Low-energy consumption system and method for staged treatment of fracturing flowback

Abstract

A low-energy consumption system and method for staged treatment of fracturing flowback. The system comprises a flowback recycling system, a softening pretreatment system, a membrane concentration system, and a solar evaporation crystallization system, connected in sequence. The membrane concentration system comprises a primary reverse osmosis unit, a secondary reverse osmosis unit, an electrodialysis unit, and an ammonia, nitrogen and boron adsorption unit. The solar evaporation crystallization system comprises a preheating circulation tank, a solar heater, a flash tank, an evaporation tank, a heat exchanger, and a thickener, the solar heater being used to circulate and preheat an electrodialysis concentrated solution in the preheating circulation tank, a liquid outlet of the preheating circulation tank being in communication with an inlet of the flash tank, a liquid phase outlet of the flash tank being connected to an inlet of the evaporation tank via the heat exchanger, a liquid phase outlet of the evaporation tank being in communication with the thickener, and a gas phase outlet of the flash tank and a gas phase outlet of the evaporation tank each being connected to a liquid inlet of the ammonia, nitrogen and boron adsorption unit by pipelines via the heat exchanger. The present invention can remove pollutants from fracturing flowback fluid in stages with low energy consumption.

Description

A low-energy consumption fracturing flowback fluid graded treatment system and method

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on September 27, 2023, with application number 202311261063.8 and invention name “A low-energy consumption fracturing return fluid graded treatment system and method”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present invention relates to a low-energy-consumption fracturing flowback fluid graded treatment system and method, belonging to the technical field of energy-saving and environmentally friendly water treatment. Background Art

[0003] In the process of oil and natural gas extraction, the shale gas and tight gas extraction technologies currently used require large-scale fracturing. The large amount of return waste liquid generated after fracturing is completed will put pressure on the environment. In the later stage of extraction, the demand for reuse of return fluid decreases, and the discharge of return fluid after treatment to meet the standards becomes an important way for the final disposal of return fluid.

[0004] Fracturing flowback fluid, the wastewater discharged from the wellhead after hydraulic fracturing, is characterized by high levels of mineralization, chlorides, hardness ions, and other contaminants. Discharging it directly without treatment can pollute the environment. Due to the mining environment and the unique characteristics of fracturing flowback fluid quality, a treatment process that meets standards must operate stably and be adaptable to a wide range of flowback fluid quality variations.

[0005] Therefore, it is of great significance to carry out research on the treatment technology of fracturing return fluid to meet the standards. Providing a new low-energy consumption fracturing return fluid graded treatment system and method has become a technical problem that needs to be solved urgently in this field.

[0006] Summary of the Invention

[0007] In order to solve the above-mentioned shortcomings and deficiencies, an object of the present invention is to provide a low-energy consumption fracturing flowback fluid staged treatment system.

[0008] Another object of the present invention is to provide a low-energy method for the graded treatment of fracturing flowback fluid. The system and method provided by the present invention remove contaminants from fracturing flowback fluid in a graded manner, enabling the reuse or discharge of fracturing flowback fluid with low energy consumption.

[0009] In order to achieve the above objectives, on the one hand, the present invention provides a low-energy consumption fracturing flowback fluid graded treatment system, wherein the low-energy consumption fracturing flowback fluid graded treatment system includes a flowback fluid recycling system, a softening pretreatment system, a membrane concentration system, and a solar evaporation crystallization system connected in sequence;

[0010] The flowback liquid recycling system includes an aeration transfer tank, an air flotation oil removal tank, a flocculation reactor and a sedimentation tank connected in sequence;

[0011] The softening pretreatment system includes a softening concentration reaction tank, an ozone oxidation reactor, a tubular microfiltration unit, a nanofiltration unit and a softening ion adsorption unit which are connected in sequence;

[0012] The membrane concentration system includes a primary reverse osmosis unit, a secondary reverse osmosis unit, an electrodialysis unit and an ammonia nitrogen and boron adsorption unit;

[0013] The solar evaporation crystallization system includes a preheating circulation tank, a solar heater, a flash tank, an evaporation tank, a heat exchanger and a thickener. The solar heater is used to circulate and preheat the electrodialysis concentrated water in the preheating circulation tank. The liquid outlet of the preheating circulation tank is connected to the inlet of the flash tank. The liquid phase outlet of the flash tank is connected to the inlet of the evaporation tank via a pipeline via the heat exchanger. The liquid phase outlet of the evaporation tank is connected to the thickener. The gas phase outlet of the flash tank and the gas phase outlet of the evaporation tank are respectively connected to the liquid inlet of the ammonia nitrogen and boron adsorption unit via pipelines via the heat exchanger.

[0014] As a specific embodiment of the above-mentioned system of the present invention, the cut-off pore size of the microfiltration membrane assembly used in the tubular microfiltration unit is ≤0.05 μm.

[0015] As a specific embodiment of the above system of the present invention, the softening and concentration reaction tank includes a primary softening tank, a secondary softening tank and a concentration tank connected in sequence.

[0016] As a specific embodiment of the above system of the present invention, the microfiltration concentrated water outlet of the tubular microfiltration unit and the nanofiltration concentrated water outlet of the nanofiltration unit are respectively connected to the inlet of the softening and concentration reaction tank through a concentrated water reflux pipe.

[0017] As a specific embodiment of the above system of the present invention, the liquid outlet of the softening ion adsorption unit is connected to the liquid inlet of the first-stage reverse osmosis unit through a pipeline via a hydraulic pressure turbine, and the fresh water outlet of the first-stage reverse osmosis unit is connected to the liquid inlet of the ammonia nitrogen and boron adsorption unit through a pipeline via a second-stage reverse osmosis unit;

[0018] The concentrated water outlet of the primary reverse osmosis unit is connected to the liquid inlet of the electrodialysis unit through a pipeline via a hydraulic pressure turbine, and the concentrated water outlet of the electrodialysis unit is connected to the inlet of the preheating circulation tank through a pipeline.

[0019] As a specific embodiment of the above system of the present invention, the fresh water outlet of the electrodialysis unit and the concentrated water outlet of the secondary reverse osmosis unit are respectively connected to the liquid inlet of the primary reverse osmosis unit through pipelines via a hydraulic pressure turbine.

[0020] As a specific embodiment of the above-mentioned system of the present invention, the liquid outlet of the softening ion adsorption unit is connected to the liquid inlet of the electrodialysis unit through a pipeline, the concentrated water outlet of the electrodialysis unit is connected to the inlet of the preheating circulation tank through a pipeline, the fresh water outlet of the electrodialysis unit is connected to the liquid inlet of the first-stage reverse osmosis unit through a pipeline via a hydraulic pressure turbine, and the fresh water outlet of the first-stage reverse osmosis unit is connected to the liquid inlet of the ammonia nitrogen and boron adsorption unit through a pipeline via a second-stage reverse osmosis unit.

[0021] As a specific embodiment of the above system of the present invention, the concentrated water outlet of the secondary reverse osmosis unit is connected to the liquid inlet of the primary reverse osmosis unit through a pipeline via a hydraulic pressure turbine.

[0022] As a specific embodiment of the above system of the present invention, the concentrated water outlet of the first-stage reverse osmosis unit is connected to the liquid inlet of the electrodialysis unit through a pipeline via a hydraulic pressure turbine.

[0023] As a specific embodiment of the system described above in the present invention, the solar evaporation crystallization system further includes a first compressor and a second compressor. The gas phase outlet of the flash tank is connected to the liquid inlet of the ammonia nitrogen and boron adsorption unit through a pipeline via the first compressor and a heat exchanger. The gas phase outlet of the evaporation tank is connected to the liquid inlet of the ammonia nitrogen and boron adsorption unit through a pipeline via the second compressor and a heat exchanger.

