Fracturing flow-back fluid treatment system and treatment method thereof

Abstract

The invention discloses a fracturing flow-back fluid treatment system and a treatment method thereof. The fracturing flow-back fluid treatment system comprises air flotation equipment, a sedimentation tank group, sand filtration equipment, nanofiltration equipment, a sedimentation-electrolysis-biochemical treatment equipment group and ozone generation equipment, the air flotation equipment, the sedimentation tank group, the sand filtration equipment and the nanofiltration equipment are sequentially communicated, the water production end of the nanofiltration equipment is communicated to the ozone generation equipment, and the concentrated water end of the nanofiltration equipment is communicated to the sedimentation-electrolysis-biochemical treatment equipment group. The invention mainly solves the problem of how to provide a fracturing flow-back fluid treatment system and a treatment method thereof. According to the invention, the emulsification state of the fracturing flow-back fluid is destroyed by utilizing the air floatation treatment stage, so that organic pollutants, colloids and oily substances in the fracturing flow-back fluid are converted into suspension states and are scraped by the slag scraping device of the air floatation equipment; therefore, demulsification and purification of the fracturing flow-back fluid are completed in the mode of being single in step, comprehensive in removal type, high in pollutant removal rate, high in treatment efficiency and low in comprehensive cost.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment systems, and particularly to a fracturing flowback fluid treatment system and a treatment method thereof. Background Art

[0002] Fracturing flowback fluid is a mixed liquid that partially returns to the ground after high-pressure operation of the fracturing fluid injected into the formation through hydraulic fracturing technology during the exploitation of unconventional oil and gas such as shale gas and tight oil and gas.

[0003] The types of pollutants contained in the fracturing flowback fluid include: organic pollutants (such as fracturing fluid additives and formation hydrocarbon substances, etc.), suspended solids and solid particles (such as proppant residues and formation debris, etc.), inorganic salts (such as calcium ions, magnesium ions and barium ions, etc.), microorganisms and heavy metals (such as mercury, lead, arsenic and cadmium, etc.).

[0004] Therefore, in the purification process of fracturing flowback fluid, the difficulties include:

[0005] 1. The fracturing flowback fluid has a high degree of emulsification:

[0006] Due to the large amount of organic pollutants contained in the fracturing flowback fluid, it is easy to form an emulsified state, making the viscosity of the fracturing flowback fluid relatively high, which directly affects the treatment efficiency of various pollutants.

[0007] Publication text of a Chinese invention patent with the publication number CN110981040A and the title "A fracturing flowback fluid treatment device and treatment method", which includes the following steps: S001: Add hydrogen peroxide with a concentration of 0.5%-1% to the oxidation tank 1 to oxidize the fracturing flowback fluid; S002: Pass the oxidized fracturing flowback fluid through the tubular electrocoagulation reactor 2 to carry out an electrochemical reaction on the fracturing flowback fluid, so that the pollutants in the fracturing flowback fluid are separated to form flocs; S003: Pass the fracturing flowback fluid flowing out of the tubular electrocoagulation reactor 2 into the pre-coated membrane filter 4, filter out the flocs and debris, and then pass it into the filtrate tank 5. In step S001, the fracturing flowback fluid is oxidized by hydrogen peroxide, which will not introduce new substances to cause secondary pollution, and break the chains of residual organic macromolecules in the flowback fluid, reducing its viscosity, which is beneficial to the electrocoagulation reaction in the next step; in step S002, after the oxidized fracturing flowback fluid enters the tubular electrocoagulation reactor 2, it undergoes electrocoagulation, air flotation, oxidation and reduction effects through the electrochemical reaction of the positive and negative electrodes in the monomer reactor 210, so that the organic matter, colloid and solid suspended matter in the fracturing flowback fluid are coagulated and destabilized to form flocs; in step S003, after the fracturing flowback fluid enters the liquid storage tank 401 of the pre-coated membrane filter 4, it is sucked into the filter drum 402 under the action of the vacuum pump 11, and pollutants such as flocs are intercepted on the circumferential surface of the filter drum 402, and the clear liquid enters the filtrate tank 5 under the suction of the negative pressure pump and can be reused on site.

