Sodium sulfate-containing wastewater treatment method and application thereof

Abstract

The invention belongs to the field of sewage treatment, and particularly discloses a treatment method and application of sodium sulfate-containing wastewater. The method is scientific and reasonable in design, sodium sulfate in the solution is crystallized and separated out through low-temperature crystallization, and then crystal water sodium sulfate solids and low-temperature filtrate are produced through centrifugal separation. Wherein the low-temperature filtrate is heated by utilizing waste heat generated in a low-temperature crystallization refrigeration process, the low-temperature filtrate is treated by a membrane filtration technology after being heated, purified water produced after treatment reaches the standard and is discharged, and the produced strong brine is frozen, crystallized and concentrated again or enters a later stage for treatment. According to the method, a freezing crystallization and membrane filtration technology is combined, so that a traditional evaporative crystallization technology is replaced to a great extent, and the investment cost and the operation cost during treatment of the sodium sulfate-containing wastewater are remarkably reduced.

Description

Technical Field

[0001] The present application belongs to the field of wastewater treatment, and specifically relates to a method for treating sodium sulfate-containing wastewater and its application. Background Art

[0002] In the field of industrial production, the treatment of high-concentration sodium sulfate wastewater (sodium sulfate mass concentration ≥ 5%) has always been a thorny problem. At present, the conventional treatment method is to first concentrate the solution containing high sodium sulfate wastewater to a mass concentration range of 12%-18% through membrane concentration technology, and then use MVR (mechanical vapor recompression technology) or multiple-effect evaporation system for evaporation and crystallization operation. However, these two common evaporation and crystallization technologies have significant disadvantages. Although MVR technology has high energy utilization efficiency, its equipment procurement cost is extremely high, and it needs to be equipped with high-performance compressors, heat exchangers and other key equipment, which makes the initial investment huge; the multiple-effect evaporation system consumes a lot of steam or other heat sources. During operation, continuous energy input makes the operating cost high. These high investment costs and operating costs are an unbearable economic burden for many high-salinity wastewater projects. This directly leads to many high-salinity wastewater projects being forced to shelve because they cannot afford the huge treatment costs, and they cannot effectively carry out wastewater treatment work, which not only causes a waste of water resources, but also poses a potential threat to the environment.

[0003] In view of this, the inventor hopes to provide a method for treating sodium sulfate-containing wastewater, aiming to effectively reduce the treatment cost of wastewater solutions containing high-concentration sodium sulfate, break the cost bottleneck of the prior art, and promote the sustainable development of the high-salt wastewater treatment industry. Summary of the invention

[0004] The purpose of this application is to solve the deficiencies of the prior art and provide a method for treating sodium sulfate-containing wastewater and its application, specifically adopting the following technical solutions:

[0005] First, the present application provides a method for treating sodium sulfate-containing wastewater, including a concentration treatment process, wherein the concentration treatment process includes the following steps:

[0006] The first waste liquid containing sodium sulfate wastewater is subjected to a first cooling crystallization, and then separated to obtain a first solid and a first filtrate. The first filtrate is heated for a first time by using heat exchange equipment with the heat generated in the first cooling crystallization to increase the temperature of the first filtrate to obtain a second filtrate; the second filtrate is membrane filtered using a high-pressure membrane to obtain a second waste liquid.

[0007] In the present application, the inventors transported the heat generated during the cooling and crystallization process to specific steps in subsequent production through heat exchange equipment, thereby achieving the recycling of heat, saving resources and avoiding waste.

[0008] In some specific implementation cases of the present application, the heat exchange equipment used in the present application is not limited to heat pumps, but also includes heat exchange equipment formed by other principles, such as partition heat exchangers, hybrid heat exchangers and heat storage heat exchangers, etc. The purpose of these heat exchange equipment is to utilize the heat energy released in the first cooling crystallization in subsequent production processes.

[0009] In some specific implementations, the treatment method includes at least 2 concentration treatment processes, and the second waste liquid obtained in the n-1th concentration treatment process is mixed with the first waste liquid of the nth time and then heated for the first time; n is a positive integer not less than 2. That is, the second waste liquid obtained in the previous batch is mixed with the sodium sulfate wastewater in the next batch and then concentrated.

