Annealing sulfuric acid scrubbing wastewater treatment and sulfuric acid recovery system
By combining pretreatment processes such as wastewater conditioning, neutralization, high-density sedimentation, filtration, and concentration, and then using a bipolar membrane device to recover sulfuric acid from annealing sulfuric acid washing wastewater, the problems of resource waste, high treatment difficulty, and high cost are solved, achieving economical and environmentally friendly sulfuric acid recovery.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-25
- Publication Date
- 2026-03-31
AI Technical Summary
In existing technologies, the treatment of annealing sulfuric acid washing wastewater suffers from problems such as resource waste, high treatment difficulty, and high treatment costs. In particular, the sulfuric acid cannot be recovered, which increases the burden on the production wastewater system.
A combined system consisting of a wastewater equalization tank, neutralization tank, high-density sedimentation tank, walnut shell filter, tubular membrane microfiltration equipment, reverse osmosis water treatment equipment, nanofiltration water treatment equipment, chelating resin softening equipment, and bipolar membrane electrodialysis equipment is used to recover sulfuric acid from wastewater through a series of physical and chemical treatments.
This method achieves efficient recovery of sulfuric acid, reduces sulfuric acid usage, lowers processing costs, and avoids the generation of wastewater and waste salt, offering both economic and environmental advantages.
Smart Images
Figure CN224062600U_ABST
Abstract
Description
Technical Field
[0001] This utility model belongs to the field of metallurgical wastewater treatment technology, specifically relating to an annealing sulfuric acid washing wastewater treatment and sulfuric acid recovery system. Background Technology
[0002] After hot rolling and annealing, stainless steel has a large amount of oxides on its surface. It usually needs to be mechanically descaled (shot blasting) to remove most of the iron oxide scale on the surface. Then, it needs to be pickled with sulfuric acid and mixed acid to remove the remaining iron oxide scale on the surface, so that the stainless steel can finally present a smooth and corrosion-resistant surface.
[0003] Stainless steel that has undergone sulfuric acid pickling retains some sulfuric acid solution and loose iron oxide particles on its surface. To prevent these from being carried into the mixed acid pickling section, it needs to be removed by a sulfuric acid brushing section before entering the mixed acid pickling stage. The wastewater discharged from the brushing system has a lower acid concentration than the pickling wastewater and cannot be discharged into the acid regeneration system. It usually needs to undergo pretreatment such as neutralization and precipitation before being discharged into the production wastewater system or separately treated by membrane concentration followed by evaporation and crystallization. However, discharging it into the production wastewater system will not recover the sulfuric acid in the pickling wastewater, resulting in resource waste and will increase the salinity of the production wastewater system, making wastewater treatment more difficult. If evaporation and crystallization are carried out separately, the treatment cost will be high, and the generated sodium sulfate byproduct will require a separate disposal method. Utility Model Content
[0004] To address the aforementioned problems, the purpose of this utility model is to provide a system for treating annealing sulfuric acid washing wastewater and recovering sulfuric acid, thereby solving the problems of resource waste, high treatment difficulty, and high treatment cost associated with conventional treatment methods.
[0005] To achieve the above objectives, this utility model provides a system for treating annealing sulfuric acid washing wastewater and recovering sulfuric acid, comprising: a wastewater equalization tank, a neutralization tank, a high-density sedimentation tank, a walnut shell filter, a tubular membrane microfiltration device, a microfiltration permeate tank, a reverse osmosis water treatment device, a nanofiltration water treatment device, a nanofiltration concentrate tank, a chelating resin softening device, and a bipolar membrane electrodialysis device, connected sequentially by pipelines; wherein,
[0006] Wastewater equalization tank is used to homogenize and equalize the collected annealing sulfuric acid washing wastewater.
[0007] Neutralization tank is used to neutralize the scrubbing wastewater after it has been homogenized and its volume adjusted.
[0008] High-density sedimentation tanks are used to remove most of the iron ions and heavy metals from neutralized wastewater to obtain sedimentation tank permeate.
[0009] Walnut shell filters are used to filter and remove oil from the permeate from sedimentation tanks.
[0010] Tubular membrane microfiltration is used to further remove iron ions and heavy metals from wastewater after oil removal filtration to obtain microfiltration permeate; the microfiltration permeate enters the microfiltration product water tank.
