A method for concentrating and separating organic matter from highly saline wastewater, while simultaneously separating salts by freezing and crystallizing the water.

Abstract

This invention relates to the technologies of waste salt resource utilization and cryocrystallization, and specifically to a method for concentrating and separating organic matter in high-salt wastewater, and simultaneously separating salt by cryocrystallization. This invention can be used to treat salt-containing wastewater containing high concentrations of organic matter, and the wastewater can be pretreated by adding it to a stabilizer in a molten state. Subsequently, the high-salt wastewater aqueous solution containing the stabilizer is cooled and concentrated to obtain an organic concentrate, and after solvent extraction and rectification, a stabilizer solution is obtained, and the organic wastewater is recovered. After low-temperature cryocrystallization of the brine from which organic matter has been removed, ice crystals and concentrate are obtained, and after gradient cryocrystallization, ice crystals and high-purity saturated brine are produced, and after centrifugal drying treatment, pure salt is obtained. The beneficial effects of this method include not only the efficient removal of organic matter from waste salt, but also the simultaneous crystallization of waste salt and separation of salt, as well as the advantages of a simple treatment process, a short treatment cycle, and modularization.

Description

Technical Field

[0001] The present invention relates to the technical fields of waste salt resource utilization and freezing crystallization technology. Specifically, it is a method for concentrating and separating organic substances in high-salt wastewater, and simultaneously performing freezing and crystallization to separate salts.

Background Art

[0002] During the production of various industries such as chemical industry, pharmaceuticals, petroleum, paper making, dairy product processing, and canned food production, a large amount of organic wastewater containing high salts is generated. The COD concentration in the wastewater is 5 g / L or more, the salt content is higher than 1.5%, and many are sodium salts or potassium salts, including sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, etc. When treating organic wastewater or waste liquid containing high salts using ordinary processes, a large amount of complex waste salts containing organic substances are generated, which belong to the category of hazardous waste and thus cannot be effectively utilized. Therefore, it has become an important technical problem that needs to be urgently solved in the industry. The multi-effect evaporation technology can increase the separation efficiency of waste salts in wastewater to a certain extent, but this technology has a high investment cost and is difficult to improve the recovery quality of salts. In recent years, the combination of membrane filtration technology and freezing crystallization technology is considered an effective high-salt wastewater treatment technology. However, this combined process is easily contaminated by organic substances, the operation is complicated, and the requirements for the freezing crystallizer are high, so the separation effect of salts is not ideal. Therefore, in order to solve the above problems, a method for concentrating and separating organic substances in high-salt wastewater, and simultaneously performing freezing and crystallization to separate salts has been developed.

Summary of the Invention

Problems to be Solved by the Invention

[0003] The object of the present invention is to provide a method for concentrating and separating organic substances in high-salt wastewater, and simultaneously performing freezing and crystallization to separate salts in order to solve the problems raised in the above background art.

Means for Solving the Problems

[0004] In order to solve the above technical problems, the present invention provides the following technical solutions.

[0005] A method for concentrating and separating organic matter in highly saline wastewater, and simultaneously separating salt by freezing and crystallizing, Step 1 involves adding organic high-salt wastewater to a heat-melt extraction stabilizer, performing a mixing pretreatment, and obtaining an organic high-salt wastewater pretreatment material. Step 2 involves pumping the organic high-salt wastewater pretreatment material obtained in Step 1 to a low-temperature crystallization tank, stirring it, and obtaining concentrated organic crystals and high-salt water. Step 3 involves thermally melting the organic concentrated crystals obtained in Step 2, purifying the solvent using a method combining back-extraction and rectification processes, and then refluxing the purified solvent to a wastewater pretreatment unit for reuse, while also recovering the organic wastewater. Step 4 involves pumping the highly saline solution obtained in Step 2 into a cryogenic crystallizer to perform primary cryogenic crystallization, obtaining a salt concentrate and primary crystalline salt, and generating pure ice crystals. Step 4 involves pumping the salt concentrate obtained in Step 4 to a cryogenic crystallizer to perform secondary cryogenic crystallization to obtain secondary crystalline salt, and then post-processing the primary and secondary crystalline salts to obtain pure salt in Step 5.

