Method and device for treating salt-containing wastewater in ion exchange desalination process

Abstract

The present application relates to salt-containing wastewater treatment technical field, and is a kind of ion exchange salt water preparation process and device for salt-containing wastewater treatment, in the former, according to the height of conductivity value, salt-containing wastewater from ion exchange salt water preparation process is classified and collected to the regeneration of anion bed and cation bed, and the low-salt wastewater after classification and collection is recycled for raw water device or circulating water device water replenishment;After a series of hardness removal and ion separation, high-salt wastewater is obtained to obtain chlorine-containing light salt water, and then reused;The latter includes cation bed, anion bed, high-salt wastewater tank, hardness removal reaction tank, ultrafiltration filter, ion exchange column, nanofiltration separation facility, salt tank, and conductivity meter is respectively fixedly arranged on the salt-containing wastewater pipeline of cation bed and anion bed outlet, first salt-containing wastewater pipeline and chlorine-containing light salt water pipeline of salt tank inlet.The present application is carried out at normal temperature, and only a small amount of reagent and electric power is consumed, so that the effect of salt-containing wastewater classification and collection treatment can be achieved.

Description

Technical Field

[0001] This invention relates to the field of saline wastewater treatment technology, and is a method and apparatus for treating saline wastewater during the process of ion exchange to produce desalinated water. Background Technology

[0002] Ion exchange water treatment processes use resin to adsorb ions from water. Hydrochloric acid and sodium hydroxide are typically used to regenerate the exhausted resin. This regeneration process generates a large amount of high-salinity wastewater, rich in cations such as sodium, calcium, and magnesium, and anions such as chloride and sulfate, with a salt content exceeding 1.5%. Direct discharge into the environment can lead to increased salinity in aquatic environments and soil salinization. Current technologies generally involve further treatment of this high-salinity wastewater in industrial wastewater treatment processes, but this results in increased salinity and reduced water quality. Some companies have constructed zero-discharge facilities for high-salinity wastewater, typically employing membrane concentration followed by evaporation and crystallization for salt extraction. However, these systems are costly to build and suffer from problems such as equipment blockage, corrosion, high steam consumption, and high operating costs.

[0003] Chinese patent document CN206108984U discloses a system for the classified collection and reuse of wastewater from boiler feedwater desalination treatment. A return water pipeline from the anion bed to the cation bed is connected between the outlet of the anion bed and the inlet of the cation bed. A first control valve is installed in the anion-to-cation bed return water pipeline, and a second control valve is installed in the mixed bed-to-cation bed return water pipeline. This system recycles the flushing wastewater from the anion and cation beds. The cation bed flushing water directly enters the anion bed, and the anion bed flushing wastewater is recycled back to the cation bed inlet. This cycle continues until the effluent meets the required standards. However, multi-series anion-cation bed systems cannot separate the effluent from each cation bed, anion bed, and mixed bed. This system is only suitable for single-series, independently operating fixed anion-cation beds and cannot be applied to multi-series, simultaneously operating fixed anion-cation beds or multi-series, floating anion-cation beds, thus limiting the widespread application of this technology. In addition, this patent collects the acid and alkali wastewater and displacement wastewater from the anion, cation, and mixed bed regeneration separately into the regeneration wastewater tank, and the remaining wastewater is recycled to the recycling tank for reuse at the inlet of the raw water pretreatment system. This patent does not collect wastewater according to the effluent indicators, and the amount of wastewater collected is insufficient.

[0004] Chinese patent document CN112032563A discloses a device and method for classifying and recycling finely treated regenerated wastewater. The device for classifying and recycling finely treated regenerated wastewater is equipped with two pipelines, valves and instruments at the outlet of the waste resin trap. It can separately recycle and reuse low-salt wastewater generated during the operation of the separation tower, cation regeneration tower and anion regeneration tower. After reducing the amount of high-salt wastewater, the amount of wastewater to be treated at the end is reduced, which greatly saves wastewater treatment costs. This patent does not involve the reduction and reuse of wastewater in the ion exchange water treatment and desalination process of the cation and anion bed regeneration process.

