Micro-nano bubble reinforced alkaline residue wastewater resourceful treatment system and method

Abstract

The invention belongs to the field of petrochemical engineering, and relates to a micro-nano bubble reinforced alkaline residue wastewater resourceful treatment system and a micro-nano bubble reinforced alkaline residue wastewater resourceful treatment method. The system comprises an alkaline residue wastewater input pipe, a pretreatment unit, a pre-oxidation unit, an oxidation unit and a product separation unit which are connected in sequence, the pretreatment unit comprises at least one pretreatment device, and at least one group of flue gas conveyors are arranged at the bottom of each pretreatment device; the pre-oxidation unit comprises at least one pre-oxidation device and a catalyst conveying pipeline, at least one group of air conveyors are arranged at the bottom of each pre-oxidation device, and the catalyst conveying pipeline is connected with each pre-oxidation device; the oxidation unit comprises a wet oxidation device and an ozone oxidation device which are connected in sequence, an ozone aeration device is arranged at the bottom of the ozone oxidation device, and the flue gas conveyor and the air conveyor are micro-nano bubble generation devices. According to the method, a large amount of S2-ions in the alkaline residue wastewater are separated and removed preferentially, the subsequent Na2CO3 separation process is simplified, and the purity of the product is improved.

Description

Technical Field

[0001] This invention belongs to the field of petrochemicals, specifically relating to a system and method for the resource-based treatment of alkaline slag wastewater enhanced by micro-nano bubble technology. Background Technology

[0002] The ethylene production process requires the use of alkali solutions to remove acidic gases, such as H2S and CO2, from the ethylene cracking gas, resulting in ethylene alkali residue wastewater. This wastewater contains large amounts of sulfides and carbonates, has a high COD, and is classified as high-salt organic wastewater. External treatment as hazardous waste within the plant significantly increases operating costs. For in-house salt recovery processes, the high salt content of the ethylene alkali residue wastewater inhibits the biological degradation of COD. Therefore, COD is often treated by oxidation, which inevitably removes sulfur dioxide (S) from the alkali residue wastewater. 2- Ions oxidized to SO4 2- and SO3 2- Subsequently, during the salt separation and recovery process, it is necessary to separate and recover Na2CO3 and Na2SO4. Since the solubility of the two is similar and their content in ethylene alkali residue wastewater is also similar, the separation is difficult and the purity of the separated product is limited.

[0003] CN105645441A discloses a method for producing soda ash and anhydrous sodium sulfate from cyclohexanone saponification waste alkaline solution. The method includes processes such as evaporation and concentration, incineration, dissolution, filtration, carbonization, drying, calcination, secondary dissolution, secondary filtration, cooling, and crystallization, which can separate and recover sodium carbonate and sodium sulfate. However, this method uses waste gas rich in CO2 (85-95%), requiring CO2 enrichment, and the process requires a high amount of sulfuric acid for sodium sulfate recovery, resulting in high process costs and requiring further improvement in economic efficiency.

[0004] CN114715921A discloses a method for high-value conversion of mixed sodium salts. The method includes dissolution, metathesis, freeze crystallization, secondary dissolution, and secondary metathesis processes, which can recover sodium carbonate and sodium sulfate. However, the process increases costs due to the additional introduction of mixed ammonium bicarbonate or ammonia gas, and the generation of ammonium sulfate during the process leads to reduced product purity and lower economic efficiency. Summary of the Invention

[0005] Ethylene alkali residue wastewater is a high-salt organic wastewater from the petrochemical industry, which is difficult to treat, as the valuable salt resources are difficult to separate and the purity of the separated products is limited. To address the challenges in the treatment and resource recovery of ethylene alkali residue, this invention provides a micro-nano bubble-enhanced system and method for the resource recovery treatment of alkali residue wastewater. This system utilizes micro-nano bubbles to enhance the pretreatment and pre-oxidation processes of ethylene alkali residue wastewater, preferentially separating and removing large amounts of sulfur from the wastewater. 2- Ions simplify the subsequent Na2CO3 separation process and improve product purity.

[0006] To achieve the above objectives, a first aspect of the present invention provides a system for the resource-based treatment of alkaline residue wastewater enhanced by micro-nano bubbles, the system comprising an alkaline residue wastewater inlet pipe, a pretreatment unit, a pre-oxidation unit, an oxidation unit, and a product separation unit connected in sequence.

[0007] The preprocessing unit includes at least one preprocessing device, and each preprocessing device has a bottom;

[0008] The pre-oxidation unit includes at least one pre-oxidation device and a catalyst delivery pipeline. At least one set of air conveyors is provided at the bottom of each pre-oxidation device, and the catalyst delivery pipeline is connected to each pre-oxidation device.

[0009] The oxidation unit includes a wet oxidation device and an ozone oxidation device connected in sequence, and the ozone oxidation device is equipped with an ozone aeration device at the bottom.

[0010] The product separation unit includes a concentration evaporation device and a freeze crystallization device connected in sequence;

[0011] Both the flue gas conveyor and the air conveyor are micro-nano bubble generators.

[0012] A second aspect of the present invention provides a method for the resource recovery treatment of alkaline sludge wastewater enhanced by micro-nano bubble technology, which employs the aforementioned system for the resource recovery treatment of alkaline sludge wastewater enhanced by micro-nano bubble technology, and includes the following steps:

[0013] S1: Input the alkaline wastewater into the pretreatment unit, and use a flue gas conveyor to transport the treated exhaust gas from the plant to pretreat the alkaline wastewater.

[0014] S2: The pretreated alkaline wastewater is transported to the pre-oxidation unit, a catalyst is added, and air is continuously supplied through an air conveyor to complete the pre-oxidation process of the alkaline wastewater.