[0006] Furthermore, the organic high-salt wastewater described in Step 1 contains one or both sodium sulfate and potassium sulfate, with a salt content of 1.5% to 10.0% and an initial COD concentration of 0.5 g / L to 4 g / L.

[0007] Furthermore, the extraction stabilizer described in Step 1 is dimethyl sulfoxide, the volume ratio of the extraction stabilizer to the wastewater is 1-5:200-300, and the thermal melting temperature described in Step 1 is 30-60°C.

[0008] Furthermore, the temperature of the low-temperature crystallization tank described in step 2 is 10-25°C, the pump speed described in step 2 is 0.1 L / min-5 L / min, and the stirring speed described in step 2 is 30-50 r / min.

[0009] Furthermore, the thermal melting temperature described in step 3 is 30-60°C, the reagent used for back extraction is N,N-dimethylformamide, and the parameters for the rectification process described in step 3 are a temperature of 80-120°C and a pressure of -0.2-0.1 MPa.

[0010] Furthermore, the low-temperature refrigerated crystallizer described in step 4 uses an OSLO horizontal continuous refrigerated crystallizer, with the parameters being an external cooler length of 80.0 cm to 150.00 cm and a diameter of 10.00 cm to 35.00 cm, and the pump speed described in step 4 being 0.1 L / min to 5 L / min, with the material being driven by an axial flow circulation pump.

[0011] Furthermore, the primary low-temperature freezing crystallization is carried out in a three-stage gradient. Specifically, in the first stage, the temperature is reduced to 10-20°C at a rate of 5-10°C / min; in the second stage, the temperature is reduced to -5-10°C at a rate of 10-20°C / min; and in the third stage, the temperature is reduced to -15--5°C at a rate of 2.0-5.0°C / min.

[0012] Furthermore, the secondary cryogenic crystallization process described in Step 5 is the same as the primary cryogenic crystallization process.

[0013] Furthermore, the post-processing step described in step 5 involves centrifuging the primary and secondary crystalline salts at low temperature, washing them with alcohol, and then performing vacuum low-temperature drying. The parameters for the low-temperature centrifugation are a temperature of 0-5°C and a centrifugal rotation speed of 500-3000 r / min, with methanol or ethanol being used for the alcohol washing. The parameters for the vacuum low-temperature drying are a temperature of -20-10°C, a vacuum level of 20-100 Pa, and a drying time of 2-6 hours.

[0014] Based on the low-temperature recrystallization characteristics of DMSO and DMF, this invention enables the concentration and separation of organic matter in highly saline wastewater under low-temperature cooling conditions by adding an extraction stabilizer to the wastewater. The extraction stabilizer is purified through back-extraction and rectification processes and can be recycled for wastewater pretreatment. The collected highly saline water undergoes gradient freezing crystallization in an OSLO horizontal continuous cooling crystallizer to remove residual stabilizers and produce salt concentrate and crystalline salt, while simultaneously discharging clean ice crystals (water). Finally, the salt concentrate is subjected to secondary freeze crystallization and centrifugal drying to obtain high-purity salt. [Effects of the Invention]

[0015] (1) The present invention innovatively selects DMSO as the solvent to wash and extract organic matter from high-salt organic wastewater, effectively stabilizing the organic matter in the DMSO medium. After cooling and crystallization, it achieves highly efficient concentration of organic matter in the wastewater. This process has high efficiency in removing organic matter from wastewater, is easy to operate, and facilitates modularization.

[0016] (2) In the method of the present invention, the extraction stabilizer DMSO is separated and recycled after DMF back-extraction and rectification, and this process has high efficiency in removing organic matter and can save costs.

[0017] (3) In the method described in the present invention, highly saline water can be subjected to a two-stage gradient freezing crystallization process in an OSLO horizontal continuous cooling crystallizer to obtain ice crystals (water), crystalline salt, and salt concentrate, respectively. This process has high wastewater treatment efficiency, low energy consumption, and high cold utilization rate.