[0005] Chinese patent document CN103508521B discloses a method for the resource-based treatment of saline wastewater. This process involves desalinating, concentrating, and initially removing hardness from saline wastewater using a conventional electrodialysis unit. The resulting low-salinity wastewater is then returned to the desalination section to prepare pure water. High-salinity wastewater undergoes further hardness removal via ion exchange. This hardened high-salinity wastewater is then processed through a bipolar membrane electrodialysis unit for resource-based treatment. During this process, the salt content in the wastewater is significantly reduced due to the dissociation of sodium chloride and water, while hydrochloric acid and sodium hydroxide are simultaneously obtained. The resulting low-salinity wastewater is then returned to the concentrate chamber of the conventional electrodialysis unit for further concentration. This process produces hydrochloric acid and caustic soda as byproducts after treating the high-salinity wastewater. While the brine recovery rate is higher than 85%, the concentrations of the hydrochloric acid and caustic soda produced are low, making them unsuitable for commercial sale. Users can only be found within or around the plant. Furthermore, when the volume of high-salinity wastewater is large, the downstream applications of the treated hydrochloric acid and caustic soda products pose challenges, limiting the widespread application of this technology.

[0006] Chinese patent document CN203486953U discloses a device for the comprehensive utilization of wastewater from a cation-anion bed system. This device includes a water treatment unit, an alkaline water collection tank, and an acidic water collection tank. The alkaline wastewater is used in a phosphoric acid scrubbing tower to absorb acidic substances from phosphoric acid tail gas, while the acidic wastewater is used in a hydrochloric acid absorption tower in a potassium hydrogen production unit of a compound fertilizer production system to increase the hydrochloric acid concentration before producing finished hydrochloric acid. This system can be used in a compound fertilizer production plant with simple modifications. However, this plant only regenerates once every 10 days, generating approximately 1 ton of wastewater containing caustic soda and 1 ton of wastewater containing hydrochloric acid. The hydrochloric acid tower and the phosphoric acid tail gas absorption tower have limited demand for acidic and alkaline water. Furthermore, the acidic water is used in the hydrochloric acid tower to absorb hydrogen chloride, resulting in a low concentration of hydrochloric acid in the product. If the concentration is high, hydrogen chloride may overflow. This hydrochloric acid contains a large amount of calcium and magnesium ions, which cannot meet the standards for industrial synthetic hydrochloric acid, thus limiting the widespread application of this technology.

[0007] Therefore, in view of the above limitations, it is necessary to invent a method for treating saline wastewater during the ion exchange process for desalination to solve the above problems. Summary of the Invention

[0008] This invention provides a method and apparatus for treating saline wastewater during the process of ion exchange to produce demineralized water, which overcomes the shortcomings of the prior art and can effectively solve the problems of large volume of high-salt wastewater and difficult post-treatment of high-salt wastewater during the process of ion exchange to produce demineralized water.

[0009] One of the technical solutions of this invention is achieved through the following measures: a method for treating saline wastewater during ion exchange demineralization, carried out according to the following method: The first step is to classify saline wastewater into low-salinity wastewater and high-salinity wastewater according to their conductivity values, and then collect them separately. The second step is to collect the low-salt wastewater and use it to replenish the raw water system or the circulating water system. The third step involves sequentially treating the high-salt wastewater through chemical reactions to remove hardness, filtration to remove hardness, and ion separation to obtain chlorinated dilute brine for reuse.

[0010] The following are further optimizations and / or improvements to one of the above-mentioned technical solutions: In the first step above, the saline wastewater includes: saline wastewater generated by the reaction of hydrochloric acid solution and demineralized water required for the cation exchange bed with the resin in the cation exchange bed, and saline wastewater generated by the reaction of caustic soda solution and demineralized water required for the anion exchange bed with the resin in the anion exchange bed. The conductivity values ​​of the resulting saline wastewater are all between 0.05 mS / cm and 35 mS / cm. Using the conductivity value of the saline wastewater as the recovery condition, the wastewater with a conductivity value higher than 1000 μS / cm is collected separately as high-salt wastewater, and the wastewater with a conductivity value lower than 1000 μS / cm is collected separately as low-salt wastewater.

[0011] The third step above, the high-salinity wastewater treatment process includes: S1, chemical reaction is carried out on high-salt wastewater to remove hardness, resulting in softened brine; S2, the softened brine is filtered to remove hardness, and brine is obtained; S3 separates the ions in the brine to obtain chlorinated brine; S4, reuse the chlorinated brine.