[0011] Reverse osmosis water treatment equipment: the microfiltration permeate is treated by a reverse osmosis membrane to obtain reverse osmosis permeate;
[0012] Nanofiltration water treatment equipment is used to filter reverse osmosis concentrate to obtain nanofiltration concentrate, which then enters a nanofiltration concentrate tank.
[0013] Chelating resin softening equipment is used to deeply remove divalent and higher metal ions from nanofiltration concentrate to obtain softened permeate.
[0014] It also includes bipolar membrane electrodialysis equipment, where softened water is treated by bipolar membranes to obtain recovered acid and recovered alkali solutions.
[0015] Furthermore, the reverse osmosis water treatment equipment consists of a primary reverse osmosis unit and a secondary reverse osmosis unit. The primary reverse osmosis unit uses a seawater desalination membrane made of polyamide, while the secondary reverse osmosis unit uses a brackish water membrane made of polyamide.
[0016] Compared with existing technologies, the process of this invention, after pretreatment such as neutralization precipitation, filtration, and concentration, fully recovers sulfuric acid from the sulfuric acid washing wastewater of hot-rolled stainless steel annealing through a bipolar membrane device, reducing the amount of sulfuric acid used in the annealing pickling process. Therefore, it has the advantages of not requiring expensive evaporators, producing no wastewater or waste salt, and being economical, environmentally friendly, and having a high resource utilization rate. Attached Figure Description
[0017] Figure 1 This is a system block diagram of the present invention. Detailed Implementation
[0018] The embodiments of this utility model will now be described in detail with reference to the accompanying drawings.
[0019] In the description of this utility model, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.
[0020] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this utility model, unless otherwise stated, "a plurality of" means two or more.
[0021] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.
[0022] The annealing sulfuric acid washing wastewater treatment and sulfuric acid recovery system of the present invention, such as Figure 1 As shown, the equipment includes, in sequence via pipelines: a wastewater equalization tank, a neutralization tank, a high-density sedimentation tank, a walnut shell filter, a tubular membrane microfiltration device, a microfiltration permeate tank, a reverse osmosis water treatment device, a nanofiltration water treatment device, a nanofiltration concentrate tank, and a bipolar membrane electrodialysis device; all of the above equipment were purchased from the market.
[0023] The bipolar membrane electrodialysis equipment consists of an electrodialysis membrane stack composed of alternating bipolar membranes, cation exchange membranes, and anion exchange membranes. Each stack comprises multiple repeating units, each containing a salt chamber, an acid chamber, and an alkali chamber. Under a direct current electric field, hydrolysis at the bipolar membrane interface produces H+ and OH-, which enter the acid and alkali chambers respectively. SO42- in the salt chamber permeates through the anion exchange membrane into the acid chamber to obtain sulfuric acid, while Na+ permeates through the cation exchange membrane into the alkali chamber to obtain liquid alkali. The bipolar membrane is a modified bipolar membrane prepared by an impregnation method, the ion exchange membrane is a perfluorosulfonic acid membrane, and the electrode solution is secondary reverse osmosis permeate. The bipolar membrane operating voltage is 1.8~2.5 V per membrane pair, the current density is 20~50 mA / cm², and the operating temperature is 25~40℃. The recovered acid solution is used as a makeup solution for the annealing sulfuric acid pickling system, and the recovered alkali solution is used as a makeup solution for the liquid alkali in the neutralization process. Example
[0024] An annealing sulfuric acid washing wastewater treatment and sulfuric acid recovery system, such as Figure 1 As shown, the system includes, in sequence via pipelines: a wastewater equalization tank, a neutralization tank, a high-density sedimentation tank, a walnut shell filter, a tubular membrane microfiltration device, a microfiltration permeate tank, a reverse osmosis water treatment device, a nanofiltration water treatment device, a nanofiltration concentrate tank, a chelating resin softening device, and a bipolar membrane electrodialysis device; its working process includes:
[0025] 1) The scrubbing wastewater is collected and sent to the wastewater equalization tank for homogenization and equalization;
[0026] The washing wastewater comes from the sulfuric acid washing section of hot-rolled stainless steel annealing. After homogenization, the sulfuric acid concentration of the waste liquid generated by different washing machines is 1.5% and the concentration of ferrous ions is 4 g / L.
