Sodium sulfate circulation process for concentrating acidified oil wastewater

Abstract

The invention relates to the field of acidified oil wastewater treatment, and particularly discloses a sodium sulfate circulation process for concentrating acidified oil wastewater. The process comprises the following steps: heating the acidified oil wastewater, adding anhydrous sodium sulfate into the acidified oil wastewater until the acidified oil wastewater is saturated, then cooling, crystallizing and separating to obtain a solid I and a concentrated solution I, detecting indexes of the concentrated solution I, if the indexes do not reach the standard, repeatedly heating the concentrated solution I, adding anhydrous sodium sulfate until the acidified oil wastewater is saturated, and then cooling, crystallizing and separating to obtain the acidified oil wastewater. And repeating the steps until the concentrated solution I reaches the standard. Freezing, crystallizing and separating the concentrated solution I to obtain a solid II and a concentrated solution II; the separated solid I and solid II are washed, heated, evaporated, dried and the like to finally obtain anhydrous sodium sulfate, and a part of the obtained anhydrous sodium sulfate can be recycled in process production. The obtained concentrated solution II can be further treated according to purposes. The process is simple to operate, low in investment and operation cost, free of pollution in the operation process and capable of realizing resource reutilization.

Description

Technical Field

[0001] The invention relates to the field of acidified oil wastewater treatment, and specifically discloses a sodium sulfate circulation process for concentrating acidified oil wastewater. Background Art

[0002] Acidified oil is a basic raw material containing fatty acids and oleic acid obtained by acidification and separation of soap stock, a byproduct of refined vegetable oil. The acidified oil processing process will produce a large amount of high-concentration strong acid wastewater, also known as acidified oil wastewater. The physical and chemical indicators of the wastewater are as follows: sulfate content is about 100,000 mg / L, chemical oxygen demand (COD) is about 80,000-200,000 mg / L, pH value ≤ 2, total phosphorus content is about 5,000-10,000 mg / L, and ammonia nitrogen content is about 600 mg / L. Acidified oil wastewater has the characteristics of low pH value, high COD, high ammonia nitrogen, high phosphorus, high salt content (sodium sulfate), high hardness and high suspended solids. General sewage treatment processes cannot meet the treatment standards at all. If it is discharged directly, it will cause great harm to the environment. With the continuous development of the acidified oil processing industry, the wastewater generated by acidified oil processing in my country has reached 4 million tons throughout the year, and the problem of acidified oil wastewater treatment is becoming increasingly serious.

[0003] At present, most of the methods for treating acidified oil wastewater at home and abroad are biochemical and chemical methods. The biochemical method makes it difficult to cultivate microorganisms due to the high salt content in the water. If water is added for dilution or other methods are used to make the salt content reach the biochemical standard, a high treatment cost is required. When using chemical methods for treatment, the acidified oil wastewater must first be concentrated for subsequent resource treatment and application. The main methods used to concentrate acidified oil wastewater are evaporation and membrane osmosis. Due to the high hardness of acidified oil wastewater, the equipment scaling problem is serious during the evaporation process, which leads to a decrease in equipment operating efficiency and high overall operating costs. When using membrane osmosis to concentrate and treat acidified oil wastewater, due to the characteristics of high COD, high hardness and high suspended solids in acidified oil wastewater, the membrane is prone to clogging. If it is replaced frequently, it will inevitably lead to excessively high treatment costs. Summary of the invention

[0004] In order to overcome the problems of serious scaling, low efficiency, easy equipment clogging, high operating costs and the like in the prior art, the present invention provides a sodium sulfate circulation process for concentrating acidified oil wastewater.

[0005] The technical solution adopted by the present invention to achieve the above-mentioned purpose is: a sodium sulfate circulation process for concentrating acidified oil wastewater, comprising the following steps:

[0006] S1: heating the liquid to be treated and adding anhydrous sodium sulfate thereto until the solution is saturated;

[0007] S2: Cooling the solution, separating after crystallization to obtain solid I and concentrated solution I;

[0008] S3: Detect the physical and chemical indicators of the concentrated solution I. If the indicators do not meet the requirements, repeat steps S1 and S2 until the indicators of the concentrated solution I meet the requirements;

[0009] S4: freezing and crystallizing the concentrated liquid I that meets the standards and then separating to obtain solid II and concentrated liquid II;

[0010] S5: washing the mixture of solid I and solid II with a saturated sodium sulfate solution, and then filtering to obtain a filtrate and solid III;

[0011] S6: heating solid III to obtain a saturated solution and glauber salt I, drying and dehydrating glauber salt I to obtain anhydrous sodium sulfate I, evaporating the obtained saturated solution and the filtrate obtained in step S5 to obtain glauber salt II and a distillate, drying and dehydrating glauber salt II to obtain anhydrous sodium sulfate II is used in step S1, and the distillate is used to prepare the saturated sodium sulfate solution in step S5;

[0012] S7: The concentrated solution II obtained in step S4 is further processed according to different uses.