[0024] As a specific embodiment of the above system of the present invention, the liquid outlet of the thickener is connected to the inlet of the evaporation tank through a pipeline.

[0025] On the other hand, the present invention also provides a low-energy consumption method for graded treatment of fracturing flowback fluid, wherein the method comprises the following steps:

[0026] (1) aeration treatment and flotation deoiling treatment are performed on the fracturing flowback fluid in sequence to obtain waste oil and effluent, and then the effluent is subjected to flocculation and sedimentation in sequence to obtain a first-stage sludge and a first-stage liquid;

[0027] (2) Softening and concentrating the primary liquid to obtain concentrated liquid and secondary sludge, ozonating the concentrated liquid and microfiltration treating the effluent to obtain microfiltration concentrated water and microfiltration fresh water, nanofiltration treating the microfiltration fresh water to obtain nanofiltration concentrated water and nanofiltration fresh water, and finally softening the nanofiltration fresh water by ion adsorption to obtain secondary liquid;

[0028] (3) When the mineralization degree of the secondary liquid is not higher than 40,000 mg / L, the secondary liquid is subjected to primary reverse osmosis to obtain primary reverse osmosis concentrated water and primary reverse osmosis fresh water, the primary reverse osmosis fresh water is subjected to secondary reverse osmosis and then subjected to ammonia nitrogen and boron adsorption on the secondary reverse osmosis fresh water; the primary reverse osmosis concentrated water is subjected to electrodialysis to obtain electrodialysis concentrated water and electrodialysis fresh water; or,

[0029] When the mineralization of the secondary liquid is higher than 40,000 mg / L, the secondary liquid is subjected to electrodialysis to obtain electrodialysis concentrated water and electrodialysis fresh water. The electrodialysis fresh water is subjected to primary reverse osmosis and secondary reverse osmosis in sequence, and then the secondary reverse osmosis fresh water is subjected to ammonia nitrogen and boron adsorption.

[0030] (4) Using a solar heater to circulate and preheat the electrodialysis concentrated water, flash-evaporating it to obtain a flash gas phase and a flash liquid phase, then evaporating the flash liquid phase after heat exchange and heating to obtain an evaporation gas phase and an evaporation liquid phase, and crystallizing the evaporation liquid phase to obtain crystalline salt; wherein the heat source used for heat exchange and heating is the heated flash gas phase, or the heated flash gas phase and the heated evaporation gas phase.

[0031] Since fracturing flowback fluid from different wells is collected on site and the water quality of the fracturing flowback fluid from different wells is different, in step (1) of the method described above, the fracturing flowback fluid from multiple wells can be first collected into an aeration transfer tank for mixing and then processed. This can reduce the water quality changes of the fracturing flowback fluid caused by a single well and effectively eliminate the impact of the water quality fluctuation of the fracturing flowback fluid on the treatment process.

[0032] As a specific embodiment of the above method of the present invention, the flocculant used in the flocculation includes polyaluminum chloride (PAC) and / or polyacrylamide (PAM) and the like.

[0033] As a specific embodiment of the above-described method of the present invention, the total suspended solids in the primary liquid obtained in step (1) are ≤15 mg / L, the total iron is ≤10 mg / L, and the petroleum substances are ≤10 mg / L. The primary liquid can be recycled as a liquid with a low hardness ion content, i.e., a total hardness of ≤2000 mg / L. In addition, the parameters used in the aeration treatment, flotation oil removal treatment, flocculation and sedimentation operations in step (1) of the present invention can be reasonably adjusted and determined according to on-site needs, as long as the total suspended solids in the primary liquid are ≤15 mg / L, the total iron is ≤10 mg / L, and the petroleum substances are ≤10 mg / L.

[0034] As a specific embodiment of the above method of the present invention, the softening is carried out in two steps, and sodium carbonate and sodium sulfate are used in the first softening step and the second softening step respectively, wherein the mass ratio of sodium carbonate to sodium sulfate is 4:1-6:1.

[0035] As a specific embodiment of the above method of the present invention, step (2) further includes:

[0036] The microfiltration concentrated water, nanofiltration concentrated water and primary liquid are transported to the softening and concentration reaction tank for softening and concentration to obtain concentrated liquid and secondary sludge.

[0037] As a specific embodiment of the above-mentioned method of the present invention, the softening ion adsorption in step (2) can be achieved using "Zhengguang" brand 001×8 strong acidic cation exchange resin to remove hardness ions.

[0038] As a specific embodiment of the above-described method of the present invention, the total hardness of the secondary liquid obtained in step (2) is ≤20 mg / L. This secondary liquid can be recycled as a liquid with a high hardness ion content, i.e., a total hardness >2000 mg / L. Furthermore, the parameters used in the softening and concentration, ozone oxidation, microfiltration, and nanofiltration processes in step (2) of the present invention can also be reasonably adjusted and determined according to site needs, as long as the total hardness of the secondary liquid is ensured to be ≤20 mg / L.

[0039] In addition, the mineralization of the secondary liquid obtained after treatment in step (1) and step (2) is substantially the same as that of the untreated fracturing flowback fluid, that is, the treatment in step (1) and step (2) has almost no effect on the mineralization of the fracturing flowback fluid.

[0040] As a specific embodiment of the above method of the present invention, when the salinity of the secondary liquid is not higher than 40,000 mg / L, step (3) further includes:

[0041] Perform primary reverse osmosis on electrodialysis fresh water and secondary reverse osmosis concentrated water.

[0042] As a specific embodiment of the above method of the present invention, when the salinity of the secondary liquid is higher than 40,000 mg / L, step (3) further includes: performing primary reverse osmosis on the secondary reverse osmosis concentrated water.

[0043] As a specific embodiment of the above method of the present invention, when the salinity of the secondary liquid is higher than 40,000 mg / L, step (3) further includes: electrodialysis of the primary reverse osmosis concentrated water.

[0044] As a specific embodiment of the above method of the present invention, in step (3), ammonia nitrogen adsorption and boron adsorption are sequentially performed on the secondary reverse osmosis fresh water.

[0045] As a specific embodiment of the method described above, the ammonia nitrogen adsorption in step (3) can be carried out by using a strong acid type uniform particle cation exchange resin or a sodium Na +The adsorption of boron can be achieved by using cation exchange resins with uniform particle size, such as Tulsimer T-42H, and ion exchange resins with large pore size and containing meglumine functional groups, such as Tulsimer Boron selective adsorption resin, etc.

[0046] As a specific embodiment of the above-described method of the present invention, the salinity of the secondary reverse osmosis fresh water obtained in step (2) should be less than 420 mg / L, and the salinity of the electrodialysis concentrate obtained should be greater than 75,000 mg / L. Furthermore, the parameters and membranes or adsorption resins used in the primary reverse osmosis, secondary reverse osmosis, electrodialysis, and ammonia nitrogen and boron adsorption operations in step (3) of the present invention can also be reasonably adjusted and selected according to site needs, as long as the salinity of the secondary reverse osmosis fresh water is less than 420 mg / L and the salinity of the electrodialysis concentrate is greater than 75,000 mg / L.

[0047] As a specific embodiment of the above method of the present invention, the circulating preheating includes: transferring part of the electrodialysis concentrated water in the preheating circulation tank to a solar heater, heating the concentrated water and then returning the concentrated water to the preheating circulation tank;

[0048] The liquid volume capacity in the preheating circulation tank is maintained at 40-60%, the heating temperature is 55-65° C., and the pressure is maintained slightly higher than atmospheric pressure, preferably 1.2-1.3 atmospheres, that is, 0.12-0.13 MPa.

[0049] As a specific embodiment of the above method of the present invention, the vacuum degree of the flash evaporation is 0.06-0.07 MPa, and the vacuum degree of the evaporation is 0.06-0.07 MPa.