[0015] S3: The pre-oxidized wastewater is transported to the oxidation unit for wet oxidation and ozone catalytic oxidation to remove COD from the wastewater;

[0016] S4: The oxidized alkaline residue wastewater enters the concentration and evaporation device to obtain concentrated liquid. The concentrated liquid is then separated and recovered from the wastewater by the freeze crystallization device.

[0017] The present invention has the following advantages:

[0018] (1) This invention employs a pretreatment unit and a pre-oxidation unit enhanced with micro-nano bubbles to preferentially separate and remove a large amount of sulfur from alkaline residue wastewater. 2- Ions simplify the subsequent Na2CO3 separation process and improve product purity.

[0019] (2) The present invention simultaneously recovers valuable products elemental sulfur and sodium carbonate, thereby improving the economic performance of alkaline residue wastewater treatment.

[0020] (3) This invention utilizes CO2 in waste gas to improve the content and purity of sodium carbonate recovered from alkaline residue wastewater.

[0021] (4) The present invention enhances the mass transfer process of micro-nano bubbles, improves the CO2 absorption and emission reduction efficiency, and improves the quality of sodium carbonate products.

[0022] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0023] Exemplary embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

[0024] Figure 1 A schematic diagram of an apparatus according to a specific embodiment of the present invention is shown.

[0025] Figure 2 A top view of a micro / nano bubble generator according to a specific embodiment of the present invention is shown.

[0026] Figure 3 The diagram shows a front view of a micro / nano bubble generator according to a specific embodiment of the present invention.

[0027] Figure 4 The diagram shows a front view of the gas-liquid mixer structure in a micro / nano bubble generator according to a specific embodiment of the present invention.

[0028] Figure 5 A schematic diagram of the distribution of a micro / nano bubble generator according to a specific embodiment of the present invention is shown.

[0029] 1. Alkali residue wastewater inlet pipe; 2. Pretreatment unit 1; 3. Micro / nano bubble generator 1; 4. Flue gas conveying pipe; 5. Pretreatment unit conveying pipe; 6. Pretreatment unit 2; 7. Micro / nano bubble generator 2; 8. Pretreatment wastewater conveying pipe; 9. Pre-oxidation unit 1; 10. Micro / nano bubble generator 3; 11. Air conveying pipe; 12. Elemental sulfur recovery pipe 1; 13. Elemental sulfur purification unit; 14. Elemental sulfur recovery pipe 2; 15. Pre-oxidation unit 2; 16. Catalyst. 17. Pre-oxidation device conveying pipe; 18. No. 4 micro-nano bubble generator; 19. Pre-treated wastewater conveying pipe; 20. Wet oxidation device; 21. Wet oxidation wastewater conveying pipe; 22. Ozone conveying pipe; 23. Ozone aeration device; 24. Ozone oxidation device; 25. Ozone wastewater conveying pipe; 26. Steam recovery pipe; 27. Concentrated evaporation device; 28. Concentrated liquid conveying pipe; 29. ​​Freeze crystallization separation device; 30. Complex salt concentrated liquid discharge pipe; 31. Na2CO3 product recovery pipe.

[0030] A1. Wastewater inlet pipe of micro / nano bubble generator; A2. Waste gas inlet pipe of micro / nano bubble generator; A3. Wastewater diversion pipe of micro / nano bubble generator; A4. Gas-liquid mixer; A5. Gas-liquid outlet; α. Hyperbola angle; β. Monobola angle. Detailed Implementation

[0031] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0032] To achieve the above objectives, a first aspect of the present invention provides a system for the resource-based treatment of alkaline residue wastewater enhanced by micro-nano bubbles, the system comprising an alkaline residue wastewater inlet pipe, a pretreatment unit, a pre-oxidation unit, an oxidation unit, and a product separation unit connected in sequence.

[0033] The pretreatment unit includes at least one pretreatment device, and each pretreatment device is provided with at least one set of flue gas conveyors at its bottom;

[0034] The pre-oxidation unit includes at least one pre-oxidation device and a catalyst delivery pipeline. At least one set of air conveyors is provided at the bottom of each pre-oxidation device, and the catalyst delivery pipeline is connected to each pre-oxidation device.

[0035] The oxidation unit includes a wet oxidation device and an ozone oxidation device connected in sequence, and the ozone oxidation device is equipped with an ozone aeration device at the bottom.

[0036] The product separation unit includes a concentration evaporation device and a freeze crystallization device connected in sequence;

[0037] Both the flue gas conveyor and the air conveyor are micro-nano bubble generators.

[0038] According to the present invention, preferably, the micro / nano bubble generator is provided with a liquid input pipe and a gas input pipe. At least two sets of liquid diversion pipes are provided at one end of the liquid input pipe. A gas inlet is provided near the liquid diversion pipe of the liquid input pipe. The gas input pipe is connected to the gas inlet. A gas-liquid mixer is provided at the end of each liquid diversion pipe. A gas-liquid outlet is provided on the gas-liquid mixer.

[0039] According to the present invention, preferably, the micro-nano bubble generator is further provided with a pump for conveying the alkaline residue wastewater in the pretreatment unit to the liquid input pipe.

[0040] According to the present invention, preferably, the gas-liquid outlet has a concave structure, and the angle between the tangent of the protruding structure at the gas-liquid outlet and the oblique line of the concave structure is defined as the α hyperbolic angle, and the angle between the tangent of the protruding structure at the gas-liquid outlet and the horizontal line is defined as the β single-curve angle. The α hyperbolic angle is 15-45°, preferably 30-40°, and the β single-curve angle is 1-15°, preferably 5-10°.

