Method for treating high-concentration salt wastewater

Abstract

The application discloses a high-concentration salt wastewater treatment method, which comprises the following steps: S1, high-concentration salt wastewater is subjected to at least twice of flash evaporation to obtain a high-saturation low-temperature mother liquor; S2, the high-saturation low-temperature mother liquor is frozen to precipitate sodium sulfate decahydrate crystals to form a crystal slurry; S3, the sodium sulfate decahydrate crystals and the frozen clear liquid in the crystal slurry are separated; S4, the sodium sulfate decahydrate crystals are heated to form a sodium sulfate decahydrate slurry; and S5, the sodium sulfate decahydrate slurry is subjected to centrifugation to separate sodium sulfate decahydrate and a centrifugal mother liquor. The high-concentration salt wastewater is subjected to at least twice of flash evaporation, so that the temperature of the high-concentration salt wastewater is gradually reduced, and the concentration is gradually increased, the temperature of the first-stage flash evaporation is ensured to be 23 DEG C to 26 DEG C, and the pretreatment energy consumption of the high-concentration salt wastewater is reduced; the solid product has high purity, can meet the industrial use, and is not treated as a solid waste, and the components in the high-concentration salt wastewater are effectively recycled and utilized.

Description

Technical Field

[0001] This invention relates to the field of comprehensive wastewater recycling, and in particular to a method for treating high-concentration saline wastewater. Background Technology

[0002] The production and recycling of lithium batteries inevitably generate large amounts of sodium sulfate solutions. Treating this sodium sulfate wastewater to produce crude sodium sulfate has significant economic value. However, existing methods for treating sodium sulfate wastewater result in solid salts that are then treated as solid waste, which is energy-intensive and adds to treatment costs and environmental pressure. Summary of the Invention

[0003] The main objective of this invention is to propose a method for treating high-concentration saline wastewater, which aims to effectively recover and utilize the components in high-concentration saline wastewater and reduce the energy consumption of high-concentration saline wastewater treatment.

[0004] To achieve the above objectives, the present invention provides a method for treating high-concentration saline wastewater, the method comprising:

[0005] S1. High-concentration salt wastewater is flash-evaporated at least twice to obtain a highly saturated low-temperature mother liquor;

[0006] S2. Freeze the highly saturated low-temperature mother liquor to precipitate sodium sulfate decahydrate crystals to form a crystalline slurry;

[0007] S3. Separate the sodium sulfate decahydrate crystals and the frozen clear liquid from the crystal slurry;

[0008] S4. Heating sodium sulfate decahydrate crystallizes to form sodium sulfate slurry.

[0009] S5. Centrifuge the sodium sulfate slurry to separate sodium sulfate and centrifugation mother liquor.

[0010] In one embodiment, the cryogenic liquid separated in step S3 exchanges heat with the steam generated by flash evaporation in steps S1 and S2, and cools the steam to form condensate.

[0011] In one embodiment, the temperature of the highly saturated low-temperature mother liquor produced in step S2 is 18-20 degrees Celsius.

[0012] In one embodiment, the step of obtaining a highly saturated low-temperature mother liquor by flash evaporating the high-concentration saline wastewater at least twice includes:

[0013] High-concentration saline wastewater is subjected to primary flash evaporation at a temperature of 23°C to 26°C and a vacuum degree of -98.3 kPa to -97.9 kPa.

[0014] The high-concentration salt wastewater after primary flash evaporation is subjected to secondary flash evaporation at a temperature of 15°C to 18°C ​​and a vacuum degree of -99.5 kPa to -99 kPa.

[0015] In one embodiment, the step of separating sodium sulfate decahydrate crystals and cryosol from the crystal slurry includes:

[0016] The crystal slurry is conveyed to a thickener to settle the sodium sulfate decahydrate crystals in the crystal slurry, and the supernatant is separated and discharged.

[0017] The settled crystal slurry was centrifuged to obtain sodium sulfate decahydrate crystals and a cryo-clean liquid.

[0018] In one embodiment, the freezing temperature in step S2 is -20°C to -5°C.

[0019] In one embodiment, in step S54, the heating temperature is 200°C to 800°C.

[0020] In one embodiment, prior to the step of flash evaporating the high-concentration saline wastewater at least twice to obtain a highly saturated low-temperature mother liquor, the following steps are included:

[0021] Real-time acquisition of the temperature of preheated high-concentration salt wastewater;

[0022] When the temperature of the high-concentration salt wastewater is below 20°C, the high-concentration salt wastewater is preheated to 30°C to 35°C.

