Anti-fouling low-energy shale gas fracturing flowback fluid wastewater treatment process
Patent Information
- Application Number
- CN202610974342.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-07-01
- Publication Date
- 2026-09-15
Smart Images
Figure SMS_3 
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Abstract
Description
Technical Field
[0001] This invention relates to the field of wastewater treatment technology, specifically to a wastewater treatment process for shale gas fracturing flowback fluid that is anti-scaling and low-energy. Background Technology
[0002] The hydraulic fracturing process for shale gas extraction generates a large amount of fracturing flowback fluid. This type of wastewater is characterized by high mineralization, high viscosity, complex organic composition, and high content of special metal ions. It contains high molecular polymers such as guar gum and drag reducers, as well as various metal ions such as calcium, magnesium, barium, and strontium. The water quality fluctuates greatly and is difficult to treat. If not handled properly, it can easily cause soil and water pollution, which will restrict the green and large-scale development of shale gas.
[0003] Currently, the industry commonly uses a combination of pretreatment, membrane desalination, and MVR evaporation to treat shale gas fracturing flowback fluid, achieving wastewater reduction and salt separation. However, existing wastewater treatment processes are only designed for conventional calcium and magnesium hardness, neglecting the presence of Ba²⁺ in fracturing flowback fluid. + Sr² + The current treatment methods for shale gas fracturing flowback fluid wastewater lead to scale buildup that hydrochloric acid cannot dissolve within 1-2 months, significantly reducing heat exchange efficiency and causing poor system stability. Furthermore, existing processes commonly use persulfate gel-breaking systems to treat high-molecular-weight polymer contaminants in the flowback fluid. This system has a slow reaction rate at room temperature, failing to quickly reduce viscosity using guar gum and drag-reducing agents, and residual polymers easily contaminate nanofiltration membranes. Moreover, nanofiltration salt separation is greatly affected by influent temperature; membrane flux decreases significantly in winter, with monovalent salt permeation less than 85% and crystalline salt purity below 95%, failing to meet industrial salt reuse standards. The produced crystalline salt can only be disposed of as hazardous waste. Therefore, there is an urgent need to develop a shale gas fracturing flowback fluid wastewater treatment process with excellent salt separation performance. Summary of the Invention
[0004] To address the above technical problems, this invention provides a shale gas fracturing flowback fluid wastewater treatment process with anti-scaling and low energy consumption. This process solves the technical problem of insufficient monovalent salt permeation in existing shale gas fracturing flowback fluid wastewater treatment processes with anti-scaling and low energy consumption.
[0005] The specific technical solution of the present invention is as follows: According to one aspect of the present invention, a shale gas fracturing flowback fluid wastewater treatment process with anti-scaling and low energy consumption is provided, comprising homogenization conditioning, oxidation breaking, air flotation oil removal, primary sedimentation for impurity removal, primary flocculation sedimentation, secondary sedimentation for impurity removal, secondary flocculation sedimentation, and post-treatment of the fracturing flowback fluid to be treated; the raw materials for the primary sedimentation for impurity removal include barium sulfate and sodium sulfate; the raw materials for the secondary sedimentation for impurity removal include sodium hydroxide and sodium carbonate; An oxidizing agent is added during the oxidative degelatination process; the oxidizing agent comprises sodium persulfate, ferrous sulfate heptahydrate, and sodium citrate.
[0006] In the above technical solution, the mass ratio of sodium persulfate, ferrous sulfate heptahydrate and sodium citrate is 5~7:2~3:1.
[0007] In the above technical solution, the pH of the fracturing flowback fluid to be treated is 4.0~10.0.
[0008] In the above technical solution, the oxidative debonding includes the following steps: after homogenization and adjustment, it is sent into the debonding reaction tank, and the oxidant is added to mix and carry out oxidative debonding.
[0009] In the above technical solution, the air flotation oil removal includes the following steps: after oxidation and debinding, the wastewater is sent to the vortex air flotation unit for oil removal, and then sent to the pressurized dissolved air flotation unit for further oil removal.
[0010] In the above technical solution, the primary sedimentation and impurity removal includes the following steps: after air flotation for oil removal, the wastewater is sent to a primary sedimentation and impurity removal reaction tank, seed crystals are added and mixed evenly, and then sodium sulfate is added and mixed to achieve primary sedimentation and impurity removal.
[0011] In the above technical solution, the primary flocculation and sedimentation includes the following steps: after primary sedimentation to remove impurities, polyaluminum chloride and cationic polyacrylamide are added to the wastewater, and after flocculation and sedimentation, a supernatant is obtained.
[0012] In the above technical solution, the secondary sedimentation and impurity removal includes the following steps: after primary flocculation and sedimentation, the wastewater is sent to a secondary sedimentation and impurity removal reaction tank, an alkaline regulator is added to adjust the pH to 10.5~11.0, sodium carbonate is added and mixed to achieve secondary sedimentation and impurity removal.
[0013] In the above technical solution, the secondary flocculation and sedimentation includes the following steps: after secondary sedimentation to remove impurities, polyaluminum chloride and cationic polyacrylamide are added to the wastewater, and after flocculation and sedimentation, a supernatant is obtained.
[0014] In the above technical solution, the post-processing includes the following steps: filtration, adsorption, nanofiltration for salt separation, and evaporation crystallization.
[0015] Compared with existing technologies, this invention provides a shale gas fracturing flowback fluid wastewater treatment process with anti-scaling and low energy consumption. During the oxidation and gel breaking process, sodium persulfate, ferrous sulfate heptahydrate, and sodium citrate are used as oxidants to improve the monovalent salt permeation rate. Sodium persulfate, as the main oxidant, can efficiently oxidize and decompose high-molecular fracturing fluid colloids such as guar gum and hydroxypropyl guar gum in the fracturing flowback fluid, breaking the cross-linked structure of macromolecules, degrading organic colloidal pollutants in the water, and preventing colloidal substances from adhering and clogging subsequent treatment units and causing scaling of membrane modules and pipelines. The trivalent iron ions generated by the reaction of ferrous sulfate heptahydrate undergo hydrolysis and acidification, automatically stabilizing the pH of the system in the suitable range of 5.5 to 6.8. This pH is exactly matched with the reaction conditions for the subsequent removal of barium and strontium ions using sulfate, ensuring the removal effect of heavy metals and scaling ions. Sodium citrate, as a complexing agent, can not only complex the metal ions in the system to prevent the local aggregation of iron ions and precipitation that affects the oxidation effect, but also optimize the stability of the reaction system, further enhancing the overall anti-scaling ability, thereby effectively improving the monovalent salt permeation rate of the nanofiltration stage. Detailed Implementation
[0016] To make the objectives, technical solutions, and advantages of this invention more apparent, the invention is described in detail below. It should be understood that the invention is not limited to the description herein.