[0008] However, this method requires oxidizing the fracturing flowback fluid with hydrogen peroxide, carrying out an electrochemical reaction on the fracturing flowback fluid through the tubular electrocoagulation reactor 2, and then passing it into the pre-coated membrane filter 4 to filter out the flocs and debris to complete the "demulsification" of the fracturing flowback fluid. Its process is numerous, and obviously the chemical agent cost, equipment cost and energy consumption are all relatively high; in addition, oxidizing the fracturing flowback fluid with hydrogen peroxide does not directly remove organic pollutants, but only converts the organic pollutants into other types, and still requires more and more complicated treatment processes to completely remove the organic pollutants.

[0009] 2. The hardness of the fracturing flowback fluid is relatively high:

[0010] The fracturing flowback fluid contains inorganic salts such as calcium ions, magnesium ions and barium ions, as well as heavy metals such as mercury, lead, arsenic and cadmium, making the hardness of the fracturing flowback fluid relatively high (more than 20000 mg / L in terms of CaCO3).

[0011] The Chinese invention patent publication with publication number CN118063049A and titled "System and method for removing iodine, barium and strontium from fracturing flowback fluid and recycling evaporation salt" has a water inlet of the de-hardening tank 200 connected to a water outlet of the residual chlorine removal tank 104. After the redox produced water enters the de-hardening tank 200, a de-hardening agent is added to the redox produced water through a de-hardening agent dosing device (not shown). The de-hardening agent specifically includes sodium hydroxide and sodium carbonate. Sodium hydroxide reacts with magnesium ions in the water to generate water-insoluble magnesium hydroxide, while sodium carbonate reacts with calcium ions in the water to generate water-insoluble calcium carbonate.

[0012] However, when the pH value is greater than or equal to 7, the reaction efficiency of sodium carbonate with calcium ions is not high when used as a de-hardening agent, which is contrary to the pH value requirement of another de-hardening agent, sodium hydroxide, and the treatment time of the fracturing return fluid is longer, which is not conducive to improving the treatment efficiency of the fracturing return fluid.

[0013] 3. The COD value of fracturing flowback fluid is relatively high. If Fenton oxidation method is used, although the COD value of fracturing flowback fluid can be effectively reduced, the cost of reagents and equipment is relatively high, and the treatment of by-product iron sludge also requires high costs.

[0014] In summary, how to provide a fracturing flowback fluid treatment system and a treatment method thereof with comprehensive pollutant removal, high pollutant removal rate, high treatment efficiency and low overall cost has become one of the problems to be solved urgently. Summary of the invention

[0015] The object of the present invention is to provide a fracturing flowback fluid treatment system and a treatment method thereof, which have excellent characteristics of comprehensive pollutant removal, high pollutant removal rate, high treatment efficiency and low comprehensive cost.

[0016] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: a fracturing flowback fluid treatment system, which includes a flotation device, a sedimentation tank group, a sand filter device, a nanofiltration device, a precipitation-electrolysis-biochemical treatment device group and an ozone generating device; the flotation device, the sedimentation tank group, the sand filter device and the nanofiltration device are connected in sequence, and the water production end of the nanofiltration device is connected to the ozone generating device, and the concentrated water end of the nanofiltration device is connected to the precipitation-electrolysis-biochemical treatment device group.

[0017] In the above technical solution, the sedimentation tank group includes a primary sedimentation tank and a secondary sedimentation tank which are connected in sequence.

[0018] In the above technical solution, the precipitation-electrolysis-biochemical treatment equipment group includes a primary pre-electrolysis sedimentation tank, a secondary pre-electrolysis sedimentation tank, an electrolysis device, a pre-aeration tank and a biochemical treatment tank which are connected in sequence.

[0019] In the above technical solution, a homogenization tank is also connected in front of the flotation equipment.

[0020] A method for treating fracturing flowback fluid applies the above-mentioned fracturing flowback fluid treatment system, and the method includes:

[0021] Flotation treatment stage:

[0022] The fracturing flowback fluid to be treated enters the flotation equipment, a demulsifier is added to the fracturing flowback fluid in the flotation equipment, and the pH value of the fracturing flowback fluid in the flotation equipment is adjusted to 10 to destroy the emulsified state of the fracturing flowback fluid, so that the organic pollutants, colloids and oil substances in the fracturing flowback fluid are converted into a suspended state. Moreover, the organic pollutants, colloids, oil substances and insoluble solids suspended in the fracturing flowback fluid are all carried to the upper layer by the bubbles generated by the flotation equipment and are scraped off by the slag scraping device of the flotation equipment;

[0023] Sedimentation treatment stage:

