MVR (Mechanical Vapor Recompression) treatment system and method for high-salinity wastewater containing sodium acetate and sodium chloride

Abstract

The invention relates to an MVR treatment system and method for high-salinity wastewater containing sodium acetate and sodium chloride, and belongs to the technical field of high-salinity wastewater treatment.The MVR treatment method comprises the following preparation steps that S1, an MVR evaporation stage is conducted, specifically, the high-salinity wastewater is added into an MVR evaporator to be evaporated, and evaporated liquor is obtained; s2, a first devitrification and leaching stage: cooling and devitrifying the evaporated liquor to obtain a first mother liquor and a first crystal, filtering and leaching the precipitated first crystal to obtain sodium chloride, and conveying the filtered and leached first leacheate into an MVR (mechanical vapor recompression) evaporator; s3, a second crystallization and leaching stage: adding water into the first mother liquor for dilution, cooling and crystallizing to obtain a second crystal and a second mother liquor, filtering and leaching the separated second crystal to obtain sodium acetate trihydrate, and conveying the second mother liquor and a second leacheate after filtering and leaching into the MVR evaporator. The method realizes continuous independent separation of sodium acetate and sodium chloride, reduces discharge of waste mother liquor, and accords with the idea of energy conservation and carbon reduction in the industry.

Description

Technical Field

[0001] The invention relates to the technical field of high-salt wastewater treatment, and in particular to an MVR treatment system and method for high-salt wastewater containing sodium acetate and sodium chloride. Background Art

[0002] In the process of industrial high-salinity wastewater treatment, evaporation and salt separation technology is an effective resource recovery method, which uses heat energy to evaporate the water in the solution and leave the salt. Evaporation and salt separation technology is widely used in chemical industry, metallurgy, environmental protection and other fields.

[0003] At present, sodium acetate and sodium chloride in high-salinity wastewater are usually separated by evaporation salt separation technology. However, the inventor believes that the evaporation salt separation technology usually has the following problems: 1. Evaporation and salt separation technology generally adopts batch production, and the process is discontinuous; 2. A large amount of mother liquor is produced, which increases the subsequent processing cost; 3. In the precipitation stage of sodium acetate trihydrate, it is usually precipitated in the form of mixed salts, thus requiring an additional purification step.

[0004] In response to the above-mentioned technical phenomenon, the inventors proposed a system and method for treating high-salinity wastewater based on MVR technology. Summary of the invention

[0005] The object of the present invention is to provide an MVR treatment system and method for high-salt wastewater containing sodium acetate and sodium chloride, which realizes the continuous and separate separation of the two salts of sodium acetate and sodium chloride, reduces the discharge of waste mother liquor, and conforms to the concept of energy saving and carbon reduction in this industry.

[0006] The present invention provides an MVR treatment method for high-salt wastewater containing sodium acetate and sodium chloride, which adopts the following technical scheme: A MVR treatment method for high-salt wastewater containing sodium acetate and sodium chloride comprises the following steps: S1, MVR evaporation stage: provide an MVR evaporator, add high-salt wastewater into the MVR evaporator for evaporation, and obtain evaporation liquid; S2, first crystallization and elution stage: cooling and crystallizing the evaporated liquid obtained in step S1 to obtain a first mother liquor and a first crystal, filtering and eluting the precipitated first crystal to obtain sodium chloride, and conveying the filtered and eluted first elution liquid to an MVR evaporator; S3, second crystallization and elution stage: dilute the first mother liquor in step S2 with water and cool it down for crystallization to obtain second crystals and a second mother liquor, filter and rinse the precipitated second crystals to obtain sodium acetate trihydrate, and transport the second mother liquor and the second elution liquid after filtration and elution to the MVR evaporator.

[0007] Preferably, a heat exchanger is provided, and the condensed water produced by the MVR evaporator in step S1 is heat-exchanged with the high-salt wastewater through the heat exchanger.

[0008] Preferably, the mass percentage of sodium chloride in the high-salt wastewater in step S1 is 9-11%; The mass percentage of sodium acetate in the high-salt wastewater in step S1 is 7-9%.

[0009] Preferably, the evaporation temperature of the MVR evaporator in step S1 is set to 90-100°C.