[0010] In some specific implementations, the slurry product obtained after the first cooling crystallization includes a first solid, and the first solid also specifically includes sodium sulfate containing crystal water. The sodium sulfate containing crystal water is subsequently evaporated and crystallized to obtain the corresponding anhydrous sodium sulfate.

[0011] Moreover, in some specific implementations, the heat required for evaporation and crystallization comes from the first cooling and crystallization, thereby achieving more effective heat utilization; in some cases, the waste heat from the first heating can also be transferred to the first solid for evaporation and crystallization.

[0012] In some specific implementations, the second waste liquid is crystallized by evaporation, and the sodium sulfate therein is subjected to removal of crystallization water to obtain anhydrous sodium sulfate.

[0013] In some specific implementations, the method further includes: subjecting the second wastewater to a second cooling and crystallization, followed by separation to obtain a second solid and a second filtrate, using a heat exchange device to heat the second filtrate for a second time using the heat generated in the second cooling and crystallization to obtain a third filtrate; and filtering the third filtrate using a high-pressure membrane to obtain a third waste liquid.

[0014] In some specific cases, the third waste liquid can also be recycled one or more times:

[0015] The third wastewater is subjected to a third cooling and crystallization, and then separated to obtain a third solid and a third filtrate. The third filtrate is heated for a third time by heat exchange equipment using the heat generated in the third cooling and crystallization to obtain a fourth filtrate. The fourth filtrate is filtered using a high-pressure membrane to obtain a fourth waste liquid.

[0016] In some specific implementations, the second waste liquid and the third waste liquid are further evaporated by MVR to produce anhydrous sodium sulfate.

[0017] In some specific implementations, the high pressure membrane includes one of a microfiltration membrane, an ultrafiltration membrane, a nanofiltration membrane, and a reverse osmosis membrane.

[0018] In some specific implementations, the temperature of the first filtrate is -5°C to 10°C; the temperature of the second filtrate is 25°C to 45°C; and the mass concentration of sodium sulfate in the second waste liquid is 8% to 18%.

[0019] Secondly, the present application also provides an application of the above-mentioned method for treating sodium sulfate-containing wastewater in the field of industrial wastewater treatment.

[0020] The beneficial effects of the present application are as follows: the present application recycles the heat in the sewage treatment process, thereby reducing the consumption of evaporated water in the process of treating wastewater containing sodium sulfate through multiple concentrations, crystallizations and separations, avoiding the waste of heat generated in the freezing crystallization process and the heat loss caused by subsequent heating, and combining with membrane filtration to reduce consumption, improve efficiency, and greatly reduce the cost of wastewater treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Shown is a schematic flow diagram of a method for treating sodium sulfate-containing wastewater;

[0022] Figure 2 Shown is a schematic flow chart of a second method for treating sodium sulfate-containing wastewater in an embodiment;

[0023] Figure 3 Shown is a schematic flow chart of the third method for treating sodium sulfate-containing wastewater in the embodiment;

[0024] Figure 4 Shown is a schematic flow chart of a fourth method for treating sodium sulfate-containing wastewater in an embodiment;

[0025] Figure 5 Shown is a schematic flow chart of the fifth method for treating sodium sulfate-containing wastewater in the embodiment. DETAILED DESCRIPTION

[0026] The following will be combined with the embodiments and drawings to clearly and completely describe the concept of the present application and the technical effects produced, so as to fully understand the purpose, scheme and effect of the present application. It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The same reference numerals used throughout the drawings indicate the same or similar parts.

[0027] First, if Figure 1 As shown, the present application provides a method for treating sodium sulfate-containing wastewater, comprising:

[0028] The first waste liquid containing sodium sulfate wastewater is subjected to a first cooling crystallization, and then separated to obtain a first solid and a first filtrate. The first filtrate is heated for a first time by using heat exchange equipment with the heat generated in the first cooling crystallization to increase the temperature of the first filtrate to obtain a second filtrate; the second filtrate is membrane filtered using a high-pressure membrane to obtain a second waste liquid.