[0024] The water produced by the flotation equipment enters the sedimentation tank group, and a hardening agent is added to the fracturing flowback fluid in the sedimentation tank group to convert the magnesium ions, barium ions and calcium ions in the solute state in the fracturing flowback fluid into solids and precipitate them to the bottom of the sedimentation tank group;

[0025] Sand filtration treatment stage:

[0026] The water produced by the sedimentation tank group enters the sand filtration equipment to filter out the solid particles suspended in the fracturing flowback fluid;

[0027] Nanofiltration treatment stage:

[0028] The water produced by the sand filtration equipment enters the nanofiltration equipment to filter out the calcium ions, magnesium ions and macromolecular organic pollutants in the solute state in the fracturing flowback fluid;

[0029] Ozone treatment stage:

[0030] The water produced by the nanofiltration equipment is treated with ozone by an ozone generating equipment to oxidize and degrade the organic matter in the fracturing flowback fluid, and then discharged;

[0031] Sedimentation - electrolysis - biochemical treatment stage:

[0032] The concentrated water produced by the nanofiltration equipment enters the sedimentation - electrolysis - biochemical treatment equipment group for sedimentation treatment, electrolysis treatment and biochemical treatment in sequence.

[0033] In the above technical solution, the sedimentation tank group includes a primary sedimentation tank and a secondary sedimentation tank connected in sequence;

[0034] The sedimentation treatment stage specifically includes:

[0035] Primary sedimentation treatment sub-stage:

[0036] The produced water of the air flotation equipment enters the primary sedimentation tank, and flaky sodium hydroxide is added to the fracturing flowback fluid in the primary sedimentation tank as a hardness removal agent, and the pH value of the fracturing flowback fluid in the primary sedimentation tank is adjusted to 12 to convert the magnesium ions and barium ions in the solute state in the fracturing flowback fluid into solids and precipitate to the bottom of the primary sedimentation tank;

[0037] Secondary sedimentation treatment sub-stage:

[0038] The produced water of the primary sedimentation tank enters the secondary sedimentation tank, and carbon dioxide is introduced into the fracturing flowback fluid in the secondary sedimentation tank as a hardness removal agent, and the pH value of the fracturing flowback fluid in the secondary sedimentation tank is adjusted to 8-9 to convert the calcium ions in the solute state in the fracturing flowback fluid into calcium carbonate and precipitate to the bottom of the secondary sedimentation tank.

[0039] In the above technical solution, the precipitation-electrolysis-biological treatment equipment group includes a primary pre-electrolysis sedimentation tank, a secondary pre-electrolysis sedimentation tank, an electrolysis equipment, a pre-aeration tank, and a biological treatment tank that are connected in sequence;

[0040] The precipitation-electrolysis-biological treatment stage specifically includes:

[0041] Primary pre-electrolysis sedimentation stage:

[0042] The concentrated water produced by the nanofiltration equipment enters the primary pre-electrolysis sedimentation tank, and carbon dioxide is introduced into the concentrated water in the primary pre-electrolysis sedimentation tank to convert the calcium ions and magnesium ions in the solute state in the concentrated water into calcium carbonate and magnesium carbonate respectively and precipitate to the bottom of the primary pre-electrolysis sedimentation tank;

[0043] Secondary pre-electrolysis sedimentation stage:

[0044] The produced water of the primary pre-electrolysis sedimentation tank enters the secondary pre-electrolysis sedimentation tank to precipitate the solid particles in the concentrated water;

[0045] Electrolysis stage:

[0046] The produced water of the secondary pre-electrolysis sedimentation tank enters the electrolysis equipment to electrolyze the salt solute in the concentrated water to generate an oxidant to oxidize and degrade the macromolecular organic pollutants in the concentrated water, break the macromolecular organic pollutants into small molecular organic pollutants, and generate metal ions to adsorb the pollutants in the concentrated water as flocs through the electrocoagulation effect of the metal ions;

[0047] Pre-aeration stage:

[0048] The water produced by the electrolysis equipment enters the pre-aeration tank, and the chloride ion concentration in the concentrated water is reduced by the aeration method to improve the biodegradability of the concentrated water.

[0049] Biochemical treatment stage:

[0050] The water produced by the pre-aeration tank enters the biochemical treatment tank, and the small-molecule organic pollutants in the concentrated water are degraded by the microorganisms in the biochemical treatment tank.