[0012] In step S1 above, the process of removing hardness from high-salt wastewater specifically includes: adding the required amounts of sodium hydroxide, sodium carbonate, and ferric chloride to the high-salt wastewater in sequence; adding sodium hydroxide to control the pH of the reaction system to be 10.2 to 11.5; adding sodium carbonate to control the excess alkali of the reaction system to be 0.30 g / L to 0.80 g / L; adding ferric chloride to each ton of high-salt wastewater to be 5 g to 50 g; and obtaining a softened brine with a calcium and magnesium ion content of less than or equal to 3.0 mg / L.

[0013] In step S2 above, the process of deep hardening removal of softened brine specifically includes: after the softened brine passes through an ultrafiltration filter and an ion exchange column in sequence, calcium and magnesium ions are deeply removed, and the calcium and magnesium ion content in the resulting brine is less than or equal to 0.02 mg / L.

[0014] In step S3 above, the process of separating ions in the brine specifically includes: using nanofiltration to separate monovalent and divalent ions in the brine, with the working pressure during the separation process being 0.25 MPa to 1.00 MPa, the calcium and magnesium ion content in the resulting chlorinated brine being less than or equal to 0.02 mg / L, and sodium chloride accounting for more than 95% of all salts in the chlorinated brine.

[0015] In step S4 above, the process of reusing the sodium chloride-containing brine specifically includes: transporting the chlorine-containing brine to the chlor-alkali unit as brine for use in the salt-making process.

[0016] The second technical solution of the present invention is achieved through the following measures: an apparatus for treating saline wastewater during the process of ion exchange to produce demineralized water, comprising a cation bed, an anion bed, a high-salinity wastewater tank, a hardening reaction tank, an ultrafiltration filter, an ion exchange column, a nanofiltration separation facility, and a salt dissolving tank. The cation bed inlet is fixedly connected to a hydrochloric acid solution and a demineralized water pipeline, the anion bed inlet is fixedly connected to a caustic soda solution and a demineralized water pipeline, the cation bed outlet is fixedly connected to the high-salinity wastewater tank inlet via a first saline wastewater pipeline, and the anion bed outlet is fixedly connected to the first saline wastewater pipeline. There is a second saline wastewater pipeline. A high-salinity wastewater pipeline is fixedly connected between the outlet of the high-salinity wastewater tank and the first inlet of the hardening reaction tank. A dosing pipeline is fixedly connected to the second inlet of the hardening reaction tank. A softened brine pipeline is fixedly connected between the outlet of the hardening reaction tank and the inlet of the ultrafiltration filter. A first brine pipeline is fixedly connected between the outlet of the ultrafiltration filter and the inlet of the ion exchange column. A second brine pipeline is fixedly connected between the outlet of the ion exchange column and the inlet of the nanofiltration separation facility. A chlorinated brine pipeline is fixedly connected between the outlet of the nanofiltration separation facility and the inlet of the salt treatment tank.

[0017] The following are further optimizations and / or improvements to the second technical solution of the above invention: The above also includes a recycling tank, a circulating water device, and a raw water device. A first reuse pipeline is fixedly connected between the first saline wastewater pipeline between the second saline wastewater pipeline and the high-salinity wastewater tank and the inlet of the recycling tank. A second reuse pipeline is fixedly connected between the first outlet of the recycling tank and the inlet of the circulating water device. A third reuse pipeline is fixedly connected between the second outlet of the recycling tank and the inlet of the raw water device. A first conductivity meter, a second conductivity meter, and a third conductivity meter are fixedly installed on the first saline wastewater pipeline, the high-salinity wastewater pipeline, and the chlorinated dilute saline water pipeline between the second saline wastewater pipeline and the first reuse pipeline.

[0018] This invention classifies and collects saline wastewater generated during the regeneration of cation and anion beds in ion exchange demineralization processes based on its conductivity. The low-salinity wastewater is recycled for use in the raw water system or as makeup water for the circulating water system. The high-salinity wastewater undergoes a series of hardness removal and separation processes to obtain chlorinated brine, which is then reused in the chlor-alkali plant for salt production. All processes in this invention are carried out at room temperature, requiring only a small amount of reagents and electricity, achieving graded treatment of saline wastewater and reducing the volume of high-salinity wastewater to be treated. Attached Figure Description

[0019] Appendix Figure 1 This is a schematic diagram of the process flow of the present invention.