[0029] The method for treating sodium sulfate-containing wastewater provided in the present application fully utilizes heat and achieves rapid treatment of wastewater through a variety of separation methods.

[0030] Example 1

[0031] Combination Figure 2 In this embodiment, the waste liquid containing sodium sulfate is called sodium sulfate raw water.

[0032] like Figure 2 As shown, this embodiment provides a method for concentrating a sodium sulfate solution, comprising the following steps:

[0033] S1, freezing and crystallizing the sodium sulfate raw water (i.e., the first waste liquid, with a mass concentration of 6%) (i.e., the first cooling crystallization) to precipitate sodium sulfate crystals to obtain a crystal slurry containing sodium sulfate solids;

[0034] S2, centrifuging the crystal slurry after crystallization to obtain a crystal water sodium sulfate solid (i.e., the first solid) and a low-temperature filtrate (i.e., the first filtrate), wherein the temperature of the low-temperature filtrate is 5° C. (in some other embodiments, the temperature is any temperature within the range of -5° C. to 10° C.);

[0035] S3, using the heat generated by the refrigeration equipment during the freezing crystallization process in step S1 to heat the low-temperature filtrate (i.e., the first filtrate) produced in step S2 through a heat pump unit (i.e., heating for the first time), thereby obtaining a high-temperature filtrate (i.e., the second filtrate) at 45° C. (in some other embodiments, the temperature is any temperature within the range of 25° C. to 45° C.);

[0036] S4, filtering the high-temperature filtrate produced in step S3 through a reverse osmosis membrane to produce pure water and a sodium sulfate solution with a mass concentration of 18% (in some other embodiments, the mass concentration of the sodium sulfate solution is any concentration in the range of 8% to 18%) high-concentration sodium sulfate solution (i.e., the second waste liquid, i.e. Figure 2 in the text).

[0037] The second waste liquid obtained from the first concentration process is mixed with the first waste liquid from the second concentration process and then subjected to freeze crystallization; that is, in this embodiment, the high-concentration sodium sulfate solution with a mass concentration of 18% is transported to step S1, mixed with the next batch of sodium sulfate raw water, and repeated crystallization is performed.

[0038] like Figure 2 As shown, the crystal water sodium sulfate solid produced in step S2 is evaporated and crystallized to remove the crystal water, thereby producing anhydrous sodium sulfate and pure water.

[0039] In this embodiment, the heat is fully utilized and the process is short, which is conducive to the rapid treatment of wastewater containing sodium sulfate.

[0040] Example 2

[0041] Combination Figure 3 In this embodiment, sodium sulfate is used as an example of sodium sulfate, but in actual work, it is not limited to the extraction of sodium sulfate from wastewater.

[0042] like Figure 3 As shown, this embodiment provides a method for concentrating a sodium sulfate solution, comprising the following steps:

[0043] S1, freezing and crystallizing the sodium sulfate raw water (i.e., the first waste liquid, with a mass concentration of 6%) (i.e., the first cooling crystallization) to precipitate sodium sulfate crystals to obtain a crystal slurry containing sodium sulfate solids;

[0044] S2, centrifuging the crystal slurry after crystallization to produce a crystal water sodium sulfate solid (i.e., the first solid) and a low-temperature filtrate (i.e., the first filtrate), wherein the temperature of the low-temperature filtrate is -5°C (in some other embodiments, the temperature is any temperature within the range of -5°C to 10°C);

[0045] S3, using the heat generated by the refrigeration equipment during the freezing crystallization process in step S1 to heat the low-temperature filtrate (i.e., the first filtrate) produced in step S2 through a heat pump unit (i.e., heating for the first time), thereby obtaining a high-temperature filtrate (i.e., the second filtrate) of 25° C. (in some other embodiments, the temperature is any temperature in the range of 25° C. to 45° C.);

[0046] S4, filtering the high-temperature filtrate produced in step S3 through a reverse osmosis membrane to produce pure water and a sodium sulfate solution with a mass concentration of 8% (in some other embodiments, the mass concentration of the sodium sulfate solution is any concentration in the range of 8% to 18%) and a high-concentration sodium sulfate solution (i.e., the second waste liquid, i.e. Figure 3 in the text).