[0051] In the above technical solution, a homogenization tank is also connected before the air flotation equipment; before the air flotation treatment stage, a homogenization stage is also included; the homogenization stage specifically is: homogenizing the influent of the fracturing flowback fluid.

[0052] In the above technical solution, in the air flotation treatment stage, the demulsifier added to the fracturing flowback fluid in the air flotation equipment is specifically flake sodium hydroxide.

[0053] Compared with the prior art, the beneficial effects of the present invention are:

[0054] 1. Utilizing the air flotation treatment stage to destroy the emulsified state of the fracturing flowback fluid, converting the organic pollutants, colloids, and oily substances in the fracturing flowback fluid into a suspended state. The organic pollutants, colloids, oily substances, and insoluble solids suspended in the fracturing flowback fluid are all carried to the upper layer by the bubbles generated by the air flotation equipment and scraped off by the slag scraping device of the air flotation equipment. Thus, in a way with a single step, comprehensive removal types, high pollutant removal rate, high treatment efficiency, and low comprehensive cost, the "demulsification" and purification of the fracturing flowback fluid are completed.

[0055] 2. Treating magnesium ions and barium ions in the fracturing flowback fluid through the primary precipitation treatment sub-stage, and treating calcium ions in the fracturing flowback fluid through the secondary precipitation treatment sub-stage, so that the magnesium ions, barium ions, and calcium ions in the fracturing flowback fluid can be treated in a refined and comprehensive manner, and the effect of reducing the hardness of the fracturing flowback fluid is better.

[0056] 3. Through the nanofiltration treatment stage, calcium ions, magnesium ions, and macromolecular organic pollutants in the solute state in the fracturing flowback fluid are filtered out, and through the electrolysis stage and the biochemical treatment stage, the macromolecular organic pollutants are sequentially subjected to chain breaking and comprehensive degradation treatment. Compared with the Fenton oxidation method, the reagent cost and equipment cost of the present invention are both lower, and no by-products are generated. Description of the drawings

[0057] Figure 1 It is a structural view of the fracturing flowback fluid treatment system of the present invention.

[0058] Figure 2 It is a process flow chart of the fracturing flowback fluid treatment method of the present invention.

[0059] The reference numerals are: 1, homogeneous tank; 2, air flotation equipment; 3, sedimentation tank group; 31, primary sedimentation tank; 32, secondary sedimentation tank; 4, sand filtration equipment; 5, nanofiltration equipment; 6, sedimentation-electrolysis-biological treatment equipment group; 61, primary pre-electrolysis sedimentation tank; 62, secondary pre-electrolysis sedimentation tank; 63, electrolysis equipment; 64, pre-aeration tank; 65, biological treatment tank; 7, ozone generation equipment. Specific embodiments

[0060] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0061] This embodiment provides a fracturing flowback fluid treatment system for purifying the fracturing flowback fluid so that the fracturing flowback fluid can meet the discharge standards.

[0062] Please refer to Figure 1 , the fracturing flowback fluid treatment system of this embodiment includes an air flotation device 2, a sedimentation tank group 3, a sand filtration device 4, a nanofiltration device 5, a sedimentation-electrolysis-biological treatment device group 6, and an ozone generation device 7.

[0063] Among them, the air flotation device 2 has a tank body based on a metal frame or a civil engineering frame, which can generate a large number of bubbles in the water body of the air flotation device 2 by means of electrolysis, impeller stirring, introducing high-pressure air, etc. In addition, a slag scraping device is arranged on the upper part of the air flotation device 2 to scrape the floating slag and foam (such as organic pollutants, colloids, oily substances, and insoluble solids) floating on the upper layer of the water body.

[0064] Among them, the sand filtration device 4 has a tank body based on a metal frame, and a filter medium composed of materials such as quartz sand, anthracite, and activated carbon is filled in the tank body, which can be used to filter out solid particles in the water body.

[0065] Among them, the nanofiltration device 5 is specifically a nanofiltration system equipped with a spiral wound nanofiltration membrane module, which can filter out divalent ions, polyvalent ions, and various substances with a molecular weight greater than 200.

[0066] Among them, the ozone generation device 7 can polymerize oxygen in the air to generate ozone by means of high-voltage discharge and / or ultraviolet irradiation, and can introduce the ozone into the water body.

