Fracturing flowback fluid treatment system and treatment method thereof

Abstract

The application discloses a fracturing flowback fluid treatment system and a treatment method thereof, which comprises a gas floatation device, a sedimentation tank group, a sand filter device, a nanofiltration device, a sedimentation-electrolysis-biochemical treatment device group and an ozone generation device; the gas floatation device, the sedimentation tank group, the sand filter device and the nanofiltration device are sequentially communicated, the water production end of the nanofiltration device is communicated to the ozone generation device, and the concentrated water end of the nanofiltration device is communicated to the sedimentation-electrolysis-biochemical treatment device group. The application mainly solves the problem of how to provide the fracturing flowback fluid treatment system and the treatment method thereof; the application utilizes the gas floatation treatment stage, destroys the emulsification state of the fracturing flowback fluid, converts the organic pollutants, colloids and oil substances in the fracturing flowback fluid into a suspended state, and scrapes off the organic pollutants, colloids and oil substances by a scraping device of the gas floatation device, so that the 'demulsification' and purification of the fracturing flowback fluid are completed in a single step, the removal types are comprehensive, the pollutant removal rate is high, the treatment efficiency is high, and the comprehensive cost is low.

Description

Technical Field

[0001] This invention relates to the field of water treatment system technology, specifically to a fracturing flowback fluid treatment system and its treatment method. Background Technology

[0002] Fracturing flowback fluid is a mixture of fracturing fluid injected into the formation through hydraulic fracturing technology during the extraction of unconventional oil and gas such as shale gas and tight oil and gas, in which a portion of the fluid returns to the surface after high-pressure operations.

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

[0004] Therefore, the difficulties in purifying fracturing flowback fluid include:

[0005] 1. High degree of emulsification in fracturing flowback fluid:

[0006] Because fracturing flowback fluid contains a large amount of organic pollutants, it is prone to emulsification, resulting in high viscosity and directly affecting the treatment efficiency of various pollutants.

[0007] The Chinese invention patent publication text with publication number CN110981040A, entitled "A fracturing flowback fluid treatment device and treatment method", includes the following steps: S001: adding hydrogen peroxide with a concentration of 0.5%-1% to the oxidation tank 1 to oxidize the fracturing flowback fluid; S002: passing the oxidized fracturing flowback fluid through a tubular electrocoagulation reactor 2 to carry out an electrochemical reaction, causing the pollutants in the fracturing flowback fluid to separate and form flocs; S003: passing the fracturing flowback fluid exiting the tubular electrocoagulation reactor 2 into a pre-coated membrane filter 4 to filter out the flocs and impurities, and then passing it into a filtrate tank 5. In step S001, the fracturing flowback fluid is oxidized with hydrogen peroxide, which does not introduce new substances and cause secondary pollution. It also breaks down the large organic molecules remaining in the flowback fluid, reducing its viscosity and facilitating the electrocoagulation reaction in the next step. In step S002, after oxidation, the fracturing flowback fluid enters the tubular electrocoagulation reactor 2. After electrochemical reactions at the positive and negative electrodes in the single reactor 210, it achieves flocculation, flotation, oxidation, and reduction, causing the organic matter, colloids, and solid suspensions in the fracturing flowback fluid to agglomerate and destabilize, forming flocs. In step S003, after the fracturing flowback fluid enters the 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. The flocs and other pollutants are trapped 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, which can be reused on site.

[0008] However, this method requires oxidation of the fracturing flowback fluid with hydrogen peroxide, electrochemical reaction of the fracturing flowback fluid in a tubular electrocoagulation reactor 2, and then filtering out flocs and impurities through a pre-coated membrane filter 4 to complete the "demulsification" of the fracturing flowback fluid. The process is complex, and obviously the cost of reagents, equipment, and energy consumption are all high. In addition, oxidation of the fracturing flowback fluid with hydrogen peroxide does not directly remove organic pollutants, but only converts them into other types. More and more complicated treatment processes are still required to completely remove organic pollutants.

[0009] 2. The fracturing flowback fluid has a high hardness:

[0010] Fracturing flowback fluid contains inorganic salts such as calcium, magnesium, and barium ions, as well as heavy metals such as mercury, lead, arsenic, and cadmium, resulting in a high hardness (greater than 20,000 mg / L as CaCO3).