[0017] A wastewater treatment process for shale gas fracturing flowback fluid that is resistant to scaling and has low energy consumption. This invention discloses a low-energy-consumption, anti-scaling shale gas fracturing flowback fluid wastewater treatment process, comprising homogenization conditioning, oxidation and gel breaking, air flotation for oil removal, primary sedimentation for impurity removal, primary flocculation sedimentation, secondary sedimentation for impurity removal, secondary flocculation sedimentation, and post-treatment of the fracturing flowback fluid to be treated; the raw materials for primary sedimentation for impurity removal include barium sulfate and sodium sulfate; the raw materials for secondary sedimentation for impurity removal include sodium hydroxide and sodium carbonate; An oxidizing agent is added during the oxidative depolymerization process; the components of the oxidizing agent include sodium persulfate, ferrous sulfate heptahydrate, and sodium citrate.
[0018] In one embodiment of the present invention, the mass ratio of sodium persulfate, ferrous sulfate heptahydrate and sodium citrate is 5~7:2~3:1, preferably 5~6:2~3:1, more preferably 5~6:2~2.5:1, and most preferably 5~5.5:2~2.5:1.
[0019] In this invention, sodium persulfate, ferrous sulfate heptahydrate, and sodium citrate are added as oxidant components. A chelation system is used to achieve efficient activation across a full temperature range of 5–30°C, breaking down the long polymer chains of guar gum and drag-reducing agents, thereby reducing the viscosity of wastewater to 5 mPa. Below s, COD removal rate ≥55%; through Fe 3+ Hydrolysis utilizes an acidification effect to automatically stabilize the system pH between 5.5 and 6.8, a pH range that perfectly matches the subsequent sulfate-based deep removal of Ba.2+ 、Sr 2+ The optimal reaction conditions are achieved without the need for further acidification, reducing reagent consumption. Only minor pH adjustments are required during extreme water quality fluctuations, eliminating the need for large amounts of acid and alkali additions.
[0020] In one embodiment of the present invention, the pH of the fracturing flowback fluid to be treated is 4.0 to 10.0.
[0021] In this invention, the homogenization adjustment includes the following steps: sending the fracturing flowback fluid to be treated into the equalization tank, and completing the homogenization and equalization of water quality and quantity through aeration and stirring.
[0022] In one embodiment of the present invention, oxidative debonding includes the following steps: after homogenization and conditioning, the mixture is fed into a debonding reaction tank, and an oxidant is added and mixed to carry out oxidative debonding.
[0023] In this invention, the amount of oxidant added is 0.6~1.8 g / L, the mixing rate is 120~150 r / min, and the mixing time is 30~45 min.
[0024] In one embodiment of the present invention, the air flotation oil removal includes the following steps: after oxidation and debinding, the wastewater is sent to a vortex air flotation unit for oil removal, and then sent to a pressurized dissolved air flotation unit for further oil removal.
[0025] In this invention, wastewater is first fed into a reagent-free vortex flotation unit to remove free floating oil particles with a diameter >50μm, and simultaneously remove more than 60% of the oil phase COD; then it is fed into a pressurized dissolved air flotation unit, where 2~10mg / L PAC polyaluminum chloride and 0.1~0.5mg / L anionic polyacrylamide can be added according to the influent water quality to control the effluent oil content <5mg / L, SS <10mg / L, and turbidity <5NTU, and simultaneously remove more than 20% of the residual COD.
[0026] In one embodiment of the present invention, wastewater is fed into a primary sedimentation and impurity removal reaction tank, seed crystals are added and mixed evenly, and then sodium sulfate is added and mixed to achieve primary sedimentation and impurity removal.
[0027] In this invention, the seed crystals are 50-100 mg / L, 300-500 mesh barium sulfate seed crystals; the Ba in the fracturing flowback fluid to be treated... 2+ molar amount and Sr 2+ The sum of the molar amounts of the components and the molar ratio of sodium sulfate are 1:1.
[0028] In one embodiment of the present invention, the primary flocculation sedimentation includes the following steps: after primary sedimentation to remove impurities, polyaluminum chloride and cationic polyacrylamide are added to the wastewater, and after flocculation sedimentation, a supernatant is obtained.
[0029] In this invention, during the primary flocculation and sedimentation process, 10-30 mg / L of polyaluminum chloride is first added to the wastewater, and flocculation is carried out for 2-3 minutes at 100-120 r / min. Then, 0.5-1.5 mg / L of cationic polyacrylamide is added and coagulation is aided for 10-20 minutes at 20-30 r / min. The mixture is then sent to a primary inclined tube sedimentation tank for static settling for 45-60 minutes to complete solid-liquid separation. Part of the bottom sludge from the sedimentation tank is recycled as seed crystals, with a water content of 75%-80% and a reflux ratio of 10%-20%.
[0030] In one embodiment of the present invention, the secondary sedimentation and impurity removal includes the following steps: after primary flocculation and sedimentation, the wastewater is sent to a secondary sedimentation and impurity removal reaction tank, an alkaline regulator is added to adjust the pH to 10.5~11.0, sodium carbonate is added and mixed to achieve secondary sedimentation and impurity removal.
[0031] In this invention, the alkalinity regulator is sodium hydroxide, and the Ca in the fracturing flowback fluid to be treated is... 2+ Residual Sr 2+ The ratio of total molar amount to sodium carbonate molar amount is 1:1.1~1.3, and the mixing time is 10 min.
[0032] In this invention, sodium hydroxide is added as an alkalinity regulator to make Mg 2+ Magnesium hydroxide precipitate is formed, with a removal rate of ≥98%.
[0033] In this invention, the Ca in the fracturing flowback fluid to be treated 2+ Residual Sr 2+ The ratio of the total molar amount to the molar amount of sodium carbonate is 1:1.1~1.3, making Ca... 2+ Residual Sr 2+ Carbonate precipitate forms, Ca 2+ Removal rate ≥98%, Sr 2+ Total removal rate ≥95%, effluent Ba 2+ +Sr 2+ Total concentration < 0.1 mg / L, total hardness < 10 mg / L.
[0034] In one embodiment of the present invention, the secondary flocculation sedimentation includes the following steps: after secondary sedimentation to remove impurities, polyaluminum chloride and cationic polyacrylamide are added to the wastewater, and after flocculation sedimentation, a supernatant is obtained.
[0035] In this invention, during the secondary flocculation and sedimentation process, 5-20 mg / L of polyaluminum chloride and 0.3-1.0 mg / L of cationic polyacrylamide are added to the wastewater for flocculation and conditioning. The wastewater is then sent to a secondary inclined tube sedimentation tank and allowed to settle for 30-45 minutes to complete solid-liquid separation, resulting in supernatant.
[0036] In one embodiment of the present invention, the post-processing includes the following steps: filtration, adsorption, nanofiltration for salt separation, and evaporation crystallization.
[0037] In this invention, the filtration process involves sequentially passing the water through a quartz sand multi-media filter and a 5μm security filter to ensure that the effluent turbidity is <1NTU and SDI is <3, thus meeting the influent requirements of the nanofiltration membrane.
[0038] In this invention, adsorption is performed using a fruit shell activated carbon filter to remove residual small molecule organic matter, color, and COD, controlling the COD of the effluent to be stable at <500mg / L, and eliminating the negative impact of organic pollutants on the downstream evaporation system. The activated carbon regeneration scheme mainly adopts offline centralized regeneration. After adsorption saturation, it is sent to a qualified manufacturer for high-temperature thermal regeneration. After regeneration, the adsorption performance recovery rate is ≥85%, and it can be recycled.