[0041] According to the present invention, preferably, the ratio of the diameter of the gas input pipe to the diameter of the liquid input pipe is 1:6 to 10.

[0042] According to the present invention, preferably, the product separation unit comprises a dual-membrane concentration device, a concentration evaporation device, and a freeze crystallization device connected in sequence.

[0043] According to the present invention, preferably, when there are ≥2 micro / nano bubble generating devices, they are arranged in a staggered pattern.

[0044] According to the present invention, preferably, the system further includes an elemental sulfur purification unit, which is connected to the pre-oxidation device via an elemental sulfur recovery pipe.

[0045] According to the present invention, preferably, the concentration evaporation device is further provided with a steam recovery pipe; the freeze crystallization separation device is provided with a double salt concentrate discharge pipe and a Na2CO3 product recovery pipe.

[0046] A second aspect of the present invention provides a method for the resource recovery treatment of alkaline sludge wastewater enhanced by micro-nano bubble technology, which employs the aforementioned system for the resource recovery treatment of alkaline sludge wastewater enhanced by micro-nano bubble technology, and includes the following steps:

[0047] S1: Input the alkaline wastewater into the pretreatment unit, and use a flue gas conveyor to transport the treated exhaust gas from the plant to pretreat the alkaline wastewater.

[0048] S2: The pretreated alkaline wastewater is transported to the pre-oxidation unit, a catalyst is added, and air is continuously supplied through an air conveyor to complete the pre-oxidation process of the alkaline wastewater.

[0049] S3: The pre-oxidized wastewater is transported to the oxidation unit for wet oxidation and ozone catalytic oxidation to remove COD from the wastewater;

[0050] S4: The oxidized alkaline residue wastewater enters the concentration and evaporation device to obtain concentrated liquid. The concentrated liquid is then separated and recovered from the wastewater by the freeze crystallization device.

[0051] According to the present invention, preferably, in step S1, the volumetric flow rate ratio of the flue gas to the alkaline residue wastewater is (50-1000):1, more preferably (200-400):1.

[0052] Preferably, the volumetric flow rate ratio of alkaline wastewater to flue gas in the flue gas conveyor is (1-10):1, and more preferably (5-8):1.

[0053] Preferably, the flue gas is the exhaust gas emitted after treatment within the factory area.

[0054] According to the present invention, preferably, in step S2, the pH of the pretreated alkaline residue wastewater is 7.0-10.0; more preferably 8.0-9.0.

[0055] Preferably, the catalyst is selected from at least one of cobalt phthalocyanine, iron phthalocyanine, and nickel phthalocyanine sulfonates; the concentration of the catalyst in the reaction system is 3-30 mg / L;

[0056] Preferably, the volumetric flow rate ratio of wastewater to air in the air conveyor is (1-10):1, more preferably (5-8):1.

[0057] According to the present invention, preferably, in step S2, S in the wastewater 2- and HS 2- Oxidized to S 0 The sulfur is recovered through a sulfur recovery pipe and sent to a sulfur purification unit for purification and separation to obtain sulfur products.

[0058] According to the present invention, preferably, in step S3, the conditions for the wet oxidation reaction include: a temperature of 110-160°C, a pressure of 3-12 MPa, and a gas-liquid ratio of (15-40):1.

[0059] Preferably, the ozone concentration in the reaction system of the ozone catalytic oxidation reaction is 5-13 mg / L.

[0060] According to the present invention, preferably, in step S3, the COD concentration after treatment is less than 100 mg / L.

[0061] According to the present invention, preferably, in step S4, the temperature of the evaporation and concentration device is controlled at 80-100°C, and the temperature of the freezing and crystallization device is controlled at 0-15°C.

[0062] Preferably, the oxidized alkaline residue wastewater first enters a dual-membrane thickener for preliminary thickening, and then enters a thickening evaporation unit.

[0063] In this invention, the oxidized alkaline residue wastewater can be directly fed into the concentration evaporation device or first undergo preliminary concentration using a double-membrane method before entering the concentration evaporation device to obtain concentrated liquid. Directly feeding into the concentration evaporation device requires less investment but has higher operating costs, while undergoing preliminary concentration using a double-membrane method before entering the concentration evaporation device requires more investment but has lower operating costs. There is no significant difference between the two methods in terms of the purity and yield of the byproduct Na2CO3.

[0064] The present invention will be further described below with reference to the embodiments, but the scope of the present invention is not limited to these embodiments.

[0065] Example 1

[0066] This embodiment provides a system for the resource-based treatment of alkaline residue wastewater enhanced by micro-nano bubble technology, such as... Figure 1 As shown, the system includes, in sequence, an alkaline residue wastewater inlet pipe 1, a first pretreatment device 2, a pretreatment device conveying pipe 5, a second pretreatment device 6, a pretreatment wastewater conveying pipe 8, a first pre-oxidation device 9, a pre-oxidation device conveying pipe 17, a second pre-oxidation device 15, a pretreatment wastewater conveying pipe 19, a wet oxidation device 20, a wet oxidation wastewater conveying pipe 21, an ozone oxidation device 24, an ozone wastewater conveying pipe 25, a concentration evaporation device 27, a concentrated liquid conveying pipe 28, a freeze crystallization separation device 29, and a Na2CO3 product recovery pipe 31.