[0050] As a specific embodiment of the above-mentioned method of the present invention, the flash gas phase and the evaporated gas phase are heated by 12-18°C and 10-15°C respectively, and then used as heat sources to exchange heat with the flash liquid phase, and the temperature of the flash liquid phase after heat exchange is set to 60-75°C.

[0051] As a specific embodiment of the above method of the present invention, the flash gas phase is compressed by a first compressor at a compression ratio of 1:1.2-1:2, and after the enthalpy value is increased, the temperature of the flash gas phase is increased by 12-18°C and enters the heat exchanger as a heat source to exchange heat with the flash liquid phase, and the temperature of the flash liquid phase after the heat exchange is 60-75°C;

[0052] After the evaporation gas phase is generated, the evaporation gas phase is compressed by the second compressor at an appropriate compression ratio. After the enthalpy value is increased, the temperature of the evaporation gas phase is increased by 10-15°C. It is used as a heat source together with the heated flash gas phase to enter the heat exchanger for heat exchange with the flash liquid phase, and the temperature of the flash liquid phase after heat exchange is made to be 60-75°C.

[0053] As a specific embodiment of the above method of the present invention, step (4) further comprises: flashing the mother liquor and the circulated preheated electrodialysis concentrated water to obtain a flash gas phase and a flash liquid phase.

[0054] Compared with the prior art, the beneficial technical effects achieved by the present invention include:

[0055] 1) The low-energy consumption fracturing flowback fluid graded treatment method provided by the present invention has a simple process and stable operation, and realizes graded treatment according to different fracturing flowback fluid water quality conditions and water output requirements.

[0056] 2) The method provided by the present invention is applicable to the practical needs of on-site shale gas treatment. By first transferring the fracturing flowback fluid from multiple wells to an aeration transfer tank, the impact of water quality fluctuations on the treatment process can be effectively eliminated. The aerated fracturing flowback fluid is first subjected to flotation deoiling, flocculation and sedimentation, and softening and concentration. The concentrated fluid is then subjected to ozone oxidation, which removes most organic matter from the fracturing flowback fluid. Ozone oxidation has been demonstrated to be the most cost-effective technology for removing organic matter from fracturing flowback fluid.

[0057] 3) In terms of the softening method for fracturing flowback fluid, the present invention combines chemical softening mainly using sodium carbonate and sodium sulfate with deep softening technologies such as microfiltration, nanofiltration, and ion exchange (i.e., softening ion adsorption), which can effectively remove hardness ions in the fracturing flowback fluid, thereby ensuring the long-term stable operation of the subsequent desalination unit, i.e., the membrane concentration system.

[0058] 4) During the reverse osmosis concentration process, the present invention uses a hydraulic pressure turbine to recover the pressure energy in the high-pressure reverse osmosis concentrated water, reducing the energy consumption during the operation process; during the electrodialysis concentrated water evaporation and crystallization stage, a combination of solar energy preheating and compressor heat energy recovery is used to save energy and achieve low energy consumption.

[0059] 5) Compared with the existing technology, the method provided by the present invention has a shorter process flow and occupies a smaller area. Specifically, other existing process flows mostly adopt the process flow of "regulating tank + flotation + catalytic oxidation + coagulation sedimentation + ultrafiltration + ion adsorption + electrodialysis + biochemical treatment + MVR evaporation", in which the biochemical pool used for biochemical treatment occupies an area of ​​about 0.2 cubic meters per ton of water. The present invention mainly adopts physical and chemical methods, and the total area occupied is reduced by more than 40%.

[0060] 6) In the method provided by the present invention, by-products can be classified and collected, and the crystallized salt can be utilized as a resource. Specifically, the by-products produced by the method include crystallized salt and sludge, wherein the sludge includes first-stage sludge and second-stage sludge. The graded collection of sludge reduces the amount of sludge, avoids the sludge from being disposed of as hazardous waste, and ensures the purity of the crystallized salt. The test results show that the quality of the crystallized salt can meet the standards of secondary industrial salt, and even the standards of primary industrial salt, so that the crystallized salt can be utilized as a resource.

[0061] 7) The system and method provided by the present invention are stable in operation. When designing the process flow, the long-term operation of the equipment in the system was taken into consideration. Since the process flow of the method involves multiple membrane treatment units (such as tubular microfiltration units, nanofiltration units, primary reverse osmosis units and secondary reverse osmosis units, etc.), the present invention has carefully designed the front-end pretreatment of each membrane treatment unit. Specifically, first, the present invention performs primary sedimentation in the sedimentation tank so that the secondary sediment, that is, the second-stage sludge, is mainly softened sediment, which reduces the load of the sedimentation tank. Secondly, a tubular microfiltration unit is set at the front end of the nanofiltration unit, and the microfiltration membrane assembly used therein has a cutoff pore size of ≤0.05μm. First, the tubular microfiltration unit can remove most of the hardness ions through chemical reaction, reducing the load of the nanofiltration unit. At the same time, the microfiltration membrane assembly with a cutoff pore size of ≤0.05μm can filter out most of the suspended particles without affecting the surface of the nanofiltration membrane used in the nanofiltration unit, thereby improving the service life of the nanofiltration membrane. In addition, the refined pretreatment can also extend the service life of the reverse osmosis (primary reverse osmosis unit and secondary reverse osmosis unit). After two years of actual operation, under the operating conditions of 12 hours / day, the nanofiltration unit and reverse osmosis unit used in the system provided by the present invention have maintained relatively stable operation, and the microfiltration unit only needs to be offline cleaned once a month. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0063] FIG1 is a schematic structural diagram of a low-energy consumption fracturing flowback fluid graded treatment system provided by Examples 1 and 2 of the present invention.

[0064] FIG2 is a schematic structural diagram of a flowback fluid recycling system in a low-energy consumption fracturing flowback fluid graded treatment system provided in Examples 1 and 2 of the present invention.

[0065] FIG3 is a schematic structural diagram of a softening pretreatment system in the low-energy consumption fracturing flowback fluid graded treatment system provided by Examples 1 and 2 of the present invention.

[0066] FIG4 is a schematic structural diagram of a membrane concentration system in a low-energy consumption fracturing flowback fluid graded treatment system provided in Example 1 of the present invention.

[0067] FIG5 is a schematic structural diagram of a solar evaporation crystallization system in a low-energy consumption fracturing flowback fluid graded treatment system provided by Examples 1 and 2 of the present invention.

[0068] FIG6 is a schematic structural diagram of a membrane concentration system in a low-energy consumption fracturing flowback fluid graded treatment system provided in Example 2 of the present invention.

[0069] Explanation of main figure numbers: 100. Flowback liquid reuse system; 200. Softening pretreatment system; 300. Membrane concentration system; 400. Solar evaporation crystallization system; 1. Aeration transfer tank; 2. Flotation oil removal tank; 3. Flocculation reactor; 4. Sedimentation tank; 5. Softening and concentration reaction tank; 6. Ozone oxidation reactor; 7. Tubular microfiltration unit; 8. Nanofiltration unit; 9. Softening ion adsorption unit; 10. Hydraulic pressure turbine; 11. Primary reverse osmosis unit; 12. Secondary reverse osmosis unit; 13. Electrodialysis unit; 14. Ammonia nitrogen and boron adsorption unit; 15. Preheating circulation tank; 16. Solar heater; 17. Flash tank; 18. Evaporation tank; 19. Heat exchanger; 20. Second compressor; 21. First compressor; 22. Thickener. DETAILED DESCRIPTION

[0070] It should be noted that the term "comprise" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products or apparatus.

