Acetylene production wastewater recovery process

Abstract

The invention relates to the technical field of wastewater treatment, in particular to an acetylene production wastewater recovery process which comprises the following steps: S1, collecting waste sodium hypochlorite liquid generated in an acetylene cleaning process and cooling wastewater generated in an acetylene cooling tower according to an actual yield ratio, pumping into a regulating tank, and homogenizing water quality and water quantity; according to the method, more than 90% of dissolved acetylene in the wastewater is efficiently recovered through micro-negative pressure desorption, resource utilization is realized, secondary phosphorus and phosphorous which are difficult to degrade are thoroughly converted into positive phosphorus through Fenton oxidation, and the total phosphorus concentration is reduced to 0.5 mg / L or below in combination with neutralization and flocculation, so that the first-grade discharge standard is met, and the method is suitable for industrial production. The pH value of the purified water is finely adjusted to 10-11, then the purified water is used as a dilution carrier to be compounded with the sodium hypochlorite working solution, and the pH value after mixing is ensured to be always greater than 9.5, so that the pH dangerous interval is fundamentally avoided, the chloroacetylene explosion hidden danger is remarkably eliminated, the safety of the whole process is improved, the whole process forms a closed cycle, and the treated water is used for completely replacing fresh water to prepare the working solution.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically a process for recovering acetylene production wastewater. Background Technology

[0002] In PVC and acetylene production, the crude acetylene gas generated from the reaction of calcium carbide and water is treated with sodium hypochlorite solution, producing a large amount of waste sodium hypochlorite solution. This wastewater has significant characteristics: First, it contains saturated dissolved acetylene, and direct discharge results in resource waste; second, it has a high phosphorus concentration (total phosphorus reaches 30-50 mg / L or even higher), and phosphine exists in the form of hypophosphite and phosphite after oxidation. Conventional aluminum and iron salt coagulation methods have low removal rates (only reducing from 30 mg / L to 22-24 mg / L), making it difficult to meet the GB8978-1996 Class I standard (total phosphorus <1 mg / L); third, it is alkaline and contains unreacted sodium hypochlorite, and direct recycling poses safety hazards. Studies have shown that mixing new wastewater at pH <5 may generate sparks or explosive chloroacetylene, requiring pH control >5.5 to improve safety; fourth, the volume is large, with the acetylene section generating hundreds of tons of cooling and cleaning wastewater daily, making treatment extremely difficult.

[0003] Traditional treatment methods often involve direct discharge or simple sedimentation and reuse, which not only leads to the loss of acetylene resources but also poses serious environmental risks. Although some studies have explored the recycling of waste sodium hypochlorite solution or Fenton oxidation for deep phosphorus removal, these methods struggle to simultaneously address the challenges of acetylene recovery, achieving total phosphorus standards (<1 mg / L), and safe reuse of waste liquid, especially failing to effectively mitigate the risk of chloroacetylene explosions. Summary of the Invention