[0067] Both the No. 1 pretreatment unit 2 and the No. 2 pretreatment unit 6 are equipped with flue gas conveyors, which are connected to the flue gas conveying pipe 4. Both the No. 1 pre-oxidation unit 9 and the No. 2 pre-oxidation unit 15 are equipped with air conveyors, which are connected to the air conveying pipe 11. Both the flue gas conveyors and the air conveyors are micro / nano bubble generators. Figure 2 and Figure 3 As shown, the micro / nano bubble generator is equipped with a wastewater inlet pipe A1 and a waste gas inlet pipe A2. A wastewater diversion pipe A3 is connected to one end of the wastewater inlet pipe A1, and a gas inlet is located near the wastewater diversion pipe A3. The waste gas inlet pipe A2 is connected to the gas inlet. A gas-liquid mixer A4 is located at the end of the wastewater inlet pipe A1, and a gas-liquid outlet A5 is provided on the gas-liquid mixer. Figure 4As shown, the gas-liquid outlet A5 has a concave structure. The angle between the tangent of the protruding structure at the gas-liquid outlet and the oblique line of the concave structure is defined as the α-hyperbolic angle, and the angle between the tangent of the protruding structure at the gas-liquid outlet and the horizontal line is defined as the β-singlebolic angle. The α-hyperbolic angle is 33°, and the β-singlebolic angle ranges from 6°. Figure 5 As shown, each pretreatment is equipped with four micro-nano bubble generators, arranged in a staggered pattern.

[0068] The No. 1 pre-oxidation unit 9 and the No. 2 pre-oxidation unit 15 are respectively equipped with a No. 1 elemental sulfur recovery pipe 12 and a No. 2 elemental sulfur recovery pipe 14, both of which are connected to the elemental sulfur purification unit 13. The ozone oxidation unit 24 is equipped with an ozone aeration device 23, which is connected to the ozone delivery pipe 22. The concentration evaporation unit 27 is also equipped with a steam recovery pipe 26; the freeze crystallization separation unit 29 is also equipped with a double salt concentrate discharge pipe 30.

[0069] The water quality conditions of the treated ethylene alkali residue wastewater are as follows: temperature 21℃, TDS 78632mg / L, total alkalinity (calculated as CaCO3) 7539mg / L, NaOH 3.3%, Na2CO3 2.2%, Na2S (after conversion of sulfur-containing substances such as Na2S2O3 and Na2SO4) 4.3%, COD 47525mg / L, TOC 1072mg / L, petroleum hydrocarbons 21mg / L, and other metal elements (Fe, Ca, Mg, etc.) 2.5mg / L;

[0070] A method for resource recovery treatment of alkaline residue wastewater enhanced by micro-nano bubbles includes the following steps:

[0071] S1: Wastewater Pretreatment

[0072] The treated ethylene alkali residue wastewater was diverted at a rate of 0.5m... 3 A flow rate of 150 m³ / h is supplied to Pretreatment Unit 1 (2) and Pretreatment Unit 2 (6). Micro-nano bubble generators 3 (3) and 7 (7) are used to transport the treated flue gas from the plant area. All gas in the micro-nano bubble generators originates from the flue gas, and the liquid is the ethylene alkali residue wastewater treated in the pretreatment units. 3The system utilizes CO2 from flue gas to convert Na2CO3 and NaOH in ethylene alkali residue wastewater into NaHCO3. As the NaHCO3 / Na2CO3 ratio increases, the pH of the ethylene alkali residue wastewater decreases. The pretreatment unit consists of two pretreatment towers to control the residence time of the ethylene alkali residue wastewater, ensuring that the pretreated effluent pH reaches 8.6. The treated wastewater circulates within the micro-nano bubble generator through the wastewater inlet pipe A1. The flue gas enters the micro-nano bubble generator through the exhaust gas inlet pipe A2. The wastewater, carrying the exhaust gas, passes through the wastewater diversion pipe A3 and enters the gas-liquid mixers A4 on both sides. After mixing in the gas-liquid mixers A4, micro-nano bubbles are generated and discharged through the gas-liquid outlet A5, carried by the wastewater. The volumetric flow ratio of wastewater to flue gas in the wastewater inlet pipe A1 and the exhaust gas inlet pipe A2 is 8:1, achieving a high proportion of wastewater recirculation and enhancing the efficiency of CO2 absorption.

[0073] S2: Wastewater pre-oxidation

[0074] The pretreated effluent is transported to pre-oxidation unit 9 (No. 1) and pre-oxidation unit 15 (No. 2), while dinuclear cobalt phthalocyanine sulfonate is added at a flow rate of 12 g / h. Air is bubbled into the bottom through micro-nano bubble generators 10 (No. 3) and 18 (No. 4), with all gas in the micro-nano bubble generators derived from air. The liquid is the ethylene alkali residue wastewater treated in the pre-oxidation unit, with O2 provided to the wastewater through the micro-nano bubble generators to complete the S-reduction process in the wastewater. 2- and HS 2- Oxidized to S 0 The sulfur is then recovered to the elemental sulfur purification unit 13 through the first elemental sulfur recovery pipe 12 and the second elemental sulfur recovery pipe 14, where it is purified and separated to obtain elemental sulfur products.

[0075] S3: Wastewater oxidation

[0076] The pre-oxidized wastewater is transported to wet oxidation unit 20 and ozone oxidation unit 24, where COD in the wastewater is degraded and residual Na2S, Na2SO3, and Na2S2O3 after pre-oxidation are oxidized to Na2SO4, and NaHCO3 is thermally decomposed to Na2CO3. The wet oxidation unit 20 has a wet oxidation temperature of 120℃, a pressure of 6MPa, and a gas-liquid ratio of 30:1. The ozone concentration in the ozone oxidation unit 24 is 10mg / L. After treatment, the COD reaches 63mg / L, and the petroleum hydrocarbons are 0mg / L.