[0071] The "range" disclosed in the present invention is given in the form of a lower limit and an upper limit. It can be one or more lower limits, and one or more upper limits respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower limit and upper limit define the boundaries of a particular range. All ranges defined in this way are combinable, i.e., any lower limit can be combined with any upper limit to form a range. For example, a range of 60-120 and 80-110 is listed for a particular parameter, and it is understood that a range of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​listed are 1 and 2, and the maximum range values ​​listed are 3, 4, and 5, then the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.

[0072] In the present invention, unless otherwise specified, the numerical range "ab" is an abbreviation for any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed in this invention, and "0-5" is merely an abbreviation for these numerical combinations.

[0073] In the present invention, unless otherwise specified, all embodiments and preferred embodiments mentioned in the present invention can be combined with each other to form a new technical solution.

[0074] In the present invention, unless otherwise specified, all technical features and preferred features mentioned in the present invention can be combined with each other to form a new technical solution.

[0075] In the present invention, unless otherwise specified, all steps mentioned herein may be performed sequentially or randomly, but are preferably performed sequentially. For example, the method comprising steps (a) and (b) indicates that the method may comprise steps (a) and (b) performed sequentially, or may comprise steps (b) and (a) performed sequentially. For example, the method further comprising step (c) indicates that step (c) may be added to the method in any order, for example, the method may comprise steps (a), (b) and (c), or may comprise steps (a), (c) and (b), or may comprise steps (c), (a) and (b), etc.

[0076] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the attached table, drawings and examples. The following embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the examples, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0077] Example 1

[0078] This embodiment provides a low-energy consumption fracturing flowback fluid graded treatment system, wherein the structural schematic diagram of the low-energy consumption fracturing flowback fluid graded treatment system is shown in FIG1 . As can be seen from FIG1 , it includes a flowback fluid recycling system 100, a softening pretreatment system 200, a membrane concentration system 300, and a solar evaporation crystallization system 400 that are connected in sequence;

[0079] The structural diagram of the flowback liquid reuse system 100 is shown in FIG2 . As can be seen from FIG2 , the flowback liquid reuse system 100 includes an aeration transfer tank 1, an air flotation oil removal tank 2, a flocculation reactor 3, and a sedimentation tank 4, which are sequentially connected through pipelines.

[0080] The structural diagram of the softening pretreatment system 200 is shown in FIG3 . As can be seen from FIG3 , the softening pretreatment system 200 includes a softening concentration reaction tank 5, an ozone oxidation reactor 6, a first pump, a tubular microfiltration unit 7, a nanofiltration unit 8, and a softening ion adsorption unit 9 that are sequentially connected; the cutoff pore size of the microfiltration membrane assembly used in the tubular microfiltration unit 7 is ≤0.05 μm;

[0081] The softening and concentrating reaction tank 5 includes a primary softening tank, a secondary softening tank and a concentrating tank connected in sequence, and the microfiltration concentrated water outlet of the tubular microfiltration unit 7 and the nanofiltration concentrated water outlet of the nanofiltration unit 8 are respectively connected to the inlet of the softening and concentrating reaction tank 5 through a concentrated water reflux pipe;

[0082] The structural diagram of the membrane concentration system 300 is shown in FIG4 . As can be seen from FIG4 , the membrane concentration system 300 includes a hydraulic pressure turbine 10 , a primary reverse osmosis unit 11 , a secondary reverse osmosis unit 12 , an electrodialysis unit 13 , and an ammonia nitrogen and boron adsorption unit 14 .

[0083] The liquid outlet of the softening ion adsorption unit 9 is connected to the liquid inlet of the first-stage reverse osmosis unit 11 through a pipeline via a hydraulic pressure turbine 10 and a second pump. The fresh water outlet of the first-stage reverse osmosis unit 11 is connected to the liquid inlet of the ammonia nitrogen and boron adsorption unit 14 through a pipeline via a third pump and a second-stage reverse osmosis unit 12.

[0084] The concentrated water outlet of the primary reverse osmosis unit 11 is connected to the liquid inlet of the electrodialysis unit 13 via a pipeline through the hydraulic pressure turbine 10, and the concentrated water outlet of the electrodialysis unit 13 is connected to the inlet of the preheating circulation tank 15 via a pipeline; the fresh water outlet of the electrodialysis unit 13 and the concentrated water outlet of the secondary reverse osmosis unit 12 are respectively connected to the liquid inlet of the primary reverse osmosis unit 11 via a pipeline through the hydraulic pressure turbine 10;

[0085] The structural schematic diagram of the solar evaporation crystallization system 400 is shown in Figure 5. As can be seen from Figure 5, the solar evaporation crystallization system 400 includes a preheating circulation tank 15, a solar heater 16, a flash tank 17, an evaporation tank 18, a heat exchanger 19 and a thickener 22. The solar heater 16 is used to circulate and preheat the electrodialysis concentrated water in the preheating circulation tank 15. The liquid outlet of the preheating circulation tank 15 is connected to the inlet of the flash tank 17 via a pipeline. The liquid phase outlet of the flash tank 17 is connected to the inlet of the evaporation tank 18 via a pipeline via the heat exchanger 19. The liquid phase outlet of the evaporation tank 18 is connected to the thickener 22 via a pipeline. The gas phase outlet of the flash tank 17 is connected to the liquid inlet of the ammonia nitrogen and boron adsorption unit 14 via a pipeline via the first compressor 21 and the heat exchanger 19. The gas phase outlet of the evaporation tank 18 is connected to the liquid inlet of the ammonia nitrogen and boron adsorption unit 14 via a pipeline via the second compressor 20 and the heat exchanger 19. The liquid outlet of the thickener is connected to the inlet of the evaporation tank via a pipeline.

[0086] Example 2

[0087] This embodiment provides a low-energy consumption fracturing flowback fluid graded treatment system, wherein the structural schematic diagram of the low-energy consumption fracturing flowback fluid graded treatment system is shown in FIG1 . As can be seen from FIG1 , it includes a flowback fluid recycling system 100, a softening pretreatment system 200, a membrane concentration system 300, and a solar evaporation crystallization system 400 that are connected in sequence;

[0088] The structural diagram of the flowback liquid reuse system 100 is shown in FIG2 . As can be seen from FIG2 , the flowback liquid reuse system 100 includes an aeration transfer tank 1, an air flotation oil removal tank 2, a flocculation reactor 3, and a sedimentation tank 4, which are sequentially connected through pipelines.

[0089] The structural diagram of the softening pretreatment system 200 is shown in FIG3 . As can be seen from FIG3 , the softening pretreatment system 200 includes a softening concentration reaction tank 5, an ozone oxidation reactor 6, a first pump, a tubular microfiltration unit 7, a nanofiltration unit 8, and a softening ion adsorption unit 9 that are sequentially connected; the cutoff pore size of the microfiltration membrane assembly used in the tubular microfiltration unit 7 is ≤0.05 μm;

[0090] The softening and concentrating reaction tank 5 includes a primary softening tank, a secondary softening tank and a concentrating tank connected in sequence, and the microfiltration concentrated water outlet of the tubular microfiltration unit 7 and the nanofiltration concentrated water outlet of the nanofiltration unit 8 are respectively connected to the inlet of the softening and concentrating reaction tank 5 through a concentrated water reflux pipe;

[0091] The structural diagram of the membrane concentration system 300 is shown in FIG6 . As can be seen from FIG6 , the membrane concentration system 300 includes a hydraulic pressure turbine 10 , a primary reverse osmosis unit 11 , a secondary reverse osmosis unit 12 , an electrodialysis unit 13 , and an ammonia nitrogen and boron adsorption unit 14 .