[0027] 2) After homogenization and adjustment, the scrubbing wastewater enters the neutralization tank for a two-stage neutralization reaction, and then passes through a high-density sedimentation tank to remove most of the iron ions and heavy metals, resulting in sedimentation tank permeate.
[0028] The reaction time in the primary neutralization tank is 40 min, and the reaction time in the secondary neutralization tank is 30 min. The ferrous ions are oxidized to ferric ions by aeration with a gas-to-water ratio of 15.
[0029] The rapid mixing time in the high-density sedimentation tank was 2 min, the flocculation time was 20 min, the surface loading rate in the clarification zone was 2 (m3 / m2•h), and the measured concentration of suspended solids in the effluent was 13 mg / L.
[0030] 3) The water produced in the sedimentation tank is first filtered through a walnut shell filter to remove oil, and then filtered through a tubular membrane microfiltration system to obtain the microfiltration permeate.
[0031] The walnut shell filter uses specially processed walnut shells as the filter medium, with a filtration speed of 25 m / h and a measured oil content of 0.8 mg / L in the effluent.
[0032] The tubular membrane microfiltration membrane is made of polyvinylidene fluoride (PVDF), with a filtration accuracy of 0.05 μm, an operating flux of 318 L / m2•h, an operating pressure of 0.3 MPa, and a microfiltration permeate with an SDI ≤ 3 and a turbidity ≤ 0.2 NTU.
[0033] 4) The microfiltration permeate is treated by the first-stage reverse osmosis membrane equipment to obtain first-stage reverse osmosis permeate and first-stage reverse osmosis concentrate; the first-stage reverse osmosis permeate is treated by the second-stage reverse osmosis membrane equipment to obtain second-stage reverse osmosis permeate and second-stage reverse osmosis concentrate. The second-stage reverse osmosis permeate is reused, and the second-stage reverse osmosis concentrate is returned to the microfiltration permeate tank through pipelines.
[0034] The first-stage reverse osmosis system uses a seawater desalination membrane made of polyamide, with a system recovery rate of ≥60% and an operating flux of 9.4 L / m²•h. The second-stage reverse osmosis system uses a brackish water membrane made of polyamide, with a system recovery rate of ≥80% and an operating flux of 12.6 L / m²•h. The permeate from the second-stage reverse osmosis system is used as fresh industrial water in the steel plant.
[0035] 5) After the primary reverse osmosis concentrate is filtered through the nanofiltration membrane of the nanofiltration water treatment equipment, nanofiltration permeate and nanofiltration concentrate are obtained. Chelating softening resin is added to the nanofiltration concentrate to deeply remove divalent and higher metal ions in the concentrate, thus obtaining softened permeate.
[0036] The nanofiltration membrane is made of polyamide, with a system recovery rate of ≥50% and an operating flux of 9.9 L / m²•h. The nanofiltration permeate is used as fresh industrial water in the steel plant, and the sodium sulfate content of the nanofiltration concentrate is 12%.
[0037] The hydraulic retention time of the chelating softening resin is 1 h, and the total amount of divalent and higher metal ions in the softened water is <0.5 mg / L.
[0038] 6) The softened permeate is treated by a bipolar membrane electrodialysis system to obtain recovered acid and recovered alkali solutions;
[0039] The bipolar membrane electrodialysis system consists of alternating bipolar membranes, cation exchange membranes, and anion exchange membranes arranged in an electrodialysis membrane stack. Each stack comprises multiple repeating units, each containing a salt chamber, an acid chamber, and an alkali chamber. Under a direct current electric field, hydrolysis at the bipolar membrane interface produces H+ and OH-, which enter the acid and alkali chambers respectively. SO42- in the salt chamber permeates through the anion exchange membrane into the acid chamber to obtain sulfuric acid, while Na+ permeates through the cation exchange membrane into the alkali chamber to obtain liquid alkali. The bipolar membrane is a modified bipolar membrane prepared by an impregnation method, the ion exchange membrane is a perfluorosulfonic acid membrane, and the electrode solution is secondary reverse osmosis permeate. The bipolar membrane operating voltage is 1.8–2.5 V per membrane pair, the current density is 20–50 mA / cm², and the operating temperature is 25–40 °C. The recovered acid solution is used as a makeup solution for the annealing sulfuric acid pickling system, and the recovered alkali solution is used as a makeup solution for the liquid alkali in the neutralization process.