[0004] The purpose of this invention is to provide a process for recovering acetylene production wastewater to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a process for recovering acetylene production wastewater, the process comprising the following steps: Step S1: Collect the waste sodium chloride solution generated from the acetylene purification process and the cooling wastewater generated from the acetylene cooling tower according to the actual production ratio and pump them into the equalization tank for water quality and quantity homogenization. Step S2: The homogenized wastewater is lifted to the desorption tower. A water ring vacuum pump is used to maintain a slight negative pressure at the top of the tower to promote the escape of acetylene from the liquid phase. The gas discharged from the top of the desorption tower enters the gas-liquid separator. The separated liquid water is returned to the desorption tower, while the gas phase is connected to the acetylene gas holder or returned to the cooling system before the acetylene generator for recovery. Step S3: The wastewater after desorption of acetylene enters the Fenton oxidation reactor to completely oxidize hypophosphite and phosphite in the wastewater into orthophosphate. Step S4: The oxidized wastewater flows by gravity into the neutralization and flocculation tank. First, a 10% sodium hydroxide solution is added to the rapid stirring zone to adjust the pH to 6.0-7.0. At this point, Fe... 3+ Ferric hydroxide colloid is formed, which co-precipitates with the orthophosphate generated by oxidation. Subsequently, anionic polyacrylamide solution is added in the slow stirring zone to promote the growth of flocculent plants. Step S5: The flocculated wastewater enters the vertical flow sedimentation tank for solid-liquid separation. The supernatant is the purified water after deep phosphorus removal. The supernatant enters the intermediate water tank. Step S6: The purified water from the intermediate water tank is pumped into the pH fine-tuning tank. Through the linkage of the online pH meter, 10% sodium hydroxide solution is automatically added to stabilize the pH at 10.0-11.0. Step S7: In the recycled waste sodium hypochlorite solution storage tank, the alkaline purified water from step S6 is used as dilution water and mixed with the high-concentration fresh sodium hypochlorite solution from the preparation system. The mixing process strictly follows online monitoring and control. Step S8: The regenerated sodium hypochlorite working solution enters the vacuum degassing tank, where trace amounts of oxygen dissolved during preparation and transportation are removed under slight negative pressure. The degassed regenerated sodium hypochlorite working solution is then pumped to the acetylene purification tower for recycling, completing the entire closed-loop cycle.

[0006] Preferably, in step S1, the waste sodium hypochlorite solution generated in the cleaning process has a temperature of 40-50℃, a pH of 7-8, a total phosphorus content of 49.5-50 mg / L, a total phosphorus content of 9.5-10 mg / L in the cooling wastewater, and a total phosphorus concentration of 20-30 mg / L in the mixed wastewater.

[0007] Preferably, in step S2, the desorption tower is a packed tower or a plate tower.

[0008] Preferably, in step S3, the Fenton oxidation reactor is a three-stage mechanically stirred reaction tank connected in series, with each stage having an effective volume corresponding to a hydraulic retention time of 20-30 minutes.

[0009] Preferably, in step S3, firstly, in the first-stage reaction tank, 20% dilute sulfuric acid is added, and the pH of the wastewater is precisely adjusted to 3.0-3.5 with stirring. Then, in the second-stage reaction tank, Fe... 2+ Add the reagents in a ratio of approximately 1:1.2 (Ferrous sulfate heptahydrate and hydrogen peroxide). The specific dosages are: 400-500 mg / L ferrous sulfate heptahydrate and 300-400 mg / L hydrogen peroxide. Stir the reaction for 40-60 minutes.

[0010] Preferably, in step S4, the molecular weight of the added anionic polyacrylamide solution is ≥1200, and the concentration of the anionic polyacrylamide solution is 0.1%.

[0011] Preferably, in step S5, the surface loading of the sedimentation tank is designed to be 0.6-0.8 m. 3 / (m 2 •h), hydraulic residence time ≥2h.

[0012] Preferably, in step S5, the chemical sludge generated at the bottom is discharged into a sludge thickening tank, dewatered into sludge cake by a plate and frame filter press, and then transported off-site for disposal. The set filtration pressure of the plate and frame filter press is 0.6-0.8 MPa.

[0013] Preferably, in step S7, the online monitoring and control includes two devices: an oxidation-reduction potentiometer and a pH meter. The effective chlorine concentration is indirectly controlled by the oxidation-reduction potentiometer, and a cleaning working solution with an effective chlorine content of 0.08-0.12% is finally prepared. The pH value is monitored by the pH meter to ensure that the pH of the mixed liquid is always >9.5.