[0092] The liquid outlet of the softening ion adsorption unit 9 is connected to the liquid inlet of the electrodialysis unit 13 through a pipeline, the concentrated water outlet of the electrodialysis unit 13 is connected to the inlet of the preheating circulation tank 15 through a pipeline, the fresh water outlet of the electrodialysis unit 13 is connected to the liquid inlet of the first-stage reverse osmosis unit 11 through a pipeline via the hydraulic pressure turbine 10 and the second pump, the fresh water outlet of the first-stage reverse osmosis unit 11 is connected to the liquid inlet of the ammonia nitrogen and boron adsorption unit 14 through a pipeline via the third pump and the second-stage reverse osmosis unit 12; the concentrated water outlet of the second-stage reverse osmosis unit 12 is connected to the liquid inlet of the first-stage reverse osmosis unit 11 through a pipeline via the hydraulic pressure turbine 10; the concentrated water outlet of the first-stage reverse osmosis unit 11 is connected to the liquid inlet of the electrodialysis unit 13 through a pipeline via the hydraulic pressure turbine 10;

[0093] The structural schematic diagram of the solar evaporation crystallization system 400 is shown in Figure 5. As can be seen from Figure 5, the solar evaporation crystallization system 400 includes a preheating circulation tank 15, a solar heater 16, a flash tank 17, an evaporation tank 18, a heat exchanger 19 and a thickener 22. The solar heater 16 is used to circulate and preheat the electrodialysis concentrated water in the preheating circulation tank 15. The liquid outlet of the preheating circulation tank 15 is connected to the inlet of the flash tank 17 via a pipeline. The liquid phase outlet of the flash tank 17 is connected to the inlet of the evaporation tank 18 via a pipeline via the heat exchanger 19. The liquid phase outlet of the evaporation tank 18 is connected to the thickener 22 via a pipeline. The gas phase outlet of the flash tank 17 is connected to the liquid inlet of the ammonia nitrogen and boron adsorption unit 14 via a pipeline via the first compressor 21 and the heat exchanger 19. The gas phase outlet of the evaporation tank 18 is connected to the liquid inlet of the ammonia nitrogen and boron adsorption unit 14 via a pipeline via the second compressor 20 and the heat exchanger 19. The liquid outlet of the thickener is connected to the inlet of the evaporation tank via a pipeline.

[0094] Example 3

[0095] This embodiment provides a low-energy consumption fracturing flowback fluid graded treatment method, which is implemented using the low-energy consumption fracturing flowback fluid graded treatment system provided in Example 1, wherein the method includes the following specific steps:

[0096] S1: Collect fracturing flowback fluid from multiple wells in a shale gas block after fracturing operations①. First, the fracturing flowback fluid enters the flowback fluid reuse system. Specifically, the fracturing flowback fluid is first passed from the lower part of the aeration transfer tank to the aeration transfer tank for continuous aeration treatment. Water is discharged from the upper part of the aeration transfer tank, and slag can be intermittently discharged from the bottom of the aeration transfer tank, i.e., aeration bottom slag②;

[0097] Then the effluent from the upper part of the aeration transfer tank enters the flotation oil removal tank, the separated waste oil can be collected, and the effluent enters the flocculation reactor, where PAC and PAM reagents are added in sequence to form flocs through flocculation reaction.

[0098] The flocs and liquid phase in the flocculation reactor are passed together into a sedimentation tank for precipitation. The effluent is used as the effluent of the return liquid recycling system, i.e., the first-level liquid ④. After testing, it is found that the total suspended solids in the first-level liquid are ≤15mg / L, the total iron is ≤10mg / L, and the petroleum substances are ≤10mg / L. It can be recycled as a liquid with a low hardness ion content. The precipitated sludge is referred to as the first-level sludge ③, which is filtered and dehydrated before being collected.

[0099] S2: The primary liquid enters a softening and concentration reaction tank, which includes a primary softening tank, a secondary softening tank, and a concentration tank connected in sequence. Sodium carbonate and sodium sulfate are added to the primary softening tank and the secondary softening tank in sequence for reaction, wherein the addition concentration of sodium carbonate is 2500 mg / L and the addition concentration of sodium sulfate is 420 mg / L. The system after the reaction enters a concentration tank for concentration. The upper liquid in the concentration tank enters an ozone oxidation reactor for oxidation treatment by ozone. The sludge settled at the bottom of the primary softening tank, the secondary softening tank, and the concentration tank is then extracted and dehydrated by filter pressing to obtain secondary sludge ⑤;

[0100] The effluent after ozone oxidation treatment is transported to the tubular microfiltration unit through the first pump, wherein the cut-off pore size of the microfiltration membrane assembly used in the tubular microfiltration unit is ≤0.05μm, the microfiltration concentrated water in the microfiltration unit enters the concentrated water reflux pipe, and the microfiltration fresh water enters the nanofiltration unit after pressurization for nanofiltration treatment, wherein the nanofiltration membrane used in the nanofiltration unit is Dow nanofiltration membrane NF90-400, and the operating pressure of the nanofiltration unit is about 1.5MPa. After the nanofiltration treatment, nanofiltration fresh water is generated, namely, filtered water and nanofiltration concentrated water ⑥, and the nanofiltration concentrated water and microfiltration concentrated water are respectively The water is returned to the softening and concentration reaction tank through the concentrated water return pipe for further treatment. The nanofiltered fresh water enters the softening ion adsorption unit to remove hardness ions through ion adsorption. The softening ion adsorption unit uses "Zhengguang" brand 001×8 strong acidic cation exchange resin for ion adsorption to remove hardness ions. The effluent of ion adsorption is the effluent of the softening pretreatment system, recorded as secondary liquid ⑦. After testing, it was found that the total hardness of the secondary liquid was ≤20mg / L. The secondary liquid can be recycled as a liquid with a high hardness ion content.

[0101] S3: The salinity of the above-mentioned secondary liquid is measured to be 11700 mg / L, which is lower than 40000 mg / L. Therefore, the membrane concentration system (membrane desalination system) shown in FIG4 is used to treat the secondary liquid, specifically comprising: firstly, the secondary liquid enters a hydraulic pressure turbine to increase the pressure, and the hydraulic pressure reaches 1.3 MPa. Then, the secondary liquid is pressurized to 6 MPa by a second pump (water pump) and then enters a first-stage reverse osmosis unit using a Dow seawater desalination membrane SW30HRLE-400 for first-stage reverse osmosis to obtain first-stage reverse osmosis concentrated water and first-stage reverse osmosis fresh water. The pressure of the first-stage reverse osmosis concentrated water reaches 5.6 MPa. After passing through the hydraulic turbine, that is, the hydraulic pressure, the secondary liquid enters a first-stage reverse osmosis unit using a Dow seawater desalination membrane SW30HRLE-400 for first-stage reverse osmosis. After the turbine, the pressure is reduced to 2 MPa. The primary reverse osmosis concentrate after the pressure reduction enters the electrodialysis unit (the electrodialysis component uses Lancytom bipolar membrane BP-2) for electrodialysis. The salinity of the primary reverse osmosis concentrate before electrodialysis is 53282 mg / L. After electrodialysis treatment in the electrodialysis unit, electrodialysis fresh water and electrodialysis concentrate are obtained. The salinity of the electrodialysis fresh water is 5600 mg / L. The electrodialysis fresh water is returned to the secondary liquid, i.e., the influent of the membrane concentration system, for further treatment. The salinity of the electrodialysis concentrate (10) reaches 84539 mg / L. It is recorded as the tertiary liquid and enters the solar evaporation crystallization system for treatment.