[0077] S4: Salt Recovery

[0078] The oxidized wastewater is transported to the salt recovery unit, which mainly consists of an evaporation and concentration unit 27 and a freeze crystallization unit 29. The evaporation and concentration unit 27 is controlled at a temperature of 90°C, and the freeze crystallization unit 29 is controlled at a temperature of 10°C. Solid Na2CO3 is obtained by centrifugation. The total alkali content (based on Na2CO3, on a dry basis) of the obtained Na2CO3 is 99.1%, the total alkali content (based on Na2CO3, on a wet basis) is 97.5%, and the sodium chloride (based on NaCl, on a dry basis) is 0.67%, which meets the requirements of Class II Grade I product in GB / T 210-2022.

[0079] Example 2

[0080] The system used in this implementation is the same as that in Implementation 1. The water quality conditions of the treated ethylene alkali residue wastewater are as follows: temperature 26℃, TDS 72685mg / L, total alkalinity (calculated as CaCO3) 6358mg / L, NaOH 3.0%, Na2CO3 2.4%, Na2S (after conversion of sulfur-containing substances such as Na2S2O3 and Na2SO4) 3.8%, COD 48277mg / L, TOC 1086mg / L, petroleum hydrocarbons 11mg / L, and other metal elements (Fe, Ca, Mg, etc.) 2.1mg / L.

[0081] A method for resource recovery treatment of alkaline residue wastewater enhanced by micro-nano bubbles includes the following steps:

[0082] S1: Wastewater Pretreatment

[0083] The treated ethylene alkali residue wastewater was discharged at a rate of 0.03m³. 3 A flow rate of / h is fed into Pretreatment Unit 1 (2) and Pretreatment Unit 2 (6). Micro-nano bubble generators 3 (3) and 7 (7) are used to transport the treated exhaust gas from the plant area. All gas in the micro-nano bubble generators originates from the exhaust gas, and the liquid is the ethylene alkali residue wastewater treated in the pretreatment units. The flue gas flow rate is 6m³ / h. 3The system utilizes CO2 from flue gas to convert Na2CO3 and NaOH in ethylene alkali residue wastewater into NaHCO3. As the NaHCO3 / Na2CO3 ratio increases, the pH of the ethylene alkali residue wastewater decreases. The pretreatment unit consists of two pretreatment towers to control the residence time of the ethylene alkali residue wastewater, ensuring that the pretreated effluent pH reaches 8.6. The treated wastewater circulates within the micro-nano bubble generator through the wastewater inlet pipe A1. The flue gas enters the micro-nano bubble generator through the exhaust gas inlet pipe A2. The wastewater, carrying the exhaust gas, passes through the wastewater diversion pipe A3 and enters the gas-liquid mixers A4 on both sides. After mixing in the gas-liquid mixers A4, micro-nano bubbles are generated and discharged through the gas-liquid outlet A5, carried by the wastewater. The volumetric flow ratio of wastewater to flue gas in the wastewater inlet pipe A1 and the exhaust gas inlet pipe A2 is 5:1, achieving a high proportion of wastewater recirculation and enhancing the efficiency of CO2 absorption.

[0084] S2: Wastewater pre-oxidation

[0085] The pretreated effluent is transported to pre-oxidation unit 9 (No. 1) and pre-oxidation unit 15 (No. 2), while dinuclear cobalt phthalocyanine sulfonate is added at a flow rate of 40 mg / h. Air is bubbled into the bottom through micro-nano bubble generators 10 (No. 3) and 18 (No. 4), with all gas in the micro-nano bubble generators derived from air. The liquid is the ethylene alkali residue wastewater treated in the pre-oxidation unit, with O2 provided to the wastewater through the micro-nano bubble generators to complete the S-reduction process in the wastewater. 2- and HS 2- Oxidized to S 0 The sulfur is then recovered to the elemental sulfur purification unit 13 through the first elemental sulfur recovery pipe 12 and the second elemental sulfur recovery pipe 14, where it is purified and separated to obtain elemental sulfur products.

[0086] S3: Wastewater oxidation

[0087] The pre-oxidized wastewater is transported to wet oxidation unit 20 and ozone oxidation unit 24 to degrade COD in the wastewater and oxidize the residual Na2S, Na2SO3, and Na2S2O3 after pre-oxidation to Na2SO4, and thermally decompose NaHCO3 to Na2CO3. The wet oxidation unit 20 has a wet oxidation temperature of 120℃, a pressure of 6MPa, and a gas-liquid ratio of 30:1. The ozone concentration in the ozone oxidation unit 24 is 12mg / L.

[0088] S4: Salt Recovery

[0089] The oxidized wastewater is transported to the salt recovery unit, which mainly consists of an evaporation and concentration unit 27 and a freeze crystallization unit 29. The temperature of the evaporation and concentration unit 27 is controlled at 93°C, and the temperature of the freeze crystallization unit 29 is controlled at 14°C. Solid Na2CO3 is obtained by centrifugation. The total alkali content (based on Na2CO3, on a dry basis) of the obtained Na2CO3 is 99.0%, the total alkali content (based on Na2CO3, on a wet basis) is 97.5%, and the sodium chloride (based on NaCl, on a dry basis) is 0.73%, which meets the requirements of Class II Grade I product in GB / T 210-2022.