[0011] The Chinese invention patent publication number CN118063049A, entitled "Treatment System and Method for Removing Iodine, Barium, and Strontium from Fracturing Flowback Fluid and Utilizing Evaporated Salt Resources," describes a hardening tank 200 whose inlet is connected to the outlet of a residual chlorine removal tank 104. After the redox product water enters the hardening tank 200, a hardening agent is added to it via a hardening agent dosing device (not shown). The hardening agent specifically includes sodium hydroxide and sodium carbonate. Sodium hydroxide reacts with magnesium ions in the water to form insoluble magnesium hydroxide, while sodium carbonate reacts with calcium ions in the water to form 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 it is used as a de-hardening agent. This contradicts the pH value requirement of another de-hardening agent, sodium hydroxide, resulting in a longer treatment time for fracturing flowback fluid and hindering the improvement of fracturing flowback fluid treatment efficiency.

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

[0014] In summary, how to provide a fracturing flowback fluid treatment system and method that can remove a wide variety of pollutants, achieve high pollutant removal rates, high treatment efficiency, and low overall cost has become one of the urgent problems to be solved. Summary of the Invention

[0015] The purpose of this invention is to provide a fracturing flowback fluid treatment system and method, which has the excellent characteristics of comprehensive pollutant removal, high pollutant removal rate, high treatment efficiency and low overall cost.

[0016] To achieve the above objectives, the present invention provides the following technical solution: a fracturing flowback fluid treatment system, comprising an air flotation device, a sedimentation tank group, a sand filter device, a nanofiltration device, a sedimentation-electrolysis-biochemical treatment equipment group, and an ozone generator; wherein the air flotation device, the sedimentation tank group, the sand filter device, and the nanofiltration device are connected in sequence, and the product water end of the nanofiltration device is connected to the ozone generator device, while the concentrate end of the nanofiltration device is connected to the sedimentation-electrolysis-biochemical treatment equipment group.

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

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

[0019] In the above technical solution, a homogenization tank is connected before the air flotation device.

[0020] A method for treating fracturing flowback fluid, employing the aforementioned fracturing flowback fluid treatment system, includes:

[0021] Air flotation treatment stage:

[0022] The fracturing flowback fluid to be treated enters the air flotation unit. A demulsifier is added to the fracturing flowback fluid in the air flotation unit, and the pH value of the fracturing flowback fluid in the air flotation unit is adjusted to 10 to destroy the emulsion state of the fracturing flowback fluid. This converts the organic pollutants, colloids, and oily substances in the fracturing flowback fluid into a suspended state. Furthermore, 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 unit and scraped off by the sludge scraping device of the air flotation unit.

[0023] Precipitation treatment stage:

[0024] The permeate from 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 fracturing flowback fluid into solids and precipitate to the bottom of the sedimentation tank group.

[0025] Sand filtration stage:

[0026] The permeate from the sedimentation tank group enters the sand filtration equipment to filter out solid particles suspended in the fracturing flowback fluid.

[0027] Nanofiltration stage:

[0028] The permeate from the sand filter enters the nanofiltration equipment to filter out calcium ions, magnesium ions, and macromolecular organic pollutants in the solute state from the fracturing flowback fluid.

[0029] Ozone treatment stage:

[0030] The permeate from the nanofiltration unit is treated with ozone by an ozone generator to oxidize and degrade the organic matter in the fracturing flowback fluid before being discharged.

[0031] Precipitation-electrolysis-biochemical treatment stages:

[0032] The concentrated water produced by the nanofiltration equipment enters the sedimentation-electrolysis-biochemical treatment equipment group, where sedimentation, electrolysis and biochemical treatment are performed 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 precipitation treatment stage specifically includes:

[0035] Primary precipitation treatment sub-stage:

[0036] The permeate from the flotation equipment enters the primary sedimentation tank. Flake sodium hydroxide is added to the fracturing flowback fluid in the primary sedimentation tank as a de-hardening agent, and the pH value of the fracturing flowback fluid in the primary sedimentation tank is adjusted to 12 to convert the magnesium and barium ions in the fracturing flowback fluid, which are in a solute state, into solids and precipitate to the bottom of the primary sedimentation tank.

[0037] Secondary precipitation treatment sub-stage:

[0038] The permeate from 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 de-hardening 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, which then precipitates to the bottom of the secondary sedimentation tank.