[0039] In this invention, nanofiltration desalination involves sending wastewater into a plate heat exchanger to exchange heat with clean condensate water at 40-55°C generated by the downstream MVR system. The nanofiltration inlet water temperature is stably controlled at 28-32°C by an automatic control system, solving the problem of deterioration in desalination effect at low temperatures. After heat exchange, the condensate water is cooled to 25-30°C and sent to the permeate recycling tank. After preheating, the wastewater enters the antifouling polyamide nanofiltration membrane unit to achieve efficient and stable separation of monovalent salts, obtaining nanofiltration permeate and nanofiltration concentrate.
[0040] In this invention, the nanofiltration permeate is evaporated and crystallized using a monovalent salt MVR to produce sodium chloride crystals with a purity ≥98.5%, meeting the Class I standard of "Industrial Salt" GB / T5462-2015, and can be utilized in compliance with regulations. The conditioned nanofiltration concentrate is treated by a mixed salt evaporation system, producing a small amount of mixed salt which is disposed of as hazardous waste. All the clean condensate produced by the two evaporation systems is sent to the permeate reuse tank and reused for fracturing fluid preparation, reagent preparation, and site cleaning, with no production wastewater discharged. All the waste heat from the condensate is used for preheating the nanofiltration feed water, forming a closed loop with zero discharge of wastewater and waste heat.
[0041] In this invention, the entire anti-scaling system is closed-loop, significantly improving the system's continuous operation cycle: through a four-stage anti-scaling system, it fully complies with the solubility product principle, achieving Ba... 2+ Removal rate ≥99.8%, Sr 2+ With a concentration of ≥95% and calcium and magnesium ≥98%, the risk of irreversible scaling in raw water and concentrate is eliminated from the source; the chemical cleaning cycle of nanofiltration membranes and evaporators is extended from 15-30 days to more than 60 days, the annual unplanned downtime is reduced by more than 60%, and the continuous operating life of the system is increased by more than 2 times.
[0042] Salt resource utilization rate has been greatly improved and hazardous waste volume has been significantly reduced: Nanofiltration waste heat constant temperature control solves the problem of low temperature salt separation deterioration in winter, and the NaCl transmission rate is stably maintained at ≥92% throughout the year; combined with fractional evaporation, the purity of crystallized salt is stable at ≥98.5%, which can be compliantly recycled; with the fractional disposal of solid waste, the amount of hazardous waste generated by the project has been reduced by more than 75%.
[0043] In this invention, evaporation crystallization is performed by treating the nanofiltration permeate with monovalent salt MVR evaporation crystallization.
[0044] In the following examples and comparative examples: the pH of the fracturing flowback fluid to be treated was 6.3, and the viscosity was 36 mPa. s, COD 2780mg / L, oil content 31mg / L, SS 112mg / L, TDS 52000mg / L, Ba 2+ 82 mg / L, Sr 2+ 124 mg / L, Ca 2+ 415 mg / L, Mg 2+ 178 mg / L, Cl - 31500mg / L, total hardness 1860mg / L.
[0045] Example 1 A low-energy, anti-scaling shale gas fracturing flowback fluid wastewater treatment process includes the following steps: The fracturing flowback fluid to be treated is fed into a regulating tank, where it is homogenized in terms of quality and quantity through aeration and stirring. Then, it is fed into a degelatinizing reaction tank, where an oxidant (0.6 g / L, composed of sodium persulfate, ferrous sulfate heptahydrate, and sodium citrate in a mass ratio of 5:3:1) is added. The mixture is stirred at 120 r / min for 45 min for oxidative degelatinization. Finally, the fluid is fed into a vortex flotation unit for oil removal. The solution is then fed into a pressurized dissolved air flotation unit, where 2 mg / L polyaluminum chloride and 0.1 mg / L cationic polyacrylamide are added for further oil removal (the oily scum from the flotation is collected separately and disposed of in compliance with HW08 hazardous waste regulations; the inorganic sludge at the bottom of the tank is discharged into a sludge thickening tank and disposed of together with the inorganic sludge); it is then fed into a primary sedimentation and impurity removal reaction tank where seed crystals (50 mg / L, 300 mesh barium sulfate seed crystals) are added and mixed at 30 r / min for 5 min, followed by the addition of sodium sulfate (Ba(I) from the fracturing flowback fluid to be treated). 2+ molar amount and Sr 2+The total molar amount of the mixture is mixed with sodium sulfate in a 1:1 molar ratio to achieve primary sedimentation and impurity removal. 10 mg / L polyaluminum chloride is added and stirred at 100 rpm for 3 min to induce flocculation. Then, 0.5 mg / L cationic polyacrylamide is added and stirred at 20 rpm for 20 min to aid coagulation. The mixture is then sent to a primary inclined tube sedimentation tank for 45 min of settling to complete solid-liquid separation. Part of the sludge from the sedimentation tank is recycled as seed crystals (75% water content, 10% recycling ratio). The remaining sludge is sent to a sludge thickening tank. The supernatant is sent to a secondary sedimentation and impurity removal reaction tank where sodium hydroxide is added to adjust the pH to 10.5 and mixed for 5 min. Sodium carbonate (Ca from the fracturing flowback fluid to be treated) is then added. 2+ Residual Sr 2+ The mixture (total molar volume to sodium carbonate molar volume ratio of 1:1.1) is used for secondary sedimentation and impurity removal. After adding 5 mg / L polyaluminum chloride and 0.3 mg / L cationic polyacrylamide for flocculation and sedimentation, it is sent to a secondary inclined tube sedimentation tank for settling for 30 minutes (the bottom sludge of the sedimentation tank is sent to a sludge thickening tank for concentration and dewatering) to obtain the supernatant. Hydrochloric acid is added to adjust the pH to 7.0, and the mixture is then treated through a quartz sand multi-media filter and a 5μm security filter before being sent to a coconut shell activated carbon filter, and finally to a plate heat exchanger to connect with the downstream MVR. The system generates 40℃ clean condensate water through inter-wall heat exchange. The nanofiltration inlet water temperature is stably controlled at 28℃ by the automatic control system. After heat exchange, the condensate water is cooled to 25℃. After preheating, the wastewater enters the polyamide nanofiltration membrane unit to obtain nanofiltration permeate and nanofiltration concentrate. The nanofiltration permeate is sent to the monovalent salt MVR evaporation and crystallization system. The nanofiltration concentrate is sent to the concentrate conditioning unit for treatment. After being pre-concentrated 3 times by high-pressure reverse osmosis, the pre-concentrated permeate is sent to the permeate reuse tank. The concentrated concentrate is sent to the mixed salt evaporation system. During the evaporation process, 5mg / L scale inhibitor is continuously added.