[0010] Preferably, the crystallization temperature in the first crystallization and elution stage in step S2 is 68-72°C; The crystallization time of the first crystallization and elution stage in step S2 is 2-4 hours; The filtration and elution temperature of the first crystallization and elution stage in step S2 is 48-52°C; The amount of rinsing water used in the first crystallization rinsing stage in step S2 is 30 kg / h.

[0011] Preferably, the suspension density of the crystals in step S2 is 300-350 kg / m 3 .

[0012] Preferably, the amount of water added to dilute the first mother liquor in the second crystallization and elution stage in step S3 is 16.3 kg / 100 kg of mother liquor.

[0013] Preferably, the crystallization temperature in the second crystallization and elution stage in step S3 is 3-7°C; The crystallization time of the second crystallization and elution stage in step S3 is 2-4h; The suspension density of the crystals in step S3 is 300-350 kg / m 3 ; The filtering and eluting temperature of the second crystallization and eluting stage in step S3 is 3-7°C.

[0014] The present invention also provides an MVR treatment system for high-salt wastewater containing sodium acetate and sodium chloride, which is applied to the MVR treatment method for high-salt wastewater containing sodium acetate and sodium chloride according to any one of claims 1 to 8, wherein the MVR treatment system comprises a compressor, an MVR evaporator, a first crystallizer, a first centrifuge, a second crystallizer, and a second centrifuge; The compressor is used to heat the material in the MVR evaporator; The first crystallizer is used to cool and crystallize the material processed by the MVR evaporator; The first centrifuge is used to filter, rinse and separate the crystal suspension from the first crystallizer; The second crystallizer is used to receive the first mother liquor separated by the first centrifuge and crystallize the first mother liquor; The second centrifuge is used to filter, rinse and separate the crystal suspension of the second crystallizer.

[0015] Preferably, the eluent from the first centrifuge is transported to an MVR evaporator; The eluent and the second mother liquor of the second centrifuge are transported to the MVR evaporator.

[0016] In summary, the present invention includes the following beneficial technical effects: 1. The present application adopts an MVR evaporator, which basically does not consume raw steam and reduces energy consumption. The evaporating liquid of the MVR evaporator is transmitted to the first crystallization and elution stage to cool the evaporating liquid and crystallize it to obtain a first crystal and a first mother liquor. The first crystal is filtered and eluted to obtain sodium chloride, and the elution liquid therein is transported to the MVR evaporator for cyclic evaporation to reduce the generation of waste liquid. The first mother liquor is transported to the second crystallization and elution stage to cool the first mother liquor and crystallize it to obtain a second crystal and a second mother liquor. The second crystal is filtered and eluted to obtain sodium acetate trihydrate. The elution liquid and the second mother liquor are transported to the MVR evaporator for cyclic evaporation to reduce the generation of waste liquid, and the process realizes continuous production.

[0017] 2. The present application avoids the precipitation of sodium chloride by diluting the first mother liquor, thereby ensuring that sodium acetate trihydrate is precipitated alone.

[0018] 3. The purity of the precipitated sodium chloride in the present application is greater than 98.5%, and the yield is greater than 95%. The purity of the precipitated sodium acetate trihydrate is greater than 98%, and the yield is greater than 95%. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The present invention is a flowchart of a specific implementation of an MVR treatment system for high-salt wastewater containing sodium acetate and sodium chloride.

[0020] Figure numerals: 1, MVR evaporator; 2, first crystallizer; 3, first centrifuge; 4, second crystallizer; 5, second centrifuge. DETAILED DESCRIPTION

[0021] The following is combined with Figure 1 The present invention is further described in detail with reference to the accompanying drawings and embodiments.

[0022] Reference Figure 1 The embodiment of the present invention provides an MVR treatment method for high-salt wastewater containing sodium acetate and sodium chloride, comprising the following steps: 1) MVR evaporation stage: provide an MVR evaporator, add high-salt wastewater with a mass percentage of 9-11% sodium chloride and 7-9% sodium acetate into the MVR evaporator for evaporation, set the evaporation temperature of the MVR evaporator to 90-100°C, the processing time to 1h, and obtain evaporated liquid; 2) First crystallization and elution stage: The evaporated liquid obtained in step 1) is cooled and crystallized, the crystallization temperature is set to 68-72°C, the crystallization time is 2-4h, and the first mother liquor and the first crystal are obtained, and the suspension density of the first crystal is ensured to be 300-350kg / m 3 , filter and rinse the first precipitated crystals, use 30 kg / h of rinsing water, maintain the filtration and rinsing temperature at 48-52°C, obtain sodium chloride, and transport the first rinsing liquid after filtration and rinsing to the MVR evaporator; 3) Second crystallization and elution stage: dilute the first mother liquor in step 2) with water and cool it down for crystallization, wherein the amount of water added to dilute the first mother liquor is 16.3 kg / 100 kg mother liquor, the crystallization temperature is 3-7 ° C, the crystallization time is 2-4 hours, and the suspension density is 300-350 kg / m 3 The precipitated second crystals are filtered and washed, and the filtering and washing temperature is maintained at 3-7° C. to obtain sodium acetate trihydrate. The second mother liquor and the second washing liquid after filtering and washing are transported to the MVR evaporator.