[0013] Furthermore, the heating temperature of step S1 is 30-50° C., and the heating time is 30-60 min. Preferably, the heating temperature is 40° C., and the heating time is 40 min.

[0014] Furthermore, the cooling temperature of step S2 is 10-20° C., the cooling time is 8-12 hours, and the cooling process is continuously stirred.

[0015] Furthermore, the physical and chemical indicators required for the concentrated solution I in step S3 are pH: 2-3, COD: 150000mg / L-200000mg / L, ammonia nitrogen: 1000mg / L-1500mg / L, and phosphate: 15000mg / L-20000mg / L.

[0016] Furthermore, the freezing temperature of step S4 is 0-5°C, and the freezing time is 4-8h. Preferably, the cooling temperature is 0°C, and the cooling time is 6h. The cooling process is continuously stirred.

[0017] Furthermore, in step S5, the pH of the saturated sodium sulfate solution is 13-14, and the temperature of the saturated sodium sulfate solution is 10-25°C, preferably 20°C.

[0018] Furthermore, the evaporation in step S6 adopts an MVR evaporation process.

[0019] Furthermore, in step S6, the drying temperature of sodium sulphate Ⅰ and sodium sulphate Ⅱ is 100° C., and the drying time is 4-6 hours.

[0020] Furthermore, the physical and chemical indicators of the distillate obtained in step S6 are pH: 5-6, COD≤300 mg / L, ammonia nitrogen≤3 mg / L, and phosphate≤2 mg / L.

[0021] Furthermore, there are four uses for step S7: the first is to use it directly as an organic-inorganic mixed biomass liquid fertilizer; the second is to use it as an external carbon source in a sewage treatment plant; the third is to enter an advanced anaerobic tower as a raw material for producing methane; and the fourth is to use it as a raw material for extracting valuable products.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. In the treatment process of the present invention, anhydrous sodium sulfate is mainly used to combine with water to become Glauber's salt to concentrate the solution. The treatment process and the equipment used are simple, and will not cause scaling, clogging and other problems, and the overall investment and operating costs are low.

[0024] 2. The treatment process of the present invention mainly involves anhydrous sodium sulfate, does not involve the use of other drugs, does not produce any substances that cause secondary pollution to the environment in the treatment process, and anhydrous sodium sulfate can be recycled.

[0025] 3. The present invention extracts sodium sulfate from the wastewater during the concentration process of acidified oil wastewater. The anhydrous sodium sulfate treated by the process has a sulfate content of ≥95%, which can be used as industrial-grade anhydrous sodium sulfate and animal feed. The present invention not only saves operating costs, but also turns waste into treasure, realizes the comprehensive utilization of renewable resources, and generates greater social and economic benefits.

[0026] 4. The salt content of the acidified oil wastewater treated by the treatment process of the present invention is greatly reduced, and a biochemical method can be used for further treatment.

[0027] 5. The concentrated liquid obtained by the present invention has a COD of up to 190,000 mg / L, ammonia nitrogen of 1,600 mg / L, phosphate of 19,000 mg / L, and calcium and magnesium of 1.72% and 1.2% respectively. It can be used as a biomass liquid organic-inorganic mixed fertilizer after a simple pH adjustment to meet the standard. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The sodium sulfate circulation process flow chart of the present invention for concentrating acidified oil wastewater;

[0029] Figure 2 The process flow chart of the treatment process unit of the present invention;

[0030] Figure 3 Schematic diagram of COD changes in acidified oil wastewater after 5 concentration cycles;

[0031] Figure 4Schematic diagram of the changes in ammonia nitrogen in acidified oil wastewater after 5 concentration cycles;

[0032] Figure 5 Schematic diagram of phosphate changes in acidified oil wastewater after 5 concentration cycles;

[0033] In the figure: 1-wastewater pool; 2-wastewater heating-cooling-concentration crystallization unit; 3-concentrate freezing crystallization unit; 4-glauber's salt crystallization pool; 5-glauber's salt pretreatment unit; 6-glauber's salt hot melting unit; 7-hot melting supernatant evaporation unit; 8-hot anhydrous sodium sulfate powder; DETAILED DESCRIPTION

[0034] The present invention is further described in detail below in conjunction with the examples and drawings, but the embodiments of the present invention are not limited thereto. Where specific conditions are not specified in the examples, the experimental detection methods used are all conventional methods, and the reagents or instruments used can be conventional products purchased commercially.

