A low-energy fracturing flowback fluid grading treatment system and method

Abstract

This invention provides a low-energy-consumption fracturing flowback fluid staged treatment system and method. The system includes a flowback fluid reuse system, a softening pretreatment system, a membrane concentration system, and a solar evaporation crystallization system 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 includes a preheating circulation tank, a solar heater, a flash tank, an evaporator, a heat exchanger, and a thickener. The solar heater is used to circulate and preheat the electrodialysis concentrate 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 evaporator via a heat exchanger. The liquid phase outlet of the evaporator is connected to the thickener. The gas phase outlets of the flash tank and the evaporator are respectively connected to the liquid inlet of the ammonia nitrogen and boron adsorption unit via pipelines and heat exchangers. This invention can remove contaminants from fracturing flowback fluid in stages with low energy consumption.

Description

Technical Field

[0001] This invention relates to a low-energy fracturing flowback fluid classification treatment system and method, belonging to the field of energy-saving and environmentally friendly water treatment technology. Background Technology

[0002] In the process of oil and gas extraction, the current shale gas and tight gas extraction technologies all require large-scale fracturing. After fracturing, a large amount of flowback waste liquid is generated, which puts pressure on the environment. In the later stages of extraction, the demand for reuse of flowback liquid decreases, and discharge of flowback liquid after treatment to meet standards becomes an important way to dispose of the flowback liquid.

[0003] Since fracturing flowback fluid is wastewater discharged from the wellhead after hydraulic fracturing, it is characterized by high levels of pollutants such as mineralization, chloride, and hardness ions. Direct discharge without treatment will pollute the environment. Due to the characteristics of the mining environment and the fracturing flowback fluid, the compliant treatment process must operate stably and be able to adapt to a wide range of changes in flowback fluid quality.

[0004] Therefore, it is of great significance to carry out research on the process technology for treating fracturing flowback fluid to meet standards. Providing a new type of low-energy fracturing flowback fluid classification treatment system and method has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] To address the aforementioned shortcomings and deficiencies, one objective of this invention is to provide a low-energy-consumption fracturing flowback fluid grading system.

[0006] Another objective of this invention is to provide a low-energy-consumption method for the graded treatment of fracturing flowback fluid. The system and method provided by this invention remove contaminants from fracturing flowback fluid in a graded manner, enabling the reuse or discharge of fracturing flowback fluid with low energy consumption.

[0007] To achieve the above objectives, on the one hand, the present invention provides a low-energy fracturing flowback fluid classification and treatment system, wherein the low-energy fracturing flowback fluid classification and treatment system includes a flowback fluid reuse system, a softening pretreatment system, a membrane concentration system, and a solar evaporation crystallization system connected in sequence.

[0008] The backflow liquid reuse system includes an aeration transfer tank, an air flotation oil removal tank, a flocculation reactor, and a sedimentation tank connected in sequence.

[0009] 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 connected in sequence.

[0010] 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;

[0011] The solar evaporation crystallization system includes a preheating circulation tank, a solar heater, a flash tank, an evaporator, a heat exchanger, and a thickener. The solar heater is used to circulate and preheat the electrodialysis concentrate in the preheating circulation tank. The liquid outlet of the preheating circulation tank is connected to the inlet of the flash tank. The liquid outlet of the flash tank is connected to the inlet of the evaporator via a pipeline through the heat exchanger. The liquid outlet of the evaporator is connected to the thickener. The gaseous outlets of the flash tank and the evaporator are respectively connected to the liquid inlets of the ammonia nitrogen and boron adsorption units via pipelines through the heat exchanger.

[0012] As a specific embodiment of the system described above in this invention, the microfiltration membrane module used in the tubular microfiltration unit has a cutoff pore size ≤ 0.05 μm.

[0013] In one specific embodiment of the system described above in this invention, the softening and concentration reaction tank includes a primary softening tank, a secondary softening tank, and a concentration tank connected in sequence.

[0014] In one specific embodiment of the system described above in this invention, the microfiltration concentrate outlet of the tubular microfiltration unit and the nanofiltration concentrate outlet of the nanofiltration unit are respectively connected to the inlet of the softening and concentration reaction tank through a concentrate return pipe.

[0015] As a specific embodiment of the system described above in this invention, the liquid outlet of the softening ion adsorption unit is connected to the liquid inlet of the first-stage reverse osmosis unit via a pipeline through a hydraulic pressure turbine, and the freshwater outlet of the first-stage reverse osmosis unit is connected to the liquid inlet of the ammonia nitrogen and boron adsorption unit via a pipeline through a second-stage reverse osmosis unit.

[0016] The concentrate outlet of the first-stage reverse osmosis unit is connected to the liquid inlet of the electrodialysis unit via a pipeline through a hydraulic pressure turbine, and the concentrate outlet of the electrodialysis unit is connected to the inlet of the preheating circulation tank via a pipeline.

[0017] In one specific embodiment of the system described above in this invention, the freshwater 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 via pipelines through a hydraulic pressure turbine.

[0018] In one specific embodiment of the system described above in this invention, the liquid outlet of the softening ion adsorption unit is connected to the liquid inlet of the electrodialysis unit via a pipeline; the concentrate outlet of the electrodialysis unit is connected to the inlet of the preheating circulation tank via a pipeline; the desalination outlet of the electrodialysis unit is connected to the liquid inlet of the first-stage reverse osmosis unit via a pipeline through a hydraulic pressure turbine; and the desalination outlet of the first-stage reverse osmosis unit is connected to the liquid inlet of the ammonia nitrogen and boron adsorption unit via a pipeline through the second-stage reverse osmosis unit.

[0019] In one specific embodiment of the system described above in this invention, the concentrate outlet of the secondary reverse osmosis unit is connected to the liquid inlet of the primary reverse osmosis unit via a pipeline through a hydraulic pressure turbine.

[0020] In one specific embodiment of the system described above in this invention, the concentrate outlet of the first-stage reverse osmosis unit is connected to the liquid inlet of the electrodialysis unit via a pipeline through a hydraulic pressure turbine.

[0021] As a specific embodiment of the system described above in this 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 via a pipeline through the first compressor and a heat exchanger. The gas phase outlet of the evaporator is connected to the liquid inlet of the ammonia nitrogen and boron adsorption unit via a pipeline through the second compressor and a heat exchanger.

[0022] In one specific embodiment of the system described above in this invention, the liquid outlet of the thickener is connected to the inlet of the evaporator via a pipeline.

[0023] On the other hand, the present invention also provides a low-energy-consumption method for the graded treatment of fracturing flowback fluid, wherein the method includes the following steps:

[0024] (1) The fracturing flowback fluid is subjected to aeration and flotation oil removal treatment in sequence to obtain waste oil and effluent. The effluent is then subjected to flocculation and sedimentation in sequence to obtain a first-stage sludge and a first-stage liquid.