[0046] Example 2 A low-energy, anti-scaling shale gas fracturing flowback fluid wastewater treatment process includes the following steps: The fracturing flowback fluid to be treated is fed into a regulating tank, where it is homogenized in terms of quality and quantity through aeration and stirring. Then, it is fed into a degelatinizing reaction tank, where an oxidant (1.2 g / L, composed of sodium persulfate, ferrous sulfate heptahydrate, and sodium citrate in a mass ratio of 5:3:1) is added. The mixture is stirred at 130 r / min for 40 min for oxidative degelatinization. Finally, it is fed into a vortex flotation unit for oil removal. The solution is then fed into a pressurized dissolved air flotation unit, where 5 mg / L polyaluminum chloride and 0.3 mg / L cationic polyacrylamide are added for further oil removal (the oily scum from the flotation is collected separately and disposed of in compliance with HW08 hazardous waste regulations; the inorganic sludge at the bottom of the tank is discharged into a sludge thickening tank and disposed of together with the inorganic sludge); it is then fed into a primary sedimentation and impurity removal reaction tank where seed crystals (80 mg / L, 400 mesh barium sulfate seed crystals) are added and mixed at 40 r / min for 5 min, followed by the addition of sodium sulfate (Ba(I) from the fracturing flowback fluid to be treated). 2+molar amount and Sr 2+ The total molar amount of the mixture is mixed with sodium sulfate in a 1:1 molar ratio to achieve primary precipitation and impurity removal. 20 mg / L polyaluminum chloride is added and stirred at 110 rpm for 2.5 min to aid flocculation. Then, 1 mg / L cationic polyacrylamide is added and stirred at 25 rpm for 18 min to assist coagulation. The mixture is then sent to a primary inclined tube sedimentation tank for 55 min of settling to complete solid-liquid separation. Part of the sludge from the sedimentation tank is recycled as seed crystals (78% water content, 15% reflux ratio). The remaining sludge is sent to a sludge thickening tank. The supernatant is sent to a secondary precipitation and impurity removal reaction tank where sodium hydroxide is added to adjust the pH to 10.8 and mixed for 5 min. Sodium carbonate (Ca from the fracturing flowback fluid to be treated) is then added. 2+ Residual Sr 2+ The mixture (total molar volume to sodium carbonate molar volume ratio of 1:1.2) is used for secondary sedimentation and impurity removal. After adding 15 mg / L polyaluminum chloride and 0.7 mg / L cationic polyacrylamide for flocculation and sedimentation, it is sent to a secondary inclined tube sedimentation tank for settling for 40 minutes (the bottom sludge of the sedimentation tank is sent to a sludge thickening tank for concentration and dewatering) to obtain the supernatant. Hydrochloric acid is added to adjust the pH to 7.5, and the solution is treated through a quartz sand multi-media filter and a 5 μm security filter, then sent to a coconut shell activated carbon filter, and finally to a plate heat exchanger to connect with the downstream MVR system. The 50℃ clean condensate is heated by heat exchange in the wall. The nanofiltration inlet water temperature is stably controlled at 30℃ by the automatic control system. After heat exchange, the condensate is cooled to 28℃. The preheated wastewater enters the polyamide nanofiltration membrane unit to obtain nanofiltration permeate and nanofiltration concentrate. The nanofiltration permeate is sent to the monovalent salt MVR evaporation and crystallization system. The nanofiltration concentrate is sent to the concentrate conditioning unit for treatment. It is pre-concentrated 4 times by high pressure reverse osmosis. The pre-concentrated permeate is sent to the permeate reuse tank. The concentrated concentrate is sent to the mixed salt evaporation system. 5mg / L scale inhibitor is continuously added during the evaporation process to prevent scaling throughout the process.
[0047] Example 3 A low-energy, anti-scaling shale gas fracturing flowback fluid wastewater treatment process includes the following steps: The fracturing flowback fluid to be treated is fed into a regulating tank, where it is homogenized in terms of quality and quantity through aeration and stirring. Then, it is fed into a degelatinizing reaction tank, where an oxidant (1.8 g / L, composed of sodium persulfate, ferrous sulfate heptahydrate, and sodium citrate in a mass ratio of 5:3:1) is added. The mixture is stirred at 150 r / min for 45 min for oxidative degelatinization. After deoiling, the fluid is fed into a vortex flotation unit for further treatment. The solution is fed into a pressurized dissolved air flotation unit, where 10 mg / L polyaluminum chloride and 0.5 mg / L cationic polyacrylamide are added for further oil removal (the oily scum from the flotation is collected separately and disposed of in compliance with HW08 hazardous waste regulations; the inorganic sludge at the bottom of the tank is discharged into a sludge thickening tank and disposed of together with the inorganic sludge); it is then fed into a primary sedimentation and impurity removal reaction tank where seed crystals (100 mg / L, 500 mesh barium sulfate seed crystals) are added and mixed at 50 r / min for 5 min, followed by the addition of sodium sulfate (Ba(I) from the fracturing flowback fluid to be treated). 2+ molar amount and Sr 2+ The total molar amount of the mixture is mixed with sodium sulfate in a 1:1 molar ratio to achieve primary precipitation and impurity removal. 30 mg / L polyaluminum chloride is added and stirred at 120 rpm for 3 min to induce flocculation. Then, 1.5 mg / L cationic polyacrylamide is added and stirred at 30 rpm for 20 min to aid coagulation. The mixture is then sent to a primary inclined tube sedimentation tank for 60 min of settling to complete solid-liquid separation. Part of the sludge from the sedimentation tank is recycled as seed crystals (80% water content, 20% recycling ratio). The remaining sludge is sent to a sludge thickening tank. The supernatant is sent to a secondary precipitation and impurity removal reaction tank where sodium hydroxide is added to adjust the pH to 11.0 and the mixture is stirred for 5 min. Sodium carbonate (Ca from the fracturing flowback fluid to be treated) is then added. 2+ Residual Sr 2+ The mixture (total molar volume to sodium carbonate molar volume ratio of 1:1.3) is used for secondary sedimentation and impurity removal. After adding 20 mg / L polyaluminum chloride and 1.0 mg / L cationic polyacrylamide for flocculation and sedimentation, it is sent to a secondary inclined tube sedimentation tank for settling for 45 minutes (the bottom sludge of the sedimentation tank is sent to a sludge thickening tank for concentration and dewatering) to obtain the supernatant. Hydrochloric acid is added to adjust the pH to 8.0, and the mixture is then treated through a quartz sand multi-media filter and a 5 μm security filter before being sent to a coconut shell activated carbon filter, and finally to a plate heat exchanger to connect with the downstream MVR system. The 55℃ clean condensate is heated by heat exchange in the wall. The nanofiltration inlet water temperature is stably controlled at 32℃ by the automatic control system. After heat exchange, the condensate is cooled to 30℃. The preheated wastewater enters the polyamide nanofiltration membrane unit to obtain nanofiltration permeate and nanofiltration concentrate. The nanofiltration permeate is sent to the monovalent salt MVR evaporation and crystallization system. The nanofiltration concentrate is sent to the concentrate conditioning unit for treatment. It is pre-concentrated 5 times by high pressure reverse osmosis. The pre-concentrated permeate is sent to the permeate reuse tank. The concentrated concentrate is sent to the mixed salt evaporation system. During the evaporation process, 10mg / L scale inhibitor is continuously added to prevent scaling throughout the process.