[0039] In the above technical solution, the precipitation-electrolysis-biochemical treatment equipment group includes a primary pre-electrolysis precipitation tank, a secondary pre-electrolysis precipitation tank, an electrolysis device, a pre-aeration tank, and a biochemical treatment tank connected in sequence.

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

[0041] Precipitation stage before primary electrolysis:

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

[0043] Precipitation stage before secondary electrolysis:

[0044] The permeate from the primary electrolysis pre-sedimentation tank enters the secondary electrolysis pre-sedimentation tank to precipitate solid particles from the concentrated water.

[0045] Electrolysis stage:

[0046] The permeate from the pre-sedimentation tank of the secondary electrolysis enters the electrolysis equipment, where the salt solutes in the concentrated water are electrolyzed to generate an oxidant, which oxidizes and degrades the macromolecular organic pollutants in the concentrated water, breaking down the macromolecular organic pollutants into smaller molecular organic pollutants. In addition, metal ions are generated, which adsorb the pollutants in the concentrated water into flocculents through the electrocoagulation effect of the metal ions.

[0047] Pre-aeration stage:

[0048] The product water from the electrolysis equipment enters the pre-aeration tank, where the chloride ion concentration in the concentrate is reduced by aeration to improve the biodegradability of the concentrate.

[0049] Biochemical treatment stage:

[0050] The permeate from the pre-aeration tank enters the biochemical treatment tank, where microorganisms degrade small-molecule organic pollutants in the concentrated water.

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

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

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

[0054] 1. By utilizing the air flotation stage, the emulsified state of the fracturing flowback fluid is disrupted, causing organic contaminants, colloids, and oily substances in the fracturing flowback fluid to be converted into a suspended state. The organic contaminants, colloids, oily substances, and insoluble solids suspended in the fracturing flowback fluid are all carried to the upper layer by the air bubbles generated by the air flotation equipment and scraped off by the scraping device of the air flotation equipment. Thus, the "demulsification" and purification of the fracturing flowback fluid are completed in a simple, comprehensive, high-contaminant removal, high-efficiency, and low-cost manner.

[0055] 2. The primary precipitation treatment stage treats magnesium and barium ions in the fracturing flowback fluid, and the secondary precipitation treatment stage treats calcium ions in the fracturing flowback fluid. This allows for a more refined and comprehensive treatment of magnesium, barium, and calcium ions in the fracturing flowback fluid, resulting in a better reduction in the hardness of the fracturing flowback fluid.

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

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

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

[0059] The attached diagram is labeled as follows: 1. Homogenization 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-biochemical treatment equipment group; 61. Sedimentation tank before primary electrolysis; 62. Sedimentation tank before secondary electrolysis; 63. Electrolysis equipment; 64. Pre-aeration tank; 65. Biochemical treatment tank; 7. Ozone generator. Detailed Implementation

[0060] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0061] This embodiment provides a fracturing flowback fluid treatment system for purifying fracturing flowback fluid so that it can be discharged in compliance with standards.

[0062] Please see Figure 1 The fracturing flowback fluid treatment system of this embodiment includes an air flotation device 2, a sedimentation tank group 3, a sand filter device 4, a nanofiltration device 5, a sedimentation-electrolysis-biochemical treatment equipment group 6, and an ozone generator 7.

[0063] The air flotation device 2 has a tank body based on a metal frame or civil engineering frame. It can generate a large number of bubbles in the water body in the air flotation device 2 through electrolysis, impeller stirring, and introduction of high-pressure air. In addition, the upper part of the air flotation device 2 is equipped with a scum scraper to scrape off the scum and foam (such as organic pollutants, colloids, oil and insoluble solids) floating on the surface of the water body.

[0064] The sand filter 4 has a tank based on a metal frame, which is filled with filter media made of materials such as quartz sand, anthracite, and activated carbon, and can be used to filter out solid particles in water.

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

[0066] The ozone generator 7 can generate ozone by polymerizing oxygen in the air through high-voltage discharge and / or ultraviolet irradiation, and can also introduce ozone into water bodies.

[0067] The air flotation equipment 2, sedimentation tank group 3, sand filter equipment 4 and nanofiltration equipment 5 are connected in sequence. The product water end of nanofiltration equipment 5 is connected to ozone generator 7, and the concentrate end of nanofiltration equipment 5 is connected to sedimentation-electrolysis-biochemical treatment equipment group 6.