[0020] The codes in the attached diagram are as follows: 1 is cation exchange bed, 2 is anion exchange bed, 3 is high-salinity wastewater tank, 4 is hardening removal reaction tank, 5 is ultrafiltration filter, 6 is ion exchange column, 7 is nanofiltration separation facility, 8 is salt treatment tank, 9 is hydrochloric acid regeneration pipeline, 10 is alkali regeneration pipeline, 11 is first saline wastewater pipeline, 12 is second saline wastewater pipeline, 13 is high-salinity wastewater pipeline, 14 is chemical dosing pipeline, 15 is softened brine pipeline, 16 is first brine pipeline, 17 is second brine pipeline, 18 is chlorinated brine pipeline, 19 is recovery water tank, 20 is circulating water device, 21 is first reuse pipeline, 22 is second reuse pipeline, 23 is raw water device, and 24 is third reuse pipeline. Detailed Implementation

[0021] This invention is not limited to the following embodiments, and specific implementation methods can be determined according to the technical solutions and actual conditions of this invention. Unless otherwise specified, all chemical reagents and chemicals mentioned in this invention are well-known and commonly used chemical reagents and chemicals in the prior art; unless otherwise specified, all percentages in this invention are mass percentages; unless otherwise specified, all solutions in this invention are aqueous solutions with water as the solvent, for example, ferric chloride solution is an aqueous solution of ferric chloride; room temperature in this invention generally refers to a temperature between 15°C and 25°C, generally defined as 25°C.

[0022] The present invention will be further described below with reference to embodiments: Example 1: As Figure 1 As shown, the method for treating saline wastewater during the ion exchange demineralization process is carried out according to the following procedure: The first step is to classify saline wastewater into low-salinity wastewater and high-salinity wastewater according to their conductivity values, and then collect them separately. The second step is to collect the low-salt wastewater and use it to replenish the raw water device 23 or the circulating water device 20. The third step involves sequentially treating the high-salt wastewater through chemical reactions to remove hardness, filtration to remove hardness, and ion separation to obtain chlorinated dilute brine for reuse.

[0023] Example 2: As an optimization of the above example, the specific process of classifying and collecting saline wastewater in the first step includes: the saline wastewater includes: saline wastewater generated by the reaction of hydrochloric acid solution and demineralized water required for cation bed 1 with the resin in cation bed 1, and saline wastewater generated by the reaction of caustic soda solution and demineralized water required for anion bed 2 with the resin in anion bed 2. The conductivity values ​​of the resulting saline wastewater are all between 0.05 mS / cm and 35 mS / cm. Using the conductivity value of the saline wastewater as the recovery condition, the wastewater with a conductivity value higher than 1000 μS / cm is collected separately as high-salt wastewater, and the wastewater with a conductivity value lower than 1000 μS / cm is collected separately as low-salt wastewater.

[0024] As needed, low-salinity wastewater with a conductivity of less than 1000 μs / cm, which is generated from cation exchange bed 1 and anion exchange bed 2, can be directly reused. Through reuse, the amount of high-salinity wastewater to be treated can be reduced by 30% per year. High-salinity wastewater with a conductivity of more than 1000 μs / cm is collected, treated to reduce its hardness and conductivity, and then recycled.

[0025] Example 3: As an optimization of the above examples, the high-salinity wastewater treatment process includes: S1, chemical reaction is carried out on high-salt wastewater to remove hardness, resulting in softened brine; S2, the softened brine is filtered to remove hardness, and brine is obtained; S3 separates the ions in the brine to obtain chlorinated brine; S4, reuse the chlorinated brine.

[0026] Example 4: As an optimization of the above example, in step S1, the process of removing hardness from high-salt wastewater specifically includes: adding the required amounts of sodium hydroxide, sodium carbonate, and ferric chloride to the high-salt wastewater in sequence; adding sodium hydroxide to control the pH value of the reaction system to be 10.2 to 11.5; adding sodium carbonate to control the excess alkali of sodium carbonate in the reaction system to be 0.30 g / L to 0.80 g / L; adding ferric chloride to each ton of high-salt wastewater to be 5 g to 50 g; and obtaining a softened brine with a calcium and magnesium ion content of less than or equal to 3.0 mg / L.

[0027] Sodium hydroxide and sodium carbonate are added to the reaction system as needed to control the pH value and excess sodium carbonate content to suitable conditions. Ferric chloride solution is used as a flocculant to remove calcium from high-salt wastewater. 2+ Mg 2+ HSiO3 2- Plasma.