[0048] Example 4 A low-energy, anti-scaling shale gas fracturing flowback fluid wastewater treatment process includes the following steps: The fracturing flowback fluid to be treated is fed into a regulating tank, where it is homogenized in terms of quality and quantity through aeration and stirring. Then, it is fed into a degelatinizing reaction tank, where an oxidant (1.2 g / L, composed of sodium persulfate, ferrous sulfate heptahydrate, and sodium citrate in a mass ratio of 6:2:1) is added. The mixture is stirred at 130 r / min for 40 min for oxidative degelatinization. Finally, it is fed into a vortex flotation unit for oil removal. The solution is then fed into a pressurized dissolved air flotation unit, where 5 mg / L polyaluminum chloride and 0.3 mg / L cationic polyacrylamide are added for further oil removal (the oily scum from the flotation is collected separately and disposed of in compliance with HW08 hazardous waste regulations; the inorganic sludge at the bottom of the tank is discharged into a sludge thickening tank and disposed of together with the inorganic sludge); it is then fed into a primary sedimentation and impurity removal reaction tank where seed crystals (80 mg / L, 400 mesh barium sulfate seed crystals) are added and mixed at 40 r / min for 5 min, followed by the addition of sodium sulfate (Ba(I) from the fracturing flowback fluid to be treated). 2+ molar amount and Sr 2+ The total molar amount of the mixture is mixed with sodium sulfate in a 1:1 molar ratio to achieve primary precipitation and impurity removal. 20 mg / L polyaluminum chloride is added and stirred at 110 rpm for 2.5 min to aid flocculation. Then, 1 mg / L cationic polyacrylamide is added and stirred at 25 rpm for 18 min to assist coagulation. The mixture is then sent to a primary inclined tube sedimentation tank for 55 min of settling to complete solid-liquid separation. Part of the sludge from the sedimentation tank is recycled as seed crystals (78% water content, 15% reflux ratio). The remaining sludge is sent to a sludge thickening tank. The supernatant is sent to a secondary precipitation and impurity removal reaction tank where sodium hydroxide is added to adjust the pH to 10.8 and mixed for 5 min. Sodium carbonate (Ca from the fracturing flowback fluid to be treated) is then added. 2+ Residual Sr 2+The mixture (total molar volume to sodium carbonate molar volume ratio of 1:1.2) is used for secondary sedimentation and impurity removal. After adding 15 mg / L polyaluminum chloride and 0.7 mg / L cationic polyacrylamide for flocculation and sedimentation, it is sent to a secondary inclined tube sedimentation tank for settling for 40 minutes (the bottom sludge of the sedimentation tank is sent to a sludge thickening tank for concentration and dewatering) to obtain the supernatant. Hydrochloric acid is added to adjust the pH to 7.5, and the solution is treated through a quartz sand multi-media filter and a 5 μm security filter, then sent to a coconut shell activated carbon filter, and finally to a plate heat exchanger to connect with the downstream MVR system. The 50℃ clean condensate is heated by heat exchange in the wall. The nanofiltration inlet water temperature is stably controlled at 30℃ by the automatic control system. After heat exchange, the condensate is cooled to 28℃. The preheated wastewater enters the polyamide nanofiltration membrane unit to obtain nanofiltration permeate and nanofiltration concentrate. The nanofiltration permeate is sent to the monovalent salt MVR evaporation and crystallization system. The nanofiltration concentrate is sent to the concentrate conditioning unit for treatment. It is pre-concentrated 4 times by high pressure reverse osmosis. The pre-concentrated permeate is sent to the permeate reuse tank. The concentrated concentrate is sent to the mixed salt evaporation system. 5mg / L scale inhibitor is continuously added during the evaporation process to prevent scaling throughout the process.
[0049] Example 5 A low-energy, anti-scaling shale gas fracturing flowback fluid wastewater treatment process includes the following steps: The fracturing flowback fluid to be treated is fed into a regulating tank, where it is homogenized in terms of quality and quantity through aeration and stirring. Then, it is fed into a degelatinizing reaction tank, where an oxidant (1.2 g / L, composed of sodium persulfate, ferrous sulfate heptahydrate, and sodium citrate in a mass ratio of 7:2:1) is added. The mixture is stirred at 130 r / min for 40 min for oxidative degelatinization. Finally, the fluid is fed into a vortex flotation unit for oil removal. The solution is then fed into a pressurized dissolved air flotation unit, where 5 mg / L polyaluminum chloride and 0.3 mg / L cationic polyacrylamide are added for further oil removal (the oily scum from the flotation is collected separately and disposed of in compliance with HW08 hazardous waste regulations; the inorganic sludge at the bottom of the tank is discharged into a sludge thickening tank and disposed of together with the inorganic sludge); it is then fed into a primary sedimentation and impurity removal reaction tank where seed crystals (80 mg / L, 400 mesh barium sulfate seed crystals) are added and mixed at 40 r / min for 5 min, followed by the addition of sodium sulfate (Ba(I) from the fracturing flowback fluid to be treated). 2+ molar amount and Sr 2+ The total molar amount of the mixture is mixed with sodium sulfate in a 1:1 molar ratio to achieve primary precipitation and impurity removal. 20 mg / L polyaluminum chloride is added and stirred at 110 rpm for 2.5 min to aid flocculation. Then, 1 mg / L cationic polyacrylamide is added and stirred at 25 rpm for 18 min to assist coagulation. The mixture is then sent to a primary inclined tube sedimentation tank for 55 min of settling to complete solid-liquid separation. Part of the sludge from the sedimentation tank is recycled as seed crystals (78% water content, 15% reflux ratio). The remaining sludge is sent to a sludge thickening tank. The supernatant is sent to a secondary precipitation and impurity removal reaction tank where sodium hydroxide is added to adjust the pH to 10.8 and mixed for 5 min. Sodium carbonate (Ca from the fracturing flowback fluid to be treated) is then added.2+ Residual Sr 2+ The mixture (total molar volume to sodium carbonate molar volume ratio of 1:1.2) is used for secondary sedimentation and impurity removal. After adding 15 mg / L polyaluminum chloride and 0.7 mg / L cationic polyacrylamide for flocculation and sedimentation, it is sent to a secondary inclined tube sedimentation tank for settling for 40 minutes (the bottom sludge of the sedimentation tank is sent to a sludge thickening tank for concentration and dewatering) to obtain the supernatant. Hydrochloric acid is added to adjust the pH to 7.5, and the solution is treated through a quartz sand multi-media filter and a 5 μm security filter, then sent to a coconut shell activated carbon filter, and finally to a plate heat exchanger to connect with the downstream MVR system. The 50℃ clean condensate is heated by heat exchange in the wall. The nanofiltration inlet water temperature is stably controlled at 30℃ by the automatic control system. After heat exchange, the condensate is cooled to 28℃. The preheated wastewater enters the polyamide nanofiltration membrane unit to obtain nanofiltration permeate and nanofiltration concentrate. The nanofiltration permeate is sent to the monovalent salt MVR evaporation and crystallization system. The nanofiltration concentrate is sent to the concentrate conditioning unit for treatment. It is pre-concentrated 4 times by high pressure reverse osmosis. The pre-concentrated permeate is sent to the permeate reuse tank. The concentrated concentrate is sent to the mixed salt evaporation system. 5mg / L scale inhibitor is continuously added during the evaporation process to prevent scaling throughout the process.