[0035] The acidified oil wastewater used in this embodiment is the acidified oil wastewater randomly obtained from the acidification tank in the fatty acid production process workshop of a certain oil and fat chemical company in Dalian.

[0036] The initial physical and chemical indicators of the acidified oil wastewater to be treated are: pH value is 2.3, chemical oxygen demand (COD) is 38000 mg / L, ammonia nitrogen is 300 mg / L, and phosphate is 4100 mg / L.

[0037] Example 1

[0038] A sodium sulfate circulation process for concentrating acidified oil wastewater comprises the following steps:

[0039] S1: The wastewater to be treated is stored in a wastewater tank, and a heating tube is used to heat the liquid to be treated to 40°C (the solubility of anhydrous sodium sulfate is the highest at this temperature), and anhydrous sodium sulfate is added thereto (the initial industrial grade anhydrous sodium sulfate purity is 99%) and stirred continuously until the solution is saturated;

[0040] S2: Place the saturated wastewater in a crystallization pool and cool it down at 10°C for crystallization. After 1 hour, crystals gradually appear in the wastewater. Stir every half an hour during the crystallization process (to ensure that the crystals are fine particles for subsequent filtration). After 10 hours, the crystals are completely crystallized. Then, the solid-liquid separation is performed through the filtration device. The upper layer is concentrated liquid I, and the lower layer is solid I. The main component of solid I is Glauber's salt.

[0041] S3: Detect the physical and chemical indicators of concentrated solution I and compare them with the required physical and chemical indicator values. The required physical and chemical indicators of concentrated solution I are pH: 2-3, COD: 150000mg / L-200000mg / L, ammonia nitrogen: 1000mg / L-1500mg / L, phosphate: 15000mg / L-20000mg / L. Since the physical and chemical indicators of concentrated solution I did not meet the standards, a second concentration was performed;

[0042] S4: The concentrated solution I is led back to the wastewater tank and heated to 40°C, and anhydrous sodium sulfate is added thereto and stirred continuously until the solution is saturated;

[0043] S5: Place the saturated wastewater in a crystallization pool, cool and crystallize at 10°C, stir continuously during the crystallization process, and complete crystallization for 10 hours. Then pass through a suction filtration device for solid-liquid separation, the upper layer is the concentrated liquid I of the second concentration, and the lower layer is the separated Glauber's salt;

[0044] S6: Continue to test the physical and chemical indicators of the concentrated solution I and compare them with the required physical and chemical indicator values. If the standards are not met, continue to concentrate for the third, fourth and fifth times, and test the physical and chemical indicators of the concentrated solution after concentration. The specific test indicator values ​​are shown in Table 1.

[0045] S7: The concentrated solution I after the fifth concentration was frozen and crystallized at 0°C for 6 hours, with continuous stirring during the process, and then solid-liquid separation was performed through a suction filtration device, the upper layer being the concentrated solution II, and the lower layer being the separated Glauber's salt. The physical and chemical indicators of the concentrated solution II after concentration were tested, and the specific test indicator values ​​are shown in Table 1.

[0046] Table 1. Physical and chemical index test values

[0047]

[0048] S8: using distilled water or distillate to prepare a saturated sodium sulfate solution at 20° C., using sodium hydroxide to adjust the pH of the saturated sodium sulfate solution to 13, and then using the saturated solution to rinse and soak the thenardite separated in each concentration process, and then filtering after a period of time, and obtaining a filtrate and relatively pure thenardite after rinsing and filtering;

[0049] S9: Place the obtained Glauber's salt in a heating device (adjust the temperature to 65°C) and heat-melt for a period of time to obtain hot saturated sodium sulfate supernatant and hot glauber's salt I. Heat glauber's salt I to 100°C, dry and dehydrate for 5 hours to obtain anhydrous sodium sulfate I. The saturated sodium sulfate solution on the upper layer and the filtrate obtained in step S8 are input into the MVR evaporation equipment for evaporation to obtain glauber's salt II and distillate. Heat glauber's salt II to 100°C, dry and dehydrate for 5 hours to obtain anhydrous sodium sulfate II, which can be recycled in step S1. The obtained distillate can be used to configure the saturated sodium sulfate solution in step S8, wherein the physical and chemical indicators of the distillate are pH: 5-6, COD≤300mg / L, ammonia nitrogen≤3mg / L, and phosphate≤2mg / L. The anhydrous sodium sulfate obtained by this process has a sulfate content of ≥95%, which can be used as industrial-grade anhydrous sodium sulfate and animal feed.