[0090] Examples A1-A9, Comparative Example 1

[0091] The same process and steps as in Example 2 are used, but the structure at the outlet of the gas-liquid mixer in step S1 is different. In Example 2, the outlet of gas-liquid mixer A4 gradually narrows along the water outlet direction, exhibiting a convex structure along the water outlet direction, but a concave structure at the outlet. This convex and concave structure at the outlet forces the wastewater in the pretreatment device to change the water outlet from a vertically upward straight line to a circular spiral shape along the concave structure at the outlet, generating a stronger hydraulic disturbance. The tangent of the convex structure at the outlet of the gas-liquid mixer is... The angle between the concave structure and the oblique line is defined as α. hyperbolic angle, and the angle between the tangent of the protruding structure at the outlet of the gas-liquid mixer and the horizontal line is defined as β. single-curve angle. In Example 2, the α. hyperbolic angle is approximately 33°, and the β. single-curve angle is approximately 6°. In Example A, the micro-nano bubble component was replaced, and the structure at the outlet of the gas-liquid mixer A4 was modified. The different outlet structures were compared to see the different effects on the turbulence of wastewater in the pretreatment device, which in turn affected the CO2 absorption efficiency and ultimately the yield and purity of the harvested Na2CO3 product. The corresponding results are shown in Table 1 below.

[0092] Table 1

[0093]

[0094] In Table 1, the β-hyperbolic angle reflects the outlet opening size, and the α-hyperbolic angle reflects the depth of the outlet concave structure. The comparison shows that when the α-hyperbolic angle is within the range of 30-40° and the β-hyperbolic angle is within the range of 5-10°, the process of this invention has a high Na2CO3 recovery rate (above 18.4 g / min) and a purity higher than 99.0%. When the α-hyperbolic angle is too small, the depth of the outlet concave structure is shallow, the vertical water velocity at the outlet is high, and the turbulence effect is poor. When the α-hyperbolic angle is too large, the depth of the outlet concave structure is deep, the outlet helix is ​​too large, and the hydraulic turbulence force on the surrounding area is reduced, resulting in a poorer turbulence effect. Similarly, when the β-hyperbolic angle is too small, the outlet opening size is too small, the vertical water velocity at the outlet is high, and the turbulence effect is poor. When the β-hyperbolic angle is too large, the outlet opening size is too large, the outlet helix is ​​too large, and the hydraulic turbulence force on the surrounding area is reduced, resulting in a poorer turbulence effect.

[0095] Comparing Example 2 with Comparative Example 1, it can be found that the concave outlet design of the gas-liquid mixer in this invention can significantly improve the absorption efficiency of CO2 by wastewater in the pretreatment unit, and increase the recovery amount and purity of Na2CO3 in the process.

[0096] Examples B1-B5, Comparative Example 2

[0097] Using the same process and steps as in Example 1, the flue gas flow rate in the pre-oxidation device was adjusted. The yield and purity of Na2CO3 products corresponding to different ratios of flue gas flow rate to the amount of wastewater treated are shown in Table 2 below.

[0098] Table 2

[0099]

[0100] Table 2 shows that comparing Example 2 with Examples B1-B5 and Comparative Example 2, it can be found that providing flue gas for wastewater pretreatment can enable wastewater to absorb CO2, thereby increasing the yield and purity of Na2CO3 in alkaline residue wastewater. An appropriate flue gas flow rate (the ratio of flue gas flow rate to the amount of wastewater treated is between (200-400):1) can save flue gas and process energy consumption while achieving a better process level, achieving a Na2CO3 recovery rate of more than 18.40 g / min, and the product purity meets the requirements of Class II Grade I in GB / T 210-2022.

[0101] Examples C1 to C9, Comparative Example 3

[0102] Using the same process and steps as in Example 2, the volumetric flow rate ratio of wastewater to flue gas in the micro / nano bubble generator within the pre-oxidation device was adjusted. Correspondingly, the bubble size in the wastewater was measured using a ZetaView instrument, and the corresponding bubble size d was determined. 50The yield and purity results of the Na2CO3 product (50% of the bubble size is smaller than this value) are shown in Table 3 below.

[0103] Table 3

[0104]

[0105]

[0106] In Table 3, in Comparative Example 3, only flue gas is introduced into the micro-nano bubble generator. Compared with Examples 2 and C1-C9, it is found that the present invention uses a micro-nano bubble generator to achieve wastewater recycling. The flue gas forms micro-nano bubbles and mixes with the wastewater, which significantly improves the yield and purity of Na2CO3 product. Comparing Examples C1-C9, it can be found that when the volume flow ratio of wastewater to flue gas in the micro-nano bubble generator is in the range of (5-8):1, the process operates well, and the yield and purity of Na2CO3 product are high. When the volume flow ratio of wastewater to flue gas continues to increase, the improvement effect is limited, and the process energy consumption increases. When the volume flow ratio of wastewater to flue gas is small, the size of the generated bubbles increases, which leads to a decrease in the efficiency of wastewater in absorbing CO2, thereby resulting in a decrease in the yield and purity of the final Na2CO3 product.

[0107] Examples D1-D9, Comparative Example 4

[0108] Using the same process and steps as in Example 2, the contact time between wastewater and flue gas and the residence time of wastewater in the pretreatment unit were adjusted, thereby controlling the pH value of the effluent from the pretreatment unit. The yield and purity of the subsequent Na2CO3 product corresponding to different effluent pH values ​​are shown in Table 4 below.

[0109] Table 4

[0110]

[0111] Table 4 shows that comparing Examples 2 with D1-D5 reveals that adjusting the pH of the effluent from the pretreatment unit can improve the yield and purity of Na2CO3 produced by the process of this invention. When the effluent pH is in the range of 8.0-9.0, the Na2CO3 yield is higher than 18.20 g / min and the purity is higher than 99.0%. When the pH is higher, it indicates that CO2 absorption is limited, and the yield and purity of Na2CO3 decrease. When the pH is further reduced, the effect of improving the yield and purity of Na2CO3 is limited, but it significantly increases the residence time of wastewater in the pretreatment unit. Therefore, this invention preferably controls the effluent pH of the pretreatment unit to meet the range of 8.0-9.0.