[0050] Example 6 A low-energy, anti-scaling shale gas fracturing flowback fluid wastewater treatment process includes the following steps: The fracturing flowback fluid to be treated is fed into a regulating tank, where it is homogenized in terms of quality and quantity through aeration and stirring. Then, it is fed into a degelatinizing reaction tank, where an oxidant (1.2 g / L, composed of sodium persulfate, ferrous sulfate heptahydrate, and sodium citrate in a mass ratio of 3:2:1) is added. The mixture is stirred at 130 r / min for 40 min for oxidative degelatinization. Finally, the fluid is fed into a vortex flotation unit for oil removal. The solution is then fed into a pressurized dissolved air flotation unit, where 5 mg / L polyaluminum chloride and 0.3 mg / L cationic polyacrylamide are added for further oil removal (the oily scum from the flotation is collected separately and disposed of in compliance with HW08 hazardous waste regulations; the inorganic sludge at the bottom of the tank is discharged into a sludge thickening tank and disposed of together with the inorganic sludge); it is then fed into a primary sedimentation and impurity removal reaction tank where seed crystals (80 mg / L, 400 mesh barium sulfate seed crystals) are added and mixed at 40 r / min for 5 min, followed by the addition of sodium sulfate (Ba(I) from the fracturing flowback fluid to be treated). 2+ molar amount and Sr 2+The total molar amount of the mixture is mixed with sodium sulfate in a 1:1 molar ratio to achieve primary precipitation and impurity removal. 20 mg / L polyaluminum chloride is added and stirred at 110 rpm for 2.5 min to aid flocculation. Then, 1 mg / L cationic polyacrylamide is added and stirred at 25 rpm for 18 min to assist coagulation. The mixture is then sent to a primary inclined tube sedimentation tank for 55 min of settling to complete solid-liquid separation. Part of the sludge from the sedimentation tank is recycled as seed crystals (78% water content, 15% reflux ratio). The remaining sludge is sent to a sludge thickening tank. The supernatant is sent to a secondary precipitation and impurity removal reaction tank where sodium hydroxide is added to adjust the pH to 10.8 and mixed for 5 min. Sodium carbonate (Ca from the fracturing flowback fluid to be treated) is then added. 2+ Residual Sr 2+ The mixture (total molar volume to sodium carbonate molar volume ratio of 1:1.2) is used for secondary sedimentation and impurity removal. After adding 15 mg / L polyaluminum chloride and 0.7 mg / L cationic polyacrylamide for flocculation and sedimentation, it is sent to a secondary inclined tube sedimentation tank for settling for 40 minutes (the bottom sludge of the sedimentation tank is sent to a sludge thickening tank for concentration and dewatering) to obtain the supernatant. Hydrochloric acid is added to adjust the pH to 7.5, and the solution is treated through a quartz sand multi-media filter and a 5 μm security filter, then sent to a coconut shell activated carbon filter, and finally to a plate heat exchanger to connect with the downstream MVR system. The 50℃ clean condensate is heated by heat exchange in the wall. The nanofiltration inlet water temperature is stably controlled at 30℃ by the automatic control system. After heat exchange, the condensate is cooled to 28℃. The preheated wastewater enters the polyamide nanofiltration membrane unit to obtain nanofiltration permeate and nanofiltration concentrate. The nanofiltration permeate is sent to the monovalent salt MVR evaporation and crystallization system. The nanofiltration concentrate is sent to the concentrate conditioning unit for treatment. It is pre-concentrated 4 times by high pressure reverse osmosis. The pre-concentrated permeate is sent to the permeate reuse tank. The concentrated concentrate is sent to the mixed salt evaporation system. 5mg / L scale inhibitor is continuously added during the evaporation process to prevent scaling throughout the process.
[0051] Example 7 A low-energy, anti-scaling shale gas fracturing flowback fluid wastewater treatment process includes the following steps: The fracturing flowback fluid to be treated is fed into a regulating tank, where it is homogenized in terms of quality and quantity through aeration and stirring. Then, it is fed into a degelatinizing reaction tank, where an oxidant (1.2 g / L, composed of sodium persulfate, ferrous sulfate heptahydrate, and sodium citrate in a mass ratio of 6:4:1) is added. The mixture is stirred at 130 r / min for 40 min for oxidative degelatinization. Finally, the fluid is fed into a vortex flotation unit for oil removal. The solution is then fed into a pressurized dissolved air flotation unit, where 5 mg / L polyaluminum chloride and 0.3 mg / L cationic polyacrylamide are added for further oil removal (the oily scum from the flotation is collected separately and disposed of in compliance with HW08 hazardous waste regulations; the inorganic sludge at the bottom of the tank is discharged into a sludge thickening tank and disposed of together with the inorganic sludge); it is then fed into a primary sedimentation and impurity removal reaction tank where seed crystals (80 mg / L, 400 mesh barium sulfate seed crystals) are added and mixed at 40 r / min for 5 min, followed by the addition of sodium sulfate (Ba(I) from the fracturing flowback fluid to be treated).2+ molar amount and Sr 2+ The total molar amount of the mixture is mixed with sodium sulfate in a 1:1 molar ratio to achieve primary precipitation and impurity removal. 20 mg / L polyaluminum chloride is added and stirred at 110 rpm for 2.5 min to aid flocculation. Then, 1 mg / L cationic polyacrylamide is added and stirred at 25 rpm for 18 min to assist coagulation. The mixture is then sent to a primary inclined tube sedimentation tank for 55 min of settling to complete solid-liquid separation. Part of the sludge from the sedimentation tank is recycled as seed crystals (78% water content, 15% reflux ratio). The remaining sludge is sent to a sludge thickening tank. The supernatant is sent to a secondary precipitation and impurity removal reaction tank where sodium hydroxide is added to adjust the pH to 10.8 and mixed for 5 min. Sodium carbonate (Ca from the fracturing flowback fluid to be treated) is then added. 2+ Residual Sr 2+ The mixture (total molar volume to sodium carbonate molar volume ratio of 1:1.2) is used for secondary sedimentation and impurity removal. After adding 15 mg / L polyaluminum chloride and 0.7 mg / L cationic polyacrylamide for flocculation and sedimentation, it is sent to a secondary inclined tube sedimentation tank for settling for 40 minutes (the bottom sludge of the sedimentation tank is sent to a sludge thickening tank for concentration and dewatering) to obtain the supernatant. Hydrochloric acid is added to adjust the pH to 7.5, and the solution is treated through a quartz sand multi-media filter and a 5 μm security filter, then sent to a coconut shell activated carbon filter, and finally to a plate heat exchanger to connect with the downstream MVR system. The 50℃ clean condensate is heated by heat exchange in the wall. The nanofiltration inlet water temperature is stably controlled at 30℃ by the automatic control system. After heat exchange, the condensate is cooled to 28℃. The preheated wastewater enters the polyamide nanofiltration membrane unit to obtain nanofiltration permeate and nanofiltration concentrate. The nanofiltration permeate is sent to the monovalent salt MVR evaporation and crystallization system. The nanofiltration concentrate is sent to the concentrate conditioning unit for treatment. It is pre-concentrated 4 times by high pressure reverse osmosis. The pre-concentrated permeate is sent to the permeate reuse tank. The concentrated concentrate is sent to the mixed salt evaporation system. 5mg / L scale inhibitor is continuously added during the evaporation process to prevent scaling throughout the process.