[0028] In actual operation, the amount of ferric chloride added can be adjusted according to the conductivity value of the high-salt wastewater.

[0029] Example 5: As an optimization of the above example, in step S2, the process of deep hardening removal of softened brine specifically includes: after the softened brine passes through the ultrafiltration filter 5 and the ion exchange column 6 in sequence, calcium and magnesium ions are deeply removed, and the calcium and magnesium ion content in the obtained brine is less than or equal to 0.02 mg / L.

[0030] Depending on the requirements, the ion exchange column 6 used can be a weak cation exchange column. The weak acidic cation exchange resin packed in the weak cation exchange column reduces the hardness of the water by exchanging with cations such as calcium and magnesium in the water.

[0031] Example 6: As an optimization of the above example, in step S3, the process of separating ions in the brine specifically includes: using nanofiltration to separate monovalent and divalent ions in the brine, with the working pressure during the separation process being 0.25 MPa to 1.00 MPa, the calcium and magnesium ion content in the resulting chlorinated brine being less than or equal to 0.02 mg / L, and sodium chloride accounting for more than 95% of all salts in the chlorinated brine.

[0032] Depending on the requirements, the nanofiltration separation facility used can be a nanofiltration membrane. Utilizing the selective permeability of the nanofiltration membrane, the sodium chloride content in the separated chlorinated brine can reach over 95%. The separated concentrated brine containing divalent ions is discharged to the wastewater treatment plant for further processing. Since scale-forming ions such as calcium and magnesium have been removed from the concentrated brine, the original high-salt wastewater will not cause scaling and clogging of the equipment after being discharged into the wastewater system, thus solving the problem of difficult discharge routes for high-salt wastewater.

[0033] Example 7: As an optimization of the above example, in step S4, the process of reusing the sodium chloride-containing brine specifically includes: transporting the chlorine-containing brine to the chlor-alkali unit and using it as brine in the salt-making process.

[0034] Depending on the needs, the salt component in chlorinated brine is mainly sodium chloride, which is used as brine, and the sodium chloride in high-salt wastewater is recycled.

[0035] Compared with traditional zero-emission salt separation processes, this reduces steam consumption during the evaporation and crystallization process and equipment corrosion problems.

[0036] Example 8: As attached Figure 1 As shown, the saline wastewater treatment device for the ion exchange demineralization process includes a cation bed 1, an anion bed 2, a high-salinity wastewater tank 3, a hardening reaction tank 4, an ultrafiltration filter 5, an ion exchange column 6, a nanofiltration separation facility 7, and a salt treatment tank 8. The inlet of the cation bed 1 is fixedly connected to a hydrochloric acid regeneration pipeline 9, and the inlet of the anion bed 2 is fixedly connected to an alkali regeneration pipeline 10. A first saline wastewater pipeline 11 is fixedly connected between the outlet of the cation bed 1 and the inlet of the high-salinity wastewater tank 3, and a second saline wastewater pipeline 12 is fixedly connected between the outlet of the anion bed 2 and the first saline wastewater pipeline 11. The outlet of the high-salinity wastewater tank 3... A high-salinity wastewater pipeline 13 is fixedly connected between the outlet of the hardening reaction tank 4 and the first inlet of the hardening reaction tank 4. A chemical dosing pipeline 14 is fixedly connected between the second inlet of the hardening reaction tank 4 and the inlet of the ultrafiltration filter 5. A softened brine pipeline 15 is fixedly connected between the outlet of the hardening reaction tank 4 and the inlet of the ultrafiltration filter 5. A first brine pipeline 16 is fixedly connected between the outlet of the ultrafiltration filter 5 and the inlet of the ion exchange column 6. A second brine pipeline 17 is fixedly connected between the outlet of the ion exchange column 6 and the inlet of the nanofiltration separation facility 7. A chlorinated brine pipeline 18 is fixedly connected between the outlet of the nanofiltration separation facility 7 and the inlet of the salt treatment tank 8.

[0037] Unless otherwise specified, all equipment and devices used in this invention are existing and commonly known in the art.

[0038] Example 9: As an optimization of the above embodiment, it also includes a recycling tank 19, a circulating water device 20, a raw water device 23, a first saline wastewater pipeline 11 between the second saline wastewater pipeline 12 and the high-salinity wastewater tank 3 and the inlet of the recycling tank 19, a first reuse pipeline 21 is fixedly connected, a second reuse pipeline 22 is fixedly connected between the first outlet of the recycling tank 19 and the inlet of the circulating water device 20, and a third reuse pipeline 24 is fixedly connected between the second outlet of the recycling tank 19 and the inlet of the raw water device 23.