[0025] (2) The primary liquid is softened and concentrated to obtain concentrated liquid and secondary sludge. The concentrated liquid is oxidized by ozone and then its effluent is micro-filtered to obtain micro-filtered concentrate and micro-filtered desalinated water. The micro-filtered desalinated water is then nano-filtered to obtain nano-filtered concentrate and nano-filtered desalinated water. Finally, the nano-filtered desalinated water is softened and ion-adsorbed to obtain secondary liquid.

[0026] (3) When the mineralization of the secondary liquid is not higher than 40000 mg / L, the secondary liquid is subjected to first-stage reverse osmosis to obtain first-stage reverse osmosis concentrate and first-stage reverse osmosis desalination. The first-stage reverse osmosis desalination is then subjected to second-stage reverse osmosis, followed by ammonia nitrogen and boron adsorption. The first-stage reverse osmosis concentrate is then subjected to electrodialysis to obtain electrodialysis concentrate and electrodialysis desalination; or,

[0027] When the mineralization of the secondary liquid is higher than 40,000 mg / L, electrodialysis is performed on the secondary liquid to obtain electrodialysis concentrate and electrodialysis desalinated water. The electrodialysis desalinated water is then subjected to first-stage reverse osmosis and second-stage reverse osmosis in sequence, and then the second-stage reverse osmosis desalinated water is subjected to ammonia nitrogen and boron adsorption.

[0028] (4) The concentrated water from electrodialysis is preheated by a solar heater and then flashed to obtain a flash vapor phase and a flash liquid phase. The flash liquid phase after heat exchange and heating is then evaporated to obtain an evaporation gas phase and an evaporation liquid phase. The evaporation liquid phase is then crystallized to obtain a crystalline salt. The heat source used for heat exchange and heating is either the flash vapor phase after heating or the flash vapor phase after heating and the evaporation gas phase after heating.

[0029] Since fracturing flowback fluid from different wells will be collected on-site, and the water quality of the fracturing flowback fluid from different wells varies, in step (1) of the method described above, the fracturing flowback fluid from multiple wells can be collected into an aeration transfer tank for mixing before being treated. This can reduce the water quality changes of the fracturing flowback fluid caused by a single well and effectively eliminate the impact of fluctuations in the influent water quality of the fracturing flowback fluid on the treatment process.

[0030] As a specific embodiment of the method described above in this invention, the flocculant used in the flocculation includes polyaluminum chloride (PAC) and / or polyacrylamide (PAM), etc.

[0031] As a specific embodiment of the method described above in this 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. This primary liquid can be recycled as a liquid with low hardness ion content, i.e., total hardness ≤2000 mg / L. In addition, the parameters used in the aeration treatment, air flotation oil removal treatment, flocculation and sedimentation operations in step (1) of this invention can be reasonably adjusted and determined according to the needs of the site, 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.

[0032] In one specific embodiment of the method described above in this invention, the softening is carried out in two steps. The first step of softening and the second step of softening use sodium carbonate and sodium sulfate, respectively, wherein the mass ratio of sodium carbonate to sodium sulfate is 4:1-6:1.

[0033] As a specific embodiment of the method described above in this invention, step (2) further includes:

[0034] The microfiltration concentrate, nanofiltration concentrate, and primary liquid are transported together to a softening and concentration reactor for softening and concentration to obtain concentrated liquid and secondary sludge.

[0035] As a specific embodiment of the method described above in this invention, the softening ion adsorption in step (2) can be achieved using "Zhengguang" brand 001×8 strong acid cation exchange resin to remove hardness ions.

[0036] In one specific embodiment of the method described above, 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 concentration, ozone oxidation, microfiltration, and nanofiltration processes in step (2) of this invention can be reasonably adjusted and determined according to on-site needs, as long as the total hardness of the secondary liquid is ≤20 mg / L.

[0037] Furthermore, the mineralization of the secondary fluid obtained after steps (1) and (2) is basically the same as that of the untreated fracturing flowback fluid, meaning that the treatments in steps (1) and (2) have almost no effect on the mineralization of the fracturing flowback fluid.

[0038] In a specific embodiment of the method described above, when the mineralization of the secondary liquid is not higher than 40000 mg / L, step (3) further includes:

[0039] The electrodialysis desalination water and the secondary reverse osmosis concentrate are subjected to primary reverse osmosis.

[0040] As a specific embodiment of the method described above in this invention, when the mineralization of the secondary liquid is higher than 40000 mg / L, step (3) further includes: performing primary reverse osmosis on the secondary reverse osmosis concentrate.

[0041] As a specific embodiment of the method described above in this invention, when the mineralization of the secondary liquid is higher than 40000 mg / L, step (3) further includes: electrodialysis of the primary reverse osmosis concentrate.

[0042] In a specific embodiment of the method described above in this invention, in step (3), ammonia nitrogen adsorption and boron adsorption are performed sequentially on the secondary reverse osmosis desalination water.

[0043] As a specific embodiment of the method described above in this invention, the ammonia nitrogen adsorption in step (3) can be performed using a strong acid type uniform particle cation exchange resin or sodium Na+. +Uniform particle size cation exchange resins, such as Tulsimer T-42H resin, can be used for boron adsorption. Large-pore ion exchange resins containing meglumine functional groups, such as... CH-99 boron selective adsorption resin and other methods are used to achieve this.

[0044] As a specific embodiment of the method described above in this invention, the mineralization of the secondary reverse osmosis desalination water obtained in step (2) should be lower than 420 mg / L, and the mineralization of the electrodialysis concentrate should be higher than 75000 mg / L. Furthermore, the parameters used in the primary reverse osmosis, secondary reverse osmosis, electrodialysis, and ammonia nitrogen and boron adsorption processes in step (3) of this invention, as well as the membranes or adsorption resins used, can be reasonably adjusted and selected according to on-site needs, as long as the mineralization of the secondary reverse osmosis desalination water is lower than 420 mg / L and the mineralization of the electrodialysis concentrate is higher than 75000 mg / L.

[0045] As a specific embodiment of the method described above in this invention, the circulating preheating includes: transferring a portion of the electrodialysis concentrate in the preheating circulation tank to a solar heater, heating it, and then returning it to the preheating circulation tank;

[0046] The liquid volume in the preheating circulation tank is maintained at 40-60%, the heating temperature is 55-65℃, and the pressure is maintained slightly higher than atmospheric pressure, preferably 1.2-1.3 atmospheres, or 0.12-0.13MPa.

[0047] In one specific embodiment of the method described above in this 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.

[0048] In a specific embodiment of the method described above in this invention, the flash vapor phase and the evaporating vapor phase are heated to 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 60-75°C.

[0049] As a specific embodiment of the method described above in this invention, the flash vapor phase is compressed by the first compressor at a compression ratio of 1:1.2-1:2. After the enthalpy value is increased, the temperature of the flash vapor phase increases 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 heat exchange is 60-75°C.

[0050] After the vapor phase is generated, the second compressor is used to compress the vapor phase at a suitable compression ratio to increase the enthalpy value. The temperature of the vapor phase increases by 10-15℃. It is then used together with the heated flash vapor phase as a heat source to enter the heat exchanger to exchange heat with the flash liquid phase, and the temperature of the flash liquid phase after heat exchange is 60-75℃.