[0018] (4) In the method described in the present invention, alcohol washing and drying of the crystalline salt using methanol or ethanol can be performed to increase the purity of the crystalline salt, and the dehydration efficiency is good, resulting in a high purity of salt obtained after drying. The purity of sodium sulfate is >80%, and the purity of potassium sulfate is >85%. [Brief explanation of the drawing]

[0019] The attached drawings are for further understanding of the present invention, form part of the specification, and are for explaining the present invention together with the embodiments of the present invention, and do not constitute a limitation to the present invention.

[0020] [Figure 1] This is the process flow of the present invention.

Embodiments for Carrying out the Invention

[0021] Hereinafter, in accordance with the drawings in the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Of course, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative labor belong to the protection scope of the present invention.

Examples

[0022] Example 1 In the method of concentrating and separating organic substances in high-salt wastewater and simultaneously performing freezing and crystallization for salt separation, the initial content of each component of the high-salt wastewater is as shown in Table 1. This method includes Step 1: Wastewater with a COD content of 0.5 g / L and a sodium sulfate content reaching 1.5% is introduced into DMSO at 30°C, and a volume ratio of 1:200 is used for pre-mixing treatment, and uniformly stirred. Step 2: The pretreated organic wastewater is pumped into a low-temperature crystallization tank at 25°C at a pump speed of 0.1 L / min, and the concentration crystallization of organic substances is realized under stirring conditions of 30 r / min, and the wastewater containing sodium sulfate is separated and collected. Step 3: After the organic concentrated crystals obtained by collection in Step 2 are thermally melted at 30°C, DMSO is back-extracted using DMF, and then, using a rectification process, under a rectification pressure of 80°C and -0.2 MPa, purification separation for DMSO is realized, the purified solvent is refluxed to the wastewater pretreatment unit for reuse, and finally the remaining organic waste liquid is recovered. The wastewater containing sodium sulfate obtained in Step 2 is pumped into an OSLO horizontal continuous cooling crystallizer at a pump speed of 5 L / min. The length of the cooler is 80 cm and the diameter is 10 cm. The remaining DMSO is removed using a three-stage gradient temperature reduction. The temperature reduction rate in the first stage is 5 °C / min, and the temperature is reduced to 10 °C. The temperature reduction rate in the second stage is 10 °C / min, and the temperature is reduced to -5 °C. The temperature reduction rate in the third stage is 2.0 °C / min, and the temperature is reduced to -15 °C. Step 4 of obtaining a sodium sulfate concentrate and sodium sulfate crystal salt and generating pure ice crystals (water), The concentrate obtained in Step 4 is pumped into a low-temperature freezing crystallizer for secondary low-temperature freezing crystallization. All sodium sulfate crystal salts are centrifuged at low temperature. After washing the sodium sulfate crystal salts with ethanol, they are dried at -20 °C under vacuum. After drying for 2 h with a vacuum degree of 20 Pa, Step 5 of obtaining pure sodium sulfate salt is provided.

[0023] Example 2 In the method of concentrating and separating organic substances in high-salt wastewater and simultaneously performing freezing and crystallization to separate salts, the initial content of each component of the high-salt wastewater is as shown in Table 1. This method includes, Step 1: Wastewater with a COD content of 1.5 g / L and a sodium sulfate content reaching 5% is put into DMSO at 30 °C, and a volume ratio of 1:300 is used for pretreatment before mixing and stirring evenly. Step 2: The pretreated organic wastewater is pumped into a low-temperature crystallization tank at 10 °C at a pump speed of 5 L / min, and the concentrated crystallization of organic substances is realized under stirring conditions of 50 r / min. The wastewater containing sodium sulfate is separated and collected. Step 3: After the organic concentrated crystals obtained in Step 2 are melted by heat at 60 °C, DMSO is back-extracted using DMF, and then, using a rectification process, under a rectification pressure of 120 °C and -0.2 MPa, the purification and separation of DMSO are realized. The purified solvent is refluxed to the wastewater pretreatment unit for reuse, and finally, the remaining organic waste liquid is recovered. Step 4 involves pumping the wastewater containing sodium sulfate collected in Step 2 to an OSLO horizontal continuous cooling crystallizer at a pump speed of 0.1 L / min. The cooler is 150 cm long and 10 cm in diameter. A three-stage gradient cooling is used to remove residual DMSO. The first stage cooling rate is 20°C / min, lowering the temperature to 10°C. The second stage cooling rate is 10°C / min, lowering the temperature to -5°C. The third stage cooling rate is 2.0°C / min, lowering the temperature to -15°C. Step 4 involves preparing a sodium sulfate concentrate and sodium sulfate crystalline salt to produce pure ice crystals (water). Step 5 involves pumping the concentrated liquid collected in Step 4 to a cryogenic crystallizer for secondary cryogenic crystallization, centrifuging all the sodium sulfate crystalline salts at low temperatures, washing the sodium sulfate crystalline salts with ethanol, and then vacuum-drying them at -20°C for 2 hours at a vacuum of 100 Pa to obtain pure sodium sulfate.