[0039] As needed, the low-salt wastewater can be recycled and used to replenish the raw water unit 23, which can replace 1% of the fresh raw water each year and reduce production costs.

[0040] Example 10: As an optimization of the above embodiment, a first conductivity meter, a second conductivity meter, and a third conductivity meter are respectively fixedly installed on the first saline wastewater pipeline 11, the high-salt wastewater pipeline 13, and the chlorinated dilute brine pipeline 18 between the second saline wastewater pipeline 12 and the first reuse pipeline 21.

[0041] Depending on the needs, the pipelines and equipment of the saline wastewater treatment device in the ion exchange demineralization process may also be equipped with conventional valves, thermometers and pressure gauges known and commonly used in the field, according to production requirements.

[0042] The saline wastewater used in the following embodiments of the present invention is saline wastewater generated during the demineralization process of a PetroChina petrochemical branch in Xinjiang using the ion exchange method. This demineralization production unit produces approximately 10 million tons of demineralized water annually, with a byproduct of approximately 200,000 tons / year of high-salinity wastewater. The composition of the high-salinity wastewater is: Cl... - 5000mg / L to 11000mg / L, Ca 2+ 1600 mg / L to 2500 mg / L, Mg 2+ : 250mg / L to 350mg / L, SS: 20mg / L to 180mg / L, conductivity: 0.5mS / cm to 35mS / cm; the ion exchange column used is an ion exchange column packed with Suqing D113FC resin; the nanofiltration separation equipment used is Toray NE8040-70 nanofiltration membrane.

[0043] Example 11: 400 tons of high-salinity wastewater were collected and homogenized in a neutralization tank. Analysis of the high-salinity wastewater revealed a conductivity of 22.1 mS / cm and a Ca content of [missing information]. 2+ Mg 2+ The concentrations were 1149 mg / L and 53 mg / L, respectively, with a sodium chloride concentration of 0.68%, accounting for 61.57% of the salts. According to the present invention, the above-mentioned high-salinity wastewater is treated as follows: S1. High-salinity wastewater is pumped into a hardening reaction tank. Sodium hydroxide is added to control the pH at 10.26; sodium carbonate is added to control the excess alkalinity at 0.56 g / L; and 6.0 kg of ferric chloride is added to remove calcium from the high-salinity wastewater. 2+ Mg 2+ HSiO3 2- Plasma is used to obtain softened brine. S2, the softened brine is passed through an ultrafiltration filter and an ion exchange column in sequence to remove hardness and obtain brine. S3. The desalinated water is passed through a nanofiltration membrane at a controlled operating pressure of 0.30 MPa to separate monovalent and divalent ions in the desalinated water, resulting in chlorinated desalinated water with a conductivity of 15.39 mS / cm, no detectable calcium and magnesium ions, a sodium chloride concentration of 0.61%, and a sodium chloride ion ratio of 95.98% in the water. The water recovery rate is 50.6%. S4, the separated sodium chloride-containing brine is sent to a chlor-alkali plant for reuse as brine.

[0044] Example 12: 400 tons of high-salinity wastewater were collected and homogenized in a neutralization tank. Analysis of the high-salinity wastewater revealed a conductivity of 29.2 mS / cm and a Ca content of [missing information]. 2+ Mg 2+ The concentrations were 2705 mg / L and 13 mg / L, respectively, with a sodium chloride concentration of 1.41%, accounting for 58.59% of the total salts. The high-salinity wastewater was treated according to the treatment method described in Example 11. The difference from Example 11 is as follows: In step S1, the pH of the reaction system is controlled at 10.5, the amount of sodium carbonate superalkali is 0.58 g / L, and the amount of ferric chloride solution added is 7.6 kg; in step S3, the nanofiltration working pressure is controlled at 0.32 MPa to obtain chlorinated dilute brine, wherein the conductivity of the chlorinated dilute brine is 25.60 mS / cm, calcium ions + magnesium ions are not detected, the sodium chloride concentration is 1.26%, the proportion of sodium chloride in the brine ions is 98.54%, and the brine recovery rate is 51.30%.