[0047] The second waste liquid obtained from the first concentration process is mixed with the first waste liquid from the second process and then subjected to freeze crystallization; that is, in this embodiment, the high-concentration sodium sulfate solution with a mass concentration of 8% is transported to step S1, mixed with the next batch of sodium sulfate raw water, and repeated crystallization is performed.

[0048] like Figure 3As shown, the heat in the first cooling crystallization and the first heating is transferred to the mother liquor containing crystallization water sodium sulfate solid obtained in step S2 by a heat pump unit as a heat exchange device, and the mother liquor is preheated to obtain a sodium sulfate solution at 40°C (in some other embodiments, the temperature is any temperature in the range of 40°C-100°C), and then the sodium sulfate solution is evaporated and crystallized to obtain anhydrous sodium sulfate and pure water.

[0049] In this embodiment, the heat is fully utilized through the circulation, thereby saving energy and producing anhydrous sodium sulfate.

[0050] Example 3

[0051] Combination Figure 4 In this embodiment, sodium sulfate is used as an example of sulfate, but in actual work, it is not limited to the extraction of sodium sulfate from wastewater.

[0052] like Figure 4 As shown, this embodiment provides a method for concentrating a sodium sulfate solution, comprising the following steps:

[0053] S1, freezing and crystallizing the sodium sulfate raw water (i.e., the first waste liquid, with a mass concentration of 6%) (i.e., the first cooling crystallization) to precipitate sodium sulfate crystals to obtain a crystal slurry containing sodium sulfate solids;

[0054] S2, centrifuging the crystal slurry after crystallization to produce a crystal water sodium sulfate solid (i.e., the first solid) and a low-temperature filtrate (i.e., the first filtrate), wherein the temperature of the low-temperature filtrate is -5°C (in some other embodiments, the temperature is any temperature within the range of -5°C to 10°C);

[0055] S3, using the heat generated by the refrigeration equipment during the freezing crystallization process in step S1 to heat the low-temperature filtrate (i.e., the first filtrate) produced in step S2 through a heat pump unit (i.e., heating for the first time), thereby obtaining a high-temperature filtrate (i.e., the second filtrate) of 25° C. (in some other embodiments, the temperature is any temperature in the range of 25° C. to 45° C.);

[0056] S4. After filtering the high-temperature filtrate produced in step S3 through a reverse osmosis membrane, pure water and a sodium sulfate solution with a mass concentration of 8% (in some other embodiments, the mass concentration of the sodium sulfate solution is any concentration in the range of 8% to 18%) are produced. High-concentration sodium sulfate solution (i.e., the second waste liquid) is produced.

[0057] like Figure 4As shown, the heat in the first cooling crystallization and the first heating is transferred to the mother liquor containing crystallization water sodium sulfate solid obtained in step S2 by a heat pump unit as a heat exchange device, and the mother liquor is preheated to obtain a sodium sulfate solution at 40°C (in some other embodiments, the temperature is any temperature in the range of 40°C-100°C), and then the sodium sulfate solution is evaporated and crystallized to obtain anhydrous sodium sulfate and pure water.

[0058] The high-concentration sodium sulfate solution (i.e., the second waste liquid) with a mass concentration of 8% is subjected to a second cooling crystallization, followed by centrifugal separation to obtain a second solid and a second filtrate, and the second solid is transported to the above-mentioned mother liquor; the heat generated in the second cooling crystallization is used to heat the second filtrate for a second time through a heat exchange device to obtain a third filtrate; the third filtrate is filtered using a high-pressure membrane to obtain concentrated sodium water containing sodium sulfate at 53° C. and 4.3 t / h (throughput rate) (i.e., the third waste liquid); and water at 53° C. and 12.7 t / h (throughput rate).