[0040] The bipolar membrane is a modified bipolar membrane prepared by impregnation, the ion exchange membrane is a perfluorosulfonic acid membrane, and the electrode solution is secondary reverse osmosis permeate. The recovered acid solution has a sulfuric acid concentration of 9.8%, and the recovered alkali solution has a sodium hydroxide concentration of 8%. The recovered acid solution is used as a makeup solution for the annealing sulfuric acid pickling system, and the recovered alkali solution is returned to the neutralization process section through pipelines as a liquid alkali makeup solution.
[0041] In this embodiment, the recovery rate of sulfuric acid in the scrubbing wastewater was 98%, mainly due to a small amount of loss caused by the water-containing sludge being carried away during the high-density tank sludge treatment process. Example
[0042] The annealing sulfuric acid washing wastewater treatment and sulfuric acid recovery system of this embodiment includes: a wastewater equalization tank, a neutralization tank, a high-density sedimentation tank, a walnut shell filter, a tubular membrane microfiltration device, a microfiltration permeate tank, a reverse osmosis water treatment device, a nanofiltration water treatment device, a nanofiltration concentrate tank, a chelating resin softening device, and a bipolar membrane electrodialysis device, connected sequentially by pipelines; its working process includes:
[0043] 1) The scrubbing wastewater is collected and sent to the wastewater equalization tank for homogenization and equalization;
[0044] The wastewater from the hot-rolled stainless steel annealing sulfuric acid washing section was obtained. After homogenization, the sulfuric acid concentration of the wastewater generated by different washing machines was 1.2%, and the concentration of ferrous ions was 3.4 g / L.
[0045] 2) The homogenized and conditioned scrubbing wastewater first undergoes a two-stage neutralization reaction, and then passes through a high-density sedimentation tank to remove most of the iron ions and heavy metals, resulting in sedimentation tank permeate.
[0046] The reaction time in the primary neutralization tank is 30 min, and the reaction time in the secondary neutralization tank is 30 min. The ferrous ions are oxidized to ferric ions by aeration with a gas-to-water ratio of 12.
[0047] The rapid mixing time in the high-density sedimentation tank was 1 min, the flocculation time was 10 min, the surface loading rate in the clarification zone was 3 (m3 / m2•h), and the measured concentration of suspended solids in the effluent was 15 mg / L.
[0048] 3) The water produced in the sedimentation tank is first filtered through a walnut shell filter to remove oil, and then filtered through a tubular membrane microfiltration system to obtain the microfiltration permeate.
[0049] The walnut shell filter uses specially processed walnut shells as the filter medium, with a filtration speed of 24 m / h and a measured oil content of 0.6 mg / L in the effluent.
[0050] The tubular membrane microfiltration membrane is made of polyvinylidene fluoride (PVDF), with a filtration accuracy of 0.05 μm, an operating flux of 313 L / m2•h, an operating pressure of 0.3 MPa, and a microfiltration permeate with an SDI ≤ 3 and a turbidity ≤ 0.2 NTU.
[0051] 4) The microfiltration permeate is treated by the first-stage reverse osmosis membrane to obtain first-stage reverse osmosis permeate and first-stage reverse osmosis concentrate; the first-stage reverse osmosis permeate is treated by the second-stage reverse osmosis membrane to obtain second-stage reverse osmosis permeate and second-stage reverse osmosis concentrate. The second-stage reverse osmosis permeate is reused, and the second-stage reverse osmosis concentrate is returned to the microfiltration permeate tank through pipelines.
[0052] The first-stage reverse osmosis system uses a seawater desalination membrane made of polyamide, with a system recovery rate of ≥60% and an operating flux of 9.8 L / m²•h. The second-stage reverse osmosis system uses a brackish water membrane made of polyamide, with a system recovery rate of ≥80% and an operating flux of 14.5 L / m²•h. The permeate from the second-stage reverse osmosis system is used as fresh industrial water in the steel plant.