[0045] Example 13: 400 tons of high-salinity wastewater were collected and homogenized in a neutralization tank. Analysis of the high-salinity wastewater revealed a conductivity of 24.0 mS / cm and a Ca content of [missing information]. 2+ Mg 2+ The concentrations were 1818 mg / L and 170 mg / L, respectively, with a sodium chloride concentration of 1.08%, accounting for 71.55% of the salts. The above-mentioned high-salinity wastewater was treated according to the treatment method in Example 11. The difference from Example 11 is as follows: In step S1, the pH of the reaction system is controlled at 11.2, the amount of sodium carbonate superalkali is 0.60 g / L, and the amount of ferric chloride solution added is 6.8 kg; in step S3, the nanofiltration working pressure is controlled at 0.30 MPa to obtain chlorinated dilute brine, wherein the conductivity of the chlorinated dilute brine is 22.300 mS / cm, calcium ions + magnesium ions are not detected, the sodium chloride concentration is 1.01%, the proportion of sodium chloride in the brine is 97.30%, and the brine recovery rate is 49.30%.

[0046] Example 14: 400 tons of high-salinity wastewater were collected and homogenized in a neutralization tank. Analysis of the high-salinity wastewater revealed a conductivity of 26.10 mS / cm and a Ca content of [missing information]. 2+ Mg 2+ The concentrations were 1608 mg / L and 7 mg / L, respectively, with a sodium chloride concentration of 0.77%, accounting for 67.68% of the salts. The above-mentioned high-salinity wastewater was treated according to the treatment method in Example 11. The difference from Example 11 is as follows: In step S1, the pH of the reaction system is controlled at 10.6, the excess sodium carbonate is 0.65 g / L, and the amount of ferric chloride solution added is 7.0 kg; in step S3, the nanofiltration working pressure is controlled at 0.31 MPa to obtain chlorinated dilute brine, wherein the conductivity of the chlorinated dilute brine is 23.60 mS / cm, calcium ions and magnesium ions are not detected, the sodium chloride concentration is 0.77%, accounting for 99.50.6% of the salts, and the brine recovery rate is 52.35%.

[0047] In Examples 11 to 14, the water quality test results of saline wastewater with different conductivity and salt content before and after treatment are shown in Table 1. As can be seen from Table 1, after treatment, calcium ions and magnesium ions were not detected in the brine, and sodium chloride accounted for more than 95% of the ions in the brine. Comparing the amount of chlorinated dilute brine with the total amount of high-salt wastewater, the brine recovery rate can reach 50%.

[0048] In summary, this invention creatively classifies and recycles saline wastewater generated during the ion exchange process for desalination. Low-salt wastewater is used in the raw water unit or recycled in the circulating water unit, reducing the amount of high-salt wastewater to be treated while also reducing the amount of fresh water to be added to the raw water unit. After hardness removal and separation, the high-salt wastewater containing sodium chloride is used in the salting pond for desalination, solving the problem of difficult disposal routes for high-salt wastewater.

[0049] The above technical features constitute various embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A method for treating saline wastewater during ion exchange demineralization, characterized in that... Perform the following steps: The first step is to classify saline wastewater into low-salinity wastewater and high-salinity wastewater according to their conductivity values, and then collect them separately. The second step is to collect the low-salt wastewater and use it to replenish the raw water system or the circulating water system. The third step involves sequentially treating the high-salt wastewater through chemical reactions to remove hardness, filtration to remove hardness, and ion separation to obtain chlorinated dilute brine for reuse.

2. The method for treating saline wastewater during the ion exchange demineralization process according to claim 1, characterized in that... In the first step, the saline wastewater includes: saline wastewater generated by the reaction of hydrochloric acid solution and demineralized water required for the cation exchange bed with the resin in the cation exchange bed, and saline wastewater generated by the reaction of caustic soda solution and demineralized water required for the anion exchange bed with the resin in the anion exchange bed. The conductivity values ​​of the resulting saline wastewater are all between 0.05 mS / cm and 35 mS / cm. Using the conductivity value of the saline wastewater as the recovery condition, the wastewater with a conductivity value higher than 1000 μS / cm is collected separately as high-salt wastewater, and the wastewater with a conductivity value lower than 1000 μS / cm is collected separately as low-salt wastewater.