[0023] This invention utilizes at least two stages of flash evaporation to gradually decrease the temperature and increase the concentration of high-concentration saline wastewater. The parameters for each stage of flash evaporation (vacuum degree and corresponding flash temperature) can be set according to requirements. It is only necessary to ensure that the temperature of the first stage flash evaporation is between 23°C and 26°C to reduce the energy consumption of pretreatment for high-concentration saline wastewater. The parameters for intermediate stages of flash evaporation can be set according to the crystallization temperature of impurities in the high-concentration saline wastewater, thereby precipitating impurities step by step during multi-stage flash evaporation. This improves the purity of the frozen sodium sulfate decahydrate crystals and the purity of the final sodium sulfate (sodium sulfate). In other words, the solid product formed in this application has high purity, meeting industrial use requirements, rather than being treated as solid waste, effectively recovering and utilizing components from high-concentration saline wastewater. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the hardware operating environment involved in the embodiments of the present invention;

[0025] Figure 2 This is a schematic flowchart of the first embodiment of the high-concentration salt wastewater treatment method of the present invention.

[0026] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0027] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0028] Please refer to Figure 1 , Figure 1 This is a schematic diagram of the hardware structure of the terminal provided in various embodiments of the present invention. The terminal includes components such as a communication module 01, a memory 02, and a processor 03. Those skilled in the art will understand that... Figure 1 The terminal shown may also include more or fewer components than illustrated, or combine certain components, or have different component arrangements. The processor 03 is connected to both the memory 02 and the communication module 01. The memory 02 stores a computer program, which is simultaneously executed by the processor 03.

[0029] The communication module 01 can connect to external devices via a network. The communication module 01 can receive data from external devices and can also send data, instructions, and information to the external devices, which can be electronic devices such as mobile phones, tablets, laptops, and desktop computers.

[0030] The memory 02 can be used to store software programs and various data. The memory 02 may mainly include a program storage area and a data storage area. The program storage area may store the operating system, at least one application program required for a function (such as real-time detection of temperature data for high-concentration saline solution), etc.; the data storage area may store data or information created based on terminal usage. Furthermore, the memory 02 may include high-speed random access memory, and may also include non-volatile memory, such as at least one disk storage device, flash memory device, or other volatile solid-state storage device.

[0031] Processor 03 is the control center of the terminal. It connects various parts of the terminal via various interfaces and lines. By running or executing software programs and / or modules stored in memory 02, and by calling data stored in memory 02, it performs various functions and processes data, thereby providing overall monitoring of the terminal. Processor 03 may include one or more processing units; preferably, processor 03 may integrate an application processor and a modem processor. The application processor mainly handles the operating system, user interface, and applications, while the modem processor mainly handles wireless communication. It is understood that the modem processor may not be integrated into processor 03.

[0032] although Figure 1 Not shown, but the above terminal may also include a circuit control module, which is used to connect to the mains power supply to realize power control and ensure the normal operation of other components.

[0033] Those skilled in the art will understand that Figure 1 The terminal structure shown does not constitute a limitation on the terminal and may include more or fewer components than shown, or combine certain components, or have different component arrangements.

[0034] Based on the above hardware structure, various embodiments of the method of the present invention are proposed.

[0035] Reference Figure 2 In the first embodiment of the high-concentration saline wastewater treatment method of the present invention, the high-concentration saline wastewater treatment method includes the following steps:

[0036] S1. High-concentration salt wastewater is flash-evaporated at least twice to obtain a highly saturated low-temperature mother liquor;

[0037] By introducing high-concentration salt wastewater into a lower-pressure flash chamber, the boiling point of the high-concentration salt wastewater will decrease accordingly when the pressure decreases, so that it will start to boil under the new pressure conditions. Some of the water in the high-concentration salt wastewater will turn into steam, accompanied by liquid-vapor two-phase separation.

[0038] In this application, high-concentration salt wastewater flows sequentially through several flash chambers with gradually decreasing pressure, evaporating and cooling down step by step. At the same time, the concentration of the high-concentration salt wastewater also increases step by step until a highly saturated low-temperature mother liquor is formed.

[0039] Furthermore, the steam generated in the previous flash evaporation stage can be used to heat the next flash evaporation stage, reducing the amount of heat source introduced and lowering energy consumption.