[0067] The air flotation device 2, the sedimentation tank group 3, the sand filtration device 4, and the nanofiltration device 5 are connected in sequence. Moreover, the water production end of the nanofiltration device 5 is connected to the ozone generation device 7, and the concentrated water end of the nanofiltration device 5 is connected to the precipitation-electrolysis-biological treatment device group 6.

[0068] Specifically, the sedimentation tank group 3 includes a primary sedimentation tank 31 and a secondary sedimentation tank 32 that are connected in sequence. Among them, both the primary sedimentation tank 31 and the secondary sedimentation tank 32 have a tank body based on a metal frame or a civil engineering frame, and are inclined tube sedimentation tanks.

[0069] Specifically, the precipitation-electrolysis-biological treatment device group 6 includes a primary pre-electrolysis sedimentation tank 61, a secondary pre-electrolysis sedimentation tank 62, an electrolysis device 63, a pre-aeration tank 54, and a biological treatment tank 65 that are connected in sequence.

[0070] Among them, both the primary pre-electrolysis sedimentation tank 61 and the secondary pre-electrolysis sedimentation tank 62 have a tank body based on a metal frame or a civil engineering frame, and are inclined tube sedimentation tanks.

[0071] Among them, the electrolysis device 63 has a tank body based on a metal frame or a civil engineering frame, and is equipped with a boron-doped diamond (BDD) thin film electrode (referred to as the "BDD electrode" for short), which can break the macromolecular organic pollutants in the water body into small molecular organic pollutants and carbon dioxide through the BDD electrode.

[0072] Among them, the pre-aeration tank 54 has a tank body based on a metal frame or a civil engineering frame, and an air pipe driven by a blower is arranged in the tank body, which can introduce a large amount of air into the water body in the pre-aeration tank 54.

[0073] Among them, the biological treatment tank 65 has a tank body based on a metal frame or a civil engineering frame, and a biofilm or sludge suitable for microbial attachment is arranged in the tank body.

[0074] Furthermore, before the air flotation device 2, a homogenization tank 1 is also connected. Among them, the homogenization tank 1 has a tank body based on a metal frame or a civil engineering frame, and is used for homogenizing the influent of the fracturing flowback fluid.

[0075] It can be understood that for the above-mentioned various tank bodies and / or devices, connection methods such as pipelines, pipelines with water pumps, direct overflow, overflow channels, and horizontal overflow grids can be selectively adopted according to actual needs to achieve connection.

[0076] This embodiment also provides a method for treating fracturing flowback fluid, which is used for purifying the fracturing flowback fluid so that the fracturing flowback fluid can meet the discharge standards.

[0077] Please refer to Figure 1 andFigure 2 , the fracturing flowback fluid treatment method of this embodiment includes:

[0078] Homogenization stage:

[0079] Perform homogenization treatment on the influent of the fracturing flowback fluid, so that the physical and chemical properties of the fracturing flowback fluid in the influent at each time period tend to be consistent.

[0080] Air flotation treatment stage:

[0081] The fracturing flowback fluid to be treated enters the air flotation device 2, add a demulsifier to the fracturing flowback fluid in the air flotation device 2, and adjust the pH value of the fracturing flowback fluid in the air flotation device 2 to 10 to destroy the emulsified state of the fracturing flowback fluid, so that the organic pollutants, colloids and oil substances in the fracturing flowback fluid are converted into a suspended state. Moreover, the organic pollutants, colloids, oil substances and insoluble solids suspended in the fracturing flowback fluid are all carried to the upper layer by the bubbles generated by the air flotation device 2 and are scraped off by the slag scraping device of the air flotation device 2.

[0082] It can be understood that there is an allowable error of ±0.5 in the pH value of the fracturing flowback fluid in the air flotation device 2.

[0083] In this embodiment, in the air flotation treatment stage, the demulsifier added to the fracturing flowback fluid in the air flotation device 2 is specifically flake sodium hydroxide.

[0084] After passing through the air flotation treatment stage, the hardness of the fracturing flowback fluid is reduced to about 17000 mg / L in terms of CaCO3.

[0085] Precipitation treatment stage:

[0086] The effluent of the air flotation device 2 enters the sedimentation tank group 3, add a hardness removal agent to the fracturing flowback fluid in the sedimentation tank group 3 to convert the magnesium ions, barium ions and calcium ions in the fracturing flowback fluid in the solute state into solids and precipitate to the bottom of the sedimentation tank group 3.