[0024] Example 3 In a method that concentrates and separates organic matter from high-salt wastewater, and simultaneously separates salt by freezing and crystallizing, the initial content of each component in the high-salt wastewater is as shown in Table 1. This method has the following properties: Step 1 involves adding wastewater containing 4.0 g / L of COD, 5% sodium sulfate, and 2.5% potassium sulfate to DMSO at 40°C, performing a pre-treatment by mixing in a volume ratio of 1:100, and then uniformly stirring. Step 2 involves pumping the pre-treated organic wastewater at a pump speed of 0.5 L / min to a 10°C low-temperature crystallization tank, achieving concentrated crystallization of organic matter under stirring conditions of 30 r / min, and separating and collecting wastewater containing sodium sulfate. Step 3 involves thermally melting the organic concentrated crystals collected in Step 2 at 40°C, back-extracting DMSO using DMF, and then achieving purification and separation of DMSO using a rectification process at 80°C and a rectification pressure of -0.1 MPa. The purified solvent is refluxed to a wastewater pretreatment unit for reuse, and finally the remaining organic waste liquid is recovered. Step 2 involves pumping wastewater containing potassium sulfate and sodium sulfate collected in Step 2 to an OSLO horizontal continuous cooling crystallizer at a pump speed of 0.5 L / min. The cooler is 80 cm long and 20 cm in diameter. A three-stage gradient cooling is used to remove residual DMSO. The first stage cooling rate is 10°C / min, lowering the temperature to 15°C. The second stage cooling rate is 10°C / min, lowering the temperature to 0°C. The third stage cooling rate is 5.0°C / min, lowering the temperature to -5°C. Step 4 involves preparing potassium sulfate and sodium sulfate concentrates and potassium sulfate and sodium sulfate crystalline salts to produce pure ice crystals (water). Step 5 involves pumping the concentrated liquid collected in Step 4 to a cryogenic crystalline apparatus for secondary cryogenic crystallization, centrifuging all potassium sulfate and sodium sulfate crystalline salts at low temperatures, washing the crystalline salts with ethanol, and then vacuum-drying them at -20°C for 2 hours at a vacuum of 60 Pa to obtain pure potassium sulfate and sodium sulfate salts.

[0025] Without adding the extraction stabilizer DMSO, and without performing back-extraction, the other conditions were the same as in Example 3, specifically, Step 1 involves pre-treating wastewater to a COD content of 4.0 g / L, sodium sulfate content of 5%, and potassium sulfate content of 2.5%. Step 2 involves pumping the pre-treated organic wastewater at a pump speed of 0.5 L / min to a 10°C low-temperature crystallization tank, achieving concentrated crystallization of organic matter under stirring conditions of 30 r / min, and separating and collecting the wastewater containing sodium sulfate and potassium sulfate. Step 3 involves preparing potassium sulfate and sodium sulfate concentrates and potassium sulfate and sodium sulfate crystalline salts to produce pure ice crystals (water). Step 4 involves pumping the concentrated liquid collected in Step 3 to a cryogenic crystallizer for secondary cryogenic crystallization, centrifuging all potassium sulfate and sodium sulfate crystalline salts at low temperatures, washing the crystalline salts with ethanol, and then vacuum-drying them at -20°C for 2 hours at a vacuum of 60 Pa to obtain pure potassium sulfate and sodium sulfate salts.