[0052] Comparative Example 1 A low-energy, anti-scaling shale gas fracturing flowback fluid wastewater treatment process includes the following steps: The fracturing flowback fluid to be treated is sent to an equalization tank, where it is homogenized in terms of water quality and quantity through aeration and stirring. Then, it is sent to a degelatinization reaction tank, where an oxidant (1.2 g / L, composed of sodium persulfate and ferrous sulfate heptahydrate at a mass ratio of 6:2) is added and mixed at 130 r / min for 40 min for oxidative degelatinization. After deoiling in a vortex flotation unit, it is then sent to a further... In the dissolved air flotation unit, 5 mg / L polyaluminum chloride and 0.3 mg / L cationic polyacrylamide are added for further oil removal (the oily scum from the flotation is collected separately and disposed of in compliance with HW08 hazardous waste regulations; the inorganic sludge at the bottom of the tank is discharged into the sludge thickening tank and disposed of together with the inorganic sludge); the mixture is then sent to the primary sedimentation and impurity removal reaction tank where seed crystals (80 mg / L, 400 mesh barium sulfate seed crystals) are added and mixed at 40 r / min for 5 min, followed by the addition of sodium sulfate (Ba(I) from the fracturing flowback fluid to be treated). 2+ molar amount and Sr 2+ The total molar amount of the mixture is mixed with sodium sulfate in a 1:1 molar ratio to achieve primary precipitation and impurity removal. 20 mg / L polyaluminum chloride is added and stirred at 110 rpm for 2.5 min to aid flocculation. Then, 1 mg / L cationic polyacrylamide is added and stirred at 25 rpm for 18 min to assist coagulation. The mixture is then sent to a primary inclined tube sedimentation tank for 55 min of settling to complete solid-liquid separation. Part of the sludge from the sedimentation tank is recycled as seed crystals (78% water content, 15% reflux ratio). The remaining sludge is sent to a sludge thickening tank. The supernatant is sent to a secondary precipitation and impurity removal reaction tank where sodium hydroxide is added to adjust the pH to 10.8 and mixed for 5 min. Sodium carbonate (Ca from the fracturing flowback fluid to be treated) is then added. 2+ Residual Sr 2 + The mixture (total molar volume to sodium carbonate molar volume ratio of 1:1.2) is used for secondary sedimentation and impurity removal. After adding 15 mg / L polyaluminum chloride and 0.7 mg / L cationic polyacrylamide for flocculation and sedimentation, it is sent to a secondary inclined tube sedimentation tank for settling for 40 minutes (the bottom sludge of the sedimentation tank is sent to a sludge thickening tank for concentration and dewatering) to obtain the supernatant. Hydrochloric acid is added to adjust the pH to 7.5, and the solution is treated through a quartz sand multi-media filter and a 5 μm security filter, then sent to a coconut shell activated carbon filter, and finally to a plate heat exchanger to connect with the downstream MVR system. The 50℃ clean condensate is heated by heat exchange in the wall. The nanofiltration inlet water temperature is stably controlled at 30℃ by the automatic control system. After heat exchange, the condensate is cooled to 28℃. The preheated wastewater enters the polyamide nanofiltration membrane unit to obtain nanofiltration permeate and nanofiltration concentrate. The nanofiltration permeate is sent to the monovalent salt MVR evaporation and crystallization system. The nanofiltration concentrate is sent to the concentrate conditioning unit for treatment. It is pre-concentrated 4 times by high pressure reverse osmosis. The pre-concentrated permeate is sent to the permeate reuse tank. The concentrated concentrate is sent to the mixed salt evaporation system. 5mg / L scale inhibitor is continuously added during the evaporation process to prevent scaling throughout the process.
[0053] Comparative Example 2 A low-energy, anti-scaling shale gas fracturing flowback fluid wastewater treatment process includes the following steps: The fracturing flowback fluid to be treated is fed into a regulating tank, where it is homogenized in terms of quality and quantity through aeration and stirring. Then, it is fed into a degelatinizing reaction tank, where an oxidant (1.2 g / L, composed of sodium persulfate, ferrous sulfate heptahydrate, and hydrochloric acid in a mass ratio of 6:2:1) is added. The mixture is stirred at 130 r / min for 40 min for oxidative degelatinization. After deoiling, the fluid is fed into a vortex flotation unit for further treatment. The solution is fed into a pressurized dissolved air flotation unit, where 5 mg / L polyaluminum chloride and 0.3 mg / L cationic polyacrylamide are added for further oil removal (the oily scum from the flotation is collected separately and disposed of in compliance with HW08 hazardous waste regulations; the inorganic sludge at the bottom of the tank is discharged into a sludge thickening tank and disposed of together with the inorganic sludge); it is then fed into a primary sedimentation and impurity removal reaction tank where seed crystals (80 mg / L, 400 mesh barium sulfate seed crystals) are added and mixed at 40 r / min for 5 min, followed by the addition of sodium sulfate (Ba(I) from the fracturing flowback fluid to be treated). 2+ molar amount and Sr 2+ The total molar amount of the mixture is mixed with sodium sulfate in a 1:1 molar ratio to achieve primary precipitation and impurity removal. 20 mg / L polyaluminum chloride is added and stirred at 110 rpm for 2.5 min to aid flocculation. Then, 1 mg / L cationic polyacrylamide is added and stirred at 25 rpm for 18 min to assist coagulation. The mixture is then sent to a primary inclined tube sedimentation tank for 55 min of settling to complete solid-liquid separation. Part of the sludge from the sedimentation tank is recycled as seed crystals (78% water content, 15% reflux ratio). The remaining sludge is sent to a sludge thickening tank. The supernatant is sent to a secondary precipitation and impurity removal reaction tank where sodium hydroxide is added to adjust the pH to 10.8 and mixed for 5 min. Sodium carbonate (Ca from the fracturing flowback fluid to be treated) is then added. 2 + Residual Sr 2+The mixture (total molar volume to sodium carbonate molar volume ratio of 1:1.2) is used for secondary sedimentation and impurity removal. After adding 15 mg / L polyaluminum chloride and 0.7 mg / L cationic polyacrylamide for flocculation and sedimentation, it is sent to a secondary inclined tube sedimentation tank for settling for 40 minutes (the bottom sludge of the sedimentation tank is sent to a sludge thickening tank for concentration and dewatering) to obtain the supernatant. Hydrochloric acid is added to adjust the pH to 7.5, and the solution is treated through a quartz sand multi-media filter and a 5 μm security filter, then sent to a coconut shell activated carbon filter, and finally to a plate heat exchanger to connect with the downstream MVR system. The 50℃ clean condensate is heated by heat exchange in the wall. The nanofiltration inlet water temperature is stably controlled at 30℃ by the automatic control system. After heat exchange, the condensate is cooled to 28℃. The preheated wastewater enters the polyamide nanofiltration membrane unit to obtain nanofiltration permeate and nanofiltration concentrate. The nanofiltration permeate is sent to the monovalent salt MVR evaporation and crystallization system. The nanofiltration concentrate is sent to the concentrate conditioning unit for treatment. It is pre-concentrated 4 times by high pressure reverse osmosis. The pre-concentrated permeate is sent to the permeate reuse tank. The concentrated concentrate is sent to the mixed salt evaporation system. 5mg / L scale inhibitor is continuously added during the evaporation process to prevent scaling throughout the process.