[0112] Comparative Example 4 did not use a pretreatment unit and directly introduced the wastewater into the pre-oxidation unit. The comparison results show that the method of the present invention, by setting up a pretreatment unit, can significantly pretreat the wastewater using CO2 in the flue gas, regulate the wastewater composition, and is beneficial to the recovery effect of elemental sulfur in the pre-oxidation unit. As a result, the subsequent salt separation and recovery unit can significantly improve the purity of the recovered Na2CO3 product and also improve the Na2CO3 recovery rate, making the salt recovery more thorough and significantly improving the economic benefits of the process.

[0113] Comparative Example 5

[0114] The same process as in Example 2 was used, but in Comparative Example 5, no pre-oxidation unit was set up. After the wastewater passed through the pretreatment unit and the oxidation unit, Na2CO3 was directly recovered. The final Na2CO3 yield was mixed with a large amount of Na2SO4, and the product purity was only 62.3%, which was far lower than 99.0% in Example 2. The product recovery effect was significantly reduced, indicating that the pre-oxidation unit set up in this invention can significantly optimize the separation of components in the wastewater. While recovering elemental sulfur products, it can also improve the purity of the final Na2CO3 yield, so that it meets the requirements of Class II Grade 1 product in GB / T 210-2022.

[0115] Comparative Example 6

[0116] A method for high-value conversion of mixed sodium salts was disclosed in CN114715921A to recover salt resources in wastewater. The main process includes dissolution, metathesis, freeze crystallization, secondary dissolution and secondary metathesis. Sodium carbonate and sodium sulfate can be recovered, and the Na2CO3 recovery rate is 13.75 g / min.

[0117] The specific operational details are as follows:

[0118] The water quality conditions of the treated ethylene alkali residue wastewater are as follows: temperature 26℃, TDS 72685mg / L, total alkalinity (calculated as CaCO3) 6358mg / L, NaOH 3.0%, Na2CO3 2.4%, Na2S (after conversion of sulfur-containing substances such as Na2S2O3 and Na2SO4) 3.8%, COD 48277mg / L, TOC 1086mg / L, petroleum hydrocarbons 11mg / L, and other metal elements (Fe, Ca, Mg, etc.) 2.1mg / L.

[0119] First, the alkaline residue wastewater is treated at high temperature to convert sulfides into sulfate ions, and the salt is dissolved in the second mother liquor to obtain mixed sodium salt. Sodium is then dissolved once at 40°C, and after sedimentation and separation, dechlorinated solid and sodium primary solution are obtained.

[0120] The solid ammonium bicarbonate and the sodium solution obtained above were mixed, and the molar ratio of total bicarbonate to total sodium in the reaction system was controlled at 1.1:1. The first metathesis reaction was carried out at 35°C for 60 min. After hydrocyclone separation and filtration separation, the first sodium bicarbonate and the first mother liquor were obtained.

[0121] The first mother liquor was cooled and crystallized at 15°C, and after filtration and separation, ammonium chloride and the cooled mother liquor were obtained.

[0122] The deammonium-removed solid, the dechlorinated solid obtained above, and the cooling mother liquor obtained above are mixed and subjected to secondary sodium dissolution at 40°C. After sedimentation and separation, ammonium sodium composite salt and sodium secondary dissolution solution are obtained.

[0123] A mixture of ammonia and carbon dioxide was mixed with the resulting sodium secondary solution, and the molar ratio of total bicarbonate to total sodium in the reaction system was controlled at 1.1:1. The second metathesis reaction was carried out at 40°C for 100 min. After hydrocyclone separation and filtration, the second sodium bicarbonate and the second mother liquor were obtained. The obtained second mother liquor was reused when the initial alkaline residue wastewater was dissolved into mixed sodium salt after high-temperature calcination.

[0124] The mixed evaporation mother liquor and the above-obtained ammonium sodium composite salt were enriched with ammonium sulfate at 85°C. After centrifugation, an ammonium sulfate-rich solution and deammonium-depleted solids were obtained. The deammonium-depleted solids were recycled for mixing with dechlorination solids and cooling mother liquor.

[0125] The obtained ammonium sulfate-rich solution was evaporated and crystallized at 95°C. After hydrocyclone separation and centrifugation, ammonium sulfate and evaporation mother liquor were obtained. The evaporation mother liquor was used to mix and dissolve with sodium ammonium salt to collect the deammonium solid.

[0126] Compared with this invention, other traditional processes often require the addition of reagents (such as ammonium bicarbonate and ammonia) to separate and recover Na2CO3 and Na2SO4, ensuring the purity of the Na2CO3 and Na2SO4 products. In this invention, sulfur is recovered in the pre-process, thus avoiding the problem of difficult separation of Na2CO3 and Na2SO4, saving the use of reagents, and is more economical than traditional processes.

[0127] Compared with Comparative Example 6, the process of this invention reduces interference in the subsequent Na2CO3 recovery and separation by pre-oxidation and pre-separation of elemental sulfur resources. In contrast, due to interference from Na2SO4 in traditional and past processes, the recovery rate of Na2CO3 is only 13.75 g / min, which is lower than 18.49 g / min in Example 2, in order to ensure the purity of Na2CO3 recovery. This shows that the pre-separation of elemental sulfur in the process of this invention reduces the difficulty of subsequent Na2CO3 product separation, and can achieve a higher recovery rate, thereby improving the economic benefits of the wastewater resource recovery process.