[0023] In step 1), a heat exchanger is also provided, and the condensed water produced by the MVR evaporator is heat-exchanged with the high-salt wastewater through the heat exchanger, so that the high-salt wastewater enters the MVR evaporator after being heated. The feed rate of the MVR evaporator is set to 3t / h, and the high-salt wastewater is fed at the boiling point, and the evaporation rate of the MVR evaporator is 2.453t / h.

[0024] In step 2), the crystallization temperature of the first crystallization and elution stage in this embodiment is optimally set to 70°C, so that sodium chloride can be precipitated to the maximum extent. The crystallization time is 2-4 hours, which provides sufficient time for the growth of the first crystal. The obtained first crystal is larger in volume and easier to filter. The suspension density of the first crystal is maintained at 300-350 kg / m 3 , providing a larger surface area for the crystallization process, which is beneficial to the growth of the first crystal. The suspension density is controlled by using a density meter to measure, and the discharge amount and overflow amount are adjusted to control the slurry content and the suspension density.

[0025] In step 3), by diluting the first mother liquor with water, the precipitation of sodium chloride is avoided, the separate precipitation of sodium acetate trihydrate is ensured, and the additional purification step of sodium acetate trihydrate is avoided. In this embodiment, the crystallization temperature of the first crystallization and elution stage is optimally set to 5°C. The lower temperature ensures that more sodium acetate is crystallized in a single time, and reduces the mother liquor circulation volume, and reduces the energy consumption caused by the temperature changes caused by the mother liquor circulation. The crystallization time is 2-4h, which provides sufficient time for the growth of the first crystal. The obtained first crystal is larger in volume and easy to filter.

[0026] Reference Figure 1 , an embodiment of the present invention further provides an MVR treatment system for high-salt wastewater containing sodium acetate and sodium chloride, comprising a compressor, an MVR evaporator, a first crystallizer, a first centrifuge, a second crystallizer and a second centrifuge; The compressor is used to heat the material in the MVR evaporator, the first crystallizer is used to cool and crystallize the material processed by the MVR evaporator, the first centrifuge is used to filter, rinse and separate the crystal suspension of the first crystallizer, the second crystallizer is used to receive the first mother liquor separated by the first centrifuge and crystallize the first mother liquor, and the second centrifuge is used to filter, rinse and separate the crystal suspension of the second crystallizer.

[0027] Reference Figure 1 In this embodiment, the first crystallizer and the second crystallizer are preferably externally cooled Oslo cooling crystallizers, and the heat of the feed liquid is replaced by low-temperature chilled water. The crystal liquid flows out through the overflow port at the upper end of the crystallizer to exchange heat with the chilled water. The temperature of the crystallizer is controlled by controlling the feed amount of chilled water.

[0028] Reference Figure 1 In this embodiment, the first centrifuge and the second centrifuge are vertical scraper bottom discharge centrifuges, in which the sodium chloride slurry in the first crystallizer enters the first centrifuge, is spread and dried, and then rinsed with clean water. The rinsing water consumption is 30kg / h, and a flow meter is used to control the rinsing amount. The rinsing water is returned to the MVR evaporator through the filtrate outlet of the first centrifuge through a circulation pump to continue evaporating and salting. Sodium chloride is weighed and packaged by an automatic packaging machine. Sodium chloride discharge is 0.3t / h, with a purity of 98.5% and a yield of 99%; The sodium acetate trihydrate slurry in the second crystallizer is centrifugally filtered using a vertical scraper bottom discharge centrifuge. The sodium acetate trihydrate suspension is discharged into the centrifuge through the centrifuge inlet, and then transported to the sodium acetate trihydrate packaging machine after being spread and dried. The sodium acetate trihydrate output is 0.39t / h, with a purity of ≥98.5% and a yield of ≥98%.