[0014] Preferably, in step S8, the air pressure of the slight negative pressure is -5 to -10 kPa.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention efficiently recovers over 90% of dissolved acetylene from wastewater through micro-negative pressure desorption, achieving resource utilization. Secondly, Fenton oxidation completely converts recalcitrant phosphorus and phosphorus into orthophosphorus, and neutralization flocculation reduces the total phosphorus concentration to below 0.5 mg / L, thus meeting Class I discharge standards. Furthermore, by finely adjusting the pH of the purified water to 10-11 and using it as a dilution carrier to prepare the sodium hypochlorite working solution, and ensuring that the pH remains above 9.5 after mixing, the dangerous pH range is fundamentally avoided, significantly eliminating the risk of chloroacetylene explosion and improving the safety of the entire process. Moreover, the entire process forms a closed-loop cycle, completely replacing fresh water with treated water to prepare the working solution, greatly saving water resources and achieving zero wastewater discharge and green regeneration and reuse of the acetylene cleaning agent. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the process flow of the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] A process for recovering acetylene production wastewater includes the following steps: Step S1, Wastewater Collection and Mixing: The waste sodium chloride solution generated from the acetylene purification process and the cooling wastewater from the acetylene cooling tower are collected according to the actual production ratio (e.g., 1:3) and pumped into the equalization tank. The equalization tank is designed to store 6-8 hours of the daily water treatment capacity. The tank is equipped with a level gauge and a stirrer (power 0.5-1.5kW / m³). 3 (Pool volume), the waste sodium hypochlorite solution is mixed with cooling wastewater to homogenize the water quality and quantity. The waste sodium hypochlorite solution produced in the purification process has a temperature of 40-50℃, a pH of 7-8, a total phosphorus content of 49.5-50 mg / L, and a total phosphorus content of 9.5-10 mg / L in the cooling wastewater. After mixing, the total phosphorus concentration in the wastewater is 20-30 mg / L. Step S2, Desorption and Recovery of Dissolved Acetylene: The homogenized wastewater is pumped to a desorption tower (packed tower or plate tower). Desorption utilizes the residual heat of the wastewater to maintain the internal temperature at 40-50℃. A water ring vacuum pump is used at the top of the tower to maintain a slight negative pressure, with an internal gas pressure of -10 to -20 kPa, which promotes the escape of acetylene from the liquid phase. The gas discharged from the top of the desorption tower (mainly acetylene, water vapor and trace amounts of air) enters the gas-liquid separator. The separated liquid water is returned to the desorption tower, while the gas phase is connected to the acetylene gas holder or returned to the cooling system before the acetylene generator for recovery. This step can recover more than 90% of the dissolved acetylene in the wastewater. Step S3, Fenton Oxidation Pretreatment for Phosphorus Removal: The wastewater after acetylene desorption enters the Fenton oxidation reactor. First, in the first-stage reaction tank, 20% dilute sulfuric acid is added, and the pH of the wastewater is precisely adjusted to 3.0-3.5 with stirring (120-150 rpm). Then, in the second-stage reaction tank, Fe... 2+ The reagent is added at a ratio of approximately 1:1.2 (mass ratio) to H2O2. The reagent is ferrous sulfate heptahydrate and hydrogen peroxide. The specific dosage is: ferrous sulfate heptahydrate (FeSO4·7H2O) 400-500 mg / L (as Fe... 2+ The concentration of hydrogen peroxide (H2O2, 30%) is approximately 80-100 mg / L. The reaction is carried out with stirring (100-120 rpm) for 40-60 minutes to completely oxidize hypophosphite and phosphite in the wastewater into orthophosphate, while