[0050] S10: The concentrated liquid II obtained in step S7 is further processed according to different uses. There are four uses: the first is to use it directly as an organic-inorganic mixed biomass liquid fertilizer; the second is to use it as an external carbon source for sewage treatment plants; the third is to enter the advanced anaerobic tower as a raw material for producing methane; the fourth is to use it as a raw material for extracting valuable products.

[0051] The concentrated liquid in the first concentrated liquid water tank can be used as a biomass liquid organic-inorganic mixed fertilizer. The concentrated liquid II obtained in this embodiment contains COD up to 190000 mg / L, ammonia nitrogen 1600 mg / L, phosphate 19000 mg / L, calcium and magnesium 1.72% and 1.2% respectively. After the pH of the COD concentrated liquid is adjusted according to the index requirements of the liquid organic-inorganic mixed fertilizer, it can be used directly.

[0052] The second is to use it as an external carbon source for sewage treatment plants. When acidified oil wastewater concentrate is used as an external carbon source for sewage treatment plants, the concentrate needs to be passed through a desalination device to separate the salt ions in the water, and then the high COD concentrated water is dephosphorized and the pH is adjusted using a chemical method to obtain a purer COD concentrate, which can be used as a carbon source for sewage treatment plants.

[0053] The third method is to produce methane for use as energy. The concentrated acidified oil wastewater is fed into an advanced anaerobic tower for treatment. The advanced anaerobic tower is preferably an IC anaerobic tower, but it can also be other forms of anaerobic equipment. The IC anaerobic reactor is a highly efficient multi-stage internal circulation reactor. The mud-water mixture inside the reactor is fully mixed with the methane produced to improve the efficiency of COD degradation. The produced methane is stored and used as energy. The multi-stage internal circulation reactor is used to fully mix the mud-water mixture inside the reactor with the methane produced to improve the efficiency of COD degradation. The produced methane is stored and used as energy.

[0054] The fourth is to extract valuable products, such as industrial crude glycerin. When high COD concentrated water is used for distillation to extract valuable products, direct distillation can be performed based on the different physical and chemical properties of the organic matter that provides the COD.

[0055] Example 2

[0056] A sodium sulfate circulation process for concentrating acidified oil wastewater comprises the following steps:

[0057] S1: The wastewater to be treated is stored in a wastewater tank, and a heating tube is used to heat the liquid to be treated to 40°C (the solubility of anhydrous sodium sulfate is the highest at this temperature), and anhydrous sodium sulfate is added thereto (the initial industrial grade anhydrous sodium sulfate purity is 99%) and stirred continuously until the solution is saturated;

[0058] S2: Place the saturated wastewater in a crystallization pool and cool it down at 20°C for crystallization. After 1 hour, crystals gradually appear in the wastewater. Stir every half an hour during the crystallization process (to ensure that the crystals are fine particles for subsequent filtration). After 10 hours, the crystals are completely crystallized. Then, the solid-liquid separation is performed through the filtration device. The upper layer is concentrated liquid I, and the lower layer is solid I. The main component of solid I is Glauber's salt.

[0059] S3: Detecting the physical and chemical indices of the concentrated solution I. For comparison with Example 1, the second, third, fourth and fifth concentrations were also performed, and the physical and chemical indices of the concentrated solution after concentration were detected. The specific detection index values ​​are shown in Table 2.

[0060] S7: The concentrated solution I after the fifth concentration was frozen and crystallized at 0°C for 6 hours, with continuous stirring during the process, and then solid-liquid separation was performed through a suction filtration device, the upper layer being the concentrated solution II, and the lower layer being the separated Glauber's salt. The physical and chemical indicators of the concentrated solution II after concentration were tested, and the specific test indicator values ​​are shown in Table 2.

[0061] Table 2. Physical and chemical index test values

[0062]

[0063] S8: using distilled water or distillate to prepare a saturated sodium sulfate solution at 20° C., using sodium hydroxide to adjust the pH of the saturated sodium sulfate solution to 13, and then using the saturated solution to rinse the sodium sulfate separated in the soaking and concentration process, and then filtering after a period of time, and obtaining a filtrate and relatively pure sodium sulfate after rinsing and filtering;

[0064] S9: At this time, the Glauber's salt is placed in a heating device (the temperature is adjusted to 65°C), and after a period of heat melting, a hot saturated sodium sulfate supernatant and hot glauber's salt I are obtained. The glauber's salt I is heated to 100°C, dried and dehydrated for 5 hours to obtain anhydrous sodium sulfate I. The saturated sodium sulfate solution on the upper layer and the filtrate obtained in step S8 are input into the MVR evaporation equipment for evaporation to obtain glauber's salt II and distillate. The glauber's salt II is heated to 100°C, dried and dehydrated for 5 hours, and anhydrous sodium sulfate II is used in step S1. The distillate is used to prepare the saturated sodium sulfate solution in step S8, wherein the physical and chemical indicators of the distillate are pH: 5-6, COD≤300mg / L, ammonia nitrogen≤3mg / L, and phosphate≤2mg / L. The anhydrous sodium sulfate obtained by this process has a sulfate content of ≥95%, which can be used as industrial-grade anhydrous sodium sulfate and animal feed.