[0059] Subsequently, the concentrated sodium water (i.e., the third waste liquid) was subjected to MVR evaporation to obtain 3.7 t / h (throughput rate) of water and 0.6 t / h (throughput rate) of sodium sulfate as miscellaneous sodium wastewater.

[0060] In this embodiment, after two freezing crystallizations, the sodium sulfate-containing wastewater is treated thoroughly, and the heat is fully utilized, which greatly reduces the waste of heat.

[0061] Example 4

[0062] Combination Figure 5 In this embodiment, a specific and detailed example is given of the application of the method for treating sodium sulfate-containing wastewater provided in the present application in the field of industrial wastewater treatment.

[0063] In this embodiment, sodium sulfate is used as an example of sulfate, but in actual work, it is not limited to the extraction, separation or concentration of sodium sulfate in wastewater.

[0064] like Figure 5 As shown, this embodiment provides a method for concentrating a sodium sulfate solution, comprising the following steps:

[0065] S1. The sodium sulfate raw water (i.e., the first waste liquid) with a temperature of 30° C. and a mass concentration of 14% is subjected to freeze crystallization (i.e., the first cooling crystallization) at a rate of 116 t / h, and the temperature is lowered to 0° C. to allow sodium sulfate to crystallize and obtain a slurry containing sodium sulfate;

[0066] S2, centrifuging the slurry at 0°C to obtain a solid of sodium sulfate (i.e., the first solid) at a throughput rate of 29 t / h, and also obtaining a low-temperature filtrate (i.e., the first filtrate) at 0°C and 87 t / h (throughput rate) with a sodium sulfate mass concentration of 3.7%;

[0067] S3, using the heat generated by the refrigeration equipment in the freezing crystallization process in step S1 to heat the low-temperature filtrate (i.e., the first filtrate) produced in step S2 through an 820KW heat pump unit (i.e., heating for the first time), thereby obtaining a high-temperature filtrate (i.e., the second filtrate) with a sodium sulfate mass concentration of 3.7% at 36.5°C and 87t / h (throughput rate);

[0068] S4. After filtering the high-temperature filtrate produced in step S3 through a reverse osmosis membrane, pure water at 36.5° C. and concentrated brine containing sodium sulfate (i.e., the second waste liquid) with a temperature of 36.5° C., a throughput rate of 23 t / h (throughput rate), and a mass concentration of 13.9% are produced at 64 t / h (throughput rate).

[0069] The mother liquor containing sodium sulfate solid with crystallization water produced in step S2 is preheated after the waste heat in the first cooling crystallization and the first heating process is transferred to the mother liquor by a 246KW heat pump unit to obtain a mother liquor containing sodium sulfate with crystallization water at 70°C and a flow rate of 35t / h (throughput rate). The mother liquor is then evaporated by MVR to obtain pure water at 19.6t / h (throughput rate) and anhydrous sodium sulfate at 15.4t / h (throughput rate).

[0070] The concentrated brine containing sodium sulfate at 36.5°C, 23 t / h (throughput rate), and 13.9% by mass concentration (i.e., the second waste liquid) is subjected to a second freezing crystallization (i.e., the second cooling crystallization) to obtain a crystal slurry at 0°C, 23 t / h (throughput rate), and then the crystal slurry is centrifuged to obtain crystal water sodium sulfate at 0°C, 6 t / h (throughput rate) (i.e., the second solid) and a cold filtrate at 0°C, 17 t / h (throughput rate), 3.5% (i.e., the second filtrate), and the second solid is transported to the mother liquor containing the crystal water sodium sulfate solid;

[0071] The heat generated in the second cooling crystallization is used by a 180KW heat pump unit to heat the second filtrate for a second time to obtain a hot filtrate (i.e., the third filtrate) at 53°C, 17 t / h (throughput rate), and 3.5%. The third filtrate is filtered using a high-pressure membrane to obtain a concentrated brine (i.e., the third waste liquid) at 53°C, 4.3 t / h (throughput rate) containing 13.9% sodium sulfate and water at 53°C, 12.7 t / h (throughput rate).