[0051] As a specific embodiment of the method described above in this invention, step (4) further includes: flash evaporating the mother liquor and the preheated electrodialysis concentrate to obtain a flash vapor phase and a flash liquid phase.

[0052] Compared with the prior art, the beneficial technical effects achieved by the present invention include:

[0053] 1) The low-energy fracturing flowback fluid classification treatment method provided by the present invention has a simple process and stable operation, and achieves classification treatment for fracturing flowback fluid with different water quality and effluent requirements.

[0054] 2) The method provided by this invention is applicable to the actual needs of shale gas field treatment. By first transporting the fracturing flowback fluid from multiple wells to an aeration transfer tank, the impact of fluctuations in the influent water quality of the fracturing flowback fluid on the treatment process can be effectively eliminated. First, the aerated fracturing flowback fluid undergoes sequential processes of air flotation for oil removal, flocculation, sedimentation, and softening concentration. Then, the concentrated liquid is subjected to ozone oxidation. Ozone oxidation can remove most of the organic matter in the fracturing flowback fluid. Practical verification has shown that ozone oxidation is the most economical and effective technology for removing organic matter contained in fracturing flowback fluid.

[0055] 3) Regarding the softening method of fracturing flowback fluid, this invention adopts a combination of chemical softening based on sodium carbonate and sodium sulfate and deep softening technologies such as microfiltration, nanofiltration, and ion exchange (i.e., softening ion adsorption), which can effectively remove hardness ions in fracturing flowback fluid, thereby ensuring the long-term stable operation of the subsequent desalination unit, i.e., the membrane concentration system.

[0056] 4) During the reverse osmosis concentration process, this invention uses a hydraulic pressure turbine to recover the pressure energy in the high-pressure reverse osmosis concentrate, reducing energy consumption during operation; in the electrodialysis concentrate evaporation and crystallization stage, a combination of solar preheating and compressor heat recovery is used to save energy and achieve low energy consumption.

[0057] 5) Compared with the prior art, the process flow of the method provided by the present invention is shorter and occupies less area. Specifically, other existing processes mostly adopt the process flow of "equalization tank + air flotation + catalytic oxidation + coagulation sedimentation + ultrafiltration + ion adsorption + electrodialysis + biochemical treatment + MVR evaporation". Among them, the biochemical tank used for biochemical treatment occupies an area of ​​about 0.2 cubic meters / ton of water, while the present invention mainly adopts physical and chemical methods, which reduces the total area occupied by more than 40%.

[0058] 6) The byproducts of the method provided by this invention can be collected in categories, and the crystalline salt can be utilized as a resource. Specifically, the byproducts generated by this method include crystalline salt and sludge, wherein the sludge includes primary sludge and secondary sludge. The sludge is collected in stages, which reduces the amount of sludge and avoids the sludge being disposed of as hazardous waste. It also ensures the purity of the crystalline salt. The test results show that the quality of the crystalline salt can reach the standard of secondary industrial salt, or even the standard of primary industrial salt, so that the crystalline salt can be utilized as a resource.

[0059] 7) The system and method provided by this invention operate stably. The long-term operation of the equipment in the system was considered during the process flow design. Since the process flow involves multiple membrane treatment units (such as tubular microfiltration units, nanofiltration units, primary reverse osmosis units, and secondary reverse osmosis units), this invention features a meticulously designed pretreatment process for each membrane treatment unit. Specifically, firstly, primary sedimentation in the sedimentation tank ensures that the secondary sediment, i.e., the second-stage sludge, is primarily softened sediment, reducing the load on the sedimentation tank. Secondly, a tubular microfiltration unit is installed at the front end of the nanofiltration unit, and the microfiltration membrane module used has a pore size ≤0.05μm. The tubular microfiltration unit can remove most hardness ions through chemical reactions, reducing the load on the nanofiltration unit. Simultaneously, the microfiltration membrane module with a pore size ≤0.05μm can filter out most suspended particles without affecting the surface of the nanofiltration membrane used in the nanofiltration unit, thus improving the service life of the nanofiltration membrane. Furthermore, the meticulous pretreatment also extends the service life of the reverse osmosis (primary and secondary reverse osmosis units). After two years of actual operation, under 12 hours / day operating conditions, the nanofiltration unit and reverse osmosis unit used in the system provided by this invention have maintained relatively stable operation, while the microfiltration unit only needs to be cleaned offline once a month. Attached Figure Description

[0060] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0061] Figure 1 This is a schematic diagram of the low-energy fracturing flowback fluid classification and treatment system provided in Embodiments 1 and 2 of the present invention.

[0062] Figure 2 This is a schematic diagram of the flowback fluid reuse system in the low-energy fracturing flowback fluid classification and treatment system provided in Embodiments 1 and 2 of the present invention.

[0063] Figure 3 This is a schematic diagram of the softening pretreatment system in the low-energy fracturing flowback fluid grading system provided in Embodiments 1 and 2 of the present invention.

[0064] Figure 4 This is a schematic diagram of the membrane concentration system in the low-energy fracturing flowback fluid classification and treatment system provided in Embodiment 1 of the present invention.

[0065] Figure 5 This is a schematic diagram of the solar evaporation crystallization system in the low-energy fracturing flowback fluid classification treatment system provided in Embodiments 1 and 2 of the present invention.

[0066] Figure 6 This is a schematic diagram of the membrane concentration system in the low-energy fracturing flowback fluid classification and treatment system provided in Embodiment 2 of the present invention.

[0067] Explanation of main icon numbers:

[0068] 100. Drainage liquid reuse system;

[0069] 200. Softening pretreatment system;

[0070] 300. Membrane concentration system;

[0071] 400. Solar-powered evaporation crystallization system;

[0072] 1. Aeration transfer tank;

[0073] 2. Air flotation oil removal tank;

[0074] 3. Flocculation reactor;

[0075] 4. Settling tank;

[0076] 5. Softening and concentration reaction tank;

[0077] 6. Ozone oxidation reactor;

[0078] 7. Tubular microfiltration unit;

[0079] 8. Nanofiltration unit;

[0080] 9. Softening ion adsorption unit;

[0081] 10. Hydraulic pressure turbine;

[0082] 11. First-stage reverse osmosis unit;

[0083] 12. Secondary reverse osmosis unit;

[0084] 13. Electrodialysis unit;

[0085] 14. Ammonia nitrogen and boron adsorption unit;

[0086] 15. Preheating circulation tank;

[0087] 16. Solar heater;

[0088] 17. Flash evaporator;

[0089] 18. Evaporator;

[0090] 19. Heat exchanger;

[0091] 20. Second compressor;

[0092] 21. First compressor;

[0093] 22. Thickener. Detailed Implementation

[0094] It should be noted that the term "comprising" and any variations thereof in the specification, claims, and accompanying drawings of this invention are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or devices.