[0087] Sand filtration treatment stage:

[0088] The effluent of the sedimentation tank group 3 enters the sand filtration device 4 to filter out the solid particles (specifically small particle calcium solids and magnesium solids) suspended in the fracturing flowback fluid.

[0089] Nanofiltration treatment stage:

[0090] The effluent of the sand filtration device 4 enters the nanofiltration device 5 to filter out the calcium ions, magnesium ions and macromolecular organic pollutants in the fracturing flowback fluid in the solute state.

[0091] Ozone treatment stage:

[0092] The produced water of the nanofiltration device 5 is treated with ozone by the ozone generation device 7 to oxidize and degrade the organic matter in the fracturing flowback fluid, and then discharged.

[0093] It can be understood that the ozone tail gas generated in the ozone treatment stage can be collected and recycled.

[0094] Precipitation - electrolysis - biochemical treatment stage:

[0095] The concentrated water (with a conductivity of about 55000 S / m) produced by the nanofiltration device 5 enters the precipitation - electrolysis - biochemical treatment equipment group 6 and undergoes precipitation treatment, electrolysis treatment, and biochemical treatment in sequence.

[0096] Specifically, the precipitation treatment stage specifically includes:

[0097] Primary precipitation treatment sub - stage:

[0098] The produced water of the air flotation device 2 enters the primary sedimentation tank 31. Flake sodium hydroxide is added to the fracturing flowback fluid in the primary sedimentation tank 31 as a hardness remover, and the pH value of the fracturing flowback fluid in the primary sedimentation tank 31 is adjusted to 12 to convert the magnesium ions and barium ions in the solute state in the fracturing flowback fluid into solids, which precipitate to the bottom of the primary sedimentation tank 31.

[0099] It can be understood that for the fracturing flowback fluid in the primary sedimentation tank 31, there is an allowable error of ±0.5 in its pH value.

[0100] After the primary precipitation treatment sub - stage, the hardness of the fracturing flowback fluid is reduced to about 14000 mg / L in terms of CaCO3.

[0101] Secondary precipitation treatment sub - stage:

[0102] The produced water of the primary sedimentation tank 31 enters the secondary sedimentation tank 32. Carbon dioxide is introduced into the fracturing flowback fluid in the secondary sedimentation tank 32 as a hardness remover, and the pH value of the fracturing flowback fluid in the secondary sedimentation tank 32 is adjusted to 8 - 9 to convert the calcium ions in the solute state in the fracturing flowback fluid into calcium carbonate, which precipitates to the bottom of the secondary sedimentation tank 32.

[0103] After the secondary precipitation treatment sub - stage, the hardness of the fracturing flowback fluid is reduced to about 2000 mg / L in terms of CaCO3, and the conductivity of the fracturing flowback fluid is reduced to about 45000 S / m.

[0104] Specifically, the precipitation - electrolysis - biochemical treatment stage specifically includes:

[0105] Primary pre - electrolysis precipitation stage:

[0106] The concentrated water produced by the nanofiltration device 5 (with its pH value controlled at 7.5) enters the primary electrolysis pre-sedimentation tank 61. Carbon dioxide is introduced into the concentrated water in the primary electrolysis pre-sedimentation tank 61 to convert the calcium ions and magnesium ions in the solute state in the concentrated water into calcium carbonate and magnesium carbonate respectively, and precipitate to the bottom of the primary electrolysis pre-sedimentation tank 61.

[0107] Secondary electrolysis pre-sedimentation stage:

[0108] The water produced by the primary electrolysis pre-sedimentation tank 61 enters the secondary electrolysis pre-sedimentation tank 62 to precipitate the solid particles in the concentrated water.

[0109] After the secondary electrolysis pre-sedimentation stage, the concentration of suspended solids (Suspended Solid, ss) in the concentrated water is greatly reduced, improving the electrolysis efficiency of the macromolecular organic pollutants in the concentrated water.

[0110] Electrolysis stage:

[0111] The water produced by the secondary electrolysis pre-sedimentation tank 62 enters the electrolysis device 63 to electrolyze the salt solute (such as NaCl) in the concentrated water, generating oxidants (such as ClO - 、·OH, etc.) to oxidize and degrade the macromolecular organic pollutants in the concentrated water, breaking the macromolecular organic pollutants into small molecular organic pollutants. And metal ions (such as Fe 2+ ) are generated to adsorb the pollutants in the concentrated water as flocs through the electrocoagulation effect of the metal ions.