[0068] Specifically, the sedimentation tank group 3 includes a primary sedimentation tank 31 and a secondary sedimentation tank 32 connected in sequence; wherein, both the primary sedimentation tank 31 and the secondary sedimentation tank 32 have tank bodies based on metal frames or civil engineering frames, and are inclined tube sedimentation tanks.

[0069] Specifically, the sedimentation-electrolysis-biochemical treatment equipment 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 biochemical treatment tank 65 connected in sequence.

[0070] Both the primary electrolysis pre-sedimentation tank 61 and the secondary electrolysis pre-sedimentation tank 62 have tank bodies based on metal frames or civil engineering frames, and are inclined tube sedimentation tanks.

[0071] The electrolysis device 63 has a pool body based on a metal frame or civil engineering frame, and is equipped with a boron-doped diamond (BDD) thin film electrode (hereinafter referred to as "BDD electrode"). The BDD electrode can break down large molecular organic pollutants in the water into small molecular organic pollutants and carbon dioxide.

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

[0073] The biochemical treatment tank 65 has a tank body based on a metal frame or 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, there is a homogenization tank 1 connected; wherein, the homogenization tank 1 has a tank body based on a metal frame or civil engineering frame, and is used to homogenize the influent of the fracturing flowback fluid.

[0075] It is understandable that the aforementioned pools and / or equipment can be connected by means of pipes, pipes with pumps, direct overflow, overflow channels, and horizontal overflow grids, depending on actual needs.

[0076] This embodiment also provides a method for treating fracturing flowback fluid, which is used to purify the fracturing flowback fluid so that it can be discharged in compliance with standards.

[0077] Please see Figure 1 and Figure 2 The fracturing flowback fluid treatment method of this embodiment includes:

[0078] Homogenization stage:

[0079] The influent of the fracturing flowback fluid is homogenized so that the physicochemical properties of the fracturing flowback fluid influent at different times tend to be consistent.

[0080] Air flotation treatment stage:

[0081] The fracturing flowback fluid to be treated enters the air flotation unit 2. A demulsifier is added to the fracturing flowback fluid in the air flotation unit 2, and the pH value of the fracturing flowback fluid in the air flotation unit 2 is adjusted to 10 to break the emulsion state of the fracturing flowback fluid. This causes the organic pollutants, colloids, and oily substances in the fracturing flowback fluid to be converted into a suspended state. Furthermore, 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 unit 2 and scraped off by the slag scraping device of the air flotation unit 2.

[0082] It is understandable that the pH value of the fracturing flowback fluid in the air flotation unit 2 is allowed to have an error of ±0.5.

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

[0084] After the air flotation treatment stage, the hardness of the fracturing flowback fluid was reduced to about 17,000 mg / L (calculated as CaCO3).

[0085] Precipitation treatment stage:

[0086] The permeate from the flotation unit 2 enters the sedimentation tank group 3. A hardening agent is added 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 into solids and precipitate to the bottom of the sedimentation tank group 3.

[0087] Sand filtration stage:

[0088] The permeate from sedimentation tank group 3 enters sand filter equipment 4 to filter out solid particles (specifically small calcium and magnesium solid particles) suspended in the fracturing flowback fluid.

[0089] Nanofiltration stage:

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

[0091] Ozone treatment stage:

[0092] The permeate from nanofiltration unit 5 is treated with ozone by ozone generator 7 to oxidize and degrade organic matter in the fracturing flowback fluid before being discharged.

[0093] Understandably, the ozone exhaust gas produced during the ozone treatment stage can be collected and recycled.

[0094] Precipitation-electrolysis-biochemical treatment stages:

[0095] The concentrated water produced by nanofiltration device 5 (with an electrical conductivity of about 55,000 S / m) enters sedimentation-electrolysis-biochemical treatment equipment group 6, where it undergoes sedimentation, electrolysis and biochemical treatment in sequence.

[0096] Specifically, the precipitation treatment stage includes:

[0097] Primary precipitation treatment sub-stage:

[0098] The permeate from the flotation unit 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 de-hardening agent, and the pH value of the fracturing flowback fluid in the primary sedimentation tank 31 is adjusted to 12 to convert the magnesium and barium ions in the fracturing flowback fluid, which are in a solute state, into solids and precipitate to the bottom of the primary sedimentation tank 31.