[0095] The "range" disclosed in this 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 and upper limits define the boundaries of the particular range. All ranges defined in this way are composable, meaning that any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for specific parameters, it is also expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if the listed minimum range values ​​are 1 and 2, and the listed maximum range values ​​are 3, 4, and 5, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.

[0096] In this invention, unless otherwise specified, the numerical range "ab" represents a shortened representation of 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" have been listed in this invention, and "0-5" is simply a shortened representation of these numerical combinations.

[0097] In this invention, unless otherwise specified, all embodiments and preferred embodiments mentioned in this invention can be combined with each other to form new technical solutions.

[0098] In this invention, unless otherwise specified, all technical features and preferred features mentioned in this invention can be combined with each other to form new technical solutions.

[0099] In this invention, unless otherwise specified, all steps mentioned herein may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0100] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying tables, drawings, and embodiments. The embodiments described below are some, but not all, embodiments of this invention, and are only used to illustrate the invention, and should not be considered as limiting the scope of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0101] Example 1

[0102] This embodiment provides a low-energy-consumption fracturing flowback fluid classification and treatment system, wherein a schematic diagram of the low-energy-consumption fracturing flowback fluid classification and treatment system is shown below. Figure 1 As shown, from Figure 1 As can be seen from the diagram, it includes a return liquid reuse system 100, a softening pretreatment system 200, a membrane concentration system 300, and a solar evaporation crystallization system 400 connected in sequence.

[0103] The structural schematic diagram of the backflow liquid reuse system 100 is shown below. Figure 2 As shown, from Figure 2 As can be seen from the above, the backflow 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 connected in sequence through pipelines.

[0104] The structural schematic diagram of the softening pretreatment system 200 is shown below. Figure 3 As shown, from Figure 3As can be seen from the above, 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 connected in sequence; the microfiltration membrane module used in the tubular microfiltration unit 7 has a cutoff pore size ≤0.05μm;

[0105] The softening and concentration reaction tank 5 includes a primary softening tank, a secondary softening tank, and a concentration tank connected in sequence. The microfiltration concentrate outlet of the tubular microfiltration unit 7 and the nanofiltration concentrate outlet of the nanofiltration unit 8 are respectively connected to the inlet of the softening and concentration reaction tank 5 through a concentrate return pipe.

[0106] The structural schematic diagram of the membrane concentration system 300 is shown below. Figure 4 As shown, from Figure 4 As can be seen from the above, the membrane concentration system 300 includes a hydraulic pressure turbine 10, a first-stage reverse osmosis unit 11, a second-stage reverse osmosis unit 12, an electrodialysis unit 13, and an ammonia nitrogen and boron adsorption unit 14.

[0107] The liquid outlet of the softening ion adsorption unit 9 is connected to the liquid inlet of the first-stage reverse osmosis unit 11 via a pipeline through a hydraulic pressure turbine 10 and a second pump. The freshwater outlet of the first-stage reverse osmosis unit 11 is connected to the liquid inlet of the ammonia nitrogen and boron adsorption unit 14 via a pipeline through a third pump and a second-stage reverse osmosis unit 12.

[0108] The concentrate outlet of the first-stage reverse osmosis unit 11 is connected to the liquid inlet of the electrodialysis unit 13 via a pipeline through a hydraulic pressure turbine 10. The concentrate outlet of the electrodialysis unit 13 is connected to the inlet of the preheating circulation tank 15 via a pipeline. The desalination outlet of the electrodialysis unit 13 and the concentrate outlet of the second-stage reverse osmosis unit 12 are respectively connected to the liquid inlet of the first-stage reverse osmosis unit 11 via a pipeline through a hydraulic pressure turbine 10.

[0109] A schematic diagram of the solar evaporation crystallization system 400 is shown below. Figure 5 As shown, from Figure 5As can be seen, the solar evaporation crystallization system 400 includes a preheating circulation tank 15, a solar heater 16, a flash tank 17, an evaporator 18, a heat exchanger 19, and a thickener 22. The solar heater 16 is used to circulate and preheat the electrodialysis concentrate 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 through a pipeline. The liquid phase outlet of the flash tank 17 is connected to the inlet of the evaporator 18 through a pipeline via the heat exchanger 19. The liquid phase outlet of the evaporator 18 is connected to the thickener 22 through 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 through a pipeline via the first compressor 21 and the heat exchanger 19. The gas phase outlet of the evaporator 18 is connected to the liquid inlet of the ammonia nitrogen and boron adsorption unit 14 through 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 evaporator through a pipeline.

[0110] Example 2

[0111] This embodiment provides a low-energy-consumption fracturing flowback fluid classification and treatment system, wherein a schematic diagram of the low-energy-consumption fracturing flowback fluid classification and treatment system is shown below. Figure 1 As shown, from Figure 1 As can be seen from the diagram, it includes a return liquid reuse system 100, a softening pretreatment system 200, a membrane concentration system 300, and a solar evaporation crystallization system 400 connected in sequence.

[0112] The structural schematic diagram of the backflow liquid reuse system 100 is shown below. Figure 2 As shown, from Figure 2 As can be seen from the above, the backflow 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 connected in sequence through pipelines.

[0113] The structural schematic diagram of the softening pretreatment system 200 is shown below. Figure 3 As shown, from Figure 3 As can be seen from the above, 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 connected in sequence; the microfiltration membrane module used in the tubular microfiltration unit 7 has a cutoff pore size ≤0.05μm;

[0114] The softening and concentration reaction tank 5 includes a primary softening tank, a secondary softening tank, and a concentration tank connected in sequence. The microfiltration concentrate outlet of the tubular microfiltration unit 7 and the nanofiltration concentrate outlet of the nanofiltration unit 8 are respectively connected to the inlet of the softening and concentration reaction tank 5 through a concentrate return pipe.

[0115] The structural schematic diagram of the membrane concentration system 300 is shown below. Figure 6 As shown, from Figure 6As can be seen from the above, the membrane concentration system 300 includes a hydraulic pressure turbine 10, a first-stage reverse osmosis unit 11, a second-stage reverse osmosis unit 12, an electrodialysis unit 13, and an ammonia nitrogen and boron adsorption unit 14.

[0116] The liquid outlet of the softening ion adsorption unit 9 is connected to the liquid inlet of the electrodialysis unit 13 via a pipeline. The concentrate outlet of the electrodialysis unit 13 is connected to the inlet of the preheating circulation tank 15 via a pipeline. The desalination outlet of the electrodialysis unit 13 is connected to the liquid inlet of the first-stage reverse osmosis unit 11 via a pipeline through a hydraulic pressure turbine 10 and a second pump. The desalination outlet of the first-stage reverse osmosis unit 11 is connected to the liquid inlet of the ammonia nitrogen and boron adsorption unit 14 via a pipeline through a third pump and a second-stage reverse osmosis unit 12. The concentrate outlet of the second-stage reverse osmosis unit 12 is connected to the liquid inlet of the first-stage reverse osmosis unit 11 via a pipeline through a hydraulic pressure turbine 10. The concentrate outlet of the first-stage reverse osmosis unit 11 is connected to the liquid inlet of the electrodialysis unit 13 via a pipeline through a hydraulic pressure turbine 10.