[0026] Comparative Example 2 Instead of using low-temperature cryogenic crystals, evaporation and concentration were performed using a triple-effect evaporator, followed by brine separation. Other conditions were the same as in Example 3, specifically, Step 1 involves adding wastewater containing 4.0 g / L of COD, 5% sodium sulfate, and 2.5% potassium sulfate to DMSO at 40°C, performing a pre-treatment by mixing in a volume ratio of 1:100, and then uniformly stirring. Step 2 involves pumping the pre-treated organic wastewater at a pump speed of 0.5 L / min to a 10°C low-temperature crystallization tank, achieving concentrated crystallization of organic matter under stirring conditions of 30 r / min, and separating and collecting the wastewater containing sodium sulfate and potassium sulfate. Step 3 involves thermally melting the organic concentrated crystals collected in Step 2 at 40°C, back-extracting DMSO using DMF, and then using a rectification process to achieve purification and separation of DMSO at 80°C and a rectification pressure of -0.1 MPa. The purified solvent is refluxed to a wastewater pretreatment unit for reuse, and finally the remaining organic waste liquid is recovered. Step 2 involves evaporating the wastewater containing potassium sulfate and sodium sulfate collected in Step 2 at a temperature of 120°C using a triple evaporator to obtain the first steam and wastewater concentrate, with an evaporation time of 5 hours. Subsequently, the wastewater concentrate is evaporated at 160°C to obtain the second steam and excess liquid I, with a total evaporation time of 5 hours. Excess liquid I is evaporated at 260°C to obtain the third steam and excess liquid II, with a total evaporation time of 3 hours. Step 4 involves obtaining potassium sulfate and sodium sulfate concentrates at a total pressure of 9 MPa during the evaporation step in the triple evaporator, followed by brine separation to obtain potassium sulfate and sodium sulfate crystalline salts, which are then washed with ethanol and subjected to vacuum low-temperature drying at -20°C at a vacuum of 60 Pa for 2 hours to obtain potassium sulfate and sodium sulfate pure salts.

[0027] [Table 1]

[0028] Measurement: The purity and COD concentration ratio of the pure salts obtained in the examples and comparative examples were calculated, and the following data was obtained.

[0029] [Table 2]

[0030] Conclusion: The methods in Examples 1-3 can achieve highly efficient concentration of organic matter of 80% or more, and the purity of the waste salt can reach 80% or more in all cases. Comparative Example 1 has lower performance compared to Example 3 because it does not contain the extraction stabilizer DMSO. Comparative Example 2 uses a multi-effect evaporator for evaporation concentration treatment instead of low-temperature cryogenic crystals, followed by brine separation, making the operation more complex compared to Example 3, resulting in lower organic matter concentration and crystalline salt purity. Therefore, the methods of the present invention not only satisfy the need for concentrated collection of organic matter in wastewater, but can also simultaneously achieve separation and purification of salts in wastewater. Furthermore, these methods have high wastewater treatment efficiency, low energy consumption, and high cold utilization rate.

[0031] In this specification, relational terms such as "first" and "second" are used solely to distinguish one entity or operation from another, without necessarily requiring or implying that such an actual relationship or order exists between these entities or operations. Furthermore, the term "including," or any other variant thereof, is intended to cover non-exclusive inclusion, so that a process, method, article, or apparatus containing a set of elements may include not only those elements but also other elements not explicitly listed, or even inherent elements of such a process, method, article, or apparatus.

[0032] Finally, although the above is merely a preferred embodiment of the present invention and is not intended to limit the invention, those skilled in the art can modify the technical aspects described in each of the above embodiments or substitute some of the technical features with equivalents, even though the invention has been described in detail with reference to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made in the spirit and principles of the invention should all be within the scope of protection of the invention.