[0102] The primary reverse osmosis fresh water is pressurized to 4 MPa by the third pump (water pump) and then enters the secondary reverse osmosis unit using the Dow Chemical brackish water membrane BW30-4040 for secondary reverse osmosis, obtaining secondary reverse osmosis concentrated water and secondary reverse osmosis fresh water⑧. After testing, it was found that the mineralization of the secondary reverse osmosis fresh water was lower than 420 mg / L, and the pressure of the secondary reverse osmosis concentrated water reached 3.6 MPa. After passing through the hydraulic pressure turbine, the pressure was reduced to 2 MPa. The reduced pressure secondary reverse osmosis concentrated water was returned to the secondary liquid, i.e., the membrane concentration system inlet water, for further treatment. The secondary reverse osmosis fresh water then entered the ammonia nitrogen and boron adsorption unit, first passing through the ammonia nitrogen adsorption resin (Tulsimer T-42H) to adsorb the ammonia nitrogen therein, and then entering the boron adsorption resin (Tulsimer Boron selective adsorption resin) adsorbs the boron therein to obtain adsorbed water;

[0103] S4: The electrodialysis concentrated water is allowed to enter the solar evaporation crystallization system for treatment, specifically including: first, the electrodialysis concentrated water is allowed to enter the preheating circulation tank, the liquid volume in the tank is kept at half of the tank body, and it is preheated by solar circulation in the solar heater to keep the liquid temperature in the tank at 65°C and the pressure at 0.13MPa; in the specific operation, part of the electrodialysis concentrated water in the preheating circulation tank is transported to the solar heating tube of the solar heater, and then returned to the preheating circulation tank after heating; part of the liquid phase after preheating enters the flash tank, the vacuum degree of the flash tank is 0.06MPa, and gas-liquid separation occurs in the flash tank, wherein the flash gas phase is compressed by the first compressor at a compression ratio of 1.5, and its temperature rises by 14°C after compression, which is about 7 5℃, the heated flash gas phase enters the heat exchanger as a heat source for heat exchange and cooling, and the flash liquid phase enters the heat exchanger for heat exchange and temperature increase with the heated flash gas phase. After the flash liquid phase is heated, the temperature reaches about 70℃, and then enters the evaporator. The vacuum degree in the evaporator is maintained at about 0.07MPa. The evaporation process occurs in the evaporator, and the flash liquid phase continues to evaporate to obtain an evaporation gas phase and an evaporation liquid phase (slurry). The evaporation gas phase is compressed by the second compressor to increase its temperature by 10-15℃ to about 75℃. The heated evaporation gas phase and the heated flash gas phase are both used as heat sources to enter the heat exchanger for heat exchange and cooling. After the two steam heat sources are heat exchanged in the heat exchanger, the temperature is lower than 50℃. The two are mixed and used as condensed water It is then transported to the ammonia nitrogen and boron adsorption unit together with the secondary reverse osmosis fresh water for ammonia nitrogen and boron adsorption. The adsorbed liquid is used as the final effluent ⑨. Finally, the evaporated liquid phase is transported to the thickener and crystallized in the thickener to produce crystalline salt. At the same time, the mother liquor is returned to the flash tank for further flash evaporation treatment.

[0104] The fracturing flowback fluid ①, electrodialysis concentrate and final effluent ⑨ in this embodiment were tested using conventional methods in the art. The main water quality indicators are shown in Table 1 below.

[0105] Table 1

[0106] Note: Total hardness includes Ca 2+ Mg 2+ 、Ba 2+ and Sr 2+ .

[0107] As can be seen from Table 1 above, the main indicators of the final effluent obtained in Example 3 of the present invention can meet the requirements of the "Integrated Sewage Discharge Standard" (GB 8978-1996) and the "Sichuan Province Water Pollutant Discharge Standard" (DB51 / 190-93).

[0108] Then the crystalline salt in this embodiment is subjected to conventional methods in the art. The quality of the product was tested, and the obtained quality test data are shown in Table 2 below.

[0109] Table 2

[0110] As can be seen from Table 2 above, the quality of the crystalline salt obtained in Example 3 of the present invention can meet the standard of secondary industrial salt and can be used as industrial salt for resource utilization.

[0111] In summary, the low-energy consumption fracturing return fluid graded treatment system and method provided in Example 3 has fewer by-products and is easier to handle. A total of four by-products are produced in this method, of which by-product No. 1 is the surface waste floating oil of the fracturing return fluid, which can be collected and transported for disposal; by-product No. 2 is the primary sedimentation sludge, i.e., the first-stage sludge; by-product No. 3 is the second-stage sludge, which is softened sludge. The first-stage sludge and the second-stage sludge are respectively subjected to two independent treatment units, i.e., the filter press dehydration unit, for solid-liquid separation, while other existing treatment processes usually only obtain the first-stage sludge, and the sludge cannot be treated separately, and the properties of the two stages of sludge in the present invention are stable and easier to dispose of subsequently; by-product No. 4 is crystalline salt, the quality of which is better than the standard of secondary industrial salt and can be utilized as a resource.

[0112] Example 4

[0113] This embodiment provides a low-energy consumption fracturing flowback fluid graded treatment method, which is implemented using the low-energy consumption fracturing flowback fluid graded treatment system provided in Example 2, wherein the method includes the following specific steps:

[0114] S1: Collect fracturing flowback fluid from multiple wells in a shale gas block after fracturing operations①. First, the fracturing flowback fluid enters the flowback fluid reuse system. Specifically, the fracturing flowback fluid is first passed from the lower part of the aeration transfer tank to the aeration transfer tank for continuous aeration treatment. Water is discharged from the upper part of the aeration transfer tank, and slag can be intermittently discharged from the bottom of the aeration transfer tank, i.e., aeration bottom slag②;

[0115] Then the effluent from the upper part of the aeration transfer tank enters the flotation oil removal tank, the separated waste oil can be collected, and the effluent enters the flocculation reactor, where PAC and PAM reagents are added in sequence to form flocs through flocculation reaction.

[0116] The flocs and liquid phase in the flocculation reactor are passed together into a sedimentation tank for precipitation. The effluent is used as the effluent of the return liquid recycling system, i.e., the first-level liquid ④. After testing, it is found that the total suspended solids in the first-level liquid are ≤15mg / L, the total iron is ≤10mg / L, and the petroleum substances are ≤10mg / L. It can be recycled as a liquid with a low hardness ion content. The precipitated sludge is referred to as the first-level sludge ③, which is filtered and dehydrated before being collected.

[0117] S2: The primary liquid enters a softening and concentration reaction tank, which includes a primary softening tank, a secondary softening tank, and a concentration tank connected in sequence. Sodium carbonate and sodium sulfate are added to the primary softening tank and the secondary softening tank in sequence for reaction, wherein the addition concentration of sodium carbonate is 2500 mg / L and the addition concentration of sodium sulfate is 420 mg / L. The system after the reaction enters a concentration tank for concentration. The upper liquid in the concentration tank enters an ozone oxidation reactor for oxidation treatment by ozone. The sludge settled at the bottom of the primary softening tank, the secondary softening tank, and the concentration tank is then extracted and dehydrated by filter pressing to obtain secondary sludge ⑤;

[0118] The effluent after ozone oxidation treatment is transported to the tubular microfiltration unit through the first pump, wherein the cut-off pore size of the microfiltration membrane assembly used in the tubular microfiltration unit is ≤0.05μm, the microfiltration concentrated water in the microfiltration unit enters the concentrated water reflux pipe, and the microfiltration fresh water enters the nanofiltration unit after pressurization for nanofiltration treatment, wherein the nanofiltration membrane used in the nanofiltration unit is Dow nanofiltration membrane NF90-400, and the operating pressure of the nanofiltration unit is about 1.5MPa. After the nanofiltration treatment, nanofiltration fresh water is generated, namely, filtered water and nanofiltration concentrated water ⑥, and the nanofiltration concentrated water and microfiltration concentrated water are respectively The water is returned to the softening and concentration reaction tank through the concentrated water return pipe for further treatment. The nanofiltered fresh water enters the softening ion adsorption unit to remove hardness ions through ion adsorption. The softening ion adsorption unit uses "Zhengguang" brand 001×8 strong acidic cation exchange resin for ion adsorption to remove hardness ions. The effluent of ion adsorption is the effluent of the softening pretreatment system, recorded as secondary liquid ⑦. After testing, it was found that the total hardness of the secondary liquid was ≤20mg / L. The secondary liquid can be recycled as a liquid with a high hardness ion content.