[0117] A schematic diagram of the solar evaporation crystallization system 400 is shown below. Figure 5 As shown, from Figure 5 As can be seen, the solar evaporation crystallization system 400 includes a preheating circulation tank 15, a solar heater 16, a flash tank 17, an evaporator 18, a heat exchanger 19, and a thickener 22. The solar heater 16 is used to circulate and preheat the electrodialysis concentrate 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 through a pipeline. The liquid phase outlet of the flash tank 17 is connected to the inlet of the evaporator 18 through a pipeline via the heat exchanger 19. The liquid phase outlet of the evaporator 18 is connected to the thickener 22 through 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 through a pipeline via the first compressor 21 and the heat exchanger 19. The gas phase outlet of the evaporator 18 is connected to the liquid inlet of the ammonia nitrogen and boron adsorption unit 14 through 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 evaporator through a pipeline.

[0118] Example 3

[0119] This embodiment provides a low-energy-consumption fracturing flowback fluid classification and treatment method, which is implemented using the low-energy-consumption fracturing flowback fluid classification and treatment system provided in Embodiment 1. The method includes the following specific steps:

[0120] S1: Collect the fracturing flowback fluid ① that is returned from the wellhead after fracturing operations in multiple wells in a certain shale gas block. First, let the fracturing flowback fluid enter the flowback fluid reuse system. Specifically, the fracturing flowback fluid is first introduced into the aeration transfer tank from the lower part of the aeration transfer tank for continuous aeration treatment. Water is discharged from the upper part of the aeration transfer tank, and slag can be discharged intermittently from the bottom, i.e., aeration bottom slag ②.

[0121] Then the effluent from the upper part of the aeration transfer tank enters the air flotation oil removal tank. The separated waste oil can be collected, and the effluent enters the flocculation reactor. PAC and PAM agents are added to the flocculation reactor in sequence to carry out the flocculation reaction and form flocs.

[0122] The flocs and liquid phase in the flocculation reactor are fed into the settling tank for sedimentation. The effluent is used as the return liquid for reuse as the system effluent, i.e., primary liquid ④. After testing, it was found that the total suspended solids in this primary liquid are ≤15mg / L, total iron is ≤10mg / L and petroleum substances are ≤10mg / L. It can be recycled as a liquid with low hardness ion content. The precipitated sludge is used as primary sludge ③. This primary sludge is collected after being dewatered by pressure filtration.

[0123] S2: The primary liquid is introduced into the softening and thickening reaction tank, which includes a primary softening tank, a secondary softening tank, and a thickening 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. The concentration of sodium carbonate is 2500 mg / L and the concentration of sodium sulfate is 420 mg / L. The system after reaction enters the thickening tank for concentration. The upper liquid in the thickening tank enters the ozone oxidation reactor and is oxidized by ozone. The sludge settled at the bottom of the primary softening tank, the secondary softening tank, and the thickening tank is then extracted and dewatered by filter press to obtain two-stage sludge ⑤.

[0124] The effluent from ozone oxidation treatment is pumped to a tubular microfiltration unit via a first pump. The microfiltration membrane module used in the tubular microfiltration unit has a pore size ≤0.05μm. The microfiltration concentrate from the microfiltration unit enters a concentrate return pipe, while the microfiltration desalinated water, after pressurization, enters a nanofiltration unit for nanofiltration treatment. The nanofiltration unit uses a Dow nanofiltration membrane NF90-400, and the operating pressure of the nanofiltration unit is approximately 1.5MPa. Nanofiltration treatment produces nanofiltration desalinated water, i.e., effluent and nanofiltration concentrate. This nanofiltration concentrate and microfiltration concentrate... Water is returned to the softening and concentration reaction tank via the concentrate return pipe for further treatment. Nanofiltration desalinated 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 acid cation exchange resin to remove hardness ions. The effluent from ion adsorption is the effluent from the softening pretreatment system, denoted as secondary liquid ⑦. After testing, it was found that the total hardness of the secondary liquid is ≤20mg / L. This secondary liquid can be recycled as a liquid with a high content of hardness ions.

[0125] S3: The mineralization of the above-mentioned secondary liquid was measured to be 11700 mg / L, which is lower than 40000 mg / L. Therefore, the following method was adopted: Figure 4 The membrane concentration system (membrane desalination system) shown treats the secondary liquid, specifically including: first, the secondary liquid enters a hydraulic pressure turbine to increase the pressure to 1.3 MPa, then is pressurized to 6 MPa by a second pump (water pump) before entering the first-stage reverse osmosis unit using a Dow SW30HRLE-400 seawater desalination membrane for first-stage reverse osmosis, producing first-stage reverse osmosis concentrate and first-stage reverse osmosis desalination. The pressure of the first-stage reverse osmosis concentrate reaches 5.6 MPa, and after passing through the hydraulic turbine (i.e., after the hydraulic pressure turbine), the pressure is reduced to 2 MPa. The depressurized first-stage reverse osmosis... The permeate concentrate enters the electrodialysis unit (the electrodialysis module uses LANCYTOM bipolar membrane BP-2) for electrodialysis. The mineralization of the first-stage reverse osmosis concentrate before electrodialysis is 53282 mg / L. After electrodialysis treatment in the electrodialysis unit, electrodialysis desalination and electrodialysis concentrate are obtained. The mineralization of the electrodialysis desalination is 5600 mg / L. The electrodialysis desalination is returned to the secondary liquid, i.e., the feed water of the membrane concentration system, for further treatment. The mineralization of the electrodialysis concentrate ⑩ reaches 84539 mg / L, which is recorded as the tertiary liquid and enters the solar evaporation crystallization system for further treatment.

[0126] The primary reverse osmosis desalination water is pressurized to 4 MPa by the third pump and then enters the secondary reverse osmosis unit using a Dow Chemical brackish water membrane BW30-4040 for secondary reverse osmosis, yielding secondary reverse osmosis concentrate and secondary reverse osmosis desalination water. Testing revealed that the salinity of the secondary reverse osmosis desalination water was below 420 mg / L. The pressure of the secondary reverse osmosis concentrate reached 3.6 MPa, which was reduced to 2 MPa after passing through a hydraulic pressure turbine. The depressurized secondary reverse osmosis concentrate was returned to the secondary liquid, i.e., the feed water of the membrane concentration system, for further treatment. The secondary reverse osmosis desalination water then enters the ammonia nitrogen and boron adsorption unit. First, it is adsorbed by the ammonia nitrogen adsorption resin (Tulsimer T-42H resin) to remove ammonia nitrogen, and then it enters the boron adsorption resin (…). The boron in the CH-99 boron selective adsorption resin is adsorbed to obtain adsorbed water.