[0099] It is understandable that the pH value of the fracturing flowback fluid in the primary sedimentation tank 31 is allowed to have an error of ±0.5.

[0100] After the initial precipitation treatment stage, the hardness of the fracturing flowback fluid decreased to approximately 14,000 mg / L (calculated as CaCO3).

[0101] Secondary precipitation treatment sub-stage:

[0102] The permeate from 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 hardening 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 then precipitates to the bottom of the secondary sedimentation tank 32.

[0103] After the secondary precipitation treatment stage, the hardness of the fracturing flowback fluid is reduced to about 2000 mg / L (calculated as CaCO3), and the conductivity of the fracturing flowback fluid is reduced to about 45000 S / m.

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

[0105] Precipitation stage before primary electrolysis:

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

[0107] Precipitation stage before secondary electrolysis:

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

[0109] After the pre-sedimentation stage before secondary electrolysis, the concentration of suspended solids (SS) in the concentrate is significantly reduced, thereby improving the electrolysis efficiency of large molecular organic pollutants in the concentrate.

[0110] Electrolysis stage:

[0111] The permeate from the pre-sedimentation tank 62 before secondary electrolysis enters the electrolysis unit 63, where the salt solutes (e.g., NaCl) in the concentrated water are electrolyzed to generate an oxidant (e.g., ClO). - ·OH and other compounds are used to oxidize and degrade large molecular organic pollutants in concentrated water, breaking them down into smaller molecules and generating metal ions (e.g., Fe). 2+ This method uses the electrocoagulation effect of metal ions to adsorb pollutants in concentrated water into flocculent matter.

[0112] Pre-aeration stage:

[0113] The product water from the electrolysis unit 63 enters the pre-aeration tank 54, where the chloride ion concentration in the concentrate is reduced by aeration to improve the biodegradability of the concentrate.

[0114] Biochemical treatment stage:

[0115] The permeate from the pre-aeration tank 54 enters the biological treatment tank 65, where microorganisms degrade small-molecule organic pollutants in the concentrate.

[0116] At this point, the concentrated water produced by nanofiltration device 5 has been treated and can be recycled back to homogenization tank 1 for further treatment, or discharged in compliance with standards.

[0117] The fracturing flowback fluid treatment system and method of this embodiment have the following characteristics:

[0118] 1. By utilizing the air flotation treatment stage, the emulsified state of the fracturing flowback fluid is disrupted, causing organic pollutants, colloids, and oily substances in the fracturing flowback fluid to be converted 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 air bubbles generated by the air flotation device 2 and scraped off by the sludge scraping device of the air flotation device 2. Thus, the "demulsification" and purification of the fracturing flowback fluid are completed in a simple, comprehensive, high pollutant removal rate, high treatment efficiency, and low overall cost manner.

[0119] 2. The primary precipitation treatment stage treats magnesium and barium ions in the fracturing flowback fluid, and the secondary precipitation treatment stage treats calcium ions in the fracturing flowback fluid. This allows for a more refined and comprehensive treatment of magnesium, barium, and calcium ions in the fracturing flowback fluid, resulting in a better reduction in the hardness of the fracturing flowback fluid.

[0120] 3. Through the nanofiltration stage, calcium ions, magnesium ions, and macromolecular organic pollutants in the solute state in the fracturing flowback fluid are filtered out. Furthermore, through the electrolysis and biochemical treatment stages, the macromolecular organic pollutants are sequentially subjected to chain breaking and complete degradation treatment. Compared with the Fenton oxidation method, the reagent and equipment costs of this embodiment are lower, and no by-products are generated.