simultaneously degrading some of the chemical oxygen demand. The Fenton oxidation reactor described above is a three-stage series mechanically stirred reaction tank, with each stage having an effective volume corresponding to a hydraulic retention time of 20-30 minutes. Step S4, Neutralization, Flocculation, and Sedimentation: The oxidized wastewater flows by gravity into the neutralization and flocculation tank. First, a 10% sodium hydroxide solution is added in the rapid stirring zone (80-100 rpm) to adjust the pH to 6.0-7.0. At this point, Fe... 3+Ferric hydroxide colloid is formed, which co-precipitates with the orthophosphate generated by oxidation. Then, anionic polyacrylamide solution is added in a slow stirring zone (30-40 rpm) at a dosage of 1-2 mg / L to promote the growth of flocs. The molecular weight of the added anionic polyacrylamide solution is ≥1200, and the concentration of the anionic polyacrylamide solution is 0.1%. Step S5, Solid-Liquid Separation: The flocculated wastewater enters a vertical flow sedimentation tank for solid-liquid separation. The surface loading of the sedimentation tank is designed to be 0.6-0.8 m³. 3 / (m 2 •h), hydraulic retention time ≥2h, the supernatant is the purified water after deep phosphorus removal, the total phosphorus concentration is reduced to <0.5mg / L, the supernatant enters the intermediate water tank, and the chemical sludge (mainly composed of iron phosphate and iron hydroxide) generated at the bottom is discharged into the sludge thickening tank, and after being dewatered by the plate and frame filter press into sludge cake with a moisture content of less than 60%, it is transported off-site for disposal. The set filtration pressure of the plate and frame filter press is 0.6-0.8MPa; Step S6, pH adjustment and safety buffering of purified water: The purified water in the intermediate water tank is pumped into the pH adjustment tank. Through the linkage of the online pH meter, 10% sodium hydroxide solution is automatically added to stabilize the pH at 10.0-11.0. This alkaline environment has two purposes: first, to further ensure the absolute safety of subsequent mixing with sodium hypochlorite, keeping it away from the pH danger range; second, to provide an alkaline carrier for replenishing new sodium hypochlorite solution. The adjusted water enters the recycled waste sodium hypochlorite solution storage tank. Step S7, Regeneration and Reconstitution of Waste Sodium Hypochlorite Solution: In the waste sodium hypochlorite solution storage tank, the alkaline purified water from Step S6 is used as dilution water and mixed with a high-concentration fresh sodium hypochlorite solution (effective chlorine content ≥10%) from the preparation system. The reconstitution process strictly follows online monitoring and control, which includes two devices: an oxidation-reduction potentiometer and a pH meter. Specifically, the effective chlorine concentration is indirectly controlled by the oxidation-reduction potentiometer, and the final solution is prepared with an effective chlorine content of 0.08-0.12%. The pH value is monitored by the pH meter to ensure that the pH of the mixed liquid is always >9.5. The key innovation of this step is to completely replace fresh water with deeply treated purified water to prepare the sodium hypochlorite working solution and to use its high pH value as a safety barrier. Step S8, Degassing and Recycling: The regenerated sodium hypochlorite working solution enters a vacuum degassing tank, where trace amounts of oxygen dissolved during preparation and transportation are removed under a slight negative pressure (the pressure of the slight negative pressure is -5 to -10 kPa), further eliminating the risk of reaction with residual reducing substances. The degassed regenerated sodium hypochlorite working solution is pumped to an acetylene purification tower for recycling, completing the entire closed-loop cycle. The system water balance is automatically adjusted by adding a small amount of fresh water and calculating evaporation loss.