[0127] S4: The electrodialysis concentrate is then processed in a solar evaporation crystallization system. Specifically, this involves: first, the electrodialysis concentrate is introduced into a preheating circulation tank, maintaining the tank at half its capacity. It is then preheated in a solar heater using solar circulation, maintaining the liquid temperature at 65°C and the pressure at 0.13 MPa. In practice, a portion of the electrodialysis concentrate in the preheating circulation tank is transferred to the solar heating element of the solar heater, heated, and then returned to the preheating circulation tank. After preheating, a portion of the liquid phase enters a flash tank with a vacuum of 0.06 MPa. Gas-liquid separation occurs in the flash tank, with the flash vapor phase compressed by a first compressor at a compression ratio of 1.5. After compression, its temperature increases by 14°C, approximately 7°C. The flash vapor phase, heated to 5℃, enters the heat exchanger as a heat source for cooling. The flash liquid phase then enters the heat exchanger to exchange heat with the heated flash vapor phase, raising its temperature to approximately 70℃. It then enters the evaporator, where a vacuum of approximately 0.07 MPa is maintained. Evaporation occurs within the evaporator, with the flash liquid phase continuously evaporating to produce an evaporating vapor phase and an evaporating liquid phase (slurry). The evaporating vapor phase is compressed by a second compressor to raise its temperature by 10-15℃ to approximately 75℃. Both the heated evaporating vapor and flash vapor phases are then used as heat sources in the heat exchanger for cooling. After heat exchange, both vapor heat sources are below 50℃ and are mixed to form condensate. The liquid, along with the secondary reverse osmosis desalinated water, is then transported to the ammonia nitrogen and boron adsorption unit for ammonia nitrogen and boron adsorption. The liquid after adsorption is used as the final effluent. Finally, the evaporated liquid phase is transported to a thickener, where crystallization produces crystalline salts. Meanwhile, the mother liquor that is ejected is returned to the flash tank for further flash evaporation.

[0128] 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.

[0129] Table 1

[0130]

[0131]

[0132] Note: Total hardness includes Ca. 2+ Mg 2+ Ba 2+ and Sr 2+ .

[0133] 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 Wastewater Discharge Standard (GB 8978-1996) and the Sichuan Provincial Water Pollutant Discharge Standard (DB51 / 190-93).

[0134] The crystalline salt in this embodiment is then processed using conventional methods existing in the art. The quality was tested, and the obtained quality test data is shown in Table 2 below.

[0135] Table 2

[0136] Crystallization salt index >92wt% <6wt% <0.35wt% <0.4wt% Secondary industrial salt standard 92.55wt% 5wt% 0.38wt% 0.59wt%

[0137] 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.

[0138] In summary, the low-energy fracturing flowback fluid classification treatment system and method provided in Example 3 produces fewer byproducts and is easier to handle. This method generates four byproducts: Byproduct 1 is surface waste oil from the fracturing flowback fluid, which can be collected and transported for disposal; Byproduct 2 is primary sedimentation sludge, i.e., first-stage sludge; Byproduct 3 is second-stage sludge, which is softened sludge. The first-stage and second-stage sludge undergo solid-liquid separation through two independent treatment units, namely, a filter press dewatering unit. Existing other treatment processes typically only produce first-stage sludge and cannot process the sludge separately. Furthermore, the two stages of sludge in this invention are stable and easier to handle subsequently; Byproduct 4 is crystalline salt, which is of higher quality than the standard of secondary industrial salt and can be utilized as a resource.

[0139] Example 4

[0140] This embodiment provides a low-energy-consumption fracturing flowback fluid classification and treatment method, which is implemented using the low-energy-consumption fracturing flowback fluid classification and treatment system provided in Embodiment 2. The method includes the following specific steps:

[0141] S1: Collect the fracturing flowback fluid ① that is returned from the wellhead after fracturing operations in multiple wells in a certain shale gas block. First, let the fracturing flowback fluid enter the flowback fluid reuse system. Specifically, the fracturing flowback fluid is first introduced into the aeration transfer tank from the lower part of the aeration transfer tank for continuous aeration treatment. Water is discharged from the upper part of the aeration transfer tank, and slag can be discharged intermittently from the bottom, i.e., aeration bottom slag ②.

[0142] Then the effluent from the upper part of the aeration transfer tank enters the air flotation oil removal tank. The separated waste oil can be collected, and the effluent enters the flocculation reactor. PAC and PAM agents are added to the flocculation reactor in sequence to carry out the flocculation reaction and form flocs.

[0143] The flocs and liquid phase in the flocculation reactor are fed into the settling tank for sedimentation. The effluent is used as the return liquid for reuse as the system effluent, i.e., primary liquid ④. After testing, it was found that the total suspended solids in this primary liquid are ≤15mg / L, total iron is ≤10mg / L and petroleum substances are ≤10mg / L. It can be recycled as a liquid with low hardness ion content. The precipitated sludge is used as primary sludge ③. This primary sludge is collected after being dewatered by pressure filtration.

[0144] S2: The primary liquid is introduced into the softening and thickening reaction tank, which includes a primary softening tank, a secondary softening tank, and a thickening 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. The concentration of sodium carbonate is 2500 mg / L and the concentration of sodium sulfate is 420 mg / L. The system after reaction enters the thickening tank for concentration. The upper liquid in the thickening tank enters the ozone oxidation reactor and is oxidized by ozone. The sludge settled at the bottom of the primary softening tank, the secondary softening tank, and the thickening tank is then extracted and dewatered by filter press to obtain two-stage sludge ⑤.

[0145] The effluent from ozone oxidation treatment is pumped to a tubular microfiltration unit via a first pump. The microfiltration membrane module used in the tubular microfiltration unit has a pore size ≤0.05μm. The microfiltration concentrate from the microfiltration unit enters a concentrate return pipe, while the microfiltration desalinated water, after pressurization, enters a nanofiltration unit for nanofiltration treatment. The nanofiltration unit uses a Dow nanofiltration membrane NF90-400, and the operating pressure of the nanofiltration unit is approximately 1.5MPa. Nanofiltration treatment produces nanofiltration desalinated water, i.e., effluent and nanofiltration concentrate. This nanofiltration concentrate and microfiltration concentrate... Water is returned to the softening and concentration reaction tank via the concentrate return pipe for further treatment. Nanofiltration desalinated 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 acid cation exchange resin to remove hardness ions. The effluent from ion adsorption is the effluent from the softening pretreatment system, denoted as secondary liquid ⑦. After testing, it was found that the total hardness of the secondary liquid is ≤20mg / L. This secondary liquid can be recycled as a liquid with a high content of hardness ions.