[0040] Specifically, the step of obtaining a highly saturated low-temperature mother liquor by flash evaporating high-concentration salt wastewater at least twice includes:

[0041] High-concentration saline wastewater is subjected to primary flash evaporation at a temperature of 23°C to 26°C and a vacuum degree of -98.3 kPa to -97.9 kPa.

[0042] The high-concentration salt wastewater after primary flash evaporation is subjected to secondary flash evaporation at a temperature of 15°C to 18°C ​​and a vacuum degree of -99.5 kPa to -99 kPa.

[0043] The main component of high-concentration saline wastewater is sodium sulfate solution. Sodium sulfate has little effect on the boiling point of water. This application uses two-stage flash evaporation to lower the temperature of high-concentration wastewater to 15°C to 18°C, forming a highly saturated low-temperature mother liquor. Industrial wastewater temperatures are generally above 30°C. The vacuum degree of the first-stage flash evaporation ranges from -98.3 kPa to -97.9 kPa, corresponding to an evaporation temperature of 23°C to 26°C. This means that, under normal circumstances, high-concentration saline wastewater can be directly introduced into the flash evaporation chamber for flash evaporation without preheating, reducing energy consumption.

[0044] The temperature of the highly saturated low-temperature mother liquor produced in step S1 is 18-20 degrees Celsius. Compared with the traditional method of heating and evaporating water followed by cooling and crystallization, the temperature at which the highly saturated low-temperature mother liquor is formed after two-stage flash evaporation in this application is lower, which can better reduce energy consumption.

[0045] S2. Freeze the highly saturated low-temperature mother liquor to precipitate sodium sulfate decahydrate crystals to form a crystalline slurry;

[0046] At low temperatures, sodium sulfate crystallizes out as sodium sulfate decahydrate. The freezing temperature is controlled between -20°C and -5°C.

[0047] S3. Separate the sodium sulfate decahydrate crystals and the frozen clear liquid from the crystal slurry;

[0048] Specifically, step S3 includes: conveying the crystal slurry to a thickener to settle the sodium sulfate decahydrate crystals in the crystal slurry, separating and releasing the supernatant;

[0049] The settled crystal slurry was centrifuged to obtain sodium sulfate decahydrate crystals and a cryo-clean liquid.

[0050] This application introduces a crystalline slurry containing sodium sulfate decahydrate crystals into a thickener. In the thickener, due to the difference in specific gravity between the crystals and the liquid, the heavier crystals slowly settle while the clear liquid gradually rises, thus separating the sodium sulfate decahydrate crystals from the liquid. The crystals that have settled to the bottom of the equipment aggregate into a thick slurry, which then enters a centrifuge through the outlet. The centrifuge centrifuges the settled sodium sulfate decahydrate crystals to obtain sodium sulfate decahydrate with high purity.

[0051] The frozen liquid separated in step S3 exchanges heat with the steam generated by flash evaporation in steps S1 and S2, and cools the steam to form condensate.

[0052] The cryogenic liquid separated from the thickener and centrifuge is a low-temperature liquid that can be neutralized by heat exchange with the steam generated in the last stage of flash evaporation, causing the steam to condense and be used in production and processing.

[0053] It is understandable that if there is any remaining steam generated by the flash evaporation, it can also be used for heat exchange and neutralization with the clear liquid separated from the thickener and centrifuge.

[0054] S4. Heating sodium sulfate decahydrate crystallizes to form sodium sulfate slurry.

[0055] S5. Centrifuge the sodium sulfate slurry to separate sodium sulfate and centrifugation mother liquor.

[0056] Sodium sulfate decahydrate is purified by evaporation and concentration, and the water of crystallization is removed by heating to obtain anhydrous sodium sulfate at a temperature of 200℃~800℃. The concentrated anhydrous sodium sulfate slurry is separated by centrifugation, and the wet anhydrous sodium sulfate is dried by flash dryer to obtain sodium sulfate.

[0057] In this embodiment, the temperature of the high-concentration saline wastewater is gradually reduced and its concentration gradually increased through at least two stages of flash evaporation. It can be understood that the parameters of each stage of flash evaporation (vacuum degree and corresponding flash temperature) are set according to requirements. It is only necessary to ensure that the temperature of the first stage flash evaporation is between 23°C and 26°C to reduce the energy consumption of the high-concentration saline wastewater pretreatment. The parameters of the intermediate stages of flash evaporation can be set according to the crystallization temperature of impurities in the high-concentration saline wastewater, thereby precipitating impurities step by step during multi-stage flash evaporation, thus improving the purity of the frozen sodium sulfate decahydrate crystals and the purity of the final sodium sulfate. That is, the solid product formed in this application has high purity and can meet industrial use requirements, rather than being treated as solid waste, effectively recovering and utilizing the components of the high-concentration saline wastewater.