[0019] To verify the effectiveness of this process, the following laboratory simulation experiments were conducted: 1. Material preparation: Simulated wastewater: Based on actual water quality, 10L of simulated acetylene mixed wastewater with a total phosphorus concentration of 30mg / L (of which hypophosphite and phosphorus nitrite account for >70%), pH=8, and a chemical oxygen demand of approximately 200mg / L was prepared using deionized water, potassium dihydrogen phosphate, sodium hypophosphite, sodium phosphite, calcium hydroxide, and acetic acid.

[0020] Experimental reagents: 20% sulfuric acid, 30% hydrogen peroxide, ferrous sulfate heptahydrate, 30% sodium hydroxide solution, anionic polyacrylamide solution (molecular weight 12 million), and 10% sodium hypochlorite solution.

[0021] Instruments: pH meter, ORP meter, magnetic stirrer, constant temperature water bath, vacuum pump, gas bag, gas chromatograph, UV-Vis spectrophotometer (for total phosphorus determination), organic matter digester in water, 250mL conical flask, burette, etc.

[0022] 2. Experimental Procedure and Parameters 2.1 Simulation of acetylene desorption: Take 2L of simulated wastewater into a stoppered conical flask, place it in a 50℃ water bath, connect a vacuum pump to -15kPa, maintain for 30 minutes, collect the desorbed gas with a gas bag, analyze the acetylene concentration in the gas bag with gas chromatography, and calculate the recovery rate.

[0023] 2.2 Deep phosphorus removal experiment: Take 1L of desorbed wastewater into a beaker and place it on a magnetic stirrer; -a. First, add 20% sulfuric acid to adjust the pH to 3.2; -b. Add 400 mg FeSO4·7H2O (equivalent to 80 mg / L Fe) 2+ The stirring speed is 120 rpm; -c. Slowly add 0.38 mL of 30% H2O2 (equivalent to 300 mg / L) and react for 60 min; -d. Add 30% NaOH to adjust the pH to 6.5, resulting in a large amount of flocculent material. -e. Add 2 drops of 0.1% PAM solution, stir slowly (40 rpm) for 5 min, and then let it stand to precipitate for 60 min; -f. Filter the supernatant and determine the total phosphorus and chemical oxygen demand.

[0024] 2.3 Safety and efficiency experiment of waste sodium chloride solution regeneration: -a. Adjust the pH of the supernatant after phosphorus removal to 10.5 using NaOH; -b. Take 100 mL of the alkaline purified water and mix it with 100 mL of sodium chloride solution (pH=12) with an available chlorine concentration of 0.40%. Observe the phenomenon and measure the available chlorine and pH of the mixture. -c. Use the regenerated liquid (diluted to 0.1% available chlorine) to conduct a purification experiment on simulated crude acetylene gas containing PH3, and detect the PH3 content in the outlet gas.

[0025] Table 1. Experimental Procedure Comparison Table Experimental data fully demonstrate that the process of this invention can efficiently recover dissolved acetylene, achieve deep removal of total phosphorus to below 0.5 mg / L through Fenton oxidation, and ensure the safety and purification efficiency of the waste sodium hydroxide solution regeneration and recycling process through a high pH buffer. The entire process flow is coherent, with clearly defined parameters, and is feasible for industrial application.

[0026] This invention recovers dissolved acetylene gas from wastewater, directly improving raw material utilization and reducing resource waste. It achieves deep phosphorus removal, consistently meeting emission standards, and solves the problem of removing hypophosphite and phosphite using conventional methods. It ensures that the total phosphorus in the effluent is consistently below the national emission standards. It creatively uses the deeply treated effluent to prepare sodium hypophosphite working solution, and through high pH control, it completely eliminates the risk of explosion during the circulation process. It achieves closed-loop circulation of waste sodium hypophosphite solution and near-zero wastewater discharge, with a water saving rate of over 70%. The process units have a high degree of coupling, and key parameters (pH, ORP, available chlorine) are monitored and automatically controlled online, ensuring stable operation and easy management.

[0027] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0028] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A process for recovering acetylene production wastewater, characterized in that, The process includes the following steps: Step S1: Collect the waste sodium chloride solution generated from the acetylene purification process and the cooling wastewater generated from the acetylene cooling tower according to the actual production ratio and pump them into the equalization tank for water quality and quantity homogenization. Step S2: The homogenized wastewater is lifted to the desorption tower. A water ring vacuum pump is used to maintain a slight negative pressure at the top of the tower to promote the escape of acetylene from the liquid phase. The gas discharged from the top of the desorption tower enters the gas-liquid separator. The separated liquid water is returned to the desorption tower, while the gas phase is connected to the acetylene gas holder or returned to the cooling system before the acetylene generator for recovery. Step S3: The wastewater after desorption of acetylene enters the Fenton oxidation reactor to completely oxidize hypophosphite and phosphite in the wastewater into orthophosphate. Step S4: The oxidized wastewater flows by gravity into the neutralization and flocculation tank. First, a 10% sodium hydroxide solution is added to the rapid stirring zone to adjust the pH to 6.0-7.