[0072] The concentrated brine was then subjected to MVR evaporation to obtain 3.7 t / h (throughput rate) of water and 0.6 t / h (throughput rate) of anhydrous sodium sulfate.

[0073] In this embodiment, the treatment of 116 tons of high-salt water per hour is taken as an example, of which the salt content is about 16 tons. With traditional technology, about 100 tons of water need to be evaporated, and the current most energy-efficient MVR technology costs about 45 yuan per ton of water evaporated, so the consumption cost of evaporating 100 tons of water is about 4,500 yuan. In contrast, this technology cools down to 0°C in the S1 stage, centrifugal separation in the S2 stage, and warms up to 36.5°C in the S3 stage, and finally only needs to evaporate about 24 tons of water, with an evaporation cost of 1,080 yuan; plus the cost of freezing crystallization and high-pressure membrane filtration is about 1,200 yuan, the total cost is about 2,280 yuan, which is only 51% of the traditional technology cost of 4,500 yuan, that is, a saving of 49%.

[0074] Although the description of the present application has been quite detailed and specifically describes several described embodiments, it is not intended to be limited to any of these details or embodiments or any particular embodiment, but should be regarded as providing a broad possible interpretation of these claims by reference to the attached claims in view of the prior art, thereby effectively covering the intended scope of the present application. In addition, the above description of the present application is based on the foreseeable embodiments of the applicant, the purpose of which is to provide a useful description, and those non-substantial changes to the present application that have not yet been foreseen may still represent equivalent changes to the present application.

Claims

1. A method for treating sodium sulfate-containing wastewater, characterized in that: The method comprises a concentration process, wherein the concentration process comprises the following steps: The first waste liquid containing sodium sulfate wastewater is subjected to a first cooling crystallization, and then separated to obtain a first solid and a first filtrate; the first filtrate is heated for a first time by using heat exchange equipment with the heat generated in the first cooling crystallization to increase the temperature of the first filtrate to obtain a second filtrate; the second filtrate is membrane filtered using a high-pressure membrane to obtain a second waste liquid.

2. A method for treating sodium sulfate wastewater according to claim 1, characterized in that: The treatment method includes at least 2 concentration treatment processes, and the second waste liquid obtained from the n-1th concentration treatment process is mixed with the first waste liquid from the nth time and then heated for the first time; n is a positive integer not less than 2.

3. A method for treating sodium sulfate wastewater according to claim 1, characterized in that: The first solid includes crystal water, and anhydrous sodium sulfate is obtained after evaporation and crystallization.

4. A method for treating sodium sulfate wastewater according to claim 3, characterized in that: The heat required for the evaporative crystallization comes from the first cooling crystallization.

5. A method for treating sodium sulfate wastewater according to claim 1, characterized in that: The second waste liquid is evaporated and crystallized to obtain anhydrous sodium sulfate.

6. A method for treating sodium sulfate wastewater according to claim 1, characterized in that: Also includes: The second wastewater is subjected to a second cooling and crystallization, and then separated to obtain a second solid and a second filtrate. The heat generated in the second cooling and crystallization is used by a heat exchange device to heat the second filtrate for a second time to obtain a third filtrate. The third filtrate is filtered using a high-pressure membrane to obtain a third waste liquid.

7. A method for treating sodium sulfate wastewater according to claim 6, characterized in that: Also includes: The second waste liquid and the third waste liquid are evaporated by MVR to produce anhydrous sodium sulfate.

8. A method for treating sodium sulfate wastewater according to claim 1, characterized in that: The high-pressure membrane includes one of a microfiltration membrane, an ultrafiltration membrane, a nanofiltration membrane and a reverse osmosis membrane.

9. A method for treating sodium sulfate wastewater according to claim 1, characterized in that: The temperature of the first filtrate is -5°C to 10°C; and / or the temperature of the second filtrate is 25°C to 45°C; and / or the mass concentration of sodium sulfate in the second waste liquid is 8% to 18%.

10. Application of the method for treating sodium sulfate-containing wastewater according to any one of claims 1 to 9 in the field of industrial wastewater treatment.

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