[0119] S3: The salinity of the above-mentioned secondary liquid ⑦ was measured to be 43700 mg / L, which is higher than 40000 mg / L. Therefore, the membrane concentration system (membrane desalination system) shown in Figure 6 was used to treat the secondary liquid, specifically comprising: first, the secondary liquid was allowed to enter the electrodialysis unit (the electrodialysis component used the LANCYTOM bipolar membrane BP-2) for electrodialysis, and the salinity of the electrodialysis concentrated water ⑩ reached 80599 mg / L, which was recorded as the tertiary liquid and entered the solar evaporation crystallization system for treatment; the salinity of the electrodialysis fresh water was 10400 mg / L, and the electrodialysis fresh water entered the hydraulic turbine and was pressurized to 1MPa, and then pressurized to 5MPa by the second pump (water pump) and then entered the first-stage reverse osmosis unit using the Dow seawater desalination membrane SW30HRLE-400 for first-stage reverse osmosis to obtain first-stage reverse osmosis concentrated water and first-stage reverse osmosis fresh water. The pressure of the first-stage reverse osmosis concentrated water reached 4.3MPa. After the hydraulic pressure turbine, its pressure is reduced to 1.5MPa, and after merging with the secondary liquid, it enters the electrodialysis unit (the electrodialysis component uses Lancytom bipolar membrane BP-2) for electrodialysis. The primary reverse osmosis fresh water is pressurized to 3.6MPa by the third pump (water pump) and then enters the secondary reverse osmosis unit using Dow Chemical brackish water membrane BW30-4040 for secondary reverse osmosis to obtain secondary reverse osmosis concentrated water and secondary reverse osmosis fresh water⑧. After testing, it was found that the mineralization of the secondary reverse osmosis fresh water was lower than 420mg / L, and the pressure of the secondary reverse osmosis concentrated water reached about 3MPa. After passing through the hydraulic pressure turbine, the pressure was reduced to 1.5MPa, and after merging with the electrodialysis fresh water, it returned to the primary reverse osmosis unit using Dow seawater desalination membrane SW30HRLE-400 for reverse osmosis. The secondary reverse osmosis fresh water then enters the ammonia nitrogen and boron adsorption unit, first passing through the ammonia nitrogen adsorption resin (Tulsimer T-42H) adsorbs ammonia nitrogen and then enters the boron adsorption resin (Tulsimer Boron selective adsorption resin) adsorbs the boron therein to obtain adsorbed water;

[0120] S4: The electrodialysis concentrated water is allowed to enter the solar evaporation crystallization system for treatment, specifically including: first, the electrodialysis concentrated water is allowed to enter the preheating circulation tank, the liquid volume in the tank is kept at half of the tank body, and it is preheated by solar circulation in the solar heater to keep the liquid temperature in the tank at 65°C and the pressure at 0.13MPa; in the specific operation, part of the electrodialysis concentrated water in the preheating circulation tank is transported to the solar heating tube of the solar heater, and then returned to the preheating circulation tank after heating; part of the liquid phase after preheating enters the flash tank, the vacuum degree of the flash tank is 0.06MPa, and gas-liquid separation occurs in the flash tank, wherein the flash gas phase is compressed by the first compressor at a compression ratio of 1.5, and its temperature rises by 14°C after compression, which is about 7 5℃, the heated flash gas phase enters the heat exchanger as a heat source for heat exchange and cooling, and the flash liquid phase enters the heat exchanger for heat exchange and temperature increase with the heated flash gas phase. After the flash liquid phase is heated, the temperature reaches about 70℃, and then enters the evaporator. The vacuum degree in the evaporator is maintained at about 0.07MPa. The evaporation process occurs in the evaporator, and the flash liquid phase continues to evaporate to obtain an evaporation gas phase and an evaporation liquid phase (slurry). The evaporation gas phase is compressed by the second compressor to increase its temperature by 10-15℃ to about 75℃. The heated evaporation gas phase and the heated flash gas phase are both used as heat sources to enter the heat exchanger for heat exchange and cooling. After the two steam heat sources are heat exchanged in the heat exchanger, the temperature is lower than 50℃. The two are mixed and used as condensed water It is then transported to the ammonia nitrogen and boron adsorption unit together with the secondary reverse osmosis fresh water for ammonia nitrogen and boron adsorption. The adsorbed liquid is used as the final effluent ⑨. Finally, the evaporated liquid phase is transported to the thickener and crystallized in the thickener to produce crystalline salt. At the same time, the mother liquor is returned to the flash tank for further flash evaporation treatment.

[0121] The fracturing flowback fluid ①, electrodialysis concentrate and final effluent ⑨ in this embodiment were tested using conventional methods in the art. The main water quality indicators are shown in Table 3 below.

[0122] Table 3

[0123] Note: Total hardness includes Ca 2+ Mg 2+ 、Ba 2+ and Sr 2+ .

[0124] As can be seen from Table 3 above, the main indicators of the final effluent obtained in Example 4 of the present invention can meet the requirements of the "Integrated Sewage Discharge Standard" (GB 8978-1996) and the "Sichuan Province Water Pollutant Discharge Standard" (DB51 / 190-93).

[0125] Then the crystalline salt in this embodiment is subjected to conventional methods in the art. The quality of the product was tested, and the obtained quality test data are shown in Table 4 below.

[0126] Table 4

[0127] As can be seen from Table 4 above, the quality of the crystalline salt obtained in Example 4 of the present invention can reach the standard of first-class industrial salt.

[0128] In summary, the low-energy consumption fracturing return fluid graded treatment system and method provided in Example 4 of the present invention has fewer by-products and is easier to handle. A total of four by-products are produced in this method, of which by-product No. 1 is the surface waste floating oil of the fracturing return fluid, which can be collected and transported for disposal; by-product No. 2 is the primary sedimentation sludge, i.e., the first-stage sludge; by-product No. 3 is the second-stage sludge, which is softened sludge. The first-stage sludge and the second-stage sludge are respectively subjected to two independent treatment units, i.e., the filter press dehydration unit, for solid-liquid separation, while other existing treatment processes usually only obtain the first-stage sludge, and the sludge cannot be treated separately, and the properties of the two stages of sludge in the present invention are stable and easier to dispose of subsequently; by-product No. 4 is crystalline salt, the quality of which is better than the standard of first-stage industrial salt and can be utilized as a resource.

[0129] The above description is merely a specific embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, substitutions of equivalent components, or equivalent changes and modifications made within the scope of patent protection, should still fall within the scope of this patent. Furthermore, the technical features of this invention may be freely combined with one another, with other technical inventions, and with other technical inventions.

Claims

1. A low-energy consumption fracturing flowback fluid classification treatment system, characterized in that: The low-energy consumption fracturing flowback fluid graded treatment system comprises a flowback fluid recycling system, a softening pretreatment system, a membrane concentration system, and a solar evaporation crystallization system which are connected in sequence; The return liquid recycling system includes an aeration transfer tank, an air flotation oil removal tank, a flocculation reactor and a sedimentation tank which are connected in sequence; The softening pretreatment system comprises a softening concentration reaction tank, an ozone oxidation reactor, a tubular microfiltration unit, a nanofiltration unit and a softening ion adsorption unit which are connected in sequence; The membrane concentration system includes a primary reverse osmosis unit, a secondary reverse osmosis unit, an electrodialysis unit and an ammonia nitrogen and boron adsorption unit; The solar evaporation crystallization system comprises a preheating circulation tank, a solar heater, a flash tank, an evaporation tank, a heat exchanger and a thickener. The solar heater is used for circulating and preheating the electrodialysis concentrated water in the preheating circulation tank. The liquid outlet of the preheating circulation tank is connected with the inlet of the flash tank. The liquid phase outlet of the flash tank is connected with the inlet of the evaporation tank through a pipeline via the heat exchanger. The liquid phase outlet of the evaporation tank is connected with the thickener. The gas phase outlet of the flash tank and the gas phase outlet of the evaporation tank are respectively connected with the liquid inlet of the ammonia nitrogen and boron adsorption unit through pipelines via the heat exchanger.