[0112] Pre-aeration stage:

[0113] The water produced by the electrolysis device 63 enters the pre-aeration tank 54 to reduce the chloride ion concentration in the concentrated water through the aeration method to improve the biodegradability of the concentrated water.

[0114] Biochemical treatment stage:

[0115] The water produced by the pre-aeration tank 54 enters the biochemical treatment tank 65 to degrade the small molecular organic pollutants in the concentrated water through the microorganisms in the biochemical treatment tank 65.

[0116] At this point, the concentrated water produced by the nanofiltration device 5 is completely treated and can be recycled to the homogenization tank 1 for further treatment or discharged up to standard.

[0117] The characteristics of the fracturing flowback fluid treatment system and its treatment method in this embodiment include:

[0118] 1. In the air flotation treatment stage, the emulsified state of the fracturing flowback fluid is disrupted, enabling the organic pollutants, colloids, and oil substances in the fracturing flowback fluid to transform into a suspended state. The organic pollutants, colloids, oil substances, and insoluble solids suspended in the fracturing flowback fluid are all carried to the upper layer by the bubbles generated by the air flotation device 2 and scraped off by the slag scraping device of the air flotation device 2. Thus, in a manner with a single step, comprehensive removal types, high pollutant removal rate, high treatment efficiency, and low comprehensive cost, the "demulsification" and purification of the fracturing flowback fluid are completed.

[0119] 2. The magnesium ions and barium ions in the fracturing flowback fluid are treated through the primary precipitation treatment sub-stage, and the calcium ions in the fracturing flowback fluid are treated through the secondary precipitation treatment sub-stage. As a result, the magnesium ions, barium ions, and calcium ions in the fracturing flowback fluid can be treated in a refined and comprehensive manner, achieving a better effect of reducing the hardness of the fracturing flowback fluid.

[0120] 3. In the nanofiltration treatment stage, the calcium ions, magnesium ions, and macromolecular organic pollutants in the solute state in the fracturing flowback fluid are filtered out. And through the electrolysis stage and the biochemical treatment stage, the macromolecular organic pollutants are sequentially subjected to chain breaking and comprehensive degradation treatment. Compared with the Fenton oxidation method, the chemical agent cost and equipment cost of this embodiment are both lower, and no by-products are generated.

[0121] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A fracturing flowback fluid treatment system, characterized in that, It includes an air flotation device, a sedimentation tank group, a sand filtration device, a nanofiltration device, a precipitation-electrolysis-biological treatment device group, and an ozone generation device; The air flotation device, the sedimentation tank group, the sand filtration device, and the nanofiltration device are connected in sequence. Moreover, the water production end of the nanofiltration device is connected to the ozone generation device, and the concentrated water end of the nanofiltration device is connected to the precipitation-electrolysis-biological treatment device group.

2. The fracturing flowback fluid treatment system according to claim 1, wherein The sedimentation tank group includes a primary sedimentation tank and a secondary sedimentation tank that are connected in sequence.

3. The fracturing flowback fluid treatment system according to claim 1, wherein The precipitation-electrolysis-biological treatment device group includes a primary pre-electrolysis sedimentation tank, a secondary pre-electrolysis sedimentation tank, an electrolysis device, a pre-aeration tank, and a biological treatment tank that are connected in sequence.

4. The fracturing flowback fluid treatment system according to claim 1, wherein Before the air flotation device, a homogenization tank is also connected.

5. A method for treating fracturing flowback fluid, which applies the fracturing flowback fluid treatment system according to any one of claims 1-4, characterized in that, This method includes: Air flotation treatment stage: The fracturing flowback fluid to be treated enters the air flotation device. A demulsifier is added to the fracturing flowback fluid in the air flotation device, and the pH value of the fracturing flowback fluid in the air flotation device is adjusted to 10 to destroy the emulsified state of the fracturing flowback fluid, so that the organic pollutants, colloids, and oily substances in the fracturing flowback fluid are converted into a suspended state. Moreover, the organic pollutants, colloids, oily substances, and insoluble solids suspended in the fracturing flowback fluid are all carried to the upper layer by the bubbles generated by the air flotation device and are scraped off by the slag scraping device of the air flotation device; Sedimentation treatment stage: The water produced by the air flotation device enters the sedimentation tank group. A hardness removal agent is added to the fracturing flowback fluid in the sedimentation tank group to convert the magnesium ions, barium ions, and calcium ions in the fracturing flowback fluid in the solute state into solids and precipitate them to the bottom of the sedimentation tank group; Sand filtration treatment stage: The water produced by the sedimentation tank group enters the sand filtration device to filter out the solid particles suspended in the fracturing flowback fluid; Nanofiltration treatment stage: The water produced by the sand filtration device enters the nanofiltration device to filter out the calcium ions, magnesium ions, and macromolecular organic pollutants in the fracturing flowback fluid in the solute state; Ozone treatment stage: The water produced by the nanofiltration device is treated with ozone by the ozone generation device to oxidize and degrade the organic matter in the fracturing flowback fluid and then discharged; Precipitation-electrolysis-biological treatment stage: The concentrated water produced by the nanofiltration device enters the precipitation-electrolysis-biological treatment device group and undergoes precipitation treatment, electrolysis treatment, and biological treatment in sequence.