[0065] The values ​​of the physical and chemical indicators of the concentrated solution obtained in each of Example 1 and Example 2 are obtained by Figure 3 , Figure 4 and Figure 5 It can be seen from the figure that the lower the cooling temperature, the better the effect of the concentration treatment.

Claims

1. A sodium sulfate circulation process for concentrating acidified oil wastewater, characterized in that: The following steps are involved: S1: heating the liquid to be treated and adding anhydrous sodium sulfate thereto until the solution is saturated; S2: Cooling the solution, crystallizing and separating to obtain solid I and concentrated solution I; S3: Detect the physical and chemical indicators of the concentrated solution I. If the indicators do not meet the requirements, repeat steps S1 and S2 until the indicators of the concentrated solution I meet the requirements; S4: freezing and crystallizing the concentrated liquid I that meets the standards and separating them to obtain solid II and concentrated liquid II; S5: washing the mixture of solid I and solid II with a saturated sodium sulfate solution, and then filtering to obtain a filtrate and solid III; S6: heating solid III to obtain a saturated solution and glauber salt I, drying and dehydrating glauber salt I to obtain anhydrous sodium sulfate I, evaporating the obtained saturated solution and the filtrate obtained in step S5 to obtain glauber salt II and a distillate, drying and dehydrating glauber salt II to obtain anhydrous sodium sulfate II is used in step S1, and the distillate is used to prepare the saturated sodium sulfate solution in step S5; S7: The concentrated solution II obtained in step S4 is further processed according to different uses.

2. The sodium sulfate circulation process for concentrating acidified oil wastewater according to claim 1, characterized in that: The heating temperature of step S1 is 30-50° C., and the heating time is 30-60 min. Preferably, the heating temperature is 40° C., and the heating time is 40 min.

3. The sodium sulfate circulation process for concentrating acidified oil wastewater according to claim 1, characterized in that: The cooling temperature of step S2 is 10-20° C., the cooling time is 8-12 hours, and the cooling process is continuously stirred.

4. The sodium sulfate circulation process for concentrating acidified oil wastewater according to claim 1, characterized in that: The physical and chemical indicators required for the concentrated solution I in step S3 are pH: 2-3, COD: 150000mg / L-200000mg / L, ammonia nitrogen: 1000mg / L-1500mg / L, phosphate: 15000mg / L-20000mg / L.

5. The sodium sulfate circulation process for concentrating acidified oil wastewater according to claim 1, characterized in that: The freezing temperature of step S4 is 0-5°C, and the freezing time is 4-8h. The preferred cooling temperature is 0°C, and the cooling time is 6h. The cooling process is continuously stirred.

6. The sodium sulfate circulation process for concentrating acidified oil wastewater according to claim 1, characterized in that: The pH of the saturated sodium sulfate solution in step S5 is 13-14, and the temperature of the saturated sodium sulfate solution is 10-25°C, preferably 20°C.

7. The sodium sulfate circulation process for concentrating acidified oil wastewater according to claim 1, characterized in that: The evaporation in step S6 adopts the MVR evaporation process.

8. The sodium sulfate circulation process for concentrating acidified oil wastewater according to claim 1, characterized in that: In step S6, the drying temperature of sodium sulphate Ⅰ and sodium sulphate Ⅱ is 100° C., and the drying time is 4-6 hours.

9. The sodium sulfate circulation process for concentrating acidified oil wastewater according to claim 1, characterized in that: The physical and chemical indicators of the distillate obtained in step S6 are pH: 5-6, COD≤300 mg / L, ammonia nitrogen≤3 mg / L, and phosphate≤2 mg / L.

10. The sodium sulfate circulation process for concentrating acidified oil wastewater according to claims 1-9, characterized in that: There are four uses for step S7: the first is to use it directly as an organic-inorganic mixed biomass liquid fertilizer; the second is to use it as an external carbon source for sewage treatment plants; the third is to enter an advanced anaerobic tower as a raw material for producing methane; and the fourth is to use it as a raw material for extracting valuable products.

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