2. The system according to claim 1, characterized in that The cut-off pore size of the microfiltration membrane assembly used in the tubular microfiltration unit is ≤0.05 μm.

3. The system according to claim 1 or 2, characterized in that: The softening and concentrating reaction tank comprises a primary softening tank, a secondary softening tank and a concentrating tank which are connected in sequence.

4. The system according to claim 1 or 2, characterized in that: The liquid outlet of the softening ion adsorption unit is connected to the liquid inlet of the primary reverse osmosis unit through a pipeline via a hydraulic pressure turbine, and the fresh water outlet of the primary reverse osmosis unit is connected to the liquid inlet of the ammonia nitrogen and boron adsorption unit through a pipeline via a secondary reverse osmosis unit; The concentrated water outlet of the primary reverse osmosis unit is connected to the liquid inlet of the electrodialysis unit through a pipeline via a hydraulic pressure turbine, and the concentrated water outlet of the electrodialysis unit is connected to the inlet of the preheating circulation tank through a pipeline.

5. The system according to claim 1 or 2, characterized in that: The fresh water outlet of the electrodialysis unit and the concentrated water outlet of the secondary reverse osmosis unit are connected to the liquid inlet of the primary reverse osmosis unit through pipelines via a hydraulic pressure turbine.

6. The system according to claim 1 or 2, characterized in that: The liquid outlet of the softening ion adsorption unit is connected to the liquid inlet of the electrodialysis unit through a pipeline, the concentrated water outlet of the electrodialysis unit is connected to the inlet of the preheating circulation tank through a pipeline, the fresh water outlet of the electrodialysis unit is connected to the liquid inlet of the primary reverse osmosis unit through a pipeline via a hydraulic pressure turbine, and the fresh water outlet of the primary reverse osmosis unit is connected to the liquid inlet of the ammonia nitrogen and boron adsorption unit through a pipeline via a secondary reverse osmosis unit.

7. The system according to claim 1 or 2, characterized in that: The concentrated water outlet of the secondary reverse osmosis unit is connected to the liquid inlet of the primary reverse osmosis unit through a pipeline via a hydraulic pressure turbine.

8. The system according to claim 1 or 2, characterized in that: The concentrated water outlet of the primary reverse osmosis unit is connected to the liquid inlet of the electrodialysis unit through a pipeline via a hydraulic pressure turbine.

9. The system according to claim 1 or 2, characterized in that: The solar evaporation crystallization system also includes a first compressor and a second compressor. The gas phase outlet of the flash tank is connected to the liquid inlet of the ammonia nitrogen and boron adsorption unit through a pipeline via the first compressor and a heat exchanger, and the gas phase outlet of the evaporation tank is connected to the liquid inlet of the ammonia nitrogen and boron adsorption unit through a pipeline via the second compressor and a heat exchanger.

10. The system according to claim 1 or 2, characterized in that: The liquid outlet of the thickener is connected to the inlet of the evaporation tank through a pipeline.

11. A low-energy consumption fracturing flowback fluid classification treatment method, characterized in that: The method comprises the following steps: (1) aerating and flotation oil removal treatments are performed on the fracturing flowback fluid in sequence to obtain waste oil and effluent, and then flocculating and settling the effluent in sequence to obtain a first-stage sludge and a first-stage liquid; (2) Softening and concentrating the primary liquid to obtain concentrated liquid and secondary sludge, ozonating the concentrated liquid and subjecting its effluent to microfiltration to obtain microfiltration concentrated water and microfiltration fresh water, nanofiltration of the microfiltration fresh water to obtain nanofiltration concentrated water and nanofiltration fresh water, and finally softening the nanofiltration fresh water by ion adsorption to obtain secondary liquid; (3) when the mineralization degree of the secondary liquid is not higher than 40000 mg / L, the secondary liquid is subjected to primary reverse osmosis to obtain primary reverse osmosis concentrated water and primary reverse osmosis fresh water, the primary reverse osmosis fresh water is subjected to secondary reverse osmosis and then subjected to ammonia nitrogen and boron adsorption on the secondary reverse osmosis fresh water; the primary reverse osmosis concentrated water is subjected to electrodialysis to obtain electrodialysis concentrated water and electrodialysis fresh water; or, When the mineralization degree of the secondary liquid is higher than 40000 mg / L, the secondary liquid is subjected to electrodialysis to obtain electrodialysis concentrated water and electrodialysis fresh water, the electrodialysis fresh water is subjected to primary reverse osmosis and secondary reverse osmosis in sequence, and then the secondary reverse osmosis fresh water is subjected to ammonia nitrogen and boron adsorption; (4) Circulating and preheating the electrodialysis concentrated water with a solar heater, flashing it to obtain a flash gas phase and a flash liquid phase, then evaporating the flash liquid phase after heat exchange and heating to obtain an evaporation gas phase and an evaporation liquid phase, and crystallizing the evaporation liquid phase to obtain a crystalline salt and a mother liquor; wherein the heat source used for heat exchange and heating is the heated flash gas phase, or the heated flash gas phase and the heated evaporation gas phase.

12. The method according to claim 11, characterized in that The flocculant used in the flocculation includes polyaluminium chloride and / or polyacrylamide.

13. The method according to claim 11 or 12, characterized in that: The softening is carried out in two steps, wherein sodium carbonate and sodium sulfate are used in the first softening step and the second softening step respectively, wherein the mass ratio of sodium carbonate to sodium sulfate is 4:1-6:

1.

14. The method according to claim 11 or 12, characterized in that: When the mineralization degree of the secondary liquid is not higher than 40000 mg / L, step (3) further comprises: The electrodialysis fresh water and the secondary reverse osmosis concentrated water are subjected to primary reverse osmosis.

15. The method according to claim 11 or 12, characterized in that: When the mineralization degree of the secondary liquid is higher than 40000 mg / L, step (3) further comprises: performing primary reverse osmosis on the secondary reverse osmosis concentrated water.

16. The method according to claim 11 or 12, characterized in that: When the mineralization degree of the secondary liquid is higher than 40000 mg / L, step (3) further comprises: performing electrodialysis on the primary reverse osmosis concentrated water.

17. The method according to claim 11 or 12, characterized in that: The circulation preheating comprises: transferring part of the electrodialysis concentrated water in the preheating circulation tank to the solar heater, and then returning the concentrated water to the preheating circulation tank after being heated; The liquid volume capacity in the preheating circulation tank is maintained at 40-60%, the heating temperature is 55-65° C., and the pressure is 0.12-0.13 MPa.

18. The method according to claim 11 or 12, characterized in that: The vacuum degree of the flash evaporation is 0.06-0.07 MPa, and the vacuum degree of the evaporation is 0.06-0.07 MPa.

19. The method according to claim 11 or 12, characterized in that: The flash gas phase and the evaporated gas phase are heated by 12-18°C and 10-15°C respectively and then used as heat sources to exchange heat with the flash liquid phase, and the temperature of the flash liquid phase after heat exchange is set to 60-75°C.

20. The method according to claim 11 or 12, characterized in that Step (4) also includes: flashing the mother liquor and the circulated preheated electrodialysis concentrated water to obtain a flash gas phase and a flash liquid phase.

Images