[0128] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

[0129] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

Claims

1. A system for the resource-based treatment of alkaline slag wastewater enhanced by micro-nano bubbles, characterized in that, The system includes an alkaline residue wastewater inlet pipe, a pretreatment unit, a pre-oxidation unit, an oxidation unit, and a product separation unit connected in sequence. The pretreatment unit includes at least one pretreatment device, and each pretreatment device is provided with at least one set of flue gas conveyors at its bottom; The pre-oxidation unit includes at least one pre-oxidation device and a catalyst delivery pipeline. At least one set of air conveyors is provided at the bottom of each pre-oxidation device, and the catalyst delivery pipeline is connected to each pre-oxidation device. The oxidation unit includes a wet oxidation device and an ozone oxidation device connected in sequence, and the ozone oxidation device is equipped with an ozone aeration device at the bottom. The product separation unit includes a concentration evaporation device and a freeze crystallization device connected in sequence; Both the flue gas conveyor and the air conveyor are micro-nano bubble generators.

2. The system according to claim 1, wherein, The micro / nano bubble generator is provided with a liquid input pipe and a gas input pipe. At least two sets of liquid diversion pipes are provided at one end of the liquid input pipe. A gas inlet is provided near the liquid diversion pipe of the liquid input pipe. The gas input pipe is connected to the gas inlet. A gas-liquid mixer is provided at the end of each liquid diversion pipe. A gas-liquid outlet is provided on the gas-liquid mixer.

3. The system according to claim 2, wherein, The micro-nano bubble generator is also equipped with a pump to transport the alkaline residue wastewater in the pretreatment unit to the liquid input pipe.

4. The system according to claim 2, wherein, The gas-liquid outlet has a concave structure. The angle between the tangent of the protruding structure at the gas-liquid outlet and the oblique line of the concave structure is defined as the α hyperbolic angle, and the angle between the tangent of the protruding structure at the gas-liquid outlet and the horizontal line is defined as the β single-curve angle. The α hyperbolic angle is 15-45°, preferably 30-40°, and the β single-curve angle is 1-15°, preferably 5-10°.

5. The system according to claim 2, wherein, The ratio of the diameter of the gas input pipe to the diameter of the liquid input pipe is 1:6 to 10.

6. The system according to claim 1, wherein, The product separation unit includes a dual-membrane concentration device, a concentration evaporation device, and a freeze crystallization device connected in sequence.

7. The system according to claim 1, wherein, When there are ≥2 micro-nano bubble generators, they are arranged in a staggered pattern.

8. The system according to claim 1, wherein, The system also includes an elemental sulfur purification unit, which is connected to the pre-oxidation device via an elemental sulfur recovery pipe.

9. The system according to claim 1, wherein, The concentration evaporation device is equipped with a steam recovery pipe; the freeze crystallization separation device is equipped with a double salt concentrate discharge pipe and a Na2CO3 product recovery pipe.

10. A method for resource-based treatment of alkaline slag wastewater enhanced by micro-nano bubbles, characterized in that, The system for resource recovery treatment of alkaline sludge wastewater enhanced by micro-nano bubbles as described in any one of claims 1-9 includes the following steps: S1: Input the alkaline wastewater into the pretreatment unit, and use a flue gas conveyor to transport flue gas to pretreat the alkaline wastewater; S2: The pretreated alkaline wastewater is transported to the pre-oxidation unit, a catalyst is added, and air is continuously supplied through an air conveyor to complete the pre-oxidation process of the alkaline wastewater. S3: The pre-oxidized wastewater is transported to the oxidation unit for wet oxidation and ozone catalytic oxidation to remove COD from the wastewater; S4: The oxidized alkaline residue wastewater enters the concentration and evaporation device to obtain concentrated liquid. The concentrated liquid is then separated and recovered from the wastewater by the freeze crystallization device.

11. The method according to claim 10, wherein, In step S1, the volume ratio of flue gas to alkaline residue wastewater is (50-1000):1, preferably (200-400):1; The volumetric flow rate ratio of alkaline residue wastewater to flue gas in the flue gas conveyor is (1-10):1, preferably (5-8):1; The flue gas is preferably the exhaust gas after treatment within the factory area.

12. The method according to claim 10, wherein, In step S2, the pH of the pretreated alkaline residue wastewater is 7.0-10.0; preferably 8.0-9.

0. The catalyst is selected from at least one of cobalt phthalocyanine, iron phthalocyanine, and nickel phthalocyanine sulfonates; the concentration of the catalyst in the reaction system is 3-30 mg / L; The volumetric flow rate ratio of wastewater to air in the air conveyor is (1-10):1, preferably (5-8):

1.

13. The method according to claim 10, wherein, In step S2, S in the wastewater 2- and HS 2- Oxidized to S 0 The sulfur is recovered through a sulfur recovery pipe and sent to a sulfur purification unit for purification and separation to obtain sulfur products.

14. The method of claim 10, wherein, In step S3, the conditions for the wet oxidation reaction include: a temperature of 110-160℃, a pressure of 3-12MPa, and a gas-liquid ratio of (15-40):

1. The ozone concentration in the reaction system of the ozone catalytic oxidation reaction is 5-13 mg / L.

15. The method according to claim 10, wherein, In step S3, the COD concentration after treatment is less than 100 mg / L.

16. The method of claim 10, wherein, In step S4, the temperature of the evaporation and concentration device is controlled at 80-100°C, and the temperature of the freezing and crystallization device is controlled at 0-15°C. Preferably, the oxidized alkaline residue wastewater first enters a dual-membrane thickener for preliminary thickening, and then enters a thickening evaporation unit.

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