Claims

1. Step 1 involves adding organic high-salt wastewater to a heat-melt extraction stabilizer, performing a mixing pretreatment, and obtaining an organic high-salt wastewater pretreatment material. Step 2 involves pumping the organic high-salt wastewater pretreatment material obtained in Step 1 to a low-temperature crystallization tank, stirring it, and obtaining concentrated organic crystals and high-salt water. Step 3 involves thermally melting the organic concentrated crystals obtained in Step 2, purifying the solvent using a method combining back-extraction and rectification processes, and then refluxing the purified solvent to a wastewater pretreatment unit for reuse, while also recovering the organic wastewater. Step 4 involves pumping the highly saline solution obtained in Step 2 to a cryogenic crystallizer to perform primary cryogenic crystallization, obtaining a salt concentrate and primary crystalline salt, and generating pure ice crystals. The primary cryogenic crystallization is performed in three stages with a gradient, specifically in Step 4: the first stage is cooled to 10-20°C at a rate of 5-10°C / min, the second stage is cooled to -5-10°C at a rate of 10-20°C / min, and the third stage is cooled to -15--5°C at a rate of 2.0-5.0°C / min. Step 4 involves pumping the salt concentrate obtained in step 4 to a cryogenic crystallizer to perform secondary cryogenic crystallization to obtain secondary crystalline salt, and then post-processing the primary and secondary crystalline salts to obtain pure salt. A method for concentrating and separating organic matter in highly saline wastewater, while simultaneously performing freezing and crystallization to separate the salts.

2. The organic high-salt wastewater described in Step 1 contains one or both sodium sulfate and potassium sulfate, with a salt content of 1.5% to 10.0% and an initial COD concentration of 0.5 g / L to 4 g / L. A method for concentrating and separating organic matter in highly saline wastewater according to feature 1, and simultaneously separating salt by freezing and crystallizing.

3. The extraction stabilizer described in Step 1 is dimethyl sulfoxide, the volume ratio of the extraction stabilizer to the wastewater is 1 to 5:200 to 300, and the thermal melting temperature described in Step 1 is 30 to 60°C. A method for concentrating and separating organic matter in highly saline wastewater according to feature 1, and simultaneously separating salt by freezing and crystallizing.

4. The temperature of the low-temperature crystallization tank described in step 2 is 10 to 25°C, the pump speed described in step 2 is 0.1 L / min to 5 L / min, and the stirring speed described in step 2 is 30 to 50 r / min. A method for concentrating and separating organic matter in highly saline wastewater according to feature 1, and simultaneously separating salt by freezing and crystallizing.

5. The thermal melting temperature described in step 3 is 30 to 60°C, the reagent used for back extraction is N,N-dimethylformamide, and the parameters for the rectification process described in step 3 are a temperature of 80 to 120°C and a pressure of -0.2 to -0.1 MPa. A method for concentrating and separating organic matter in highly saline wastewater according to feature 1, and simultaneously separating salt by freezing and crystallizing.

6. The low-temperature refrigerated crystallizer described in step 4 uses an OSLO horizontal continuous refrigerated crystallizer, with the parameters being an external cooler length of 80.0 cm to 150.00 cm and a diameter of 10.00 cm to 35.00 cm, and the pump speed described in step 4 being 0.1 L / min to 5 L / min, with the material being driven by an axial flow circulation pump. A method for concentrating and separating organic matter in highly saline wastewater according to feature 1, and simultaneously separating salt by freezing and crystallizing.

7. The secondary cryogenic crystallization process described in Step 5 is the same as the primary cryogenic crystallization process. A method for concentrating and separating organic matter in highly saline wastewater according to feature 1, and simultaneously separating salt by freezing and crystallizing.

8. The post-processing step described in step 5 involves centrifuging the primary and secondary crystalline salts at low temperature, washing them with alcohol, and then performing vacuum low-temperature drying. The parameters for the low-temperature centrifugation are a temperature of 0 to 5°C and a centrifugal rotation speed of 500 to 3000 r / min, with methanol or ethanol being used for the alcohol washing. The parameters for the vacuum low-temperature drying are a temperature of -20 to 10°C, a vacuum level of 20 to 100 Pa, and a drying time of 2 to 6 hours. A method for concentrating and separating organic matter in highly saline wastewater according to feature 1, and simultaneously separating salt by freezing and crystallizing.

Images