[0058] In one embodiment, before step S1, the method further includes...

[0059] Real-time acquisition of the temperature of preheated high-concentration salt wastewater;

[0060] When the temperature of the high-concentration salt wastewater is below 20°C, the high-concentration salt wastewater is preheated to 30°C to 35°C.

[0061] In this application, when conveying high-concentration saline wastewater, the temperature is monitored in real time by a temperature sensor. A buffer tank is set up, and temperature sensors are installed at the front end of the buffer tank along the conveying direction and inside the buffer tank. When the temperature sensor at the front end detects that the temperature of the high-concentration saline wastewater is below 20°C, heating is activated to preheat the high-concentration saline wastewater in the buffer tank. When the high-concentration saline wastewater in the buffer tank is heated to 30°C to 35°C, and the temperature sensor at the front end detects that the temperature of the high-concentration saline wastewater is above 20°C, heating is stopped. The double confirmation by two temperature sensors avoids overheating and underheating, ensuring the effectiveness of the first-stage flash evaporation.

[0062] The present invention also proposes a computer-readable storage medium having a computer program stored thereon. The computer-readable storage medium may be... Figure 1 The memory 02 in the terminal may also be at least one of ROM (Read-Only Memory) / RAM (Random Access Memory), magnetic disk, optical disk, etc. The computer-readable storage medium includes several information to enable the terminal to perform the methods described in the various embodiments of the present invention.

[0063] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or system that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or system. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or system that includes that element.

[0064] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0065] Through the above description of the embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of software plus necessary general-purpose hardware platforms. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method.

[0066] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural or procedural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. A method for treating high-concentration saline wastewater, characterized in that, The method includes: S1. High-concentration salt wastewater is flash-evaporated at least twice to obtain a highly saturated low-temperature mother liquor; S2. Freeze the highly saturated low-temperature mother liquor to precipitate sodium sulfate decahydrate crystals to form a crystalline slurry; S3. Separate the sodium sulfate decahydrate crystals and the frozen clear liquid from the crystal slurry; S4. Heating sodium sulfate decahydrate crystallizes to form sodium sulfate slurry. S5. Centrifuge the sodium sulfate slurry to separate sodium sulfate and centrifugation mother liquor; The step of obtaining a highly saturated low-temperature mother liquor by flash evaporating high-concentration salt wastewater at least twice includes: High-concentration saline wastewater is subjected to primary flash evaporation at a temperature of 23°C to 26°C and a vacuum degree of -98.3 kPa to -97.9 kPa. The high-concentration salt wastewater after primary flash evaporation is subjected to secondary flash evaporation at a temperature of 15°C to 18°C ​​and a vacuum degree of -99.5 kPa to -99 kPa.

2. The method for treating high-concentration saline wastewater according to claim 1, characterized in that, The frozen liquid separated in step S3 exchanges heat with the steam generated by flash evaporation in steps S1 and S2, and cools the steam to form condensate.

3. The method for treating high-concentration saline wastewater according to claim 1, characterized in that, The temperature of the highly saturated low-temperature mother liquor produced in step S2 is 18-20 degrees Celsius.

4. The method for treating high-concentration saline wastewater according to any one of claims 1 to 3, characterized in that, The step of separating sodium sulfate decahydrate crystals and cryosol from the crystal slurry includes: The crystal slurry is conveyed to a thickener to settle the sodium sulfate decahydrate crystals in the crystal slurry, and the supernatant is separated and discharged. The settled crystal slurry was centrifuged to obtain sodium sulfate decahydrate crystals and a cryo-clean liquid.

5. The method for treating high-concentration saline wastewater according to any one of claims 1 to 3, characterized in that, In step S2, the freezing temperature is -20℃ to -5℃.

6. The method for treating high-concentration saline wastewater according to claim 5, characterized in that, In step S4, the heating temperature is 200℃~800℃.

7. The method for treating high-concentration saline wastewater according to any one of claims 1 to 3, characterized in that, Before the step of obtaining a highly saturated low-temperature mother liquor by flash evaporating the high-concentration saline wastewater at least twice, the following steps are included: Real-time acquisition of the temperature of preheated high-concentration salt wastewater; When the temperature of the high-concentration salt wastewater is below 20°C, the high-concentration salt wastewater is preheated to 30°C to 35°C.

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