[0029] The above are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A MVR treatment method for high-salt wastewater containing sodium acetate and sodium chloride, characterized in that: The following steps are involved: S1, MVR evaporation stage: provide an MVR evaporator, add high-salt wastewater into the MVR evaporator for evaporation, and obtain evaporation liquid; S2, first crystallization and elution stage: cooling and crystallizing the evaporated liquid obtained in step S1 to obtain a first mother liquor and a first crystal, filtering and eluting the precipitated first crystal to obtain sodium chloride, and conveying the filtered and eluted first elution liquid to an MVR evaporator; S3, second crystallization and elution stage: dilute the first mother liquor in step S2 with water and cool it down for crystallization to obtain second crystals and a second mother liquor, filter and rinse the precipitated second crystals to obtain sodium acetate trihydrate, and transport the second mother liquor and the second elution liquid after filtration and elution to the MVR evaporator.

2. The MVR treatment method for high-salt wastewater containing sodium acetate and sodium chloride according to claim 1, characterized in that: A heat exchanger is provided, and the condensed water produced by the MVR evaporator in step S1 is heat exchanged with the high-salt wastewater through the heat exchanger.

3. The MVR treatment method for high-salt wastewater containing sodium acetate and sodium chloride according to claim 1, characterized in that: The mass percentage of sodium chloride in the high-salt wastewater in step S1 is 9-11%; The mass percentage of sodium acetate in the high-salt wastewater in step S1 is 7-9%.

4. The MVR treatment method for high-salt wastewater containing sodium acetate and sodium chloride according to claim 1, characterized in that: In step S1, the evaporation temperature of the MVR evaporator is set to 90-100° C., and the processing time is 1 hour.

5. The MVR treatment method for high-salt wastewater containing sodium acetate and sodium chloride according to claim 3, characterized in that: The crystallization temperature of the first crystallization and elution stage in step S2 is 68-72°C; The crystallization time of the first crystallization and elution stage in step S2 is 2-4 hours; The filtration and elution temperature of the first crystallization and elution stage in step S2 is 48-52°C; The amount of rinsing water used in the first crystallization rinsing stage in step S2 is 30 kg / h.

6. The MVR treatment method for high-salt wastewater containing sodium acetate and sodium chloride according to claim 3, characterized in that: The suspension density of the crystals in step S2 is 300-350 kg / m 3 .

7. The MVR treatment method for high-salt wastewater containing sodium acetate and sodium chloride according to claim 1, characterized in that: The amount of water added to dilute the first mother liquor in the second crystallization and elution stage in step S3 is 16.3 kg / 100 kg of mother liquor.

8. The MVR treatment method for high-salt wastewater containing sodium acetate and sodium chloride according to claim 3, characterized in that: The crystallization temperature of the second crystallization and elution stage in step S3 is 3-7°C; The crystallization time of the second crystallization and elution stage in step S3 is 2-4h; The suspension density of the crystals in step S3 is 300-350 kg / m 3 ; The filtering and eluting temperature of the second crystallization and eluting stage in step S3 is 3-7°C.

9. An MVR treatment system for high-salinity wastewater containing sodium acetate and sodium chloride, applied to the MVR treatment method for high-salinity wastewater containing sodium acetate and sodium chloride according to any one of claims 1 to 8, characterized in that: The MVR processing system includes a compressor, an MVR evaporator, a first crystallizer, a first centrifuge, a second crystallizer, and a second centrifuge; The compressor is used to heat the material in the MVR evaporator; The first crystallizer is used to cool and crystallize the material processed by the MVR evaporator; The first centrifuge is used to filter, rinse and separate the crystal suspension from the first crystallizer; The second crystallizer is used to receive the first mother liquor separated by the first centrifuge and crystallize the first mother liquor; The second centrifuge is used to filter, rinse and separate the crystal suspension of the second crystallizer.

10. An MVR treatment system for high-salinity wastewater containing sodium acetate and sodium chloride, characterized in that: The eluent from the first centrifuge is transported to the MVR evaporator; The eluent and the second mother liquor of the second centrifuge are transported to the MVR evaporator.

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