of the molten steel slag in the steel slag treatment process. The sensible heat of the molten steel slag causes the water in the high-concentration brine to evaporate, the salt to solidify, and the salt to be encapsulated in the glass phase of the molten steel slag, forming a non-toxic inert solid solution.

3. The method for reducing and disposing of steel production wastewater according to claim 1, characterized in that, The negative pressure flash evaporation includes pressure reduction, expansion and vapor-liquid separation in sequence, and the absolute pressure of the negative pressure flash evaporation decreases step by step, with the absolute pressure of the first stage being 25 kPa to 35 kPa.

4. The method for reducing and disposing of steel production wastewater according to claim 1, characterized in that, The spray density for both the initial spray and the subsequent spray is 0.6 m. 3 / (m·h)~0.8 m 3 / (m·h).

5. A wastewater reduction and disposal system for steel production, characterized in that, Along the logistics direction, the following are included in sequence: Water quality equalization tank, which is equipped with a steel production wastewater inlet and a homogenized integrated wastewater outlet; A circulating water supply pump, wherein the inlet of the circulating water supply pump is connected to the homogenized integrated sewage outlet of the water quality regulating tank, and the outlet of the circulating water supply pump is connected to the spray inlet of the evaporator; The evaporator is provided with a spray inlet, a steam inlet, a secondary steam outlet, a concentrated brine outlet, and a product water outlet; A defluorination device, wherein the inlet of the defluorination device is connected to the concentrated brine outlet of the evaporator, and the outlet of the defluorination device is connected to the inlet of the circulating water pump; A flue gas online heat extraction device, wherein the flue gas online heat extraction device is provided with a flue gas inlet, a demineralized water inlet, and a waste heat hot water outlet; A flash evaporator, wherein the hot water inlet of the flash evaporator is connected to the waste heat hot water outlet of the flue gas online heat extraction device, and the steam outlet of the flash evaporator is connected to the steam inlet of the evaporator; A vacuum pump, which is connected to the vapor phase space of the evaporator, is used to reduce the absolute pressure of the final stage of the evaporator to below 15 kPa. The steel slag treatment process interface is connected to the high-concentration brine discharge valve of the evaporator, and is used to introduce high-concentration brine into the steel slag treatment process for solidification and disposal.

6. The steel production wastewater reduction and disposal system according to claim 5, characterized in that, The evaporator is a horizontal tube falling film evaporator with no less than three effects. Each effect is equipped with a concentrated brine collection tank, and the concentrated brine collection tank of the last effect is connected to the interface of the steel slag treatment process through a high-concentration brine discharge valve.

7. The steel production wastewater reduction and disposal system according to claim 5, characterized in that, The flue gas online heat extraction device is a corrosion-resistant finned tube heat exchanger.

8. The steel production wastewater reduction and disposal system according to claim 5, characterized in that, The defluorination device is a fluidized bed crystallization reactor, in which natural mineral powder with a particle size of 40-60 mesh is added to form fluoride particles with a diameter of 1-3 mm. The fluidized bed crystallization reactor is equipped with a fluoride particle discharge port.

9. The steel production wastewater reduction and disposal system according to claim 5, characterized in that, The system also includes a water reuse network. The inlet of the water reuse network is connected to the water outlet of the evaporator, and the outlet of the water reuse network is connected to the water supply ports of the ironmaking, steelmaking, hot rolling and cold rolling processes, respectively, so as to realize the reuse of water throughout the plant.

10. The steel production wastewater reduction and disposal system according to claim 5, characterized in that, The system also includes a seawater cooling circuit, the seawater inlet of which is connected to the cooling side inlet of the last-effect condenser of the evaporator, and the warm water outlet of which is connected to the inlet of the thermal seawater desalination unit, for recovering the low-temperature waste heat discharged from the last-effect condenser.

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