[0146] S3: The mineralization of the above-mentioned secondary liquid ⑦ was measured to be 43700 mg / L, which is higher than 40000 mg / L. Therefore, the following method was adopted: Figure 6The membrane concentration system (membrane desalination system) shown treats the secondary liquid, specifically including: firstly, the secondary liquid enters the electrodialysis unit (the electrodialysis module uses LANCYTOM bipolar membrane BP-2) for electrodialysis. The mineralization of the electrodialysis concentrate ⑩ reaches 80599 mg / L, which is recorded as the tertiary liquid and then enters the solar evaporation crystallization system for further treatment; the mineralization of the electrodialysis desalination water is 10400 mg / L. The electrodialysis desalination water enters the hydraulic turbine and is pressurized to 1 MPa, then pressurized to 5 MPa by a second pump (water pump) before entering the primary reverse osmosis unit using Dow seawater desalination membrane SW30HRLE-400 for primary reverse osmosis, obtaining primary reverse osmosis concentrate and primary reverse osmosis desalination water. The pressure of the primary reverse osmosis concentrate reaches 4.3 MPa, and after passing through the hydraulic pressure turbine, its pressure is reduced to 1.5 MPa, which is then combined with the secondary liquid. After the liquids are combined, they enter the electrodialysis unit (the electrodialysis module uses LANCYTOM bipolar membrane BP-2) for electrodialysis. The primary reverse osmosis desalination water is pressurized to 3.6 MPa 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 concentrate and secondary reverse osmosis desalination water. After testing, it was found that the mineralization of the secondary reverse osmosis desalination water was less than 420 mg / L, and the pressure of the secondary reverse osmosis concentrate reached about 3 MPa. After passing through the hydraulic pressure turbine, the pressure was reduced to 1.5 MPa. After being combined with the electrodialysis desalination water, it returned to the primary reverse osmosis unit using Dow seawater desalination membrane SW30HRLE-400 for reverse osmosis. The secondary reverse osmosis desalination water then enters the ammonia nitrogen and boron adsorption unit. First, it is adsorbed by the ammonia nitrogen adsorption resin (Tulsimer T-42H resin) and then enters the boron adsorption resin (…). The boron in the CH-99 boron selective adsorption resin is adsorbed to obtain adsorbed water.

[0147] S4: The electrodialysis concentrate is then processed in a solar evaporation crystallization system. Specifically, this involves: first, the electrodialysis concentrate is introduced into a preheating circulation tank, maintaining the tank at half its capacity. It is then preheated in a solar heater using solar circulation, maintaining the liquid temperature at 65°C and the pressure at 0.13 MPa. In practice, a portion of the electrodialysis concentrate in the preheating circulation tank is transferred to the solar heating element of the solar heater, heated, and then returned to the preheating circulation tank. After preheating, a portion of the liquid phase enters a flash tank with a vacuum of 0.06 MPa. Gas-liquid separation occurs in the flash tank, with the flash vapor phase compressed by a first compressor at a compression ratio of 1.5. After compression, its temperature increases by 14°C, approximately 7°C. The flash vapor phase, heated to 5℃, enters the heat exchanger as a heat source for cooling. The flash liquid phase then enters the heat exchanger to exchange heat with the heated flash vapor phase, raising its temperature to approximately 70℃. It then enters the evaporator, where a vacuum of approximately 0.07 MPa is maintained. Evaporation occurs within the evaporator, with the flash liquid phase continuously evaporating to produce an evaporating vapor phase and an evaporating liquid phase (slurry). The evaporating vapor phase is compressed by a second compressor to raise its temperature by 10-15℃ to approximately 75℃. Both the heated evaporating vapor and flash vapor phases are then used as heat sources in the heat exchanger for cooling. After heat exchange, both vapor heat sources are below 50℃ and are mixed to form condensate. The liquid, along with the secondary reverse osmosis desalinated water, is then transported to the ammonia nitrogen and boron adsorption unit for ammonia nitrogen and boron adsorption. The liquid after adsorption is used as the final effluent. Finally, the evaporated liquid phase is transported to a thickener, where crystallization produces crystalline salts. Meanwhile, the mother liquor that is ejected is returned to the flash tank for further flash evaporation.

[0148] 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.

[0149] Table 3

[0150] color Dark yellow colorless colorless pH 6-9 8.4 7.5 Total hardness, mg / L 1650 32 13 Total suspended solids content, mg / L 1378 23 9.1 Total iron content, mg / L 34 3.2 0.05 Ammonia nitrogen, mg / L 98 23 8 Chloride ions, mg / L 27541 4.7939 142 COD, mg / L 1054 21 14 Total dissolved solids content, mg / L 43700 80599 241

[0151] Note: Total hardness includes Ca. 2+ Mg 2+ Ba 2+ and Sr 2+ .

[0152] 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 Wastewater Discharge Standard (GB 8978-1996) and the Sichuan Provincial Water Pollutant Discharge Standard (DB51 / 190-93).

[0153] The crystalline salt in this embodiment is then processed using conventional methods existing in the art. The quality was tested, and the obtained quality test data is shown in Table 4 below.

[0154] Table 4

[0155] Crystallization salt index >98.26wt% <0.21wt% <0.03wt% <0.20wt% Grade I industrial salt standard 95wt% 3.5wt% 0.1wt% 0.5wt%

[0156] As can be seen from Table 4 above, the quality of the crystalline salt obtained in Example 4 of the present invention can meet the standard of first-grade industrial salt.

[0157] In summary, the low-energy fracturing flowback fluid classification treatment system and method provided in Embodiment 4 of this invention produces fewer byproducts and is easier to handle. This method generates a total of four byproducts. Byproduct 1 is surface waste oil from the fracturing flowback fluid, which can be collected and transported for disposal. Byproduct 2 is primary sedimentation sludge, i.e., first-stage sludge. Byproduct 3 is second-stage sludge, which is softened sludge. The first-stage and second-stage sludge are separated into solid and liquid phases through two independent treatment units, i.e., a filter press dewatering unit. Other existing treatment processes usually only produce first-stage sludge and cannot process the sludge separately. Moreover, the two stages of sludge in this invention are stable and easier to dispose of. Byproduct 4 is crystalline salt, which is of higher quality than the standard of first-grade industrial salt and can be utilized as a resource.

[0158] 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, any substitution of equivalent components or equivalent changes and modifications made within the scope of protection of this patent should still fall within the scope of this patent. Furthermore, the technical features, technical features and technical inventions, and technical inventions in this invention can be freely combined and used.

Claims

1. A low-energy-consumption fracturing flowback fluid classification and treatment system, characterized in that, The low-energy fracturing flowback fluid classification and treatment system includes a flowback fluid reuse system, a softening pretreatment system, a membrane concentration system, and a solar evaporation crystallization system connected in sequence. The backflow liquid reuse system includes an aeration transfer tank, an air flotation oil removal tank, a flocculation reactor, and a sedimentation tank connected in sequence. 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 connected in sequence. The microfiltration concentrate outlet of the tubular microfiltration unit and the nanofiltration concentrate outlet of the nanofiltration unit are respectively connected to the inlet of the softening concentration reaction tank through a concentrate return pipe. The microfiltration membrane module used in the tubular microfiltration unit has a pore size ≤0.05μm. The membrane concentration system includes a hydraulic pressure turbine, a primary reverse osmosis unit, a secondary reverse osmosis unit, an electrodialysis unit, and an ammonia nitrogen and boron adsorption unit. The secondary reverse osmosis desalination outlet of the secondary reverse osmosis unit is connected to the ammonia nitrogen and boron adsorption unit through a pipeline. The solar evaporation crystallization system includes a preheating circulation tank, a solar heater, a flash tank, an evaporator, a heat exchanger, and a thickener. The solar heater is used to circulate and preheat the electrodialysis concentrate produced from the electrodialysis unit 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 evaporator via a pipeline through the heat exchanger. The liquid phase outlet of the evaporator is connected to the thickener. 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 via a pipeline through the first compressor and the heat exchanger. The gas phase outlet of the evaporator is connected to the liquid inlet of the ammonia nitrogen and boron adsorption unit via a pipeline through the second compressor and the heat exchanger.