[0053] 5) After the primary reverse osmosis concentrate is filtered through a nanofiltration membrane, nanofiltration permeate and nanofiltration concentrate are obtained. The nanofiltration concentrate is then subjected to chelating softening resin to further remove divalent and higher metal ions from the concentrate, resulting in softened permeate.
[0054] The nanofiltration membrane is made of polyamide, with a system recovery rate of ≥50% and an operating flux of 9.8 L / m²•h. The nanofiltration permeate is used as fresh industrial water in the steel plant, and the nanofiltration concentrate has a sodium sulfate content of 10%.
[0055] The hydraulic retention time of the chelating softening resin is 1 h, and the total amount of divalent and higher metal ions in the softened water is <0.5 mg / L.
[0056] 6) The softened permeate is treated by a bipolar membrane to obtain recovered acid and recovered alkali solutions;
[0057] The bipolar membrane was a modified bipolar membrane prepared by impregnation, the ion exchange membrane was a perfluorosulfonic acid membrane, and the electrode solution was secondary reverse osmosis permeate. The recovered acid solution had a sulfuric acid concentration of 8.5%, and the recovered alkali solution had a sodium hydroxide concentration of 7%. The recovered acid solution was used as a makeup solution for the annealing sulfuric acid pickling system, and the recovered alkali solution was used as a makeup solution for the neutralization process.
[0058] In this embodiment, the recovery rate of sulfuric acid in the scrubbing wastewater was 99%, with a small amount of loss mainly occurring during the high-density sludge treatment process due to it being carried away by the water-containing sludge.
[0059] The present invention has been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above-described embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Many other changes and modifications made without departing from the concept and scope of the present invention should be considered within the protection scope of the present invention.
[0060] In the description of this specification, specific features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.
[0061] The above description is merely a specific embodiment of this utility model, but the protection scope of this utility model is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this utility model should be included within the protection scope of this utility model. Therefore, the protection scope of this utility model should be determined by the protection scope of the claims.
Claims
1. An annealing sulfuric acid scrubbing wastewater treatment and sulfuric acid recovery system characterized by, The application relates to a wastewater treatment device. The wastewater treatment device comprises the following devices connected in sequence through pipelines: a wastewater conditioning tank, a neutralization tank, a high-density sedimentation tank, a walnut shell filter, a tubular membrane microfiltration device, a microfiltration water tank, a reverse osmosis water treatment device, a nanofiltration water treatment device, a nanofiltration concentrated water tank, a chelating resin softening device and a bipolar membrane electrodialysis device. The wastewater conditioning tank is used for homogenously and equally conditioning collected annealing sulfuric acid brushing wastewater. The neutralization tank is used for neutralization reaction of the homogenously and equally conditioned brushing wastewater. The high-density sedimentation tank is used for removing most of iron ions and heavy metals in the neutralized wastewater to obtain sedimentation tank water. The walnut shell filter is used for filtering and removing oil from the sedimentation tank water. The tubular membrane microfiltration is used for further removing iron ions and heavy metals from the wastewater after the oil removal to obtain microfiltration permeate; the microfiltration permeate enters the microfiltration water tank. The reverse osmosis water treatment device is used for treating the microfiltration permeate through a reverse osmosis membrane to obtain reverse osmosis water. The nanofiltration water treatment device is used for filtering and treating the reverse osmosis concentrated water to obtain nanofiltration concentrated water; the nanofiltration concentrated water enters the nanofiltration concentrated water tank. The chelating resin softening device is used for deeply removing metal ions with a valence of two or more in the nanofiltration concentrated water to obtain softening water. The bipolar membrane electrodialysis device is used for treating the softening water through a bipolar membrane to obtain recovered acid liquid and recovered alkali liquid.
2. The annealing sulfuric acid brush pickling wastewater treatment and sulfuric acid recovery system according to claim 1, characterized in that, The reverse osmosis water treatment device is composed of a first-level reverse osmosis device and a second-level reverse osmosis device; the first-level reverse osmosis device adopts a seawater desalination membrane, and the membrane material is polyamide; the second-level reverse osmosis device adopts a brackish water membrane, and the membrane material is polyamide.