3. The method for treating saline wastewater during the ion exchange demineralization process according to claim 1 or 2, characterized in that... The third step, the high-salinity wastewater treatment process, includes: S1, chemical reaction is carried out on high-salt wastewater to remove hardness, resulting in softened brine; S2, the softened brine is filtered to remove hardness, and brine is obtained; S3 separates the ions in the brine to obtain chlorinated brine; S4, reuse the chlorinated brine.

4. The method for treating saline wastewater during the ion exchange demineralization process according to claim 3, characterized in that... In step S1, the process of removing hardness from high-salt wastewater specifically includes: adding the required amounts of sodium hydroxide, sodium carbonate, and ferric chloride to the high-salt wastewater in sequence; adding sodium hydroxide to control the pH of the reaction system to be 10.2 to 11.5; adding sodium carbonate to control the excess alkali of the reaction system to be 0.30 g / L to 0.80 g / L; adding 5 g to 50 g of ferric chloride per ton of high-salt wastewater; and obtaining a softened brine with a calcium and magnesium ion content of less than or equal to 3.0 mg / L.

5. The method for treating saline wastewater during the ion exchange desalination process according to claim 3 or 4, characterized in that... In step S2, the process of deep hardening removal of softened brine specifically includes: after the softened brine passes through an ultrafiltration filter and an ion exchange column in sequence, calcium and magnesium ions are deeply removed, and the calcium and magnesium ion content in the resulting brine is less than or equal to 0.02 mg / L.

6. The method for treating saline wastewater during the ion exchange desalination process according to claim 3, 4, or 5, characterized in that... In step S3, the process of separating ions in the brine specifically includes: using nanofiltration to separate monovalent and divalent ions in the brine, with the working pressure during the separation process being 0.25 MPa to 1.00 MPa, the calcium and magnesium ion content in the resulting chlorinated brine being less than or equal to 0.02 mg / L, and sodium chloride accounting for more than 95% of all salts in the chlorinated brine.

7. The method for treating saline wastewater during the ion exchange demineralization process according to claim 3, 4, 5, or 6, characterized in that... In step S4, the process of reusing the sodium chloride-containing brine specifically includes: transporting the chloride-containing brine to the chlor-alkali unit as brine for use in the salt-making process.

8. A saline wastewater treatment device for the ion exchange demineralization process according to any one of claims 1 to 7, characterized in that... The system includes a cation exchange bed, an anion exchange bed, a high-salinity wastewater tank, a hardening reaction tank, an ultrafiltration filter, an ion exchange column, a nanofiltration separation facility, and a salt dissolving tank. The cation exchange bed inlet is fixedly connected to a hydrochloric acid regeneration pipeline, the anion exchange bed inlet is fixedly connected to an alkali regeneration pipeline, the cation exchange bed outlet is fixedly connected to the high-salinity wastewater tank inlet to a first saline wastewater pipeline, the anion exchange bed outlet is fixedly connected to the first saline wastewater pipeline to a second saline wastewater pipeline, the high-salinity wastewater tank outlet is fixedly connected to the first inlet of the hardening reaction tank to a high-salinity wastewater pipeline, the hardening reaction tank second inlet is fixedly connected to a chemical dosing pipeline, the hardening reaction tank outlet is fixedly connected to the ultrafiltration filter inlet to a softened brine pipeline, the ultrafiltration filter outlet is fixedly connected to the ion exchange column inlet to a first brine pipeline, the ion exchange column outlet is fixedly connected to the nanofiltration separation facility inlet to a second brine pipeline, and the nanofiltration separation facility outlet is fixedly connected to the salt dissolving tank inlet to a chlorinated brine pipeline.

9. A saline wastewater treatment device for the ion exchange demineralization process according to claim 8, characterized in that... It also includes a recycling pool, a circulating water device, and a raw water device. A first reuse pipeline is fixedly connected between the first saline wastewater pipeline between the second saline wastewater pipeline and the high-salt wastewater pool and the inlet of the recycling pool. A second reuse pipeline is fixedly connected between the first outlet of the recycling pool and the inlet of the circulating water device. A third reuse pipeline is fixedly connected between the second outlet of the recycling pool and the inlet of the raw water device.

10. A saline wastewater treatment device for the ion exchange demineralization process according to claim 9, characterized in that... A first conductivity meter, a second conductivity meter, and a third conductivity meter are fixedly installed on the first saline wastewater pipeline, the high-salinity wastewater pipeline, and the chlorinated dilute saline water pipeline between the second saline wastewater pipeline and the first reuse pipeline.

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