2. The system according to claim 1, characterized in that, The softening and concentration reaction tank includes a primary softening tank, a secondary softening tank, and a concentration tank connected in sequence.

3. 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 first-stage reverse osmosis unit via a pipeline through a hydraulic pressure turbine, and the freshwater outlet of the first-stage reverse osmosis unit is connected to the liquid inlet of the ammonia nitrogen and boron adsorption unit via a pipeline through a second-stage reverse osmosis unit. The concentrate outlet of the first-stage reverse osmosis unit is connected to the liquid inlet of the electrodialysis unit via a pipeline through a hydraulic pressure turbine, and the concentrate outlet of the electrodialysis unit is connected to the inlet of the preheating circulation tank via a pipeline.

4. The system according to claim 3, characterized in that, The freshwater 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 via pipelines through a hydraulic pressure turbine.

5. 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 via a pipeline. The concentrate outlet of the electrodialysis unit is connected to the inlet of the preheating circulation tank via a pipeline. The desalination outlet of the electrodialysis unit is connected to the liquid inlet of the first-stage reverse osmosis unit via a pipeline through a hydraulic pressure turbine. The desalination outlet of the first-stage reverse osmosis unit is connected to the liquid inlet of the ammonia nitrogen and boron adsorption unit via a pipeline through the second-stage reverse osmosis unit.

6. The system according to claim 5, characterized in that, The concentrate outlet of the secondary reverse osmosis unit is connected to the liquid inlet of the primary reverse osmosis unit via a pipeline through a hydraulic pressure turbine.

7. The system according to claim 5, characterized in that, The concentrate outlet of the first-stage reverse osmosis unit is connected to the liquid inlet of the electrodialysis unit via a pipeline through a hydraulic pressure turbine.

8. The system according to claim 1 or 2, characterized in that, The liquid outlet of the thickener is connected to the inlet of the evaporator via a pipeline.

9. A low-energy-consumption method for the graded treatment of fracturing flowback fluid, characterized in that, The method is implemented using the low-energy fracturing flowback fluid classification and treatment system according to any one of claims 1-8, and includes the following steps: (1) The fracturing flowback fluid is subjected to aeration and flotation oil removal treatment in sequence to obtain waste oil and effluent. The effluent is then subjected to flocculation and sedimentation in sequence to obtain a first-stage sludge and a first-stage liquid. (2) The primary liquid is softened and concentrated to obtain concentrated liquid and secondary sludge. The concentrated liquid is oxidized by ozone and then its effluent is micro-filtered to obtain micro-filtered concentrate and micro-filtered desalinated water. The micro-filtered desalinated water is then nano-filtered to obtain nano-filtered concentrate and nano-filtered desalinated water. Finally, the nano-filtered desalinated water is softened and ion-adsorbed to obtain secondary liquid. (3) When the mineralization of the secondary liquid is not higher than 40000 mg / L, the secondary liquid is subjected to first-stage reverse osmosis to obtain first-stage reverse osmosis concentrate and first-stage reverse osmosis desalination. The first-stage reverse osmosis desalination is subjected to second-stage reverse osmosis, and then the second-stage reverse osmosis desalination is subjected to ammonia nitrogen and boron adsorption. The first-stage reverse osmosis concentrate is subjected to electrodialysis to obtain electrodialysis concentrate and electrodialysis desalination; or, When the mineralization of the secondary liquid is higher than 40,000 mg / L, electrodialysis is performed on the secondary liquid to obtain electrodialysis concentrate and electrodialysis desalinated water. The electrodialysis desalinated water is then subjected to first-stage reverse osmosis and second-stage reverse osmosis in sequence, and then the second-stage reverse osmosis desalinated water is subjected to ammonia nitrogen and boron adsorption. (4) The concentrated water from electrodialysis is preheated by a solar heater and then flashed to obtain a flash vapor phase and a flash liquid phase. The flash liquid phase after heat exchange and heating is then evaporated to obtain an evaporated gas phase and an evaporated liquid phase. The evaporated liquid phase is then crystallized to obtain crystalline salt and mother liquor. The heat source used for heat exchange and heating is the flash vapor phase after heating, or the flash vapor phase after heating and the evaporated gas phase after heating. The flash vapor phase after heat exchange with the flash liquid phase, or the flash vapor phase and the evaporated gas phase, are then used together with the secondary reverse osmosis desalinated water for ammonia nitrogen and boron adsorption. The circulating preheating includes: transferring a portion of the electrodialysis concentrate in the preheating circulation tank to the solar heater, heating it, and then returning it to the preheating circulation tank; The liquid volume in the preheating circulation tank is maintained at 40-60%, the heating temperature is 55-65℃, and the pressure is 0.12-0.13MPa. 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. Specifically, the first compressor and the second compressor are used to compress the flash vapor phase and the evaporation gas phase respectively, so that the flash vapor phase and the evaporation gas phase are heated by 12-18℃ and 10-15℃ respectively, and then used as heat sources to exchange heat with the flash liquid phase, so that the temperature of the flash liquid phase after heat exchange is 60-75℃.

10. The method according to claim 9, characterized in that, The flocculants used in the flocculation include polyaluminum chloride and / or polyacrylamide.

11. The method according to claim 9 or 10, characterized in that, The softening process is carried out in two steps. The first and second softening steps use sodium carbonate and sodium sulfate, respectively, with a mass ratio of sodium carbonate to sodium sulfate of 4:1 to 6:

1.

12. The method according to claim 9 or 10, characterized in that, When the mineralization of the secondary liquid is not higher than 40,000 mg / L, step (3) further includes: The electrodialysis desalination water and the secondary reverse osmosis concentrate are subjected to primary reverse osmosis.

13. The method according to claim 9 or 10, characterized in that, When the mineralization of the secondary liquid is higher than 40000 mg / L, step (3) also includes: performing primary reverse osmosis on the secondary reverse osmosis concentrate.

14. The method according to claim 9 or 10, characterized in that, When the mineralization of the secondary liquid is higher than 40,000 mg / L, step (3) also includes: electrodialysis of the primary reverse osmosis concentrate.

15. The method according to claim 9 or 10, characterized in that, Step (4) also includes: flash evaporating the mother liquor and the preheated electrodialysis concentrate to obtain a flash vapor phase and a flash liquid phase.

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