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

Claims

1. A method for treating fracturing flowback fluid, comprising a fracturing flowback fluid treatment system; The fracturing flowback fluid treatment system includes an air flotation unit, a sedimentation tank group, a sand filter unit, a nanofiltration unit, a sedimentation-electrolysis-biochemical treatment unit group, and an ozone generator. The air flotation device, the sedimentation tank group, the sand filter device, and the nanofiltration device are connected in sequence. The product water end of the nanofiltration device is connected to the ozone generator, and the concentrate end of the nanofiltration device is connected to the sedimentation-electrolysis-biochemical treatment equipment group. The method includes: Air flotation treatment stage: The fracturing flowback fluid to be treated enters the air flotation unit. A demulsifier is added to the fracturing flowback fluid in the air flotation unit, and the pH value of the fracturing flowback fluid in the air flotation unit is adjusted to 10 to destroy the emulsion state of the fracturing flowback fluid. This converts the organic pollutants, colloids, and oily substances in the fracturing flowback fluid into a suspended state. Furthermore, 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 unit and scraped off by the sludge scraping device of the air flotation unit. Precipitation treatment stage: The permeate from 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 fracturing flowback fluid into solids and precipitate to the bottom of the sedimentation tank group. Sand filtration stage: The permeate from the sedimentation tank group enters the sand filtration equipment to filter out solid particles suspended in the fracturing flowback fluid. Nanofiltration stage: The permeate from the sand filter enters the nanofiltration equipment to filter out calcium ions, magnesium ions, and macromolecular organic pollutants in the solute state from the fracturing flowback fluid. Ozone treatment stage: The permeate from the nanofiltration unit is treated with ozone by an ozone generator to oxidize and degrade the organic matter in the fracturing flowback fluid before being discharged. Precipitation-electrolysis-biochemical treatment stages: The concentrated water produced by the nanofiltration equipment enters the sedimentation-electrolysis-biochemical treatment equipment group, where sedimentation, electrolysis and biochemical treatment are performed in sequence.

2. The fracturing flowback fluid treatment method according to claim 1, characterized in that, A homogenization tank is connected before the air flotation device; Prior to the air flotation stage, a homogenization stage is also included; The homogenization stage specifically involves homogenizing the influent of the fracturing flowback fluid.

3. The fracturing flowback fluid treatment method according to claim 1, characterized in that, In the air flotation treatment stage, the demulsifier added to the fracturing flowback fluid in the air flotation equipment is specifically flake sodium hydroxide.

4. The fracturing flowback fluid treatment method according to claim 1, characterized in that, The sedimentation tank group includes a primary sedimentation tank and a secondary sedimentation tank connected in sequence; The precipitation treatment stage specifically includes: Primary precipitation treatment sub-stage: The permeate from the flotation equipment enters the primary sedimentation tank. Flake sodium hydroxide is added to the fracturing flowback fluid in the primary sedimentation tank as a de-hardening agent, and the pH value of the fracturing flowback fluid in the primary sedimentation tank is adjusted to 12 to convert the magnesium and barium ions in the fracturing flowback fluid, which are in a solute state, into solids and precipitate to the bottom of the primary sedimentation tank. Secondary precipitation treatment sub-stage: The permeate from 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 de-hardening 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, which then precipitates to the bottom of the secondary sedimentation tank.

5. The fracturing flowback fluid treatment method according to claim 1, characterized in that, 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 connected in sequence. The precipitation-electrolysis-biochemical treatment stage specifically includes: Precipitation stage before primary electrolysis: The concentrated water produced by the nanofiltration equipment enters the pre-sedimentation tank before primary electrolysis. Carbon dioxide is introduced into the concentrated water in the pre-sedimentation tank to convert the calcium and magnesium ions in the concentrated water into calcium carbonate and magnesium carbonate, respectively, and precipitate them to the bottom of the pre-sedimentation tank before primary electrolysis. Precipitation stage before secondary electrolysis: The permeate from the primary electrolysis pre-sedimentation tank enters the secondary electrolysis pre-sedimentation tank to precipitate solid particles from the concentrated water. Electrolysis stage: The permeate from the pre-sedimentation tank of the secondary electrolysis enters the electrolysis equipment, where the salt solutes in the concentrated water are electrolyzed to generate an oxidant, which oxidizes and degrades the macromolecular organic pollutants in the concentrated water, breaking down the macromolecular organic pollutants into smaller molecular organic pollutants. In addition, metal ions are generated, which adsorb the pollutants in the concentrated water into flocculents through the electrocoagulation effect of the metal ions. Pre-aeration stage: The product water from the electrolysis equipment enters the pre-aeration tank, where the chloride ion concentration in the concentrate is reduced by aeration to improve the biodegradability of the concentrate. Biochemical treatment stage: The permeate from the pre-aeration tank enters the biochemical treatment tank, where microorganisms degrade small-molecule organic pollutants in the concentrated water.

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