6. The fracturing flowback fluid treatment method according to claim 5, wherein, The sedimentation tank group includes a primary sedimentation tank and a secondary sedimentation tank that are connected in sequence; The sedimentation treatment stage specifically includes: Primary sedimentation treatment sub-stage: The water produced by the air flotation device enters the primary sedimentation tank. Flake sodium hydroxide is added to the fracturing flowback fluid in the primary sedimentation tank as a hardness removal agent, and the pH value of the fracturing flowback fluid in the primary sedimentation tank is adjusted to 12 to convert the magnesium ions and barium ions in the fracturing flowback fluid in the solute state into solids and precipitate them to the bottom of the primary sedimentation tank; Secondary sedimentation treatment sub-stage: The water produced by the primary sedimentation tank enters the secondary sedimentation tank. Carbon dioxide is introduced into the fracturing flowback fluid in the secondary sedimentation tank as a hardness remover, and the pH value of the fracturing flowback fluid in the secondary sedimentation tank is adjusted to 8-9 to convert the calcium ions in the solute state in the fracturing flowback fluid into calcium carbonate, which precipitates to the bottom of the secondary sedimentation tank.

7. The fracturing flowback fluid treatment method according to claim 5, wherein The precipitation-electrolysis-biological treatment equipment group includes a primary pre-electrolysis sedimentation tank, a secondary pre-electrolysis sedimentation tank, an electrolysis device, a pre-aeration tank, and a biological treatment tank that are connected in sequence. The precipitation-electrolysis-biological treatment stage specifically includes: Primary pre-electrolysis sedimentation stage: The concentrated water produced by the nanofiltration device enters the primary pre-electrolysis sedimentation tank. Carbon dioxide is introduced into the concentrated water in the primary pre-electrolysis sedimentation tank to convert the calcium ions and magnesium ions in the solute state in the concentrated water into calcium carbonate and magnesium carbonate respectively, which precipitate to the bottom of the primary pre-electrolysis sedimentation tank. Secondary pre-electrolysis sedimentation stage: The water produced by the primary pre-electrolysis sedimentation tank enters the secondary pre-electrolysis sedimentation tank to precipitate the solid particles in the concentrated water. Electrolysis stage: The water produced by the secondary pre-electrolysis sedimentation tank enters the electrolysis device to electrolyze the salt solute in the concentrated water to generate an oxidant to oxidize and degrade the macromolecular organic pollutants in the concentrated water, breaking the macromolecular organic pollutants into small molecular organic pollutants. And metal ions are generated to adsorb the pollutants in the concentrated water as flocs through the electrocoagulation effect of the metal ions. Pre-aeration stage: The water produced by the electrolysis device enters the pre-aeration tank, and the chloride ion concentration in the concentrated water is reduced by the aeration method to improve the biodegradability of the concentrated water. Biological treatment stage: The water produced by the pre-aeration tank enters the biological treatment tank, and the small molecular organic pollutants in the concentrated water are degraded by the microorganisms in the biological treatment tank.

8. The fracturing flowback fluid treatment method according to claim 5, characterized in that, Before the air flotation device, a homogenization tank is also connected. Before the air flotation treatment stage, a homogenization stage is also included. The homogenization stage is specifically: performing homogenization treatment on the influent of the fracturing flowback fluid.

9. The fracturing flowback fluid treatment method according to claim 5, wherein In the air flotation treatment stage, the demulsifier added to the fracturing flowback fluid in the air flotation device is specifically flake sodium hydroxide.

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