0. At this point, Fe... 3+ Ferric hydroxide colloid is formed, which co-precipitates with the orthophosphate generated by oxidation. Subsequently, anionic polyacrylamide solution is added in the slow stirring zone to promote the growth of flocculent plants. Step S5: The flocculated wastewater enters the vertical flow sedimentation tank for solid-liquid separation. The supernatant is the purified water after deep phosphorus removal. The supernatant enters the intermediate water tank. Step S6: The purified water from the intermediate water tank is pumped into the pH fine-tuning tank. Through the linkage of the online pH meter, 10% sodium hydroxide solution is automatically added to stabilize the pH at 10.0-11.

0. Step S7: In the recycled waste sodium hypochlorite solution storage tank, the alkaline purified water from step S6 is used as dilution water and mixed with the high-concentration fresh sodium hypochlorite solution from the preparation system. The mixing process strictly follows online monitoring and control. Step S8: The regenerated sodium hypochlorite working solution enters the vacuum degassing tank, where trace amounts of oxygen dissolved during preparation and transportation are removed under slight negative pressure. The degassed regenerated sodium hypochlorite working solution is then pumped to the acetylene purification tower for recycling, completing the entire closed-loop cycle.

2. The acetylene production wastewater recovery process according to claim 1, characterized in that: In step S1, the waste sodium hypochlorite solution generated in the cleaning process has a temperature of 40-50℃, a pH of 7-8, a total phosphorus content of 49.5-50 mg / L, a total phosphorus content of 9.5-10 mg / L in the cooling wastewater, and a total phosphorus concentration of 20-30 mg / L in the mixed wastewater.

3. The acetylene production wastewater recovery process according to claim 1, characterized in that: In step S2, the desorption tower is a packed tower or a plate tower.

4. The acetylene production wastewater recovery process according to claim 1, characterized in that: In step S3, the Fenton oxidation reactor is a three-stage mechanically stirred reaction tank connected in series, with each stage having an effective volume corresponding to a hydraulic retention time of 20-30 minutes.

5. The acetylene production wastewater recovery process according to claim 4, characterized in that: In step S3, firstly, in the first-stage reaction tank, 20% dilute sulfuric acid is added, and the pH of the wastewater is precisely adjusted to 3.0-3.5 with stirring. Then, in the second-stage reaction tank, Fe... 2+ Add the reagents in a ratio of approximately 1:1.2 (Ferrous sulfate heptahydrate and hydrogen peroxide). The specific dosages are: 400-500 mg / L ferrous sulfate heptahydrate and 300-400 mg / L hydrogen peroxide. Stir the reaction for 40-60 minutes.

6. The acetylene production wastewater recovery process according to claim 1, characterized in that: In step S4, the molecular weight of the added anionic polyacrylamide solution is ≥1200, and the concentration of the anionic polyacrylamide solution is 0.1%.

7. The acetylene production wastewater recovery process according to claim 1, characterized in that: In step S5, the surface loading of the sedimentation tank is designed to be 0.6-0.8 m. 3 / (m 2 •h), hydraulic residence time ≥2h.

8. The acetylene production wastewater recovery process according to claim 1, characterized in that: In step S5, the chemical sludge generated at the bottom is discharged into a sludge thickening tank, dewatered into sludge cake by a plate and frame filter press, and then transported off-site for disposal. The set filtration pressure of the plate and frame filter press is 0.6-0.8 MPa.

9. The acetylene production wastewater recovery process according to claim 1, characterized in that: In step S7, the online monitoring and control includes two devices: an oxidation-reduction potentiometer and a pH meter. The effective chlorine concentration is indirectly controlled by the oxidation-reduction potentiometer. Finally, a cleaning working solution with an effective chlorine content of 0.08-0.12% is prepared. The pH value is monitored by the pH meter to ensure that the pH of the mixed liquid is always >9.

5.

10. The acetylene production wastewater recovery process according to claim 1, characterized in that: In step S8, the air pressure of the slight negative pressure is -5 to -10 kPa.

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