[0054] Performance testing: Viscosity of the effluent after gel breaking: The viscosity of the effluent was determined according to the rotation method specified in the national standard GB / T 10247-2008 "Viscosity Measurement Method"; COD removal rate: The COD removal rate was determined according to the method specified in standard HJ 828-2017 "Determination of Chemical Oxygen Demand in Water - Dichromate Method", where COD removal rate = (COD + COD + COD) / COD + ... 待处理压裂返排液 -COD 破胶出水 COD 待处理压裂返排液 ×100%; System pH: The system pH was tested according to the method specified in standard HJ 1147-2020 "Determination of pH Value of Water by Electrode Method"; Ba 2+ Removal rate: Ba was tested according to the method specified in standard HJ 603-2011 "Determination of Barium in Water by Flame Atomic Absorption Spectrophotometry". 2+ Removal rate, Ba 2+ Removal rate = [ρ 待处理压裂返排液 (Ba 2+ )-ρ 破胶出水 (Ba 2+ )] / ρ 待处理压裂返排液 (Ba 2 + )×100%; The performance of each embodiment and comparative example after testing is shown in Table 1.
[0055] Table 1 Test results of Examples 1-7 and Comparative Examples 1-2
[0056] Viscosity, COD removal rate, and Ba2O3 content of effluent after gel breaking in Examples 1-7 2+ The removal rates were all higher than those of comparative examples 1-2, indicating that the present invention improved the treatment efficiency of the debinding system by adding sodium persulfate, ferrous sulfate heptahydrate and sodium citrate as oxidants, thereby increasing the permeability of monovalent salts.
[0057] Viscosity, COD removal rate, and Ba2O3 content of effluent after gel breaking in Examples 1-5 2+ The removal rates were all higher than those in Examples 6 and 7, indicating that the present invention further improved the treatment efficiency of the debinding system by adding sodium persulfate, ferrous sulfate heptahydrate and sodium citrate in a mass ratio of 5-7:2-3:1 as oxidants, thereby increasing the permeability of monovalent salts.
[0058] The NaCl transmittance test data for Example 2 are shown in Table 2 below; NaCl transmission rate is in accordance with standard HJ 84-2016 "Water Quality Inorganic Anions (F)". - Cl - NO2 - ,Br - NO3 - PO4 3- SO3 2- SO4 2- Determination of NaCl by Ion Chromatography (ρ) 纳滤透过液 (Cl - ) / ρ 待处理压裂返排液 (Cl - )×100%.
[0059] Table 2 Performance test data of Example 2
[0060] The data from Example 2 show that the monovalent salt in this scheme has excellent monovalent salt permeability.
[0061] A shale gas fracturing flowback fluid wastewater treatment system with anti-scaling and low energy consumption operated continuously and stably for 66 days, with nanofiltration influent Ba 2+ 0.011 mg / L, Sr 2+ The total organic matter content was 0.054 mg / L, total hardness 15.2 mg / L, COD 320 mg / L, and total phosphorus 0.32 mg / L; the final product water had TDS of 210 mg / L and COD of 38 mg / L, and the remaining indicators were not detected. This indicates that the solution can improve the continuous operation cycle of the system and increase the chemical cleaning cycle of the nanofiltration membrane and evaporator.
[0062] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. An anti-fouling low energy consumption wastewater treatment process for shale gas fracturing flowback fluid, characterized in that, The process includes homogenization conditioning, oxidation breaking, air flotation oil removal, primary sedimentation for impurity removal, primary flocculation sedimentation, secondary sedimentation for impurity removal, secondary flocculation sedimentation, and post-treatment of the fracturing flowback fluid to be treated; the raw materials for primary sedimentation for impurity removal include barium sulfate and sodium sulfate; the raw materials for secondary sedimentation for impurity removal include sodium hydroxide and sodium carbonate. An oxidizing agent is added during the oxidative degelatination process; the oxidizing agent comprises sodium persulfate, ferrous sulfate heptahydrate, and sodium citrate.
2. The anti-fouling low energy consumption wastewater treatment process for shale gas fracturing flow-back fluid according to claim 1, characterized in that, The mass ratio of sodium persulfate, ferrous sulfate heptahydrate, and sodium citrate is 5~7:2~3:
1.
3. The shale gas fracturing flowback fluid wastewater treatment process according to claim 1, characterized in that, The pH of the fracturing flowback fluid to be treated is 4.0~10.
0.
4. The shale gas fracturing flowback fluid wastewater treatment process according to claim 1, characterized in that, The oxidative debonding includes the following steps: after homogenization and conditioning, the mixture is fed into a debonding reaction tank, and the oxidant is added to carry out oxidative debonding.
5. The shale gas fracturing flowback fluid wastewater treatment process according to claim 4, characterized in that, The air flotation oil removal process includes the following steps: after oxidation and degelatinization, the wastewater is sent to the vortex air flotation unit for oil removal, and then sent to the pressurized dissolved air flotation unit for further oil removal.
6. The shale gas fracturing flowback fluid wastewater treatment process according to claim 1, characterized in that, The primary sedimentation and impurity removal process includes the following steps: after air flotation for oil removal, the wastewater is sent to a primary sedimentation and impurity removal reaction tank, seed crystals are added and mixed evenly, and then sodium sulfate is added and mixed to achieve primary sedimentation and impurity removal.
7. The shale gas fracturing flowback fluid wastewater treatment process according to claim 1, characterized in that, The primary flocculation and sedimentation includes the following steps: after primary sedimentation to remove impurities, polyaluminum chloride and cationic polyacrylamide are added to the wastewater, followed by flocculation and sedimentation to obtain the supernatant.
8. The shale gas fracturing flowback fluid wastewater treatment process according to claim 1, characterized in that, The secondary sedimentation and impurity removal includes the following steps: after primary flocculation and sedimentation, the wastewater is sent to a secondary sedimentation and impurity removal reaction tank, an alkaline regulator is added to adjust the pH to 10.5~11.0, sodium carbonate is added and mixed to achieve secondary sedimentation and impurity removal.
9. The shale gas fracturing flowback fluid wastewater treatment process according to claim 1, characterized in that, The secondary flocculation and sedimentation includes the following steps: after secondary sedimentation to remove impurities, polyaluminum chloride and cationic polyacrylamide are added to the wastewater, and after flocculation and sedimentation, a supernatant is obtained.
10. The shale gas fracturing flowback fluid wastewater treatment process according to claim 1, characterized in that, The post-processing includes the following steps: filtration, adsorption, nanofiltration for salt separation, and evaporation crystallization.